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LANIAKEA SUPERCLUSTER_ The Milky Way Is Just a Tiny Part of This · Boring Science

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Speaker 1: Most people can tell you their street address, their city,
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their country, and if they are paying attention in school,
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maybe even the name of the galaxy they live in.
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But ask them to go one level higher, one step
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further out, and almost everyone goes quiet. There is a
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structure above the galaxy. There is a structure above the
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galaxy cluster. There is an address most people have never
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been given, and it belongs to a place so enormous
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that the number of galaxies inside it runs to roughly
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one hundred thousand. We live inside it right now. Most
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people have never heard its name. That silence matters. It
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is not a gap in trivia. It is a gap
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in something more basic, the question of where exactly you are.
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Humans have spent thousands of years getting better at answering
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that question. Apped the continents, we track the planets. We
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measured the distance to the Sun, to nearby stars, to
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the edge of our own galaxy. Every generation pushed the
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answer a little further out, and then for a long
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stretch the answer stalled. The galaxy was as far as
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most people got, and the Milky Way became the edge
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of the mental map beyond it. In this informal accounting
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was just space undifferentiated, unmapped vast. The truth is stranger
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and more structured than that. The universe at its largest
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scales is not a smooth, even fog of galaxies scattered
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randomly in every direction. It has bones, It has architecture.
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Galaxies cluster together, Clusters gather into super clusters. Superclusters are
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themselves embedded in a web of filaments and voids, stretching
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across hundreds of millions of light years. This structure exists,
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whether or not we know about it, and we are
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inside it. The question was never whether there was a
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larger address. The question was whether anyone would ever figure
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out what it was. In twenty fourteen, a team of
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astronomers did. What they published that year was not just
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a new measurement or a refined catalog. It was a
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map of something that had never been mapped before, the
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full supercluster that contains the Milky Way, defined for the
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first time with a clear boundary, a coherent shape, and
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a name. The structure stretches five hundred twenty million light
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years across. Its total mass runs to something like a
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hundred quadrillion suns. It holds roughly one hundred thousand large
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galaxies inside it, all of them flowing slowly and gravitationally
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toward a common center, and almost nobody outside of astronomy
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has heard of it. The name comes from Hawaiian. The
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team behind the discovery was based at the University of Hawaii,
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and when the time came to name the structure, they
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consulted with Hawaiian language experts rather than reaching for the
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usual Latin or Greek. The word they settled on is
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lania kia. Lani means heaven or sky, Akia means spacious, open, immeasurable.
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Together the phrase means something close to immense heaven. There
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is something right about that. Polynesian navigators once crossed the
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open Pacific with no instruments and no landmarks, reading the
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sky to find where they were in the world. The
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name given to our supercluster reaches back to those same navigators,
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and it carries that same orientation looking up to understand
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your place. Most people have a cosmic address they have
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never been told street, city, country, planet, solar system, galaxy, galaxy, cluster, supercluster.
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That last entry is the missing one. That is the
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level where the address has until recently been blank. For decades,
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astronomers thought the Virgo supercluster was the best answer, a
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structure about one hundred million light years across that the
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Milky Way sat on the edge of. But that picture
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was incomplete. The Virgo supercluster turned out to be a
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small piece of something much larger. What replaced it is deeper, wider, stranger,
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and harder to picture. It took a new way of
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thinking about the problem entirely, not just pointing telescopes, but
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rethinking what a supercluster even is before anyone could see
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it clearly. That discovery, how it was made, what it
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revealed about the structure we are embedded in, and what
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it means for the question of where you are. That
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is what the rest of this is about. The name
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is Lania Kia, and understanding what it is changes everything
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about how you think about where you are. For decades,
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if you asked an astronomer where the Milky Way sat
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in the largest known structure, the answer was the Virgo supercluster.
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That was the official answer. That was what the textbook said,
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and for a long time it felt like enough. To
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understand why that answer seemed satisfying, you have to walk
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through the hierarchy that astronomers had assembled, piece by piece
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over the twentieth century. Start at the bottom Earth orbits
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the Sun. The Sun is one star among several hundred
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billion in the Milky Way. The Milky Way, a barred
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spiral galaxy roughly one hundred thousand light years across, belongs
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to a small cluster of galaxies called the Local Group.
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The Local Group contains around eighty galaxies in total, most
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of them small and dim, gravitationally bound to each other
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and to the two dominant members, the Milky Way and
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the Andromeda galaxy. That cluster spans roughly ten million light years.
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Beyond the Local Group, things get larger much lower. The
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Virgo Supercluster was the next rung on that ladder. It
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stretched roughly one hundred million light years across an enormous
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region of space, containing thousands of galaxies organized into smaller
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clusters and groups, all loosely associated around a gravitational center.
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At that center sat the Virgo Cluster, itself, one of
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the nearest large galaxy clusters to us, holding several thousand
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galaxies packed into a region roughly eight million light years wide.
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The Local Group sat on the outer edge of this structure,
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a minor outpost well away from the dense central regions.
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That was the address, That was the picture. The man
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most responsible for assembling it was a French American astronomer
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named Gerard de Vaucouleur. Working in the nineteen fifteen es,
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Devoculur noticed something that had been hiding in plain sight.
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When he plotted the positions of nearby galaxies across the sky,
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they weren't scattered randomly. They clustered preferentially along a flattened plane,
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A great disk of galaxies tilted roughly six degrees relative
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to the celestial equator. He called this the local supercluster.
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Other astronomers were skeptical. The concept of superclusters enormous structures
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containing multiple clusters of galaxies, was not universally accepted at
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the time. Some researchers argued that what Devoculur was seeing
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was just a statistical accident, a coincidence in the distribution
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of nearby galaxies, rather than a genuine physical structure. The
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debate went on for decades. Gradually, as observations improved and
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galaxy catalogs grew larger, the reality of the local supercluster
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became harder to dismiss. By the nineteen eighties, most astronomers
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had accepted that Devoculur had been right. The Virgo Supercluster
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was real, and once it was accepted, the picture felt
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remarkably complete. You had a clean hierarchy. Planets orbited stars,
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Stars gathered in galaxies, Galaxies gathered in clusters, clusters gathered
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in superclusters. The universe was organized, nested, logical. The Virgo
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Supercluster was the top of that nesting, the largest box
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that contained our box, and it had a sensible size
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about one hundred million light years and a sensible shape.
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It was centered on a visible, well studied cluster of galaxies.
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You could point to it on a map. Cosmologic speaking,
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the address problem seemed solved. Then the data started behaving strangely.
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The universe is expanding. Edwin Hubble established this in nineteen
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twenty nine, and by the second half of the twentieth
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century it was one of the most thoroughly confirmed facts
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in all of science. Galaxies are receding from us and
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from each other at speeds proportional to their distances. The
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further away a galaxy is, the faster it appears to
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move away. This is not galaxies moving through space so
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much as space itself stretching, carrying galaxies along with it.
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If you know a galaxy's recession speed, you can calculate
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its distance. This relationship, called the Hubble flow, forms the
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backbone of how astronomers measure the large scale universe. The
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problem was that real galaxies didn't follow the Hubble flow exactly.
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When astronomers measured individual galaxy velocities carefully and compared them
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to what pure Hubble expansion predicted, there were systematic leftovers.
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Galaxies were moving at speeds and in directions that pure
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expansion could not account for. These deviations had a name
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peculiar velocities, and in small amounts, peculiar velocities were expected.
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Local gravity, the pull of a nearby galaxy cluster, the
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tug of a neighboring group would naturally push galaxies slightly
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off the smooth expansion baseline. That was normal. That was understood.
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What was not understood was the scale of what astronomers
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were beginning to see. By the nineteen seventies and into
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the nineteen eighties, galaxy surveys were growing large enough that
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a troubling pattern was becoming visible. Galaxies across an enormous
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volume of space, far larger than any individual cluster, far
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larger even than the Virgo supercluster, seemed to be drifting
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coherently in roughly the same direction. Not just a handful
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of galaxies, not just one cluster. Thousands of galaxies spread
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across hundreds of millions of light years were showing a
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systematic motion that pointed toward a particular region of the sky,
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somewhere in the direction of the constellations Centaurus and Norma.
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The motion was subtle, but it was measurable, and it
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was consistent. Something was pulling on a scale the existing
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maps see would not explain the Virgo supercluster alone, could
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not account for it. The gravitational influence of the Virgo
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cluster and d its surrounding structure was well understood, and yes,
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it tugged on the local group. But this new signal
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was different, larger, deeper, coming from a direction and on
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a scale that pointed to something much more massive, sitting
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further out, something that had never been properly identified or mapped.
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The clean hierarchy began to look incomplete. The top rung
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of the ladder seemed to be missing something, or rather,
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it seemed to be sitting on top of something larger
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that nobody had noticed. For a generation of astronomers, this
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was the uncomfortable feeling at the edge of the known map.
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The Virgo supercluster was real, The hierarchy was real, but
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the hierarchy wasn't the whole story. The galaxies weren't just
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expanding outward uniformly. They were being pulled subtly, but unmistakably
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towards something nobody had fully mapped. In the nineteen seventies,
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when astronomers first produced detailed maps of the cosmic microwave
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background radiation, something immediately looked wrong. The CMB is the
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oldest light in the universe, A faint glow left over
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from roughly three hundred eighty thousand years after the Big Bang,
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spread almost perfectly uniformly across the sky. Almost When scientists
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looked carefully at their new maps, they noticed that one
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side of the sky was slightly warmer than the other.
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Not dramatically, not in a way that leapt off the page.
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But the asymmetry was real, and it was consistent, and
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it meant something specific. The Milky Way was moving, not
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just spinning in place, not just orbiting the center of
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our galaxy. The entire local group was being carried in
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a direction at a speed of roughly six hundred kilometers
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per second toward a ragye on of the sky nobody
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had properly investigated. Six hundred kilometers per second is not
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a small number that is fast enough to cross the
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continental United States in under ten seconds. At that speed,
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something is doing the pulling. The simple model of cosmic
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expansion galaxies moving apart uniformly in all directions, like raisins
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in a rising loaf of bread, predicted no such drift.
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Everything should be moving outward from everything else, no preferred direction,
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no net flow toward any particular point. What the CMB
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maps were showing was a deviation from that picture. The
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local group had what astronomers call a peculiar velocity, meaning
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a velocity that cannot be counted for by the ordinary
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expansion of space alone. Something gravitational was adding an extra tug.
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Peculiar velocities are the fingerprints of structure. In a perfectly
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smooth universe, galaxies would have no peculiar velocities at all.
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They would simply ride the expansion of space outward evenly
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in all directions. But the universe is not smooth. Matter
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is clumped into galaxies, clusters filaments. Wherever mass concentrates, it
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pulls neighboring objects toward it, giving those objects a velocity
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component that points toward the mass rather than simply away
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from everything else. Measure enough peculiar velocities across a large
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enough volume of space, and you can reconstruct where the
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hidden mass is sitting. The CMB dipole was the first
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crude map of a percure peculiar velocity on the largest
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scale anyone had yet considered. It was telling astronomers that
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a significant mass concentration xi stead somewhere in the direction
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the local group was streaming toward, and that this concentration
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was large enough to accelerate thousands of galaxies simultaneously. Through
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the late nineteen seventies and into the nineteen eighties, several
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independent teams began measuring peculiar velocities for galaxies beyond the
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local group. What they found was alarming in its consistency.
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Galaxies in our general neighborhood were not just drifting outward
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with the hubble flow. They were streaming. Hundreds of galaxies
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spread across enormous distances were all showing a common component
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of motion pointed in roughly the same direction. This was
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not noise. This was a coherent bulk flow, a river
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of galaxies being carried together towards something. Astronomers called this
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the Great Attractor, and the name was chosen carefully. Whatever
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was out there was not a single object. It was
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a region, a concentration of matter so vast and so
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massive that its gravity was reaching hundreds of millions of
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light years in every direction and bending the trajectories of
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everything it touched. The nineteen eighty six paper that gave
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the Great Attractor its name came from a group of
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seven astronomers who would become known informally as the Seven Samurai.
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Donald Lynden Bell, Sandra Faber, and five colleagues had spent
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years building a catalog of elliptical galaxies with measured distances
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and velocities. When they analyzed the streaming motions in their data,
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they found that the bulk flow pointed toward a specific
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region of the sky, the direction of the constellation's normal
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and centaurous crux, roughly in the southern sky. Their best
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estimate placed the source of the gravitational pull at somewhere
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between one hundred fifty and two hundred fifty million light
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years away. The mass required to produce the observed streaming
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was staggering ten million billion solar masses that is a
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ten followed by fifteen zeros that is, tea and quadrillion
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suns concentrated into one region of space, exerting gravitational influence
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across a volume that makes our entire local group look
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like a single grain of sand on a beach. Stop
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and hold that number for a moment. Ten million billion
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solar masses. Our sun is already so large that a
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million earths would fit inside it. The Milky Way contained
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somewhere around two hundred to four hundred billion stars. The
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entire mass of everything in the local group, every star,
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every galaxy, all the dark matter, all the gas, is
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perhaps a few trillion solar masses. The Greater Tractor was
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something altogether different. It was not a cluster of galaxies
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in the ordinary sense. It was a concentration of mass
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that dwarfed entire superclusters, pulling the Milky Way and everything
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around it toward it at hundreds of kilometers per second,
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And it had apparently been doing this for billions of years,
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And yet for most of the nineteen eighties, nobody could
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see it properly. This is where the story gets genuinely strange.
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The Greater Tractor was not a subtle signal buried in
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noisy data. Its gravitational effect was measurable across hundreds of
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millions of light years. Thousands of galaxies were streaming toward it.
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The CMB dipole was pointing at it. And yet when
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astronomers turned their telescopes toward the region of Norma and
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Centaurus and tried to actually observe this gravitational engine directly,
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they ran into a wall, not a metaphorical wall, something
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physical sitting between us and the attractor, blocking the view
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the Milky Way itself. Our galaxy is a disc. We
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are embedded inside that disc, roughly two thirds of the
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way out from the center. When we look outward in
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the plane of the disc, toward what we see as
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the band of the Milky Way stretching across the night sky,
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we are looking through the maximum concentration of our own galaxy, stars, gas,
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and dust. There are hundreds of billions of stars between
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us and the edge of the galactic disk in that direction,
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along with enormous clouds of molecular gas and thick lanes
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of interstellar dust that absorb and scatter visible light almost completely.
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Anything sitting behind that disc invisible wavelengths is essentially invisible.
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Astronomers have a name for this region of the sky.
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They call it the zone of avoidance. The zone of
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avoidance covers a significant band across the entire sky. It
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is not a narrow slit. In some directions. It extends
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twenty to thirty degrees above and below the galactic plane.
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A substantial fraction of the entire sky, perhaps twenty percent
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or more of the observable universe as seen from Earth,
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is abs skewed or seriously compromised in optical wavelengths by
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our own galaxy's disc. This would be merely inconvenient if
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the objects behind it were distributed randomly, but they are not.
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The greater tractor sits squarely in this zone. The densest,
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most consequential structure in our corner of the universe happens
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to lie almost perfectly behind the thickest part of the
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galactic plane, as seen from our position within the Milky Way.
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You could not design a more effective obstacle if you tried.
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Astronomers throughout the nineteen eighties and into the nineteen nineties
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pushed hard against this limitation. They turned to radio telescopes,
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which can detect the twenty one centimeter emission line of
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neutral hydrogen through almost any amount of dust. They used
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X ray observatories, which can detect the hot gas in
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galaxy clusters even through substantial obscuration. They developed infrared surveys
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that could cut through dust far more effectively than optical light. Slowly, painfully,
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the picture behind the zone of avoidance began to clarify.
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The normal cluster emerged from the murk, a rich cluster
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of galaxies sitting right at the heart of the attractor region,
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dense with thousands of galaxies threaded through with hot gas.
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It was not the totality of the Great Attractor, but
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it was a confirmation that something mass sieve was genuinely there.
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The gravitational signal was real, the streaming was real, The
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thing causing it was real. What was almost absurd about
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the situation was the irony embedded in it. Here was
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the most gravitationally dominant structure within hundreds of millions of
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light years of the Milky Way, something pulling our entire
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galactic neighborhood toward it at enormous speed, something that had
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been shaping the large scale motion of galaxies in our
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region for billions of years. And the reason we could
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barely study it was not a technological limitation or a
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fundamental physical barrier. It was us. The very galaxy we
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live in was blocking our view of the gravitational engine
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at the center of our cosmic home. Imagine trying to
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map a city while standing in the middle of a
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thick forest that circles the entire downtown core. You can
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see what is directly around you. You can see patches
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of sky above, but the buildings at the center, the streets,
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the whole layout of the place you are trying to understand,
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all of it is blocked by the trees. That is
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roughly the situation astronomer's face when they try to observe
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the region of the universe sitting behind the plane of
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the Milky Way. The forest is our own galaxy, and
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it does not move. The problem has a name. Astronomers
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call it the zone of avoidance, which sounds like something
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you would find on a nautical chart warning ships away
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from shallow water. The name fits. It is a band
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running all the way around the sky, tracing the galactic plane,
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where the Milky Way's own stars, gas and dust absorb
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and scatter the light coming from anything beyond. In optical wavelengths,
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the kind of light human eyes can see. This band
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is essentially opaque. Galaxies that sit behind it are not dimmed,
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they are gone. Their light never makes it through. The
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zone of avoidance covers roughly twenty percent of the entire
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sky that is not a narrow strip you can work around.
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That is a fifth of everything running in a continuous
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band around the full equator of our celestial sphere. What
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makes this strange is that the obscuring material is not
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particularly thick by cosmic standards. The dust and gas clouds
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responsible for the blockage are relatively diffuse, but they are
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spread across tens of thousands of light years of galactic disk,
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and when you stack that much material between yourself and
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a distant galaxy, even thin stuff adds up. The total
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extinction in some parts of the galactic plane is enormous.
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Light from distant objects gets absorbed, scattered, and reddened into
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invisibility long before it reaches a telescope on Earth. Are
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not helpless. They found workarounds, and the workarounds are clever.
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Infrared light has longer wavelengths than visible light, and longer
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wavelengths cut through dust far more effectively. An infrared telescope
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can detect galaxies behind the galactic plane that are completely
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invisible to an optical instrument. X ray observations help as well.
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High energy X rays punch through interstellar dust with relatively
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little scattering, which is how some of the galaxy clusters
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lurking behind the zone of avoidance were first identified. Radio
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wavelengths work too. The twenty one centimeter emission line from
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neutral hydrogen passes straight through the galactic dust without any
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significant absorption, which means radio surveys can map hydrogen in
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distant galaxies even when those galaxies are sitting directly behind
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the Milky Way's thickest regions. These tools opened up parts
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of the zone of avoidance that had been completely dark before.
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The normal Cluster, one of the major structures near the
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Greater Tractor, was partly mapped through these techniques. Several previously
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unknown galaxy clusters were found hiding in the obscured region
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during the nineteen nineties and two thousands, when systematic infrared
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and radio surveys swept across the galactic plane for the
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first time. Each discovery reminded astronomers how much had been
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missed simply because of where they happened to be sitting.
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But here is the thing. Even with infrared, X ray
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and radio data combined, the zone of avoidance remains the
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worst characterized region of the nearby universe. The tools that
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cut through dust come with their own limitations. Infrared surveys
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still struggle with the bright emission from our own galaxy stars,
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which floods the detectors and makes faint background sources hard
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to extract. Radio surveys measure hydrogen, but mis galaxies with
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little neutral gas. X ray observations pick up hot cluster gas,
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but not the full picture of galaxy distribution. No single
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alternative method gives you what optical astronomy gives you. Everywhere else,
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the coverage is patchier, the catalogs are less complete, the
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distance measurements are harder to make and less reliable. When
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Brent Tully's team built the cosmic flows to catalog, the
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one that would eventually define Laniakia, the data thinned out
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and degraded precisely in the directions behind the galactic plane.
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The map had a whole in it, and the whole
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sat right over one of the most gravitationally significant regions
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in the local universe. There is a particular irony in
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all of this that is hard to ignore. The Milky
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Way is not a distant obstacle. It is not some
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intervening object that happens to lie in an unfortunate direction.
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It is the galaxy we live inside. The stars blocking
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our view of the Great Attractor are the same stars
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that make up the bright band of the Milky Way
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that humans have looked up at for all of recorded history.
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The dust blocking the light from thousands of background galaxies
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is the same dust that fills the spiral arms of
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our own home. We are embedded so deeply inside this
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structure that it wraps completely around us, and because of that,
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there is a ring around our entire sky where the
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universe versus functionally hidden. The very thing that makes us
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astronomers having a galaxy to stand in is the same
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day nung that blinds us to a fifth of what
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surrounds us. For years, the Greater Tractor sat squarely behind
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this veil, its true nature hidden behind the very structure
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that contains every star you can see on a clear night.
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The breakthrough that produced Laniaka was not a new telescope
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or a new piece of hardware. It was a new
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idea about what astronomers should be measuring. For most of
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the twentieth century, when astronomers tried to map the large
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scale structure of the universe, they did it by counting.
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They would survey a region of sky, catalog the galaxies
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they found, and draw boundaries around the densest concentrations. Where
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galaxies clumped together, that was a cluster. Where clusters grouped together,
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that was a supercluster. It was a logical approach. It
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was also, it turned out, incomplete. Density maps can tell
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you where matter piled up, but they cannot tell you
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what belongs together gravitationally. A city map that only shows
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population density misses the fact that commuters from far flung
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suburbs are functionally part of the same metropolitan system, even
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if they live in a sparse neighbourhood at the edge.
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Brent Tully understood this problem. Tully is an astronomer at
33:38
the University of Hawaii's Institute for Astronomy, and by twenty
33:43
fourteen he had spent decades building the most precise catalogs
33:48
of galaxy distances and velocities that the field had ever produced.
33:53
He had already made his name decades earlier, co developing
33:57
the Tullyfisher relation, unique that links a spiral galaxy's rotation
34:03
speed to its true brightness and allows astronomers to infer
34:07
distances from observations alone. That earlier work was groundbreaking, but
34:14
by the two thousands, Tully was working on something with
34:18
even larger implications. He was thinking about what the motions
34:23
of galaxies could reveal, not just their positions. Here is
34:27
the key concept. When astronomers measure the velocity of a
34:31
distant galaxy, they typically get two signals mixed together. One
34:37
is the velocity from the expansion of the universe, the
34:41
background hum of space itself stretching, which makes every galaxy
34:46
appear to be moving away from us faster with distance.
34:52
The second signal is something subtler. It is the galaxy's
34:57
individual motion on top of that exten banshion caused by
35:01
the gravitational tug of everything around it. Astronomers call this
35:06
the peculiar velocity. It is the deviation from pure expansion
35:12
and It is a direct fingerprint of the local gravitational field.
35:17
If you could map the peculiar velocities of thousands of
35:21
galaxies across hundreds of millions of light years, you would
35:25
not be looking at where galaxies happen to be sitting
35:28
right now. You would be looking at where gravity is
35:32
pulling them. You would see the underlying skeleton of the
35:36
mass distribution, not just its surface appearance. This is what
35:42
Tully and his collaborators set out to do. The analogy
35:46
that makes this clearest is a watershed stand somewhere in
35:51
the rocky mountains, and the rain that falls on your
35:54
left flows eventually toward the Pacific. The rain that falls
36:00
on your right flows toward the Atlantic or the Gulf
36:04
of Mexico. There is a dividing line running along the
36:07
mountain ridges where these drainage basins meet. On either side
36:12
of that line, water flows in fundamentally different directions. Neither
36:18
side knows anything about the other. They belong to different systems. Now,
36:24
imagine the same thing at cosmic scale. Galaxies are not
36:29
sitting still. They are flowing very slowly by human standards,
36:34
toward the nearest major gravitational concentration in one region, they
36:39
flow toward one center of mass. In an adjacent region,
36:44
they flow toward a different one. The boundary between those
36:48
two regions, the cosmic equivalent of the continental divide, is
36:54
where the peculiar velocities reverse direction. That boundary defines where
37:00
one supercluster ends and another begins, not a density threshold,
37:06
a water shed. This was the conceptual breakthrough. A supercluster,
37:12
under Tully's definition, is not simply a region where galaxies
37:16
are dense. It is a basin of attraction, a volume
37:20
of space inside which all galaxy motions, once you subtract
37:25
the background expansion, are directed inward toward the same gravitational center.
37:31
The boundaries are determined not by how many galaxies you
37:35
can count per cubic megaparsec, but by where the flow
37:39
changes direction. The method required data, enormous amounts of it.
37:46
To construct a meaningful map of peculiar velocities across hundreds
37:50
of millions of light years. You need precise, independent distances
37:55
for thousands of galaxies. Redshift alone does not work, because
38:00
redshift conflates the expansion velocity with the peculiar velocity. You
38:07
cannot separate them without an independent distance measurement. Tully and
38:13
his colleagues had been building toward this for years. The
38:17
result was the Cosmic Flows two catalog, containing measured distances
38:23
for more than eight thousand, one hundred galaxies spread across
38:27
a substantial volume of the nearby universe. Each distance was
38:33
derived using one or more of the established techniques, primarily
38:37
the Tullyfisher relation for spirals, along with other methods for
38:42
other galaxy types. The CATA log represented the most complete
38:48
and precise data set of its kind ever. Assembled. With
38:51
those distances, the team could calculate each galaxy's peculiar velocity directly,
38:57
subtract the expected expansion v velocity, and what remains is
39:02
real motion gravitational flow. When you plot those flow vectors
39:08
across thousands of galaxies, patterns emerge filaments of flow converging
39:14
toward the same point boundaries where flow directions diverge, the
39:20
invisible architecture of gravity made visible through the motion of light.
39:25
The computation was not trivial. Converting raw distance and velocity
39:31
measurements for thousands of galaxies into a coherent three dimensional
39:36
flow map required sophisticated mathematical reconstruction. The team had to
39:43
account for gaps in coverage, errors in individual distance measurements,
39:49
and the contaminating effects of the zone of avoidance where
39:53
peculiar velocity data was thin or absent. They developed techniques
39:58
to smooth and reconstruc the flow field across poorly sampled regions,
40:03
using the surrounding data to fill in the gaps as
40:06
accurately as possible. It was as much mathematical craft as
40:12
astronomical observation. When the paper landed in Nature on September four,
40:18
twoenty fourteen, it presented not just a new structure, but
40:23
a new framework. Every previous map of the local supercluster
40:29
had drawn its borders based on galaxy density. Tulley's map
40:34
drew borders based on gravitational coherence. The result was a
40:39
structure vastly larger than anyone had previously outlined, one that
40:44
absorbed the old Virgo supercluster as a single component, that
40:49
stretched five hundred twenty million light years from one side
40:53
to the other, and that contained roughly one hundred thousand
40:57
large galaxies, all flowing, however slowly, toward a common gravitational center.
41:05
The Greater Tractor, which had mystified astronomers for decades, turned
41:11
out to be the heart of this basin. It was
41:14
not a strange anomaly in an otherwise simple universe. It
41:19
was the gravitational flow of the largest structure any of
41:23
us had ever lived inside. What made the work genuinely
41:27
significant was not the size of what it found, though
41:31
the size was staggering. It was the redefinition of the
41:35
thing being measured. Tully's team did not discover that the
41:40
universe was bigger than we thought. They changed the question.
41:44
Instead of asking where the galaxies are, they asked where
41:48
the galaxies are going. That shift in question produced a
41:53
shift in structure, a new way of drawing the map
41:57
of our cosmic address that nobody had managed before. When
42:02
they applied it to over eight thousand galaxies with measured
42:06
distances and velocities, the shape that emerged from the data
42:12
was enormous, coherent, and unlike anything on the existing maps.
42:18
The structure that emerged from Tully's maps was five hundred
42:22
twenty million light years across. That number is easy to
42:27
type and almost impossible to hold in your mind, but
42:31
let's try the milky Way. Our galaxy, the one containing
42:37
our sun and every star visible on a clear night,
42:41
stretches roughly one hundred thousand light years from one edge
42:45
to the other. That already sounds enormous. Light traveling at
42:51
one hundred eighty six thousand miles per second, takes one
42:55
hundred thousand years just to cross it. Yet, if you
42:59
want to line up Milky Way sized galaxies end to
43:03
end and span the full width of Lanyakia, you would
43:07
need five thousand of them, not five, not fifty five
43:13
thousand galaxies, each containing hundreds of billions of stars laid
43:18
side by side, and you still haven't reached the other end.
43:23
That is what five hundred twenty million light years means
43:26
in practical terms. It is a number that defeats ordinary
43:31
intuition entirely. The mass locked up inside this structure is
43:35
just as staggering. Laniakia contains roughly one hundred thousand large galaxies.
43:42
Each of those galaxies is, by any human measure, incomprehensibly large.
43:49
But the total mass of Laniakia isn't just the mass
43:52
of the stars inside those galaxies. It includes the dark
43:57
matter halos wrapped around each one, the hot gas filling
44:02
the space between galaxies, and the gravitational glue holding clusters together.
44:09
Add it all up and you get something in the
44:11
range of ten to the power of seventeen solar masses.
44:16
That's a one, followed by seventeen zeros measured in suns
44:21
one hundred quadrillion suns. Written out as a number, it
44:25
has so many digits that the number itself becomes meaningless
44:29
to read. The human brain simply doesn't have a reference
44:33
frame for it. There is no analogy that fully survives
44:37
contact with this scale. What does Laniakia actually look like?
44:42
This is where it gets genuinely strange. It is not
44:46
a sphere. It is not a uniform cloud. It does
44:49
not have smooth edges or a clean center. If you
44:53
could somehow generate an image of it in three dimensions
44:57
and step back far enough to see the whole at once,
45:01
what you would see look something like a crumpled, sprawling web,
45:07
dense bright knots mark where massive galaxy clusters sit. Thin
45:13
threads connect them, filaments made of galaxies and gas, stretching
45:19
for hundreds of millions of light years Between the nodes
45:23
and between those filaments, there is almost nothing vast regions
45:28
of dark empty space where galaxies are rare or absent entirely.
45:34
The structure has shape and anatomy. But nothing about that
45:38
shape is neat or symmetrical. Think of it less like
45:42
a ball and more like a handful of soap bubbles
45:45
smashed together and stretched. The walls of the bubbles are
45:49
the filaments, the places where galaxies concentrate the air. Inside
45:55
each bubble is a void where multiple bubbles meet the
46:00
concentration of matter is highest. Those are the clusters. Laniakia
46:06
is the region defined by one connected system of these
46:10
filaments and flows, all of it draining gravitationally toward a
46:15
common center. That center is what astronomers call the Great Attractor,
46:21
a region deep inside Laniakia where the gravitational pull is strongest.
46:28
Galaxies across the full five hundred twenty million light year
46:33
span of the structure are moving slowly in that direction,
46:38
not because they are being pushed, but because gravity has
46:42
been pulling on them for billions of years and they
46:45
have built up a drift. This motion is subtle, you
46:50
would not notice it over a human lifetime, but measured
46:54
in kilometers per second, the infall toward the Great Attractor
46:58
is real and detectable. It is what allowed Tully's team
47:03
to define the structure in the first place. The watershed
47:07
flows all run toward this gravitational basin. That's where the
47:12
center of Laniakia is. Now Here is the part that
47:16
changes how you think about where you are. The Milky
47:20
Way does not sit anywhere near that center. It sits
47:24
on the edge, the outskirts the rim, depending on how
47:30
you measure it. Our local group is somewhere around one
47:34
hundred fifty to two hundred fifty million light years from
47:38
the greater tractor. That means we are not in the
47:41
middle of Laniakia. We are roughly halfway to the edge,
47:45
on the outer fringe, in a relatively sparse and quiet
47:49
part of the structure. There are no major galaxy clusters nearby.
47:54
There is no dramatic concentration of matter in our immediate vicinity.
48:00
We are in the low density outer region of an
48:03
enormous gravitational basin, and the heart of that basin is
48:08
hundreds of millions of light years away. This should be
48:12
a genuinely disorienting realization. For most of human history, humans
48:18
assumed they occupied a special or central place in the cosmos.
48:23
Copernicus moved the Earth away from the center of the
48:27
Solar system. Later work moved the Sun away from the
48:31
center of the galaxy. Now Laniakia moves us away from
48:36
the center of our own supercluster. Whatever the center of
48:40
things might be, we are not near it. We are peripheral.
48:44
In every structure we have ever managed to identify, there
48:49
is something worth sitting with there. The greater tractor is
48:53
pulling us toward it. Our local group is drifting incredibly
48:58
slowly in that dire, but we are not falling fast.
49:04
The distance is so enormous and the drift so gradual
49:08
that it will take billions of years to cover even
49:11
a fraction of it, and dark energy, the force accelerating
49:16
the expansion of the universe, will likely pull the outer
49:20
regions of Laniakia apart before any dramatic convergence happens. We
49:27
are moving toward the center of our supercluster, but the
49:31
supercluster itself is dissolving as we go. It is not
49:36
a destination we will ever reach. The overall architecture of
49:40
Lania KaiA, when you map it out with the flows
49:43
and the clusters and the filaments, divides into several major regions.
49:48
There is the part containing the Virgo cluster and our
49:52
local group, the part containing the hydra and Centaurus clusters,
49:57
the region around the normal cluster near the Greater Tractor itself,
50:02
and the Pavo Indus supercluster region further out. These are
50:08
not cleanly separated neighbourhoods. They are connected by filaments blending
50:14
into each other the way the suburbs of a city
50:17
blend into its outskirts. But the rough anatomy is there,
50:22
and it all connects into a single coherent gravitational basin.
50:29
One thing that the three dimensional maps make very clear
50:33
is how much empty space there is. The filaments are thin,
50:38
the clusters are relatively compact. Most of the volume of
50:42
Laniakir is void. If you were a traveler moving through
50:46
this structure at random, you would spend the vast majority
50:50
of your journey in near empty darkness, far from any galaxy.
50:55
The bright connected web that shows up on the maps
50:59
represents a t miny fraction of the total volume. Most
51:03
of Laniakia is nothing. And yet, even knowing all that
51:08
one hundred thousand large galaxies is not a small number
51:14
spread across five hundred twenty million light years, they fill
51:18
this structure with an almost uncountable number of stars, planets,
51:24
and everything else. The Milky Way alone has somewhere between
51:29
one hundred and four hundred billion stars. Multiply that by
51:34
one hundred thousand galaxies, and even a rough estimate becomes
51:39
a number that no human can meaningfully visualize. Whatever is
51:43
out there in Laniakia, whatever is in those galaxies, on
51:48
those planets, around those stars, it exists at a scale
51:53
that makes the entire history of human civilization look like
51:58
a footnote written in pens on the last page of
52:01
a book inside a library that fills a continent. The
52:06
structure is real. It is not a theoretical construct or
52:10
a statistical artifact. It is a physical feature of the
52:14
universe we live in, defined by the actual motions of
52:18
actual galaxies across actual space. And the Milky Way, with
52:24
all its hundreds of billions of stars, sits near the
52:28
outer edge of this a small dot on the rim
52:31
of something almost too large to picture. When the time
52:36
came to name the structure, Brent Tully did not reach
52:40
for Greek or Latin. Most astronomical discoveries get named after
52:44
their discoverers, or after constellations, or after the catalogs they
52:49
appeared in. Tully's team was working at the University of Hawaii.
52:55
They were embedded in a place with its own deep language,
52:59
its own history of navigating enormous and featureless expanses, and
53:05
its own tradition of reading the sky. So Tully did
53:10
something unusual. He consulted with Hawaiian language experts to find
53:15
a name that fit what they had actually found. The
53:19
word they landed on was Lani akaia. It comes from
53:22
two Hawaiian roots. Lani means heaven or sky, or the
53:27
celestial realm above, a KaiA means spacious, open, immeasurable. Together
53:34
the phrase means something like immense heaven or the expansive sky,
53:39
a realm of stars so vast it resists ordinary description.
53:45
The name was suggested by Nawa'a Napoleon, an associate professor
53:49
of Hawaiian language at Capiolani Community College. It were not
53:54
a casual choice. It captured something real about the scale
53:59
of the thing being named. A structure five hundred twenty
54:03
million light years across containing one hundred thousand galaxies, bigger
54:09
than anything our nearest ancestors could have conceived. Immense heaven
54:15
is not an exaggeration. It is barely adequate. But there
54:19
is something stranger and more interesting here than just a
54:23
well chosen word. The name carries a cultural weight that
54:28
runs directly parallel to the science behind it. Polynesian navigators
54:34
cross the Pacific Ocean, the largest body of water on Earth,
54:39
without compasses, without GPS, without charts in the modern sense.
54:45
They crossed it by reading the sky. They memorized the
54:49
rising and setting points of hundreds of stars. They understood
54:54
how ocean swells move relative to wind and island chains.
54:58
They track the color of the water, the flight paths
55:02
of birds, the feeling of current against a hull. But
55:06
above all, they read the heavens. The sky was their map.
55:11
The sky told them where they were. These were not
55:15
short journeys. The Pacific spans more than twelve thousand miles
55:19
at its widest. Ancient Polynesian navigators reached Hawaii, New Zealand,
55:25
Easter Island, and dozens of other island groups, separated by
55:30
thousands of miles of open ocean, with no landmarks visible
55:34
from the water. They did it by knowing the sky
55:38
better than any civilization in history. The sky was not
55:42
decoration to them, It was orientation. It told you which
55:47
way was home. Now consider what Tully's team actually did.
55:52
They spent years mapping how eight thousand galaxies moved through space.
55:57
They tracked the floes, the cony urgencies, the divergences, the
56:03
subtle gravitational currents running beneath the smooth expansion of the universe,
56:09
and by reading those flows, they found our address, not
56:13
our street address, not our galaxy, our supercluster. They used
56:19
the motion of the cosmos to figure out where we
56:21
are inside it. They navigated by reading the sky. The
56:26
parallel is not decorative, it is exact. The navigators who
56:31
crossed the Pacific were doing something that looks from the
56:34
outside like it should be impossible. How do you find
56:39
a small island in an ocean that wide using only
56:42
the sky? The answer is that you know the sky
56:46
well enough that it becomes a coordinate system, a live
56:51
map of your position and heading. Tully's team was doing
56:55
something that also looks from the outside like it should
56:59
be impossible. How do you find the shape of a
57:02
structure five hundred twenty million light years across when you
57:06
are inside it and can only observe from a single point.
57:11
The answer is that you read the flows well enough
57:15
that they reveal the shape of the basin you are
57:18
sitting in. There is something almost too fitting about this.
57:23
The name Laniakia honors a tradition of navigation that solved
57:28
the same fundamental problem at a completely different scale. Where
57:34
are we? Which way is home? How do you find
57:38
your position in a featureless expanse with no obvious landmarks.
57:43
The Polynesian answer was the stars. Tully's answer was the
57:48
motion of galaxies. Both are forms of reading the sky
57:52
to find your place within it. Na Napoleon's suggestion was
57:57
not just linguistically appropriate, it was philosophically accurate. The sky
58:03
to Polynesian navigators was not a background. It was a
58:07
location system. And that is precisely what lania Kia is.
58:12
A location, a place in the cosmos that has a structure,
58:17
a shape, a center, a set of flows defining its edges.
58:22
For the first time in history, we have a name
58:25
for the largest structure we belong to, and that name
58:29
comes from a people whose entire civilization was built around
58:33
the idea that the sky tells you where you are.
58:37
That is a strange kind of symmetry. The navigators who
58:41
crossed the Pacific by reading the heavens had no way
58:44
of knowing what those heavens were embedded in. They knew
58:48
the stars as guides. They did not know those stars
58:52
were part of a galaxy, or that the galaxy was
58:55
part of a supercluster, or that the supercluster had an aim.
59:01
Now it does. The people who learned to cross the
59:04
Pacific by reading the sky gave their language to the
59:08
discovery of where that sky actually sits in the universe.
59:13
The Virgo Supercluster did not disappear when Laniakir was defined.
59:19
It simply shrank in significance. For decades, the Virgo Supercluster
59:24
was the best answer astronomers had to the question of
59:28
our large scale cosmic home. It was a genuine structure.
59:33
It was real, roughly one hundred million light years across,
59:38
centered on a dense knot of galaxies in the direction
59:42
of the constellation Virgo. It had been identified in the
59:46
nineteen fifties by astronomer Gerrard de Vaucouleur and refined by
59:52
generations of researchers who followed him. If you had asked
59:56
a cosmologist in nineteen ninety where the the Milky Way
1:00:00
lived in the largest known structure, the answer was the
1:00:04
Virgo Supercluster. And that answer felt solid, It felt complete.
1:00:11
It had been tested and mapped and written into textbooks.
1:00:16
When Lanyakir arrived in twenty fourteen, it did not invalidate
1:00:21
any of that work. It just revealed that the work
1:00:25
had been describing a neighborhood without realizing the city extended
1:00:30
far beyond it. The Virgo Cluster itself sits near the
1:00:34
heart of this older structure, and it is worth pausing
1:00:38
on what that cluster actually is. Several thousand galaxies packed
1:00:44
into a region roughly fifteen million light years across, not
1:00:49
a loose scattering, but a genuine gravitational city, one of
1:00:54
the richest concentrations of galaxies within several hundred million lights
1:01:00
of Earth. It anchors the Virgo Supercluster the way a
1:01:05
downtown core anchors a metropolitan region. Its mass pulls on
1:01:10
everything around it. The local group, the small collection of
1:01:15
roughly eighty galaxies that includes the Milky Way and Andromeda,
1:01:20
is moving toward the Virgo Cluster right now, very slowly,
1:01:25
tugged by its gravity across fifty to sixty million light
1:01:30
years of intervening space. The Virgo Cluster is not abstract.
1:01:37
It is a real gravitati onal presence, something our entire
1:01:42
galactic neighborhood feels, but the local group's position in all
1:01:46
of this is worth examining closely roughly eighty galaxies, most
1:01:52
of them small satellites orbiting either the Milky Way or Andromeda.
1:01:57
The two dominant members, our galaxy and its large neighbour
1:02:02
are themselves unremarkable spiral galaxies by the standards of the
1:02:07
broader universe. The local group sits in the outer regions
1:02:12
of the Virgo supercluster, not near its center. Then the
1:02:17
Virgo supercluster itself, as Laniakia revealed, occupies an outer region
1:02:22
of Laniakia. Stack these positions together and a clear picture forms.
1:02:29
We are not near the center of our galaxy cluster.
1:02:33
Our cluster is not near the center of the Virgo supercluster.
1:02:38
The Virgo supercluster is not near the center of Lania KaiA.
1:02:43
At every level of the hierarchy, we are somewhere on
1:02:47
the periphery, a pattern that seems almost deliberate, but is
1:02:51
simply what the data shows. The conceptual demotion this represents
1:02:57
is worth sitting with every level of our cosmic address
1:03:02
that had felt like a meaningful designation. Virgo Supercluster home
1:03:08
the largest structure we belonged to turned out to be
1:03:12
a subdivision of something larger. It is like being told
1:03:17
that the city you have lived in your whole life,
1:03:20
the city whose name you gave when people asked where
1:03:24
you were from, is not a city at all. It
1:03:28
is a district, and the actual city is five times bigger,
1:03:34
extends in directions you were not looking, and contains structures
1:03:39
in its other districts you have never seen. The name
1:03:42
on your driver's license did not change, You did not move,
1:03:47
but your sense of where you are shifted completely. This
1:03:52
kind of conceptual reshuffling has happened before. In astronomy. Earth
1:03:57
was not the center of the Solar System, the Sun
1:04:00
was not the center of the galaxy. The Milky Way
1:04:04
was not the only galaxy. Each revision followed the same pattern.
1:04:10
A structure that seemed like the largest relevant frame turned
1:04:13
out to be a component of something larger. The Virgo
1:04:18
supercluster joining this list was not a shock to anyone
1:04:22
paying attention to the history of the field, but it
1:04:25
was still a genuine revision of the scientific record. Every
1:04:30
textbook that had listed the Virgo supercluster as our supercluster
1:04:35
needed an asterisk, if not a rewrite. What Laniakia absorbed
1:04:41
was not just a name on a map. The Virgo
1:04:44
Supercluster had been associated with a specific picture of cosmic structure,
1:04:49
a set of boundaries, a hierarchy. That picture was not
1:04:54
wrong exactly. The galaxies are still where they were, the
1:04:59
flows are rear. The Virgo Cluster still dominates its local
1:05:03
region of space. But the boundaries that defined the Virgo
1:05:08
Supercluster as an independent entity were revealed to be permeable,
1:05:13
artificial in a certain sense, drawn around a density peak
1:05:18
rather than around a true gravitational basin. When Tully's team
1:05:24
redrew those boundaries using flow patterns instead of density, the
1:05:29
Virgo Supercluster was absorbed. It became one region in a
1:05:33
much larger structure, like a borough absorbed into a growing
1:05:37
metropolis that had expanded far beyond its original limits. There
1:05:43
is something almost vertiginous about this if you follow it
1:05:46
all the way down. The Milky Way is one of
1:05:50
roughly eighty galaxies in the Local Group. The Local Group
1:05:55
is one of perhaps a thousand groups and clusters in
1:05:58
the Virgo Supercluster. The Virgo Supercluster is one of several
1:06:04
major components within Laniakia. Laniakia contains something on the order
1:06:10
of one hundred thousand large galaxies spread across five hundred
1:06:15
twenty million light years. At each step, the scale multiplies
1:06:21
and the previous frame of reference shrinks. Our galaxy, which
1:06:26
contains hundreds of billions of stars, is a minor entry
1:06:30
in a minor cluster on the outer edge of a
1:06:34
supercluster component that is, itself an outer region of the
1:06:39
structure we actually live in. None of this diminishes what
1:06:43
the Vergo Supercluster is. It is still a real and
1:06:48
massive structure. The gravitational influence of the Virgo Cluster on
1:06:53
our local group is real and measurable. But calling the
1:06:58
Virgo Supercluster our home supercluster, the way astronomers did for
1:07:04
half a century was like calling a suburb the city.
1:07:09
What we had called home for half a century turned
1:07:12
out to be one small corner of a much larger room.
1:07:16
Laniaka is not a smooth, uniform cloud of galaxies. It
1:07:20
has bones. If you could somehow pull back far enough
1:07:24
to see the whole structure at once, the way you
1:07:27
might look down at a city from altitude on a
1:07:30
clear night, what you would see is not a featureless glow.
1:07:35
You would see something more like a nervous system, bright
1:07:39
knots of light where clusters sit, long faint threads connecting them,
1:07:45
and between those threads enormous darkness, not empty by accident,
1:07:52
but empty because gravity spent billions of years pulling matter
1:07:56
away from those regions and piling it somewhere else. The
1:08:01
voids are not gaps in the data. They are real features,
1:08:05
as much a part of the structure as the clusters themselves.
1:08:10
The major galaxy clusters inside Laniakia red like a catalog
1:08:15
of the southern and equatorial sky. Virgo is the closest
1:08:20
significant one to us. Hydra and Centaurus sit deeper in
1:08:25
part of a dense complex that blends into the gravitational
1:08:28
center of the whole structure. The normal cluster lies close
1:08:32
to the greater tractor itself, embedded in the most crowded
1:08:36
region of Laniakia's interior. Ophiucus is one of the most
1:08:41
massive clusters in the entire supercluster, holding an enormous concentration
1:08:46
of hot gas and hundreds of galaxies bound tightly together.
1:08:52
Fornax and Eridanus anchor a separate region of the structure,
1:08:57
part of the southern extension of the film entry Web.
1:09:01
These are not just names on a list. Each one
1:09:05
represents a gravitational knot that has been accumulating matter for
1:09:10
most of the age of the universe. A galaxy cluster
1:09:14
forms because the universe was never perfectly smooth. In the
1:09:19
earliest moments after the Big Bang, there were tiny variations
1:09:24
in density. Some regions had slightly more matter, some slightly less.
1:09:30
Those differences were almost imperceptibly small, but gravity is patient.
1:09:37
Over hundreds of millions of years, the slightly denser regions
1:09:42
pulled more matter toward themselves that made them denser. Still,
1:09:47
other matter fell in from surrounding areas. Eventually those regions
1:09:53
collapsed into the first galaxies. Galaxies fell toward each other,
1:09:59
grouping into clusterters, and clusters gathered into superclusters. What you
1:10:05
see in Laniakia now is the result of that process,
1:10:08
running for roughly thirteen billion years. The clusters are where
1:10:13
gravity won most decisively. The voids are where it why
1:10:18
it's too thinly spread to win at all. The assembly
1:10:22
process did not stop once the initial clusters formed. Smaller
1:10:27
clusters and galaxy groups continued falling into larger ones throughout
1:10:31
cosmic history. Their mergers, releasing tremendous energy. A massive cluster
1:10:38
like Virgo or Centaurus did not reach its present configuration
1:10:43
until relatively recently. On cosmic time scales, clusters continue to
1:10:49
grow and evolve, incorporating isolated galaxies that venture too close
1:10:55
to their gravitational influence. The largest clusters have been aque,
1:11:00
cumulating matter steadily for billions of years, and some are
1:11:04
still in the process of merging with neighboring structures today.
1:11:09
This ongoing accretion gradually reshapes the cluster environment and increases
1:11:15
total mass. The clusters visible in Laniakia are not static
1:11:20
monuments to ancient gravity b up dynamic systems, still assembling
1:11:26
and growing, drawing matter inward through the cosmic web. Inside
1:11:30
a cluster like Virgo or Norma, individual galaxies are not
1:11:35
sitting still. They move at speeds of hundreds or even
1:11:39
thousands of kilometers per second, orbiting the cluster's center of
1:11:44
mass the way bees circle a hive. The space between
1:11:48
them is filled with extremely hot diffuse gas so hot
1:11:53
it emits X rays, and all of it is held
1:11:56
together by the combined gravity of the galaxies. The gas
1:12:01
the dark matter that makes up the majority of the
1:12:04
cluster's total mass. A rich cluster can contain anywhere from
1:12:09
hundreds to several thousand galaxies. The Virgo cluster alone holds
1:12:15
several thousand. That kind of density is genuinely strange when
1:12:21
you think about what galaxies are. Each one of those
1:12:25
is a structure containing hundreds of billions of stars. They
1:12:30
are packed together tightly enough to interact, distort each other,
1:12:34
and occasionally merge. The filaments that connect these clusters are
1:12:39
harder to see, but just as real. They are elongated
1:12:43
structures rivers of galaxies flowing between the dense nodes of
1:12:48
the web. A single filament inside Laniakia might stretch for
1:12:53
one hundred million light years or more, containing thousands of
1:12:58
galaxies arranged loosely along its length. These are not solid structures.
1:13:04
There is enormous space between the galaxies inside a filament,
1:13:09
but statistically the galaxy density along a filament is meaningfully
1:13:15
higher than in the surrounding voids. Gravity draws matter toward
1:13:20
the filaments, and the filaments drain toward the clusters at
1:13:24
their ends. The whole thing flows slowly toward the densest concentrations.
1:13:32
Then there are the voids. Cosmological voids are among the
1:13:37
strangest objects in the universe, if you can call an
1:13:41
absence an object. They range in diameter from about thirty
1:13:45
million light years on the small end to three hundred
1:13:49
million light years for the largest known examples. Inside a void,
1:13:54
the mean density of matter is less than a tenth
1:13:58
of the cosmic average. Galaxies are not absent entirely. There
1:14:03
are isolated galaxies and small groups scattered through void regions,
1:14:08
but they are so sparse that the void is, on
1:14:12
cosmic terms, essentially empty. If you lived in a galaxy
1:14:18
inside one of the large voids bordering Laniakaia, your view
1:14:22
of the night sky would be far lonelier than ours.
1:14:26
The nearest large galaxy cluster might be a hundred million
1:14:31
light years away. The universe would look far emptier than
1:14:35
it do as from our position. What makes this architecture
1:14:40
striking is that it is not unique to Laniakia. The
1:14:44
same pattern clusters at the nodes, filaments connecting them, voids
1:14:51
filling the space between, appears everywhere in the observable universe.
1:14:56
At these scales, cosmologists call it the cosmic It is
1:15:01
the large scale structure of the universe, and it was
1:15:05
not designed. It emerged naturally from gravity acting on the
1:15:10
tiny density fluctuations left over from the earliest moments of
1:15:15
cosmic history. Simulations that start from the conditions of the
1:15:20
early universe and run the physics forward reproduce this filamentary
1:15:25
structure automatically. The web was always going to form this
1:15:30
way given those initial conditions. Laniakia is one node in
1:15:36
that larger web, surrounded by neighboring superclusters that have the
1:15:41
same e internal architecture of clusters filaments voids, each one
1:15:48
connected to others across distances that dwarf even Laniakia itself.
1:15:53
This matters for how you think about what Laniakia is.
1:15:57
It is not a bounded object floating in empty space.
1:16:01
It is a region of the cosmic web that has
1:16:04
a coherent gravitational basin, a region where galaxy motions converge
1:16:10
toward a common center, but its edges blend into surrounding
1:16:14
structures that are themselves organized the same way. The filaments
1:16:20
inside Laniakia connect outward to filaments in neighboring superclusters. The
1:16:26
voids inside Laniakia open onto voids that extend far beyond
1:16:31
its defined boundary. The structure has no sharp walls. It fades,
1:16:37
bleeds outward, continues from inside. Living in a galaxy on
1:16:43
the outer edge of one of the smaller filamentary extensions,
1:16:48
you see almost none of this. You see a sky
1:16:51
full of stars that all belong to your galaxy. You
1:16:56
see a handful of nearby galaxies with a telescope. If
1:17:01
you look at the distribution of distant galaxies across the
1:17:04
whole sky with a powerful enough survey, you start to
1:17:09
see hints of the filamentary structure over dense regions in
1:17:13
some directions, under dense regions in others. But the full
1:17:19
three dimensional picture the bones of Laniakia only becomes visible
1:17:25
when you map thousands of galaxies across hundreds of millions
1:17:29
of light years and trace how they are moving. This
1:17:33
is not a structure you would recognize from the inside.
1:17:38
That is exactly why it took until two thy fourteen
1:17:42
for anyone to draw its full outline. Here is the
1:17:45
strange part Laniakia is not actually held together. There is
1:17:50
a difference between a gravitationally bound structure and a basin
1:17:54
of attraction. A gravitationally bound structure is one where gravity
1:18:00
he wins, where the objects inside it are locked together
1:18:04
tightly enough that expansion cannot pull them apart. Galaxy clusters
1:18:10
are bound. The Virgo cluster, sitting near the center of
1:18:14
our local corner of Laniakia, holds thousands of galaxies in
1:18:19
a gravitational grip. They will never escape. Those galaxies are
1:18:24
not going anywhere. They will continue orbiting, colliding, eventually merging
1:18:31
over tens of billions of years into something unrecognizable. But
1:18:35
they will stay together. Our own local group is bound.
1:18:41
The Milky Way and the Andromeda galaxy are falling toward
1:18:45
each other right now, closing the gap at roughly one
1:18:49
hundred ten kilometers per second. In about four point five
1:18:54
billion years, they will collide. That is a gravitationally bound
1:18:59
system behavior exactly as bound systems do. Laniakia is something different.
1:19:05
Its galaxies are not locked to each other. They are
1:19:09
simply flowing in the same direction, pulled toward the greater tractor,
1:19:14
the way water flows toward the lowest point in a valley.
1:19:18
The structure has coherence because the flows are real and measurable,
1:19:24
but coherence is not the same as a bond. A
1:19:27
river has coherence the water moves together in a shared
1:19:33
direction following the same gradient. But the river does not
1:19:37
hold itself together. It flows because the landscape underneath it
1:19:42
slopes a certain way. Remove the slope and the river stops.
1:19:49
Laniakia is similar. Its structure exists because the gravitational landscape
1:19:54
of this region of space slopes inward toward the greater tractor.
1:20:00
The galaxies follow that slope right now in this epoch
1:20:05
of cosmic history. T hat slope is real enough to
1:20:09
define an enormous coherent supercluster. But there is something else
1:20:14
shaping that landscape. Dark energy is real. It is the
1:20:19
dominant energy component of the universe, and it is working
1:20:23
against gravity at every scale large enough for the expansion
1:20:28
of space to matter. On the scale of galaxy clusters,
1:20:33
gravity wins. On the scale of superclusters, the contest is
1:20:38
closer on the scale of Laniakia. Dark energy is already winning.
1:20:44
At the outer edges. The expansion of the universe is
1:20:48
not uniform in its effects. Galaxies that are gravitationally bound
1:20:53
to each other are immune. The expansion of space does
1:20:57
not reach in and tear apart structures the are already
1:21:00
gravitationally locked, But galaxies on the outer fringes of Laniakia,
1:21:06
where the gravitational pull from the center is weaker and
1:21:10
the distances are greater, are in a different situation. For
1:21:15
those galaxies, the outward push of cosmic expansion is already
1:21:20
comparable too or greater than the inward pull of gravity.
1:21:26
Over time, that balance tips further toward expansion. The outer
1:21:32
galaxies drift, then they accelerate away. The boundary of the
1:21:38
structure does not hold. Think about what this means practically.
1:21:43
Right now, a galaxy near the edge of Laniakia is
1:21:47
technically part of the supercluster. Its motion if you subtract
1:21:52
out the general expansion of the universe points inward. It
1:21:57
is part of the flow. Over hundreds of billions of years,
1:22:02
the expansion rate increases relative to the gravitational attraction, and
1:22:08
at some point that galaxy's peculiar velocity, the inward drift
1:22:14
that makes it part of Laniakia, gets overwhelmed by the
1:22:18
expanding universe, carrying it away. The galaxy tips over the
1:22:23
watershed divide and effectively leaves the supercluster, not dramatically, not suddenly,
1:22:31
just gradually, inexorably, as cosmic expansion stretches the space between
1:22:37
it and the Greater Tractor until gravity can no longer
1:22:41
bridge the gap. This happens first at the edges and
1:22:46
works inward. The filaments connecting distant clusters weaken and eventually dissolve.
1:22:54
The clusters themselves remain intact. They are bound, but the
1:22:59
threads thinking them across hundreds of millions of light years
1:23:03
slowly break. The supercluster's architecture. That web of bright nodes
1:23:09
connected by strands of galaxies gradually loses its connections. The
1:23:16
nodes persist, the web does not. The Greater Tractor does
1:23:21
not switch off. It remains a massive concentration of matter,
1:23:26
and it continues pulling nearby galaxies toward it. But its
1:23:30
gravitational reach has a limit, and that limit gets shorter
1:23:34
as dark energy drives space to expand faster. Currently, the
1:23:40
Greater Tractor's influence extends across the full scale of Laniakia,
1:23:45
roughly two hundred and fifty million light years in all
1:23:48
directions over hundreds of billions of years. The region where
1:23:54
its gravity beats out expansion contracts. More and more of
1:23:58
the supercluster's outer volume crosses over into territory where expansion wins.
1:24:04
What you are left with Eventually is not Laniakia. You
1:24:09
are left with a collection of bound galaxy clusters, each isolated,
1:24:14
each intact within itself, but separated from all the others
1:24:19
by expanding voids too large for gravity to bridge. The
1:24:24
greater tractor's neighbourhood survives as a dense core. The outlying
1:24:30
regions drift away into the darkness. Nothing remains to show
1:24:35
that these clusters were ever connected, that galaxies across five
1:24:40
hundred twenty million light years once all flowed toward the
1:24:44
same gravitational basin. This is the strange status Laniakia holds.
1:24:51
It is real, the flows that define it are measurable.
1:24:55
The structure that Brent Tully's team drew in twenty fourteen
1:24:59
is coherent and meaningful, and yet it is not permanent
1:25:03
in the way that a galaxy is permanent, or a
1:25:06
star or a planet. It exists as a structure only
1:25:10
because we happen to be living in an epoch when
1:25:13
its coherence is intact, when the gravitational flows are strong
1:25:18
enough relative to expansion to give it definable shape and
1:25:23
definable borders. In a universe older than ours by a
1:25:27
factor of ten or one hundred, there would be no
1:25:31
Laniarka to find, there would be no flow to map.
1:25:37
We mapped it just in time, in a sense, a
1:25:40
structure coherent enough to define today but destined to dissolve
1:25:45
over time scales longer than the current age of the universe.
1:25:49
To define a structure by how galaxies move, you first
1:25:53
have to know where those galaxies actually are. That sounds obvious,
1:25:58
it is in practice one of the hardest problems in
1:26:02
observational astronomy, and solving it took the better part of
1:26:06
five decades. Here is the core difficulty. You cannot lay
1:26:11
a measuring tape across space. You cannot bounce a signal
1:26:15
off a galaxy one hundred million light years away, and
1:26:18
time the echo. Every method astronomers have for measuring cosmic
1:26:23
distances is indirect. Each one rests on a physical relationship
1:26:29
something that connects a property you can observe to a
1:26:32
property you cannot directly measure, and each one carries error.
1:26:38
Small errors in distance, when converted into peculiar velocities, produce
1:26:43
large errors in the flow maps. The flow maps are
1:26:48
only as clean as the distances underneath them. Everything that
1:26:52
makes Laniakir real and mappable and coherent traces back to
1:26:57
this unglamorous problem of actually pinning down where things are.
1:27:01
The way astronomers approach this is through what they call
1:27:05
the distance ladder. The idea is to build outward in steps.
1:27:11
Each step uses a method that works reliably over a
1:27:14
certain range of distances but fails beyond it. Each new
1:27:19
method gets calibrated against the previous one before you trust
1:27:23
it at greater distances. The bottom rungs of the ladder
1:27:28
are close enough that geometry alone can do the work. Parallax,
1:27:34
the tiny apparent shift in a nearby star's position, as
1:27:38
Earth orbits the Sun, works out to a few thousand
1:27:42
light years above that. You switch to a different technique
1:27:47
at each transition. You are trusting that the calibration between
1:27:51
methods is solid, because any error there propagates upward through
1:27:56
every measurement you make at greater distances. To reach galaxies
1:28:01
hundreds of millions of light years away, you need methods
1:28:05
that work at truly enormous scales. Two of the most
1:28:10
important are the Tullyfisher relation and the fundamental plane, and
1:28:15
together they are responsible for most of the data that
1:28:19
went into defining Laniakia. The Tullyfisher relation applies to spiral galaxies.
1:28:27
It was noticed in nineteen seventy seven by Brent Tully
1:28:32
and J. Richard Fisher, and the same Tully would later
1:28:36
lead the Laniakia team. What they found was a tight
1:28:40
correlation between how fast a spiral galaxy rotates and how
1:28:44
intrinsically luminous it is. A galaxy spinning faster is more massive,
1:28:51
and more massive galaxies are brighter. If you measure a
1:28:55
spiral galaxy's rotation speed, you can infer how bright it
1:28:59
truly is. Then you compare that true brightness to how
1:29:04
bright it appears in the sky. The difference tells you
1:29:08
how far away the light must have traveled to look
1:29:11
as faint as it does. It's the same logic as
1:29:15
knowing how powerful a light bulb is and using its
1:29:18
apparent dimness to estimate how far down the street it sits.
1:29:23
The challenge is precision. Small uncertainties in the rotation speed
1:29:29
measurement translate into distance errors. Calibrating the relation required extensive
1:29:35
work across nearby galaxies, where independent checks were possible. For
1:29:41
elliptical galaxies, which don't rotate the same way, a different
1:29:46
method applies elliptical galaxies follow what astronomers call the fundamental plane,
1:29:54
a relationship involving three observable quantities the galaxy size, its
1:30:00
surface brightness, and the velocity dispersion of its stars, basically
1:30:06
how fast the stars are moving relative to each other. Internally,
1:30:11
these three properties are not independent. They are linked by
1:30:16
the underlying physics of how elliptical galaxies form and evolve.
1:30:21
If you measure two of them, you can infer the third,
1:30:25
and from the inferred properties you can extract the true luminosity,
1:30:30
which again gives you distance. The fundamental plane is messier
1:30:34
than Tullyfisher in some respects, with more scatter in the relationship,
1:30:39
but it extends the distance ladder to galaxy types that
1:30:42
Tullyfisher cannot reach. The Cosmic Flows project, led by tully
1:30:48
in his team, was built to gather these measurements in
1:30:51
systematic large numbers. The Cosmic Flows two catalog, which fed
1:30:58
directly into the two thousand, five fourteen Laniakia paper, contained
1:31:02
distances for more than eight thousand, one hundred galaxies. That
1:31:08
number sounds large until you realize how vast the volume
1:31:12
of space being mapped actually is. At the outer edges
1:31:16
of the survey, the coverage was thin. Individual galaxies were
1:31:21
separated by gaps where no measurements existed. The flow maps
1:31:27
in those regions were smooth interpolations between real data points.
1:31:32
Every boundary on the Laniakia map is only as sharp
1:31:36
as the data density behind it allows. What cosmic flows
1:31:41
for released years later brought was scale nearly fifty six
1:31:46
thousand galaxy distances, gathered using eight separate methodologies cross checked
1:31:52
against each other. The expanded catalog allowed the flow maps
1:31:57
to extend further and resolve structure more finely. It also
1:32:02
allowed genuine tests of whether the twoenty fourteen boundaries held
1:32:08
up under scrutiny from a data set seven times larger.
1:32:13
Mostly they did, which is itself a statement about how
1:32:18
solid the original analysis was despite the sparse coverage. It
1:32:24
is worth being specific about how much human effort this represents.
1:32:28
Measuring rotation curves for thousands of spiral galaxies requires deep
1:32:34
spectroscopic observations, long nights at large telescopes, careful sky subtraction,
1:32:41
and painstaking reduction of the raw data. It requires doing
1:32:46
this for galaxies that appear as faint smudges in the sky.
1:32:51
It requires going back and remeasuring, checking for systematic errors,
1:32:57
updating calibrations as better nearby act INCA points become available.
1:33:02
The Cosmic flows catalogs reflect observational campaigns stretching back to
1:33:08
the nineteen seventies, accumulated across hundreds of telescope nights at
1:33:14
facilities from Hawaii to the Canary Islands to Chile. Nobody
1:33:20
did this in a single coordinated push. It accumulated peace
1:33:25
by piece, researcher by researcher over four decades, until the
1:33:31
database was large enough and reliable enough to trace the
1:33:35
floes that outlined Laniakia. The map of Laniakia is only
1:33:40
as reliable as the distances that went into building it,
1:33:44
which means it rests on decades of unglamorous observational work
1:33:50
that most people never hear about. If Laniakia had a neighbourhood,
1:33:55
the Shapleigh Supercluster would be its nearest significant neighbour, and
1:34:01
the relationship between them is not simple. The Shapleigh Supercluster
1:34:07
sits roughly six hundred fifty million light years away, That
1:34:13
is several hundred million light years further out than the
1:34:16
Greater Tractor, which already sits one hundred fifty to two
1:34:21
hundred fifty million light years from the Milky Way. By
1:34:26
any measure, Shapley is distant, but distant does not mean irrelevant.
1:34:33
Shapley is one of the most massive concentrations of matter
1:34:37
in the observable universe, and its gravitational influence reaches far
1:34:42
beyond its own boundaries. When astronomers began measuring the peculiar
1:34:48
velocities of galaxies throughout and around Laniakia, something strange kept
1:34:54
showing up in the data. The greater tractor was not
1:34:58
just pulling nearby galaxy toward itself, it was also moving.
1:35:04
The entire gravitational center of Laniakia was drifting, being pulled
1:35:09
in Shapley's direction. This is where the picture gets complicated.
1:35:15
Laniakia was defined as a basin of attraction, a region
1:35:19
where galaxy motions converge inward toward a shared gravitational center.
1:35:25
That definition worked cleanly within its mapped boundaries. But the
1:35:30
greater tractor at Laniakia's core is itself part of a
1:35:34
larger flow. Something with even more mass is pulling on
1:35:39
it from further out. The Shapley concentration, as astronomers sometimes
1:35:45
call it, generates a gravitational pull strong enough to tug
1:35:50
on a structure containing one hundred quadrillion solar masses, which
1:35:55
raises a real question. Is Laniakia truly an independent basin
1:36:01
or is it a smaller valley inside a larger one,
1:36:04
one that drains ultimately towards Shapley. There is no clean
1:36:09
answer yet. Some analyzes suggest Laniakia and the off Yucus
1:36:14
cluster region form a combined basin that flows towards Shapleigh,
1:36:19
which would make Laniakia a sub basin rather than a
1:36:23
top level structure. Others maintain that the flow patterns are
1:36:27
distinct enough to treat them separately. The boundary is fuzzy.
1:36:33
That fuzziness is not a failure of science. It reflects
1:36:38
the fact that the universe does not organize itself into
1:36:41
tidy boxes. Gravity does not stop at the edges of
1:36:46
whatever structure we choose to name. Then something else turned
1:36:50
up entirely. In twenty twenty, a team of astronomers announced
1:36:55
the discovery of a massive structure lying just beyond Laniakia's boundary.
1:37:01
They called it the South Pole Wall. The name comes
1:37:05
from its orientation in the sky, concentrated near the south
1:37:09
celestial pole and extending outward in a great sweeping arc.
1:37:15
The scale of it is hard to take in. The
1:37:18
south Pole Wall stretches across roughly two hundred degrees of sky,
1:37:23
more than a semicircle. It wraps around Laniakia like an arm.
1:37:29
The densest part of the structure sits about five hundred
1:37:32
million light years from the Milky Way, but following the
1:37:36
arc northward, it curves inward to within three hundred million
1:37:40
light years of us. It is not some distant background feature,
1:37:46
it is immediately adjacent. What makes the south Pole Wall
1:37:50
particularly striking is how long it went unnoticed. Part of
1:37:55
the answer is the zone of avoidance. A significant porsche
1:38:00
of this structure lies behind the galactic plane, hidden behind
1:38:04
the dust and gas of the Milky Way. The tools
1:38:08
that revealed it, the same peculiar velocity mapping technique used
1:38:13
to define lania KaiA, are better at seeing through that
1:38:16
obstruction than optical surveys. The South Pole Wall is a
1:38:22
reminder that Laniakia does not float in empty space. It
1:38:27
sits within a rich, dense cosmic environment, bordered by enormous
1:38:32
structures that we are still in the process of cataloging.
1:38:36
In twenty twenty three, a study using the Cosmic Flow's
1:38:40
four catalog pushed this work further. Cosmic Flows four contains
1:38:46
distances for nearly fifty six thousand galaxies compared to the
1:38:50
eight thousand, one hundred used in the original two thy
1:38:54
fourteen Laniakia paper. With that much more data, the wa
1:39:00
watershed technique could be applied at larger scales and with
1:39:04
better precision. The result was a map that confirmed Laniakia's
1:39:09
size and shape and simultaneously identified five neighbouring superclusters using
1:39:15
the same method. Those neighbours are Shapley, Perseus Pisces, Hercules, Leapus,
1:39:22
and APUs. Each one is a distinct gravitational basin in
1:39:27
its own right, a region where galaxy motions converge inward,
1:39:32
just as they do within Laniakia. Each one is enormous,
1:39:36
and each one sits adjacent to Laniakia in a way
1:39:40
that makes the entire local region of the universe feel
1:39:44
increasingly crowded and interconnected. Perseus Pisces is one of the
1:39:50
largest concentrations of matter in the nearby universe, a long,
1:39:56
filamentary structure stretching across hundreds of millions of light years
1:40:01
in a completely different direction from Shapley Hercules sits further out,
1:40:08
a less concentrated but still massive structure. Lepus and APUs
1:40:13
are less studied, less well characterized, identified primarily through the
1:40:19
flow signatures in the cosmic flows for data, rather than
1:40:23
through dense optical surveys. These are not minor footnotes. They
1:40:29
are superclusters, and Laniakia sits among them, not at the
1:40:34
edge of organized structure, but deep inside a web of it.
1:40:39
This brings in the Pisces Setus supercluster complex. This is
1:40:43
an even larger organizational level, a structure that contains Laniakia, Perseus,
1:40:49
Pisces Cetus, and several other components in a single elongated
1:40:55
complex stretching across roughly a billion light years. The Pisce's
1:41:00
Cetus complex is among the largest known structures in the
1:41:04
observable universe. Laniakia is its inner component, its central region,
1:41:11
which means the structure we spent so much effort defining,
1:41:15
the one that took decades of observational work to map,
1:41:19
is itself a neighborhood inside something far larger. There is
1:41:24
a pattern here. Before twenty fourteen, our largest named home
1:41:30
was the Virgo supercluster. Then Lanyakia absorbed it and grew
1:41:35
the answer by a factor of five in diameter. Now,
1:41:39
Laniakia sits inside the Pisce's Cetus complex and flows towards Shapley.
1:41:45
Each time astronomers step back and look at a larger volume,
1:41:49
The structure does not end. It continues. New walls, new clusters,
1:41:56
new basins of attraction keep appearing at the edges of
1:41:59
whatever app was just completed. This is not a coincidence.
1:42:04
It is what the physics predicts. Gravity has been operating
1:42:08
on matter for thirteen billion years, pulling density enhancements into
1:42:13
galaxy clusters, pulling clusters toward each other along filaments, pulling
1:42:19
superclusters into still larger flows. There is no obvious scale
1:42:25
at which this process terminates. The cosmic web extends across
1:42:30
the entire observable universe ninety three billion light years in diameter,
1:42:36
and on that scale, the largest structures observable are only
1:42:41
a small fraction of the whole. Laniakia, at five hundred
1:42:46
twenty million light years, is enormous by human standards and
1:42:50
unremarkable by universal ones. What lies beyond Laniakia, then, is
1:42:56
not emptiness. It is more structure, more flow, more mass
1:43:01
concentrations pulling on each other across distances that make Laniakir
1:43:06
itself look modest. The south pole wall wraps around it shaply,
1:43:12
pulls on it from one direction. Perseus Pisces anchors a
1:43:17
different gravitational basin nearby. The cosmic Flows four catalog has
1:43:22
already pushed the frontier outward, and the catalogs that follow
1:43:26
will push it further still. Every boundary we draw around
1:43:31
our cosmic home turns out to have something larger just
1:43:35
outside it. From far enough out, the universe looks like
1:43:39
a net, not a metaphor, not a poetic approximation. When
1:43:46
astronomers map the distribution of galaxies across hundreds of millions
1:43:50
of light years, the actual image that comes back looks
1:43:55
like a three dimensional mesh, bright filaments running between dens
1:44:00
its nodes, with vast dark holes where almost nothing lives.
1:44:05
Superclusters sit at the intersections, filaments run between them, and
1:44:11
the space in between. Most of the volume of the
1:44:15
universe is nearly empty. This is the cosmic web, and
1:44:20
Laniakia is one small piece of it. The scale of
1:44:25
the observable universe is roughly ninety three billion light years
1:44:29
across Laniakia spans about five hundred twenty million light years
1:44:36
do the math our entire supercluster, with its one hundred
1:44:41
thousand galaxies and mass equivalent to one hundred quadrillion suns,
1:44:46
occupies less than one percent of the observable universe's diameter.
1:44:51
Drop it into the full cosmic map, and it becomes
1:44:55
difficult to find. The web extends in every direction, repeating
1:45:00
its pattern of filaments and voids and dense nodes all
1:45:04
the way to the edge of what we can see.
1:45:07
Laniakia is one node in that pattern. Nothing about its
1:45:12
location is obviously special, nothing marks it as unusual among
1:45:17
the thousands of similar structures scattered across the cosmic map.
1:45:22
The voids are the part that most people don't expect.
1:45:26
When you picture the universe packed with galaxies, you are
1:45:30
picturing the bright parts, the filaments and clusters. But the voids,
1:45:36
those enormous dark regions between the filaments, are not exceptions
1:45:41
to the rule. They are the rule. The voids dominate.
1:45:47
A single void can stretch one hundred to three hundred
1:45:50
million light years across some of the largest the supervoids
1:45:56
are even bigger. The density inside them is less than
1:46:00
a tenth of the average density of the universe. Galaxy
1:46:04
after galaxy, cluster after cluster, essentially nothing for hundreds of
1:46:10
millions of light years in any direction. The universe, by volume,
1:46:15
is mostly darkness. The bright web we trace is a
1:46:20
thin skeleton stretched across an enormous emptiness. What makes this
1:46:25
structure strange is that it was predictable. Scientists did not
1:46:30
discover the cosmic web by looking at the sky and
1:46:33
then scrambling to explain what they saw. They predicted it
1:46:37
first from the mathematics of gravity and the initial conditions
1:46:42
of the early universe, and then confirmed it through observation.
1:46:47
The Millennium simulation, run in two thousand five by a
1:46:51
team including Folka, Springle and hundreds of collaborators, started with
1:46:57
conditions matching the early universe and ran gravity forward across
1:47:02
thirteen billion years of simulated time. The result was a
1:47:07
filamentary web of structure that matched the observed distribution of
1:47:12
galaxies with uncomfortable precision. Uncomfortable because nothing about the early
1:47:19
universe looked like it was headed toward this. The early
1:47:23
universe was almost perfectly smooth, almost not quite The temperature
1:47:29
variations in the cosmic microwave background are tiny one part
1:47:34
in one hundred thousand, but they were there baked into
1:47:38
the universe by quantum fluctuations in the first fraction of
1:47:41
a second. After the Big Bang. Inflation stretched those quantum
1:47:46
variations to macroscopic scales. Gravity did the rest. Regions that
1:47:53
were slightly denser than average pulled in more matter. Regions
1:47:58
that were slightly less dense long lost matter to their neighbours.
1:48:02
Over hundreds of millions of years, the slight variations grew,
1:48:07
dense regions became filaments, The densest intersections of filaments became
1:48:13
clusters and superclusters. The under dense regions became voids. The
1:48:19
same process, operating on the same initial conditions produces the
1:48:24
same web pattern every time you run the simulation. The
1:48:27
cosmic web is not accidental. It is the inevitable output
1:48:32
of simple physics applied to a nearly uniform starting state.
1:48:37
The Illustrious simulation and its successor Illustrious TNNG pushed this further.
1:48:45
These models incorporated not just gravity, but gas dynamics, star formation,
1:48:51
black hole feedback, and the influence of dark energy. The
1:48:56
resulting simulated universes looked at large scale almost indistinguishable from
1:49:02
what we observe. Filaments in the right places, voids of
1:49:07
roughly the right size, clusters of roughly the right mass.
1:49:13
The match is not perfect. There are still open questions
1:49:17
about the precise distribution of matter on small scales, but
1:49:22
the broad architecture of the cosmic web has been reproduced
1:49:26
repeatedly from first principles. This is one of the more
1:49:30
remarkable facts in all of modern cosmology. The largest structures
1:49:35
we can observe were written into the universe before the
1:49:39
first star ever formed. Laniakia sits in this web the
1:49:44
way any other supercluster does. It is a gravitational basin,
1:49:49
a node where filaments converge and matter has pooled over
1:49:54
billions of years. On the full cosmic map, at the
1:49:58
scale where lania Kaya becomes a recognizable object, dozens of
1:50:03
similar structures are visible in every direction. The Shaply supercluster,
1:50:08
the Perseus Pisces chain, the Hercules supercluster, each one a
1:50:14
basin like Laniakia, each one pulling its local collection of
1:50:18
galaxies inward, each one connected to its neighbours by filaments
1:50:23
and separated by voids. The cosmic web at this scale
1:50:28
looks almost biological dense nodes connected by thin, bright threads
1:50:34
vast dark cavities in between. If you have ever seen
1:50:39
an image of neurons under a microscope, or a leaf's
1:50:42
vein structure, or the foam that forms when soap bubbles
1:50:46
crowd together, those images all resemble the cosmic web for
1:50:52
the same mathematical reason that different physical systems driven by
1:50:57
similar branching processes tend to produce similar geometric patterns. There
1:51:03
is nothing cosmologically remarkable about Laniakir's position in this web.
1:51:08
It is not at the center of anything. It is
1:51:11
not the most massive node within reach. It is one
1:51:15
of many similar structures spread across a universe that extends
1:51:19
unimaginably far beyond what any current telescope can probe. The
1:51:25
only thing that makes Laniyakir unusual is our location inside it.
1:51:30
Because we are here, we can study it in detail
1:51:33
that is impossible for any other supercluster. We know its shape,
1:51:38
its mass, its internal flows, the positions of its major clusters,
1:51:44
the behavior of its filaments. We have mapped it at
1:51:48
a resolution no other supercluster will achieve in any telescope
1:51:53
that currently exists. That is the advantage of being inside
1:51:58
something rather than looking at it from across the universe.
1:52:03
Laniakia is one knot in that net, not special in
1:52:07
any obvious cosmological sense, but the knot we happen to
1:52:11
be able to examine from the inside. One of the
1:52:15
earliest clues that something was pulling our region of the
1:52:19
universe came not from counting galaxies, but from measuring temperature.
1:52:25
In the nineteen seventies, when physicists first mapped the cosmic
1:52:30
microwave background in fine detail, they expected to find something
1:52:35
close to uniform. The CMB is the afterglow of the
1:52:39
Big Bang light released roughly three hundred eighty thousand years
1:52:45
after the universe began, now cool to just a few
1:52:49
degrees above absolute zero, arriving at our detectors from every
1:52:55
direction in the sky. If the universe were perfectly smooth,
1:53:00
and we were sitting still relative to that background, the
1:53:04
temperature would be essentially the same in every direction. It
1:53:08
is not. One side of the sky runs slightly warmer,
1:53:12
the opposite side runs slightly cooler. The difference is tiny,
1:53:18
on the order of a thousandth of a degree, but
1:53:21
it is real, clean and impossible to ignore that asymmetry
1:53:26
is called the CMB dipole, and what it tells you
1:53:30
is motion. When you move toward a source of light,
1:53:33
the waves compress slightly and shift toward higher energy, higher temperature,
1:53:39
move away, and they stretch, cooling down. The dipole in
1:53:44
the CMB is a Doppless signature. Our entire region of
1:53:49
the universe is moving, moving fast, roughly six hundred kilometers
1:53:54
per second relative to the background radiation that fills all
1:53:58
of space. That the number raised an immediate question. Six
1:54:02
hundred kilometers per second is not slow. It is not
1:54:06
something you can attribute to the gravity of a nearby
1:54:09
galaxy cluster or even a modest supercluster. Something with enormous
1:54:15
gravitational pull had to be responsible, and when astronomers tried
1:54:20
to account for all the known mass in the local universe,
1:54:24
all the visible galaxy clusters within a few hundred million
1:54:28
light years, they could not explain it. The pull of
1:54:33
known structures was not enough. There was a missing source.
1:54:38
That gap was one of the first signs pointing toward
1:54:42
what would eventually be called the Greater tractor, the gravitational
1:54:48
engine sitting near the center of Laniakir, pulling our local
1:54:52
group and thousands of other galaxies toward a common point
1:54:57
hundreds of millions of light years away. What made this
1:55:01
early evidence particularly strange was that the bulk flow was
1:55:05
not just ours. Individual galaxies near by were showing anomalous
1:55:10
velocities in the same general direction. Galaxy clusters across a
1:55:16
wide region of space were all drifting toward the same
1:55:19
part of the sky, faster than the cosmic expansion alone
1:55:24
could explain. This is what peculiar velocities look like in practice,
1:55:30
not random noise scattered in all directions, but a coherent
1:55:35
drift a tide millions of galaxies all leaning the same way.
1:55:41
The CMB dipole was the loudest signal, but the galaxy
1:55:46
velocities were the conformation that the effect was real and widespread.
1:55:52
The problem with early peculiar velocity data was that it
1:55:56
depended entirely on galaxy distance measurements that carry their own uncertainties.
1:56:02
If your distances are slightly wrong, your inferred velocities are wrong.
1:56:08
A pattern that looks coherent might dissolve under better measurements.
1:56:13
Astronomers needed a way to check the velocity field independently,
1:56:18
using a completely different physical process that check eventually arrived
1:56:23
in the form of a phenomenon called the kinetic Sunyayev
1:56:26
Zeldevich effect. Here is the basic picture. Galaxy clusters contain
1:56:32
enormous clouds of hot gas plasma at tens of millions
1:56:36
of degrees, threaded through the space between individual galaxies. When
1:56:42
CMB photons travel through this hot gas, they interact with
1:56:47
the fast moving electrons. If the cluster itself is moving
1:56:51
relative to the CMB rest frame, this interaction leaves a
1:56:55
subtle imprint on those photons moving toward us. The cluster
1:57:01
slightly boosts the energy of passing photons moving away, it
1:57:06
slightly reduces it. The effect is extraordinarily small. Detecting it
1:57:13
requires precise microwave observations, careful subtraction of other signals, and
1:57:19
large statistical samples of clusters. But it is physically distinct
1:57:24
from anything in the galaxy distance measurements, no Tully fissure relations,
1:57:30
no fundamental pe Lane corrections, no distance ladder, just microwave
1:57:37
photons and hot gas and the Doppler shift of a
1:57:40
moving cluster read directly from the sky. When researchers began
1:57:45
applying kinetic sunya of Zeldevich measurements to galaxy clusters across
1:57:49
the local universe. The results were striking. The clusters showed
1:57:54
bulk motion, not random velocities pointing in scattered directions, but
1:58:00
a coherent flow in roughly the direction of the greater tractor,
1:58:05
consistent with what the peculiar velocity surveys had been showing
1:58:09
for decades. This was not a marginal overlap. The independent probe,
1:58:16
built on entirely different physics, pointed toward the same gravitational
1:58:21
basin that Tully's watershed analysis had defined using galaxy flows.
1:58:26
What this convergence means is important. A recurring concern whenever
1:58:32
a large scale structure gets mapped from peculiar velocities is
1:58:37
that the result might be an artifact, a product of
1:58:41
which galaxies happened to be measured, that surveys covered, which
1:58:46
parts of the sky, which distance methods were applied. Lanyakir
1:58:51
was defined using a specific catalog of roughly eight thousand galaxies,
1:58:57
that is, a finite sample with finite coverage. If the
1:59:01
pattern were statistical noise, independent probes using different physics on
1:59:07
different objects should produce a different picture. They do not.
1:59:12
The CMB dipole. The bulk flow studies of the nineteen
1:59:17
eighties and nineteen nineties, the kinetic Sunyayev Zeldovich measurements from
1:59:23
large microwave surveys all describe the same motion across the
1:59:28
same enormous volume of space. Multiple independent methods of measuring
1:59:33
motion at cosmic scales now point toward the same picture,
1:59:38
a coherent flow of galaxies across hundreds of millions of
1:59:43
light years converging on the same gravitational basin. We do
1:59:48
not live near the heart of Lanyakir. The Milky Way
1:59:53
sits out near the edge, somewhere on the outer rim
1:59:57
of a structure five hundred twenty million light years across,
2:00:01
pulled slowly but measurably toward the gravitational center. Slowly is
2:00:07
the key word. The distance between us and the greater
2:00:12
tractor is somewhere between one hundred fifty and two hundred
2:00:16
fifty million light years at our current in full velocity,
2:00:21
reaching it would take far longer than the current age
2:00:24
of the universe, and dark energy will almost certainly intervene
2:00:30
before any arrival is possible. So we are falling inward technically,
2:00:35
but we are never going to get there we are
2:00:38
permanent residents of the outskirts. What would it look like
2:00:42
to live somewhere else. Imagine the Milky Way had formed
2:00:47
closer to the dense core of Lania Ka, near one
2:00:51
of the major clusters at the heart of the structure.
2:00:55
The sky would look different in ways that are hard
2:00:57
to fully picture. Galaxy density near the center is dramatically higher.
2:01:04
Neighboring galaxies would be closer. Interactions and mergers between galaxies
2:01:11
happen far more frequently in dense environments, and those collisions
2:01:16
drive bursts of star formation, reshape spiral arms, heat the
2:01:21
surrounding gas, and feed supermassive black holes into periods of
2:01:25
intense activity. A galaxy in that environment would be a
2:01:30
different kind of place, noisier, more active, more frequently disrupted.
2:01:37
The quiet spiral structure of the Milky Way, which has
2:01:40
remained relatively undisturbed for billions of years, is partly a
2:01:45
product of where we ended up. The outskirts are calm
2:01:49
out here, the galaxy density drops in some directions. The
2:01:55
voids open up regions tens of millions or hundreds of
2:01:59
million millions of light years across where almost nothing lives.
2:02:04
These are not empty in an absolute sense, but the
2:02:07
density of matter is less than a tenth of the
2:02:10
universe's average, and galaxies in voids are rare and isolated things.
2:02:17
We have voids opening up around us in certain directions
2:02:20
right now. The local group is not completely alone, but
2:02:25
it is a small association of galaxies in a relatively
2:02:29
sparse region far from the nearest major cluster. That is
2:02:34
just the reality of living on the periphery of a supercluster.
2:02:39
The closest large cluster to us, the Virgo cluster, is
2:02:44
still fifty to sixty million light years away. In cosmic terms,
2:02:50
that is a neighbour. In any other terms, it is
2:02:54
an almost meaningless distance. There is something worth sitting with here.
2:03:00
The fact that we ended up in this particular location,
2:03:03
on the quiet edge rather than the turbulent core, is
2:03:07
not a coincidence in the way luck is a coincidence.
2:03:12
It is the outcome of processes that were set in
2:03:15
motion almost fourteen billion years ago, and this is where
2:03:20
the story gets genuinely strange. The structure of Laniakia, the
2:03:25
reason the Greater Tractor exists where it does, the reason
2:03:30
the Milky Way formed in the specific region of space
2:03:33
it occupies. All of it traces back to conditions in
2:03:37
the first fractions of a second after the Big Bang.
2:03:41
The early universe was almost perfectly uniform. Almost There were
2:03:47
tiny fluctuations in density, variations so small that the temperature
2:03:53
difference they created in the cosmic microwave background is measured
2:03:57
in hundred thousandths of a degree. These fluctuations were not
2:04:02
random in the classical sense. They were quantum mechanical. At
2:04:07
the smallest scales, imaginable quantum uncertainty produces unavoidable variations in
2:04:14
energy density in the very early universe. During the period
2:04:19
cosmologists call inflation, space expanded so violently and so fast
2:04:26
that those microscopic quantum fluctuations were stretched to cosmic scales.
2:04:32
A variation that existed across a distance smaller than a
2:04:35
proton became after inflation, a variation spread across what would
2:04:41
eventually be millions of light years. T He universe locked
2:04:46
those fluctuations in as it expanded. Gravity did the rest.
2:04:51
Over billions of years. Regions that were even slightly denser
2:04:55
than average pulled in surrounding matter. The denser they got,
2:05:00
the more they pulled, the emptier regions got emptier. As
2:05:05
matter drained away toward the denser ones, What started as
2:05:09
a near uniform gas of hydrogen and helium slowly organized
2:05:14
itself into the cosmic web filaments and clusters and voids
2:05:19
over time, scales measured in billions of years. The greater Tractor,
2:05:25
the dense concentration of mass at the heart of Laniaka,
2:05:29
formed because gravity amplified a slight over density that had
2:05:34
its origin in a quantum event that happened before a
2:05:37
single atom existed. That is not a small claim. The
2:05:42
reason the Milky Way is where it is, the reason
2:05:46
we are on the outskirts of this particular structure rather
2:05:49
than somewhere else, traces back to a quantum fluctuation that
2:05:55
was inflated to cosmic scales before the universe was a
2:05:59
second old. There was no inevitability to the specific location.
2:06:05
If the fluctuations had been arranged slightly differently, the large
2:06:10
scale structure would have assembled differently. The Greater Tractor would
2:06:15
be somewhere else, the Milky Way would be somewhere else.
2:06:21
The whole map changes with tiny differences in those initial conditions.
2:06:27
We are here because of randomness that occurred at the
2:06:30
very bottom of physical reality. And was then enlarged to
2:06:35
a scale of hundreds of millions of light years. This
2:06:38
is not philosophy drifting away from the science. It is
2:06:42
the science. Cosmologists can take the measured fluctuations in the
2:06:47
cosmic microwave background, run them forward through simulations using known physics,
2:06:54
and reproduce structures that look like the cosmic web we
2:06:57
actually observe. Emulations produce filaments, voids, clusters, and superclusters in
2:07:06
roughly the right proportions and at roughly the right scales.
2:07:10
The structure is predictable. The specific arrangement is not. The
2:07:17
quantum randomness of the earliest moments of the universe, amplified
2:07:22
by gravity over thirteen billion years is what put us
2:07:26
where we are, on the quiet edge of an immense heaven.
2:07:32
If you wanted to write out where you live in
2:07:34
the most complete way possible, the address would be longer
2:07:38
than most people expect. Start with the obvious part. Earth
2:07:44
a rocky planet about eight thousand miles across, orbiting an
2:07:49
average star roughly ninety three million miles away. That star
2:07:54
is the Sun, and the Sun sits inside a solar
2:07:57
system that stretches roughly foa to five light hours out
2:08:01
to Neptune, and considerably further if you count the loose
2:08:06
halo of comets at its outer edge. That whole region,
2:08:11
every planet, every moon, every chunk of rock and ice
2:08:16
that gravitationally belongs to our star fits inside a bubble
2:08:21
perhaps two light years across at its most generous estimate.
2:08:26
That is your street address, a two light year bubble
2:08:30
in a cosmos ninety three billion light years wide. Step outward,
2:08:37
the Sun is one of somewhere between two hundred and
2:08:39
four hundred billion stars in the Milky Way galaxy. The
2:08:44
Milky Way is a barred spiral, a flat rotating disc
2:08:49
about one hundred thousand light years across and roughly one
2:08:53
thousand light years thick through much of its disk. The
2:08:57
Sun sits about twenty six thousand light years from the
2:09:01
galactic centre, out in one of the spiral arms, in
2:09:06
a fairly quiet and unremarkable neighbourhood. The Solar System is
2:09:11
so small compared to the Milky Way that if you
2:09:15
shrunk the galaxy to the size of North America, the
2:09:19
entire Solar system would be smaller than a dime. The
2:09:23
Milky Way is your city, and it is already almost
2:09:28
incomprehensibly large, but the Milky Way is not alone. It
2:09:33
belongs to a collection of galaxies called the Local Group,
2:09:37
a gravitationally bound cluster of roughly eighty known galaxies spread
2:09:43
across approximately ten million light years. Most of these eighty
2:09:48
galaxies are small. The dominant members are the Milky Way
2:09:53
and Andromeda, two large spirals falling toward each other at
2:09:57
several hundred kilometers per second and expected to collide in
2:10:02
about four billion years. The Local Group is your region,
2:10:08
your county. If you're keeping the metaphor, running ten million
2:10:12
light years is one hundred times the width of the
2:10:15
Milky Way, hold that ratio in your head, because it
2:10:20
is about to repeat itself. The Local Group is one
2:10:25
small cluster among many in the Virgo Supercluster. This structure,
2:10:30
which astronomers had considered our home supercluster for decades before
2:10:35
twenty fourteen, stretches roughly one hundred million light years across.
2:10:42
It contains something on the order of one hundred galaxy
2:10:46
groups and clusters. The Virgo Cluster itself a dense concentration
2:10:52
of several thousand galaxies, sitting roughly fifty to sixty million
2:10:57
light years from the Milky Way anchors the structure. The
2:11:03
Virgo supercluster is ten times wider than the local group.
2:11:08
Each step outward in this address multiplies the scale by
2:11:12
a factor that should feel staggering, but somehow keeps arriving
2:11:16
as a routine number in the equations. This is part
2:11:20
of what makes cosmic scales genuinely difficult. The jumps are
2:11:25
not gradual, they are sudden and enormous. And then there
2:11:30
is Laniakia. The Virgo supercluster, it turns out, is not
2:11:35
a standalone structure. It is one subdivision, one lobe of Laniakia,
2:11:42
the supercluster defined in twenty fourteen by tracing the gravitational
2:11:47
flow of galaxies rather than just their density. Laniakia stretches
2:11:53
five hundred twenty million light years across. It contains roughly
2:11:58
one hundred thousand and large galaxies. Its total mass is
2:12:03
something in the neighborhood of ten to the power of
2:12:06
seventeen solar masses, which is one hundred quadrillion suns, a
2:12:11
number that stops being a number and becomes a symbol.
2:12:16
The Virgo supercluster, which felt enormous when it was considered
2:12:20
the top of the hierarchy, is approximately one fifth the
2:12:25
width of Laniakia. What we called the largest structure we
2:12:30
belonged to was a suburb, a small neighbourhood in something
2:12:35
vastly larger that nobody had successfully outlined until fairly recently.
2:12:41
Beyond Laniakia, the address continues. The greater tractor at Laniakia's
2:12:47
center is itself moving toward the Shapleigh Supercluster, several hundred
2:12:52
million light years further out. Laniakia is likely part of
2:12:56
the pissy Seatus supercluster complex, a structure so large it
2:13:01
dwarfs even Laniakia. The south Pole wall wraps around Laniakia's
2:13:07
edge like an arm. These structures together form part of
2:13:12
the cosmic web, the large scale architecture of the observable universe,
2:13:18
filaments of galaxies hundreds of millions of light years long,
2:13:23
connecting nodes like Laniakia, surrounding voids up to three hundred
2:13:28
million light years across, where almost nothing lives. The full
2:13:34
observable universe spans roughly ninety three billion light years. Laniakia,
2:13:41
at five hundred twenty million light years, represents less than
2:13:46
one percent of that diameter. The challenge of communicating all
2:13:50
of this is real. The human mind handles a few
2:13:53
orders of magnitude comfortably. It can picture a city being
2:13:58
larger than a neighbourhood, a country being larger than a city.
2:14:02
But the jump from the Solar system to the Milky
2:14:05
Way is a factor of roughly a billion in linear scale.
2:14:10
The jump from there to Lania Kia is another factor
2:14:14
of five million. These are not differences in degree. They
2:14:19
are differences that exhaust the imagination. It is the same
2:14:24
problem physicists face when trying to hold atoms and solar
2:14:28
systems in the same mental picture simultaneously. The scale range
2:14:34
is simply too large for intuition to carry without breaking.
2:14:39
What astronomers mean when they talk about a cosmic address
2:14:43
is something genuinely new in human history. For most of
2:14:47
our existence as a species, the question of where exactly
2:14:51
we sat in the universe had no real answer. The
2:14:55
sky was overhead. Beyond that, the answers we stories. Even
2:15:02
one hundred years ago, astronomers were still debating whether the
2:15:06
Milky Way was the entire universe or just one of
2:15:10
many island galaxies. The idea that those galaxies organized into groups, clusters,
2:15:17
and superclusters came later. The idea that those superclusters were
2:15:23
themselves components of even larger basins of gravitational attraction. Came
2:15:29
later still, in twenty fourteen, in a paper in Nature,
2:15:34
each generation has extended the address by one more line.
2:15:40
This is not trivia. It is the most complete answer
2:15:43
to the question of where we are that any human
2:15:46
civilization has ever been able to give. Dark energy is
2:15:51
the reason Laniakia will not survive. That sentence sounds dramatic,
2:15:56
but it is just physics. To understand what it means,
2:16:01
you have to understand what dark energy actually is. And
2:16:04
the honest answer is that nobody fully does. What astronomers
2:16:10
know is this. Dark energy is the dominant energy component
2:16:14
of the universe, accounting for roughly sixty eight percent of everything.
2:16:20
It does not clump, It does not interact with light
2:16:24
or matter in any detectable way. It is invisible, massless,
2:16:29
and spread perfectly uniformly across all of space. The only
2:16:35
thing it appears to do is cause space itself to expand,
2:16:39
and it does this with a persistence that nothing in
2:16:42
the universe can overcome at large enough scales. For most
2:16:46
of the twentieth century, physicists assumed the expansion of the
2:16:50
universe was slowing down. This made intuitive sense. The Big
2:16:55
Bang flung matter outward, gravity pulls matter together. Over time,
2:17:01
gravity should gradually win, decelerating the expansion, the way a
2:17:06
ball thrown upward gradually loses speed. The only real question
2:17:13
was whether gravity would win completely, stopping the expansion and
2:17:18
reversing it into an eventual collapse, or whether the universe
2:17:22
would expand forever at a diminishing rate. Both options assumed
2:17:28
the same direction, expansion slowing over time. Then, in nineteen
2:17:34
ninety eight, two independent teams of astronomers studying distant Type
2:17:39
one A supernova published results that were almost impossible to believe.
2:17:46
The supernovae were fainter than they should have been. They
2:17:49
were farther away than the models predicted. The expansion was
2:17:54
not slowing down, It was speeding up. Space was not
2:17:59
fighting groundvity to a standstill. Something was actively pushing it
2:18:03
apart faster with every passing era. That discovery earned its
2:18:09
lead researchers the Nobel Prize in Physics in twenty eleven,
2:18:14
and it rewrote cosmology in a single year. The force
2:18:19
responsible for this acceleration is what physicists called dark energy,
2:18:25
a label that carries a lot of honesty in it.
2:18:28
The word dark here means unknown. It is not dark matter,
2:18:33
which at least has well understood gravitational effects. Dark energy
2:18:39
is stranger than that. It behaves like a property of
2:18:42
empty space itself, a baseline energy that the vacuum carries,
2:18:48
sometimes called the cosmological constant, a term Einstein introduced and
2:18:54
then famously abandoned, and then turned out to be correct
2:18:57
about after all. As space expands, a new volume of
2:19:02
empty space is created, the total amount of dark energy
2:19:06
grows with it. This is why the expansion accelerates over time,
2:19:12
rather than settling into a constant rate. More space means
2:19:16
more dark energy, which drives more expansion, which creates more space.
2:19:22
The feedback loop is slow by human standards, but relentless
2:19:26
on cosmological time scales. Now Here is where Lania KaiA
2:19:31
enters the picture. Gravity and dark energy are in a
2:19:35
continuous contest, and which one wins depends on scale. On
2:19:41
small scales, gravity wins easily. The atoms in your body
2:19:46
are not being pulled apart by dark energy. Planets, solar systems, galaxies,
2:19:53
even galaxy clusters. These are all gravitationally bound. The matter
2:19:59
in them is low together tightly enough that the gentle
2:20:02
outward pressure of dark energy is irrelevant. But as you
2:20:07
move to larger and larger scales, gravity becomes weaker and
2:20:12
dark energy becomes more significant. Superclusters occupy exactly the zone
2:20:18
where this contest becomes interesting. Laniakia is not gravitationally bound.
2:20:25
This was established when it was first defined in twenty fourteen,
2:20:30
and it is worth sitting with. The structure is real,
2:20:34
the galaxy flows are real, The inward motion toward the
2:20:38
Greater Tractor is real. The basin of attraction exists, but
2:20:43
the outer regions of Laniakia do not have enough gravitational
2:20:47
connection to the center to resist the expansion of space indefinitely.
2:20:53
The Greater Tractor exerts a genuine gravitational pull estimated at
2:20:59
roughly ten mins, billion billion solar masses of influence that
2:21:03
sounds enormous against dark energy operating across five hundred million
2:21:09
light years. It is not enough. The outer galaxies of
2:21:14
Laniakia are already in a kind of slow tug of
2:21:17
war right now for our epoch of cosmic history. The
2:21:22
gravity of the Greater Tractor remains strong enough to draw
2:21:26
our local group and billions of nearby galaxies toward its basin.
2:21:32
This infall will continue for billions of years, but the
2:21:37
boundary of that influence is not fixed. As the universe
2:21:41
expans and the distances between outer regions of Laniakia and
2:21:46
its gravitational center grow, the gravitational force between them weakens.
2:21:53
Dark energy's push does not weaken with distance the way
2:21:57
gravity does, so the balance tip. Galaxies near Laniakia's periphery
2:22:03
will eventually cross a threshold where expansion carries them away
2:22:08
faster than gravity can draw them back. The filaments at
2:22:12
the edges will thin, the outer clusters will drift. The
2:22:17
structure will not collapse or explode. It will simply dissolve
2:22:22
gradually and quietly over time scales that are hard to
2:22:27
write down meaningfully. What does the far future universe actually
2:22:32
look like? Astronomers have modeled this, and the picture is
2:22:37
striking in its emptiness. The local group itself, the Milky
2:22:42
Way Andromeda, and roughly eighty smaller companions, is bound. In
2:22:48
several billion years, the Milky Way and Andromeda will merge
2:22:53
into a single massive galaxy. That merge structure will remain
2:22:58
gravitationally locked, but beyond the local group, the rest of
2:23:03
Laniakir will gradually recede. The Virgo cluster will eventually pass
2:23:09
beyond the boundary where gravitational connection is possible. The Hydra
2:23:15
and Centaurus clusters, the Normer Cluster, the hundreds of groups
2:23:20
that today participate in the infall toward the greater tractor,
2:23:25
all of them will drift beyond reach on time scales
2:23:29
of hundreds of billions of years. What remains will be
2:23:32
isolated islands of gravitationally bound matter, separated from each other
2:23:38
by expanding voids that grow wider with every passing eon.
2:23:43
The universe will still exist, stars will still burn for
2:23:48
a while. But the large scale structure we can see today,
2:23:52
the filaments, the clusters, the flowing basins of attraction, the
2:23:58
shape that Brent Tully's team apped in twoenty fourteen, none
2:24:03
of that will be visible. An observer in that far
2:24:07
future universe, looking outward from whatever remains of our local
2:24:11
group would see nothing but darkness in all directions, no
2:24:17
neighboring galaxies close enough to identify, no structure at all.
2:24:23
The cosmic web will have stretched beyond any possible detection.
2:24:28
Whatever civilization existed then would have no way of knowing
2:24:32
that a supercluster had once surrounded them half a billion
2:24:37
light years of galaxies flowing together in a coherent structure,
2:24:42
with a name that meant immense heaven. In the far future,
2:24:47
nothing observable will remain to show that hundreds of thousands
2:24:52
of gala zis once flowed together toward a common center
2:24:56
across half a billion light years of space. The five
2:25:00
fourteen paper that named Laniakia was not the end of
2:25:03
the story. It was more like the first reliable map
2:25:07
of a territory that had previously been described only in rumours.
2:25:12
Tully's team had used a catalog of roughly eight thousand,
2:25:15
one hundred galaxies with measured distances and velocities. That number
2:25:20
sounds large for a structure five hundred twenty million light
2:25:25
years across, it is actually quite thin coverage, like trying
2:25:30
to map an entire continent from a few hundred survey
2:25:33
points scattered unevenly across it. The researchers knew this. The
2:25:39
paper itself acknowledged the gaps. What they had produced was
2:25:44
a framework, a first outline, and the work of filling
2:25:48
it in had barely started. Cosmic Flows three came next,
2:25:54
released in twenty sixteen. It pushed the galaxy count to
2:25:57
around eighteen thousand. More galaxies meant denser sampling, which meant
2:26:03
the flow patterns could be traced with finer resolution. The
2:26:07
boundaries of Laniakia didn't collapse under the new data. The
2:26:12
basic shape held, but the details shifted. Some filaments resolved
2:26:18
more clearly. Some previously ambiguous regions near the edges snapped
2:26:23
into focus. The watershed boundaries, which in the original paper
2:26:28
had been somewhat blurry in certain directions, tightened in some
2:26:33
places and softened in others. This is how science actually works,
2:26:40
not a single revelation, but a slow accumulation of better measurements,
2:26:45
each one adjusting the picture slightly. The twoenty fourteen map
2:26:51
wasn't wrong, it was coarse then Cosmic flows four arrived
2:26:57
in twenty twenty three, and the number jumped to nearly
2:27:01
fifty six thousand galaxies, that is roughly seven times the
2:27:06
original data set. Eight different distance measurement techniques fed into
2:27:10
the catalog. The Tullyfisher relation for spiral galaxies, the fundamental
2:27:16
plane for ellipticals, and several others all cross checked against
2:27:21
each other. The result was a peculiar velocity map of
2:27:26
the local universe with a level of detail that would
2:27:29
have been unthinkable in twenty fourteen. The twoenty twenty three
2:27:35
analysis confirmed Laniakia's overall size and shape five hundred twenty
2:27:42
million light years across roughly one hundred thousand large galaxies mass,
2:27:48
sitting around ten to the seventeenth solar masses. The original
2:27:53
outline held, but the same watershed technique that had defined
2:27:58
Laniakia in two twenty fourteen now revealed five neighboring superclusters
2:28:04
incomparable detail, shaply, Perseus, Pisces, Hercules, Leapus, and APIs, each
2:28:12
one its own basin of gravitational attraction, each one adjacent
2:28:17
to Laniakia in the larger cosmic web. The local universe
2:28:22
suddenly had neighbours with names and borders. There are debates,
2:28:26
though not everyone agrees that Laniakia's boundaries are drawn in
2:28:30
exactly the right places. Some researchers argue that the edges
2:28:35
of the structure are sensitive to which galaxies are included
2:28:39
in the catalog and how distances are weighted. At large radii,
2:28:45
the zone of avoidance still creates real gaps in the data.
2:28:49
Galaxies behind the Milky Way's disc are underrepresented in every
2:28:53
version of cosmic flows, which means the flow maps in
2:28:57
those directions are less reliable. If significant structures are hidden
2:29:03
in those gaps, the boundary of Laniakia in that region
2:29:07
of sky could shift when better data eventually fills the
2:29:10
blind spot. These are not fatal objections. They are exactly
2:29:16
the kind of edge case uncertainties you expect at the
2:29:19
frontier of a measurement campaign. The core of the structure
2:29:24
is solid, the edges are still being negotiated. What comes
2:29:29
next is more data orders of magnitude. More spectroscopic surveys
2:29:36
now underway or in planning will measure galaxy redshifts for
2:29:40
tens of millions of objects. The Dark Energy Spectroscopic Instrument
2:29:46
already operating in Arizona is accumulating galaxy spectra at a
2:29:51
rate that would have seemed impossible a decade ago. Surveys
2:29:56
like these won't just extend the cosmic flows approach, they
2:30:00
will transform it. Peculiar velocity maps derived from millions of
2:30:05
galaxies instead of tens of thousands will resolve structures that
2:30:10
currently appear as vague suggestions in the data. The flow
2:30:15
patterns around Laniakia's edges, where the supercluster's influence fades and
2:30:21
the influence of neighboring structures takes over, will become far clearer.
2:30:26
The extremely large telescope currently under construction in Chile's Attacama
2:30:31
Desert will add something different. Its light gathering power is
2:30:36
so far beyond existing instruments that it will be able
2:30:40
to measure distances and velocities for galaxies that are simply
2:30:45
too faint for current surveys to handle reliably. This reaches
2:30:51
further out and fills in the picture at larger scales.
2:30:55
Whether structures like the South Pole Wall, the enormous arc
2:31:00
discovered in twenty twenty just beyond Laniakia connect to Lania
2:31:06
Kia's flow patterns, or belong to entirely separate basins is
2:31:11
exactly the kind of question that next generation instruments are
2:31:16
positioned to answer. The map of our cosmic neighborhood is
2:31:21
not finished. That might sound like a limitation, but it
2:31:25
is also the honest state of things, and it means
2:31:29
the most interesting results may not be the ones already published.
2:31:34
Every time the catalog has expanded, something unexpected has appeared
2:31:39
at the new resolution. More galaxies revealed cleaner filaments. Better
2:31:45
coverage revealed neighboring superclusters that the original data could only
2:31:51
hint at. There is no obvious reason to expect that
2:31:55
pattern to stop. The outline that Tully's team drew in
2:31:59
two thousand and four has held up, but the details
2:32:02
inside it are still being filled in, and the territory
2:32:06
just outside it keeps turning out to be larger than
2:32:08
anyone expected. Every civilization that ever looked up at the
2:32:12
sky had some answer to the question of where they
2:32:15
were in it. The Babylonians placed themselves beneath the Dome
2:32:20
of Gods. Medieval astronomers put Earth at the center of
2:32:24
nested crystalline spheres. Polynesian navigators read the sky not as theology,
2:32:31
but as a map, and they used it to cross
2:32:34
the largest ocean on the planet, without instruments, without landmarks,
2:32:40
without anything except an extraordinarily precise knowledge of the heavens
2:32:45
above them. Every one of those civilizations had an answer.
2:32:51
None of them had the right one. We are the
2:32:55
first generation in human history that does. That answer is
2:33:00
strange enough to stop you cold. If you sit with it,
2:33:04
you are not at the center of your galaxy. You
2:33:07
are not at the center of your galaxy cluster. You
2:33:10
are not at the center of your supercluster. The Milky
2:33:15
Way sits near the outer edge of Laniakia, in a
2:33:19
relatively quiet, relatively sparse region, far from the dense clusters
2:33:24
where galaxy interactions are frequent and the cosmic environment is violent.
2:33:31
We are on the rim. We are in the suburbs
2:33:34
of an immense structure that stretches five hundred and twenty
2:33:38
million light years from one side to the other, and
2:33:42
we are being slowly pulled toward its heart by a
2:33:46
gravitational concentration so massive it took decades just to find it.
2:33:53
That pool will never complete. Dark energy will likely win
2:33:58
before we get anywhere near the center. We are drifting outward,
2:34:03
even a as we fall inward, passengers in a structure
2:34:07
that is quietly dissolving at its edges. And yet this
2:34:11
unremarkable outpost is the only place, as far as anyone knows,
2:34:16
where the question has ever been asked that asymmetry is strange.
2:34:22
The Greater Tractor sits at the gravitational heart of lania KaiA,
2:34:27
surrounded by some of the densest concentrations of galaxies in
2:34:32
our cosmic neighborhood. Nobody there is asking anything. The rich
2:34:38
clusters of the normous supercluster region, the dense nodes where
2:34:43
filaments converge, silent, The vast empty voids that occupy most
2:34:49
of Laniakia's volume silent. One minor spiral galaxy, far from
2:34:55
anything particularly remarkable, produce the only observed us in the
2:35:00
known universe who looked outward and wanted to understand the
2:35:04
structure they were part of. That is not an answer
2:35:08
to anything. It is just the fact, and the fact
2:35:13
is strange. Think about what Tully's team actually did. The
2:35:17
Polynesian navigators used the sky to find their place in
2:35:21
the ocean. They read the stars, the swells, the flight
2:35:26
paths of birds, and they triangulated themselves into a location.
2:35:31
Tully's team did something that rhymes with that, but runs deeper.
2:35:35
They didn't use the sky to find their place in
2:35:38
the world. They used the motion of one hundred thousand
2:35:41
galaxies to find their place within the structure that contains
2:35:45
the sky itself. The navigators crossed the Pacific. The astronomers
2:35:51
mapped the Pacific and discovered it was part of a
2:35:54
continent they hadn't known existed. The Hawaiian name connects those
2:35:59
two as across centuries, the same language, the same sky,
2:36:05
an entirely different scale of understanding. What that understanding gives
2:36:11
us is a complete address not just Earth, not just
2:36:15
the Solar System, not just the Milky Way or the
2:36:19
local group, but the full hierarchy extending outward to Laniakia
2:36:24
and beyond. For most of human history, that address was
2:36:28
unknown past the level of a few nearby stars. A
2:36:32
century ago, we didn't know other galaxies existed. Fifty years ago,
2:36:38
we didn't know what was pulling our region of the
2:36:40
universe off course. Ten years ago, we didn't have a
2:36:44
name for the supercluster we live in. The discovery is
2:36:48
genuinely recent. The picture is genuinely incomplete. There are structures
2:36:54
beyond Laniakia still being traced, boundaries still being debated, being
2:37:00
extended from eight thousand galaxies to fifty six thousand, and
2:37:06
eventually further still. The twoenty fourteen paper was a door opening,
2:37:13
not a door closing. What sits on the other side
2:37:16
of that door is uncomfortable and astonishing in equal measure.
2:37:22
We are peripheral. We are temporary in the sense that
2:37:26
the structure we belong to will not survive on cosmological
2:37:30
time scales. The outer filaments of Laniakia are already losing
2:37:36
coherence to dark energy. In hundreds of billions of years,
2:37:41
the flows that define our cosmic home will disperse into
2:37:45
an expanding void. Laniakia will not exist in any meaningful sense.
2:37:51
The immense heaven will dissolve. This is not a reason
2:37:56
for distress. It is just the physics. The structure was real,
2:38:01
the flows were real. The answer to where we are
2:38:05
is real, even if the structure itself is temporary. Somewhere
2:38:10
on the outer rim of an immense heaven there is
2:38:13
a small spiral galaxy, and on one of its unremarkable arms,
2:38:18
something learned to ask where it was, and is only
2:38:22
now beginning to find out