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The Strangest Objects in the Universe You_ve Never Seen · Boring Science

0:00
Speaker 1: Hello, and welcome to Boring Science to 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 take a gentle journey towards some of
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Speaker 1: the most unusual objects in the universe, beginning not with
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Speaker 1: distant galaxies, but much closer to home. You'll move quietly
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Speaker 1: through icy worlds, strange planetary systems, wandering planets, distant stars,
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Speaker 1: eventually toward the far future of the cosmos, where even
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Speaker 1: the brightest lights slowly begin to fade. But there is
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Speaker 1: nothing you need to remember, and nothing you need to
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Speaker 1: understand perfectly. You are safe, there's nothing to do, just
0:43
Speaker 1: listen and drift. Before you settle in, if you truly
0:46
Speaker 1: enjoy these calm journeys through interesting science, you're welcome to
0:51
Speaker 1: like this video and subscribe, only if it feels right
0:54
Speaker 1: for you. And when you're ready, Let me know in
0:57
Speaker 1: the comments where you're listening from, and what time it
1:00
Speaker 1: is right now. It's always a quiet joy to see
1:04
Speaker 1: how many places and moments gather here together. Now, dim
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Speaker 1: the lights, let your surroundings become quiet, perhaps let a
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Speaker 1: fan hum softly in the background, and allow yourself to
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Speaker 1: become a little more still. Tonight, we begin with a
1:21
Speaker 1: small world, quietly turning in the darkness between Mars and Jupiter.
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Speaker 1: and there is something surprisingly strange waiting there. You can
1:30
Speaker 1: begin by imagining the solar system not as a neat
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Speaker 1: diagram of planets arranged in a row, but as an enormous,
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Speaker 1: quiet landscape, filled with countless smaller worlds that are easy
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Speaker 1: to overlook. The sun is still warm and bright behind you,
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Speaker 1: Mars is somewhere nearby, and beyond it, between Mars and Jupiter,
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Speaker 1: there is a broad region filled with rocky fragments, ancient
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Speaker 1: pieces of material left over from the early formation of
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Speaker 1: the solar system. This is the asteroid belt, and somewhere
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Speaker 1: within it you find Ceres. At first, Ceres does not
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Speaker 1: seem like the sort of place that should be especially mysterious.
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Speaker 1: It is small compared with Earth, small compared with Jupiter,
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Speaker 1: and surrounded by countless pieces of rock. And yet, when
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Speaker 1: you look more closely, Ceres begins to feel less like
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Speaker 1: a simple asteroid. and more like a small world with
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Speaker 1: a story of its own. Ceres is the largest and
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Speaker 1: most massive object in the asteroid belt, and its own
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Speaker 1: gravity is strong enough to pull most of its material
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Speaker 1: into a rounded shape. That simple fact makes it different
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Speaker 1: from many of the irregular rocks around it. A smaller
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Speaker 1: asteroid might look like a potato, or a fragment of stone,
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Speaker 1: with sharp edges and uneven sides. But Ceres has gradually
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Speaker 1: settled into something more rounded, more planet-like, as though gravity
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Speaker 1: has slowly gathered the world inward, smoothing its shape over
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Speaker 1: immense stretches of time. And beneath that quiet, rounded surface,
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Speaker 1: there is rock, ice, and material that still carries clues
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Speaker 1: from the solar system's distant past. Water has become one
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Speaker 1: of the most interesting parts of the story. Evidence gathered
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Speaker 1: by NASA's Dawn spacecraft showed that water ice exists on Ceres,
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Speaker 1: while other observations revealed materials associated with water and hydrated minerals.
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Speaker 1: So even here, in the asteroid belt, where you might
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Speaker 1: imagine nothing more than cold rock turning endlessly around the Sun,
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Speaker 1: there is evidence that water has played a role. You
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Speaker 1: can almost picture the world in darkness, its surface covered
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Speaker 1: with ancient craters, its sunlight weak compared with the warm
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Speaker 1: daylight you know on Earth. And then, in the middle
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Speaker 1: of that muted landscape, something catches the light. Bright patches.
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Speaker 1: When dawn began returning detailed images of Ceres, two unusually
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Speaker 1: bright areas became especially fascinating. They appeared inside a large crater,
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Speaker 1: almost like small pools of pale light resting on the surface.
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Speaker 1: Later observations connected these bright deposits with sodium carbonate and
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Speaker 1: other materials, helping scientists understand that the strange brightness was
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Speaker 1: not simply ordinary ice reflecting sunlight. There were also signs
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Speaker 1: that Ceres may not be completely frozen and unchanged. Its
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Speaker 1: surface appears to have experienced gradual alteration, and the presence
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Speaker 1: of water-related materials suggests that its interior and surface have
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Speaker 1: had a more complicated history than you might expect from
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Speaker 1: such a small world. You do not need to imagine
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Speaker 1: anything dramatic happening there. No great eruption needs to rise
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Speaker 1: into the darkness. Instead, think of something much quieter. A
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Speaker 1: tiny world, changing so slowly that an entire human lifetime
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Speaker 1: would pass without noticing. A little water moving, a little
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Speaker 1: ice shifting, minerals forming. the surface gradually being reshaped. And
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Speaker 1: all the while, Ceres continues its quiet journey around the Sun.
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Speaker 1: Not far away, another large body in the asteroid belt
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Speaker 1: tells a different story, Vesta. Vesta is one of the
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Speaker 1: largest objects in the asteroid belt, but unlike Ceres, it
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Speaker 1: is noticeably irregular. Its shape is not rounded enough for
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Speaker 1: it to be classified as a dwarf planet. And that
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Speaker 1: difference is rather beautiful. Two neighbouring worlds can exist in
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Speaker 1: the same region of space, formed from the same ancient era,
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Speaker 1: yet become completely different. Ceres is rounded, relatively rich in
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Speaker 1: water-related materials, and intriguing for the signs of change beneath
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Speaker 1: its surface. Vesta is more like an ancient piece of rock,
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Speaker 1: shaped and scarred by impacts, carrying the marks of a
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Speaker 1: much harsher history. Together, They remind you that the asteroid
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Speaker 1: belt is not simply a collection of identical rocks. It
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Speaker 1: is more like an old, quiet archive. Each object preserves
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Speaker 1: a slightly different memory of the solar system's beginning. And
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Speaker 1: as you drift farther outward, the sunlight becomes weaker. The
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Speaker 1: familiar planets begin to disappear behind you. Jupiter is now
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Speaker 1: far away. Saturn is farther still. Uranus becomes a distant point.
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Speaker 1: And eventually... Neptune appears at the edge of the familiar
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Speaker 1: solar system. Beyond it lies a much colder region, filled
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Speaker 1: with small worlds that receive only a faint fraction of
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Speaker 1: the sunlight that warms Earth. One of them is Orcus.
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Speaker 1: Orcus travels far beyond Neptune and is one of the
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Speaker 1: larger distant icy objects in the outer solar system. It
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Speaker 1: has a moon, Vanth, and observations have revealed strong evidence
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Speaker 1: for water ice on its surface. Its journey around the
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Speaker 1: sun is long and distant, carrying it through a region
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Speaker 1: where the sunlight is already very faint. And because Orcus
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Speaker 1: is large enough to be nearly round, but has not
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Speaker 1: been officially recognised as a dwarf planet, it occupies an
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Speaker 1: interesting place among the distant worlds. It is a world
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Speaker 1: waiting quietly on the edge of classification. Alongside it are
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Speaker 1: other large icy bodies, including Gonggong, Quawar, and 2002 MS4,
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Speaker 1: all candidates that have drawn attention because of their size
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Speaker 1: and their place in the distant Kuiper belt. You can
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Speaker 1: let those names drift past without needing to hold onto them.
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Speaker 1: They are simply distant worlds, cold worlds, slow worlds, worlds
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Speaker 1: moving through a darkness that has been waiting for them
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Speaker 1: for billions of years. And perhaps that is the first
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Speaker 1: unusual thing to notice tonight. The solar system is not
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Speaker 1: only the bright collection of planets you learned as a child.
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Speaker 1: It extends much farther. It contains worlds that are small
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Speaker 1: enough to be overlooked, yet large enough to have their
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Speaker 1: own gravity, their own history, their own frozen surfaces, and
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Speaker 1: perhaps their own hidden changes. And as you continue outward,
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Speaker 1: beyond Neptune and deeper into the cold, the idea of
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Speaker 1: a planet itself begins to feel less certain. Some worlds
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Speaker 1: have enormous rings, some may wander without a star at all,
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Speaker 1: and somewhere in the darkness there are places where even
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Speaker 1: the warmth of sunlight may no longer be necessary to
8:42
Speaker 1: keep a world from being completely frozen. You have already
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Speaker 1: moved beyond Neptune now, and the sun behind you is
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Speaker 1: becoming smaller. Its light is still there, still travelling outward
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Speaker 1: in every direction, but here at the distant edge of
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Speaker 1: the solar system, It feels softer, weaker, almost like a
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Speaker 1: memory of daylight. The worlds around you are cold. They
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Speaker 1: move slowly. And yet, even here, there are objects that
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Speaker 1: seem almost impossible when compared with the quiet planets you know. Imagine,
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Speaker 1: for a moment, a world surrounded by rings so enormous
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Speaker 1: that they would stretch across a distance greater than the
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Speaker 1: distance between Earth and the Sun. Not one narrow ring
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Speaker 1: like the familiar rings of Saturn, but a vast system
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Speaker 1: made of many separate bands, gaps and layers of material,
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Speaker 1: all moving together in a slow gravitational dance. This kind
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Speaker 1: of system has been proposed around a distant object known
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Speaker 1: as J1407b. The observations that led to the idea suggest
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Speaker 1: a remarkably large ring system, with many individual ring structures,
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Speaker 1: and broad gaps between them. One interpretation proposed that a
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Speaker 1: large moon might be moving within the rings, gradually clearing
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Speaker 1: a path through the material around the planet. You do
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Speaker 1: not need to imagine the rings as perfectly solid circles.
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Speaker 1: They would be made of countless pieces of material, each
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Speaker 1: one following its own path, while together they create the
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Speaker 1: appearance of enormous pale bands. From a distant moon, if
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Speaker 1: such a moon existed, the sky might look completely unfamiliar.
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Speaker 1: Instead of seeing a simple blue sky with one bright sun,
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Speaker 1: you might see a wide arc of dust and ice
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Speaker 1: stretching across the darkness, catching the faint light of a
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Speaker 1: distant star. The rings would not roar. They would not
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Speaker 1: crash together like waves. They would simply move. quietly, almost imperceptibly,
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Speaker 1: and somewhere within that great system a gap could appear,
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Speaker 1: a long, clean space separating one ring from another. Astronomers
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Speaker 1: can sometimes wonder whether a gap like this might be
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Speaker 1: created by the gravity of a moon. The idea is
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Speaker 1: wonderfully simple. A moon moving through a ring system can
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Speaker 1: gently influence the particles around it, gradually changing their paths.
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Speaker 1: and clearing a region along its orbit. You can think
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Speaker 1: of it as a small traveller leaving a faint trail
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Speaker 1: through a field of drifting snow. But there is an
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Speaker 1: important softness to this story. The proposed moon has not
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Speaker 1: been directly seen. The ring system itself comes from observations
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Speaker 1: and interpretation, and the exact nature of the object remains uncertain.
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Speaker 1: So tonight, you can let it remain a possibility. A
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Speaker 1: distant world, a vast ring system, and perhaps, somewhere inside
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Speaker 1: the darkness between those rings, a moon quietly moving through
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Speaker 1: the gap. Then, slowly, let your attention drift even farther outward.
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Speaker 1: Because a planet does not always need a star, there
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Speaker 1: may be worlds that travel through space entirely alone. These
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Speaker 1: are often called rogue planets, but you can simply think
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Speaker 1: of them as wandering worlds. Worlds without a sunrise. Worlds
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Speaker 1: without a sunset. Worlds moving through the darkness between stars.
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Speaker 1: Some may once have belonged to planetary systems like our own.
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Speaker 1: Long ago, perhaps, several large planets moved together around a
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Speaker 1: young star, their gravity tugged gently on one another. And sometimes,
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Speaker 1: over immense stretches of time, those interactions could send one
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Speaker 1: world away, not destroyed, not broken apart, simply released from
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Speaker 1: its original family. After that, the planet would continue moving
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Speaker 1: through the galaxy, carrying its own mass and its own history,
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Speaker 1: but with no star close enough to warm its surface.
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Speaker 1: Other planetary mass objects may form more independently, inside clouds
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Speaker 1: of gas and dust, rather than around a mature star.
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Speaker 1: The exact population and origins of such wandering worlds remain
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Speaker 1: areas of active research. One of the fascinating things about
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Speaker 1: these objects is that they are extremely difficult to see.
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Speaker 1: A normal planet is often found because it passes in
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Speaker 1: front of its star, or because its gravity gently pulls
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Speaker 1: on the star it orbits. A wandering planet has no
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Speaker 1: nearby star to illuminate it. So instead, astronomers can sometimes
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Speaker 1: notice what it does to light from something farther away.
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Speaker 1: Imagine you are standing in darkness, unable to see a
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Speaker 1: small object moving toward you. Then, for just a moment,
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Speaker 1: the light from a distant lamp behind it changes. The
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Speaker 1: object itself remains invisible, but its gravity has bent the
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Speaker 1: path of the light. This is called gravitational microlensing. You
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Speaker 1: can simply think of it as seeing an invisible world
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Speaker 1: through the tiny distortion it creates in the light behind it.
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Speaker 1: Some observations have suggested that the galaxy may contain enormous
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Speaker 1: numbers of these wandering planetary objects, although estimating their true
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Speaker 1: population remains difficult. And among the most intriguing examples is
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Speaker 1: an extremely cold nearby object, known as WISE 0855-0714. It
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Speaker 1: is not a familiar planet circling a bright star. Instead,
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Speaker 1: It is a very cold planetary mass object, discovered through
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Speaker 1: infrared observations, where its faint warmth becomes easier to detect.
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Speaker 1: Its atmosphere may contain clouds made from water and other substances,
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Speaker 1: under conditions far colder than anything you experience on Earth.
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Speaker 1: And this gives you a strange image to carry with you.
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Speaker 1: A world with no ordinary sunrise, no warm afternoon, no
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Speaker 1: bright star hanging overhead. only a faint cold glow emerging
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Speaker 1: from the object itself. Yet even such a world may
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Speaker 1: not necessarily be completely without warmth. If a wandering planet
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Speaker 1: is large enough, heat can remain trapped deep inside it.
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Speaker 1: Some of that warmth can come from the energy left
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Speaker 1: over from its formation. Some can come from the slow
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Speaker 1: natural decay of radioactive elements within its rocks, and beneath
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Speaker 1: a thick layer of ice, that internal warmth could, in
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Speaker 1: some circumstances, help maintain liquid water for a very long time.
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Speaker 1: The surface might remain frozen, the sky might remain almost
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Speaker 1: completely dark, but deep below, hidden from the empty night,
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Speaker 1: there could still be a place where ice slowly gives
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Speaker 1: way to water. This is a theoretical possibility, not evidence
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Speaker 1: that such a hidden ocean has been found. And that
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Speaker 1: distinction matters. You are not being asked to imagine life
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Speaker 1: beneath the ice. You are simply imagining that even a
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Speaker 1: world without a star may not be completely lifeless in
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Speaker 1: the physical sense. It may still contain heat. It may
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Speaker 1: still contain water. It may still be changing, very slowly,
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Speaker 1: beneath a frozen surface. And perhaps that is what makes
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Speaker 1: these wandering worlds so unusual. They remind you that sunlight
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Speaker 1: is not the only source of warmth in the universe.
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Speaker 1: A star can disappear from the sky, and yet a
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Speaker 1: planet may continue carrying a little of its own ancient warmth.
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Speaker 1: Far away, another world may be drifting in the same darkness,
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Speaker 1: and another, and another. The galaxy may contain countless places
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Speaker 1: where there is no sunrise at all, only darkness, slow motion,
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Speaker 1: and the faint warmth hidden inside matter. And as you
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Speaker 1: drift among these lonely worlds, you begin to leave behind
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Speaker 1: the idea that every journey must have a destination. Sometimes
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Speaker 1: a world simply wanders. Sometimes a planet carries its own
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Speaker 1: quiet warmth through the darkness. And somewhere far beyond the
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Speaker 1: last familiar planet, there is an even larger emptiness waiting,
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Speaker 1: an emptiness so wide that the distance between stars begins
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Speaker 1: to feel like the main landscape itself. You have been
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Speaker 1: drifting among worlds without suns, watching them move quietly through
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Speaker 1: the darkness. And now, slowly, you begin to leave even
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Speaker 1: those worlds behind. The distant planets disappear into the darkness.
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Speaker 1: Neptune is far behind you. The asteroid belt is only
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Speaker 1: a memory. And somewhere in the distance, the sun that
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Speaker 1: once seemed enormous is becoming smaller and smaller. You can
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Speaker 1: still imagine it there. shining into the darkness, sending light
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Speaker 1: outward in every direction. But from here, that light feels different.
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Speaker 1: It is no longer the warm centre of your sky.
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Speaker 1: It is becoming just another star. And this is where
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Speaker 1: the scale of the journey begins to change. Inside the
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Speaker 1: solar system, even enormous distances can feel manageable. You can
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Speaker 1: move from Earth to the Moon, from Earth toward Mars,
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Speaker 1: from Mars toward Jupiter, and still remain inside the same
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Speaker 1: gravitational family. But between the stars there is something very different.
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Speaker 1: There is space. A great deal of space, and very
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Speaker 1: little else. Humanity has already sent small machines outward into
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Speaker 1: that emptiness. The Voyager spacecraft are among the most distant
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Speaker 1: objects ever sent from Earth, continuing their long journeys outward
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Speaker 1: after decades of travel. They are moving much more slowly
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Speaker 1: than light, but they have already crossed the boundary between
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Speaker 1: the familiar planetary neighbourhood and the much quieter space beyond it.
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Speaker 1: You can imagine one of them now, a small machine,
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Speaker 1: carrying traces of Earth, moving through darkness. No engine roar,
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Speaker 1: no sound, no road beneath it. Only momentum, carrying it
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Speaker 1: farther from the Sun, and this simple idea reveals something
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Speaker 1: important about space travel. Once you are moving through space,
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Speaker 1: you do not always need to keep pushing. The difficult
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Speaker 1: part is gaining enough speed in the first place. One
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Speaker 1: of the clever ways spacecraft have done this is by
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Speaker 1: using gravity. A spacecraft can pass close to a moving
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Speaker 1: planet and allow the planet's gravity to bend its path.
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Speaker 1: During the encounter, the spacecraft can gain some of the
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Speaker 1: planet's orbital energy and leave with a little more speed.
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Speaker 1: You can imagine it almost like stepping onto a moving walkway.
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Speaker 1: You do not create all of the motion yourself. You
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Speaker 1: simply approach at the right moment, let the moving surface
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Speaker 1: carry you forward, and then continue on your way. This
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Speaker 1: technique is called a gravity assist. It has helped spacecraft
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Speaker 1: travel much farther than they could have managed by carrying
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Speaker 1: all of their required energy from Earth. But there is
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Speaker 1: a quiet limitation. Planets are not everywhere. Once you leave
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Speaker 1: the major planets behind, there are fewer opportunities to borrow
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Speaker 1: their motion. Eventually, the solar system becomes too empty. There
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Speaker 1: are no convenient worlds waiting ahead. No moving planets positioned
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Speaker 1: exactly where you need them. Just darkness. and the destination,
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Speaker 1: if you are travelling toward another star, may still be
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Speaker 1: unimaginably far away. The nearest star system to the Sun
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Speaker 1: is Alpha Centauri, more than four light years away. A
20:52
Speaker 1: light year is simply a measure of distance, meaning the
20:56
Speaker 1: distance light travels in one year. And light travels extraordinarily fast,
21:02
Speaker 1: so fast that even the nearest stars are separated from
21:05
Speaker 1: us by years of light travel. For a spacecraft built
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Speaker 1: with today's technology, the journey would be vastly longer. This
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Speaker 1: is why interstellar travel is such a difficult dream. The
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Speaker 1: problem is not simply reaching another planet. It is crossing
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Speaker 1: the enormous emptiness between two suns. And perhaps the gentlest
21:25
Speaker 1: way to imagine future propulsion is through ion engines. Instead
21:30
Speaker 1: of producing a powerful burst of thrust, an ion engine
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Speaker 1: gives a spacecraft a tiny, continuous push. Small particles are
21:39
Speaker 1: electrically charged and accelerated away from the spacecraft, producing a
21:44
Speaker 1: very gentle force in the opposite direction. The acceleration is
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Speaker 1: almost too small to feel, but if that tiny push
21:51
Speaker 1: continues for a very long time, the spacecraft can gradually
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Speaker 1: build up considerable speed. It is less like being thrown
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Speaker 1: forward by an explosion, and more like being quietly breathed
22:04
Speaker 1: upon by space itself. This makes ion propulsion attractive for
22:09
Speaker 1: long missions, although today's systems do not provide enough power
22:14
Speaker 1: for a rapid journey between the stars. Another possibility comes
22:18
Speaker 1: from nuclear propulsion. Nuclear energy contains an enormous amount of
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Speaker 1: energy in a very small amount of material. Future spacecraft
22:27
Speaker 1: could potentially use that energy to heat or accelerate propellant
22:31
Speaker 1: more efficiently than many conventional systems. This might allow much
22:35
Speaker 1: faster journeys through the solar system, but nuclear propulsion brings
22:40
Speaker 1: its own challenges. Radiation must be managed, heat must be removed,
22:46
Speaker 1: engines must survive extreme conditions, and the technology needed for
22:50
Speaker 1: a truly interstellar mission remains far beyond what has been built.
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Speaker 1: So perhaps you begin to wonder whether there is another way.
22:59
Speaker 1: Instead of pushing a spacecraft harder and harder, What if
23:03
Speaker 1: space itself could somehow become part of the journey? This
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Speaker 1: is where the idea of a warp drive appears. It
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Speaker 1: is not a working engine. It is not a technology
23:13
Speaker 1: sitting inside a laboratory. It is a theoretical idea based
23:18
Speaker 1: on the strange fact that space and time are not
23:21
Speaker 1: completely rigid. Gravity can curve space-time. Mass can change the
23:27
Speaker 1: geometry around it. And in theory, Physicists have explored mathematical
23:32
Speaker 1: models in which a region of spacetime could be shaped
23:36
Speaker 1: around a spacecraft. The spacecraft would not simply race through
23:40
Speaker 1: space faster than light in the ordinary sense. Instead, the
23:44
Speaker 1: space around it would be altered. Space could contract ahead
23:48
Speaker 1: of the region and expand behind it, carrying the spacecraft
23:52
Speaker 1: with the changing geometry. It sounds almost like folding the
23:56
Speaker 1: distance rather than crossing it. But there are enormous difficulties.
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Speaker 1: The required conditions remain theoretical, and no practical method is
24:05
Speaker 1: known for creating such a warp bubble. So for now,
24:09
Speaker 1: the idea belongs to mathematics and imagination, rather than engineering.
24:15
Speaker 1: And perhaps that is enough for tonight. You do not
24:17
Speaker 1: need to build the engine. You only need to imagine
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Speaker 1: the possibility. A small craft drifting through darkness, surrounded by
24:25
Speaker 1: nothing but stars. while the geometry of space itself becomes
24:29
Speaker 1: part of the journey. There is also a more physically
24:32
Speaker 1: grounded idea that feels almost wonderfully delicate. A tiny spacecraft
24:37
Speaker 1: could carry a thin sail. Instead of burning fuel on board,
24:41
Speaker 1: it could be pushed by powerful beams of light from
24:44
Speaker 1: far behind it. This is the basic idea behind concepts
24:49
Speaker 1: such as breakthrough starshot, which has proposed sending very small
24:53
Speaker 1: probes toward the Alpha Centauri system using laser-driven sails. The
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Speaker 1: spacecraft would be tiny. The journey would still take years.
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Speaker 1: And the technology required remains extremely challenging. But the image
25:09
Speaker 1: is beautiful. A small, almost weightless sail. A beam of light.
25:14
Speaker 1: A distant star. And between them, nothing but the quiet dark.
25:19
Speaker 1: For a moment, you can let yourself float there. The
25:23
Speaker 1: sun behind you. The stars ahead. No road. No sound,
25:28
Speaker 1: no hurry, only a very small spacecraft carrying a very
25:32
Speaker 1: old human dream, moving slowly toward another light. And somewhere ahead,
25:38
Speaker 1: more than four light-years away, three stars wait together in
25:42
Speaker 1: the darkness, one of them much smaller and quieter than
25:46
Speaker 1: the others, yet surrounded by a world that has become
25:49
Speaker 1: one of the most intriguing places humanity has ever imagined visiting.
25:56
Speaker 1: You are still moving through the darkness. Behind you, the
26:00
Speaker 1: sun has become a very small point of light. Ahead,
26:04
Speaker 1: after years of imagined travel, another group of stars begins
26:09
Speaker 1: to gather in the distance. At first, they appear almost
26:13
Speaker 1: like any other stars. Three small lights. Three distant suns.
26:19
Speaker 1: But as you drift closer, you begin to see that
26:21
Speaker 1: they belong to the same stellar neighbourhood. This is the
26:24
Speaker 1: Alpha Centauri system. Two of its stars, Alpha Centauri A
26:30
Speaker 1: and Alpha Centauri B, are relatively similar to the Sun,
26:34
Speaker 1: although they differ in size, temperature and brightness. A third star,
26:39
Speaker 1: Proxima Centauri, is much smaller and much cooler. It is
26:43
Speaker 1: a red dwarf, and it is the closest individual star
26:47
Speaker 1: to our own Sun. From far away, the entire system
26:51
Speaker 1: might look almost impossibly peaceful. Three stars moving through the galaxy.
26:56
Speaker 1: bound together by gravity, slowly travelling through the enormous darkness.
27:02
Speaker 1: There is no sound, no visible wind, nothing that you
27:06
Speaker 1: could touch, only light crossing space. And somewhere near the
27:10
Speaker 1: smallest of those three stars, there is a planet, Proxima
27:14
Speaker 1: Centauri b. You can imagine approaching it very slowly. The
27:19
Speaker 1: planet is interesting because it lies within the region around
27:22
Speaker 1: its star where temperatures could, under suitable atmospheric conditions, allow
27:27
Speaker 1: liquid water to exist on the surface. Astronomers often call
27:31
Speaker 1: this region the habitable zone. The phrase can sound more
27:35
Speaker 1: certain than it really is. It does not mean that
27:39
Speaker 1: the planet is inhabited. It does not even mean that
27:42
Speaker 1: the surface is comfortable. It simply means that, at the
27:45
Speaker 1: planet's distance from its star, the amount of received energy
27:49
Speaker 1: could potentially allow temperatures suitable for liquid water to depending
27:54
Speaker 1: on the atmosphere and many other conditions. So you can
27:58
Speaker 1: let the word habitable remain soft. It is an invitation
28:02
Speaker 1: to wonder, not a promise. And Proxima Centauri has another
28:07
Speaker 1: personality that makes the planet especially interesting. The star is small,
28:13
Speaker 1: cool and active. It can produce powerful stellar flares, sudden
28:18
Speaker 1: releases of energy that can make the star brighten dramatically.
28:23
Speaker 1: For a planet so close to its star, this activity
28:27
Speaker 1: could have important consequences. Imagine standing beneath a red sun
28:32
Speaker 1: that sometimes becomes much brighter, sending bursts of energetic radiation outward.
28:39
Speaker 1: You would not see the radiation itself as a glowing
28:42
Speaker 1: wave passing overhead. Instead, you would simply know that the
28:46
Speaker 1: star had changed. And over very long periods, Repeated stellar
28:51
Speaker 1: activity could influence a planet's atmosphere. Some atmospheric gases might
28:57
Speaker 1: be lost to space. Others could remain. The final outcome
29:02
Speaker 1: would depend on the planet's magnetic environment, atmosphere, geological history,
29:08
Speaker 1: and many other factors. So when you picture Proxima Centauri
29:12
Speaker 1: B tonight, you do not need to picture a second Earth.
29:17
Speaker 1: It may be rocky, it may have an atmosphere, It
29:20
Speaker 1: may have water, or it may be a much harsher place.
29:24
Speaker 1: We simply do not yet know enough to tell the
29:26
Speaker 1: complete story, and that uncertainty is part of what makes
29:30
Speaker 1: it beautiful. There is also the possibility of another planet
29:34
Speaker 1: in the same system, sometimes referred to as Proxima Centauri C.
29:38
Speaker 1: Its existence and exact nature have been debated, and observations
29:44
Speaker 1: continue to refine what we know. For now, you can
29:48
Speaker 1: let that possible world remain somewhere in the background, another
29:52
Speaker 1: faint possibility moving through the same distant system. Three stars,
29:57
Speaker 1: perhaps more than one planet, and more than four light
30:00
Speaker 1: years separating this system from your own. The distance is
30:04
Speaker 1: almost difficult to feel. So instead of trying to imagine
30:07
Speaker 1: the number, imagine the light. The light from Alpha Centauri
30:12
Speaker 1: leaves its stars and begins crossing the darkness. It travels
30:17
Speaker 1: for years, and eventually some of those photons reach Earth.
30:21
Speaker 1: They enter telescopes. They touch mirrors. They become tiny signals
30:26
Speaker 1: recorded by instruments. And from those faint signals, you begin
30:30
Speaker 1: to learn about worlds that you cannot yet visit. This
30:34
Speaker 1: is one of the quiet miracles of astronomy. You can
30:37
Speaker 1: know something about a distant world without ever standing on it.
30:41
Speaker 1: You can learn about a star's temperature from its light.
30:44
Speaker 1: You can notice a planet by the tiny movement it
30:47
Speaker 1: causes in its star. You can sometimes infer the presence
30:50
Speaker 1: of an atmosphere from subtle changes in the light passing
30:53
Speaker 1: through it. The universe speaks very softly. and astronomy is
30:58
Speaker 1: often the art of listening carefully. But one day, perhaps,
31:01
Speaker 1: humanity may try to do more than listen. One proposed
31:05
Speaker 1: idea is to send extremely small spacecraft toward Alpha Centauri
31:10
Speaker 1: using powerful lasers. The spacecraft would carry thin reflective sails.
31:16
Speaker 1: A beam of light from far behind them could push
31:19
Speaker 1: gently against those sails, gradually accelerating the tiny probes to
31:24
Speaker 1: a significant fraction of the speed of light. This is
31:27
Speaker 1: the basic idea behind Breakthrough Starshot. It remains a proposal,
31:32
Speaker 1: not a completed mission. There are enormous engineering challenges. The
31:37
Speaker 1: sail must survive intense laser light. The tiny spacecraft must
31:42
Speaker 1: remain stable while moving at extraordinary speed. The laser system
31:46
Speaker 1: would need immense power, and after the long journey, the
31:50
Speaker 1: probe would have only a brief opportunity to observe the
31:54
Speaker 1: distant system as it passed through. Still, the idea gives
31:58
Speaker 1: you a quiet image, a tiny sail leaving Earth, a
32:02
Speaker 1: beam of light behind it, the sun becoming smaller, the
32:06
Speaker 1: stars becoming larger, and eventually, after many years, the faint
32:12
Speaker 1: red glow of Proxima Centauri appearing ahead. No spacecraft has
32:17
Speaker 1: yet crossed that distance. No human has stood beneath another sun,
32:22
Speaker 1: but the possibility has already changed the way you imagine
32:25
Speaker 1: the night sky. The stars no longer need to be
32:28
Speaker 1: unreachable points of light. They can become places. Distant places, yes.
32:35
Speaker 1: Almost impossibly distant. But places nonetheless. And as you float
32:40
Speaker 1: near this quiet three-star system, you can imagine what the
32:43
Speaker 1: sky might look like from a world moving among several suns.
32:47
Speaker 1: Perhaps one star would rise, while another was already hanging
32:51
Speaker 1: low above the horizon. Perhaps the shadows would have strange shapes.
32:56
Speaker 1: Perhaps the nights would sometimes glow with more than one
32:59
Speaker 1: faint point of light, and somewhere much farther away, another
33:04
Speaker 1: kind of stellar system makes even this arrangement seem simple,
33:08
Speaker 1: a system where not three stars are bound together, but six,
33:13
Speaker 1: six suns sharing one vast gravitational family, quietly turning together
33:18
Speaker 1: through the darkness. You have left the quiet neighbourhood of
33:24
Speaker 1: Alpha Centauri behind now, and the three stars that once
33:27
Speaker 1: seemed so unusual are slowly becoming smaller in the distance.
33:32
Speaker 1: Three suns, three points of light sharing one gravitational family.
33:37
Speaker 1: It is already difficult to imagine what a planet might
33:40
Speaker 1: look like beneath such a sky. But the universe has
33:43
Speaker 1: arrangements that are even more unusual. Farther away, in the
33:47
Speaker 1: constellation Gemini, there is a system known as Castor. From Earth,
33:53
Speaker 1: Castor appears as a single bright point of light. But
33:57
Speaker 1: when astronomers look more carefully, the simple point begins to
34:00
Speaker 1: separate into something much more intricate. Castor is not one star,
34:06
Speaker 1: it is not even two, it is a system containing
34:09
Speaker 1: six stars. The reason is wonderfully simple, even if the
34:13
Speaker 1: arrangement itself is rare. The system has three major stellar components.
34:18
Speaker 1: and each of those three components is itself a pair
34:21
Speaker 1: of stars orbiting together. So you have one pair, another pair,
34:26
Speaker 1: and another pair. Six stars in total, all connected within
34:30
Speaker 1: the same vast gravitational family. You can let that image
34:34
Speaker 1: settle gently into your mind. Six suns, not arranged neatly
34:39
Speaker 1: in a straight line, but moving through space in nested orbits,
34:43
Speaker 1: each pair circling its own companion, while the larger groups
34:47
Speaker 1: remain connected across much greater distances. From Earth, all six
34:52
Speaker 1: are seen as one bright object, because the stars are
34:55
Speaker 1: so far away that their individual positions blur together in
34:59
Speaker 1: the night sky. And perhaps the most peaceful way to
35:03
Speaker 1: imagine Castor is to imagine standing on a hypothetical planet,
35:08
Speaker 1: somewhere within such a system. You look upward. There is
35:11
Speaker 1: no single sun. Instead, there are several sources of light.
35:16
Speaker 1: One might be bright, another could appear warmer and softer,
35:20
Speaker 1: another might be much fainter. The sky would not have
35:24
Speaker 1: the simple rhythm you know. There could be several sunrises,
35:28
Speaker 1: several sunsets, several shadows moving across the landscape at different times.
35:34
Speaker 1: The night itself might sometimes be interrupted by another distant
35:37
Speaker 1: star rising above the horizon. And yet, from the surface
35:41
Speaker 1: of such a world, all of this might eventually feel ordinary.
35:46
Speaker 1: the strange becomes familiar when you live beneath it. Just
35:49
Speaker 1: as you do not normally stop to wonder why your
35:52
Speaker 1: own sun is alone in your daytime sky, an imagined
35:55
Speaker 1: world beneath several stars might simply accept its many lights
36:00
Speaker 1: as part of the landscape. The formation of systems like
36:03
Speaker 1: Castor remains an interesting question. Astronomers have proposed several possibilities.
36:10
Speaker 1: Multiple stars may form together. when a large cloud of
36:13
Speaker 1: gas and dust breaks apart into several collapsing regions. They
36:17
Speaker 1: may also develop from a rotating disk of material surrounding
36:21
Speaker 1: a young forming star, where the disk itself becomes unstable
36:26
Speaker 1: and separates into several concentrations. Other ideas involve stars coming
36:31
Speaker 1: close enough for gravity to capture them into a long-term relationship.
36:36
Speaker 1: The details can be complicated, but the quiet idea beneath
36:40
Speaker 1: them is simple. Stars are not always born alone. Sometimes,
36:45
Speaker 1: the same ancient cloud gives birth to several stars at
36:49
Speaker 1: nearly the same time, allowing them to remain connected as
36:53
Speaker 1: they travel through the galaxy. The Castor system is thought
36:57
Speaker 1: to have formed from one molecular cloud during the same
37:00
Speaker 1: general period, rather than being a random collection of unrelated
37:04
Speaker 1: stars that happen to pass nearby. So you can imagine
37:07
Speaker 1: the beginning, a vast, cold cloud, No stars yet. Only
37:13
Speaker 1: gas and dust floating together in darkness. Then gravity begins
37:18
Speaker 1: to gather the material. The cloud slowly changes. Small concentrations appear.
37:24
Speaker 1: They become denser. They warm. And eventually, several young stars
37:29
Speaker 1: emerge from the same ancient cloud. Six lights where there
37:33
Speaker 1: had once been darkness. There is something almost gentle about
37:37
Speaker 1: that picture. Not six stars appearing suddenly. but six points
37:41
Speaker 1: of light gradually taking shape over enormous stretches of time.
37:46
Speaker 1: And when you are ready, you can allow the image
37:48
Speaker 1: to grow even larger, because Castor is unusual for having
37:52
Speaker 1: six stars. But there are also systems where two stars
37:56
Speaker 1: are so massive and so close together that they almost
38:00
Speaker 1: seem to share the same space. One of these is
38:03
Speaker 1: My Camelopardalis. The name sounds complicated when written down, so
38:09
Speaker 1: for tonight, You can simply think of it as my Camelopardalis,
38:13
Speaker 1: a pair of enormous stars far across the Milky Way.
38:18
Speaker 1: The two stars are young, hot blue giants. One is
38:21
Speaker 1: estimated to contain roughly 38 times the mass of our Sun,
38:26
Speaker 1: while its companion contains about 32 times the Sun's mass.
38:30
Speaker 1: Their outer atmospheres are so close that they nearly touch.
38:34
Speaker 1: Imagine that. Our Sun is already enormous compared with Earth.
38:38
Speaker 1: Now imagine two stars, each many times heavier than the Sun,
38:43
Speaker 1: turning around one another in a space so narrow that
38:47
Speaker 1: their outer layers almost meet. They complete one orbit in
38:51
Speaker 1: roughly 28 hours, less than a day and a quarter.
38:55
Speaker 1: For comparison, the Sun takes about 26 Earth days to
38:59
Speaker 1: rotate once. The stars of my Camelopardalis are moving through
39:04
Speaker 1: their shared orbit much more quickly, completing their graceful gravitational
39:09
Speaker 1: dance in little more than a single day. And because
39:12
Speaker 1: the stars are so close, one can pass in front
39:15
Speaker 1: of the other from our perspective. The light we receive
39:18
Speaker 1: from the system can gently rise and fall. For a
39:22
Speaker 1: long time, this changing brightness made the system difficult to understand.
39:27
Speaker 1: It had once appeared to be a single bright and
39:29
Speaker 1: changeable star. Only later did observations reveal that there were
39:34
Speaker 1: actually two stars moving together. You can imagine watching that
39:38
Speaker 1: distant light from Earth. It brightens, then it fades, then
39:43
Speaker 1: it brightens again. Nothing dramatic happens from our perspective. No
39:48
Speaker 1: sound reaches you. No visible movement crosses the sky. Only
39:53
Speaker 1: a tiny change in brightness arrives after travelling across the
39:57
Speaker 1: immense distance between the stars and Earth. And yet that
40:01
Speaker 1: tiny change tells a story. Two enormous stars. Two young suns,
40:07
Speaker 1: moving together, so close that their outer atmospheres nearly touch. Eventually,
40:13
Speaker 1: systems like this can become important laboratories for understanding how
40:18
Speaker 1: massive stars live and change. Their closeness allows the stars
40:23
Speaker 1: to influence one another, exchanging material and energy as their
40:28
Speaker 1: lives unfold. And because massive stars live much shorter lives
40:33
Speaker 1: than stars like our Sun, their evolution can move quickly
40:36
Speaker 1: by cosmic standards. Their story is not measured only in
40:40
Speaker 1: billions of years. Sometimes, the universe begins to move a
40:45
Speaker 1: little faster. Two enormous stars circle one another. Their light
40:50
Speaker 1: crosses the darkness. Their lives unfold together, and while they
40:55
Speaker 1: are still young, another quiet process is already waiting beneath
40:59
Speaker 1: the surface. Because every star, no matter how bright or
41:03
Speaker 1: how strange, begins with the same ancient question, how does
41:08
Speaker 1: a cloud of cold material become a shining star? You
41:14
Speaker 1: can let the image of those two enormous stars remain
41:18
Speaker 1: with you for a little while. Two young stars turning
41:21
Speaker 1: together in the darkness, carrying many times the mass of
41:25
Speaker 1: our sun, their outer layers almost touching. And beneath that
41:29
Speaker 1: image is a much older one. Before there were stars,
41:33
Speaker 1: there were clouds, cold clouds. Vast clouds of gas and
41:37
Speaker 1: tiny grains of dust spread through the spaces between existing stars.
41:43
Speaker 1: From a distance, These clouds can appear almost empty, but
41:47
Speaker 1: inside them there may be enough material to eventually form
41:51
Speaker 1: thousands or even millions of stars. You can imagine drifting
41:56
Speaker 1: quietly through one of these clouds. There is no solid
41:59
Speaker 1: floor beneath you, no clear boundary around you, only a
42:04
Speaker 1: soft mixture of gas and dust, floating through an enormous
42:08
Speaker 1: volume of space. The temperature is extremely low, the particles
42:12
Speaker 1: move gently. Everything seems almost still. And yet, gravity is
42:18
Speaker 1: already working. Very slowly, the material begins to gather. A
42:22
Speaker 1: region inside the cloud becomes slightly denser than the material
42:26
Speaker 1: around it. Because it contains more matter, its gravity becomes
42:30
Speaker 1: a little stronger. It begins pulling more material inward. More
42:35
Speaker 1: material makes the region heavier. More weight creates stronger gravity.
42:40
Speaker 1: And gradually, almost imperceptibly, the cloud begins to collapse. Nothing
42:46
Speaker 1: needs to rush. The process can take a very long time.
42:50
Speaker 1: You can simply imagine the cloud becoming slightly more concentrated,
42:54
Speaker 1: as though an enormous, almost invisible hand were gently gathering
42:59
Speaker 1: mist toward the centre. As the material falls inward, the
43:03
Speaker 1: developing object becomes warmer. This is the beginning of a protostar.
43:08
Speaker 1: It is not yet a fully functioning star. There is
43:11
Speaker 1: no sustained fusion at its centre. It is simply a
43:15
Speaker 1: growing concentration of matter, becoming denser and hotter as gravity
43:20
Speaker 1: continues to draw material inward. And as more material arrives
43:25
Speaker 1: the temperature continues to rise. Eventually deep within the centre
43:29
Speaker 1: the conditions become hot and dense enough for something remarkable
43:33
Speaker 1: to begin. Hydrogen nuclei begin combining together. In this process,
43:39
Speaker 1: a small amount of mass is transformed into energy. You
43:43
Speaker 1: do not need to picture the individual particles. You can
43:46
Speaker 1: simply imagine countless tiny pieces of matter moving closer and
43:51
Speaker 1: closer together, until their interactions begin releasing a steady flow
43:56
Speaker 1: of energy. The dark cloud has become a source of light.
44:00
Speaker 1: A star has begun to shine. This is the quiet
44:03
Speaker 1: transformation that turns cold interstellar material into a sun. And
44:08
Speaker 1: once the star reaches a stable balance between the inward
44:12
Speaker 1: pull of gravity and the outward pressure produced by the
44:15
Speaker 1: energy inside it, it enters the long stage known as
44:19
Speaker 1: the main sequence. For a star like our Sun, this
44:22
Speaker 1: stage lasts for billions of years. During this time, hydrogen
44:27
Speaker 1: in the core is gradually transformed into helium. The process
44:31
Speaker 1: happens continuously, deep beneath the visible surface. From far away,
44:37
Speaker 1: the star appears almost unchanged. You see the same round disc,
44:42
Speaker 1: the same steady light, the same warm colour, but inside,
44:47
Speaker 1: the star is slowly using its fuel. This is one
44:50
Speaker 1: of the quietest ideas in astronomy. A star can appear
44:54
Speaker 1: completely stable while changing continuously within. The sun you see
44:59
Speaker 1: today is not exactly the same sun that existed billions
45:03
Speaker 1: of years ago. It has been shining for a very
45:05
Speaker 1: long time, and it will continue shining for a very
45:09
Speaker 1: long time. But its interior is always evolving. Eventually, the
45:14
Speaker 1: hydrogen in the core becomes much less abundant. The balance
45:18
Speaker 1: inside the star begins to change. The central region contracts,
45:23
Speaker 1: the outer layers expand, and the star can become much larger.
45:28
Speaker 1: A star like the Sun eventually enters a red giant phase.
45:32
Speaker 1: Its outer atmosphere expands outward, while its surface becomes cooler
45:37
Speaker 1: and redder. If you could somehow watch from a safe distance,
45:41
Speaker 1: the change would not look like a sudden transformation. It
45:45
Speaker 1: would be extraordinarily slow. The familiar star would gradually swell.
45:50
Speaker 1: Its surface would move outward. Its light would become softer
45:54
Speaker 1: and more reddish. The star would become a very different object.
45:59
Speaker 1: And yet the same gravity that gathered the original cloud
46:02
Speaker 1: billions of years earlier would still be part of the story.
46:07
Speaker 1: This is what makes stellar evolution so beautiful. The life
46:10
Speaker 1: of a star is not a single event. It is
46:13
Speaker 1: a long sequence of adjustments. Gravity gathers. Pressure pushes outward.
46:19
Speaker 1: Nuclear reactions produce energy. The star settles. Then its internal
46:24
Speaker 1: fuel changes. The balance changes. And the star changes with it.
46:29
Speaker 1: The mass of the star plays an especially important role.
46:33
Speaker 1: A small or medium-mass star, like our Sun, follows one path.
46:39
Speaker 1: A much more massive star follows another. Massive stars are
46:43
Speaker 1: hotter and brighter. They consume their nuclear fuel much more quickly.
46:48
Speaker 1: So although they may seem powerful and almost permanent, their
46:53
Speaker 1: lives are actually much shorter. This is why a star
46:56
Speaker 1: such as Mycamelopodalis can be thought of as living intensely
47:00
Speaker 1: compared with the quiet, long life of the Sun. Its
47:04
Speaker 1: greater mass gives it enormous energy, but it also causes
47:08
Speaker 1: that energy to be used at a much faster rate.
47:11
Speaker 1: You can imagine two candles burning. One is small and
47:15
Speaker 1: burns gently for a long time. The other is much
47:18
Speaker 1: larger and brighter, but consumes its material rapidly. Stars are
47:23
Speaker 1: not exactly candles, of course, but the comparison gives you
47:26
Speaker 1: a soft way to feel the difference. A massive star
47:30
Speaker 1: shines fiercely because of what is happening deep inside it.
47:33
Speaker 1: and because its internal processes are so energetic, it moves
47:37
Speaker 1: through its life much faster. Eventually the paths begin to separate.
47:42
Speaker 1: Stars like the sun will shed their outer layers and
47:46
Speaker 1: leave behind compact white dwarfs. Massive stars can undergo much
47:50
Speaker 1: more dramatic transformations, eventually ending their lives in enormous stellar explosions.
47:57
Speaker 1: And from those endings come some of the most unusual
48:00
Speaker 1: objects in the universe, white dwarfs. neutron stars, black holes,
48:06
Speaker 1: the quiet remnants of stars that once filled their surroundings
48:10
Speaker 1: with light. But before you drift toward those remnants, you
48:13
Speaker 1: can pause here for a moment. You are floating inside
48:17
Speaker 1: the memory of a stellar nursery. The cloud is cold.
48:21
Speaker 1: Gravity is gathering material. A small centre begins to warm.
48:25
Speaker 1: Light appears. And somewhere, billions of years later, that same
48:30
Speaker 1: light may still be crossing the galaxy. A star is
48:34
Speaker 1: never truly still. Even when it seems unchanged, something inside
48:39
Speaker 1: it is slowly moving. Hydrogen is becoming helium. The core
48:44
Speaker 1: is adjusting. Energy is flowing outward. And time is quietly passing.
48:50
Speaker 1: The stars above you tonight may look eternal, but each
48:54
Speaker 1: one is somewhere along its own long journey. Some are
48:57
Speaker 1: only beginning. Some are comfortably shining in the middle of
49:01
Speaker 1: their lives. And some are already approaching the quiet transformation
49:05
Speaker 1: that waits at the end. Far away, a massive star
49:09
Speaker 1: may be preparing to leave behind something far denser than itself,
49:14
Speaker 1: something so compact that an entire star can become a
49:18
Speaker 1: tiny remnant of matter. and in that quiet remnant gravity
49:23
Speaker 1: takes on an entirely different character. You can remain for
49:29
Speaker 1: a little while beside the stars we have been following,
49:32
Speaker 1: the young stars in their clouds, the bright stars burning steadily,
49:37
Speaker 1: the enormous companions of my Camelopodalis, circling one another through
49:42
Speaker 1: the darkness. All of them are changing. Some changes happen
49:46
Speaker 1: so slowly that a human lifetime can barely notice them.
49:50
Speaker 1: And eventually, every star reaches a point where its long
49:54
Speaker 1: balance begins to change. For a star like our sun,
49:58
Speaker 1: the ending is relatively quiet. There is no need for
50:02
Speaker 1: an enormous explosion. Instead, The outer layers of the star
50:06
Speaker 1: gradually move away, drifting into space and leaving the central
50:11
Speaker 1: part behind. What remains is a white dwarf. A white
50:16
Speaker 1: dwarf is small compared with the star it once was,
50:20
Speaker 1: yet it contains a large fraction of that star's remaining
50:23
Speaker 1: material packed into a remarkably compact object. You can imagine
50:28
Speaker 1: taking something as large as the Sun and gradually removing
50:31
Speaker 1: its outer atmosphere until only a dense, glowing core remains.
50:36
Speaker 1: The object is roughly comparable in size to Earth, while
50:40
Speaker 1: containing a mass of stellar proportions. It is difficult to
50:44
Speaker 1: picture because the ordinary relationship between size and weight no
50:49
Speaker 1: longer feels familiar. A white dwarf can be small enough
50:52
Speaker 1: to imagine as a planet-sized sphere, yet heavy enough to
50:56
Speaker 1: contain material from a star. Because there is no longer
51:00
Speaker 1: active hydrogen fusion in its core, producing the same steady
51:04
Speaker 1: energy as before, the white dwarf simply begins to cool,
51:09
Speaker 1: very slowly. There is no dramatic moment, no sudden darkness,
51:14
Speaker 1: just a long fading. One of the best known examples
51:18
Speaker 1: is Sirius B, the small companion of Sirius. From Earth,
51:23
Speaker 1: Sirius appears as one of the brightest stars in our
51:26
Speaker 1: night sky. But beside that brilliant star is a much
51:31
Speaker 1: fainter white dwarf, almost hidden by the glare of its companion.
51:36
Speaker 1: You can imagine the contrast, one star blazing brightly, the
51:40
Speaker 1: other a compact remnant, quietly releasing the stored heat left
51:46
Speaker 1: from its earlier life. A white dwarf does not immediately
51:49
Speaker 1: become cold, it begins extremely hot, but with no new
51:54
Speaker 1: supply of nuclear energy at its centre, its stored heat
51:58
Speaker 1: gradually leaks away into space. The process takes an enormous
52:02
Speaker 1: amount of time, and as you let your imagination follow
52:05
Speaker 1: that cooling object farther into the future, the light becomes softer,
52:10
Speaker 1: the temperature falls, the glow weakens, the star becomes quieter. Eventually,
52:17
Speaker 1: in a future so distant that ordinary human time becomes
52:20
Speaker 1: almost meaningless, such remnants are expected to become black dwarfs,
52:25
Speaker 1: theoretical objects that have cooled so much that they no
52:29
Speaker 1: longer shine with visible light. No black dwarfs exist today
52:33
Speaker 1: as confirmed objects. The universe is simply not old enough
52:37
Speaker 1: for ordinary white dwarfs to have had enough time to
52:40
Speaker 1: cool that far. So even the coldest future stars you
52:43
Speaker 1: can imagine are still waiting somewhere in the enormous future.
52:48
Speaker 1: But not every star ends so quietly. A much more
52:52
Speaker 1: massive star can reach a point where its core can
52:54
Speaker 1: no longer support itself in the same way. The central
52:58
Speaker 1: region collapses, the outer layers respond, and the star can
53:03
Speaker 1: explode in a supernova. For a brief period, the dying
53:07
Speaker 1: star may become extraordinarily bright, releasing an immense amount of
53:11
Speaker 1: energy and scattering newly formed elements into surrounding space. The
53:16
Speaker 1: quiet atoms that will eventually become part of rocks, planets,
53:21
Speaker 1: oceans and living things can be forged and distributed through
53:25
Speaker 1: these stellar deaths. So when you imagine a supernova, you
53:29
Speaker 1: do not need to imagine only destruction. You can imagine redistribution.
53:34
Speaker 1: A star reaching the end of its life, and its
53:38
Speaker 1: material returning to the galaxy. Dust drifting away, gas expanding,
53:44
Speaker 1: heavy elements spreading through space. And from that material, much later,
53:50
Speaker 1: new stars and planets may form. The universe continually reuses
53:55
Speaker 1: what its stars leave behind. but deep inside some massive stars,
53:59
Speaker 1: the ending can become even stranger. If the collapsing core
54:04
Speaker 1: is massive enough, the material can be compressed into a
54:07
Speaker 1: neutron star. A neutron star is extraordinarily compact. A whole
54:12
Speaker 1: stellar core can be squeezed into an object only a
54:15
Speaker 1: few tens of kilometres across. That is roughly the scale
54:19
Speaker 1: of a large city, yet the object can contain more
54:22
Speaker 1: mass than the Sun. It is difficult to imagine such density.
54:27
Speaker 1: So rather than trying to calculate it, picture a star
54:31
Speaker 1: that has been gently shrinking, larger, smaller, smaller still, until
54:37
Speaker 1: almost all of the empty space within its atoms has
54:39
Speaker 1: been removed. The material becomes incredibly dense. The star has
54:44
Speaker 1: become a small, darkly glowing sphere of matter, unlike anything
54:48
Speaker 1: familiar on Earth. Some neutron stars rotate very rapidly. As
54:53
Speaker 1: they spin, they can send beams of radiation outward from
54:57
Speaker 1: their magnetic poles. If one of those beams happens to
55:00
Speaker 1: sweep across Earth again and again, astronomers can detect regular pulses.
55:06
Speaker 1: These objects are called pulsars. You can imagine one far away,
55:11
Speaker 1: turning silently in the darkness. Each rotation sends another faint
55:16
Speaker 1: signal outward, another pulse, then another. The rhythm can be
55:20
Speaker 1: remarkably regular. A distant lighthouse, not shining across an ocean,
55:25
Speaker 1: but across interstellar space. The beam arrives, then darkness, then
55:30
Speaker 1: another beam, then darkness again. Nothing about the star needs
55:34
Speaker 1: to be loud. The universe simply continues turning, and beyond
55:39
Speaker 1: neutron stars lies another possible ending, a black hole. When
55:44
Speaker 1: a sufficiently massive stellar core collapses, gravity can become so
55:48
Speaker 1: strong that that a region forms from which light itself
55:52
Speaker 1: cannot escape. The boundary around that region is called the
55:56
Speaker 1: event horizon. You do not need to imagine it as
55:59
Speaker 1: a physical surface. It is better to think of it
56:02
Speaker 1: as a point of no return. Once something crosses that boundary,
56:07
Speaker 1: it cannot return information to the outside universe in the
56:10
Speaker 1: ordinary way. Black holes are often imagined as cosmic vacuum cleaners,
56:16
Speaker 1: endlessly sucking in everything around them. But that picture is misleading.
56:21
Speaker 1: At a distance, the gravity of a black hole behaves
56:24
Speaker 1: like the gravity of any other object with the same mass.
56:28
Speaker 1: A planet could, in principle, orbit a black hole just
56:32
Speaker 1: as it could orbit a star, provided the orbit were
56:35
Speaker 1: stable and the surrounding environment were suitable. The strange part
56:40
Speaker 1: is not that black holes pull everything toward them. The
56:43
Speaker 1: strange part is what happens when you approach too closely.
56:47
Speaker 1: Space and time behave in ways that no ordinary experience
56:51
Speaker 1: can prepare you for, and around some black holes, material
56:56
Speaker 1: falling inward can form a hot, glowing disk. Gas spirals.
57:01
Speaker 1: Friction heats it. Radiation escapes before the material disappears beyond
57:06
Speaker 1: the event horizon. So even an object that cannot itself
57:10
Speaker 1: shine can sometimes be surrounded by brilliant light. A dark centre.
57:16
Speaker 1: A glowing ring. a quiet contradiction in the night. And now,
57:21
Speaker 1: as you let that image slowly fade, you can see
57:24
Speaker 1: the larger pattern. A star is born from cold material.
57:28
Speaker 1: It shines for a time, it changes, and eventually its
57:32
Speaker 1: material takes another form, a white dwarf, a neutron star, or,
57:38
Speaker 1: for some of the most massive stars, a black hole.
57:42
Speaker 1: The light of the original star may disappear, but its
57:45
Speaker 1: story does not end there. its material returns to the galaxy.
57:50
Speaker 1: Its elements may become part of another cloud, another star,
57:54
Speaker 1: another planet, another world. And far beyond even those future worlds,
57:59
Speaker 1: the universe itself is changing too. Stars will not shine forever.
58:05
Speaker 1: Even the longest-lived lights will eventually fade. And when the
58:08
Speaker 1: stars become fewer and the galaxies grow darker, the universe
58:12
Speaker 1: will begin to enter a very different kind of age.
58:16
Speaker 1: an age where darkness itself becomes the most familiar landscape.
58:23
Speaker 1: You can remain beside the small white dwarf for a
58:25
Speaker 1: little while. It is still glowing, not brightly perhaps, but
58:30
Speaker 1: enough to remind you that this object was once part
58:33
Speaker 1: of a living star. Its outer layers are gone, its
58:36
Speaker 1: nuclear fire has ended, and now there is only stored
58:41
Speaker 1: heat slowly escaping into space. You can imagine the white
58:45
Speaker 1: dwarf floating alone among distant stars, its surface gradually becoming cooler,
58:51
Speaker 1: its light becoming softer, almost imperceptibly softer. Nothing dramatic happens,
58:57
Speaker 1: there is no final flash, no sudden disappearance, only cooling,
59:03
Speaker 1: and cooling can take an almost unimaginable amount of time.
59:07
Speaker 1: The universe is patient, so patient, that the lifetime of
59:11
Speaker 1: a human civilization becomes almost like a single breath. For
59:16
Speaker 1: an ordinary white dwarf, the journey toward complete darkness takes
59:20
Speaker 1: far longer than the current age of the universe. That
59:24
Speaker 1: is why the object you are imagining tonight has no
59:28
Speaker 1: reason to hurry. It can simply remain there, quietly releasing
59:32
Speaker 1: its remaining warmth. And eventually, in a future unimaginably far
59:37
Speaker 1: beyond the present age, such a remnant could become what
59:40
Speaker 1: astronomers call a black dwarf. The name sounds mysterious, but
59:45
Speaker 1: the idea is gentle. A black dwarf would be a
59:48
Speaker 1: white dwarf that has cooled so thoroughly that it no
59:52
Speaker 1: longer shines with visible light. No confirmed black dwarfs have
59:56
Speaker 1: ever been observed. The universe is simply too young. The
1:00:00
Speaker 1: first stars have not existed long enough for ordinary white
1:00:04
Speaker 1: dwarfs to complete such an immense cooling process. The attached
1:00:09
Speaker 1: source describes this distant stage as one that lies far
1:00:12
Speaker 1: beyond the current stellar age of the universe. So when
1:00:16
Speaker 1: you look into the night sky tonight, every faint star
1:00:20
Speaker 1: is still part of a relatively young universe. There are
1:00:24
Speaker 1: still stars being born. There are still clouds of gas collapsing.
1:00:29
Speaker 1: There are still bright stellar nurseries. There are still enormous
1:00:33
Speaker 1: blue stars shining intensely. The universe is, in a sense,
1:00:39
Speaker 1: still in its bright season. But that season will not
1:00:42
Speaker 1: last forever. Eventually, galaxies will gradually use up much of
1:00:47
Speaker 1: the cold gas from which new stars can form. The
1:00:51
Speaker 1: great stellar nurseries will become quieter. Fewer new stars will appear.
1:00:56
Speaker 1: The stars that already exist will continue through their lives.
1:01:00
Speaker 1: Some will become white dwarfs. Some will leave neutron stars.
1:01:04
Speaker 1: Some will become black holes. And slowly, the universe will
1:01:09
Speaker 1: begin to lose its brightest lights. You can imagine standing
1:01:12
Speaker 1: in a galaxy during that distant age. At first, the
1:01:16
Speaker 1: sky might still contain many stars. Then fewer. Then fewer still.
1:01:22
Speaker 1: The spaces between them would seem larger. The darkness would
1:01:26
Speaker 1: become more noticeable, not because space had suddenly changed, but
1:01:31
Speaker 1: because there would simply be less light to fill it.
1:01:34
Speaker 1: The universe would become quieter, and in that quiet, the
1:01:38
Speaker 1: long-lived remnants would remain. White dwarfs, brown dwarfs, neutron stars,
1:01:45
Speaker 1: black holes, cold objects travelling through enormous expanses of almost
1:01:50
Speaker 1: empty space. This distant period is sometimes described as as
1:01:55
Speaker 1: an era dominated by stellar remnants, a long transition, in
1:02:00
Speaker 1: which the brilliant stars of the present become increasingly rare.
1:02:04
Speaker 1: The attached source describes a sequence beginning with the current
1:02:08
Speaker 1: star-filled universe, followed by a much longer period in which
1:02:12
Speaker 1: white dwarfs and other remnants dominate, before an even more
1:02:16
Speaker 1: distant age associated with black holes and eventually extreme darkness.
1:02:22
Speaker 1: You do not need to imagine this as a disaster.
1:02:25
Speaker 1: There is no explosion waiting at the end. There is
1:02:28
Speaker 1: no final moment when the universe suddenly switches off. Instead,
1:02:33
Speaker 1: the change is almost impossibly slow. Light becomes rarer. Energy
1:02:38
Speaker 1: becomes more dispersed. Stars disappear one by one across stretches
1:02:44
Speaker 1: of time that are difficult even to name, and the
1:02:47
Speaker 1: galaxies themselves continue to drift apart as space expands. The
1:02:53
Speaker 1: universe becomes larger. The distances become greater. The remaining sources
1:02:58
Speaker 1: of light become more isolated. You might imagine one final
1:03:02
Speaker 1: galaxy glowing faintly in an enormous darkness. Then, much later,
1:03:07
Speaker 1: even that glow becomes harder to find. Black holes may
1:03:11
Speaker 1: remain among the longest-lived structures. They can appear almost eternal
1:03:16
Speaker 1: when compared with the lifetime of a star. But even
1:03:19
Speaker 1: black holes are not necessarily permanent. According to modern theoretical physics,
1:03:25
Speaker 1: black holes can slowly lose energy through a process known
1:03:29
Speaker 1: as Hawking radiation. For very large black holes, this process
1:03:34
Speaker 1: would take an extraordinarily long time, so long that the
1:03:38
Speaker 1: numbers become almost meaningless to the human imagination. You do
1:03:42
Speaker 1: not need to remember the numbers. Simply imagine waiting, and waiting,
1:03:47
Speaker 1: and waiting again. A black hole that once contained the
1:03:51
Speaker 1: remains of a massive star slowly becoming lighter over an
1:03:55
Speaker 1: interval of time vastly longer than the entire history of stars. Eventually,
1:04:01
Speaker 1: in the deepest future described by these models, even the
1:04:04
Speaker 1: black holes would disappear. What remains would be an increasingly
1:04:08
Speaker 1: thin universe, filled with extremely diffuse energy and matter. The
1:04:13
Speaker 1: great structures that seem permanent today would have become memories
1:04:17
Speaker 1: written into the history of space. No bright sun, No
1:04:22
Speaker 1: blue-white stars, no glowing nebulae, no familiar Milky Way filled
1:04:27
Speaker 1: with thousands of visible points. Only darkness. And yet, even here,
1:04:33
Speaker 1: you do not need to imagine emptiness as something frightening.
1:04:37
Speaker 1: Think instead of a very quiet room after everyone has
1:04:40
Speaker 1: gone to sleep. The room has not ceased to exist.
1:04:44
Speaker 1: Nothing is broken. There is simply less movement, less light,
1:04:49
Speaker 1: less warmth. The universe may approach something similar on a
1:04:53
Speaker 1: cosmic scale, although the physical details of its ultimate future
1:04:57
Speaker 1: remain subjects of scientific study and uncertainty. The attached material
1:05:02
Speaker 1: describes the final stage as an era of eternal darkness,
1:05:07
Speaker 1: with space continuing to expand and energy sources becoming increasingly scarce.
1:05:13
Speaker 1: And perhaps the most peaceful part of this enormous story
1:05:16
Speaker 1: is that none of it needs to happen quickly. You
1:05:19
Speaker 1: do not need to worry about the stars tonight. The
1:05:22
Speaker 1: sun will continue to shine for billions of years. The
1:05:25
Speaker 1: Milky Way will continue to turn. New stars will continue
1:05:30
Speaker 1: to appear. Planets will continue to orbit. And somewhere, far
1:05:34
Speaker 1: beyond anything you can see from your window, the universe
1:05:38
Speaker 1: will continue its extraordinarily slow transformation. From cold clouds to stars.
1:05:45
Speaker 1: From stars to remnants. from remnants to darkness. A journey
1:05:51
Speaker 1: that begins with light, and eventually becomes almost entirely quiet.
1:05:56
Speaker 1: You can let yourself drift back toward the present now,
1:06:00
Speaker 1: back through the distant ages, past the black dwarfs that
1:06:03
Speaker 1: have not yet had time to exist, past the cooling
1:06:07
Speaker 1: white dwarfs, past the ancient supernovae, past the massive stars,
1:06:13
Speaker 1: past the strange six-star systems, past Proxima Centauri, past the
1:06:18
Speaker 1: distant icy worlds, past Ceres, quietly turning in the asteroid belt,
1:06:25
Speaker 1: and finally, back toward the small blue world where you began.
1:06:30
Speaker 1: The stars above you tonight are still shining, their light
1:06:33
Speaker 1: is still crossing the darkness, and for now, the universe
1:06:37
Speaker 1: is still young enough to be filled with them, so
1:06:40
Speaker 1: you can simply rest here, beneath this temporary brightness, knowing
1:06:45
Speaker 1: that the cosmos has no need to hurry. There is
1:06:48
Speaker 1: nothing to do, nothing to solve. You are safe. Just listen,
1:06:53
Speaker 1: and drift. The stars will continue their slow journeys while
1:06:56
Speaker 1: you rest, and somewhere beyond them, space will keep expanding,
1:07:01
Speaker 1: quietly carrying the universe forward, far beyond the edge of
1:07:05
Speaker 1: anything you need to know tonight. And now, you can
1:07:11
Speaker 1: let the universe become quiet again. You have travelled beyond
1:07:15
Speaker 1: the familiar planets, past icy worlds and distant rings, past
1:07:20
Speaker 1: planets wandering alone through the darkness, and towards stars that
1:07:24
Speaker 1: seemed almost impossible to imagine. You have watched distant suns
1:07:28
Speaker 1: gather in threes, and then in sixes, moving together through
1:07:33
Speaker 1: the slow gravity of the galaxy. You have drifted beside
1:07:37
Speaker 1: enormous stars, watched them change, and followed their stories toward
1:07:42
Speaker 1: white dwarfs, neutron stars, and black holes. And eventually, you
1:07:48
Speaker 1: travelled even farther, into a future where the stars themselves
1:07:52
Speaker 1: begin to fade. But for now, you can return gently
1:07:55
Speaker 1: to the present. The night sky above you is still
1:07:58
Speaker 1: filled with light. The stars are still shining. Some are young,
1:08:03
Speaker 1: some are ancient. Some may already have changed into something else,
1:08:07
Speaker 1: while their old light is only now reaching you across
1:08:10
Speaker 1: the darkness. And somewhere, far beyond what your eyes can see,
1:08:15
Speaker 1: Icy worlds continue to turn. Rogue planets continue to wander.
1:08:20
Speaker 1: Distant suns continue their quiet dances. And black holes continue
1:08:24
Speaker 1: to wait in the deep spaces between galaxies. There is
1:08:28
Speaker 1: nothing you need to understand completely tonight. There is nothing
1:08:32
Speaker 1: you need to remember. You have already travelled far enough.
1:08:36
Speaker 1: So let the images slowly become softer now. The frozen
1:08:40
Speaker 1: worlds can drift away. The strange rings can become faint
1:08:44
Speaker 1: arcs of light. The six distant suns can slowly disappear
1:08:49
Speaker 1: into the darkness. The massive stars can continue their ancient
1:08:53
Speaker 1: lives without you. And the far future of the universe
1:08:57
Speaker 1: can remain far away, beyond any moment you need to
1:09:01
Speaker 1: think about. For now, you are here. You are safe.
1:09:05
Speaker 1: There is nothing to do. Just breathe gently, listen quietly,
1:09:10
Speaker 1: and allow yourself to drift. The universe is enormous, but
1:09:15
Speaker 1: you do not need to travel through all of it tonight.
1:09:18
Speaker 1: It will still be there tomorrow. The stars will keep shining,
1:09:21
Speaker 1: the planets will keep turning, the distant worlds will keep wandering,
1:09:26
Speaker 1: and beyond them all, space will continue to stretch quietly
1:09:30
Speaker 1: into the darkness. So rest now. Let the sounds around
1:09:34
Speaker 1: you become softer. Let your thoughts become slower. And if
1:09:38
Speaker 1: another strange world appears somewhere in the darkness of your imagination,
1:09:42
Speaker 1: you do not have to follow it. You can simply
1:09:45
Speaker 1: watch it drift away. Quietly. Slowly. until even the stars
1:09:50
Speaker 1: begin to fade into sleep, and the universe carries on
1:09:54
Speaker 1: softly around you while you rest. Good night.