Latest / Star Trails: From Backyard Astronomy to Cosmic Wonder / The Hidden Universe: Cosmic Structures in the Dark

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The Hidden Universe: Cosmic Structures in the Dark · Star Trails: From Backyard Astronomy to Cosmic Wonder

0:07
Howdy Star Gazers and welcome to this episode
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of Star Trails. My name is Drew, and I'll be
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your guide to the night sky for the week of May
0:15
17th to the 23rd. This week we venture deeper
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into darkness. We'll continue our discussion
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of galaxies, but we'll probe the invisible structures
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that hide the secrets of the universe. dark matter,
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gravitational lenses, a stellar blind spot, and
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the mysterious cosmic web, which connects almost
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everything we know. Later in the show we'll cover
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what you can expect to see in this week's sky
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and discover why one humble constellation seems
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to be home to so many unique galaxies. Whether
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you're tuning in from the backyard or the balcony,
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I'm glad you're here. So grab a comfortable spot
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under the night sky, and let's get started. Astronomers
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today have more access to information about the
1:12
sky than we've ever had. With instruments like
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the James Webb Space Telescope peering deep into
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the darkness, and new projects such as the Vera
1:23
Rubin Observatory, It's easy to maybe get a bit
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jaded. What else is out there, and is there anything
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new left to discover? But what if I told you
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that, even today, entire galaxies may still be
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hiding from us. Not because they're too far away,
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but because the universe, and sometimes even
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our own galaxy, has a way of keeping secrets.
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Tonight, we're stepping into one of the strangest
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corners of modern astronomy. We're going to talk
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about galaxies that barely shine, invisible structures
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made of unknown matter, gravity that bends light
2:03
like a lens, and a cosmic web so vast that it
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makes our home galaxy seem almost insignificant.
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This is the hidden universe. If you've ever seen
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a long exposure image of the night sky, or perhaps
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a deep astrophoto of a distant galaxy, it's tempting
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to think that the universe is clean and orderly.
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Point a telescope in a direction, gather enough
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light, and eventually the cosmos reveals itself.
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But the reality is messier. Our home galaxy,
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the Milky Way, is a spectacular spiral of stars,
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gas, dust, and dark nebula. From a dark sky,
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it arches overhead like a glowing river. But
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for astronomers trying to look through it, the
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Milky Way can be a problem. Dense dust clouds
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absorb visible light. Thick fields of foreground
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stars clutter the view. Gas clouds scatter and
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obscure what lies beyond. For decades, astronomers
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noticed something strange. In certain parts of
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the sky, distant galaxies seemed to disappear.
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Not entirely, but the number of visible galaxies
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dropped dramatically. It almost looked as if
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there were empty patches in the universe itself.
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Of course, there weren't. Astronomers eventually
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realized that the missing galaxies weren't missing
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at all. They were simply hidden behind the thick
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disk of our own galaxy. This region became known
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as the Zone of Avoidance, a blind spot in our
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map of the cosmos. Imagine trying to study the
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skyline of a distant city while looking through
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a dirty windshield filled with bugs, dust, and
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glare. That's what parts of the universe look
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like when we try to peer through the galactic
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plane. Astronomers began learning to see in different
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ways. Instead of relying only on visible light,
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they turned to infrared detectors and radio telescopes.
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Infrared light can slip through dust more easily
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than visible light. Radio waves, especially the
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faint 21 centimeter signal emitted by neutral
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hydrogen, can pass through regions that would
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otherwise appear opaque. In some cases, astronomers
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don't discover galaxies by seeing stars at all.
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They find them by detecting the faint radio whisper
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of hydrogen gas drifting through intergalactic
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space. And sometimes what they find is stranger
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still. Not every galaxy blazes with the brilliance
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of a spiral like the Andromeda Galaxy. Some galaxies
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are so faint that they almost disappear into
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the background noise of the universe. These are
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sometimes called ghost galaxies or ultra -diffuse
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galaxies. Vast collections of stars spread so
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thinly across space that they glow only faintly.
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One of the most famous examples is Dragonfly
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44, a ghostly galaxy discovered in the Coma Cluster.
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At first glance, it looks like little more than
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a faint smudge, but measurements suggest it may
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contain the mass of tens or perhaps even hundreds
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of billions of stars. Think about that for a
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moment. A galaxy with the mass of a giant spiral
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yet so dim you could almost miss it entirely.
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And that brings us to one of the greatest mysteries
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in astronomy. For nearly a century, astronomers
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have noticed that stars and galaxies orbit far
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too quickly for the visible matter alone to hold
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them together. Something unseen appears to be
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there. Something massive. Something that exerts
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gravity, but doesn't emit or reflect light. Of
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course, I'm talking about dark matter. Every
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galaxy we've studied, including the Milky Way,
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appears to sit inside an enormous halo of this
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invisible material. The stars we see may only
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be the lanterns hanging inside a much larger
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unseen structure. The glowing spiral arms, the
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clusters, the nebula, they're like a visible
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campfire surrounded by an invisible forest of
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matter. Astronomer Vera Rubin helped bring this
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mystery into focus by studying how galaxies rotate.
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If gravity worked only with the matter we could
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actually see, stars, gas, dust, nebula, and so
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on, then stars near the outer edges of galaxies
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should orbit more slowly than stars near the
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center, much like planets in our own solar system.
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Mercury races around the sun much faster than
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distant Neptune, because most of the sun's mass
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is concentrated in one space. Galaxies should
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behave in much the same way, but they don't.
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When Ruben and her colleagues measured the outer
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stars in spiral galaxies, they found something
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astonishing. Those stars weren't slowing down
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at all. In many cases, they were moving just
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as fast as stars much closer to the galactic
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core. According to the physics we understand,
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galaxies spinning that fast should tear themselves
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apart. And yet they don't. And the mystery only
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deepened. When astronomers study galaxy clusters,
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that's vast gatherings of hundreds or even thousands
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of galaxies, they find the same problem. The
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galaxies inside those clusters are moving far
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too quickly for the visible mass alone to keep
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them gravitationally bound. There simply isn't
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enough visible matter there. But how do you study
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something that can't be seen? Sometimes you don't
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look at the object itself. You look at what it
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does to the light behind it. This phenomenon
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is called gravitational lensing, and its story
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begins more than a century ago, when Albert Einstein
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published his theory of general relativity. Einstein
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proposed gravity isn't just a force pulling objects
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together. Instead, massive objects actually warp
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spacetime itself. Imagine placing a bowling ball
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on a stretched rubber sheet. The sheet bends
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under the weight. Now imagine a marble rolling
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nearby. Instead of traveling in a straight line,
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its path curves around the bowling ball. According
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to Einstein, light behaves in much the same way.
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If a beam of light passes near something extremely
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massive, a galaxy, a cluster of galaxies, or
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an enormous concentration of dark matter, its
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path bends as it travels through warped space
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-time. Under just the right alignment, that distant
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light can be stretched into glowing arcs, duplicated
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into multiple images, or even bent into a nearly
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perfect circle known as an Einstein ring. Einstein's
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theory was proved in 1919. During a total solar
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eclipse, astronomers measured the apparent positions
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of stars near the sun and found that their light
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had shifted exactly as Einstein predicted. It
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was one of the first major confirmations of general
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relativity. But in modern astronomy, gravitational
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lensing has become something even more powerful.
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When NASA first released images from the James
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Webb Space Telescope in July of 2022, one of
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the very first images shown to the world was
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a galaxy cluster known as SMAX0723. At first
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glance, it looked like a dense gathering of galaxies
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suspended in darkness. But if you looked carefully
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around the cluster, you could see something extraordinary.
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Faint red arcs and distorted streaks of light
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wrapped around it. Those were entire galaxies
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far beyond the cluster itself, whose light had
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been bent and magnified by the enormous mass
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of the foreground cluster. The combined gravity
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of thousands of galaxies, along with huge concentrations
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of dark matter, had effectively turned that cluster
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into a natural telescope in space. SMAX 0723
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was acting like a cosmic magnifying glass. And
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that's what makes gravitational lensing so powerful.
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It allows astronomers to study galaxies so distant
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and so faint that even our most advanced telescopes
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might otherwise miss them entirely. It helps
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us map the invisible distribution of dark matter
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and weigh entire galaxy clusters. In some cases
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it allows us to peer farther back in time, closer
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to cosmic dawn, than we could ever see otherwise.
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So, when researchers calculate how much visible
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matter should be there, stars, gas and dust,
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the math still comes up short. Thanks to gravitational
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lensing, we can see that the cluster bends light
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more strongly than visible matter alone can explain.
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Again and again, across different scales and
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different methods, the universe keeps pointing
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to the same conclusion. There appears to be far
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more mass out there than we can actually see,
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and that must be dark matter. And if that wasn't
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strange enough, there's another mystery hiding
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behind the dust of our own Milky Way. In the
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late 20th century, astronomers began measuring
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how galaxies move relative to the expansion of
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the universe. And what they found was deeply
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unsettling. Our galaxy isn't just drifting through
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space, it's falling. The Milky Way, along with
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our neighboring galaxies and entire galaxy clusters,
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appears to be moving toward a region of space
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at roughly 600 kilometers per second, which is
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well over a million miles per hour. It seems
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like something enormous is pulling us. Astronomers
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named this mysterious region the Great Attractor.
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And here's the truly eerie part. It lies in the
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direction of the Zone of Avoidance, the very
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part of the sky obscured by our own galaxy's
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dust and stars. For years it was like feeling
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the pull of something massive in the darkness
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without being able to see it clearly. Today,
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astronomers think the Great Attractor isn't a
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single monster object, but part of a much larger
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concentration of galaxies, clusters, and dark
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matter, spread across immense distances. This
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hidden region contains the mass of tens of thousands
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of galaxies, but for a time, it was one of the
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most unsettling clues that the universe might
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be hiding far more structure than we realized.
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And then, if we zoom out even farther, far beyond
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individual galaxies, clusters, and beyond the
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scale most of us can intuitively grasp, we discover
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something even more astonishing. Galaxies aren't
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scattered randomly through space. They're connected.
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Across billions of light years, galaxies gather
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into vast filaments, thread -like rivers of matter
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stretching across the cosmos. Where these filaments
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intersect, galaxies pile up into dense regions
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called nodes, where galaxy clusters and superclusters
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form, and between them lie enormous voids, cosmic
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deserts, where comparatively few galaxies exist
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at all. These structures form what astronomers
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call the cosmic web, a vast ghostly scaffold
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upon which galaxies are arranged. Zoom far enough
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out and galaxies stop looking like islands in
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space. They begin to look like neurons, like
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strands in a structure so immense that it almost
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feels alive. A ghostly nervous system stretching
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across the observable universe. And according
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to our best models, much of that scaffolding
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may be built not from stars or glowing gas, but
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from invisible dark matter. whose gravity helped
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shape where galaxies formed in the first place.
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Long before the first galaxies began to shine,
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the scaffolding may already have been there.
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After a quick break, we'll be back with this
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week's night sky. Stay with us. Welcome back.
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The week begins under beautifully dark skies
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thanks to the new moon on May 16th, making this
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one of the better weeks of May to get outside
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with binoculars, a telescope, or just your eyes.
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Tonight, the moon returns as a razor thin, waxing
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crescent low in the western sky shortly after
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sunset, and each evening afterward it grows a
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little brighter, becoming a more obvious crescent
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by week's end. This makes the first half of the
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week ideal for deep sky observing, especially
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before moonlight begins to interfere later. If
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you look west shortly after sunset, brilliant
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Venus dominates the twilight. On the evening
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of May 18th, the thin crescent moon passes close
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to Venus, an easy naked eye pairing and a lovely
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photo opportunity. This should make for a beautiful
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post -sunset scene, especially if you have trees,
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building, or some sort of foreground subject
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to frame it. Jupiter is still an evening planet
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located in the west and higher than Venus. It's
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been making its way closer to the horizon month
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by month. If you're up before dawn, look east
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for Saturn and Mars. Saturn will be the brighter
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of the pair, lingering in Pisces. Mars is lower
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and to the left. You'll only have a narrow window
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to catch the red planet before it's lost in the
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glare of the rising sun. If you enjoy taking
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photos of the Milky Way, now is a good time to
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grab your wide -angle lens and capture the galactic
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core. With darker skies earlier in the week,
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venture out around midnight to see the core of
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our home galaxy rising in the southeast. By the
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pre -dawn hours, the rich star clouds near Sagittarius
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and Scorpius begin climbing into view. For listeners
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with darker skies, this is the beginning of true
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Milky Way core season. The Etta Aquarids, debris
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from Halley's Comet, peaked earlier in the month,
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but the shower remains active through May 28th.
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By this week, activity is lower, but if you're
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out before dawn under dark skies, you might still
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catch a few swift meteors streaking through the
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southeast. Before we jump into this week's galaxy
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targets, you may have noticed something over
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the past few episodes. We keep coming back to
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the constellation Canes Venetici, the hunting
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dogs. And that's no accident. For backyard astronomers,
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especially in spring, this relatively modest
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constellation happens to sit in one of the richest
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windows into the nearby universe. Part of the
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reason comes down to perspective. When we look
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towards Canes Venetici, we're looking away from
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the thick crowded plane of our own Milky Way.
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That means there's less dust, less gas, and fewer
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foreground stars cluttering the view. In other
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words, we're peering through a cleaner patch
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of cosmic glass, one that opens up into deep
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extra -galactic space. But it's not just that
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the view is clearer. This region of the sky also
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happens to lie near a broader concentration of
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galaxies associated with our local cosmic neighborhood,
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including loose galaxy groups and larger structures
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connected to the Virgo Coma region. I'll talk
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about three galaxies that are all located in
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Canes Venetici. One of my favorites this week
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is the Sunflower Galaxy. Through a modest telescope,
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it appears as a soft, glowing oval with a bright
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core. But long exposure images reveal a complex,
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spiral structure that gives it its floral nickname.
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What makes this galaxy especially fascinating
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is that astronomers have found faint, stellar
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streams surrounding it. Ghostly trails of stars
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that suggest it may have cannibalized smaller
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companion galaxies in the distant past. In other
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words, even galaxies carry scars. A little farther
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along, hunt down Messier 106, another springtime
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showpiece. At first glance, it may look like
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just another bright spiral, but this galaxy is
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anything but ordinary. Deep studies have revealed
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strange extra arms made not of stars but of energized
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gas, structures thought to be influenced by the
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activity of a supermassive black hole at its
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core. And if you're looking for something a little
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more unusual, try tracking down the whale galaxy.
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This edge -on galaxy gets its nickname from its
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long, slightly warped profile, which in photographs
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really does resemble a whale suspended in space.
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That distortion is likely the result of gravitational
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interactions with nearby galaxies. That's going
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to do it for this week. If tonight's episode
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sparked your curiosity or maybe gave you something
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new to think about the next time you look up,
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I'd be honored if you shared Star Trails with
21:07
someone who might also enjoy the journey. You
21:10
can always find the latest episodes, show notes,
21:14
and extras at StarTrails .Show. And, if you'd
21:19
like to help support the show, there's also a
21:21
little Buy Me a Coffee link on the site. It genuinely
21:24
helps keep these stories coming. Be sure to follow
21:28
Star Trails on Blue Sky and YouTube. Links are
21:32
in the show notes. Until we meet again beneath
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the stars, clear skies everyone.