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Imagine you're in a spaceship,

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and you're going back in time, back to the early universe,

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like a few hundred million years after the Big Bang,

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and you come across this huge galaxy,

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blazing with light from new stars forming.

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But as you get closer to the center,

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there's this incredible gravitational pull.

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It's like something you've never encountered before.

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It's an engine black hole,

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a black hole billions of times the mass of our sun.

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But here's the thing,

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those black holes shouldn't even exist yet.

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Welcome to Cosmos and applaud the Space and Astronomy series.

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Please like, comment, share, and subscribe.

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Absolutely.

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So the question is, how did these giant black holes form

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so early in the universe?

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Yeah, that's a really great question,

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and it's a mystery that's been puzzling astronomers

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for decades.

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The usual way we think black holes form

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is from a dying star collapsing in on itself.

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But that takes a really long time, billions of years.

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And the universe just wasn't old enough back then

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for stars to die and create black holes that big.

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Okay, so we're saying that the standard model

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of how black holes form isn't wrong.

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It just doesn't explain these supermassive ones.

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Exactly, it works fine for the smaller black holes,

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but for these supermassive ones,

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especially the ones we see in the early universe,

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it just doesn't quite add up.

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Yeah, so what are some of the other ideas

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about how they formed?

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Well, one idea is something called primordial black holes.

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Primordial black holes.

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Yeah.

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Those are the ones that formed right after the Big Bang.

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Exactly.

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Imagine the conditions back then,

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so much energy and density, everything packed together.

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Yeah.

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Some scientists think that little puppets

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and all that chaos could have collapsed

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and formed black holes right away, no stars needed.

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Wow, so like seeds of black holes

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scattered through the early universe.

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Right, and that would give them a huge head start

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to grow into those supermassive ones.

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But we haven't actually found any

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of these primordial black holes.

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Not yet.

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It's a cool idea, but we need more evidence.

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OK, so we've got the standard model, which might be too slow,

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and the primordial black hole idea,

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which we haven't proven.

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What else is there?

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Well, the most likely explanation right now

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is something called direct collapse.

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Direct collapse.

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Yeah, instead of a single star collapsing,

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you have a massive cloud of gas, millions

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of times the mass of the sun, collapsing directly

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into a black hole.

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So they skip the whole star phase altogether.

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Exactly, and this could explain how

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those supermassive black holes form so fast.

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OK, but even with direct collapse,

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wouldn't they still need to grow incredibly quickly?

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That's the next part of the puzzle.

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We have to look at some extreme processes,

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like super-Eddington accretion and the role of galaxy mergers.

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OK, I'm hooked.

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Let's talk about that.

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Great, so we know these black holes

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would have to grow super fast, even with that direct collapse

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start.

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Yeah, how does that happen?

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Well, it comes down to something called accretion.

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I know that black holes suck in stuff, anything

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that gets too close.

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Right, but it's not as simple as just falling straight in.

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All that gas and dust spirals inward around the black hole,

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and it forms this swirling disk.

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Oh yeah, I've seen pictures of those accretion disks.

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And they get incredibly hot because of all the friction,

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and that releases a ton of energy.

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So it's not just a silent, invisible process.

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They're blazing with energy.

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Exactly, but there's a limit to how fast a black hole

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can grow this way.

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As it pulls in more matter, all that energy from the disk

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can actually start pushing away incoming gas.

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So it's like a back pressure.

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Exactly, and that limit on how fast it can grow

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is called the Eddington limit.

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But you said these early black holes had to grow super fast.

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So how do they get around that limit?

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Right, well, some black holes might

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have gone through periods of super Eddington accretion.

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Super Eddington accretion?

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Yeah, basically they were breaking the speed limit.

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Whoa, is there any proof of that?

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Actually, yes.

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The James Webb SACE telescope saw a black hole

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growing 40 times faster than the Eddington limit.

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40 times?

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That's insane.

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What could make them grow that fast?

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One idea is that those powerful jets

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we see coming from black holes could be playing a role.

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Those beams of energy.

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Right, they blast out from the black holes poles,

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and they might be diverting some of the energy away

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from the accretion disk.

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So more material can fall in.

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Yeah, it's a complex process, but the JWST

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is giving us a closer look.

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OK, so super Eddington accretion is part of it,

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but where does all that material even

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come from in the first place?

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It's not like there's an endless buffet out there.

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That's a great question, and that leads us to galaxy mergers.

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When galaxies crash into each other.

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Exactly, and when that happens, the black holes

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at their centers get pulled together by gravity.

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Oh, wow.

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They start orbiting each other, getting closer and closer.

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It's a spectacular dance.

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So it's not just a one-time meal.

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It's like a constant feast fueled by these mergers.

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Exactly, and these mergers are amazing.

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They can trigger bursts of star formation,

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creating these beautiful cosmic fireworks.

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It's mind-blowing to think about,

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but even black holes can't keep growing forever, right?

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You're right.

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They do have a lifespan.

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They eventually run out of fuel as the universe expands

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and everything spreads out.

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So what happens then?

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What's the final act?

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It involves something called Hawking radiation.

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OK, I've heard of that, but I don't really get it.

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It's based on quantum mechanics.

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You see, even the empty space around a black hole

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is full of these things called virtual particles.

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Virtual particles.

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Yeah, it's like pairs of particles constantly popping

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in and out of existence.

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They borrow energy from the vacuum of space,

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and they usually destroy each other almost instantly.

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But near a black hole, something weird can happen.

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What happens?

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Sometimes one particle falls into the black hole,

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and the other one escapes.

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And that escaping particle takes some of the black hole's energy

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with it.

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So even though nothing can escape from inside the black hole,

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it's still losing energy.

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Exactly.

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And over a really, really long time,

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this energy leak called Hawking radiation

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makes the black hole shrink.

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And then what happens in the end?

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So we were talking about Hawking radiation

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and how black holes lose a tiny bit of energy over time.

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Right.

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But what happens when it's all gone, when there's

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no more black hole left?

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Well, it's not exactly an explosion,

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but it's kind of like one.

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OK.

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All that energy trapped inside has to go somewhere.

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So it releases this huge burst of energy and particles.

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So the black hole disappears in a burst of energy.

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Yeah, you could say that.

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It's more like an evaporation, though.

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So no more black hole, just a little echo of radiation.

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Right, and that radiation just spreads out into the universe.

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It's kind of sad in a way, these giant black holes just

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fading away.

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I guess so.

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But remember, this takes an incredibly long time,

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much longer than the current age of the universe.

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Yeah, that's true.

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And it brings us to this idea of the heat death

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of the universe.

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Heat death.

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That sounds ominous.

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It's just a theory, but it fits with what

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we know about physics.

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OK.

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Imagine a universe where everything has run out of fuel.

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All the stars are dead.

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All the black holes have evaporated.

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So just a cold, empty universe.

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Pretty much, just a faint sea of particles

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spread out over unimaginable distances.

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No more stars, no more galaxies, just darkness and silence.

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It's the ultimate end state of the universe,

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according to thermodynamic.

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Oh, wow.

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It's kind of amazing to think about.

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It is.

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It makes you realize how precious our time

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in the universe is.

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We're lucky to be here when things are still happening.

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Exactly.

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We get to see stars being born, galaxies colliding,

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black holes growing.

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It's a pretty special time.

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I agree.

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Well, this has been a fascinating deep dive

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into the world of supermassive black holes.

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It has.

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And who knows what new discoveries

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await us in the future.

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That's right.

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There's always more to learn.

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Absolutely.

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Thanks for joining us on Cosmos in a Pod.

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It was my pleasure.

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And to all our listeners, don't forget

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to subscribe to our YouTube channel

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for more explorations of the universe.

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And keep looking up at the stars.

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Until next time.