Latest / Boring Science / Something Huge May Be Hiding Beyond Neptune

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Something Huge May Be Hiding Beyond Neptune · Boring Science

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  Speaker 1: Hello, and welcome to Boring Science to Sleep, a quiet
• 0:03
  Speaker 1: place where science becomes slow, soft, and easy to drift through. Tonight,
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  Speaker 1: you're going to gently explore the distant worlds and enormous
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  Speaker 1: spaces beyond our familiar sky, not to learn everything, but
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  Speaker 1: simply to notice it slowly, calmly, one quiet idea at
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  Speaker 1: a time. But before you settle in, if you truly
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  Speaker 1: enjoy these calm journeys through interesting facts about science and
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  Speaker 1: the universe, You're welcome to like this video and subscribe,
• 0:33
  Speaker 1: only if it feels right for you. And when you're ready,
• 0:36
  Speaker 1: let me know in the comments where you're listening from
• 0:39
  Speaker 1: and what time it is right now. It's always a
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  Speaker 1: quiet joy to see how many places and moments gather
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  Speaker 1: here together. Now, dim the lights, perhaps let a fan
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  Speaker 1: hum softly in the background, allow your body to become
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  Speaker 1: comfortable and let your thoughts become a little lighter. You
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  Speaker 1: are safe, there is nothing to do you can simply
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  Speaker 1: listen and drift. For a moment, you can remain exactly
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  Speaker 1: where you are, beneath the familiar sky, on the familiar earth,
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  Speaker 1: while somewhere far above you, the universe continues its slow
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  Speaker 1: and almost silent movement. And gradually, without needing to hurry,
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  Speaker 1: you can imagine yourself rising, not quickly, not dramatically, just
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  Speaker 1: gently enough to leave the ground behind. Below you, the
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  Speaker 1: room becomes smaller, then the building, then the streets and lights,
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  Speaker 1: until the whole landscape begins to soften into a quiet
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  Speaker 1: pattern beneath you. The earth appears, blue oceans, pale clouds,
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  Speaker 1: dark continents, a thin atmosphere glowing softly around the edge.
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  Speaker 1: From here, the planet does not look busy anymore. The
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  Speaker 1: roads disappear, the buildings disappear, the borders between countries disappear.
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  Speaker 1: You can simply see a small world turning slowly in
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  Speaker 1: the darkness, carrying everything you know, everything familiar, everything that
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  Speaker 1: has ever felt like home. And for a little while,
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  Speaker 1: you can stay there. You don't need to leave immediately.
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  Speaker 1: You can simply watch the earth turning beneath you, quietly
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  Speaker 1: illuminated by the sun. Then you begin to move farther away.
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  Speaker 1: The moon passes behind you. The earth becomes smaller. The
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  Speaker 1: sun remains bright, But even the Sun begins to look
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  Speaker 1: different as the distance grows. You are entering the solar
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  Speaker 1: system from the outside, looking back toward the place where
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  Speaker 1: all of its familiar planets travel. There are worlds here
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  Speaker 1: that you know by name. Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.
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  Speaker 1: But the planets themselves occupy only a small inner portion
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  Speaker 1: of the enormous space belonging to the Sun. Beyond Neptune,
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  Speaker 1: the solar system does not simply end. It becomes quieter,
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  Speaker 1: much quieter. There are distant worlds of ice and rock,
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  Speaker 1: small frozen bodies moving through deep darkness, remnants from the
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  Speaker 1: early history of the planetary system. Some travel on long,
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  Speaker 1: slow paths around the sun. Some are so distant that
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  Speaker 1: sunlight has become only a faint suggestion. And farther still,
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  Speaker 1: Scientists expect an enormous, loosely scattered population of icy objects
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  Speaker 1: surrounding the solar system in a distant region known as
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  Speaker 1: the Oort Cloud. You can think of it not as
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  Speaker 1: a solid shell and not as a wall, but as
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  Speaker 1: an unimaginably large and gentle outskirts where small frozen objects
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  Speaker 1: may remain separated by enormous amounts of empty space. The
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  Speaker 1: solar system stretches much farther than the neat diagram you
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  Speaker 1: may remember from school. The planets are only the familiar centre.
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  Speaker 1: Beyond them, there is distance, then more distance, and then
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  Speaker 1: still more. Even the farthest known regions of our solar
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  Speaker 1: system are tiny compared with the space between stars. You
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  Speaker 1: continue outward. The sun becomes smaller. Its light becomes softer.
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  Speaker 1: The planets disappear one by one behind you. until they
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  Speaker 1: are no longer visible at all. And now, something changes.
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  Speaker 1: You are no longer simply travelling through the neighbourhood of planets.
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  Speaker 1: You are beginning to enter interstellar space, the great region
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  Speaker 1: between one star system and another. There is no obvious doorway,
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  Speaker 1: no boundary that you can see, no sign telling you
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  Speaker 1: that you have crossed from one place into another. The
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  Speaker 1: transition is almost impossibly gentle. The sun simply becomes another
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  Speaker 1: star behind you, and the darkness around you grows. If
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  Speaker 1: you could measure this distance using the language of light,
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  Speaker 1: you would use a light year, which is simply the
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  Speaker 1: distance that light travels during one year. It sounds like
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  Speaker 1: a measurement of time, but it is really a measurement
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  Speaker 1: of distance. And light moves very quickly, yet even light
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  Speaker 1: needs years to cross the space between some stars. That
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  Speaker 1: is how wide the quiet becomes. You continue drifting, The
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  Speaker 1: sun is now only one point among many. Around you,
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  Speaker 1: other stars begin to stand out. Some are brighter, some
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  Speaker 1: are fainter, some are larger than the sun, some are
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  Speaker 1: much smaller, and some are so close by cosmic standards
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  Speaker 1: that they belong to our immediate stellar neighbourhood. One of
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  Speaker 1: them is Proxima Centauri, a small red star more than
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  Speaker 1: four light-years away, four years for light. and much, much
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  Speaker 1: longer for anything moving at the speeds available to you today.
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  Speaker 1: You do not need to imagine crossing that distance. You
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  Speaker 1: only need to notice it. A star can be relatively close,
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  Speaker 1: and still be separated from you by an ocean of darkness.
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  Speaker 1: That is one of the quiet truths of space. Things
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  Speaker 1: can be near each other, and yet unimaginably far apart.
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  Speaker 1: The sun behind you. Proxima Centauri somewhere ahead. and between
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  Speaker 1: them almost nothing. Not absolutely nothing. There are tiny particles
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  Speaker 1: of gas and dust. There are faint magnetic fields. There
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  Speaker 1: are traces of ancient material drifting between stars. But compared
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  Speaker 1: with the spaces we know on Earth, the emptiness is immense.
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  Speaker 1: And as you continue outward, you may begin to notice
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  Speaker 1: that the darkness itself has become part of the journey.
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  Speaker 1: There is no need to fill it. There is nothing missing.
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  Speaker 1: The space between the stars is simply there, quiet and patient,
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  Speaker 1: holding the distant lights apart. You are safe. There is
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  Speaker 1: nothing to do. The sun can remain behind you. The
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  Speaker 1: stars can remain far ahead. And for now, you can
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  Speaker 1: simply float between them, listening to the quiet distance, while
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  Speaker 1: somewhere in that darkness, another small star waits to become visible.
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  Speaker 1: The small star ahead of you is Proxima Centauri, glowing
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  Speaker 1: faintly against the darkness, and as you drift toward it,
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  Speaker 1: you begin to notice something quietly remarkable. It is not
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  Speaker 1: a bright star like the Sun. It is smaller, cooler,
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  Speaker 1: and much fainter, a red dwarf star, one of the
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  Speaker 1: many small stars that make up much of the stellar
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  Speaker 1: population around us. Its light has a softer, deeper colour,
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  Speaker 1: and from the darkness between the stars, it almost seems
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  Speaker 1: less like a distant sun and more like a tiny
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  Speaker 1: ember floating in an enormous room. You do not need
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  Speaker 1: to hurry toward it. You can simply watch it grow,
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  Speaker 1: very slowly, as the darkness between you and the star
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  Speaker 1: becomes a little smaller. Proxima Centauri belongs to the same
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  Speaker 1: broad stellar neighbourhood as two other stars, Alpha Centauri A
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  Speaker 1: and Alpha Centauri B. Together, the three stars form our
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  Speaker 1: nearest stellar system, a small gathering of suns, compared with
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  Speaker 1: the enormous number of stars spread throughout the Milky Way.
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  Speaker 1: And somewhere around Proxima Centauri, there are worlds. One of
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  Speaker 1: them is known as Proxima Centauri b. The name is technical,
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  Speaker 1: but the world itself is easier to imagine. It is
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  Speaker 1: a planet moving around a small red star, travelling through
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  Speaker 1: a darkness that is very different from the darkness around Earth.
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  Speaker 1: Because Proxima Centauri is so much cooler and dimmer than
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  Speaker 1: the Sun, the planet needs to orbit much closer to
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  Speaker 1: its star to receive a similar amount of warmth. And
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  Speaker 1: that closeness creates a strange possibility. Over immense stretches of time,
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  Speaker 1: the gravitational pull of the star may have slowed the
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  Speaker 1: planet's rotation until one side continually faces the star, while
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  Speaker 1: the other side continually turns away. Astronomers call this tidal locking,
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  Speaker 1: but you can simply imagine a world that has slowly
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  Speaker 1: settled into one particular orientation, one face always turned toward
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  Speaker 1: its distant red sun. On one side, the star would
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  Speaker 1: remain in almost the same part of the sky. On
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  Speaker 1: the other side, darkness would stretch across the surface. Between
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  Speaker 1: these two regions there could be a broad transition. a
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  Speaker 1: place where permanent day and permanent night meet. Whether Proxima
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  Speaker 1: Centauri b actually has an atmosphere, and what that atmosphere
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  Speaker 1: might be like, remains uncertain. The star itself can produce
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  Speaker 1: powerful bursts of activity, releasing energetic radiation into the space
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  Speaker 1: around it. So even though the planet receives a potentially
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  Speaker 1: interesting amount of warmth, that does not automatically mean it
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  Speaker 1: is comfortable, or Earth-like, or even able to hold onto
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  Speaker 1: an atmosphere for a long time. This is one of
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  Speaker 1: the quiet lessons of distant worlds. A planet can be
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  Speaker 1: in a place where temperatures seem promising, and still be
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  Speaker 1: very different from Earth. Distance from a star is only
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  Speaker 1: one part of the story. The atmosphere matters. The star matters.
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  Speaker 1: The planet's history matters. Even the way the planet turns
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  Speaker 1: can matter. And so you continue drifting, without needing to
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  Speaker 1: decide what this distant world is like. You simply let
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  Speaker 1: it remain a possibility in the darkness. Farther away, another
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  Speaker 1: nearby star waits. Barnard's Star is an old, small red dwarf,
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  Speaker 1: moving through the sky relatively quickly compared with many of
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  Speaker 1: the stars around it. It is only a few light
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  Speaker 1: years from the sun, yet that simple phrase, a few
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  Speaker 1: light years, still represents an enormous distance. The light reaching
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  Speaker 1: you from Barnard's Star began its journey years before you
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  Speaker 1: saw it, and around this old star, astronomers have found
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  Speaker 1: evidence for a planet. It is thought to be a
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  Speaker 1: cold world, much farther from its star than Proxima Centauri
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  Speaker 1: b is from its own. There have even been ideas
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  Speaker 1: that such a planet might hide warmth deep beneath its surface,
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  Speaker 1: perhaps in an underground environment where pressure and internal heat
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  Speaker 1: behave very differently from anything you experience on Earth. Again,
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  Speaker 1: you do not need to imagine oceans beneath the ground.
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  Speaker 1: You only need to let the possibility drift quietly through
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  Speaker 1: your thoughts. A cold world, A distant star, a little
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  Speaker 1: warmth hidden somewhere beneath the surface. And then, almost without noticing,
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  Speaker 1: you move toward another familiar point of light. Sirius. From Earth,
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  Speaker 1: Sirius is the brightest star in our night sky. It
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  Speaker 1: appears bright and almost solitary, but it is actually part
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  Speaker 1: of a binary system. There are two stars there. Sirius
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  Speaker 1: A is the brighter one, while Sirius B is a
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  Speaker 1: much smaller white dwarf. A white dwarf is what remains
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  Speaker 1: after a star has passed through much of its life
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  Speaker 1: and released its outer layers, leaving behind a compact stellar core.
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  Speaker 1: The word white makes it sound gentle, and in a
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  Speaker 1: way the light can be beautiful, but the object itself
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  Speaker 1: is remarkably dense. A great deal of stellar material has
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  Speaker 1: been compressed into a tiny volume, leaving behind a remnant
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  Speaker 1: that is much smaller than an ordinary star. You can
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  Speaker 1: imagine the two stars together. one bright and familiar, the
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  Speaker 1: other small and compact, both moving quietly through the darkness.
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  Speaker 1: Nothing about the scene needs to be dramatic. Stars can change,
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  Speaker 1: stars can age, stars can leave behind remnants, and still,
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  Speaker 1: from far away, the whole process looks almost motionless. That
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  Speaker 1: is one of the strange comforts of astronomy. Events that
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  Speaker 1: would be enormous on a human scale can become almost
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  Speaker 1: invisible when stretched across millions or billions of years. You
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  Speaker 1: can watch them without needing to see them happen. And
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  Speaker 1: as you drift farther through this nearby stellar neighbourhood, more
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  Speaker 1: worlds begin to appear in your imagination. Some are rocky.
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  Speaker 1: Some may be wrapped in thick atmospheres. Some may be frozen.
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  Speaker 1: Some may be warmer. Some may have moons. Some may
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  Speaker 1: have nothing resembling the familiar landscapes of Earth. The stars
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  Speaker 1: themselves are different too. Small red dwarfs, bright stars, old stars,
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  Speaker 1: dense stellar remnants, and around them, planets following their own
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  Speaker 1: quiet paths. The more stars you encounter, the less useful
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  Speaker 1: it becomes to think of planets as variations of one
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  Speaker 1: single pattern. There is no single way for a world
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  Speaker 1: to exist. There are countless arrangements of gravity, light, temperature, atmosphere,
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  Speaker 1: and time. And somewhere ahead, beyond these nearest stars, the
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  Speaker 1: number of known worlds begins to grow. Not just a few,
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  Speaker 1: not just dozens, but thousands of planets discovered around other stars,
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  Speaker 1: each one offering another small reminder that the universe does
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  Speaker 1: not need to repeat the same design. For now, though,
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  Speaker 1: you can remain among the nearest stars. The sun is
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  Speaker 1: far behind you. Proxima Centauri is becoming smaller again, Barnard's
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  Speaker 1: star fades into the surrounding darkness. Sirius remains a bright
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  Speaker 1: point somewhere behind and to one side. And ahead, there
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  Speaker 1: are still more worlds waiting quietly in the distance. You
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  Speaker 1: do not need to visit all of them. There is
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  Speaker 1: no destination you must reach. You can simply drift onward,
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  Speaker 1: knowing that beyond these familiar neighbouring stars are planets where
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  Speaker 1: oceans may hide beneath ice, where rock may glow beneath
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  Speaker 1: permanent daylight, where even the atmosphere itself can become part
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  Speaker 1: of the story. The darkness ahead is still very large,
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  Speaker 1: and somewhere within it another kind of world is beginning
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  Speaker 1: to appear. The darkness ahead is still very large, and
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  Speaker 1: somewhere within it another kind of world is beginning to appear.
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  Speaker 1: You have already passed the nearest stars, the quiet red
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  Speaker 1: dwarfs and the brighter points of light, but now you
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  Speaker 1: can begin to notice something even more interesting. The stars
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  Speaker 1: are not alone. Many of them have worlds moving quietly
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  Speaker 1: around them, just as Earth moves around the Sun. These
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  Speaker 1: worlds are called exoplanets, a simple word for planets that
• 16:01
  Speaker 1: belong to other stars. You do not see most of
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  Speaker 1: them directly. They are usually much too small and too faint,
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  Speaker 1: especially beside the brilliant stars they orbit. Instead, you notice
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  Speaker 1: their presence through tiny changes. A planet may pass in
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  Speaker 1: front of its star, causing the star's light to become
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  Speaker 1: just slightly dimmer, or the gravity of an unseen planet
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  Speaker 1: may make its star move almost imperceptibly, back and forth,
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  Speaker 1: as though the two are gently circling an invisible balance point.
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  Speaker 1: These changes are small, very small, and yet, from across
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  Speaker 1: the darkness between stars, they can reveal another world. As
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  Speaker 1: you drift onward, one of these worlds begins to take
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  Speaker 1: shape in your imagination. It is called GJ 1214b. The
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  Speaker 1: name is rather dry, almost like an entry in a catalogue,
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  Speaker 1: but the world itself may be anything but ordinary. It
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  Speaker 1: has been studied as a possible ocean-rich planet, a world
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  Speaker 1: where water may make up a substantial part of its
• 17:08
  Speaker 1: interior and and this is where water begins to behave
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  Speaker 1: in ways that feel almost unfamiliar. On Earth, water is
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  Speaker 1: usually something you know as a liquid, a gentle flow
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  Speaker 1: across a surface, or as ice when temperatures fall low enough.
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  Speaker 1: But deep inside a large water-rich planet, pressure can become
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  Speaker 1: so enormous that water is forced into completely different arrangements.
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  Speaker 1: It can become dense forms of ice, have little resemblance
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  Speaker 1: to the ice floating in a glass of water. The
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  Speaker 1: strange part is that these forms do not necessarily require
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  Speaker 1: extreme cold. They can be created by pressure. Water can
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  Speaker 1: be squeezed so tightly that its molecules settle into structures
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  Speaker 1: that simply do not occur in ordinary environments on Earth.
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  Speaker 1: You can imagine descending slowly into such a world. There
• 18:02
  Speaker 1: is no need to picture a hard boundary between ocean
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  Speaker 1: and ice. Instead, The deeper you go, the greater the
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  Speaker 1: pressure becomes, and the familiar behaviour of water gradually gives
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  Speaker 1: way to something more unusual. Liquid, then denser material, then
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  Speaker 1: forms of ice created not by winter, but by enormous pressure.
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  Speaker 1: The world becomes a quiet experiment in physics, performed naturally,
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  Speaker 1: without a laboratory, without a machine, simply because the planet
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  Speaker 1: is large enough and heavy enough to squeeze its own interior.
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  Speaker 1: And somewhere beyond this water-rich world is another planet with
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  Speaker 1: an entirely different story, K2141b. It orbits extremely close to
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  Speaker 1: its star, so close that a complete year there passes
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  Speaker 1: in only a matter of hours. The planet is probably
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  Speaker 1: tidally locked, meaning that it may always show the same
• 19:00
  Speaker 1: face to its star. One side remains beneath almost continuous starlight.
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  Speaker 1: the other side remains turned away. And between these two
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  Speaker 1: extremes is a world of remarkable contrast. The day side
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  Speaker 1: can become hot enough for rock to melt, not just
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  Speaker 1: a little warmer than the rocks beneath your feet on
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  Speaker 1: a summer afternoon, hot enough that the surface may become
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  Speaker 1: a vast ocean of molten rock, a lava ocean. You
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  Speaker 1: can imagine the landscape from very far away, without trying
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  Speaker 1: to stand upon it, a dark world, one side glowing
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  Speaker 1: beneath its star, the surface softened into molten material, the
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  Speaker 1: opposite side falling into deep cold, and above the hot
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  Speaker 1: region some of the material from the surface may rise
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  Speaker 1: into the atmosphere. Rock itself can be part of the air.
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  Speaker 1: Minerals can vaporise under the heat, rising from the glowing
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  Speaker 1: surface and moving through the thin atmosphere. Then, as these
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  Speaker 1: materials travel toward the cooler side of the planet, they
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  Speaker 1: can begin to condense again. The atmosphere becomes part of
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  Speaker 1: a slow planetary circulation. Material rises, it moves, it cools,
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  Speaker 1: it falls, and eventually some of it may return toward
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  Speaker 1: the hotter region, where it can melt or vaporise once more.
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  Speaker 1: The entire planet becomes a quiet cycle of heat and cooling,
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  Speaker 1: a world with no familiar ocean of water, but perhaps
• 20:32
  Speaker 1: an ocean of rock, a world where the weather may
• 20:35
  Speaker 1: be made partly from minerals and a world where the
• 20:38
  Speaker 1: difference between ground and sky becomes less certain. And yet,
• 20:43
  Speaker 1: even here, the same simple rules are still at work.
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  Speaker 1: Gravity holds the planet together. The star provides energy. The
• 20:52
  Speaker 1: planet absorbs some of that energy. Heat moves from one
• 20:56
  Speaker 1: region toward another. Material changes its state. Nothing needs to
• 21:01
  Speaker 1: be forced into place. The planet simply follows the conditions
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  Speaker 1: it has been given. And that is perhaps one of
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  Speaker 1: the most beautiful things about these distant worlds. They do
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  Speaker 1: not need to resemble Earth in order to make sense.
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  Speaker 1: They only need gravity, matter, energy and time. Change the
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  Speaker 1: distance from the star and the temperature changes. Change the
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  Speaker 1: size of the planet and the pressure changes. Change the
• 21:27
  Speaker 1: atmosphere and heat moves differently. Change the rotation and the
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  Speaker 1: pattern of day and night changes. And slowly... a completely
• 21:36
  Speaker 1: different world appears. Somewhere, water may cover a planet. Somewhere else,
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  Speaker 1: water may be trapped beneath immense pressure. Somewhere, rock may
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  Speaker 1: glow like a furnace. Somewhere, an atmosphere may carry vaporized
• 21:52
  Speaker 1: minerals through the sky. And farther away, there are worlds
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  Speaker 1: that we have not yet seen clearly enough to understand.
• 21:59
  Speaker 1: You can let those possibilities remain in the distance. There
• 22:03
  Speaker 1: is no need to name them all, There is no
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  Speaker 1: need to remember every planet. You can simply notice how
• 22:10
  Speaker 1: many different ways a world can exist. The universe does
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  Speaker 1: not seem to have one preferred design. It has variations.
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  Speaker 1: Endless variations. Small worlds and large worlds. Warm worlds and
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  Speaker 1: frozen worlds. Worlds wrapped in thick atmospheres. Worlds perhaps stripped
• 22:29
  Speaker 1: almost bare. Worlds where oceans may lie beneath ice. worlds
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  Speaker 1: where oceans may glow with heat, and each one is
• 22:37
  Speaker 1: quietly moving through space, following its own path around its
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  Speaker 1: own star. For a moment, you can drift beside them.
• 22:46
  Speaker 1: You do not need to land. You do not need
• 22:49
  Speaker 1: to understand everything below the clouds. You can simply watch
• 22:53
  Speaker 1: the distant star overhead, the faint curve of a world
• 22:57
  Speaker 1: beneath it, and the slow movement of heat across a
• 23:00
  Speaker 1: surface that no human has ever touched. Then, as you
• 23:04
  Speaker 1: continue outward, the planets begin to fade behind you once more.
• 23:09
  Speaker 1: The stars remain. The darkness remains. And beyond these strange worlds,
• 23:14
  Speaker 1: another story is waiting, not about planets this time, but
• 23:18
  Speaker 1: about the stars themselves and the long lives they quietly
• 23:22
  Speaker 1: carry through the darkness. The strange worlds behind you are
• 23:28
  Speaker 1: beginning to fade into the darkness, and as you continue
• 23:32
  Speaker 1: drifting outward... your attention slowly moves away from the planets
• 23:37
  Speaker 1: and back toward the stars that gave them their light.
• 23:41
  Speaker 1: For a moment, you can simply watch them, small points
• 23:45
  Speaker 1: of light, some young, some old, some bright and restless,
• 23:50
  Speaker 1: others quiet and fading. From a great distance, they all
• 23:54
  Speaker 1: seem almost the same. But each star carries its own history.
• 23:59
  Speaker 1: A star does not simply appear and remain unchanged forever.
• 24:03
  Speaker 1: It begins somewhere, usually deep inside a cold cloud of
• 24:08
  Speaker 1: gas and dust, where enormous amounts of material are gathered
• 24:11
  Speaker 1: together in the darkness. Very slowly, gravity begins to draw
• 24:16
  Speaker 1: some of that material inward. There is no sudden moment
• 24:20
  Speaker 1: that you would see from far away. The cloud simply
• 24:23
  Speaker 1: becomes a little denser, then denser again, the material gathers,
• 24:29
  Speaker 1: the centre becomes warmer, and eventually, a young star begins
• 24:34
  Speaker 1: to take shape. You can imagine this as a very
• 24:37
  Speaker 1: slow gathering of light, almost as though the darkness itself
• 24:41
  Speaker 1: were quietly folding inward. Around the young star, clouds of
• 24:46
  Speaker 1: dust and gas may still remain. The star is not
• 24:50
  Speaker 1: finished becoming itself. It is still surrounded by the material
• 24:54
  Speaker 1: from which it was born. And somewhere in the nearby
• 24:57
  Speaker 1: darkness is a young star called AP Columbae. It is
• 25:02
  Speaker 1: only a small part of the enormous stellar population of
• 25:05
  Speaker 1: the Milky Way, but it offers scientists a glimpse into
• 25:08
  Speaker 1: the early stages of a star's life. One of the
• 25:11
  Speaker 1: clues to its youth comes from lithium. Lithium is a
• 25:15
  Speaker 1: light chemical element, but inside a young star it can
• 25:19
  Speaker 1: tell a quiet story about age. As stars mature, their
• 25:24
  Speaker 1: internal conditions change, and the amount of lithium that remains
• 25:28
  Speaker 1: can help astronomers recognise a star that has only recently
• 25:32
  Speaker 1: begun its long journey. AP Columbiae is also an active star.
• 25:38
  Speaker 1: Its brightness can change. Its surface can release material. Its
• 25:43
  Speaker 1: young energy can create powerful bursts that would make the
• 25:47
  Speaker 1: space around it a restless place for any nearby planet.
• 25:51
  Speaker 1: But from far away, all of this still looks almost peaceful.
• 25:56
  Speaker 1: A small star, a faint glow, a little flicker of brightness.
• 26:01
  Speaker 1: and then darkness again. You can let the young star
• 26:04
  Speaker 1: remain behind you as you continue. The universe does not
• 26:08
  Speaker 1: hurry its stars. A young star may spend enormous stretches
• 26:12
  Speaker 1: of time changing very slowly, while the planets and clouds
• 26:16
  Speaker 1: around it move through their own quiet histories. Eventually the
• 26:21
  Speaker 1: star begins to age. Hydrogen deep inside it is gradually
• 26:25
  Speaker 1: used as fuel. The star changes from within. Its inner
• 26:29
  Speaker 1: regions become different. its outer layers begin to expand, and
• 26:34
  Speaker 1: after enough time, a star that once looked relatively ordinary
• 26:39
  Speaker 1: can become something enormous, a red giant. Ahead of you
• 26:43
  Speaker 1: now is one such star, CW Leonis. It is hundreds
• 26:48
  Speaker 1: of light-years away, and it is so large that if
• 26:51
  Speaker 1: you could place it where the Sun is now, its
• 26:54
  Speaker 1: outer layers would extend far beyond the inner planets. But
• 26:58
  Speaker 1: size alone does not tell the whole story. CW Leonis
• 27:02
  Speaker 1: is an ageing star. Its outer layers have become cool
• 27:06
  Speaker 1: and extended compared with the hotter interior, giving the star
• 27:10
  Speaker 1: its deep reddish appearance. And the star does not remain
• 27:14
  Speaker 1: perfectly still. It gently expands and contracts. Its brightness changes
• 27:20
  Speaker 1: over long periods. The material in its outer regions rises
• 27:24
  Speaker 1: and falls, responding to changes deep within the star. You
• 27:28
  Speaker 1: can imagine the entire enormous sphere breathing very slowly, not
• 27:33
  Speaker 1: like a living creature. There is no heartbeat, no breath,
• 27:38
  Speaker 1: only the gradual movement of stellar material, expanding and contracting
• 27:43
  Speaker 1: over periods so long that a human lifetime becomes almost
• 27:47
  Speaker 1: invisible beside them. When the star expands, its outer layers
• 27:51
  Speaker 1: become thinner. When those layers contract, they become denser again.
• 27:56
  Speaker 1: The cycle continues. slowly, quietly, again and again, and sometimes
• 28:03
  Speaker 1: material from the outer layers escapes into space. This is
• 28:07
  Speaker 1: one of the most beautiful parts of an aging star.
• 28:11
  Speaker 1: It does not simply disappear when its life changes, it
• 28:14
  Speaker 1: gives something back. Gas and dust begin to surround the star.
• 28:19
  Speaker 1: A vast cloud slowly forms around it, extending outward into
• 28:24
  Speaker 1: the darkness. Within this material are different chemical ingredients, including carbon, oxygen, water,
• 28:32
  Speaker 1: and ammonia. You do not need to picture these as
• 28:36
  Speaker 1: separate objects floating around like tiny labels. Instead, imagine a
• 28:41
  Speaker 1: faint veil of material spreading outward from the star, carrying
• 28:45
  Speaker 1: the remains of its long history into space. Some of
• 28:48
  Speaker 1: that material may eventually become part of other things, a
• 28:52
  Speaker 1: future cloud, a future star, a future planet. Perhaps, after
• 28:58
  Speaker 1: enough time, material released by an ageing star can become
• 29:03
  Speaker 1: part of a completely different system, far from the place
• 29:06
  Speaker 1: where it began. The universe has a quiet habit of
• 29:09
  Speaker 1: recycling its ingredients. Stars gather material. Stars transform material. And
• 29:16
  Speaker 1: stars eventually return some of that material to space. The
• 29:20
  Speaker 1: darkness between the stars is therefore not completely empty. It
• 29:24
  Speaker 1: contains traces of old stars, dust, gas, atoms that have
• 29:30
  Speaker 1: travelled through stellar interiors, molecules formed in the cool outer
• 29:35
  Speaker 1: regions of dying stars, tiny pieces of ancient history drifting
• 29:39
  Speaker 1: between distant suns. And as you float beside CW Leonis,
• 29:44
  Speaker 1: the enormous red star seems less like an ending and
• 29:48
  Speaker 1: more like a transition. Its outer layers continue moving outward.
• 29:52
  Speaker 1: Its surrounding cloud becomes larger. The star itself continues changing.
• 29:58
  Speaker 1: Far in the future, its remaining core will become a
• 30:01
  Speaker 1: much smaller and denser object, while the material it released
• 30:05
  Speaker 1: will continue travelling outward. The star will become quieter, its
• 30:10
  Speaker 1: surrounding cloud will slowly mix with the space around it,
• 30:14
  Speaker 1: and eventually the material will become difficult to distinguish from
• 30:18
  Speaker 1: the wider interstellar medium. But the atoms will remain, the
• 30:23
  Speaker 1: carbon will remain, the oxygen will remain, the other elements
• 30:27
  Speaker 1: will remain. They will simply move somewhere else. Perhaps into
• 30:32
  Speaker 1: another cloud. Perhaps into another star. Perhaps into another world.
• 30:38
  Speaker 1: You can let that thought rest gently for a moment.
• 30:41
  Speaker 1: Nothing in the universe needs to remain exactly where it began.
• 30:44
  Speaker 1: A star can become a cloud. A cloud can become
• 30:48
  Speaker 1: a star. A star can create the ingredients for planets.
• 30:52
  Speaker 1: And planets can carry those ingredients for billions of years.
• 30:56
  Speaker 1: The story keeps moving. Even when everything appears still, you
• 31:01
  Speaker 1: drift a little farther from CW Leonis. Its red light
• 31:05
  Speaker 1: becomes smaller. Its surrounding cloud fades into the darkness. The
• 31:10
  Speaker 1: young star you passed earlier is now far behind you.
• 31:14
  Speaker 1: Between them lies an enormous stretch of space, filled with
• 31:18
  Speaker 1: the quiet remains of countless stellar lives. And somewhere in
• 31:22
  Speaker 1: that darkness, there are stars that have become much more
• 31:25
  Speaker 1: compact than CW Leonis. Stars compressed into astonishingly small remnants,
• 31:31
  Speaker 1: spinning through space and sending out precisely timed pulses of light.
• 31:36
  Speaker 1: For now, you can simply let that distant rhythm remain
• 31:40
  Speaker 1: ahead of you. A faint pulse, then darkness, another pulse,
• 31:45
  Speaker 1: then darkness again. And slowly, you begin to drift toward it.
• 31:52
  Speaker 1: A faint pulse, then darkness, another pulse. then darkness again.
• 31:58
  Speaker 1: As you drift toward that distant rhythm, you begin to
• 32:01
  Speaker 1: approach one of the quiet remnants left behind, when a
• 32:05
  Speaker 1: massive star reaches the end of its ordinary life. The
• 32:09
  Speaker 1: object itself is small, much smaller than the star that
• 32:13
  Speaker 1: came before it, but its density is almost impossible to imagine.
• 32:18
  Speaker 1: This is a neutron star. A neutron star is what
• 32:21
  Speaker 1: can remain after the core of a massive star has
• 32:24
  Speaker 1: been compressed enormously, leaving most of the former star's material
• 32:29
  Speaker 1: packed into a sphere only a few tens of kilometres across.
• 32:34
  Speaker 1: From far away, it might look like almost nothing. A
• 32:38
  Speaker 1: tiny point, a faint source of light, and yet, hidden
• 32:43
  Speaker 1: inside that small object is an extraordinary amount of matter.
• 32:47
  Speaker 1: You do not need to picture the pressure. You do
• 32:49
  Speaker 1: not need to imagine what it would feel like to
• 32:51
  Speaker 1: stand there. There is nowhere to stand. You can simply
• 32:55
  Speaker 1: let the contrast remain in your mind. A star that
• 32:59
  Speaker 1: once stretched across an enormous distance has become a tiny,
• 33:02
  Speaker 1: dense remnant, turning quietly in the darkness. Some neutron stars
• 33:08
  Speaker 1: rotate very quickly, and some send beams of radiation outward
• 33:13
  Speaker 1: from their magnetic regions. As the star turns, these beams
• 33:18
  Speaker 1: sweep across space. If one of them happens to pass
• 33:21
  Speaker 1: in your direction, you see a brief signal. Then the
• 33:25
  Speaker 1: star turns. The light disappears. Then it returns. Again. And again.
• 33:32
  Speaker 1: These objects are called pulsars. The name comes from the
• 33:36
  Speaker 1: regular pulses they produce, but the underlying process is simply
• 33:40
  Speaker 1: a rotating stellar remnant carrying beams of energy through space.
• 33:45
  Speaker 1: You can imagine yourself floating far away, watching the rhythm.
• 33:50
  Speaker 1: A pulse. Darkness. A pulse. Darkness. The timing can be
• 33:55
  Speaker 1: extraordinarily precise. Some pulsars behave almost like natural clocks, keeping
• 34:00
  Speaker 1: their rhythm over long periods of time. And around at
• 34:04
  Speaker 1: least one pulsar, astronomers have found something even more unusual.
• 34:09
  Speaker 1: A planet. It is a world moving around the remains
• 34:12
  Speaker 1: of a dead star. The planet is thought to be
• 34:15
  Speaker 1: extremely dense, and its environment would be very different from
• 34:19
  Speaker 1: anything familiar on Earth. Its star is no longer a warm,
• 34:23
  Speaker 1: stable sun like ours. Instead, it is a compact remnant,
• 34:28
  Speaker 1: spinning through space and sending radiation outward. You can simply
• 34:32
  Speaker 1: let the little system remain in the distance, a dark planet,
• 34:36
  Speaker 1: a tiny star, a regular pulse moving outward through the
• 34:40
  Speaker 1: surrounding space. It is another reminder that planets can survive,
• 34:45
  Speaker 1: or perhaps form, in places very different from the gentle
• 34:49
  Speaker 1: environment around our own sun. And as you drift away
• 34:53
  Speaker 1: from the pulsar, the pulses become softer, the rhythm fades,
• 34:57
  Speaker 1: the darkness grows wider. Ahead, there is another kind of object.
• 35:03
  Speaker 1: This time, there is no visible surface, no solid world,
• 35:08
  Speaker 1: no glowing star, only gravity. You are approaching a black hole.
• 35:13
  Speaker 1: The name can sound dramatic, But a black hole is
• 35:16
  Speaker 1: not a hole in space in the ordinary sense. It
• 35:19
  Speaker 1: is a region where matter has become so deeply compressed
• 35:23
  Speaker 1: that gravity creates an extreme boundary around it. Once something
• 35:27
  Speaker 1: crosses that boundary, even light cannot return to the outside.
• 35:32
  Speaker 1: This boundary is called the event horizon. But you do
• 35:36
  Speaker 1: not need to imagine a physical wall. There is no
• 35:39
  Speaker 1: surface you would touch. It is simply a point of
• 35:42
  Speaker 1: no return in the geometry of space and time. From
• 35:46
  Speaker 1: far away, the black hole itself may be dark, but
• 35:50
  Speaker 1: its surroundings can be bright. Gas and dust can fall inward,
• 35:54
  Speaker 1: moving faster and faster as they respond to the intense gravity.
• 35:59
  Speaker 1: Before reaching the black hole, some of this material can
• 36:03
  Speaker 1: form a wide, glowing disk around it. This is an
• 36:07
  Speaker 1: accretion disk. The word sounds technical, but the idea is simple.
• 36:13
  Speaker 1: Material gathers around the darkness, it moves, it becomes hot,
• 36:17
  Speaker 1: it shines. And because the black hole itself cannot be
• 36:21
  Speaker 1: seen directly, the light from this surrounding material can become
• 36:25
  Speaker 1: one of the ways we know the black hole is there.
• 36:28
  Speaker 1: There is another quiet clue as well. Gravity can bend light.
• 36:33
  Speaker 1: If a massive invisible object passes between you and a
• 36:35
  Speaker 1: more distant source of light, the path of that light
• 36:39
  Speaker 1: can curve around the object. The distant light may appear shifted,
• 36:43
  Speaker 1: stretched or distorted. This effect is called gravitational lensing. It
• 36:48
  Speaker 1: is another way the invisible can leave a visible trace.
• 36:52
  Speaker 1: And this idea becomes especially important when you look toward
• 36:55
  Speaker 1: the centre of your own galaxy. There, hidden among an
• 37:00
  Speaker 1: extraordinarily dense region of stars, is a supermassive black hole
• 37:05
  Speaker 1: called Sagittarius A star. It contains roughly four million times
• 37:11
  Speaker 1: as much mass as our Sun, yet from our position
• 37:14
  Speaker 1: in the Milky Way, it is not something you see
• 37:17
  Speaker 1: shining in the night sky. Instead, astronomers learn about it
• 37:21
  Speaker 1: by watching what happens around it. Stars orbit nearby. Gas
• 37:26
  Speaker 1: moves through the central region. Light travels through the crowded environment.
• 37:32
  Speaker 1: The motions of those stars reveal the presence of something
• 37:35
  Speaker 1: enormously massive at the centre. You can imagine pulling back slowly.
• 37:40
  Speaker 1: The black hole becomes smaller and The stars around it
• 37:43
  Speaker 1: become more numerous. The crowded centre of the galaxy begins
• 37:46
  Speaker 1: to appear, and then the centre itself becomes part of
• 37:50
  Speaker 1: something much larger, the Milky Way. The black hole is
• 37:54
  Speaker 1: not the galaxy. It is only one object inside it.
• 37:58
  Speaker 1: A remarkable object, certainly. But still only one part of
• 38:02
  Speaker 1: a much greater structure. You have moved from the death
• 38:05
  Speaker 1: of a star to the remains of its core. From
• 38:09
  Speaker 1: a neutron star to a pulsar. from a pulsar to
• 38:13
  Speaker 1: a black hole. And now, without needing to hurry, you
• 38:17
  Speaker 1: can begin to turn around. Behind you are the planets
• 38:21
  Speaker 1: you passed earlier. Farther behind them are the nearby stars.
• 38:26
  Speaker 1: Farther still are the young stars, the ageing giants, the
• 38:29
  Speaker 1: faint remnants, and the distant worlds orbiting other suns. All
• 38:34
  Speaker 1: of them are part of the same enormous galaxy, the
• 38:37
  Speaker 1: Milky Way. And as you begin to drift away from
• 38:41
  Speaker 1: Sagittarius A star, the crowded centre slowly becomes less crowded.
• 38:46
  Speaker 1: The stars spread apart, the darkness between them becomes wider,
• 38:51
  Speaker 1: the central glow begins to fade behind you. You are
• 38:54
  Speaker 1: moving outward now, away from the deepest region of the galaxy.
• 38:58
  Speaker 1: And for the first time, you can begin to sense
• 39:01
  Speaker 1: that the Milky Way is not simply a collection of stars,
• 39:05
  Speaker 1: it has a shape. It has a structure. It has
• 39:08
  Speaker 1: a vast outer region surrounding its bright inner disk. The
• 39:12
  Speaker 1: individual stars are becoming less important, the galaxy itself is
• 39:16
  Speaker 1: beginning to appear, and somewhere ahead, beyond the crowded centre,
• 39:21
  Speaker 1: the great spiral shape of the Milky Way is waiting
• 39:25
  Speaker 1: to unfold. The Crowded Centre of the Milky Way is
• 39:31
  Speaker 1: slowly fading behind you. The stars around Sagittarius A star
• 39:35
  Speaker 1: begin to spread apart. The bright central region becomes softer,
• 39:40
  Speaker 1: less crowded, and more distant, and as you continue drifting outward,
• 39:46
  Speaker 1: something changes in the way you see the galaxy. You
• 39:49
  Speaker 1: are no longer looking at individual stars, you are beginning
• 39:53
  Speaker 1: to see the shape that holds them. The Milky Way
• 39:56
  Speaker 1: is an enormous spiral galaxy, with a broad disk of stars,
• 40:01
  Speaker 1: gas and dust extending outward from its central region. At
• 40:05
  Speaker 1: the very heart is a dense concentration of stars. Around
• 40:09
  Speaker 1: that centre is a long structure of stars, stretching through
• 40:13
  Speaker 1: the inner galaxy like a quiet bar of light, and
• 40:16
  Speaker 1: from this central region, the galaxy gradually opens outward. The
• 40:21
  Speaker 1: stars become arranged in broad, curved patterns. These are the
• 40:26
  Speaker 1: spiral arms. They are not solid arms, like the arms
• 40:30
  Speaker 1: of something you could touch. They are enormous regions where
• 40:34
  Speaker 1: stars and clouds of gas become more concentrated, creating the
• 40:38
  Speaker 1: familiar spiral shape that you might see when imagining our
• 40:42
  Speaker 1: galaxy from far above. You can slowly rise above the
• 40:46
  Speaker 1: galactic disk now, Below you, the Milky Way begins to
• 40:50
  Speaker 1: resemble a vast whirl of faint light. The centre glows
• 40:54
  Speaker 1: more brightly, the outer regions become thinner, and along the
• 40:58
  Speaker 1: spiral arms, clouds of gas and dust gather in places
• 41:02
  Speaker 1: where new stars can begin to form. Some of the
• 41:05
  Speaker 1: brightest stars in the galaxy are young. They have not
• 41:09
  Speaker 1: been shining for very long, compared with the age of
• 41:12
  Speaker 1: the Milky Way. Around them are clouds where future stars
• 41:15
  Speaker 1: may still be gathering. The galaxy is therefore not simply
• 41:19
  Speaker 1: an old collection of stars. It is still changing, still forming,
• 41:24
  Speaker 1: still recycling its material, and somewhere along one quieter region
• 41:28
  Speaker 1: of one of these spiral arms is your home. The
• 41:31
  Speaker 1: solar system is not at the centre of the Milky Way.
• 41:34
  Speaker 1: It is not close to the outermost edge either. It
• 41:38
  Speaker 1: lies within a smaller region, often called the Orion Spur,
• 41:42
  Speaker 1: a quieter branch between larger spiral structures. From here, The
• 41:47
  Speaker 1: Sun is only one star among an enormous number of others.
• 41:51
  Speaker 1: And Earth is only one small planet around that star.
• 41:55
  Speaker 1: You can pause here for a moment. Imagine looking down
• 41:58
  Speaker 1: toward the solar system from above. You would not see
• 42:02
  Speaker 1: Earth as a bright blue world. You probably would not
• 42:05
  Speaker 1: see the planets at all. The entire solar system would
• 42:08
  Speaker 1: be reduced to a tiny point. And even that point
• 42:12
  Speaker 1: would be almost impossible to distinguish among the surrounding stars.
• 42:16
  Speaker 1: The Milky Way is simply too large. Its scale is
• 42:20
  Speaker 1: difficult to hold in the mind. So you continue outward.
• 42:24
  Speaker 1: The spiral arms begin to blend together. The bright disk
• 42:28
  Speaker 1: stretches beneath you. And then you notice something strange. Some
• 42:32
  Speaker 1: parts of the galaxy appear dark. Long, irregular bands of
• 42:36
  Speaker 1: darkness cross the glowing background of stars. But this darkness
• 42:41
  Speaker 1: is not empty. It is made partly from dust. Tiny
• 42:44
  Speaker 1: grains of material gather in enormous clouds, blocking some of
• 42:48
  Speaker 1: the visible light coming from stars behind them. This dark
• 42:52
  Speaker 1: region is sometimes called the Great Rift. From Earth it
• 42:55
  Speaker 1: can appear as a long, shadowy lane running through the
• 42:58
  Speaker 1: Milky Way. But if you could look at it in
• 43:01
  Speaker 1: other kinds of light, the darkness would begin to change.
• 43:05
  Speaker 1: Radio waves can reveal material hidden inside. Infrared light can
• 43:10
  Speaker 1: pass through some of the dust. and show stars that
• 43:13
  Speaker 1: visible light cannot easily reach. So once again, the universe
• 43:17
  Speaker 1: reminds you that darkness does not always mean emptiness. Sometimes
• 43:22
  Speaker 1: darkness is simply something standing between you and the light.
• 43:26
  Speaker 1: You drift beyond the bright disk now. The stars become fewer.
• 43:31
  Speaker 1: The spiral pattern becomes harder to see. The Milky Way
• 43:35
  Speaker 1: begins to lose its familiar shape. Around the galaxy is
• 43:39
  Speaker 1: a much larger and much fainter region. the galactic halo. Here,
• 43:44
  Speaker 1: stars are scattered more sparsely than in the bright disk.
• 43:48
  Speaker 1: Some are extremely old. Some gather in dense, ancient groups
• 43:52
  Speaker 1: called globular clusters, small spherical collections of stars that have
• 43:57
  Speaker 1: remained together for billions of years. You can imagine one
• 44:01
  Speaker 1: of these clusters from a distance. Hundreds of thousands of
• 44:05
  Speaker 1: stars gathered into a faint sphere, not crowded in the
• 44:08
  Speaker 1: way the galactic centre is crowded. but bound together across
• 44:12
  Speaker 1: enormous distances. Some of the stars inside these clusters are
• 44:17
  Speaker 1: among the oldest stars in the galaxy. They carry memories
• 44:21
  Speaker 1: of a much earlier Milky Way, from a time when
• 44:24
  Speaker 1: the galaxy itself looked different. And now, as you move
• 44:28
  Speaker 1: even farther outward, the visible stars become increasingly sparse. The
• 44:34
  Speaker 1: bright disk is far behind you. The halo stretches around you.
• 44:38
  Speaker 1: There are stars here, but there is much more space
• 44:41
  Speaker 1: between them, and this is where another invisible part of
• 44:44
  Speaker 1: the galaxy begins to become important. Something appears to be
• 44:49
  Speaker 1: surrounding the Milky Way, extending far beyond the stars we
• 44:53
  Speaker 1: can see. We cannot observe it directly through ordinary light.
• 44:58
  Speaker 1: We know it is there because of the way the
• 45:00
  Speaker 1: visible stars move. The stars near the outer regions of
• 45:04
  Speaker 1: the galaxy are orbit as though they are being held
• 45:07
  Speaker 1: by much more mass than the stars, gas and dust
• 45:11
  Speaker 1: we can see. Astronomers call this unseen material dark matter.
• 45:16
  Speaker 1: The name is simple. The idea is less simple. It
• 45:21
  Speaker 1: does not mean ordinary darkness. It does not mean a
• 45:24
  Speaker 1: cloud blocking the stars. It means something whose presence is
• 45:27
  Speaker 1: inferred from gravity, even though it does not appear to
• 45:31
  Speaker 1: shine like ordinary matter. You can imagine the galaxy as
• 45:34
  Speaker 1: a vast luminous disk, surrounded by something almost completely invisible.
• 45:40
  Speaker 1: The stars are the light you can see. The unseen
• 45:43
  Speaker 1: mass is known through the way that light moves, and
• 45:46
  Speaker 1: the farther you travel from the bright centre, the more
• 45:49
  Speaker 1: this invisible structure becomes part of the story. The Milky
• 45:53
  Speaker 1: Way is therefore larger than the stars alone, much larger.
• 45:58
  Speaker 1: The bright spiral disk is only the part that your
• 46:00
  Speaker 1: eyes would recognise. Beyond it lies the faint halo. Beyond
• 46:05
  Speaker 1: the halo lies an even greater region of space. And
• 46:09
  Speaker 1: somewhere far above and below the galactic centre are enormous
• 46:13
  Speaker 1: structures that seem to preserve traces of powerful activity from
• 46:17
  Speaker 1: the distant past. They are known as the Fermi Bubbles,
• 46:21
  Speaker 1: vast regions extending outward from the centre of the Milky Way.
• 46:26
  Speaker 1: Their exact origin remains uncertain. Perhaps they were created by
• 46:30
  Speaker 1: ancient activity around the central black hole. Perhaps by powerful
• 46:35
  Speaker 1: bursts of star formation. Whatever their origin, they are like
• 46:39
  Speaker 1: a faint memory written into the space around the galaxy.
• 46:43
  Speaker 1: You can let that mystery remain unresolved. You do not
• 46:47
  Speaker 1: need to solve it tonight. You simply drift farther away.
• 46:52
  Speaker 1: The Milky Way now stretches behind you as a broad
• 46:55
  Speaker 1: glowing disk. The sun is somewhere inside it. Earth is
• 46:59
  Speaker 1: somewhere around the sun, and all the stars you have
• 47:02
  Speaker 1: visited are now part of one enormous pattern. From this distance,
• 47:07
  Speaker 1: individual worlds no longer matter. Individual stars begin to disappear
• 47:12
  Speaker 1: into the whole. The galaxy becomes a single shape, a
• 47:16
  Speaker 1: soft spiral of light surrounded by darkness. And as you
• 47:21
  Speaker 1: continue moving outward, even that spiral will begin to look smaller,
• 47:26
  Speaker 1: because beyond the Milky Way, There are other galaxies, many others.
• 47:31
  Speaker 1: And soon, the quiet journey will carry you away from
• 47:34
  Speaker 1: your own galaxy, toward the neighbouring island of stars, known
• 47:39
  Speaker 1: as Andromeda. The Milky Way is becoming smaller behind you.
• 47:45
  Speaker 1: Its spiral shape is still visible, but the details have
• 47:49
  Speaker 1: begun to disappear. The bright centre is now only a
• 47:53
  Speaker 1: soft glow. The spiral arms have become delicate curves. The
• 47:58
  Speaker 1: stars that once seemed countless are now blending into a
• 48:02
  Speaker 1: single distant pattern of light. And slowly, gently, you continue outward.
• 48:08
  Speaker 1: There is no boundary around the Milky Way, no edge
• 48:11
  Speaker 1: that you suddenly cross. The galaxy simply becomes smaller as
• 48:16
  Speaker 1: the space between you and it becomes larger. Behind you
• 48:20
  Speaker 1: is your home galaxy. Ahead of you is another. At first,
• 48:25
  Speaker 1: it is only a faint patch of light. a soft
• 48:28
  Speaker 1: glow against the darkness. But as you drift closer, the
• 48:32
  Speaker 1: shape begins to emerge. A broad disk, a brighter centre,
• 48:37
  Speaker 1: curving arms, a galaxy turning quietly through space. This is Andromeda.
• 48:44
  Speaker 1: It is the nearest major galaxy to the Milky Way,
• 48:47
  Speaker 1: lying roughly two and a half million light-years away. That
• 48:51
  Speaker 1: distance is difficult to imagine, so you do not need
• 48:54
  Speaker 1: to measure it. Instead, Imagine light leaving the Milky Way
• 48:59
  Speaker 1: and travelling outward for more than two million years before
• 49:03
  Speaker 1: finally reaching Andromeda. Or, imagine light leaving Andromeda and beginning
• 49:09
  Speaker 1: a journey toward Earth long before human civilisation had taken
• 49:14
  Speaker 1: its modern shape. When you look toward Andromeda, you are
• 49:17
  Speaker 1: not seeing it exactly as it is now. You are
• 49:20
  Speaker 1: seeing ancient light, light that has been travelling through darkness
• 49:24
  Speaker 1: for an enormous length of time. The galaxy you see
• 49:28
  Speaker 1: is a message from the distant past, arriving quietly after
• 49:33
  Speaker 1: a journey that began millions of years ago. Andromeda itself
• 49:37
  Speaker 1: is enormous. Its disk stretches across a region of space
• 49:41
  Speaker 1: much wider than the distance from one edge of our
• 49:43
  Speaker 1: familiar solar system to the other. Within that disk are
• 49:47
  Speaker 1: vast numbers of stars. Some are young, some are ancient,
• 49:52
  Speaker 1: some are gathered in bright clusters. Others are scattered quietly
• 49:56
  Speaker 1: through the galaxy. There are clouds of gas and dust.
• 50:00
  Speaker 1: There are regions where new stars are forming. There are
• 50:04
  Speaker 1: older regions, where the galaxy's earlier history is preserved in
• 50:07
  Speaker 1: the light of ancient stars. From a distance, Andromeda looks peaceful.
• 50:13
  Speaker 1: But like the Milky Way, it has a long history
• 50:15
  Speaker 1: of change. Galaxies do not always grow alone. They can meet.
• 50:21
  Speaker 1: They can pass close to one another. They can pull
• 50:24
  Speaker 1: on one another with gravity. And sometimes, over immense stretches
• 50:28
  Speaker 1: of time, they can merge. Andromeda carries traces of such encounters.
• 50:34
  Speaker 1: Around it are smaller satellite galaxies, small companions held nearby
• 50:39
  Speaker 1: by gravity. Among them are M32 and M110. They are
• 50:44
  Speaker 1: much smaller than Andromeda itself, but they belong to its
• 50:48
  Speaker 1: wider family, and some of the structures around Andromeda may
• 50:52
  Speaker 1: be the remains of galaxies that came too close in
• 50:55
  Speaker 1: the distant past. Stars can be pulled away, gas can
• 51:00
  Speaker 1: be stretched into long streams, The shape of a galaxy
• 51:03
  Speaker 1: can slowly change. The process is not like two solid
• 51:07
  Speaker 1: objects crashing together. There is far too much empty space
• 51:11
  Speaker 1: between individual stars. Instead, a galactic encounter is something much
• 51:17
  Speaker 1: slower and more delicate. Two enormous collections of stars pass
• 51:21
  Speaker 1: through one another. Their gravity reshapes their paths. Gas clouds interact.
• 51:28
  Speaker 1: New regions of star formation may appear. and over millions
• 51:32
  Speaker 1: or billions of years, the two galaxies can gradually become one.
• 51:36
  Speaker 1: Andromeda itself appears to preserve memories of such encounters. You
• 51:41
  Speaker 1: can imagine faint streams of stars extending away from the
• 51:44
  Speaker 1: main disk, almost like traces left behind by something that
• 51:48
  Speaker 1: passed through long ago. The galaxy does not keep its
• 51:52
  Speaker 1: history in a written record. It keeps it in motion,
• 51:56
  Speaker 1: in the paths of its stars, in the shape of
• 51:59
  Speaker 1: its clouds. In the faint structures surrounding its bright centre,
• 52:04
  Speaker 1: even the centre of Andromeda is unusual. Astronomers have observed
• 52:08
  Speaker 1: a strange double structure there, with two concentrations of stars
• 52:13
  Speaker 1: that do not appear perfectly centred in the same way.
• 52:16
  Speaker 1: The exact origin of this arrangement remains uncertain. It may
• 52:20
  Speaker 1: be connected to an ancient interaction with another galaxy. It
• 52:24
  Speaker 1: may reflect the complicated movement of stars around the massive
• 52:28
  Speaker 1: object at Andromeda's centre. Whatever the explanation, you can let
• 52:33
  Speaker 1: the uncertainty remain. A galaxy can be beautiful without being
• 52:37
  Speaker 1: completely understood. Andromeda continues turning. Its stars continue moving. Its
• 52:44
  Speaker 1: smaller companions continue orbiting. Its ancient light continues travelling outward.
• 52:50
  Speaker 1: And somewhere within that enormous galaxy, new stars are still
• 52:54
  Speaker 1: being born. You can drift past its outer regions now.
• 52:58
  Speaker 1: And as you move farther away... Another change begins. Andromeda
• 53:03
  Speaker 1: is no longer the only galaxy in view. The Milky
• 53:06
  Speaker 1: Way is behind you. Andromeda is nearby, and somewhere between
• 53:11
  Speaker 1: and around them are many smaller galaxies, faint companions scattered
• 53:15
  Speaker 1: through the darkness. Another larger spiral galaxy begins to appear,
• 53:20
  Speaker 1: the Triangulum Galaxy. It is smaller than both the Milky
• 53:24
  Speaker 1: Way and Andromeda, but it is still a vast collection
• 53:27
  Speaker 1: of stars, gas... dust and planets. Together, these galaxies form
• 53:34
  Speaker 1: part of a much larger neighbourhood. The Milky Way, Andromeda, Triangulum,
• 53:40
  Speaker 1: and many smaller galaxies. They are not simply arranged randomly.
• 53:45
  Speaker 1: Gravity connects them. They move through the same broad region
• 53:49
  Speaker 1: of space, influencing one another across enormous distances. Astronomers call
• 53:55
  Speaker 1: this neighbourhood the Local Group. The name sounds almost modest. Local. Group.
• 54:01
  Speaker 1: But from the perspective of Earth, this local neighbourhood is
• 54:05
  Speaker 1: already unimaginably large. It stretches across millions of light years,
• 54:10
  Speaker 1: and within it are dozens upon dozens of galaxies, most
• 54:14
  Speaker 1: of them much smaller and fainter than the great spirals
• 54:17
  Speaker 1: you can see more easily. Some are tiny dwarf galaxies.
• 54:22
  Speaker 1: Some contain relatively few stars. Some have been shaped by
• 54:26
  Speaker 1: their larger neighbours. Others may be remnants of ancient encounters,
• 54:31
  Speaker 1: and yet they all belong to the same broad gravitational family.
• 54:35
  Speaker 1: You can now slowly turn around. The Milky Way is
• 54:39
  Speaker 1: one island of stars. Andromeda is another. Triangulum is another.
• 54:45
  Speaker 1: Small galaxies drift around them like faint points of light.
• 54:49
  Speaker 1: The solar system is somewhere inside the Milky Way, too
• 54:52
  Speaker 1: small to distinguish from this distance. Earth is smaller still.
• 54:56
  Speaker 1: and you are farther away than you have ever been
• 54:59
  Speaker 1: in this journey. The universe is beginning to change scale. Earlier,
• 55:04
  Speaker 1: the stars seemed enormous. Then the Milky Way seemed enormous.
• 55:08
  Speaker 1: Then Andromeda seemed enormous. Now even these galaxies are becoming
• 55:14
  Speaker 1: pieces of something larger. The local group itself is beginning
• 55:18
  Speaker 1: to look small. And beyond it, the darkness is no
• 55:22
  Speaker 1: longer completely empty. Farther away are other groups. other clusters,
• 55:28
  Speaker 1: other galaxies, other enormous arrangements of matter. You can see
• 55:33
  Speaker 1: them beginning to gather along distant regions of light. The
• 55:37
  Speaker 1: familiar island of the local group is slowly fading behind you.
• 55:41
  Speaker 1: And ahead lies something even larger, something that cannot be
• 55:46
  Speaker 1: understood by looking at one galaxy at a time. A
• 55:49
  Speaker 1: wider pattern is beginning to emerge. The galaxies are not
• 55:53
  Speaker 1: scattered randomly. They gather. They stretch. They form long, faint
• 55:59
  Speaker 1: structures across space. And between those structures are regions where
• 56:03
  Speaker 1: very few galaxies can be found. As you drift toward
• 56:07
  Speaker 1: that wider pattern, the spaces between the galaxies begin to
• 56:10
  Speaker 1: matter as much as the galaxies themselves. The local group
• 56:17
  Speaker 1: is slowly becoming smaller behind you. The Milky Way is
• 56:21
  Speaker 1: now only one faint spiral among the darkness. Andromeda is another.
• 56:26
  Speaker 1: Triangulum is smaller still. The many little galaxies around them
• 56:30
  Speaker 1: are becoming difficult to distinguish, until the whole neighbourhood begins
• 56:34
  Speaker 1: to look like a handful of soft points of light.
• 56:38
  Speaker 1: But as you drift farther away, you begin to notice
• 56:41
  Speaker 1: something unexpected. The galaxies are not scattered evenly through space.
• 56:46
  Speaker 1: Some regions are more crowded. Others are almost empty. And
• 56:50
  Speaker 1: when you pull back far enough, the separate galaxies begin
• 56:54
  Speaker 1: to form patterns. Groups gather into larger groups. Clusters of
• 56:59
  Speaker 1: galaxies gather together, and between them, long regions of space
• 57:04
  Speaker 1: stretch outward, carrying galaxies along enormous structures that are almost
• 57:08
  Speaker 1: impossible to imagine from within. You are beginning to see
• 57:12
  Speaker 1: the large-scale structure of the universe. At first, it may
• 57:16
  Speaker 1: look almost random, tiny points, faint patches, little clusters of light,
• 57:23
  Speaker 1: but gradually, a pattern begins to emerge. Some galaxies lie
• 57:28
  Speaker 1: along long, thin regions. Others gather where several of these
• 57:32
  Speaker 1: regions meet, and between them are enormous areas containing far
• 57:38
  Speaker 1: fewer galaxies. Astronomers often describe these long structures as filaments.
• 57:44
  Speaker 1: The word is simple. The scale is not. A filament
• 57:48
  Speaker 1: can extend across immense distances, carrying galaxies through a vast
• 57:52
  Speaker 1: cosmic landscape. You can imagine stepping farther and farther away
• 57:57
  Speaker 1: from the local group until the individual galaxies begin to
• 58:01
  Speaker 1: disappear and only the larger arrangement remains. The galaxies become points.
• 58:07
  Speaker 1: The points become threads. The threads begin to connect. And
• 58:11
  Speaker 1: the universe starts to resemble a delicate pattern of light
• 58:14
  Speaker 1: and darkness. This is sometimes called the cosmic web. It
• 58:19
  Speaker 1: is not a physical web hanging in space. There are
• 58:22
  Speaker 1: no threads you could touch. Instead, it is a way
• 58:25
  Speaker 1: of describing how matter has gathered across the universe over
• 58:29
  Speaker 1: enormous stretches of time. Gravity slowly pulls matter together. Regions
• 58:35
  Speaker 1: that begin slightly denser can attract more material. Gas gathers.
• 58:40
  Speaker 1: Galaxies form. Galaxies gather into groups and clusters. And the
• 58:45
  Speaker 1: spaces between these denser regions become increasingly empty. The process
• 58:50
  Speaker 1: is incredibly slow. so slow that even the lifetime of
• 58:54
  Speaker 1: a star is only a brief moment compared with the
• 58:57
  Speaker 1: history of the cosmic structure around it. You can simply
• 59:01
  Speaker 1: watch the pattern from a distance. Light here. Darkness there.
• 59:06
  Speaker 1: Another group of galaxies farther away. Another phantom filament extending
• 59:11
  Speaker 1: beyond it. And then, between these structures, a region where
• 59:16
  Speaker 1: almost nothing seems to be happening. A void. Cosmic voids
• 59:20
  Speaker 1: are among the quietest places in the universe. They are
• 59:24
  Speaker 1: not completely empty. There can still be thin gas. There
• 59:28
  Speaker 1: can still be isolated galaxies. There can still be particles
• 59:31
  Speaker 1: and traces of matter moving through them. But compared with
• 59:35
  Speaker 1: the crowded regions of galaxy clusters, a void contains remarkably little.
• 59:41
  Speaker 1: You are moving toward one now. The galaxies behind you
• 59:44
  Speaker 1: become fewer. The bright clusters become distant. The long structures
• 59:49
  Speaker 1: of the cosmic web begin to fade, and the darkness
• 59:53
  Speaker 1: between them becomes wider. One of the nearby examples is
• 59:57
  Speaker 1: known as the local void. It lies close to the
• 1:00:01
  Speaker 1: larger structures containing our own local group, yet it contains
• 1:00:05
  Speaker 1: relatively few galaxies. From the inside, it would not necessarily
• 1:00:10
  Speaker 1: look like a dramatic empty chamber. There would be no
• 1:00:13
  Speaker 1: visible wall separating the void from the surrounding universe. There
• 1:00:17
  Speaker 1: would simply be more and more distance between the galaxies.
• 1:00:21
  Speaker 1: A galaxy here, a galaxy much farther away. then a
• 1:00:25
  Speaker 1: long stretch of darkness, then perhaps another faint galaxy. The
• 1:00:31
  Speaker 1: emptiness grows gradually, and that gradualness is part of what
• 1:00:35
  Speaker 1: makes it so difficult to imagine. You might expect space
• 1:00:39
  Speaker 1: to be filled evenly with stars and galaxies, but the
• 1:00:42
  Speaker 1: universe does not arrange itself that way. It has crowded
• 1:00:46
  Speaker 1: places and quiet places, bright regions and dark regions, places
• 1:00:53
  Speaker 1: where gravity has gathered enormous amounts of matter, and places
• 1:00:57
  Speaker 1: where comparatively little matter has gathered. As you drift farther
• 1:01:01
  Speaker 1: into this quiet region, you may notice a small galaxy
• 1:01:05
  Speaker 1: far away. It is known as NGC 6503. Its name
• 1:01:11
  Speaker 1: is simply a catalogue name, useful to astronomers but not
• 1:01:15
  Speaker 1: especially meaningful to you tonight. What matters is its settings.
• 1:01:20
  Speaker 1: This small galaxy lies in a relatively isolated region of space,
• 1:01:25
  Speaker 1: surrounded by an environment much less crowded than the dense
• 1:01:28
  Speaker 1: neighbourhoods of many other galaxies. And perhaps that makes it
• 1:01:32
  Speaker 1: a fitting companion for the final part of this journey.
• 1:01:36
  Speaker 1: A small galaxy, a huge surrounding emptiness, light travelling quietly
• 1:01:41
  Speaker 1: across the darkness. Even in a region that seems almost empty,
• 1:01:45
  Speaker 1: a galaxy can continue to shine. Its stars continue moving.
• 1:01:51
  Speaker 1: Its gas continues changing. Its light continues travelling outward. And perhaps,
• 1:01:57
  Speaker 1: somewhere inside that galaxy, there are worlds orbiting distant stars,
• 1:02:02
  Speaker 1: just as Earth orbits the Sun. You can let that
• 1:02:05
  Speaker 1: thought remain very small. You do not need to follow it,
• 1:02:10
  Speaker 1: because now you are pulling back again. Farther and farther.
• 1:02:14
  Speaker 1: The local void becomes smaller. The local group becomes smaller.
• 1:02:19
  Speaker 1: The Milky Way becomes smaller. Andromeda becomes smaller. The galaxies
• 1:02:24
  Speaker 1: become points. The filaments become faint patterns. The cosmic web
• 1:02:29
  Speaker 1: becomes something almost too large to recognise. And beyond all
• 1:02:33
  Speaker 1: of this is the observable universe, the portion of the
• 1:02:36
  Speaker 1: cosmos whose light has had enough time to reach us
• 1:02:40
  Speaker 1: since the universe became transparent to light. You do not
• 1:02:44
  Speaker 1: need to imagine its edge. There is no wall waiting there.
• 1:02:48
  Speaker 1: It is simply the limit of what we can observe
• 1:02:50
  Speaker 1: from our position in space and time. Beyond what we
• 1:02:54
  Speaker 1: can see, there may be much more, but tonight you
• 1:02:57
  Speaker 1: do not need to travel there. You can simply remain here,
• 1:03:01
  Speaker 1: floating in the darkness between the galaxies. The journey that
• 1:03:05
  Speaker 1: began beside Earth has carried you outward through the solar system,
• 1:03:10
  Speaker 1: past the distant icy regions, between nearby stars, past strange
• 1:03:15
  Speaker 1: worlds of water and rock. beyond young stars and ageing giants,
• 1:03:20
  Speaker 1: past pulsars and the dark presence of black holes, through
• 1:03:24
  Speaker 1: the Milky Way, beyond Andromeda, out into the local group,
• 1:03:29
  Speaker 1: and finally toward the enormous spaces between galaxies, you have
• 1:03:34
  Speaker 1: travelled farther and farther away, and with every step outward
• 1:03:38
  Speaker 1: there has been more space, more darkness, more distance, until
• 1:03:43
  Speaker 1: the universe begins to feel less like a collection of
• 1:03:46
  Speaker 1: objects and more like a quiet balance between light and emptiness.
• 1:03:51
  Speaker 1: A galaxy here, a galaxy there, a faint filament stretching
• 1:03:56
  Speaker 1: across the distance, a great void between them. And everywhere,
• 1:04:01
  Speaker 1: enormous amounts of space. You can let that idea become
• 1:04:05
  Speaker 1: softer now. You do not need to understand the whole universe.
• 1:04:09
  Speaker 1: You do not need to remember the names. You do
• 1:04:12
  Speaker 1: not need to hold on to the distances. The stars
• 1:04:15
  Speaker 1: can continue moving without you watching them. The galaxies can
• 1:04:20
  Speaker 1: continue turning. The cosmic web can remain where it is.
• 1:04:24
  Speaker 1: The distant voids can remain quiet. And you can simply rest.
• 1:04:29
  Speaker 1: The darkness around you is not something missing. It is
• 1:04:32
  Speaker 1: simply space. Wide, quiet, unhurried. Far behind you, the Milky
• 1:04:38
  Speaker 1: Way continues to shine. And somewhere inside that distant spiral...
• 1:04:42
  Speaker 1: The sun continues its slow journey around the galaxy. Earth
• 1:04:47
  Speaker 1: continues turning. The oceans continue moving. Night continues passing into morning.
• 1:04:54
  Speaker 1: And for now, you can let yourself become still. You
• 1:04:57
  Speaker 1: are safe. There is nothing to do, nothing to solve,
• 1:05:01
  Speaker 1: nothing you need to reach. The universe is already moving
• 1:05:05
  Speaker 1: without effort. The stars are already shining without asking to
• 1:05:09
  Speaker 1: be noticed. And the great spaces between them are already
• 1:05:13
  Speaker 1: holding everything quietly apart. So you can simply drift here
• 1:05:17
  Speaker 1: for a while. Perhaps there are galaxies farther away than
• 1:05:21
  Speaker 1: you can imagine. Perhaps there are still larger structures beyond
• 1:05:25
  Speaker 1: the ones we have mapped. Perhaps there are spaces so
• 1:05:28
  Speaker 1: wide that even the idea of distance begins to lose
• 1:05:31
  Speaker 1: its meaning. You do not need to follow them tonight.
• 1:05:35
  Speaker 1: You can let the questions remain open. You can let
• 1:05:37
  Speaker 1: the darkness remain wide. And somewhere... Very far away, a
• 1:05:42
  Speaker 1: small point of light continues travelling through the quiet.