Latest / Daniel and Kelly’s Extraordinary Universe / How did supermassive black holes get so big?

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How did supermassive black holes get so big? · Daniel and Kelly’s Extraordinary Universe

• 0:08
  Speaker 1: Hey, Daniel, I have a question for you about how
• 0:10
  Speaker 1: big things are. Is this a question about my pandemic
• 0:14
  Speaker 1: snacking habit? No, No, I'm wondering. How do you think
• 0:18
  Speaker 1: about the massive size of things? Like there are so
• 0:21
  Speaker 1: many big things out during the universe. I know you mean,
• 0:23
  Speaker 1: like how the sun is a million times bigger than
• 0:26
  Speaker 1: our earth. Yeah, I'm wondering there are things out there
• 0:28
  Speaker 1: there are even millions or billions of times bigger than
• 0:31
  Speaker 1: our sun. Yeah, you know, some things out there are
• 0:33
  Speaker 1: incredibly massive. Maybe they've been doing some pandemic snacking of
• 0:37
  Speaker 1: their own. You mean, like eating whole stars between meals.
• 0:41
  Speaker 1: I wouldn't recommend it, just three stars per day? Is
• 0:44
  Speaker 1: there a doctor's recommendation? Yes, we are doctors. I am
• 1:03
  Speaker 1: forhanda cartoonists and the creator of PhD comics. Hi, I'm Daniel.
• 1:07
  Speaker 1: I'm a particle physicist and technically i'm a doctor. But
• 1:10
  Speaker 1: please don't follow my medical advice. Yes, physicists don't make
• 1:14
  Speaker 1: the best lifestyle examples. No, that's true, and particle physics
• 1:18
  Speaker 1: especially is not a very practical degree. You can't collide
• 1:22
  Speaker 1: the germs in your body. Oh that sounds like fun. Actually,
• 1:24
  Speaker 1: I'm going to write that proposal. I think most people
• 1:27
  Speaker 1: would love to collide a certain virus right now in
• 1:30
  Speaker 1: your super collider. But welcome to our podcast. Daniel and
• 1:33
  Speaker 1: Jorge explain the university production of I Heart Radio, in
• 1:36
  Speaker 1: which we explore all the crazy and amazing things in
• 1:39
  Speaker 1: the universe colliding them with your brain, from the very
• 1:42
  Speaker 1: smallest particles to the weird stuff happening on our scale,
• 1:45
  Speaker 1: to the very big, the very enormous, the very super
• 1:49
  Speaker 1: duper mysteries of the universe. Yeah, the biggest mysteries out
• 1:52
  Speaker 1: there and also the most massive mysteries. Because Massa's is
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  Speaker 1: such a fun thing to think about. You know, it
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  Speaker 1: makes stuff stuff if you think about it. I don't
• 2:00
  Speaker 1: like to think about my mass very much. Actually, actually,
• 2:03
  Speaker 1: I'm getting pretty fit in this pandemic. I've been doing
• 2:06
  Speaker 1: more exercise and normal to say that I'm getting some exercise.
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  Speaker 1: But mass is incredible because on one hand, there's so
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  Speaker 1: much space out there that's just empty, like most of
• 2:18
  Speaker 1: the universe is just emptiness. But then there are these
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  Speaker 1: incredible clumps of amazing density, these blobs of stuff. They
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  Speaker 1: know the size of a planet, the size of Jupiter,
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  Speaker 1: the size of the Sun, and then even monstrously bigger
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  Speaker 1: than that. Yeah, because there are things out there that
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  Speaker 1: are so massive and so dense that they actually turn
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  Speaker 1: into black holes. And you know, black holes, I think
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  Speaker 1: we people tend to think of them as one thing,
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  Speaker 1: like once you become a black hole, that's it. You're
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  Speaker 1: a black hole. But actually there's a big variety of
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  Speaker 1: black holes out there in the universe, that's right. Black
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  Speaker 1: Holes come in all shapes and sizes. Some of them spin,
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  Speaker 1: some of them have electric charge, Some of them are
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  Speaker 1: quite small, some of them are incredibly super duper huge.
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  Speaker 1: They come in different ship apes. Can they come in
• 3:00
  Speaker 1: different shapes depending on the stuff around them, So it
• 3:03
  Speaker 1: depends on what you call part of the black hole.
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  Speaker 1: They're mostly spears, but some of them have disks of
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  Speaker 1: stuff around them that are bigger and smaller. Some of
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  Speaker 1: them are on their own, and so I guess maybe
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  Speaker 1: they don't have different shapes, they have different clothing, They're
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  Speaker 1: dressed differently. Can you have like a banana shade black hole? Probably?
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  Speaker 1: You know, you get a decretion disc with stuff is
• 3:22
  Speaker 1: swirled only on one side that would look a lot
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  Speaker 1: like a banana. So I'm gonna go with yes. It's
• 3:26
  Speaker 1: likely that out there somewhere there's a huge gas banana
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  Speaker 1: getting sucked into a black hole. Official word here, ladies
• 3:33
  Speaker 1: and gentlemen from your doctor. That's right. And so, yeah,
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  Speaker 1: some of these black holes can be really, really, really heavy.
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  Speaker 1: Some of them are millions of times more massive than
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  Speaker 1: our sun, which is crazy to imagine. Like imagine a
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  Speaker 1: million sons crowned into one place, I know. And when
• 3:49
  Speaker 1: you think a million sons, you instantly think something that's
• 3:53
  Speaker 1: super duper bright, right, But of course a black hole
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  Speaker 1: is not that bright. It's huge, it's massive, but it's
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  Speaker 1: not actually that bright. Right. All that mass works together
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  Speaker 1: to create this strange fold in space where space becomes
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  Speaker 1: like one directional. It's like a one directional portal in
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  Speaker 1: space where once you go in it, you can't come out.
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  Speaker 1: It doesn't matter how fast you're moving, if you're a
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  Speaker 1: massless photon or a very very fast neutrino or a
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  Speaker 1: blob of stuff, there's just no way out. It's not
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  Speaker 1: about your speed or about your energy, it's just space
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  Speaker 1: has become folded in this bizarre way, right, And so
• 4:25
  Speaker 1: they're one of the most amazing mysteries of physics. Yeah,
• 4:28
  Speaker 1: it's like one direction. The boy band also a black
• 4:30
  Speaker 1: hole in music. I think that was a career black hole.
• 4:33
  Speaker 1: But yeah, Harry Styles somehow managed to escape that that
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  Speaker 1: black hole. But but yeah, but that's that's like an
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  Speaker 1: average black hole. Like a black hole that's millions of
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  Speaker 1: times more massive than our sun. That's like a small
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  Speaker 1: black hole that doesn't impress you. I mean, it's impressive
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  Speaker 1: to me, but sure the universe can impress me even more.
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  Speaker 1: That's right. And the incredible thing about these black holes
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  Speaker 1: is that they have to form, right, You've got to
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  Speaker 1: make them. They gotta somehow get that big by gobbling
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  Speaker 1: stuff up. And there are black holes that are so
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  Speaker 1: big out there that scientists don't really know how they
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  Speaker 1: got that big. Yeah, there are black holes out there.
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  Speaker 1: There are billions of times more massive than the sun. Right,
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  Speaker 1: Like we take our sun and get a million of
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  Speaker 1: them together, get a thousand of those together. That's like
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  Speaker 1: a that's a super massive black hole. That's really pretty impressive.
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  Speaker 1: I mean, I think that that should be called super
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  Speaker 1: duper massive black hole, not just supermassive. And that's actually
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  Speaker 1: the official name for them, right, isn't it? Super Massive
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  Speaker 1: black holes like supermassive black holes is the official name
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  Speaker 1: used by actual black hole scientists. I like to call
• 5:35
  Speaker 1: them super duper massive because it just conveys better how
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  Speaker 1: impressive they really are. Super duper mega awesome black holes,
• 5:42
  Speaker 1: califragilistic black holes. Can't run out of enough superlatives. Alright,
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  Speaker 1: So these giant supermassive black holes, they're really big and
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  Speaker 1: nobody seems to know how they get formed. So to
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  Speaker 1: be on the podcast, we'll be asking the question, how
• 6:01
  Speaker 1: do super massive black holes get so big? I mean,
• 6:05
  Speaker 1: do they even lift? Man? Did they go to the gym? Like,
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  Speaker 1: how did they get so big? What? What? What did
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  Speaker 1: they do for the core? Exactly? Don't skip leg day
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  Speaker 1: black holes. You know, it's not all about being ripped.
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  Speaker 1: Are they doing the t X something something? I bet
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  Speaker 1: they're doing something more holistic, right, you know, they've got
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  Speaker 1: that nice, perfectly spherical shape of the event horizon, so
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  Speaker 1: it's definitely some core strength. I bet there's a lot
• 6:26
  Speaker 1: of yoga, downward dog and all that stuff. Yeah, so
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  Speaker 1: they're super duper massive and really big and people don't
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  Speaker 1: know how they got that big. But we were wondering
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  Speaker 1: how many of our listeners out there know or think
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  Speaker 1: about how these black holes get so big. That's right,
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  Speaker 1: because they are really pretty incredibly big, and it's hard
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  Speaker 1: to make a black hole that big in the short
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  Speaker 1: amount of time we've had in our universe. So I
• 6:50
  Speaker 1: sent this question to our friendly volunteers. Thank you to
• 6:53
  Speaker 1: everybody who signed up to answer random questions, and if
• 6:56
  Speaker 1: you like to participates for future episodes, please they're u
• 7:00
  Speaker 1: with a line to questions at Daniel and Jorge dot com.
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  Speaker 1: Before you listen to these answers, think about it for
• 7:04
  Speaker 1: a second. If someone ask you how does supermassive black
• 7:09
  Speaker 1: holes get so supermassive? What would you answer? Here's what
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  Speaker 1: people had to say. My guess is that black holes
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  Speaker 1: become super massive by simply absorbing neighboring planets, stars, gas,
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  Speaker 1: any other type of matter nearby the black hole. When
• 7:27
  Speaker 1: it comes into existence, it has to be large enough
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  Speaker 1: where it doesn't just evaporate due to hawking radiation, and
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  Speaker 1: it needs to be close enough to other sources of
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  Speaker 1: matter so that it can pull them in and gain
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  Speaker 1: their mass to become supermassive. The obvious answer would be
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  Speaker 1: that just by you know, gobbling up nearby stuff. So
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  Speaker 1: I think that all the supermassive blig holes are originating
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  Speaker 1: from the early stages of the universe when it was
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  Speaker 1: much then, and I think it was just easier for
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  Speaker 1: existing black holes to eat up the surrounding planets or
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  Speaker 1: other stars. If they start one size and gain more material,
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  Speaker 1: it makes sense that they would grow. The event horizon
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  Speaker 1: would grow. Certainly the more mass is in it, probably
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  Speaker 1: number one would be merging with another or more black holes.
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  Speaker 1: Black holes get to be super massive by emerging with
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  Speaker 1: other black holes, such as when two galaxies flide and
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  Speaker 1: their central black holes merge. Maybe by you know, as
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  Speaker 1: they keep absorbing more matter into it. All right, so
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  Speaker 1: some pretty good answers there somewhere are like, wow, I
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  Speaker 1: didn't know that they does seem really possible. Yeah, the
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  Speaker 1: general sense seems to be like, well, black holes get
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  Speaker 1: bigger by eating stuff. So you want to get supermassive,
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  Speaker 1: you gotta eat a supermassive amount of stuff. That's what
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  Speaker 1: black holes do, right. They can't do anything else. They
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  Speaker 1: can only consume, you know. It's not like they can
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  Speaker 1: poop stuff out or anything. And it's like that's all
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  Speaker 1: that's all they were intended to do by the universes
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  Speaker 1: is sucks stuff? It is that not enough for you?
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  Speaker 1: Like incredible folds in space gobbling up matter and incredible rates,
• 9:13
  Speaker 1: and you're like, what else do you got I'm saying.
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  Speaker 1: I'm saying they have a limited range of skills there,
• 9:19
  Speaker 1: but you know, they're a niche player. They're the best
• 9:21
  Speaker 1: in the universe at what they do. And I think
• 9:23
  Speaker 1: in terms that we're talking careers here, that's really the
• 9:26
  Speaker 1: right way to go, right, stick to your niche, that's right.
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  Speaker 1: But I think the thing that's missing from these answers
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  Speaker 1: is an understanding of how you can get so big
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  Speaker 1: in the limited time we've had in our universe. Like, yeah,
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  Speaker 1: the universe is fourteen billion years old, but these black
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  Speaker 1: holes are so big that we don't understand how they
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  Speaker 1: got so big in that amount of time. Wow, that's weird.
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  Speaker 1: It's weird that we can't explain that, Like that, we
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  Speaker 1: have these things in the universe that are not small,
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  Speaker 1: they're big and significant, like they're helping to hold the
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  Speaker 1: galaxies together, right, and we don't know how they got
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  Speaker 1: to how they are. But this is a really important
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  Speaker 1: part of how we do science. We look at the
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  Speaker 1: stuff that's out there in the universe, and we say,
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  Speaker 1: do we understand how it got here? We have a
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  Speaker 1: model of the early universe. We think we know the
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  Speaker 1: laws that determine how things interact and how things grow
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  Speaker 1: and change. So we should be able to then look
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  Speaker 1: around and describe basically what we see. So if there's
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  Speaker 1: something out there that we can't explain that we don't
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  Speaker 1: think should be there, it tells us there must be
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  Speaker 1: something wrong in our understanding, either of the initial conditions
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  Speaker 1: how things started or of the rules for how things change.
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  Speaker 1: All right, so let's jump right into it. Daniel and
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  Speaker 1: I think we can assume that most of our listeners
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  Speaker 1: know what a black hole is, which is an accumulation
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  Speaker 1: of a mass so intense that it creates like a
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  Speaker 1: pocket or a hole in the universe out of which
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  Speaker 1: nothing can escape. I think we can assume most people
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  Speaker 1: know that, But maybe what people don't know is kind
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  Speaker 1: of how big or what how they can vary in size.
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  Speaker 1: So step us through, like, what's a normal black hole?
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  Speaker 1: So a normal black hole is the kind that you
• 10:53
  Speaker 1: might be familiar with that comes when a star dies.
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  Speaker 1: Stars this big blob of gas, and it's a balance
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  Speaker 1: between the graph compressing it and the energy released from
• 11:03
  Speaker 1: the fusion and the burning, and when the burning stops,
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  Speaker 1: then the star collapses because all that's left is gravity,
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  Speaker 1: and sometimes it collapses so much that you get a
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  Speaker 1: black hole. And these black holes tend to be around
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  Speaker 1: the size of the masses of stars because they were
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  Speaker 1: made by one star. And so the units are usually
• 11:20
  Speaker 1: the mass of our Sun because it's a convenient thing.
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  Speaker 1: It's not like the official star or the universe, but
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  Speaker 1: it's the one we use to measure the masses of things.
• 11:28
  Speaker 1: And so the typical range of a stellar black hole
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  Speaker 1: when they came from a star is a few times
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  Speaker 1: the mass of our Sun, you know, like a few
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  Speaker 1: up to maybe ten twenty. The biggest one we've seen
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  Speaker 1: in this category is like, you know, seventy or eighty
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  Speaker 1: times the mass of our Sun, because they come from
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  Speaker 1: when the stars go supernova, right, and that's kind of
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  Speaker 1: the only way they can form from stars, right, that's right,
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  Speaker 1: you have a gravitational collapse, the burning stops, everything collapses
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  Speaker 1: in then you sometimes get a supernova that blows out
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  Speaker 1: a huge amount of material and then what's left to
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  Speaker 1: the core or is a black hole. And so you
• 12:01
  Speaker 1: don't always get all of the stuff from the star
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  Speaker 1: into the black hole. Right, You lose some stuff, it burned,
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  Speaker 1: it got sent away, there was radiation, there was a
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  Speaker 1: supernova blew some of that gas out into the universe.
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  Speaker 1: But at the core you get that black hole. So
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  Speaker 1: some fraction of the mass of the star turns into
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  Speaker 1: the black hole. So for black holes that come from
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  Speaker 1: a star, the mass of the black hole is a
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  Speaker 1: little bit less than the mass of the original star, right,
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  Speaker 1: and those stars can be as big as seventy or
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  Speaker 1: eighty times the size of our sun. Yeah, there are
• 12:29
  Speaker 1: stars out there that are much more massive than our star,
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  Speaker 1: and so they can be you know, up to a
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  Speaker 1: hundred times the mass of our star, which leads to
• 12:36
  Speaker 1: black holes up to like, you know, eighty times the
• 12:38
  Speaker 1: mass of our sun. All right, So those are the
• 12:41
  Speaker 1: kind of the regular black holes because they form from stars,
• 12:45
  Speaker 1: and there are a lot of stars out there in
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  Speaker 1: the universe, and those can get pretty big. I mean,
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  Speaker 1: eighty times the size of our sun. That's not nothing,
• 12:52
  Speaker 1: that's nothing to scoff at. You know, there's eighty million
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  Speaker 1: earths all packed into a tiny little blob. It's pretty impressive.
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  Speaker 1: But the incredible thing about the universe is that every
• 13:02
  Speaker 1: time you turn around, there's something that dwarfs what you
• 13:04
  Speaker 1: were previously impressed by. Like why you thought the Earth
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  Speaker 1: was huge. Look at Jupiter, you thought Jubiter was big.
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  Speaker 1: Look at the Sun, you thought the Sun was big.
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  Speaker 1: And it just keeps going and going and going, and
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  Speaker 1: there's all these different scales that each one blow your mind.
• 13:18
  Speaker 1: That's the experience of, you know, understanding the depths of
• 13:21
  Speaker 1: the scales of the And so that's one sort of
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  Speaker 1: category of black holes that we see or think are
• 13:27
  Speaker 1: there in the universe, you know, the sort of like
• 13:30
  Speaker 1: one to eighty times the size of our sun. But
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  Speaker 1: then there's sort of another big category of black holes,
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  Speaker 1: which is kind of like way out there, much bigger.
• 13:39
  Speaker 1: That's right, there's not like an even distribution. It's not
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  Speaker 1: like black holes start from a few solar masses and
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  Speaker 1: go all the way up to millions and billions. There
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  Speaker 1: are two different kinds of black holes. The ones we
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  Speaker 1: just talked about that come from a star, and then
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  Speaker 1: this other category of really massive black holes that are
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  Speaker 1: like hundreds of thousands of times the mass of a
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  Speaker 1: star up to millians and billions of times the mass
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  Speaker 1: of our sun, and so these are what we call
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  Speaker 1: supermassive black holes, and there's like a gap there. You
• 14:08
  Speaker 1: don't see any black holes that are like a thousand
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  Speaker 1: times the mass of the Sun or five dred times.
• 14:13
  Speaker 1: There's just nothing there. It's like two distinct classes. Yeah,
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  Speaker 1: and it tells you that there's like two different ways
• 14:18
  Speaker 1: to make black holes, are two different populations, that these
• 14:20
  Speaker 1: things have a lot in common, but they're also really
• 14:23
  Speaker 1: different and they probably have a different history. Now, are
• 14:25
  Speaker 1: we sure that we haven't seen any in the middle
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  Speaker 1: sizes or is it that we just can't theoretically come
• 14:30
  Speaker 1: up with them. We have not seen any in those
• 14:32
  Speaker 1: middle sizes. That's right, And the problem is not that
• 14:35
  Speaker 1: we can't come up with them. The problem is that
• 14:37
  Speaker 1: we can't explain how these ones got so big. It's
• 14:39
  Speaker 1: easier to explain smaller black holes than the ones we
• 14:43
  Speaker 1: see because there's more time for to accumulate gas and
• 14:46
  Speaker 1: to grow. The hard thing is to explain how you've
• 14:48
  Speaker 1: got these really really big black holes. And these big
• 14:51
  Speaker 1: black holes they're not just like floating out there in
• 14:53
  Speaker 1: the universe or part of a galaxy the way like
• 14:56
  Speaker 1: a stellar black hole is from a collapse of a star.
• 14:58
  Speaker 1: These guys tend to be at the center of a galaxy.
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  Speaker 1: That's usually we'll we see them. We don't see them
• 15:03
  Speaker 1: floating around on their own. We definitely do not. And
• 15:06
  Speaker 1: every galaxy has one, and usually exactly one. Like, you
• 15:09
  Speaker 1: don't have two supermassive black holes in a single galaxy.
• 15:12
  Speaker 1: It's like, you know, this town is only big enough
• 15:14
  Speaker 1: for the one of us. And that's kind of funny,
• 15:18
  Speaker 1: isn't it. Like you only see one in the center
• 15:21
  Speaker 1: of each galaxy, and most galaxies have them, that's right,
• 15:24
  Speaker 1: And there's a reason you only see one, and that's
• 15:26
  Speaker 1: because they're so big and massive. Like if you get
• 15:28
  Speaker 1: two galaxies that collide and that they merge, then the
• 15:32
  Speaker 1: two supermassive black holes at their centers will orbit each
• 15:35
  Speaker 1: other for a little while, but eventually they'll merge and
• 15:37
  Speaker 1: become one. So they can't really stay separate because they're
• 15:40
  Speaker 1: each so powerful and sucking in the other on like Highlander,
• 15:43
  Speaker 1: that can only be one, that's right. And the other
• 15:47
  Speaker 1: thing that to understand is these black holes are a
• 15:50
  Speaker 1: really big part of a galaxy. It's not just like, Okay,
• 15:52
  Speaker 1: you've got a big black hole, but the galaxy is
• 15:55
  Speaker 1: much much bigger, Like each of these black holes is
• 15:58
  Speaker 1: on average about one one since the mass of the
• 16:01
  Speaker 1: entire galaxy, which you know has like hundreds of billions
• 16:04
  Speaker 1: of stars, but this black hole really dwarfs any other
• 16:08
  Speaker 1: object in the galley. It's like probably millions of times
• 16:11
  Speaker 1: bigger than anything else in the galaxy. Yeah, exactly. And
• 16:14
  Speaker 1: so the biggest ones we've seen are billions and billions
• 16:17
  Speaker 1: of times the mass of the Sun. And the amazing
• 16:19
  Speaker 1: thing is that some of them are really really old.
• 16:22
  Speaker 1: Like we've seen black holes that are billions of times
• 16:26
  Speaker 1: the mass of the Sun and have been around since
• 16:28
  Speaker 1: the universe was only a billion years old. What how
• 16:31
  Speaker 1: do we know their age? Black holes don't have any
• 16:33
  Speaker 1: wrinkles or you can't ask them. It's pearl cream, man.
• 16:38
  Speaker 1: They just look great. Well, we see an old picture
• 16:40
  Speaker 1: of them, Like if we're looking at something really really
• 16:42
  Speaker 1: far away, we're seeing old lights. So the picture we
• 16:44
  Speaker 1: see of them is really old. So the short answers
• 16:47
  Speaker 1: we're seeing really really massive black holes very far away,
• 16:51
  Speaker 1: which means that they happened a long time ago because
• 16:53
  Speaker 1: I have an old picture because the light is taking
• 16:56
  Speaker 1: billions of years to get here. It's it's an old
• 16:58
  Speaker 1: picture and they're still there. Yes, so we know that
• 17:01
  Speaker 1: after only a billion years of universe formation, that were
• 17:05
  Speaker 1: already super massive black holes that were billions of times
• 17:09
  Speaker 1: the mass of our sun. Man, all right, let's get
• 17:12
  Speaker 1: into how we can see these black holes, and let's
• 17:16
  Speaker 1: get into the mystery of how they got so big.
• 17:18
  Speaker 1: But first let's take a quick break. All right, Daniel,
• 17:33
  Speaker 1: we're talking about super duper awesome, ginormous black holes, and
• 17:40
  Speaker 1: there's a big mystery about how they get so big,
• 17:42
  Speaker 1: because they're much bigger than the regular black holes that
• 17:45
  Speaker 1: we see floating around in space. And so I guess
• 17:48
  Speaker 1: the question is how do we First of all, how
• 17:49
  Speaker 1: do we see them? How do we see black holes?
• 17:51
  Speaker 1: So black holes we can never see directly, so we
• 17:54
  Speaker 1: have no like, really direct proof that black holes actually exist.
• 17:58
  Speaker 1: We just have a lot of really good circumstantial evidence,
• 18:01
  Speaker 1: and all of our evidence essentially is gravitational. Basically, the
• 18:04
  Speaker 1: argument is always there's a huge amount of mass in
• 18:07
  Speaker 1: a small amount of space, and nothing else can do that,
• 18:11
  Speaker 1: so it must be a black hole. We see nothing
• 18:13
  Speaker 1: else there, you know, like you can see a big
• 18:16
  Speaker 1: swirl of gas surrounding some black object, and that gas
• 18:20
  Speaker 1: is obviously under incredible pressure because it's emitting a lot
• 18:23
  Speaker 1: of radiation. Or you can see other stars moving around
• 18:27
  Speaker 1: this object in space on crazy orbits that would require
• 18:31
  Speaker 1: intense gravitational fields that are only consistent with an object
• 18:35
  Speaker 1: that's very small and very massive. And so then we conclude, okay,
• 18:39
  Speaker 1: there must be a black hole there, and we can
• 18:41
  Speaker 1: calculate its mass based on the orbits of stars around
• 18:45
  Speaker 1: and but those are the regular ones. The one at
• 18:47
  Speaker 1: the center of galaxy is the one that we know
• 18:49
  Speaker 1: are really old and big. How do we like, how
• 18:51
  Speaker 1: do we see it? Can you can you actually see
• 18:54
  Speaker 1: the stars going around it in a galaxy so far away?
• 18:56
  Speaker 1: In our galaxy, you can see the stars going around it.
• 18:59
  Speaker 1: Like we have looked directly at the path of stars
• 19:02
  Speaker 1: zipping around the black hole at the center of our galaxy,
• 19:04
  Speaker 1: which is called Sagittarius A. So we know that one
• 19:07
  Speaker 1: pretty well. In terms of other galaxies, like ones really
• 19:10
  Speaker 1: far away in the old early universe, we see them
• 19:13
  Speaker 1: because the radiation of the gas that they're squeezing around them,
• 19:17
  Speaker 1: So this is disc of stuff around them that's swirling around,
• 19:20
  Speaker 1: waiting to get sucked in and it's getting squeezed and
• 19:23
  Speaker 1: pulled by the tidal forces, the gravitational pressure, and so
• 19:26
  Speaker 1: it's emitting a huge amount of light. And those are
• 19:28
  Speaker 1: actually some of the brightest things in the universe. Sort
• 19:32
  Speaker 1: of weird, these really massive dark objects actually end up
• 19:35
  Speaker 1: being some of the brightest things, and they're called quasars.
• 19:38
  Speaker 1: That's how they were originally discovered. So we saw these
• 19:41
  Speaker 1: really bright objects in the sky and we didn't understand
• 19:43
  Speaker 1: what could be emitting so much radiation. Right, so we
• 19:45
  Speaker 1: can actually see them. They glow, or at least that
• 19:48
  Speaker 1: the stuff around them glows. Yes, then how do you
• 19:50
  Speaker 1: how do you tell how massive they are? Yes, so
• 19:52
  Speaker 1: the stuff around them glows, right. The black hole itself
• 19:54
  Speaker 1: is black, with the exception of Hawking radiation, which nobody
• 19:57
  Speaker 1: has ever seen. It emits no light, but you know,
• 19:59
  Speaker 1: the stuff are round that it's entourage is very very bright.
• 20:02
  Speaker 1: And that's how we see these really distant ones. But
• 20:05
  Speaker 1: you can also just watch stars move around them and
• 20:07
  Speaker 1: just track their path and do the calculation and say,
• 20:10
  Speaker 1: for this start to bend so much in space, how
• 20:13
  Speaker 1: much mass would there have to be in that black hole?
• 20:15
  Speaker 1: And that's how you can estimate their mass. It also
• 20:17
  Speaker 1: gives you a limit on their size, right because you
• 20:19
  Speaker 1: can see the star moved near the black hole, so
• 20:22
  Speaker 1: you know how big the black hole isn't all? Right,
• 20:24
  Speaker 1: So there's this whole category of black holes that are
• 20:27
  Speaker 1: super massive, much bigger than the regular ones that form
• 20:30
  Speaker 1: from supernovas. And so I guess the big mystery you
• 20:34
  Speaker 1: were telling me is that we don't know how they
• 20:35
  Speaker 1: get started or how they get so big. What does
• 20:38
  Speaker 1: that mean? How can we not know how black hole
• 20:40
  Speaker 1: gets Do they just eat or stuff? Yeah, so it's
• 20:42
  Speaker 1: sort of a two part mystery. Right. You need your
• 20:45
  Speaker 1: black hole to get big, so you just feed it
• 20:47
  Speaker 1: a lot, right, Well, if you start from a stellar
• 20:49
  Speaker 1: mass black hole, like one the size of a few suns,
• 20:53
  Speaker 1: then there just isn't enough time to feed that to
• 20:55
  Speaker 1: make it big. Why not? You want to grow a
• 20:57
  Speaker 1: plant in your backyard? Is a limit to how fast
• 21:00
  Speaker 1: as they can grow? And the same is true for
• 21:01
  Speaker 1: black holes. Really, why is there a limit on how
• 21:04
  Speaker 1: fast it can grow? Can't just sucks stuff in at
• 21:06
  Speaker 1: an incredible rate? There is there a limit. There is
• 21:09
  Speaker 1: actually a limit, And because there's a feedback, like as
• 21:12
  Speaker 1: the black hole gets more powerful, it starts to excite
• 21:15
  Speaker 1: the gas around it, which gives off a lot of radiation,
• 21:18
  Speaker 1: and so it actually pushes stuff away from it. So
• 21:21
  Speaker 1: the faster you feed a black hole, then the heavier
• 21:24
  Speaker 1: it gets, the more it pushes stuff away from it.
• 21:26
  Speaker 1: So it's really delicate balance. This is called the Eddington limit.
• 21:30
  Speaker 1: If you want to grow your black hole, you can
• 21:32
  Speaker 1: either feed it a little bit at a time right
• 21:34
  Speaker 1: and avoid that radiation. You dump too much stuff in it,
• 21:37
  Speaker 1: it's gonna blow all of the fuel away. So you've
• 21:39
  Speaker 1: got to find this right balance. You gotta feed it
• 21:41
  Speaker 1: at just the right rate to get the maximum growth curve.
• 21:44
  Speaker 1: Oh I see if you if you try to feed
• 21:45
  Speaker 1: it too fast, it's actually going to create an explosion
• 21:49
  Speaker 1: which is going to blow all your food away. That's right,
• 21:51
  Speaker 1: because remember these quasars, these the brightest things in the universe.
• 21:54
  Speaker 1: That's an enormous amount of radiation. So it's going to
• 21:57
  Speaker 1: clear out all the space near it, which is going
• 21:59
  Speaker 1: to prevent it for growing any further. So it's not
• 22:01
  Speaker 1: like a physical limitation. Is no law that says the
• 22:04
  Speaker 1: black hole can't grow faster. It's just a question of
• 22:06
  Speaker 1: like getting that stuff into the black hole while its
• 22:09
  Speaker 1: meanwhile pumping out a bunch of radiation. Right, But I
• 22:12
  Speaker 1: guess doesn't that all doesn't assume that the stuff goes
• 22:16
  Speaker 1: in kind of in a spiral. What is stuff just
• 22:18
  Speaker 1: goes in directly? Yeah, if you have really cold gas,
• 22:21
  Speaker 1: then it can go in, but it's got to get
• 22:23
  Speaker 1: past all that radiation. Remember, you're surrounded by there's always
• 22:27
  Speaker 1: going to be some warm gas, some stuff surrounding the
• 22:30
  Speaker 1: black hole that's going to radiated. So it's it's like
• 22:33
  Speaker 1: an environmental question. First they suck up all the cold gas,
• 22:36
  Speaker 1: the stuff that's not gonna swirl, but then what's left
• 22:39
  Speaker 1: is the hot gas, and so that takes longer to
• 22:41
  Speaker 1: get in, all right, So then there's a maximum rate
• 22:45
  Speaker 1: or speed at which you can black holes can eat.
• 22:47
  Speaker 1: And so the mystery said, if you take that speed
• 22:50
  Speaker 1: and you're multiplied by the age of the universe, that
• 22:52
  Speaker 1: doesn't give you enough stuff. You can't get enough stuff
• 22:54
  Speaker 1: into the black hole to explain how big they are. Now,
• 22:57
  Speaker 1: that's right. If you start from really small black holes
• 23:00
  Speaker 1: you go with the maximum speed of growth, you don't
• 23:02
  Speaker 1: get to millions and billions of masses of black holes.
• 23:06
  Speaker 1: They just stay too small. In our simulation, and so
• 23:09
  Speaker 1: you need to figure out a way to make them
• 23:10
  Speaker 1: grow faster, which we don't understand, or you need to
• 23:13
  Speaker 1: start from bigger black holes in the early universe, so
• 23:16
  Speaker 1: you sort of like get ahead, start right, like maybe
• 23:19
  Speaker 1: they started big, that's right. The major mysteries on understanding
• 23:22
  Speaker 1: how these black holes could have formed in the very
• 23:25
  Speaker 1: early universe and started out really big. So there's a
• 23:28
  Speaker 1: few ideas there for how you could have really big
• 23:30
  Speaker 1: seeds of black holes in the early universe. All right,
• 23:33
  Speaker 1: step us through. What are some of the different ways
• 23:35
  Speaker 1: in which you could start with a really big black hole. Well,
• 23:38
  Speaker 1: one of the ways is really theoretical and speculative and
• 23:41
  Speaker 1: probably wrong, but it's also really fun. You guys have
• 23:45
  Speaker 1: to make that call all the time. They're like, wow,
• 23:47
  Speaker 1: this is obviously wrong, but it sounds fun. So I'm
• 23:50
  Speaker 1: going to spend the next three months thinking about it. Yeah,
• 23:53
  Speaker 1: it's the idea that we talked about a few weeks ago.
• 23:54
  Speaker 1: It's called primordial black holes. That is, maybe black holes
• 23:58
  Speaker 1: were made not by a collapse of stars, but some
• 24:01
  Speaker 1: of them were made in the very early universe before
• 24:04
  Speaker 1: we even had matter. Like these are called primordial black
• 24:07
  Speaker 1: holes that were formed out of the early energy fluctuations
• 24:10
  Speaker 1: just after the Big Bang. You mean like that, that's
• 24:14
  Speaker 1: just how they form from the primordial soup of the universe.
• 24:17
  Speaker 1: Like they just as the universe expanded and exploded. They're
• 24:20
  Speaker 1: just happened to be some random, you know, blip in
• 24:23
  Speaker 1: the quantum fluctuations that created a big black hole. Yeah,
• 24:26
  Speaker 1: the pictures that you start out with this homogeneous, smooth
• 24:29
  Speaker 1: universe immediately after the Big Bank, then there are quantum fluctuations.
• 24:33
  Speaker 1: Things get a little denser here, a little less dense there,
• 24:36
  Speaker 1: And in places where you happen to have a really
• 24:39
  Speaker 1: big quantum fluctuation, you can get enough energy density to
• 24:42
  Speaker 1: create a black hole. Even before the universe cools enough
• 24:46
  Speaker 1: to make particles, and those particles turned into atoms, and
• 24:48
  Speaker 1: those atoms turned into gas which collect to grow stars
• 24:52
  Speaker 1: and eventually become black holes. You circumvent that whole process
• 24:55
  Speaker 1: and just make a black hole boom right from the
• 24:58
  Speaker 1: get go. So these are called primar real black holes,
• 25:01
  Speaker 1: and we have no idea if they actually exist. We
• 25:03
  Speaker 1: had a really fun podcast about them. But if they do,
• 25:05
  Speaker 1: we expect they exist from the very very small sizes
• 25:09
  Speaker 1: up to really enormous sizes, and so this is one
• 25:12
  Speaker 1: way to get black holes really big in the early universe, right,
• 25:15
  Speaker 1: And that may kind of makes sense to me, But
• 25:18
  Speaker 1: why is it so speculative and why is it such
• 25:20
  Speaker 1: a crazy theory? Well, nobody's ever seen one. We don't
• 25:22
  Speaker 1: know if they're out there. We know the black holes
• 25:24
  Speaker 1: are out there, we know that stars can form black holes,
• 25:26
  Speaker 1: we know there are supermassive black holes, but nobody's ever
• 25:29
  Speaker 1: seen a primordial black hole, I guess. I mean, how
• 25:32
  Speaker 1: how do we know that the supermassive black holes are
• 25:34
  Speaker 1: not primordial black holes. We don't. And it's possible that
• 25:37
  Speaker 1: primordial black holes are the seeds of supermassive black holes.
• 25:41
  Speaker 1: That would explain a lot, but it's a bit too convenient,
• 25:44
  Speaker 1: and the theory is is sort of weird, And we
• 25:46
  Speaker 1: would expect to see primordial black holes sort of at
• 25:48
  Speaker 1: all masses, not just really really big and not just
• 25:51
  Speaker 1: really really small, but also sort of in the intermediate range,
• 25:54
  Speaker 1: and they would be doing stuff that we should be
• 25:56
  Speaker 1: able to see, like sometimes they would pass through a
• 25:58
  Speaker 1: star and cause disturbances on its surface, or sometimes if
• 26:02
  Speaker 1: they were really small, they would decay with hawking radiation
• 26:05
  Speaker 1: in these bright flashes of light at the edge of galaxies,
• 26:08
  Speaker 1: we would expect to see some primordial black holes if
• 26:11
  Speaker 1: they had been around them. We've never seen one, so
• 26:13
  Speaker 1: that makes it a bit awkward. I see, if these
• 26:17
  Speaker 1: came from primordial black holes, we would expect to see
• 26:19
  Speaker 1: more of these primordial black holes floating around, don't But
• 26:22
  Speaker 1: we don't. So maybe only primordial black holes were made
• 26:25
  Speaker 1: on the larger sizes, which is a little bit awkward
• 26:27
  Speaker 1: cosmologically to like come up with a model that only
• 26:30
  Speaker 1: makes really really big primordial black holes, So it gets
• 26:33
  Speaker 1: less and less attractive as an option the more you
• 26:35
  Speaker 1: have to like tweak it and cram it into this box.
• 26:37
  Speaker 1: All right, So then what's another possible reason that we
• 26:40
  Speaker 1: have these massive black holes. Well, it could be that
• 26:43
  Speaker 1: in the very early universe, stars were much bigger than
• 26:46
  Speaker 1: they are today. So you could have had like horses,
• 26:50
  Speaker 1: like courses used to be ginormals the size of a bus. Yeah,
• 26:53
  Speaker 1: horses used to be three hundred times the mass of
• 26:55
  Speaker 1: the sun. It turns out it's a big horse, of course. No,
• 27:01
  Speaker 1: So these days stars are you know, range up to
• 27:04
  Speaker 1: you know, maybe a hundred times the mass of the Sun.
• 27:06
  Speaker 1: But it could be that the very early universe stars
• 27:09
  Speaker 1: were bigger that the first stars, the ones made out
• 27:12
  Speaker 1: of just hydrogen that came out of the Big Bang
• 27:15
  Speaker 1: that had no metals in them, were able to form
• 27:17
  Speaker 1: to be like really big three D four hundred even
• 27:20
  Speaker 1: five hundred times the mass of the Sun. Interesting because
• 27:24
  Speaker 1: just from the from having like the purity of hydrogen,
• 27:27
  Speaker 1: or is it that the conditions of space themselves were different.
• 27:30
  Speaker 1: It's from having the purity of hydrogen. Like if you
• 27:33
  Speaker 1: have heavier stuff around, if you have carbon and nickel
• 27:37
  Speaker 1: and heavier elements around from previous stars, that changes the
• 27:40
  Speaker 1: way the gas is condensed. It makes it easier for
• 27:43
  Speaker 1: gas to cool because you have these heavier elements. That's
• 27:46
  Speaker 1: what's needed for a big blob of gas to turn
• 27:48
  Speaker 1: into the stars that has sort of cool together. If
• 27:50
  Speaker 1: it's hot enough, gravity will never attract it down into clumps, right,
• 27:54
  Speaker 1: It needs to cool enough to form a star. And
• 27:57
  Speaker 1: so if you have all hydrogen, it's harder to cool
• 28:01
  Speaker 1: small clumps, and so they tend to cool in these
• 28:03
  Speaker 1: big blobs, and so you get these really massive early stars.
• 28:07
  Speaker 1: Now nobody's ever seen these. They're called population three stars
• 28:11
  Speaker 1: and they're the very first population of stars in the
• 28:13
  Speaker 1: universe really big, would have burned really fast, wouldn't have
• 28:17
  Speaker 1: lived very long, but they could have then collapsed to
• 28:20
  Speaker 1: form pretty massive black holes like two hundred three hundred
• 28:24
  Speaker 1: times the mass of the Sun, which could form seeds
• 28:27
  Speaker 1: that give us super massive black holes today. WHOA, So
• 28:31
  Speaker 1: we have a hypothetical giant star at the beginning of
• 28:34
  Speaker 1: the universe that somehow becomes a hypothetical medium sized black hole,
• 28:39
  Speaker 1: but then grows to become the super massive black holes
• 28:42
  Speaker 1: we see today. That's right, that's the idea, and it's
• 28:45
  Speaker 1: pretty cool and it makes some sense and you don't
• 28:47
  Speaker 1: have to like invoke any new magic physics or anything.
• 28:50
  Speaker 1: But it's also doesn't quite work. One reason is, like,
• 28:54
  Speaker 1: how many of these could there have been? Like, the
• 28:56
  Speaker 1: theory suggests that we don't expect enough of these to
• 28:59
  Speaker 1: explain all the supermassive black holes that we see. What
• 29:02
  Speaker 1: do you mean you don't see enough? Well, we see
• 29:04
  Speaker 1: a supermassive black hole in the center of every single galaxy,
• 29:07
  Speaker 1: and we don't expect every single proto galaxy to form
• 29:11
  Speaker 1: these supermassive stars like it happens sometimes, but not enough
• 29:15
  Speaker 1: to give us all the supermassive black holes that we
• 29:17
  Speaker 1: see today, So it might explain some fraction of them,
• 29:21
  Speaker 1: but not all of them. And the other problem is
• 29:24
  Speaker 1: that they're not quite big enough. Like three d four
• 29:27
  Speaker 1: hundred times the mass of the sun. That's pretty good.
• 29:29
  Speaker 1: It's better than starting from you know, five times the
• 29:31
  Speaker 1: mass of the sun. But if you start from there,
• 29:34
  Speaker 1: you've got to grow with the maximum rate the entire
• 29:36
  Speaker 1: time to get close to the supermassive black holes. And
• 29:39
  Speaker 1: it's really on the edge. And nobody thinks the black
• 29:42
  Speaker 1: holes can grow at the Eddington limit at the maximum
• 29:46
  Speaker 1: rate their entire lifetime. It requires like exact, delicate balance
• 29:50
  Speaker 1: of gases being fed in just the right way to
• 29:53
  Speaker 1: hit that maximum. So it's kind of precarious. And can
• 29:57
  Speaker 1: you have even bigger stars or is or a limit
• 30:00
  Speaker 1: to how big a star can be? Yeah, we don't
• 30:02
  Speaker 1: think that these population three stars can get much bigger
• 30:05
  Speaker 1: than that, and so that sort of limits the size
• 30:07
  Speaker 1: of those seeds. Right, So then what's the third way
• 30:10
  Speaker 1: in which supermassive black holes can form. Well, the third
• 30:13
  Speaker 1: way is to skip the star formation and say let's
• 30:16
  Speaker 1: have a big blob of gas in the early universe.
• 30:19
  Speaker 1: And let's assume that there's a really like dense blob
• 30:21
  Speaker 1: of dark matter in the center of it. Dark matter.
• 30:24
  Speaker 1: We know there's more dark matter than any other matter
• 30:27
  Speaker 1: in the universe. It's this invisible stuff that's around us,
• 30:30
  Speaker 1: but it has gravity, and it's the most of the
• 30:33
  Speaker 1: gravity in the universe, and so it plays a big
• 30:35
  Speaker 1: role in how stuff clumps together. So if you've got
• 30:38
  Speaker 1: a big blob of dark matter around in this early gas,
• 30:41
  Speaker 1: it could have collapsed a huge blob of stuff down
• 30:44
  Speaker 1: straight to a black hole like skip the whole star
• 30:47
  Speaker 1: step just from the dark matter. Just from the dark matter.
• 30:50
  Speaker 1: I mean, dark matter creates a gravitational well, right, so
• 30:53
  Speaker 1: all this stuff falls into it and it doesn't have
• 30:56
  Speaker 1: the outward pressure of of gas pushing out, and so
• 31:00
  Speaker 1: stuff can just fall in. And if that happens, people
• 31:02
  Speaker 1: have these models where you can form black holes in
• 31:04
  Speaker 1: the very early universe that are already like thousands or
• 31:08
  Speaker 1: tens of thousands of masses of the sun. Oh. I see,
• 31:10
  Speaker 1: like the dark matter gives you that extra boost, like
• 31:13
  Speaker 1: the secret steroid or something. Yeah, you're like no, no, no,
• 31:17
  Speaker 1: dark matter, like the super different high protein diet kind
• 31:21
  Speaker 1: of that's right exactly. I don't recommend the dark matter diet,
• 31:25
  Speaker 1: but you will lose weight. So this gives you higher
• 31:27
  Speaker 1: mass black holes, which is cool. It gets you like
• 31:30
  Speaker 1: further up the ladder, gets you closer. You don't have
• 31:32
  Speaker 1: to grow as much and as aggressively to get to
• 31:35
  Speaker 1: the black holes we see today. But it's also less
• 31:38
  Speaker 1: likely and so these things might happen, but there would
• 31:42
  Speaker 1: be more rare. So they also can't explain all the
• 31:45
  Speaker 1: supermassive black holes that we see out. Why do we
• 31:47
  Speaker 1: think that they're rare? Is in dark matter everywhere? And
• 31:50
  Speaker 1: couldn't these concentrations of dark matter happen all the time? Yes,
• 31:54
  Speaker 1: dark matter is everywhere and there's a lot of it.
• 31:56
  Speaker 1: But to make a big black hole out of a
• 31:59
  Speaker 1: blob of stuff, you need a big fluctuation in the
• 32:01
  Speaker 1: amount of dark matter, and so that's just less likely happened,
• 32:04
  Speaker 1: like in the density of it. Yeah, exactly, it's like
• 32:06
  Speaker 1: a statistical argument. You know, you distribute dark matter randomly
• 32:09
  Speaker 1: through the universe, you're gonna get clumps. How big are
• 32:12
  Speaker 1: those clumps? Well, to get really big clumps, it's going
• 32:14
  Speaker 1: to be less likely. I guess a question I have
• 32:17
  Speaker 1: is if you have a black hole with dark matter
• 32:20
  Speaker 1: in it, the dark matter can leave either. That's right,
• 32:23
  Speaker 1: dark matters also gravitationally bound. Everything is gravitationally bound, neutrinos, photons,
• 32:29
  Speaker 1: dark matter. Because remember, it's not just like a powerful
• 32:33
  Speaker 1: force holding onto you that you could maybe ignore if
• 32:36
  Speaker 1: you're a particle that doesn't have the right charges. It's
• 32:38
  Speaker 1: a shape of space, like inside the black hole. Space
• 32:41
  Speaker 1: is one directional, So if you're inside the black hole,
• 32:44
  Speaker 1: any direction you go brings you closer to the center
• 32:47
  Speaker 1: of the black hole. So it doesn't really matter how
• 32:49
  Speaker 1: fast or strong or weak you are. All right, Now,
• 32:52
  Speaker 1: let's get into how they could possibly grow as much
• 32:56
  Speaker 1: as they are now and if we could ever escape
• 32:59
  Speaker 1: these super mess black holes. But first let's take another
• 33:01
  Speaker 1: quick break. Alright, we're talking about super massive black holes
• 33:17
  Speaker 1: and how they form, which is a big mystery. So
• 33:20
  Speaker 1: the main idea that I guess you're telling me is
• 33:22
  Speaker 1: that maybe super massive black holes started out big. That's right.
• 33:26
  Speaker 1: They were always big. They were always be that's what
• 33:29
  Speaker 1: you're telling me. It's like the baby came out huge,
• 33:32
  Speaker 1: you know, that's why he's so tall. He came out tall. Oh,
• 33:36
  Speaker 1: that's terrifying from the parenting point of view. So there
• 33:40
  Speaker 1: are three possibilities. Maybe they formed huge in the primordial
• 33:43
  Speaker 1: soup of the universe, or maybe they came from really
• 33:47
  Speaker 1: big stars, or maybe dark matter was involved. And so
• 33:50
  Speaker 1: does that mean that they came into being as big
• 33:54
  Speaker 1: as they are now or would they still need to
• 33:56
  Speaker 1: grow some to see what we see now? Well, the
• 33:58
  Speaker 1: black holes that we see now are much bigger than
• 34:01
  Speaker 1: those seeds we just talked about. Those seeds get up
• 34:03
  Speaker 1: to like maybe tens of thousands of times the mass
• 34:06
  Speaker 1: of the sun. The black holes we see out there,
• 34:08
  Speaker 1: they get up to, you know, like five ten billion
• 34:11
  Speaker 1: times the mass of the sun. And so you definitely
• 34:14
  Speaker 1: got to grow it. It's like that's a good seedling.
• 34:17
  Speaker 1: You know, if you're a gardener, you know, it's much
• 34:18
  Speaker 1: harder to get something growing from a little seed up
• 34:21
  Speaker 1: to a big, robust plant. Somebody gives you a seedling
• 34:23
  Speaker 1: than boom, you can just water it and sun it.
• 34:25
  Speaker 1: You have something giving you tomatoes, it's already going. Yeah,
• 34:29
  Speaker 1: it's already going. And so these are basically like black
• 34:32
  Speaker 1: hole seedlings, but you still got to grow them to
• 34:34
  Speaker 1: get them as big as the stuff that we see
• 34:36
  Speaker 1: and is there a mystery there or you know, if
• 34:39
  Speaker 1: you if you start with like a ten thousand solar
• 34:42
  Speaker 1: mass black hole, can you get up to those billions
• 34:45
  Speaker 1: of super massive black holes? You can? But it's hard,
• 34:48
  Speaker 1: like you gotta really ride the edge. You know. These
• 34:51
  Speaker 1: are questions that are not like physical limits. It's not
• 34:53
  Speaker 1: like there's some reason why a black hole can't get
• 34:56
  Speaker 1: any bigger. In fact, there's no theoretical limit on the
• 34:59
  Speaker 1: size of a black hole, but there are sort of
• 35:01
  Speaker 1: environmental limits, Like you need to create the situation where
• 35:05
  Speaker 1: a black hole has the stuff it needs to eat,
• 35:07
  Speaker 1: because tends to just like gobble of stuff around it
• 35:09
  Speaker 1: and then push the stuff away. So that's this balance
• 35:12
  Speaker 1: we were talking about earlier, right, because black holes emit
• 35:15
  Speaker 1: a lot of radiation and sort of in all directions,
• 35:18
  Speaker 1: pushing away from themselves the stuff that they would need
• 35:20
  Speaker 1: to eat to get bigger. Right, And also like you know,
• 35:23
  Speaker 1: if it has to eat that much, where does it
• 35:25
  Speaker 1: get all that food? Like if a black hole is
• 35:28
  Speaker 1: ten million times the size of the Sun, it has
• 35:30
  Speaker 1: to eat ten million sons. Yeah, precisely, And for example,
• 35:33
  Speaker 1: the black hole the center of our galaxy, how much
• 35:36
  Speaker 1: bigger could it get. It could only get about a
• 35:38
  Speaker 1: thousand times bigger, because that's all the mass that's in
• 35:42
  Speaker 1: our galaxy. If it ate every single star and blob
• 35:45
  Speaker 1: of stuff in the galaxy, that would only give it
• 35:47
  Speaker 1: a factor of a thousand. So if you see a
• 35:50
  Speaker 1: black hole out there that's a million or a billion
• 35:53
  Speaker 1: times the size of the Sun, that means it it
• 35:56
  Speaker 1: ate that much. And so you know, I like, how
• 35:59
  Speaker 1: much big or what's the galaxy? He sounds so judgmental,
• 36:02
  Speaker 1: like somebody who you know, had to pop their bells
• 36:04
  Speaker 1: after dinner, like, hey man, you shouldn't have had that
• 36:06
  Speaker 1: sixth plate. I think if you eat a few billion sons, Yeah, yeah, exactly.
• 36:15
  Speaker 1: And it's just sort of hard to arrange the stuff
• 36:18
  Speaker 1: and the right conveyor belt to get it there. And
• 36:20
  Speaker 1: so they've calculated what is the maximum effective rate that
• 36:23
  Speaker 1: a black hole can grow. It's called this Eddington limit,
• 36:26
  Speaker 1: and it's possible to sometimes have what they call super
• 36:30
  Speaker 1: Eddington growth, but only very very briefly. And it's because
• 36:34
  Speaker 1: the radiation that increases a lot and blows out the gas.
• 36:36
  Speaker 1: The highest stable rate requires a special configuration. You've got
• 36:40
  Speaker 1: to have just the right amount of cold gas falling
• 36:42
  Speaker 1: into the black hole and just the right way. It's
• 36:44
  Speaker 1: a bit tricky to arrange. Instead of get these seedlings
• 36:48
  Speaker 1: up to the massive black holes that we see today,
• 36:51
  Speaker 1: requires a sort of unusual, unlikely arrangement of stuff to
• 36:55
  Speaker 1: fall into the black hole at just the right rate,
• 36:58
  Speaker 1: like perfectly funnel into it with causing a big message. Yeah.
• 37:02
  Speaker 1: And you know another way these things can get bigger
• 37:04
  Speaker 1: is by merging, Like you can merge two galaxies. Two
• 37:07
  Speaker 1: galaxies collides because you know, on the scale of like
• 37:09
  Speaker 1: the universe, each galaxy is like a dot, and you
• 37:12
  Speaker 1: can think of it like a particle and a gas
• 37:14
  Speaker 1: flying around, and occasionally they get close to each other
• 37:16
  Speaker 1: and they emerge, like our galaxy the Milky Way is
• 37:19
  Speaker 1: going to merge with Andromeda in a few billion years.
• 37:22
  Speaker 1: And Andromeda's black holes even bigger than hours. It's like
• 37:25
  Speaker 1: dwarfs our black hole. And and so these two things
• 37:29
  Speaker 1: are going to collide, and eventually those two black holes
• 37:31
  Speaker 1: in the center will spiral around each other and via
• 37:34
  Speaker 1: the emission of gravitational waves, become one and so will
• 37:37
  Speaker 1: become an even bigger black hole. Wow. I guess one
• 37:41
  Speaker 1: curious question I have is um, you know, why do
• 37:43
  Speaker 1: we see them at the center of galaxies? Like, you
• 37:46
  Speaker 1: never see a supermassive black hole not inside of a galaxy,
• 37:50
  Speaker 1: do you know? You don't. And the reason is that
• 37:52
  Speaker 1: they need stuff to grow. Like if you had the
• 37:55
  Speaker 1: seed of a supermassive black hole just out there in
• 37:57
  Speaker 1: the middle of the universe, it couldn't grow. It's got
• 38:00
  Speaker 1: to be surrounded by stuff. That's why there's like a
• 38:02
  Speaker 1: correlation between the size of the supermassive black hole and
• 38:05
  Speaker 1: the size of the galaxy. Bigger galaxies have bigger black
• 38:09
  Speaker 1: holes at their centers just because there's more fuel for
• 38:12
  Speaker 1: them to eat, and smaller galaxies have smaller black holes
• 38:15
  Speaker 1: because there's less fuel for them to eat. And so
• 38:18
  Speaker 1: it makes sense, But it sounds sort of like a coincidence.
• 38:21
  Speaker 1: Almost did these supermassive black holes? Are they one of
• 38:25
  Speaker 1: the reasons the galaxy form? Or is it sort of
• 38:28
  Speaker 1: a coincidence that you've got of galaxy forming and you
• 38:32
  Speaker 1: also had a seedling for a massive black hole in
• 38:34
  Speaker 1: the middle, and so that's why you have them in
• 38:36
  Speaker 1: the middle of galaxies. I think it's the opposite. I
• 38:38
  Speaker 1: think that larger galaxies are going to form supermassive black
• 38:42
  Speaker 1: holes just because they have the fuel around. And so
• 38:44
  Speaker 1: I think if you take a big distribution of galaxies
• 38:47
  Speaker 1: of different sizes and you put a seedling at the
• 38:49
  Speaker 1: center of each one of them, the larger galaxies will
• 38:52
  Speaker 1: grow their black holes faster, and we'll get to bigger sizes. Oh,
• 38:55
  Speaker 1: I see, So galaxies form for other reasons. But they
• 38:58
  Speaker 1: all sort had a sprinkle of super massive black holes,
• 39:02
  Speaker 1: the seeds of super massive black holes, And so the
• 39:05
  Speaker 1: seeds that fell and the larger galaxies got bigger. Yeah,
• 39:08
  Speaker 1: and the galaxies formed because actually of dark matter, right,
• 39:11
  Speaker 1: dark matter forms these gravitational wells somewhere out there. Dark
• 39:15
  Speaker 1: matter is not just smoothly distributed through the universe like
• 39:18
  Speaker 1: some soup. It's got blobs and and chunks to it,
• 39:21
  Speaker 1: and galaxies form in those blobs and chunks. It's the
• 39:24
  Speaker 1: reason we have galaxies. If you delete dark matter from
• 39:27
  Speaker 1: the universe, you don't even get galaxies by ten billion years.
• 39:30
  Speaker 1: You've gotta wait a lot longer for gravity to pull
• 39:33
  Speaker 1: just the normal matter together. So the reason you have
• 39:35
  Speaker 1: these galaxies and those seed things together is because the
• 39:38
  Speaker 1: dark matter sort of like forming the pot in which
• 39:40
  Speaker 1: all this stuff is growing, all right, and all that
• 39:43
  Speaker 1: points are kind of a maximum size of black holes.
• 39:45
  Speaker 1: You're saying that the maximum size that a black hole
• 39:49
  Speaker 1: can be is about ten billion sons. Yeah, so why
• 39:52
  Speaker 1: is it? Is it just because we don't see galaxies
• 39:55
  Speaker 1: that are bigger than ten billion times the mass of
• 39:57
  Speaker 1: our sun? Yeah, it's not a theoretical limit, right, could
• 40:00
  Speaker 1: in principle form a black hole that's larger. But if
• 40:02
  Speaker 1: you ask, like, what's the largest size black hole we
• 40:05
  Speaker 1: expect to exist in the universe right now, given the
• 40:08
  Speaker 1: time they've had to form in the size of galaxies,
• 40:11
  Speaker 1: then we think that's about ten billion times the mass
• 40:13
  Speaker 1: of the Sun. So it's an environmental limit, not a
• 40:16
  Speaker 1: fundamental limit. And these biggest black holes, the ones that
• 40:20
  Speaker 1: are like billions of times of the mass of the Sun,
• 40:23
  Speaker 1: we see them in galaxies that have very little gas
• 40:26
  Speaker 1: means they've already sucked up most of the fuel. Okay,
• 40:29
  Speaker 1: so the ones that are smaller have more fuel around them,
• 40:32
  Speaker 1: they still have a place to grow, and so there's
• 40:35
  Speaker 1: not really much more room for them to grow unless
• 40:37
  Speaker 1: they merge with another supermassive black hole. Could you have
• 40:40
  Speaker 1: had like a really big galaxy you know, could you
• 40:43
  Speaker 1: have formed a really much bigger galaxy or is that rare? Yeah,
• 40:47
  Speaker 1: that's a really fun idea. You know. It's a question
• 40:48
  Speaker 1: of like how big could a galaxy get? And remember
• 40:52
  Speaker 1: we talked about this in our episode last week about
• 40:54
  Speaker 1: the sort of structure formation of the universe. Things sort
• 40:56
  Speaker 1: of form bottom up and clump together, and there's a
• 41:00
  Speaker 1: balanced there between like the initial velocity of this stuff
• 41:03
  Speaker 1: and the gravity to pull it together. And so space
• 41:06
  Speaker 1: is expanding and pulling stuff apart, and things have velocities
• 41:10
  Speaker 1: which prevent them from clumping together and this gravity pulling
• 41:13
  Speaker 1: stuff together. So what limits sort of the size of
• 41:16
  Speaker 1: the galaxy is just like how much stuff you can
• 41:18
  Speaker 1: get together in a gravitational well before dark energy takes
• 41:22
  Speaker 1: over and starts pulling things apart. And so we think
• 41:24
  Speaker 1: that there is a limit to how big galaxies could
• 41:27
  Speaker 1: have gotten in the early universe. I see, which then
• 41:29
  Speaker 1: limits the black hole. It does unfortunately, I know, thankfully,
• 41:33
  Speaker 1: I guess maybe. I mean, if you were that black hole,
• 41:36
  Speaker 1: you probably want to get bigger, or maybe you'd be like,
• 41:39
  Speaker 1: thank you for putting that stuff away in the fridge
• 41:41
  Speaker 1: so I don't eat too much. Yeah, you know, like,
• 41:44
  Speaker 1: we'll slow down there, you know, I think you've had enough.
• 41:48
  Speaker 1: You know, limits are good? All right? Well, um, so
• 41:51
  Speaker 1: that's a big mystery, I guess. And and do we
• 41:53
  Speaker 1: do we have to worry about these super massive black holes,
• 41:55
  Speaker 1: like are they dangerous or maybe they help galaxies actually
• 41:59
  Speaker 1: stay together? They do help galaxy stay together. And there
• 42:02
  Speaker 1: is one really big one at the center of our galaxy.
• 42:05
  Speaker 1: You know, it's like four million times the mass of
• 42:07
  Speaker 1: the Sun, which is big and incredible, but on the
• 42:10
  Speaker 1: scale of supermassive black holes, not that big. And it's
• 42:14
  Speaker 1: like sixty million kilometers in diameter, which again seems massive,
• 42:19
  Speaker 1: but compared to other black holes, is really not that large.
• 42:22
  Speaker 1: For a black hole, the size of it, the distance
• 42:25
  Speaker 1: from the center to the event horizon, grows linearly with mass,
• 42:29
  Speaker 1: so you're like, you double the amount of stuff in it,
• 42:31
  Speaker 1: the radius gets twice as big, which weirdly means they're
• 42:34
  Speaker 1: not actually that dense. Like a supermassive black hole has
• 42:38
  Speaker 1: about the density of water. What you mean where the
• 42:42
  Speaker 1: event horizon starts, Yeah, exactly, Like all the stuff contained
• 42:46
  Speaker 1: in the black hole, divided by the volume of the
• 42:48
  Speaker 1: black hole has about the density of water and it's
• 42:51
  Speaker 1: incredible amount of gravity because it's just so much stuff.
• 42:55
  Speaker 1: But when you double the amount of stuff inside your
• 42:58
  Speaker 1: black hole, you double the radius, which makes the volume
• 43:01
  Speaker 1: go up by a factor of eight, and so the
• 43:03
  Speaker 1: density actually goes down. So the largerer black hole, the
• 43:06
  Speaker 1: less the density. It's like dark waters. I don't recommend
• 43:10
  Speaker 1: drinking it. You know, get one of those filters or something.
• 43:13
  Speaker 1: But in our galaxy, the black hole doesn't eat a
• 43:15
  Speaker 1: star that often. It's like every ten thousand years or
• 43:18
  Speaker 1: so a star will get sucked into the black hole.
• 43:20
  Speaker 1: It's pretty rare really. Mostly it's just sitting there. But
• 43:24
  Speaker 1: is it Is it eating gas? Like, are there funnels
• 43:26
  Speaker 1: of gas going in? There are funnels of gas that
• 43:28
  Speaker 1: it's still eating. But you know, the stars are mostly
• 43:31
  Speaker 1: in stable orbits. The ones that we're going to fall
• 43:33
  Speaker 1: in have mostly fallen in, just like our Earth is
• 43:36
  Speaker 1: in mostly a stable orbit around the Sun. We don't
• 43:38
  Speaker 1: expect to fall into the Sun at any time soon. Now,
• 43:42
  Speaker 1: something could come along and disturb our orbit and give
• 43:44
  Speaker 1: us a bump, and then we fall into the Sun.
• 43:46
  Speaker 1: The same way. If two stars collide, one of them
• 43:48
  Speaker 1: could end up getting gobbled up by the black hole.
• 43:51
  Speaker 1: But mostly the star is going to escape the black hole.
• 43:53
  Speaker 1: They're just gonna be in orbit around it for a
• 43:55
  Speaker 1: long long time. And you can think like, well, what
• 43:57
  Speaker 1: about in ten trillion years, like do those orbits eventually
• 44:01
  Speaker 1: decay because of interactions with interstellar medium? But you know,
• 44:05
  Speaker 1: we don't know the future of dark energy or anything
• 44:07
  Speaker 1: for ten trillion years, so it's pretty hard to imagine
• 44:09
  Speaker 1: what's going to happen that far into the future. Right,
• 44:12
  Speaker 1: to think of black holes as pretty scary, But if
• 44:14
  Speaker 1: you think about it, our sun is also pretty scary.
• 44:16
  Speaker 1: You don't want to fall into the sun either. Our
• 44:18
  Speaker 1: sun is pretty scary, and the center of our Earth
• 44:20
  Speaker 1: is also scary. You don't want to get down there.
• 44:23
  Speaker 1: Anything that's got a lot of gravity is pretty intense
• 44:26
  Speaker 1: situation and you know, a good place to avoid. Yeah,
• 44:29
  Speaker 1: you don't want to take that situation too lightly. You know,
• 44:31
  Speaker 1: it's pretty massive, going to give it the right amount
• 44:33
  Speaker 1: of gravity? All right, Well that's the mystery of super
• 44:37
  Speaker 1: massive black holes. How do they form so big? How
• 44:40
  Speaker 1: big were they when there were babies? Nobody knows? And
• 44:43
  Speaker 1: who's been feeding them secretly at the maximum possible woman, No,
• 44:48
  Speaker 1: it's like a fun question like how big could a
• 44:50
  Speaker 1: tree get if you fit it at just the right rate,
• 44:52
  Speaker 1: or with the largest cucumber or pumpkin you could grow
• 44:55
  Speaker 1: in your backyard before like implodes into a pumpkin black hole? Right, yeah,
• 45:00
  Speaker 1: because it's kind of weird to think that things can
• 45:03
  Speaker 1: scale like that, you know, like you could have a
• 45:05
  Speaker 1: technically a giant pumpkin, like just like once we had
• 45:07
  Speaker 1: giant horses running around, that's right. And if you google
• 45:11
  Speaker 1: giant pumpkin, you will be amazed at the size of
• 45:14
  Speaker 1: these gourds that people actually can't throw in their backyards
• 45:17
  Speaker 1: or in their farms. It's impressive. Could one of these
• 45:19
  Speaker 1: collapse into a black hole? Daniel, I think we're pretty safe,
• 45:23
  Speaker 1: all right. Well, we hope you enjoyed that. And the
• 45:25
  Speaker 1: next time you look out into the universe once again,
• 45:28
  Speaker 1: remember the big mysteries that are out there, and even
• 45:31
  Speaker 1: the super massive mysteries. That's right, The biggest things out
• 45:35
  Speaker 1: there in the universe are things that are not yet understood.
• 45:37
  Speaker 1: Scientists are working on this, their eyes puzzled about it
• 45:40
  Speaker 1: as we are, which means that their curiosity is your curiosity.
• 45:44
  Speaker 1: And it also means that somebody out there, maybe you,
• 45:47
  Speaker 1: maybe your kids will be the person to unravel the
• 45:50
  Speaker 1: mystery of super massive black holes. That would be super
• 45:53
  Speaker 1: massively cool. So thanks for joining us, See you next time. Yea,
• 46:04
  Speaker 1: thanks for listening, and remember that Daniel and Jorge Explain
• 46:07
  Speaker 1: the Universe is a production of I Heart Radio. For
• 46:10
  Speaker 1: more podcast for my heart Radio, visit the I Heart
• 46:13
  Speaker 1: Radio Apple Apple Podcasts, or wherever you listen to your
• 46:17
  Speaker 1: favorite shows.