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Hubble Found a Black Hole Running Away _ And It Left Stars Behind · Boring Science

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  Speaker 1: Hello, and welcome to Boring Science for Sleep, a quiet
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  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 something very strange, something that
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  Speaker 1: Hubble once noticed as a thin, almost impossibly straight line
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  Speaker 1: across the darkness of deep space. Not to learn everything
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  Speaker 1: about it, and not to remember every detail, but simply
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  Speaker 1: to notice it slowly, calmly. one small idea at a time.
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  Speaker 1: Because somewhere far beyond the familiar stars, something enormous appears
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  Speaker 1: to be moving through space, and behind it, strangely enough,
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  Speaker 1: there may be a trail of newborn stars. Before you
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  Speaker 1: settle in, if you truly enjoy these calm journeys through
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  Speaker 1: interesting science, you're welcome to like this video and subscribe,
• 0:51
  Speaker 1: but only if it feels right for you. And when
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  Speaker 1: you're ready, you can let me know in the comments
• 0:57
  Speaker 1: where you're listening from, and what time it is right now.
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  Speaker 1: It's always a quiet joy to imagine how many different rooms,
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  Speaker 1: cities and little moments are gathered here together. Now, dim
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  Speaker 1: the lights, perhaps let a fan hum softly in the
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  Speaker 1: background and allow your body to become a little heavier.
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  Speaker 1: There's nothing to do. You are safe. You can simply listen,
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  Speaker 1: breathe slowly and drift with the story as we begin
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  Speaker 1: looking toward a very distant line of light. You can
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  Speaker 1: begin by imagining that you are very far away from home,
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  Speaker 1: not on a distant planet, not inside a spacecraft, but
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  Speaker 1: simply floating in the darkness between galaxies, where there is
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  Speaker 1: almost nothing around you, and where distance becomes so large
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  Speaker 1: that ordinary human measurements begin to feel strangely small. There
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  Speaker 1: is no wind here, no sound passes through the emptiness,
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  Speaker 1: no ground beneath you and no ceiling above you. only darkness,
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  Speaker 1: scattered with faint points of light. You are safe here,
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  Speaker 1: with nothing to do, nothing to solve, nothing you need
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  Speaker 1: to remember. You can simply look. And as you look
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  Speaker 1: into that darkness, imagine that you are holding a photograph
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  Speaker 1: taken by the Hubble Space Telescope. At first, it seems
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  Speaker 1: like an ordinary deep space image. There are distant galaxies,
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  Speaker 1: tiny points of light and and enormous regions of darkness
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  Speaker 1: between them. The stars are so far away that even
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  Speaker 1: the brightest ones appear delicate, almost weightless. Then, slowly, your
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  Speaker 1: attention settles on something unusual. A line. A very thin,
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  Speaker 1: very long line stretching through the darkness. It is almost
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  Speaker 1: unnaturally straight. It does not look quite like a galaxy.
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  Speaker 1: It does not look quite like a familiar stream of stars.
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  Speaker 1: It simply seems to continue, quietly, across an enormous distance.
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  Speaker 1: And if you could somehow stretch that line across our
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  Speaker 1: own galaxy, it would reach for almost twice the width
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  Speaker 1: of the Milky Way. Nearly 200,000 light years. A distance
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  Speaker 1: so vast that even light, moving faster than anything we know,
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  Speaker 1: would need nearly 200,000 years to cross it. So you
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  Speaker 1: can take your time looking at it. There is no
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  Speaker 1: need to hurry. The line is not going anywhere in
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  Speaker 1: the photograph. It simply waits there, suspended in the ancient darkness.
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  Speaker 1: And yet, there is something particularly strange about it. The
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  Speaker 1: light along this narrow trail does not appear to come
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  Speaker 1: from an old population of stars. Instead, many of the
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  Speaker 1: stars appear young. They are blue, bright, and relatively fresh
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  Speaker 1: on the cosmic timescale, as though something had recently encouraged
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  Speaker 1: new stars to gather along this otherwise empty-looking path. That
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  Speaker 1: makes the line harder to explain. A galaxy can be long,
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  Speaker 1: a galaxy can be distorted, a galaxy can be viewed
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  Speaker 1: from an unusual angle. But this structure seemed different. It
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  Speaker 1: was almost as if something had passed through space and
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  Speaker 1: left a narrow trace behind. At first, however, there was
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  Speaker 1: a much simpler possibility. Perhaps the line was not real
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  Speaker 1: at all, Perhaps it was a small mistake in the image.
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  Speaker 1: A cosmic ray striking the telescope's detector, or some other
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  Speaker 1: artefact created by the camera itself, can sometimes produce an
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  Speaker 1: unwanted streak of light. So, before imagining anything extraordinary, you
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  Speaker 1: begin with the ordinary explanation. You look again. You check.
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  Speaker 1: You wonder whether the strange line is simply a trick
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  Speaker 1: of the telescope's eye. And this is one of the
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  Speaker 1: quiet things about astronomy. Sometimes discovery begins not with certainty,
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  Speaker 1: but with doubt. You notice something that seems out of place,
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  Speaker 1: and instead of immediately believing it, you gently ask whether
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  Speaker 1: the instrument could have made the mistake. The image is
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  Speaker 1: examined more carefully. The strange feature remains. It is not
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  Speaker 1: so easily dismissed. And now the line becomes a little
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  Speaker 1: more interesting. because it seems to have a relationship with
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  Speaker 1: a distant galaxy nearby. One end of the trail points
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  Speaker 1: back toward a compact galaxy, a small and active place
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  Speaker 1: where stars are forming. The other end stretches away into
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  Speaker 1: the darkness. You can imagine yourself slowly turning around in space,
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  Speaker 1: looking from the distant trail toward that galaxy, then back
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  Speaker 1: again toward the empty region beyond it. The trail seems
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  Speaker 1: to have a direction. it seems to remember where it
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  Speaker 1: came from. And somewhere near the far end, there appears
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  Speaker 1: to be something associated with the beginning of the trail,
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  Speaker 1: something that is not easy to see directly, something enormous.
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  Speaker 1: At this stage, you do not yet need to name it.
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  Speaker 1: You can simply imagine a silent traveller moving through a
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  Speaker 1: nearly empty universe. As it moves, the surrounding gas is disturbed,
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  Speaker 1: very thin clouds of material, almost invisible against the darkness.
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  Speaker 1: are gently pushed and compressed. And behind the traveller something remains.
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  Speaker 1: Not a glowing road, not a beam of light, but
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  Speaker 1: a trail, awake, like the faint disturbance left behind when
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  Speaker 1: something passes through a quiet medium. Except here the medium
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  Speaker 1: is not water, it is the thin, almost imperceptible gas
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  Speaker 1: spread through the space around a galaxy. And the trail
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  Speaker 1: is not made by a ship, It is made from stars,
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  Speaker 1: gas and light. The more carefully astronomers looked, the more
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  Speaker 1: unusual the line became. At one end, the gas was
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  Speaker 1: glowing in a peculiar way. Atoms of oxygen had been energised,
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  Speaker 1: causing them to release light. You do not need to
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  Speaker 1: picture complicated chemistry. You can simply imagine tiny pieces of
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  Speaker 1: gas receiving a little burst of energy, becoming disturbed and
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  Speaker 1: then glowing faintly as they settle again. The light itself
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  Speaker 1: becomes a message, a very old message, travelling across billions
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  Speaker 1: of years of space before finally reaching the telescope. And slowly,
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  Speaker 1: the image begins to suggest that this strange line may
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  Speaker 1: not be a fixed structure at all, it may be
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  Speaker 1: the remains of movement. Something may have crossed the darkness,
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  Speaker 1: something powerful enough to disturb the gas around it. something
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  Speaker 1: fast enough to leave a trail almost 200,000 light-years long.
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  Speaker 1: And somewhere in that distant darkness, at the front of
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  Speaker 1: the trail, the traveller may still be moving. For now,
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  Speaker 1: you can simply remain there for a moment, floating beside
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  Speaker 1: the image. The stars are quiet, the line is quiet,
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  Speaker 1: the distant galaxy is quiet, and the universe seems almost
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  Speaker 1: completely still. Yet beneath that stillness, there is a story
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  Speaker 1: of motion, A story written not in ink, but in
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  Speaker 1: glowing gas and young stars. And as you continue to look,
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  Speaker 1: very slowly, the question begins to change. It is no
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  Speaker 1: longer only, what is this strange line? It becomes something softer.
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  Speaker 1: What could have passed through the darkness and left something
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  Speaker 1: like this behind? You are still floating beside that distant image,
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  Speaker 1: looking at the long, narrow line, that seems to have
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  Speaker 1: been drawn across the darkness. For a moment, you do
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  Speaker 1: not need to decide what it is. You can simply
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  Speaker 1: let the possibilities pass through your mind, slowly, one by one.
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  Speaker 1: Perhaps it is a galaxy. Perhaps it is a stream
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  Speaker 1: of stars. Perhaps it is something created by an active
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  Speaker 1: black hole. Or perhaps it is something much more ordinary,
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  Speaker 1: something produced by the telescope itself. There is nothing wrong
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  Speaker 1: with beginning with the simplest explanation. In fact, that is
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  Speaker 1: often how astronomy moves forward. You look at something strange,
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  Speaker 1: and before you imagine something extraordinary, you ask whether nature
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  Speaker 1: has already given you a familiar answer. So you can
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  Speaker 1: imagine turning the line gently in your mind, viewing it
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  Speaker 1: from different directions, wondering whether it might simply be a
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  Speaker 1: very thin galaxy seen from the side. galaxies can take
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  Speaker 1: many shapes. Some are broad and glowing, some are wrapped
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  Speaker 1: into graceful spirals, and some are distorted by the slow
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  Speaker 1: pull of neighbouring galaxies. But this particular line remains unusual.
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  Speaker 1: It is too narrow, too straight, and perhaps most importantly,
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  Speaker 1: the stars along it appear remarkably young. Young stars often
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  Speaker 1: have a different kind of light. They can appear blue
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  Speaker 1: and bright, because they are still relatively new compared with
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  Speaker 1: the ancient populations that fill much of a mature galaxy.
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  Speaker 1: So when you look at this trail, you are not
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  Speaker 1: looking at a fossil from the distant past alone. you
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  Speaker 1: are looking at something that seems to contain relatively fresh stars.
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  Speaker 1: And that creates another quiet question. Why would a long,
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  Speaker 1: narrow path through space contain so many young stars? You
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  Speaker 1: might imagine a field of tiny lights appearing one after
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  Speaker 1: another along a line, as though someone had walked through
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  Speaker 1: darkness carrying a lantern, leaving little points of brightness behind.
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  Speaker 1: But stars do not simply appear because something passes nearby.
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  Speaker 1: They need material, they need clouds of gas, and they
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  Speaker 1: need gravity to gather that gas into dense enough regions
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  Speaker 1: for stars to begin forming. So now the faint trail
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  Speaker 1: becomes connected to another question. Where did its gas come from,
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  Speaker 1: and what happened to it? The answer begins to hide
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  Speaker 1: inside the light itself. Astronomers can do something rather beautiful
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  Speaker 1: with distant light. They can spread that light out and
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  Speaker 1: examine the tiny variations within it. Instead of seeing light
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  Speaker 1: as one smooth glow, they can look for subtle patterns,
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  Speaker 1: like reading a message written in colours that are almost
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  Speaker 1: too delicate for the human eye. Different atoms leave different signatures. Oxygen,
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  Speaker 1: hydrogen and other elements can reveal themselves through particular kinds
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  Speaker 1: of light, and along this strange trail the gas was
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  Speaker 1: not behaving as quietly as ordinary starlight might suggest. Near
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  Speaker 1: one end, The oxygen in the gas appeared unusually energised.
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  Speaker 1: You can imagine tiny atoms disturbed by their surroundings, receiving
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  Speaker 1: energy and then releasing some of that energy again as light.
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  Speaker 1: The light travels outward, across the enormous distance, across billions
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  Speaker 1: of years, until eventually it reaches a telescope on Earth.
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  Speaker 1: And by reading that faint glow, astronomers could begin to
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  Speaker 1: sense that something energetic had happened there. The trail was
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  Speaker 1: not simply a collection of young stars. There was gas involved,
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  Speaker 1: and the gas seemed disturbed. At first, another possibility could
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  Speaker 1: be considered. Perhaps the line was a jet. Some galaxies
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  Speaker 1: contain enormous black holes at their centres, and when those
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  Speaker 1: black holes are surrounded by actively feeding material, powerful streams
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  Speaker 1: can sometimes emerge from their central regions. These streams can
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  Speaker 1: travel vast distances through space. So perhaps, for a moment,
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  Speaker 1: you can imagine the strange line as one of these
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  Speaker 1: enormous cosmic jets, a narrow stream reaching outward from a galaxy.
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  Speaker 1: It would be a reasonable thought, but when astronomers looked
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  Speaker 1: more carefully, the shape did not fit comfortably. The feature
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  Speaker 1: did not behave like the familiar jets seen around active galaxies.
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  Speaker 1: Its structure was unusual. Its relationship to the nearby galaxy
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  Speaker 1: was unusual. and the farther the astronomers looked, the more
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  Speaker 1: the line seemed to have a direction that mattered. It
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  Speaker 1: appeared to begin near the galaxy and extend outward, almost
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  Speaker 1: as though something had departed. That idea is subtle, because
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  Speaker 1: if something had simply exploded, you might expect material to
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  Speaker 1: spread outward in many directions. If a galaxy had been
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  Speaker 1: stretched by gravity, its stars might form a broader stream,
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  Speaker 1: but here, the structure remained remarkably narrow, a long trace
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  Speaker 1: through an almost empty environment, and that is when the
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  Speaker 1: idea of a wake begins to feel more natural. A
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  Speaker 1: wake is not an object that existed before the traveller.
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  Speaker 1: It is something created by movement. You see a boat
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  Speaker 1: after it has passed through water, and the boat itself
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  Speaker 1: may already be far ahead. But the water remembers, briefly,
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  Speaker 1: that something moved through it. There is a disturbance. a
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  Speaker 1: soft line, a changing texture. The water does not tell
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  Speaker 1: you everything about the boat, but it tells you that
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  Speaker 1: something passed. Now imagine that idea on a much larger scale.
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  Speaker 1: Imagine gas, so thin that you would barely notice it
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  Speaker 1: if you were drifting through it. Then imagine something enormous
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  Speaker 1: moving through that gas at an extraordinary speed. The gas
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  Speaker 1: would not remain perfectly undisturbed. It would be pushed, compressed, heated.
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  Speaker 1: and left in a different state behind the traveller. The
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  Speaker 1: strange line in the Hubble image began to look less
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  Speaker 1: like a road and more like a memory, a memory
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  Speaker 1: written into the material between galaxies. But there was still
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  Speaker 1: a problem. If something was moving through the gas, where
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  Speaker 1: was it? The answer seemed to lie near the front
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  Speaker 1: of the trail, and this was where the observations became
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  Speaker 1: especially interesting. Hubble had shown the shape. The light had
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  Speaker 1: revealed young stars and energised gas. But another kind of
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  Speaker 1: observation was needed to understand motion. Because light does not
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  Speaker 1: only tell you what something is made of, it can
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  Speaker 1: also tell you how that material is moving. Tiny shifts
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  Speaker 1: in the light can reveal whether gas is approaching or
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  Speaker 1: moving away, and how quickly its motion changes across a region.
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  Speaker 1: So astronomers looked again. They examined the glowing gas along
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  Speaker 1: the trail. And the farther they looked, the more the
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  Speaker 1: story began to resemble something passing through space, rather than
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  Speaker 1: something simply sitting there. The gas was changing. Its motion
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  Speaker 1: was changing. Its energy was changing. And somewhere near the
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  Speaker 1: front of that long trail, something appeared to be moving
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  Speaker 1: fast enough to reshape the gas around it. You can
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  Speaker 1: remain there for a moment, beside that faint blue line.
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  Speaker 1: Nothing is rushing toward you. Nothing is exploding around you.
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  Speaker 1: There is only an ancient photograph, a distant galaxy, and
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  Speaker 1: a trail of light that seems to remember a journey.
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  Speaker 1: And slowly, almost without noticing, you begin to look toward
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  Speaker 1: the front of the trail. Because that is where the
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  Speaker 1: quietest clue may be waiting. Not another galaxy. Not a
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  Speaker 1: distant jet. But a traveller so massive that its presence
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  Speaker 1: is easier to recognise by the disturbance it leaves behind.
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  Speaker 1: than by the darkness of the traveller itself. You are
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  Speaker 1: still looking toward the far end of the trail. The
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  Speaker 1: farther you look, the thinner the line seems to become,
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  Speaker 1: until it almost disappears into the darkness. And somewhere there,
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  Speaker 1: at the front of this enormous wake, is the clue
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  Speaker 1: that changes the way you see everything behind it. It
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  Speaker 1: is not a bright star. It is not another galaxy.
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  Speaker 1: It is something much darker, something whose presence is easier
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  Speaker 1: to recognise through the space around it than through light
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  Speaker 1: coming directly from it. A black hole. More precisely, a
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  Speaker 1: supermassive black hole, an object containing the mass of millions
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  Speaker 1: of suns gathered into an extraordinarily compact region. You can
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  Speaker 1: pause there for a moment. A mass greater than 10
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  Speaker 1: million suns moving through the distant universe. It is difficult
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  Speaker 1: to picture how because there is no familiar object quite
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  Speaker 1: like it. You might imagine all the stars in a
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  Speaker 1: vast stellar neighbourhood gathered together into something that cannot be
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  Speaker 1: seen in the ordinary way. And yet this enormous object
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  Speaker 1: is not resting quietly at the centre of a galaxy.
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  Speaker 1: It is moving, very quickly. The latest measurements suggest that
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  Speaker 1: this black hole, known as RBH1, is travelling at roughly
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  Speaker 1: 950 kilometres every second, nearly a thousand kilometres every second,
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  Speaker 1: as it crosses the thin gas surrounding the galaxy and
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  Speaker 1: moves outward into the vast space between galaxies. For you,
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  Speaker 1: floating beside it, the motion would not look like a
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  Speaker 1: dramatic rush. Space is too large for that. Instead, it
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  Speaker 1: would feel almost completely still. The black hole would move
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  Speaker 1: through darkness, and the darkness would seem unchanged, but the
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  Speaker 1: gas around it would know Even the thinnest material can
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  Speaker 1: respond when something enormously massive passes through it at such
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  Speaker 1: a speed. Imagine yourself drifting through a very thin mist,
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  Speaker 1: so thin that you can almost forget it is there.
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  Speaker 1: Now imagine that something large moves through the mist ahead
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  Speaker 1: of you. The mist gathers. It becomes compressed. It changes direction.
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  Speaker 1: Some of it becomes warmer. Some of it begins to glow.
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  Speaker 1: And behind the moving object... the mist no longer looks
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  Speaker 1: quite the same as it did before. That is, in
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  Speaker 1: a gentle way, what happens around the runaway black hole.
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  Speaker 1: The surrounding gas is extremely diffuse, but it is not
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  Speaker 1: perfectly empty. The black hole moves through it, and the
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  Speaker 1: material in front of the black hole is pushed and compressed.
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  Speaker 1: This creates a broad region of disturbed gas at the
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  Speaker 1: leading edge. Astronomers call this a bow shock. The name
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  Speaker 1: comes from something familiar on Earth. When a boat moves
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  Speaker 1: through water, the water gathers around its front. When something
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  Speaker 1: moves through air, the air is pushed aside. Here, the
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  Speaker 1: same basic idea occurs on an enormous cosmic scale. Except
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  Speaker 1: the material being disturbed is incredibly thin, and the traveller
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  Speaker 1: is an object whose mass is millions of times greater
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  Speaker 1: than our sun. There is something particularly peaceful about this
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  Speaker 1: idea when you slow it down. The black hole does
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  Speaker 1: not need to roar. It does not need to shine.
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  Speaker 1: It does not need to announce itself. Its movement is enough.
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  Speaker 1: The surrounding gas simply responds, and Webb looking more carefully
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  Speaker 1: at this distant region, helped reveal something important. The gas
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  Speaker 1: near the front of the trail showed a sudden change
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  Speaker 1: in its motion. It was not moving as though everything
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  Speaker 1: were calm. The material was being strongly disturbed. The pattern
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  Speaker 1: was consistent with something moving through the gas at a
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  Speaker 1: speed greater than the pressure waves in that gas could travel.
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  Speaker 1: In other words, the traveller was moving supersonically through its surroundings.
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  Speaker 1: You do not need to imagine a sound. There is
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  Speaker 1: no atmosphere here like the one around you now, and
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  Speaker 1: no sound is travelling through the vacuum of space. The
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  Speaker 1: word simply describes a relationship between movement and the speed
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  Speaker 1: at which pressure changes can travel through the surrounding material.
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  Speaker 1: The black hole is moving faster than those changes can
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  Speaker 1: spread ahead of it, so the gas cannot gently move
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  Speaker 1: out of the way. Instead, it gathers into a compressed front,
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  Speaker 1: a bow shock. And once you know this, the long
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  Speaker 1: trail behind it begins to make more sense. The trail
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  Speaker 1: is no longer just a strange line of blue stars.
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  Speaker 1: It is part of a moving system. At the front,
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  Speaker 1: gas is compressed and disturbed. Behind that front, the gas
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  Speaker 1: can begin to change again. It can release some of
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  Speaker 1: its heat. It can mix with surrounding material. It can
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  Speaker 1: gradually become cooler and denser. And farther along the path,
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  Speaker 1: some of that material can eventually become the birthplace of stars.
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  Speaker 1: But you are not there yet. For now, you are
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  Speaker 1: simply beside the front of the wake. You can imagine
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  Speaker 1: the runaway black hole moving silently ahead of you, invisible
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  Speaker 1: against the darkness. Behind it stretches a trail almost 200,000
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  Speaker 1: light-years long. That distance represents an immense amount of time.
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  Speaker 1: The light reaching Hubble and Webb today began its journey
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  Speaker 1: billions of years ago, so when you look at the trail,
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  Speaker 1: you are not seeing something happening now in the ordinary
• 22:12
  Speaker 1: human sense. You are seeing ancient light, a record carried
• 22:17
  Speaker 1: across the universe, a long message from a time when
• 22:21
  Speaker 1: our own planet, and everything familiar around you tonight, was
• 22:25
  Speaker 1: very different, and perhaps the most remarkable part is that
• 22:29
  Speaker 1: the black hole itself does not need to be bright
• 22:32
  Speaker 1: for its journey to become visible. Its surroundings tell the story.
• 22:37
  Speaker 1: The gas tells the story. The young stars tell the story.
• 22:41
  Speaker 1: The long, narrow wake tells the story. Like footprints across
• 22:45
  Speaker 1: a quiet landscape, each part of the trail preserves a
• 22:49
  Speaker 1: little memory of where the traveller has been. You can
• 22:53
  Speaker 1: let that image rest gently in your mind. A dark
• 22:56
  Speaker 1: object moving through an almost empty universe, a faint cloud
• 23:00
  Speaker 1: of gas gathering ahead of it, a soft disturbance spreading
• 23:04
  Speaker 1: through the material, and behind the traveller a trail slowly
• 23:08
  Speaker 1: taking shape. There is something almost backwards about it. You
• 23:13
  Speaker 1: might expect a black hole to leave only emptiness behind. Instead,
• 23:18
  Speaker 1: the path seems to contain light, young stars, glowing gas,
• 23:23
  Speaker 1: and the quiet evidence of material being rearranged. The black
• 23:28
  Speaker 1: hole is not creating these things from itself. It is
• 23:31
  Speaker 1: not turning its own darkness into stars. It is simply
• 23:35
  Speaker 1: moving through material that was already there, changing the conditions
• 23:39
  Speaker 1: around it. And sometimes, in the right conditions, a disturbance
• 23:44
  Speaker 1: can become the beginning of something new. So as you
• 23:47
  Speaker 1: continue drifting beside this ancient trail, you can slowly look
• 23:51
  Speaker 1: behind the black hole rather than ahead. The shock remains
• 23:55
  Speaker 1: at the front, the traveller continues onward. and farther behind
• 23:59
  Speaker 1: the gas begins its much slower transformation. It cools, it gathers,
• 24:04
  Speaker 1: it becomes denser, and somewhere within that long, quiet wake,
• 24:09
  Speaker 1: gravity begins to pull small regions of gas together, very gently,
• 24:15
  Speaker 1: very slowly, almost as though the universe is taking a
• 24:18
  Speaker 1: long breath. And this is where the strange trail becomes
• 24:22
  Speaker 1: stranger still. because the wake of a runaway black hole
• 24:26
  Speaker 1: may not simply be a trail of disturbed gas. It
• 24:29
  Speaker 1: may also be a place where new stars are quietly
• 24:32
  Speaker 1: beginning to appear. You are still drifting beside the long trail.
• 24:39
  Speaker 1: Ahead of you, the runaway black hole continues its silent journey,
• 24:43
  Speaker 1: almost impossible to see against the darkness. Behind it, the
• 24:48
  Speaker 1: gas is changing. At first, the changes are small. A
• 24:52
  Speaker 1: little more pressure here. A little more warmth there. Tiny
• 24:57
  Speaker 1: regions of gas beginning to move differently from the material
• 25:00
  Speaker 1: around them. And slowly, the trail begins to tell a
• 25:04
  Speaker 1: more surprising story. Because this is not simply a trail
• 25:07
  Speaker 1: of disturbed gas. It is also a trail in which
• 25:11
  Speaker 1: new stars may be forming. That idea can feel almost backwards.
• 25:17
  Speaker 1: When you hear the words black hole, You might naturally
• 25:20
  Speaker 1: imagine something that takes things away, matter falling inward, light disappearing,
• 25:26
  Speaker 1: a region of space from which nothing can return once
• 25:29
  Speaker 1: it passes too close. But the runaway black hole is
• 25:33
  Speaker 1: doing something different here. It is not creating stars from
• 25:37
  Speaker 1: its own material. It is not turning darkness into light.
• 25:41
  Speaker 1: It is simply passing through gas that was already present,
• 25:45
  Speaker 1: changing the conditions around that gas as it moves. And sometimes,
• 25:50
  Speaker 1: a change in conditions is enough to begin something very slow.
• 25:54
  Speaker 1: You can imagine a quiet cloud floating through space. It
• 25:58
  Speaker 1: is extremely thin, much thinner than any cloud you might
• 26:01
  Speaker 1: see in the sky above you. There are enormous spaces
• 26:05
  Speaker 1: between its particles. Nothing about it looks solid or crowded.
• 26:10
  Speaker 1: It simply drifts. Then the black hole passes through. The
• 26:14
  Speaker 1: gas in front of it is compressed. Some of that
• 26:17
  Speaker 1: gas becomes hotter. the particles move more energetically, and the
• 26:21
  Speaker 1: region becomes disturbed. This is part of the bow shock
• 26:25
  Speaker 1: you have already seen forming around the front of the journey.
• 26:28
  Speaker 1: But behind the shock, the story becomes slower. The gas
• 26:31
  Speaker 1: begins to lose some of the energy it received. It
• 26:35
  Speaker 1: releases heat through light and other forms of energy, gradually
• 26:39
  Speaker 1: becoming cooler. You can picture a warm mist slowly fading
• 26:43
  Speaker 1: into the cool air of evening. Nothing happens suddenly. There
• 26:47
  Speaker 1: is no single instant when the gas changes from one
• 26:51
  Speaker 1: thing into another. Instead, the material slowly settles. It cools.
• 26:56
  Speaker 1: It mixes. It gathers. And that gentle cooling is important.
• 27:01
  Speaker 1: When gas becomes cooler, it can sometimes remain in denser
• 27:05
  Speaker 1: structures instead of spreading apart as readily. The surrounding material
• 27:10
  Speaker 1: continues to move. Hot and cooler gas meet. They mingle.
• 27:15
  Speaker 1: Their boundaries become less clear. This restless mixing of different
• 27:19
  Speaker 1: temperatures can help move energy around the wake, allowing some
• 27:24
  Speaker 1: cooler material to remain and gather. Astronomers use more precise
• 27:29
  Speaker 1: language to describe these processes, including turbulent mixing and radiative cooling,
• 27:35
  Speaker 1: but you do not need to hold on to those names.
• 27:37
  Speaker 1: The important picture is much simpler. The gas is disturbed.
• 27:42
  Speaker 1: The gas slowly releases heat. The gas mixes. and some
• 27:46
  Speaker 1: parts become denser than they were before. You can let
• 27:49
  Speaker 1: that sequence repeat quietly in your mind. Disturbed, cooling, mixing, gathering.
• 27:56
  Speaker 1: There is no hurry. The universe has an enormous amount
• 28:00
  Speaker 1: of time, and gravity is patient. Once a small region
• 28:04
  Speaker 1: of gas becomes dense enough, gravity begins to pull more
• 28:08
  Speaker 1: material toward it. The gathering becomes a little stronger. More
• 28:12
  Speaker 1: gas drifts inward. the region becomes denser still. You can
• 28:17
  Speaker 1: imagine tiny particles, separated by enormous distances, slowly finding themselves
• 28:22
  Speaker 1: a little closer together, then closer again. Not because anything
• 28:27
  Speaker 1: is pushing them into place with a hand, but because
• 28:30
  Speaker 1: gravity is always quietly present. It is one of the
• 28:33
  Speaker 1: simplest ideas in the universe, and one of the most persistent.
• 28:38
  Speaker 1: Mass attracts mass. And when enough material gathers together, that
• 28:43
  Speaker 1: attraction becomes increasingly important. Eventually, within sufficiently dense regions of gas,
• 28:50
  Speaker 1: gravity can overcome the tendency of the material to remain
• 28:54
  Speaker 1: spread out. The cloud begins to collapse inward. Some of
• 28:58
  Speaker 1: the material becomes compressed. The centre becomes denser. The temperature rises,
• 29:05
  Speaker 1: and over a long period of time, a new star
• 29:08
  Speaker 1: can begin to take shape. You do not need to
• 29:11
  Speaker 1: imagine a sudden flash. Instead, imagine a very slow gathering,
• 29:16
  Speaker 1: a dark cloud becoming slightly denser, then slightly warmer, then
• 29:21
  Speaker 1: a little more concentrated, until, eventually, deep within that quiet region,
• 29:27
  Speaker 1: a young star begins to shine, a small point of
• 29:30
  Speaker 1: light appearing inside the darkness, then another, and another. Far
• 29:36
  Speaker 1: behind the runaway black hole, the trail can therefore become sluggish,
• 29:40
  Speaker 1: remarkably different from the violent image you might have expected.
• 29:44
  Speaker 1: It becomes a kind of nursery. Not because the black
• 29:47
  Speaker 1: hole is a creator in the ordinary sense, but because
• 29:51
  Speaker 1: its passage has disturbed the surrounding material in a way
• 29:54
  Speaker 1: that can encourage star formation. This distinction matters. The black
• 29:59
  Speaker 1: hole does not manufacture stars. The gas was already there.
• 30:04
  Speaker 1: The ingredients were already present. The stars are formed by
• 30:08
  Speaker 1: gravity acting on that material. The black hole simply changes
• 30:12
  Speaker 1: the environment through which the material is passing. It is
• 30:16
  Speaker 1: more like a traveller changing the shape of a landscape
• 30:19
  Speaker 1: without carrying the landscape with it. The traveller moves on,
• 30:23
  Speaker 1: the material remains, and the material slowly rearranges itself. you
• 30:29
  Speaker 1: can look down the length of the wake again. Near
• 30:32
  Speaker 1: the front, the gas is being strongly disturbed. Farther behind,
• 30:38
  Speaker 1: the material has had more time to cool and mix.
• 30:41
  Speaker 1: And farther still, some of the denser regions may have
• 30:45
  Speaker 1: begun their long gravitational collapse. So the trail becomes a
• 30:49
  Speaker 1: kind of timeline, not a clock with numbers, not a
• 30:53
  Speaker 1: line marked with dates, but a record of different stages
• 30:57
  Speaker 1: of change. Near the moving black hole you find disturbance,
• 31:02
  Speaker 1: farther behind, cooling, then mixing, then gathering, and eventually young stars.
• 31:09
  Speaker 1: It is almost as though the universe has written the
• 31:11
  Speaker 1: history of the black hole's movement into the material around it,
• 31:15
  Speaker 1: and those young stars carry another quiet message. They tell
• 31:20
  Speaker 1: you that the disturbance did not simply pass through the
• 31:23
  Speaker 1: gas and disappear, some part of its influence remained. The
• 31:27
  Speaker 1: gas remembered. Gravity took over, and the process continued long
• 31:32
  Speaker 1: after the original disturbance had moved onward. You can imagine
• 31:36
  Speaker 1: one tiny cloud somewhere inside that enormous trail. At first,
• 31:41
  Speaker 1: it is almost invisible. Then it becomes a little denser.
• 31:45
  Speaker 1: Its particles move closer. Gravity gathers more material. The cloud contracts.
• 31:51
  Speaker 1: The centre becomes warmer. And eventually, a faint new light appears.
• 31:57
  Speaker 1: a star that did not exist before, a star born
• 32:01
  Speaker 1: far from the centre of any familiar galaxy, inside a
• 32:04
  Speaker 1: trail created by an object that itself has been thrown
• 32:09
  Speaker 1: out into the darkness. And this is perhaps the gentlest
• 32:13
  Speaker 1: way to understand the strange paradox. The black hole does
• 32:17
  Speaker 1: not give birth to the stars, it simply passes through.
• 32:20
  Speaker 1: The gas responds, the gas cools, gravity gathers what remains.
• 32:26
  Speaker 1: and the stars appear in the wake. For a moment,
• 32:29
  Speaker 1: you can simply rest with that picture, a dark traveller
• 32:32
  Speaker 1: moving forward, a trail of cooling gas behind it, and
• 32:36
  Speaker 1: tiny new lights slowly beginning to glow. The traveller continues
• 32:41
  Speaker 1: into the distance, while the stars remain behind, quietly shining
• 32:45
  Speaker 1: in the path it has already crossed. And when you
• 32:48
  Speaker 1: follow that path far enough backward, the trail begins to
• 32:52
  Speaker 1: point toward an even stranger place. a distant meeting of
• 32:56
  Speaker 1: galaxies whose unusual shape has given it a remarkably gentle name.
• 33:03
  Speaker 1: You can let your attention rest for a while on
• 33:06
  Speaker 1: the trail. The runaway black hole is moving away from
• 33:09
  Speaker 1: the place it once called home, but the trail behind
• 33:13
  Speaker 1: it seems to remember that home. If you follow the
• 33:16
  Speaker 1: line backward, away from the direction of travel, you begin
• 33:20
  Speaker 1: to approach a distant galaxy. Not a perfectly ordinary galaxy,
• 33:25
  Speaker 1: but a peculiar pair of galaxies whose shapes create an
• 33:29
  Speaker 1: almost playful pattern in the darkness. From our distant viewpoint,
• 33:34
  Speaker 1: the system has come to be known as the Cosmic Owl,
• 33:38
  Speaker 1: and once you see it, the name is easy to understand.
• 33:42
  Speaker 1: Two bright, ring-like structures form something resembling a pair of eyes.
• 33:47
  Speaker 1: Between them, another region glows, a place where the galaxies
• 33:51
  Speaker 1: have interacted with and where new stars are being formed.
• 33:55
  Speaker 1: The whole arrangement is faint and ancient, but there is
• 33:59
  Speaker 1: something wonderfully simple about it. Two enormous galaxies, slowly changing
• 34:04
  Speaker 1: one another. You can imagine yourself drifting toward them through
• 34:08
  Speaker 1: the darkness. The closer you move, the more the rings
• 34:12
  Speaker 1: begin to take shape. They are not perfect circles, of course.
• 34:16
  Speaker 1: They are enormous structures of stars and gas, shaped by
• 34:20
  Speaker 1: a rare kind of galactic encounter. The two galaxies appear
• 34:24
  Speaker 1: to have passed through one another in a nearly head-on collision,
• 34:28
  Speaker 1: and when galaxies collide, they do not behave like solid objects.
• 34:33
  Speaker 1: There are no hard surfaces striking together. There is mostly space.
• 34:38
  Speaker 1: Stars are separated by enormous distances, so individual stars can
• 34:42
  Speaker 1: pass through a galactic collision without ever touching another star.
• 34:47
  Speaker 1: But the gas is different. Gas clouds can interact. gravity
• 34:52
  Speaker 1: can rearrange entire regions, streams of material can be compressed,
• 34:57
  Speaker 1: and new waves of star formation can begin. In the
• 35:01
  Speaker 1: cosmic owl, one region of the collision is especially interesting.
• 35:06
  Speaker 1: It lies between the two ring-like galaxies, creating what can
• 35:10
  Speaker 1: look like the owl's beak. This region contains cold molecular gas,
• 35:15
  Speaker 1: the quiet raw material from which stars can eventually form.
• 35:20
  Speaker 1: You can picture this gas as an enormous, dim reservoir
• 35:23
  Speaker 1: drifting through the darkness. It is not bright on its own.
• 35:28
  Speaker 1: It does not announce itself. But inside it are the
• 35:32
  Speaker 1: ingredients needed for future stars. When the galaxies interact, some
• 35:37
  Speaker 1: of this material can become compressed. And when gas becomes denser,
• 35:42
  Speaker 1: gravity has more opportunity to gather it. So the collision
• 35:46
  Speaker 1: becomes a place of creation as well as motion. New
• 35:49
  Speaker 1: stars begin to appear. The galaxies slowly change shape. And
• 35:54
  Speaker 1: somewhere inside this complicated dance, the central black holes of
• 35:59
  Speaker 1: the galaxies may also begin a much longer journey toward
• 36:02
  Speaker 1: one another. This part is easy to imagine incorrectly. You
• 36:06
  Speaker 1: might picture two galaxies meeting, their black holes immediately colliding,
• 36:12
  Speaker 1: and one dramatic event following another. But the universe is
• 36:16
  Speaker 1: rarely in such a hurry. The galaxies can merge over
• 36:19
  Speaker 1: immense stretches of time. Their central black holes can become
• 36:23
  Speaker 1: bound together. Two enormous black holes may begin orbiting one another,
• 36:28
  Speaker 1: forming what astronomers call a binary black hole. You can
• 36:32
  Speaker 1: simply imagine two dark objects circling one another in the
• 36:36
  Speaker 1: deep centre of a changing galaxy. They are separated by
• 36:40
  Speaker 1: a great distance at first. They continue their slow dance.
• 36:44
  Speaker 1: Stars move around them. Gas moves around them. The galaxy
• 36:48
  Speaker 1: itself continues to evolve, and the two black holes gradually
• 36:51
  Speaker 1: lose energy and draw closer. The timescale can be enormous.
• 36:56
  Speaker 1: Millions of years can pass, then more millions. From the
• 37:00
  Speaker 1: perspective of a human life, almost nothing seems to happen.
• 37:04
  Speaker 1: But from the perspective of the universe, the orbit is changing.
• 37:09
  Speaker 1: Very slowly. Very patiently. And this slow orbital movement matters,
• 37:15
  Speaker 1: because eventually... If the black holes come close enough, they
• 37:18
  Speaker 1: can merge. When two black holes merge, the event sends
• 37:23
  Speaker 1: gravitational waves outward through the universe. You do not need
• 37:27
  Speaker 1: to imagine these waves as sound. They are not ripples
• 37:30
  Speaker 1: travelling through air. They are changes moving through space and
• 37:34
  Speaker 1: time itself, a little like the expanding pattern created when
• 37:39
  Speaker 1: you gently disturb the surface of still water, except the water,
• 37:44
  Speaker 1: in this comparison, is the structure of the universe. The
• 37:48
  Speaker 1: waves carry energy away. And if the two black holes
• 37:52
  Speaker 1: are not perfectly balanced, the waves do not necessarily leave
• 37:56
  Speaker 1: in exactly equal patterns in every direction. There can be
• 38:00
  Speaker 1: an imbalance. And that imbalance can matter greatly for what
• 38:03
  Speaker 1: happens afterward. But for now, you can leave that future
• 38:07
  Speaker 1: event waiting quietly in the distance. You are still looking
• 38:11
  Speaker 1: at the cosmic owl, still looking at the rings, still
• 38:15
  Speaker 1: looking at the glowing region between them, still looking at
• 38:18
  Speaker 1: the cold gas. The system is more than a beautiful shape.
• 38:23
  Speaker 1: It may be a kind of birthplace for the story
• 38:25
  Speaker 1: you are following, because if the runaway black hole really
• 38:28
  Speaker 1: came from this environment, then the trail stretching through space
• 38:32
  Speaker 1: is also a path through time. At one end, you
• 38:36
  Speaker 1: have the black hole moving away. Behind it, you have
• 38:40
  Speaker 1: the long wake of gas and young stars. Farther back,
• 38:44
  Speaker 1: You find the region where the gas was disturbed and
• 38:47
  Speaker 1: where stars were forming. And farther still, you find the
• 38:51
  Speaker 1: galaxy system that may have held the black hole before
• 38:53
  Speaker 1: its journey began. It is almost like following footprints backward
• 38:57
  Speaker 1: through snow. The footprints do not show you the person directly.
• 39:02
  Speaker 1: They simply tell you where something has passed. Here, the
• 39:06
  Speaker 1: footprints are made from light, gas, stars, and motion. And
• 39:10
  Speaker 1: because the universe is so vast... The light carrying these
• 39:14
  Speaker 1: clues has travelled for billions of years before reaching you.
• 39:18
  Speaker 1: You are looking into the past without needing to leave
• 39:21
  Speaker 1: your quiet place. The cosmic owl itself is ancient by
• 39:25
  Speaker 1: the time you see it. Its light began travelling toward
• 39:29
  Speaker 1: Earth long before you. modern cities, long before written history,
• 39:33
  Speaker 1: long before anyone was here to wonder what might be
• 39:36
  Speaker 1: moving between the galaxies. And yet the story remains visible.
• 39:40
  Speaker 1: Two rings, a glowing collision region, cold gas, young stars, and, perhaps,
• 39:48
  Speaker 1: the beginning of a long gravitational dance. You can imagine
• 39:52
  Speaker 1: those two enormous black holes slowly circling one another, hidden
• 39:57
  Speaker 1: deep within the crowded centres of their galaxies. Nothing dramatic
• 40:01
  Speaker 1: needs to happen yet. They can simply continue orbiting. The
• 40:05
  Speaker 1: galaxy can continue turning. Gas can continue drifting. Stars can
• 40:11
  Speaker 1: continue forming. Time can continue passing. And eventually … After
• 40:17
  Speaker 1: an almost unimaginable span of quiet movement, the two black
• 40:21
  Speaker 1: holes may approach the moment when their slow orbit becomes
• 40:24
  Speaker 1: something else, a merger, a new black hole, and a
• 40:29
  Speaker 1: burst of gravitational waves that may not leave the newborn
• 40:32
  Speaker 1: object perfectly still. So the trail you began following is
• 40:36
  Speaker 1: beginning to reveal a deeper history. The traveller did not
• 40:40
  Speaker 1: simply appear in empty space. It may have been born
• 40:43
  Speaker 1: from a long chain of events involving galaxies, gas, stars,
• 40:49
  Speaker 1: two enormous black holes, and millions of years of patient
• 40:53
  Speaker 1: gravitational motion. And somewhere within that distant cosmic owl, the
• 40:58
  Speaker 1: final step of that story may have given the black
• 41:01
  Speaker 1: hole a push strong enough to send it away from home.
• 41:04
  Speaker 1: You can remain there for another quiet moment, watching the
• 41:08
  Speaker 1: ancient rings drift beneath the faint light. The galaxies continue
• 41:12
  Speaker 1: their slow dance. The gas continues to gather. The stars
• 41:17
  Speaker 1: continue to shine. And deep within the darkness, two black
• 41:21
  Speaker 1: holes continue circling one another, moving gradually toward a meeting
• 41:26
  Speaker 1: that will change the direction of one of them forever.
• 41:31
  Speaker 1: By now, you can almost picture the scene from far away.
• 41:35
  Speaker 1: Two galaxies slowly passing through one another. their enormous shapes
• 41:40
  Speaker 1: changing over millions of years, their stars drifting through one
• 41:44
  Speaker 1: another without colliding very often, while the clouds of gas
• 41:48
  Speaker 1: around them are compressed, disturbed, and gathered into new shapes.
• 41:53
  Speaker 1: And somewhere deep inside those galaxies, something much smaller in appearance,
• 41:58
  Speaker 1: but unimaginably heavier, is happening. Two supermassive black holes are
• 42:04
  Speaker 1: moving closer together. You do not need to imagine them rushing.
• 42:08
  Speaker 1: There is no sudden flash, no dramatic collision that you
• 42:12
  Speaker 1: could watch with your eyes. Instead, you can imagine two
• 42:16
  Speaker 1: immense dark objects slowly circling within the crowded centres of
• 42:21
  Speaker 1: merging galaxies, gradually losing energy, gradually drawing nearer, as gravity
• 42:27
  Speaker 1: quietly does its work. You are safe here. There is
• 42:31
  Speaker 1: nothing you need to solve. You can simply listen and
• 42:35
  Speaker 1: let the picture remain soft in your mind. The galaxies
• 42:38
  Speaker 1: themselves may take millions of years to change, and the
• 42:41
  Speaker 1: black holes, too, can spend an extraordinarily long time moving
• 42:46
  Speaker 1: toward one another, slowly, quietly, almost patiently. Yet eventually, if
• 42:53
  Speaker 1: the conditions are right, the two black holes can become one.
• 42:57
  Speaker 1: And that is where the story of RBH1 becomes especially interesting,
• 43:02
  Speaker 1: because when two supermassive black holes merge... The event does
• 43:06
  Speaker 1: not always leave the newly formed black hole, perfectly balanced
• 43:10
  Speaker 1: in the centre of its galaxy. The merger can send
• 43:14
  Speaker 1: waves through space itself, gravitational waves. You do not need
• 43:19
  Speaker 1: to picture these waves as something violent or sharp. Instead,
• 43:24
  Speaker 1: imagine the fabric of space being gently disturbed, ripples spreading
• 43:28
  Speaker 1: outward from a place where two enormous objects have finally
• 43:32
  Speaker 1: become one. and if those waves are released unevenly, something
• 43:36
  Speaker 1: very subtle happens. The new black hole receives a push,
• 43:41
  Speaker 1: a recoil, a kick, a movement in the opposite direction.
• 43:46
  Speaker 1: It is almost like two people pushing against one another and,
• 43:50
  Speaker 1: when one suddenly lets go, the other moves backward. Except here,
• 43:55
  Speaker 1: the people are enormous black holes, the room is a galaxy,
• 43:59
  Speaker 1: and the push comes from ripples moving through space. This
• 44:04
  Speaker 1: is sometimes called gravitational wave recoil. You do not need
• 44:08
  Speaker 1: to remember the name, just remember the feeling of it.
• 44:12
  Speaker 1: Two black holes become one. The surrounding space carries away
• 44:16
  Speaker 1: energy in waves, and the newborn black hole receives a quiet,
• 44:21
  Speaker 1: powerful kick. For RBH1, this may have been the beginning
• 44:25
  Speaker 1: of its long journey away from home. There was another
• 44:28
  Speaker 1: possibility too. Earlier in the investigation … astronomers considered whether
• 44:33
  Speaker 1: three supermassive black holes might have become involved. When galaxies merge,
• 44:39
  Speaker 1: their central black holes can eventually form a pair, and
• 44:42
  Speaker 1: if another massive black hole enters the crowded region, the
• 44:46
  Speaker 1: three can interact through their gravity. The situation becomes a
• 44:50
  Speaker 1: little like three heavy objects moving around one another in
• 44:54
  Speaker 1: a very delicate gravitational dance. Sometimes one object can be
• 44:58
  Speaker 1: pushed away, and if the conditions are right, that object
• 45:03
  Speaker 1: can receive enough speed to leave the galaxy entirely. This
• 45:07
  Speaker 1: is known as a three-body gravitational interaction. Again, you do
• 45:12
  Speaker 1: not need to hold on to the name. The important
• 45:15
  Speaker 1: idea is simply this. A black hole does not necessarily
• 45:18
  Speaker 1: have to remain where it was born. Gravity can rearrange
• 45:22
  Speaker 1: the pieces. A galaxy can merge with another galaxy. Two
• 45:27
  Speaker 1: central black holes can become a pair. A third black
• 45:30
  Speaker 1: hole can enter the system. and one of them can
• 45:33
  Speaker 1: be sent outward, into the darkness. For a while, this
• 45:37
  Speaker 1: three-body explanation was one of the possibilities considered for RBH1,
• 45:42
  Speaker 1: but as more observations became available, another explanation began to
• 45:47
  Speaker 1: fit the evidence better, a merger between two black holes,
• 45:52
  Speaker 1: and one clue was especially important, the mass. RBH1 is
• 45:58
  Speaker 1: not a small black hole, It appears to have a
• 46:01
  Speaker 1: mass greater than 10 million times that of our Sun.
• 46:05
  Speaker 1: That is a tremendous amount of mass. And when astronomers
• 46:09
  Speaker 1: considered the different ways a black hole might be expelled
• 46:12
  Speaker 1: from a galaxy, this large mass made the merger and
• 46:16
  Speaker 1: recoil explanation especially interesting. In a three-body interaction, the lighter
• 46:22
  Speaker 1: black hole is generally the easier one to throw outward.
• 46:26
  Speaker 1: The heavier objects tend to remain behind, but in a merger,
• 46:30
  Speaker 1: the two black holes become one larger object, and that
• 46:34
  Speaker 1: newly formed larger black hole can itself receive the recoil.
• 46:38
  Speaker 1: So the very thing that seems so surprising about RBH1,
• 46:42
  Speaker 1: its enormous mass, also helps tell the story of how
• 46:46
  Speaker 1: it may have left. You can let that idea settle quietly.
• 46:51
  Speaker 1: A black hole heavier than millions of suns, born from
• 46:55
  Speaker 1: an ancient encounter, and then instead of remaining in the
• 46:59
  Speaker 1: centre of its galaxy, moving outward, further, and further, until
• 47:05
  Speaker 1: eventually the galaxy was behind it. There is something strangely
• 47:09
  Speaker 1: peaceful about imagining this on the scale of cosmic time.
• 47:13
  Speaker 1: Nothing happens quickly here. Even a black hole moving at
• 47:17
  Speaker 1: nearly a thousand kilometres every second is still travelling through
• 47:21
  Speaker 1: a universe so enormous that its journey takes millions of years.
• 47:26
  Speaker 1: The galaxy behind it does not suddenly disappear, the stars
• 47:30
  Speaker 1: do not scatter like dust. The black hole simply continues, forward,
• 47:36
  Speaker 1: away from its former home, through the thin gas surrounding
• 47:40
  Speaker 1: the galaxy, and beyond that, into the much emptier space
• 47:44
  Speaker 1: between galaxies. As it moves, its gravity is still present,
• 47:49
  Speaker 1: its darkness is still there, but the most visible evidence
• 47:53
  Speaker 1: of its journey is not the black hole itself. It
• 47:56
  Speaker 1: is the trail, the long thin trail of gas and
• 47:59
  Speaker 1: young stars, a quiet record of something that passed through,
• 48:04
  Speaker 1: and this is perhaps the most beautiful part of the story.
• 48:08
  Speaker 1: You cannot easily see a black hole travelling through darkness.
• 48:12
  Speaker 1: A black hole does not shine like a star, it
• 48:15
  Speaker 1: does not announce its position with a bright surface. Instead,
• 48:19
  Speaker 1: you notice what happens around it. The gas remembers, the
• 48:23
  Speaker 1: young stars remember. The space behind the traveller carries a
• 48:27
  Speaker 1: faint signature of its passage. The black hole itself may
• 48:31
  Speaker 1: be almost invisible, but the wake tells you that something
• 48:35
  Speaker 1: enormous has been there. Something moved through the gas. Something
• 48:39
  Speaker 1: disturbed it. Something changed the quiet surroundings, and then kept going.
• 48:45
  Speaker 1: You can imagine standing nowhere in particular, simply floating beside
• 48:50
  Speaker 1: this enormous trail. There is no ground beneath you, no sound,
• 48:54
  Speaker 1: no wind, only darkness scattered with distant galaxies. And somewhere ahead,
• 49:01
  Speaker 1: beyond what your eyes could easily follow, the runaway black
• 49:04
  Speaker 1: hole continues its slow crossing of the cosmic night. Behind it,
• 49:09
  Speaker 1: a thin ribbon of young stars remains, a trail almost 200,000
• 49:15
  Speaker 1: light-years long. And far behind that trail, the ancient galaxy
• 49:19
  Speaker 1: system where the story began. The home it left behind.
• 49:23
  Speaker 1: The place where two galaxies once collided. The place where
• 49:27
  Speaker 1: two enormous black holes may once have slowly circled each other.
• 49:31
  Speaker 1: The place where gravitational waves may have carried away energy.
• 49:35
  Speaker 1: And where an imbalance in those waves may have given
• 49:38
  Speaker 1: the newborn black hole its final push, you can let
• 49:41
  Speaker 1: the whole picture become softer now. The galaxies, the black holes,
• 49:47
  Speaker 1: the waves, the gentle recoil, the long journey outward. Nothing
• 49:52
  Speaker 1: is asking you to remember every detail. There is nothing
• 49:55
  Speaker 1: to do. You are safe. Just listen and drift. Because
• 49:59
  Speaker 1: somewhere in the darkness, the universe is still carrying out
• 50:03
  Speaker 1: these slow movements. Galaxies merge. Black holes meet. Space itself
• 50:09
  Speaker 1: carries waves away. And sometimes, very rarely, something enormous is
• 50:14
  Speaker 1: sent wandering into the quiet space between galaxies. And perhaps
• 50:18
  Speaker 1: the strangest thing is that the runaway black hole did
• 50:21
  Speaker 1: not leave only emptiness behind. It left something new. A
• 50:26
  Speaker 1: trail of young stars. A long, faint line of light.
• 50:30
  Speaker 1: A place where gas gathered and cooled. a place where
• 50:34
  Speaker 1: gravity quietly began another story. And as you rest here,
• 50:38
  Speaker 1: you can almost imagine that distant trail stretching away into
• 50:41
  Speaker 1: the darkness, with the black hole somewhere far ahead, still moving,
• 50:47
  Speaker 1: still leaving the smallest disturbance in the enormous silence. And perhaps,
• 50:52
  Speaker 1: somewhere beyond what we can see, the darkness is already
• 50:55
  Speaker 1: waiting for another traveller. And now... you can let yourself
• 51:02
  Speaker 1: drift a little farther away, farther from the galaxy, farther
• 51:06
  Speaker 1: from the place where this long story began. The runaway
• 51:10
  Speaker 1: black hole is still moving, nearly a thousand kilometres every second,
• 51:15
  Speaker 1: crossing a darkness so enormous that even this extraordinary speed
• 51:20
  Speaker 1: feels almost gentle when you imagine it against the scale
• 51:24
  Speaker 1: of the universe. There is no road beneath it, no
• 51:28
  Speaker 1: destination marked ahead, No sign telling it where to go,
• 51:32
  Speaker 1: only space, vast, quiet and almost completely empty. You can
• 51:38
  Speaker 1: imagine yourself floating beside it for a moment, without needing
• 51:41
  Speaker 1: to follow, without needing to understand, simply watching this enormous
• 51:46
  Speaker 1: dark object move through the distance. You are safe, there
• 51:50
  Speaker 1: is nothing to do, just listen and drift. Behind the
• 51:55
  Speaker 1: black hole, the galaxy is becoming more distant. The stars
• 51:59
  Speaker 1: of that galaxy slowly blend into the background. The familiar
• 52:03
  Speaker 1: glow of the galactic centre fades. The thin veil of
• 52:07
  Speaker 1: gas surrounding the galaxy becomes thinner and thinner. And eventually,
• 52:13
  Speaker 1: the black hole begins to travel through the enormous space
• 52:16
  Speaker 1: between galaxies. This region is not completely empty. It only
• 52:21
  Speaker 1: feels empty. There is still gas here, spread incredibly thinly
• 52:26
  Speaker 1: across enormous distances. There are faint particles drifting through the darkness.
• 52:32
  Speaker 1: There are distant galaxies, separated from one another by millions
• 52:36
  Speaker 1: of light-years, and there is still gravity, quietly reaching across
• 52:41
  Speaker 1: the space between everything. The runaway black hole moves through
• 52:46
  Speaker 1: this thin material, and because it is moving so quickly,
• 52:50
  Speaker 1: the gas cannot simply flow gently around it. Instead, the
• 52:54
  Speaker 1: gas is disturbed, compressed, heated, pushed aside. A soft but
• 53:00
  Speaker 1: enormous disturbance forms in front of the moving black hole.
• 53:03
  Speaker 1: You can imagine it as a shape made not from
• 53:06
  Speaker 1: solid material, but from pressure and motion. The black hole
• 53:10
  Speaker 1: itself remains dark, almost invisible, but the gas around it
• 53:14
  Speaker 1: begins to reveal where it is. This is one of
• 53:17
  Speaker 1: the quiet paradoxes of the story. The thing that is
• 53:21
  Speaker 1: hardest to see becomes visible through what it changes. You
• 53:24
  Speaker 1: cannot look directly at the black hole and see a surface.
• 53:28
  Speaker 1: There is no surface to see. But you can look
• 53:31
  Speaker 1: at the gas. You can look at the stars behind it.
• 53:35
  Speaker 1: You can look at the long trail stretching across the darkness.
• 53:38
  Speaker 1: And gradually, the invisible traveller becomes easier to recognise. The
• 53:43
  Speaker 1: disturbance at its front is sometimes called a bow shock.
• 53:47
  Speaker 1: You do not need to remember the name. Just picture
• 53:50
  Speaker 1: a moving object passing through something that surrounds it. creating
• 53:54
  Speaker 1: a compressed region ahead of itself. The black hole moves.
• 53:59
  Speaker 1: The gas responds. And behind the disturbance, the gas begins
• 54:03
  Speaker 1: a slower process. It cools. It mixes. It gathers. Again
• 54:09
  Speaker 1: and again. The same quiet sequence. Disturbed. Cooling. Mixing. Gathering.
• 54:16
  Speaker 1: You can let those four words move slowly through your mind. Disturbed. Cooling. Mixing. Gathering.
• 54:23
  Speaker 1: The gas does not remain in the same state forever.
• 54:26
  Speaker 1: As it loses heat, some of it can become denser.
• 54:30
  Speaker 1: As different regions of gas mix together, their motions become
• 54:34
  Speaker 1: more complicated. And where enough material gathers, gravity can begin
• 54:39
  Speaker 1: to pull it closer together. Eventually, small regions can become
• 54:43
  Speaker 1: dense enough for stars to form. So the trail behind
• 54:47
  Speaker 1: the black hole is not simply a line of disturbed material.
• 54:51
  Speaker 1: It can become a place where new stars appear. Young stars.
• 54:56
  Speaker 1: Blue stars. Stars that did not exist when the black
• 54:59
  Speaker 1: hole began its journey. You can imagine them as tiny
• 55:03
  Speaker 1: lights appearing quietly along the path of something almost completely dark.
• 55:08
  Speaker 1: And this makes the trail feel almost like a memory.
• 55:12
  Speaker 1: The black hole moves onward. The gas changes behind it.
• 55:16
  Speaker 1: The stars remain. A traveller continues forward. its footprints stay behind.
• 55:22
  Speaker 1: Except these footprints are not marks in soil, they are stars,
• 55:26
  Speaker 1: and the footprint is almost 200,000 light-years long. 200,000 light-years.
• 55:33
  Speaker 1: It is difficult to hold such a distance in the mind,
• 55:36
  Speaker 1: so you do not need to. You can simply imagine
• 55:39
  Speaker 1: a thin line of light stretching farther than you can see,
• 55:43
  Speaker 1: passing through darkness, disappearing toward a distant galaxy. The trail
• 55:48
  Speaker 1: is narrow, compared with its enormous length. That is part
• 55:52
  Speaker 1: of what makes it so unusual. It is not a
• 55:55
  Speaker 1: broad cloud filling a region of space. It is a long,
• 55:59
  Speaker 1: almost delicate structure, a thin wake, a quiet trace. And
• 56:04
  Speaker 1: somewhere near the front of it, the runaway black hole
• 56:07
  Speaker 1: continues moving. This is why astronomers can learn something about
• 56:11
  Speaker 1: an object that is almost impossible to see directly. They
• 56:15
  Speaker 1: can study the trail. They can examine the gas. They
• 56:19
  Speaker 1: can observe the young stars, they can look at the
• 56:22
  Speaker 1: way the material moves, and from these quiet clues they
• 56:26
  Speaker 1: can reconstruct the journey. It is a little like arriving
• 56:30
  Speaker 1: at an empty landscape after something has passed through. The
• 56:34
  Speaker 1: traveller is gone from view, but the surroundings still carry evidence.
• 56:39
  Speaker 1: A disturbed patch of air, a trail through mist, a
• 56:43
  Speaker 1: line of footprints. The landscape remembers. In the same way,
• 56:48
  Speaker 1: the gas around RBH1 remembers. It carries the record of motion.
• 56:53
  Speaker 1: The young stars carry another part of the record, and
• 56:56
  Speaker 1: the direction of the trail points backward, toward the region
• 57:00
  Speaker 1: where the black hole may once have belonged. You can
• 57:03
  Speaker 1: imagine following that line backward, slowly, not rushing, just tracing
• 57:08
  Speaker 1: it through the darkness. One young star, then another, then another.
• 57:14
  Speaker 1: The trail continues, and farther back, the surrounding space becomes
• 57:19
  Speaker 1: connected to the galaxy system where the black hole may
• 57:22
  Speaker 1: have begun its escape. The trail becomes a kind of timeline.
• 57:26
  Speaker 1: Its oldest regions lie farther behind. Its newer regions lie
• 57:30
  Speaker 1: closer to the moving black hole. The farther you look
• 57:34
  Speaker 1: along it, the farther back in the story you are looking.
• 57:38
  Speaker 1: And so, without seeing the entire event itself, you can
• 57:42
  Speaker 1: begin to understand what may have happened. A galaxy merger?
• 57:47
  Speaker 1: a crowded galactic centre, two enormous black holes, a long
• 57:52
  Speaker 1: gravitational dance, a final merger, waves spreading through space, a recoil,
• 57:59
  Speaker 1: and then one black hole moving away, slowly at first
• 58:03
  Speaker 1: in the imagination, then steadily, nearly a thousand kilometres every second, outward, away,
• 58:12
  Speaker 1: into the darkness the galaxy cannot easily follow. the black
• 58:16
  Speaker 1: hole does not need to stop. The universe is large
• 58:19
  Speaker 1: enough to give it room, and after millions of years,
• 58:22
  Speaker 1: the distance between the black hole and its former home
• 58:25
  Speaker 1: can become enormous. The black hole may travel beyond the
• 58:28
  Speaker 1: central region of the galaxy, beyond the visible disk, beyond
• 58:33
  Speaker 1: the thinner outer regions, beyond much of the surrounding gas,
• 58:37
  Speaker 1: and eventually it may pass into the vast space between galaxies,
• 58:42
  Speaker 1: a place where there are fewer stars, less gas. less light,
• 58:47
  Speaker 1: more darkness. But even there, the journey does not become
• 58:51
  Speaker 1: completely invisible. The gas remains. The motion remains. The wake remains.
• 58:58
  Speaker 1: And for a while, the black hole continues to write
• 59:01
  Speaker 1: its story into that faint material, not with ink, not
• 59:06
  Speaker 1: with light from its own surface, but with pressure, with motion,
• 59:11
  Speaker 1: with heat, with cooling, with gravity, and eventually with stars,
• 59:17
  Speaker 1: you can rest with that idea now. A black hole
• 59:21
  Speaker 1: moving through darkness, leaving behind a trail of light, something
• 59:25
  Speaker 1: almost invisible creating something we can see, Not because the
• 59:30
  Speaker 1: black hole is making stars out of itself. It is not.
• 59:34
  Speaker 1: The black hole is not a container of material being
• 59:37
  Speaker 1: turned into stars. Instead, its passage changes the surrounding gas.
• 59:43
  Speaker 1: The gas responds. The gas cools. The gas gathers. And
• 59:47
  Speaker 1: gravity does what gravity has always quietly done. It brings
• 59:51
  Speaker 1: matter together. From that gathering, stars can be born. So
• 59:56
  Speaker 1: the black hole becomes, indirectly, part of the story of
• 1:00:00
  Speaker 1: their beginning, and then it keeps moving. That may be
• 1:00:04
  Speaker 1: the strangest part. The stars remain behind. The trail remains behind.
• 1:00:10
  Speaker 1: The galaxy remains far behind. But the black hole itself
• 1:00:14
  Speaker 1: continues onward. You can picture it becoming smaller in the distance,
• 1:00:19
  Speaker 1: not because it has changed size, but because the space
• 1:00:23
  Speaker 1: around it has become so enormous. Its former home fades.
• 1:00:28
  Speaker 1: The trail stretches behind. The universe opens wider. And somewhere ahead,
• 1:00:34
  Speaker 1: there are more galaxies. More thin clouds of gas. More
• 1:00:38
  Speaker 1: quiet regions of space. More darkness. The black hole has
• 1:00:43
  Speaker 1: become a traveller between worlds. And perhaps, as you drift
• 1:00:47
  Speaker 1: here in the quiet, you can imagine that there are
• 1:00:50
  Speaker 1: other travellers too. Other dark objects moving through the universe.
• 1:00:55
  Speaker 1: Other trails waiting to be noticed. Other faint disturbances hidden
• 1:00:59
  Speaker 1: inside the darkness. Because RBH1 may not be the only one.
• 1:01:04
  Speaker 1: It may simply be the first one that has left
• 1:01:07
  Speaker 1: a trail bright enough for us to notice. And if
• 1:01:10
  Speaker 1: that is true, then the darkness around the galaxies may
• 1:01:13
  Speaker 1: be filled with more stories like this. Quiet stories written
• 1:01:17
  Speaker 1: across immense distances, waiting patiently for someone to look, and perhaps...
• 1:01:23
  Speaker 1: Somewhere far beyond the trail you can see tonight, another
• 1:01:27
  Speaker 1: faint line of stars is already stretching into the darkness.
• 1:01:34
  Speaker 1: And now, as you continue to drift through the darkness,
• 1:01:37
  Speaker 1: you can let the trail behind RBH1 become a little
• 1:01:40
  Speaker 1: softer in your mind. The long line of young stars
• 1:01:44
  Speaker 1: is still there. The distant galaxy is still far behind.
• 1:01:49
  Speaker 1: and the black hole itself is still moving through the
• 1:01:51
  Speaker 1: enormous space between galaxies, almost a thousand kilometres every second,
• 1:01:57
  Speaker 1: carried onward through a universe that gives it more room
• 1:02:01
  Speaker 1: than you could ever imagine. But tonight, we are not
• 1:02:04
  Speaker 1: going to follow it any farther. Instead, you can simply
• 1:02:08
  Speaker 1: pause beside that trail, and look around, because if one
• 1:02:12
  Speaker 1: runaway supermassive black hole can exist, quietly travelling away from
• 1:02:17
  Speaker 1: its former home, Perhaps the universe has made others. Perhaps
• 1:02:21
  Speaker 1: there are other enormous dark objects wandering through the spaces
• 1:02:25
  Speaker 1: between galaxies. Perhaps some have been moving for millions of years.
• 1:02:30
  Speaker 1: Perhaps some are much closer to their original galaxies. And
• 1:02:33
  Speaker 1: perhaps some have already become so distant that their former
• 1:02:37
  Speaker 1: homes are only faint lights behind them. You are safe.
• 1:02:41
  Speaker 1: There is nothing to do. You do not need to
• 1:02:44
  Speaker 1: search the darkness. Just listen and drift. Astronomers have been
• 1:02:49
  Speaker 1: looking for signs of these wandering black holes for some time,
• 1:02:53
  Speaker 1: and before RBH1 became the clearest confirmed example, there were
• 1:02:57
  Speaker 1: already several unusual objects that had attracted attention. One of
• 1:03:02
  Speaker 1: them is known as J0437-2456. Another is associated with the
• 1:03:04
  Speaker 1: enormous galaxy cluster Abel 2261. These objects have been discussed
• 1:03:14
  Speaker 1: as possible examples of black holes that may have moved
• 1:03:17
  Speaker 1: away from the centres of their galaxies. But there is
• 1:03:20
  Speaker 1: an important difference. Possible is not the same as confirmed.
• 1:03:25
  Speaker 1: Astronomy often works this way. You see something unusual. You
• 1:03:30
  Speaker 1: notice that it does not fit the simplest picture. You
• 1:03:33
  Speaker 1: consider several explanations. And then you wait. You gather more observations.
• 1:03:39
  Speaker 1: You compare different possibilities. You look again. and sometimes, years later,
• 1:03:45
  Speaker 1: another telescope sees something that makes the original mystery much clearer.
• 1:03:50
  Speaker 1: That is part of what makes RBH-1 so interesting. The
• 1:03:54
  Speaker 1: discovery did not begin with a telescope watching a black
• 1:03:56
  Speaker 1: hole being kicked from a galaxy. No one saw the
• 1:04:00
  Speaker 1: exact moment of the ejection. No one watched the merger happen.
• 1:04:05
  Speaker 1: No one stood beside the black hole and measured its
• 1:04:07
  Speaker 1: journey from beginning to end. Instead, Astronomers found the evidence afterward.
• 1:04:13
  Speaker 1: A trail. A strange trail. A long, narrow line of
• 1:04:18
  Speaker 1: young stars and disturbed gas stretching through space. And near
• 1:04:23
  Speaker 1: its front, a moving object whose behaviour fits the picture
• 1:04:27
  Speaker 1: of a runaway supermassive black hole. The evidence became stronger
• 1:04:32
  Speaker 1: as new observations arrived. The Hubble Space Telescope first revealed
• 1:04:37
  Speaker 1: the remarkable linear feature. Later observations helped show that the
• 1:04:41
  Speaker 1: gas around the leading end was being compressed in a
• 1:04:45
  Speaker 1: way expected from a fast-moving object, and observations with the
• 1:04:49
  Speaker 1: James Webb Space Telescope provided an even clearer view of
• 1:04:53
  Speaker 1: the shock and the environment around the trail. Piece by piece,
• 1:04:58
  Speaker 1: the picture became easier to see. A black hole was
• 1:05:02
  Speaker 1: not simply sitting quietly in the centre of a galaxy.
• 1:05:06
  Speaker 1: It appeared to be moving, and behind it, Something had happened.
• 1:05:10
  Speaker 1: Stars had formed. Gas had been disturbed. A long wake
• 1:05:15
  Speaker 1: had been left behind. You can imagine the universe as
• 1:05:18
  Speaker 1: a very dark room. Not a frightening room, just a
• 1:05:22
  Speaker 1: very large one. And somewhere inside that room, a small
• 1:05:26
  Speaker 1: line of light appears. Then another. Then another. At first,
• 1:05:31
  Speaker 1: you do not know what they mean. You simply notice them.
• 1:05:35
  Speaker 1: The more carefully you look, the more the lights begin
• 1:05:38
  Speaker 1: to form a pattern, a direction, a path, a story.
• 1:05:43
  Speaker 1: That is what happened here. The trail gave astronomers something
• 1:05:47
  Speaker 1: to follow, and once they began following it, they could
• 1:05:51
  Speaker 1: trace it backward toward the galaxy system where the black
• 1:05:54
  Speaker 1: hole may have originated. The trail became a clue to
• 1:05:57
  Speaker 1: the past, and the black hole became a clue to
• 1:06:00
  Speaker 1: the trail. Each helped explain the other. You can let
• 1:06:04
  Speaker 1: that circular feeling settle for a moment. The invisible object
• 1:06:08
  Speaker 1: reveals itself through the visible trail. The visible trail points
• 1:06:12
  Speaker 1: back toward the invisible object. Neither is the entire story
• 1:06:16
  Speaker 1: by itself. Together, they form something much clearer. And this
• 1:06:21
  Speaker 1: may change the way you imagine black holes. You may
• 1:06:25
  Speaker 1: have heard of black holes as places where matter disappears.
• 1:06:29
  Speaker 1: Dark centres surrounded by glowing material. Objects hidden inside galaxies.
• 1:06:35
  Speaker 1: objects that grow by quietly gathering matter around them. But
• 1:06:39
  Speaker 1: not every black hole stays where it was born. Some
• 1:06:43
  Speaker 1: may move, some may be pushed, some may recoil, some
• 1:06:48
  Speaker 1: may wander. And when a supermassive black hole is moving
• 1:06:51
  Speaker 1: quickly through thin gas, its surroundings can reveal the journey.
• 1:06:56
  Speaker 1: That means the universe may contain a population of wandering
• 1:07:00
  Speaker 1: black holes that we simply have not recognised yet. not
• 1:07:04
  Speaker 1: because they are rare in an absolute sense, perhaps because
• 1:07:08
  Speaker 1: they are difficult to see. Imagine looking across an ocean
• 1:07:11
  Speaker 1: at night. You cannot see every current beneath the surface.
• 1:07:16
  Speaker 1: You cannot see every small wave. You cannot see every
• 1:07:20
  Speaker 1: movement of water. But sometimes, a passing boat leaves a wake,
• 1:07:25
  Speaker 1: and the wake tells you that something has passed through.
• 1:07:29
  Speaker 1: In deep space, a runaway black hole can create something similar.
• 1:07:33
  Speaker 1: Not a bright trail made directly by the black hole itself,
• 1:07:36
  Speaker 1: but a disturbance in the thin gas around it. And
• 1:07:40
  Speaker 1: under the right conditions, that disturbance can become a place
• 1:07:43
  Speaker 1: where new stars form. So perhaps some wandering black holes
• 1:07:47
  Speaker 1: are hidden. Perhaps they are travelling quietly through enormous regions
• 1:07:51
  Speaker 1: of space. Perhaps they leave wakes too faint for our
• 1:07:55
  Speaker 1: current telescopes to notice. And perhaps there are other trails
• 1:07:59
  Speaker 1: waiting to be found. This is where the future becomes interesting.
• 1:08:03
  Speaker 1: although you do not need to make it exciting. There
• 1:08:06
  Speaker 1: is no need for urgency. The universe is patient. New
• 1:08:10
  Speaker 1: telescopes are simply opening wider windows. The Euclid mission can
• 1:08:14
  Speaker 1: survey enormous regions of the sky and help astronomers study
• 1:08:18
  Speaker 1: galaxies and the large-scale structure of the universe. The Nancy
• 1:08:23
  Speaker 1: Grace Roman Space Telescope will also examine vast areas of
• 1:08:28
  Speaker 1: the sky, looking deeply and widely for distant cosmic objects.
• 1:08:33
  Speaker 1: With observations covering more of the universe, astronomers may begin
• 1:08:37
  Speaker 1: to notice more unusual linear structures, more faint wakes, more
• 1:08:42
  Speaker 1: displaced black holes, more galaxies that seem to have lost
• 1:08:47
  Speaker 1: the massive object expected at their centres, and perhaps, slowly,
• 1:08:52
  Speaker 1: a pattern will appear. One trail may be an unusual accident,
• 1:08:57
  Speaker 1: two may be a coincidence, but many trails could suggest
• 1:09:01
  Speaker 1: something larger. A population. A quiet population of runaway black
• 1:09:06
  Speaker 1: holes travelling through the spaces between galaxies. You can imagine
• 1:09:12
  Speaker 1: a dark night sky filled with galaxies. Each galaxy is
• 1:09:16
  Speaker 1: a small island of light. and between those islands there
• 1:09:19
  Speaker 1: is darkness. For a long time, you might think of
• 1:09:23
  Speaker 1: that darkness as empty. But perhaps it is not empty
• 1:09:26
  Speaker 1: at all. Perhaps there are black holes moving through it.
• 1:09:30
  Speaker 1: Objects too dark to see directly. Objects carrying the history
• 1:09:34
  Speaker 1: of ancient galaxy mergers with them. Objects that once lived
• 1:09:38
  Speaker 1: at the centres of galaxies and now travel alone. And sometimes,
• 1:09:43
  Speaker 1: if the conditions are right, their passage may leave a
• 1:09:46
  Speaker 1: narrow trail behind. A line of young stars. A faint
• 1:09:50
  Speaker 1: glow in the gas. A small disturbance in the enormous quiet.
• 1:09:55
  Speaker 1: You can let the image become very simple. A galaxy.
• 1:09:59
  Speaker 1: A traveller. A trail. Nothing more. And perhaps the most
• 1:10:03
  Speaker 1: remarkable thing is that we are only beginning to learn
• 1:10:07
  Speaker 1: how to recognise these travellers. The universe has been moving
• 1:10:11
  Speaker 1: for billions of years. Galaxies have merged. Black holes have met.
• 1:10:16
  Speaker 1: Gravity has rearranged enormous structures, waves have carried energy away,
• 1:10:22
  Speaker 1: and some black holes may have been sent outward, leaving
• 1:10:25
  Speaker 1: their original homes behind. RBH1 gives astronomers something rare, not
• 1:10:31
  Speaker 1: just an unusual object, but a visible trace of a journey.
• 1:10:36
  Speaker 1: A way to look at an event that happened tens
• 1:10:39
  Speaker 1: of millions of years ago and still find its quiet
• 1:10:42
  Speaker 1: consequences today. You can imagine the trail again, The young stars,
• 1:10:48
  Speaker 1: the cooling gas, the distant galaxy, and the black hole
• 1:10:52
  Speaker 1: at the front, continuing into darkness. Perhaps it is still travelling.
• 1:10:58
  Speaker 1: Perhaps its trail is still slowly fading. Perhaps the stars
• 1:11:02
  Speaker 1: it helped form will live for millions of years after
• 1:11:05
  Speaker 1: the black hole has moved far beyond them. And perhaps,
• 1:11:09
  Speaker 1: one day, another telescope will look into another quiet region
• 1:11:13
  Speaker 1: of the sky and notice something strange. A thin line.
• 1:11:17
  Speaker 1: A faint wake. A galaxy sitting slightly farther from where
• 1:11:22
  Speaker 1: its central black hole should be. Something small at first.
• 1:11:26
  Speaker 1: Something easy to overlook. And then, with enough observations, the
• 1:11:31
  Speaker 1: pattern may begin to appear again. Another traveller. Another trail.
• 1:11:36
  Speaker 1: Another ancient story written quietly across space. For now, you
• 1:11:42
  Speaker 1: do not need to go looking for it. You can
• 1:11:44
  Speaker 1: simply rest here. The universe is large enough to contain
• 1:11:48
  Speaker 1: mysteries without asking anything from you. You can let the
• 1:11:51
  Speaker 1: galaxies remain distant. You can let the stars become soft
• 1:11:55
  Speaker 1: points of light. You can let the black holes move
• 1:11:58
  Speaker 1: through the darkness without following them. There is nothing to solve.
• 1:12:02
  Speaker 1: You are safe. Just listen and drift. And somewhere beyond
• 1:12:07
  Speaker 1: the faint trail of RBH1, perhaps another enormous black hole
• 1:12:12
  Speaker 1: is already crossing the dark space between galaxies. leaving behind
• 1:12:16
  Speaker 1: a disturbance so delicate that we have not yet learned
• 1:12:20
  Speaker 1: how to see it, perhaps waiting quietly for another night
• 1:12:24
  Speaker 1: and another telescope to notice that something has passed. And so,
• 1:12:32
  Speaker 1: our journey quietly comes to an end. The black hole
• 1:12:35
  Speaker 1: keeps moving through the darkness, the stars behind it continue
• 1:12:39
  Speaker 1: to shine, and the universe carries on in its slow,
• 1:12:43
  Speaker 1: silent way. You are safe. There is nothing left to do,
• 1:12:48
  Speaker 1: nothing left to understand. Just rest, breathe softly, and let
• 1:12:53
  Speaker 1: yourself drift. The galaxies will keep turning, the stars will
• 1:12:58
  Speaker 1: keep shining, and the universe will keep moving gently around
• 1:13:01
  Speaker 1: you while you sleep. Good night.