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Do all galaxies have central black holes? · Daniel and Kelly’s Extraordinary Universe

• 0:08
  Speaker 1: Hey, Daniel, have you started planning for your retirement retirement?
• 0:13
  Speaker 2: Why would I ever retire?
• 0:14
  Speaker 1: I mean, you're gonna be a physicist forever to you're
• 0:16
  Speaker 1: dying breath.
• 0:18
  Speaker 2: I don't see myself burning out of questions.
• 0:20
  Speaker 1: Well, I guess eventually the Sun is gonna expand blow
• 0:23
  Speaker 1: up and burn the Earth, right, so at some point you.
• 0:26
  Speaker 2: Have to stop. I guess so, And eventually the galaxy
• 0:29
  Speaker 2: will collapse into a black hole. But that doesn't mean
• 0:31
  Speaker 2: we have to stop.
• 0:33
  Speaker 1: You're gonna be doing physics inside of the black hole.
• 0:37
  Speaker 2: Absolutely, I'll be writing papers about the singularity that nobody
• 0:40
  Speaker 2: can ever read.
• 0:41
  Speaker 1: Oh, because you're inside the black hole, right, unless I'm
• 0:45
  Speaker 1: like closer to the center, in which case you could
• 0:47
  Speaker 1: still technically send me the paper.
• 0:49
  Speaker 2: Yeah, and I could never get your comments back. Hey,
• 0:51
  Speaker 2: that sounds pretty good.
• 0:52
  Speaker 1: Actually, it's a win win situation or a lose lose situation.
• 0:57
  Speaker 1: It's a wind lose wind loose situation.
• 0:58
  Speaker 2: I'll be waiting for pure you literally forever.
• 1:17
  Speaker 3: Hi.
• 1:17
  Speaker 1: I'm Jorge, cartoonist and the creator of PhD comics.
• 1:20
  Speaker 2: Hi. I'm Daniel. I'm a particle physicist and a professor
• 1:23
  Speaker 2: at UC Irvine, and I do plan on doing this.
• 1:25
  Speaker 1: Forever, forever, even after your death.
• 1:30
  Speaker 2: I'm hoping my ideas live on.
• 1:32
  Speaker 1: Are you going to program an AI to do research
• 1:35
  Speaker 1: for you and make your children feel guilty after you're gone.
• 1:40
  Speaker 2: I'm going to upload my intelligence into the cloud so
• 1:43
  Speaker 2: I can continue to live as some sort of weird
• 1:45
  Speaker 2: mixture between biological and mechanical intelligence. But even that eventually
• 1:50
  Speaker 2: will fall into the galactic center and be gobbled up
• 1:52
  Speaker 2: by the black hole.
• 1:53
  Speaker 1: M But I guess why wait? I mean we could
• 1:56
  Speaker 1: technically generate this podcast with AI right now.
• 1:58
  Speaker 2: Can How do you know we haven't already? Who do
• 2:01
  Speaker 2: you think he's writing these outlines? Oh? My god?
• 2:03
  Speaker 1: Am I talking to an AI right now?
• 2:06
  Speaker 2: Maybe I'm talking to an AI right now? Maybe AI
• 2:09
  Speaker 2: are listening to this podcast.
• 2:10
  Speaker 1: He did seem smarter than usual.
• 2:12
  Speaker 2: That's the real Daniel.
• 2:15
  Speaker 1: And the real Danger. But anyways, welcome to our podcast
• 2:18
  Speaker 1: Daniel and Jorge Explain the Universe, a production of our
• 2:21
  Speaker 1: Heart Radio.
• 2:22
  Speaker 2: In which we use are still limited biological intelligence to
• 2:26
  Speaker 2: try to understand how the universe works. We want to
• 2:29
  Speaker 2: know everything that's out there. We want to know how
• 2:32
  Speaker 2: it works on the microscopic scale, to weave itself together
• 2:35
  Speaker 2: into reality that we experience and that we want to understand.
• 2:40
  Speaker 2: We cast our minds out into the farthest reaches of
• 2:42
  Speaker 2: space and hope to understand what they might encounter out there.
• 2:46
  Speaker 1: That's right, because it is a very perplexing universe full
• 2:49
  Speaker 1: of interesting mysteries for us to go out there explore
• 2:52
  Speaker 1: and try to uncover, and try to understand and try
• 2:55
  Speaker 1: to explain to others.
• 2:56
  Speaker 2: Some mysteries have lasted for decades or centuries or millennia,
• 3:00
  Speaker 2: but others have succumbed to the onslaught of human intelligence.
• 3:03
  Speaker 2: We have sometimes actually managed to crack puzzles of the
• 3:07
  Speaker 2: universe and understand what's going on at the atomic scale
• 3:11
  Speaker 2: or the subatomic scale, or how space bends to form
• 3:14
  Speaker 2: black holes. So there are times when our limited intelligence
• 3:17
  Speaker 2: is enough.
• 3:18
  Speaker 1: Why I make it sound like we're masters of the universe?
• 3:21
  Speaker 1: How far along are we are? We up to like
• 3:23
  Speaker 1: one percent of the universe by now.
• 3:25
  Speaker 2: I think that's probably a pretty generous estimate. But it's promising.
• 3:29
  Speaker 2: You know, we are making progress and we are understanding things,
• 3:32
  Speaker 2: and the understanding is coming faster and faster. So far,
• 3:36
  Speaker 2: there's no evidence that we're going to hit some wall
• 3:38
  Speaker 2: of understanding.
• 3:39
  Speaker 1: Especially with the AIS. Could we train AIS or just
• 3:42
  Speaker 1: ask AIS to do research for us?
• 3:44
  Speaker 2: I use AIS in my research all the time. We
• 3:46
  Speaker 2: have AIS answering questions. The big challenge is understanding what
• 3:49
  Speaker 2: they're doing. Are they doing physics for themselves or are
• 3:52
  Speaker 2: they doing it for us?
• 3:54
  Speaker 1: What do you mean for themselves? Like for their own curiosity?
• 3:58
  Speaker 1: Oh my god, are yet that already?
• 4:00
  Speaker 2: Well? We have AIS generating YouTube videos that are mostly
• 4:03
  Speaker 2: watched by other AIS to generate response videos, and now
• 4:07
  Speaker 2: we have AIS generating physics research, and at some point
• 4:10
  Speaker 2: AIS are going to be reading that physics research and
• 4:12
  Speaker 2: summarizing it for themselves.
• 4:15
  Speaker 1: Huh. So I wonder if the AI science community is
• 4:17
  Speaker 1: going to have as much politics and drama as the
• 4:20
  Speaker 1: real physics community, or maybe even more right, more drama.
• 4:25
  Speaker 1: But it's all artificial drama.
• 4:26
  Speaker 2: So all drama is artificial, and.
• 4:31
  Speaker 1: It happens faster, I guess, which is good.
• 4:33
  Speaker 2: Though there might be some real drama going on at
• 4:35
  Speaker 2: the center of our galaxy, as the black hole there
• 4:39
  Speaker 2: keeps sucking things in that's swirling around it.
• 4:42
  Speaker 1: Yes, we discussed on this podcast. There's a lot going
• 4:44
  Speaker 1: on at the center of galaxies, including some very big mysteries.
• 4:48
  Speaker 2: That's right, as we peer towards the center of our
• 4:51
  Speaker 2: own galaxy, we notice a very very large black hole
• 4:54
  Speaker 2: sitting there, gobbling up anything that comes near it, and
• 4:58
  Speaker 2: while we are safely swirling around it at tens of
• 5:01
  Speaker 2: thousands of light years away, eventually we think that everything
• 5:05
  Speaker 2: might fall into that black hole, flush down, the gravitational.
• 5:09
  Speaker 1: Drain down physics toilet? Is that really the case? Eventually? Like,
• 5:14
  Speaker 1: there's no prediction where we don't get sucked into that
• 5:16
  Speaker 1: black hole.
• 5:16
  Speaker 2: There are some variations. If the universe keeps expanding at
• 5:20
  Speaker 2: a faster and faster rate and something called phantom energy
• 5:23
  Speaker 2: takes over and creates enough space between us and the
• 5:26
  Speaker 2: central black hole to distance us from it. But if
• 5:29
  Speaker 2: dark energy stays at the level that it is, the
• 5:31
  Speaker 2: prediction is that the universe ends up with a bunch
• 5:33
  Speaker 2: of isolated galaxies, each of which collapse into their own
• 5:37
  Speaker 2: black holes.
• 5:38
  Speaker 1: Wait wait, wait, did you just say phantom energy.
• 5:40
  Speaker 2: Phantom energy exactly like.
• 5:44
  Speaker 4: The Phantom Menace named after that movie exactly. Not a coincidence,
• 5:48
  Speaker 4: m I guess we'll have to dig into that in
• 5:50
  Speaker 4: another episode. But it is interesting how as you said
• 5:53
  Speaker 4: that every galaxy has a black hole.
• 5:56
  Speaker 2: It is pretty cool to have a black hole the
• 5:58
  Speaker 2: center of our galaxy, and it makes us wonder if
• 6:00
  Speaker 2: that required for every galaxy. Is that a necessary product
• 6:04
  Speaker 2: of a galaxy? Do you have to have a black
• 6:06
  Speaker 2: hole to form a galaxy? Do galaxies form black holes?
• 6:09
  Speaker 2: Do black holes create galaxies?
• 6:11
  Speaker 1: It's a deep question, and so today on the podcast
• 6:14
  Speaker 1: we'll be asking the question, does every galaxy have a
• 6:22
  Speaker 1: black hole at its center? You mean, like like a
• 6:25
  Speaker 1: tasty snack or something like are there any defective galaxies
• 6:30
  Speaker 1: that they didn't get a black hole in the middle?
• 6:32
  Speaker 2: You mean, like you'd be disappointed to bite into a
• 6:34
  Speaker 2: galaxy and be like, oh, I didn't get a black
• 6:36
  Speaker 2: hole in the middle.
• 6:37
  Speaker 1: I know, that's the tastiest part. It's got the richest flavor.
• 6:41
  Speaker 2: So deep. That's interesting because black holes have mass, but
• 6:44
  Speaker 2: I wonder if they actually have calories. Like if you
• 6:45
  Speaker 2: eat a black hole, do you lose weight?
• 6:47
  Speaker 1: Or is the secret to a new diet?
• 6:50
  Speaker 2: I guess really the black hole eats you and it
• 6:52
  Speaker 2: gains weight, so you become part of the black hole.
• 6:55
  Speaker 1: Something gets eaten and it's you, which I guess is
• 6:59
  Speaker 1: a diet in a way you lose a lot more
• 7:02
  Speaker 1: than weight.
• 7:02
  Speaker 2: Though, definitely do not take health advice from either of us.
• 7:06
  Speaker 1: That's right, from either physicist or cartoonists, not the healthiest
• 7:10
  Speaker 1: people in the world or the universe.
• 7:12
  Speaker 2: We are totally unqualified to dispense health advice. I know
• 7:15
  Speaker 2: that doesn't stop most podcasters, but it does give us pause.
• 7:18
  Speaker 1: So, yeah, this is an interesting question. Does every galaxy
• 7:22
  Speaker 1: have a black hole at its center? I guess a
• 7:24
  Speaker 1: lot of galaxies have black holes at their centers.
• 7:26
  Speaker 2: We certainly have seen a black hole in the center
• 7:28
  Speaker 2: of our galaxy and a few others. But it's a
• 7:31
  Speaker 2: really interesting question both about how black holes get formed
• 7:34
  Speaker 2: and how galaxies get formed. It seems like there's a
• 7:37
  Speaker 2: fascinating dance between the two.
• 7:39
  Speaker 1: I guess. Kind of the deeper question is like, do
• 7:41
  Speaker 1: you need to have a black hole at the center
• 7:44
  Speaker 1: to have a galaxy?
• 7:45
  Speaker 2: Yeah? Exactly does it count as a galaxy if it's
• 7:47
  Speaker 2: just a bunch of stars?
• 7:49
  Speaker 1: So, as usual, we were wondering how many people have
• 7:51
  Speaker 1: asked this question, whether every galaxy has a black hole?
• 7:54
  Speaker 1: So Daniel went out there into the wilds of the
• 7:56
  Speaker 1: internet to ask folks, does every galaxy a black hole
• 8:00
  Speaker 1: at its center.
• 8:01
  Speaker 2: Thanks very much, my enduring gratitude to everybody who participates
• 8:04
  Speaker 2: in this segment. But remember it's open to everyone. If
• 8:08
  Speaker 2: you've been listening to pod and learning for years and
• 8:10
  Speaker 2: feel ready to answer a random questions, please don't be shy.
• 8:15
  Speaker 2: Write to me two questions at Danielandjorge dot com. We
• 8:18
  Speaker 2: want to hear from you.
• 8:19
  Speaker 1: So think about it for a second. You think every
• 8:22
  Speaker 1: galaxy has a black hole. Here's what people had to say.
• 8:26
  Speaker 5: Man, who knows if black holes even exist? Like, what
• 8:29
  Speaker 5: if they're just all dark stars like you guys talked
• 8:33
  Speaker 5: about earlier on the show. There could be wormholes or
• 8:36
  Speaker 5: something that we haven't even thought of yet. So no,
• 8:39
  Speaker 5: not all galaxies.
• 8:40
  Speaker 6: A galaxy is a cluster of a bunch of objects
• 8:44
  Speaker 6: in space swirling around a massive object in the middle.
• 8:48
  Speaker 6: And the only massive object you can have is a
• 8:50
  Speaker 6: black hole or a store I guess, and you can't
• 8:53
  Speaker 6: have such a big star. So I think every galaxy
• 8:56
  Speaker 6: has to have a black hole in the middle.
• 8:58
  Speaker 3: Probably there's got to be something like holding it all together.
• 9:03
  Speaker 3: But sence space is really big. Maybe there's some galaxies
• 9:07
  Speaker 3: that don't and they're just like really dense packed like
• 9:12
  Speaker 3: stars spinning around each other.
• 9:15
  Speaker 2: I would guess that just because you're asking the question,
• 9:18
  Speaker 2: the answer is no, But I don't know. I would
• 9:22
  Speaker 2: for you guys to explain it to me.
• 9:24
  Speaker 1: All Right, some people we have some conspiracy theories, apparently
• 9:28
  Speaker 1: as listeners, some galactic conspiracy theorists.
• 9:31
  Speaker 2: Well, we are guilty of promoting those black hole conspiracy
• 9:34
  Speaker 2: theories right when we talk on the podcast about how
• 9:36
  Speaker 2: black holes might be dark stars or fuzzballs or something else.
• 9:40
  Speaker 2: Even weirder, are you seen?
• 9:41
  Speaker 1: We're ground Sero or the black hole ism movement.
• 9:45
  Speaker 2: Black hole truthers. Yeah, this is the dark Horse podcast
• 9:48
  Speaker 2: for black holes exactly.
• 9:50
  Speaker 1: Maybe if we switched our podcast name to like universal
• 9:53
  Speaker 1: conspiracies or conspiracies about everything, maybe our ranking will go up.
• 9:59
  Speaker 2: It might go up, we might get a bigger audience.
• 10:00
  Speaker 2: But I don't think we'd get a better audience.
• 10:04
  Speaker 1: I mean, isn't physics, after all, just like the Hunt
• 10:07
  Speaker 1: for the Conspiracy.
• 10:08
  Speaker 2: Of the Universe.
• 10:10
  Speaker 1: You're like, there's something going on here, There's some sort
• 10:14
  Speaker 1: of plan or structure. We got to find out what
• 10:17
  Speaker 1: it is. We got to find out the truth. Man,
• 10:19
  Speaker 1: Isn't that what physics is all about.
• 10:20
  Speaker 2: Yeah, but conspiracies are usually built on wild speculation and
• 10:23
  Speaker 2: a lack of evidence.
• 10:25
  Speaker 1: Isn't that every other episode we discussed on the podcast.
• 10:29
  Speaker 2: Yeah, but we don't trust strong conclusions based on our
• 10:32
  Speaker 2: lack of knowledge. We talk about what we don't know
• 10:34
  Speaker 2: and how we might actually figure it out. We're trying
• 10:37
  Speaker 2: to build evidence. We're looking for data when we're happy
• 10:40
  Speaker 2: to disprove our ideas if the universe shows us we're wrong.
• 10:43
  Speaker 1: It sounds like something someone involved in a conspiracy would say.
• 10:46
  Speaker 2: And you've just proven that you can make a conspiracy
• 10:48
  Speaker 2: about anything with no information.
• 10:50
  Speaker 1: But anyways, this is an interesting question. Does every galaxy
• 10:52
  Speaker 1: have a black hole at its center? And, as you said,
• 10:55
  Speaker 1: there is one at the center of our galaxy. The
• 10:57
  Speaker 1: last podcast were recorded talked about how there's a big
• 11:00
  Speaker 1: one at the center of our galaxy, along with a
• 11:02
  Speaker 1: whole bunch of other stuff going on down there.
• 11:04
  Speaker 2: We certainly think that there is a black hole at
• 11:07
  Speaker 2: the center of our galaxy.
• 11:08
  Speaker 1: What do you say, we think?
• 11:09
  Speaker 2: Yeah, we don't really ever know for sure. I mean,
• 11:12
  Speaker 2: our galactic center is the one that's closest to us,
• 11:14
  Speaker 2: so it's easiest to study. It's also shrouded in gas
• 11:17
  Speaker 2: and dust, so it's complicated to study, and in the end,
• 11:20
  Speaker 2: all of our evidence for black holes is always a
• 11:23
  Speaker 2: little bit indirect. Usually the observations tell us that there's
• 11:27
  Speaker 2: something there that's very massive, something that's very small and
• 11:31
  Speaker 2: also has a lot of gravity, but we've never actually
• 11:34
  Speaker 2: observed an event horizon directly. It's always a little bit indirect.
• 11:39
  Speaker 1: I guess it's kind of hard to see a black
• 11:40
  Speaker 1: hole because they don't emit light themselves.
• 11:42
  Speaker 2: They might emit light. There might be gentle hawking radiation
• 11:46
  Speaker 2: from black holes, which would be very powerful direct evidence
• 11:48
  Speaker 2: for black holes, but that's not something we've ever seen.
• 11:51
  Speaker 2: The story of black holes for the last few decades
• 11:53
  Speaker 2: is an increasing belief that black holes probably are real.
• 11:57
  Speaker 2: As we identify these very massive objects and we put
• 11:59
  Speaker 2: limits on how big they can be, we see things
• 12:02
  Speaker 2: approaching closer and closer to the black hole the center
• 12:05
  Speaker 2: of our galaxy, which tells us more and more about
• 12:07
  Speaker 2: how small it has to be. And there are only
• 12:10
  Speaker 2: a few things out there that could satisfy all of
• 12:12
  Speaker 2: those constraints that are that massive and that compact. Black
• 12:16
  Speaker 2: holes of course the most classic example. But now we
• 12:19
  Speaker 2: have a few other candidates, dark stars, fuzzballs, et cetera,
• 12:22
  Speaker 2: et cetera.
• 12:23
  Speaker 1: Yeah, it's still a big mystery talking about the ones
• 12:25
  Speaker 1: that are at the center of galaxies. Let's maybe break
• 12:27
  Speaker 1: it down for folks and talk about black holes a
• 12:30
  Speaker 1: little bit in general, and the different kinds of black
• 12:32
  Speaker 1: holes that are out there and that could be at
• 12:34
  Speaker 1: the center of different galaxies.
• 12:36
  Speaker 2: When we hear about black holes, we're often thinking about
• 12:38
  Speaker 2: stellar black holes. Like a star burns for billions of
• 12:42
  Speaker 2: years until eventually it's fusion peters out and it loses
• 12:46
  Speaker 2: the battle with gravity, so the gravity collapses the star
• 12:49
  Speaker 2: into a black hole, meaning that there's a region of
• 12:52
  Speaker 2: space where there's so much mass and energy that space
• 12:55
  Speaker 2: becomes so dramatically curved that every path within the event
• 12:59
  Speaker 2: horizon leads towards the center. That any particle that passes
• 13:03
  Speaker 2: into that event horizon will eventually find its way to
• 13:06
  Speaker 2: this center of that region. There are no paths out.
• 13:09
  Speaker 2: Space within the event horizon is so bent that every
• 13:12
  Speaker 2: timelike path for a particle leads towards the center. So
• 13:16
  Speaker 2: that's a stellar black hole. And those are awesome, which
• 13:19
  Speaker 2: is why we call them stellar, but also because they
• 13:21
  Speaker 2: collapse from individual stars, and they can be quite big,
• 13:24
  Speaker 2: like ten times the mass of our Sun, but they're
• 13:27
  Speaker 2: small compared to the kinds of black holes we're going
• 13:29
  Speaker 2: to talk about today.
• 13:30
  Speaker 1: Yeah, those are called super massive black holes.
• 13:33
  Speaker 2: Yeah, there's basically two categories of black holes. The stellar
• 13:36
  Speaker 2: mass black holes that are like a few tens of masses,
• 13:39
  Speaker 2: and then we jump up to really really really big
• 13:43
  Speaker 2: black holes, things like ten thousand or one hundred thousand
• 13:46
  Speaker 2: times the mass of our Sun in one huge black hole.
• 13:50
  Speaker 2: But they get much much bigger than that as well.
• 13:52
  Speaker 2: There are black holes that are millions or even billions
• 13:55
  Speaker 2: of times the mass of our Sun. And these are
• 13:58
  Speaker 2: the ones found at the hearts of galaxies.
• 14:01
  Speaker 1: Yeah, you can sort of see them even in distant,
• 14:03
  Speaker 1: faraway galaxies, right, Like when you look at little Fuzzz
• 14:06
  Speaker 1: out there in the night sky with special telescopes, you
• 14:09
  Speaker 1: can actually kind of see the black hole in the middle. Right.
• 14:11
  Speaker 2: Yeah, that's a really interesting and complicated question, like how
• 14:14
  Speaker 2: do we see these black holes in the milky way?
• 14:17
  Speaker 2: We have actually a lot of really interesting and cool
• 14:19
  Speaker 2: ways to look at the black hole because it's so close.
• 14:22
  Speaker 2: Like some of the best evidence we have is a
• 14:24
  Speaker 2: picture of the black hole released by the event Horizon telescope,
• 14:27
  Speaker 2: which is actually a picture of the accretion disk around
• 14:30
  Speaker 2: the black hole, the hot gas that's swirling very very
• 14:33
  Speaker 2: close to it and radiating light because it's so hot,
• 14:37
  Speaker 2: so we can see that. We can also see stars
• 14:40
  Speaker 2: orbiting very very close to the black hole the center
• 14:43
  Speaker 2: of our galaxy. There's this one star in particular S two,
• 14:46
  Speaker 2: with zooms super close to the black hole and whips
• 14:49
  Speaker 2: around it. We've actually seen an entire orbit of that
• 14:52
  Speaker 2: star all the way around the black hole, which won
• 14:54
  Speaker 2: a Nobel prize very recently. So the black hole the
• 14:56
  Speaker 2: center of our galaxy we've observed very closely. Black Holes
• 14:59
  Speaker 2: in other galaxies are harder to spot because those galaxies
• 15:02
  Speaker 2: are further away now.
• 15:04
  Speaker 1: For the one at the center of our galaxy. Even
• 15:06
  Speaker 1: that one, we're not one hundred percent sure it is
• 15:07
  Speaker 1: a black hole, right, It could still be something else
• 15:10
  Speaker 1: super massive there, or are we pretty sure it's a
• 15:12
  Speaker 1: super mass black hole.
• 15:13
  Speaker 2: I think both of those things are true. We don't
• 15:15
  Speaker 2: have direct evidence that it's a black hole. We know
• 15:18
  Speaker 2: that there's a lot of mass there because we see
• 15:20
  Speaker 2: the influence of that object on the nearby stars and
• 15:23
  Speaker 2: all the gas and dust. We know that it's not
• 15:25
  Speaker 2: emitting any light itself, so it's compact, it's dark, and
• 15:29
  Speaker 2: it's massive. So most physicists, I think, are pretty convinced
• 15:33
  Speaker 2: that it's a black hole. But that's just sort of
• 15:35
  Speaker 2: like the best idea we have. There are these alternative
• 15:37
  Speaker 2: theories that it could be a very rapidly collapsing region
• 15:40
  Speaker 2: of space which is going to bounce back and turn
• 15:42
  Speaker 2: into a white hole, for example. So there are other
• 15:45
  Speaker 2: theories there, but I think the mainstream physics community is
• 15:48
  Speaker 2: pretty convinced that it's a black.
• 15:49
  Speaker 1: Hole, all right, So then how do we see them
• 15:52
  Speaker 1: in other galaxies?
• 15:53
  Speaker 2: There's sort of two ways to see black holes in
• 15:55
  Speaker 2: other galaxies. One is when they're feeding. When black holes
• 15:59
  Speaker 2: are eating stuff, when they have like a lot of
• 16:01
  Speaker 2: gas swirling very close to them and falling in, it
• 16:04
  Speaker 2: tends to get hot and that gas radiates and they
• 16:07
  Speaker 2: can generate very very powerful beams of light. These are
• 16:11
  Speaker 2: things we call quasars, and we can see these from
• 16:13
  Speaker 2: like across the universe. There's some objects that are super
• 16:17
  Speaker 2: duper far away but incredibly bright, and when they were
• 16:20
  Speaker 2: discovered decades ago, people couldn't believe that they were actually
• 16:23
  Speaker 2: that far away because they look super bright already here
• 16:27
  Speaker 2: on Earth, and if they're also very very distant, that
• 16:29
  Speaker 2: means that at their source they're incredibly bright. And that's
• 16:33
  Speaker 2: exactly what's happening. The gas around in the black hole
• 16:35
  Speaker 2: is getting very very heated up, and as it falls in,
• 16:37
  Speaker 2: it radiates, and it radiation gets channeled by the magnetic
• 16:40
  Speaker 2: field of the black hole, and you get these very
• 16:42
  Speaker 2: powerful beams emitted from above and below the black hole,
• 16:47
  Speaker 2: and we can see those from very very far away.
• 16:49
  Speaker 2: So those are quasars. But we can only see that
• 16:51
  Speaker 2: for black holes that are like actively feeding and growing,
• 16:54
  Speaker 2: and that tends to happen sort of early in the
• 16:56
  Speaker 2: life cycle of the universe. Quasars peaked about ten billion
• 16:59
  Speaker 2: years ago, so that's good for seeing like young super
• 17:02
  Speaker 2: massive black holes very very far away.
• 17:05
  Speaker 1: So not every super massive black hole is a quasar, right,
• 17:09
  Speaker 1: There are some that could be out there just sitting
• 17:11
  Speaker 1: there being big.
• 17:12
  Speaker 2: Exactly most of the super massive black holes we think
• 17:15
  Speaker 2: are not quasars. We think that a lot of them
• 17:17
  Speaker 2: stop sort of quazing billions of years ago and are
• 17:20
  Speaker 2: now more like dark relics, huge black holes sitting at
• 17:23
  Speaker 2: the centers of galaxies but not being quasars anymore. But
• 17:27
  Speaker 2: we can still spot those by looking at the motion
• 17:30
  Speaker 2: of stars around them. So pick them nearby galaxy and
• 17:33
  Speaker 2: look at the stars that are near the center of it.
• 17:36
  Speaker 2: You can't resolve them individually. We don't have telescopes that
• 17:38
  Speaker 2: can say here's a star, there's a star, there's a star.
• 17:41
  Speaker 2: But we can look at stellar populations at the hearts
• 17:43
  Speaker 2: of other galaxies, and we can measure their velocities, we
• 17:47
  Speaker 2: can measure their brightness. It's really complicated and very computationally expensive,
• 17:51
  Speaker 2: but we can build a model of how fast those
• 17:54
  Speaker 2: stars are moving around the center of that galaxy, and
• 17:57
  Speaker 2: from that we can infer the mass of the black hole.
• 18:00
  Speaker 2: How heavy does the thing have to be at the
• 18:02
  Speaker 2: center of the galaxy to support this super fast radial
• 18:05
  Speaker 2: motion by those stars.
• 18:07
  Speaker 1: All right, well, let's get into whether every galaxy has
• 18:11
  Speaker 1: a black hole and what would it mean for a
• 18:13
  Speaker 1: galaxy to not have a black hole at its center.
• 18:15
  Speaker 1: But first let's take a quick break. All right, we're
• 18:30
  Speaker 1: asking the question does every galaxy have a black hole
• 18:33
  Speaker 1: at its center? Like, does every galaxy have a dark
• 18:36
  Speaker 1: soul or something?
• 18:37
  Speaker 2: I'll leave you the philosophical and moral implications of it.
• 18:39
  Speaker 2: But from a physics point of view, it's a trend
• 18:41
  Speaker 2: that we're noticing that galaxies have these black holes, and
• 18:44
  Speaker 2: so we wonder if it's a rule. You know, it's
• 18:46
  Speaker 2: basically our strategy in physics is like, look out of
• 18:48
  Speaker 2: the universe, find patterns, wonder if those patterns reflecting like
• 18:52
  Speaker 2: deep rules of the universe. Figure out what those rules
• 18:54
  Speaker 2: have to be. So, you know, we're still in like
• 18:56
  Speaker 2: step two here.
• 18:57
  Speaker 1: Hmmm, Now, I guess what is it to say, Like,
• 19:01
  Speaker 1: you know, we can see traillions of galaxies out there
• 19:03
  Speaker 1: in space, can we tell what percentage of them have
• 19:06
  Speaker 1: black holes? Or does every galaxy we've seen have a
• 19:08
  Speaker 1: black hole in it that we can tell?
• 19:10
  Speaker 2: Yeah, that's a great point. You're right that we can
• 19:12
  Speaker 2: see zillions and zillions of galaxies out there, like the
• 19:14
  Speaker 2: Hubble deep field or the James Web deep field. Whenever
• 19:17
  Speaker 2: it focuses on some random patch of space and resolves it,
• 19:22
  Speaker 2: you can see evidence for so many galaxies in every
• 19:25
  Speaker 2: tiny little corner of space. So we know there are
• 19:27
  Speaker 2: lots and lots of galaxies out there. Very few of those, however,
• 19:31
  Speaker 2: have we identified a super massive black hole, in a
• 19:34
  Speaker 2: few very distant ones that happen to be koasars where like, okay,
• 19:37
  Speaker 2: that's definitely a super massive black hole, and some nearby
• 19:41
  Speaker 2: ones where we can watch the stellar populations and infer
• 19:44
  Speaker 2: that there must be something very very heavy at the core.
• 19:47
  Speaker 2: But most of those we can't do either because they're
• 19:50
  Speaker 2: either too far away or too quiet. But every galaxy
• 19:53
  Speaker 2: that's close enough for us to watch the stars, we
• 19:56
  Speaker 2: have seen a super massive black hole at its center.
• 19:59
  Speaker 2: So there's lots of galaxies out there, only very small
• 20:01
  Speaker 2: number can we check for a black hole, And every
• 20:04
  Speaker 2: single time we've checked, we've found one.
• 20:06
  Speaker 5: Mmmm.
• 20:07
  Speaker 1: So, like Andromeda, isn't it? Andromeda the closest galaxy to us.
• 20:10
  Speaker 2: Andromeda is the closest galaxy to us, and we think
• 20:13
  Speaker 2: it has a huge black hole at its center, and
• 20:17
  Speaker 2: it's close enough that we can pretty well model the
• 20:19
  Speaker 2: velocities of the stars at the center of that galaxy,
• 20:23
  Speaker 2: and so we're pretty sure there has to be something
• 20:25
  Speaker 2: super massive and very dense at the heart of Andromeda,
• 20:28
  Speaker 2: very likely a black hole.
• 20:30
  Speaker 1: All right, So then the data kind of suggests that,
• 20:32
  Speaker 1: like if you look at the galaxies that we can't
• 20:34
  Speaker 1: look at we do see a black hole in the
• 20:36
  Speaker 1: middle there, or something that is probably a black hole,
• 20:39
  Speaker 1: but why else would we extrapolate that to every galaxy
• 20:42
  Speaker 1: in the universe.
• 20:43
  Speaker 2: Yeah, that's a good question. And to underscore sort of
• 20:45
  Speaker 2: our lack of knowledge here, we really identified black holes
• 20:49
  Speaker 2: in an approximately like one hundred to two hundred galaxies.
• 20:52
  Speaker 2: So of the zillions of galaxies that we've seen, only
• 20:55
  Speaker 2: a very small number have we been able to do
• 20:58
  Speaker 2: this check. And so you're tentative when you're extrapolating from
• 21:01
  Speaker 2: like a few hundred examples two trillions of objects out there.
• 21:05
  Speaker 2: On the other hand, it's every single one that we've
• 21:07
  Speaker 2: seen so far, right, so we wonder if it really
• 21:10
  Speaker 2: is a theory.
• 21:10
  Speaker 1: So there's no black hole nearby, then we can check
• 21:13
  Speaker 1: that they didn't have a black hole in it, or
• 21:15
  Speaker 1: would we know or I guess what are you saying.
• 21:17
  Speaker 2: I'm saying there's no galaxy nearby that we can check
• 21:20
  Speaker 2: that hasn't had a black hole in it, and that
• 21:22
  Speaker 2: includes really large galaxies like Andrameda, and also even dwarf
• 21:26
  Speaker 2: galaxies like there's a dwarf galaxy called RGG one one
• 21:30
  Speaker 2: eight and they recently found what they call a teeny
• 21:33
  Speaker 2: tiny super massive black hole in it.
• 21:35
  Speaker 1: Where is that the actual scientific name? Teeny tiny supermassive?
• 21:40
  Speaker 2: That was the title of the press release. I don't
• 21:41
  Speaker 2: know if that ended up in the paper or not.
• 21:44
  Speaker 1: Doesn't that just average to a small black hole.
• 21:46
  Speaker 2: It's only fifty thousand times the mass of the Sun,
• 21:49
  Speaker 2: So for a super massive black hole, it's pretty teeny
• 21:52
  Speaker 2: tiny compared to the Sun. It's pretty much a monster.
• 21:55
  Speaker 2: It depends on your perspective. But there's something else going
• 21:57
  Speaker 2: on here that makes us suspect that maybe every single
• 22:01
  Speaker 2: galaxy has a black hole in it. It's not just
• 22:04
  Speaker 2: that every single one we've seen has a black hole
• 22:06
  Speaker 2: in it, but we see this very tight pattern. We
• 22:09
  Speaker 2: notice this very close connection between the mass of the
• 22:11
  Speaker 2: super massive black hole and the mass of the galaxy.
• 22:16
  Speaker 2: And that might not be a surprise. You figure, like, look,
• 22:18
  Speaker 2: more stuff means a bigger galaxy, means more stars means
• 22:22
  Speaker 2: bigger black hole, right, And that's true. But if you
• 22:25
  Speaker 2: run those simulations, you get kind of a scatter like
• 22:27
  Speaker 2: you get some bigger black holes and some smaller black holes.
• 22:30
  Speaker 2: But what we notice when we plot, like the mass
• 22:32
  Speaker 2: of the black hole versus the mass of the galaxy
• 22:34
  Speaker 2: is a much tighter correlation than you would expect. Just
• 22:38
  Speaker 2: from like more stuff means bigger black hole, you get
• 22:41
  Speaker 2: this very very compact line that suggests that there's like
• 22:45
  Speaker 2: some feedback between the black hole and the galaxy.
• 22:48
  Speaker 1: So you mean, like when we look at a black
• 22:50
  Speaker 1: hole in another galaxy, we can tell its size first
• 22:52
  Speaker 1: of all, And if you compare the size of the
• 22:55
  Speaker 1: black hole to the size with the galaxy, it's like
• 22:58
  Speaker 1: it's like almost one to one.
• 22:59
  Speaker 2: Kind and if you're just made bigger and smaller galaxies
• 23:02
  Speaker 2: and guess how big the black holes would be, then
• 23:04
  Speaker 2: the same size galaxy shouldn't always give you the same
• 23:07
  Speaker 2: size black hole. Depends a little bit on like where
• 23:09
  Speaker 2: the stuff is and how much falls in, etc. But
• 23:12
  Speaker 2: what we notice is a very very close connection, as
• 23:14
  Speaker 2: you say, like one to one, that the mass of
• 23:17
  Speaker 2: the galaxy and the mass of the black hole track
• 23:19
  Speaker 2: very very closely.
• 23:20
  Speaker 1: Meaning that there's no small galaxy with a big black hole,
• 23:23
  Speaker 1: and there's no big galaxy with a small black.
• 23:25
  Speaker 2: Hole exactly, and two galaxies with the same size that
• 23:27
  Speaker 2: basically exactly the same size black hole at their heart.
• 23:31
  Speaker 2: There's almost no variation there, and that tells us that
• 23:34
  Speaker 2: there must be some sort of connection, that there's something
• 23:37
  Speaker 2: about how the black hole is forming and how the
• 23:39
  Speaker 2: galaxy is forming that connects these two things. I mean,
• 23:42
  Speaker 2: even from a spatial point of view, it's kind of
• 23:43
  Speaker 2: weird that like this dot at the very very center
• 23:46
  Speaker 2: of the galaxy. I remember, these things are very massive,
• 23:48
  Speaker 2: but they're also very very small, So it's weird that
• 23:51
  Speaker 2: this dot at the center of the galaxy is influenced
• 23:54
  Speaker 2: by like the mass of the whole huge galaxy that's
• 23:57
  Speaker 2: like one hundred thousand light years across. So there must
• 24:01
  Speaker 2: be some sort of connection between them, some information passing
• 24:03
  Speaker 2: back and forth, some process that's controlling both of them.
• 24:07
  Speaker 2: And if that's the case, and that makes us think, oh,
• 24:09
  Speaker 2: there must be a connection between the two. And so
• 24:12
  Speaker 2: probably every galaxy does have one of these.
• 24:14
  Speaker 1: Things, because, like you're saying, if it's sort of inevitable
• 24:19
  Speaker 1: for a galaxy to get a black hole in the
• 24:21
  Speaker 1: middle when it forms, then there probably isn't any galaxies
• 24:25
  Speaker 1: without black.
• 24:26
  Speaker 2: Holes, Yeah, exactly. And if there's some feedback mechanisms, something
• 24:30
  Speaker 2: which is controlling both of these things, then probably generated
• 24:34
  Speaker 2: both at the same time. It controls the stars that
• 24:36
  Speaker 2: form in the galaxy and also controls the mass of
• 24:38
  Speaker 2: the black hole. There must be some process tying these
• 24:41
  Speaker 2: things together, and being weirdly vague about that process because
• 24:45
  Speaker 2: we don't know what it is. There's a bunch of
• 24:47
  Speaker 2: theories about how the black hole might form and grow
• 24:51
  Speaker 2: and then the radiation from the black hole stops it
• 24:53
  Speaker 2: from growing, and the same process might control how stars
• 24:56
  Speaker 2: are formed and how they collapse from blobs of gas
• 24:59
  Speaker 2: and dust into stars. So there's a bunch of different
• 25:01
  Speaker 2: ideas out there, but they're all very vague and nobody
• 25:04
  Speaker 2: can really agree about it, or at the point where
• 25:06
  Speaker 2: we're just like, it seems like there's something going on here,
• 25:08
  Speaker 2: but we don't know what it is.
• 25:11
  Speaker 1: Although this relationship between the black hole and the galaxy
• 25:14
  Speaker 1: size comes from data of galaxies that we found that
• 25:18
  Speaker 1: have black holes, right, Like, maybe there's still the possibility
• 25:21
  Speaker 1: that won and in a thousand galaxies doesn't have a
• 25:23
  Speaker 1: black hole.
• 25:24
  Speaker 2: Yeah, it's certainly possible that that's the case. There's a
• 25:26
  Speaker 2: small number of galaxies here. Also, people might remember there
• 25:29
  Speaker 2: was recently this crazy idea that super massive black holes
• 25:33
  Speaker 2: or the hearts of galaxies are connected to the cosmic acceleration,
• 25:37
  Speaker 2: that they're really like bubbles of dark energy. And a
• 25:40
  Speaker 2: crucial thing that people notice that fueled that idea was
• 25:43
  Speaker 2: that there's a connection between the expansion of the universe
• 25:46
  Speaker 2: and the size of these black holes. That the black
• 25:49
  Speaker 2: holes seem to be more closely connected to the cosmic
• 25:51
  Speaker 2: expansion than their own galaxies. So that might seem like
• 25:55
  Speaker 2: it's in contradiction of what we're saying here today. Today
• 25:57
  Speaker 2: we're saying, oh, the black holes of the hearts of
• 25:59
  Speaker 2: galaxies are very closely connected to the size of their galaxies,
• 26:03
  Speaker 2: and a few weeks ago we said, no, they're not.
• 26:04
  Speaker 2: They're more closely connected to the universe. And the way
• 26:07
  Speaker 2: to untangle it is to remember that there's two different
• 26:09
  Speaker 2: kinds of black holes that we're seeing. We're talking about
• 26:11
  Speaker 2: black holes we see very very close to us, and
• 26:14
  Speaker 2: in those the black holes very tightly connected to the
• 26:17
  Speaker 2: mass of the galaxy, versus black holes that are very
• 26:19
  Speaker 2: far away, very old black holes those are from quasars,
• 26:23
  Speaker 2: So those are the ones that seem to be connected
• 26:26
  Speaker 2: to the cosmic expansion. So, long story short, there's a
• 26:29
  Speaker 2: lot we still don't understand about super massive black holes.
• 26:32
  Speaker 1: Even how they form, right, Like, that's still a big mystery.
• 26:36
  Speaker 2: Absolutely, we have no idea how these things even got
• 26:38
  Speaker 2: to exist. If you just start from like a big
• 26:40
  Speaker 2: blob of stuff and watch it form a galaxy, like
• 26:43
  Speaker 2: in simulation, you get a black hole at the center,
• 26:46
  Speaker 2: that's not a mystery, but it's not this big. Like
• 26:49
  Speaker 2: we look back in time by looking at old light
• 26:51
  Speaker 2: and looking at really early galaxies, and we notice that
• 26:54
  Speaker 2: they have huge black holes at their hearts, like already
• 26:57
  Speaker 2: billions of times the mass of the Sun, like the
• 27:00
  Speaker 2: first billion years of the universe. These are again the
• 27:03
  Speaker 2: very distant, very old black holes we see from quasars,
• 27:07
  Speaker 2: and we can't explain how that happens. In our simulations.
• 27:10
  Speaker 2: That just doesn't happen so quickly. It takes much longer
• 27:13
  Speaker 2: for these black holes to get so big. So there's
• 27:15
  Speaker 2: something else going on to form these black holes that
• 27:18
  Speaker 2: we don't understand.
• 27:19
  Speaker 1: So we really have no idea what could be going on.
• 27:21
  Speaker 1: I mean, it kind of seems like maybe there's a
• 27:24
  Speaker 1: simple explanation in there somehow, Like you know, if you
• 27:27
  Speaker 1: start with a big cloud of gas, and yeah, the
• 27:29
  Speaker 1: galaxy is going to be bigger, and the black hole
• 27:31
  Speaker 1: in the middle is going to be bigger, Like what's
• 27:33
  Speaker 1: the big mystery there?
• 27:34
  Speaker 2: Yeah, and that would give you a correlation that would
• 27:36
  Speaker 2: say that in general, masses of galaxies should be connected
• 27:40
  Speaker 2: to the masses of the black hole. And we see that.
• 27:42
  Speaker 2: But again we see a much tighter connection than you
• 27:44
  Speaker 2: would expect just from that simple explanation. We see that
• 27:48
  Speaker 2: galaxies with the same mass have basically exactly the same
• 27:52
  Speaker 2: mass black hole. There's like no variation there. So the
• 27:55
  Speaker 2: connection is just tighter than what you would expect from
• 27:57
  Speaker 2: that simple argument. So there must be something else going on.
• 28:00
  Speaker 2: Is it true that we have no idea? I mean,
• 28:02
  Speaker 2: people definitely have ideas, and I read like ten papers
• 28:05
  Speaker 2: about ten different ideas for what could be controlling it
• 28:08
  Speaker 2: complicated theories about how the gas gets blown in or out,
• 28:11
  Speaker 2: or gets heated up or cool down. We have lots
• 28:13
  Speaker 2: of ideas, we just don't know which one might represent reality.
• 28:17
  Speaker 1: Interesting And now, is it possible, I guess, for a
• 28:20
  Speaker 1: galaxy to not have a black hole? Like why couldn't
• 28:23
  Speaker 1: that happen?
• 28:23
  Speaker 2: Yeah, that's a great question. And there's sort of two
• 28:25
  Speaker 2: questions there, right, Like one is could you make a
• 28:28
  Speaker 2: galaxy without a black hole. Is it possible to pull
• 28:31
  Speaker 2: all those stars and all that dark matter together without
• 28:34
  Speaker 2: making a black hole? And we think the answer to
• 28:37
  Speaker 2: that is no, That every time you get enough stuff together,
• 28:41
  Speaker 2: whatever is pulling that together is going to form a
• 28:43
  Speaker 2: black hole at its center. That's just inevitable.
• 28:45
  Speaker 1: Why do we think it's inevitable?
• 28:46
  Speaker 2: Well, I guess for a couple of reasons. To summarize,
• 28:48
  Speaker 2: One is every galaxy we've seen so far has a
• 28:52
  Speaker 2: black hole at it's heart, right, We've never seen a
• 28:54
  Speaker 2: galaxy where we're able to check whether there's a black
• 28:57
  Speaker 2: hole and haven't found one, though there's an asterisk there
• 28:59
  Speaker 2: which will get to in just a minute. And number
• 29:01
  Speaker 2: two is this connection between the sizes of them that
• 29:03
  Speaker 2: tells us that there's probably some mechanism that's controlling both
• 29:07
  Speaker 2: the mass of the galaxy and the mass of the
• 29:09
  Speaker 2: black hole together. So back to the asterisk, there actually
• 29:12
  Speaker 2: are a couple of galaxies nearby that we've looked at
• 29:15
  Speaker 2: that don't have a black hole at the center. And
• 29:17
  Speaker 2: that points to another potentially fascinating story, which is whether
• 29:21
  Speaker 2: it's possible for a galaxy to form a black hole
• 29:24
  Speaker 2: and then eject it like can a galaxy form, make
• 29:27
  Speaker 2: its own black hole and then lose that black hole.
• 29:30
  Speaker 1: Wait, wait, wait, wait, we're seeing that there are galaxies
• 29:32
  Speaker 1: we've seen that don't have a black hole in them
• 29:34
  Speaker 1: in the middle.
• 29:35
  Speaker 2: There are a small number of galaxies we've seen that
• 29:38
  Speaker 2: have a black hole, but it's no longer at the
• 29:40
  Speaker 2: middle of the galaxy.
• 29:41
  Speaker 1: Wait, what where is it? Like at the edge or
• 29:44
  Speaker 1: really far away from it? What do you mean?
• 29:46
  Speaker 2: So there's a few variations. In one case, we've seen
• 29:48
  Speaker 2: a super massive black hole that's like displaced from the
• 29:51
  Speaker 2: center and has a pretty high speed away from the center.
• 29:55
  Speaker 2: So there's this possibility that galaxies could form make a
• 29:59
  Speaker 2: black hole the center, and then through some dynamical process,
• 30:02
  Speaker 2: some like interaction with other galaxies, their black hole could
• 30:05
  Speaker 2: get like kicked out of the center. And we've actually
• 30:08
  Speaker 2: seen this in a few galaxies.
• 30:09
  Speaker 1: What are the other ones like that don't have a
• 30:11
  Speaker 1: black hole in the middle.
• 30:12
  Speaker 2: So there's the one example called CID forty two, which
• 30:15
  Speaker 2: is about four billion light years away. It has a
• 30:17
  Speaker 2: super massive black hole, but it's near the center, but
• 30:20
  Speaker 2: it's sort of displaced from the center. And then there's
• 30:22
  Speaker 2: another observation just a few weeks ago where they see
• 30:26
  Speaker 2: a streak of light shooting out of the galaxy. The
• 30:29
  Speaker 2: streak of light is like two hundred thousand light years long,
• 30:32
  Speaker 2: and at the end of it there's a black hole.
• 30:34
  Speaker 2: And so it looks sort of like the black hole
• 30:36
  Speaker 2: was ejected from this galaxy. It's like a runaway black
• 30:40
  Speaker 2: hole and left this streak of stars in hot gas
• 30:43
  Speaker 2: in its wake.
• 30:44
  Speaker 1: Well, it can actually see like the skid marks of it.
• 30:47
  Speaker 2: Yeah, exactly, And so we think that this might happen
• 30:51
  Speaker 2: sometimes when galaxies merge. We know that galaxies merge, that
• 30:54
  Speaker 2: that's a very normal thing. We think the Milky Way
• 30:56
  Speaker 2: is formed by a bunch of galactic mergers. And Dromeda
• 30:59
  Speaker 2: is so big because because it's a combination of a
• 31:01
  Speaker 2: bunch of baby galaxies that all got merged together. And
• 31:04
  Speaker 2: the normal thing to happen when galaxies merge is that
• 31:06
  Speaker 2: the black holes also merge. I mean, you have two
• 31:09
  Speaker 2: clouds of stars, each with a black hole at their center.
• 31:12
  Speaker 2: They're all going to orbit each other. Eventually, the black
• 31:15
  Speaker 2: holes that their hearts are going to orbit each other,
• 31:17
  Speaker 2: and then because of friction and gravitational radiation, they'll eventually
• 31:20
  Speaker 2: collapse into a single black hole. That's like the normal
• 31:23
  Speaker 2: thing to happen, but there's some variations there. When two
• 31:27
  Speaker 2: black holes collapse into one, they also emit a lot
• 31:30
  Speaker 2: of radiation. Like the mass of the two black holes
• 31:33
  Speaker 2: doesn't one hundred percent go into the mass of the
• 31:35
  Speaker 2: final black hole. It loses some mass and it generates
• 31:39
  Speaker 2: a bunch of gravitational waves. That's how we see these
• 31:42
  Speaker 2: black hole mergers. We talked about Logo and Virga and
• 31:45
  Speaker 2: all these observations that see these ripples in space time
• 31:48
  Speaker 2: generated by these black hole collisions. You get those ripples
• 31:51
  Speaker 2: because the black holes are accelerating as they orbit each other,
• 31:54
  Speaker 2: and that radiates a way energy, so it loses some mass. Now,
• 31:58
  Speaker 2: sometimes that radiation is in every direct like it just
• 32:01
  Speaker 2: sprays gravitational waves everywhere, but sometimes in special circumstances that
• 32:05
  Speaker 2: gravitational radiation tends to be in one direction rather than another,
• 32:09
  Speaker 2: and then it acts sort of like a recoil. It's
• 32:11
  Speaker 2: like shooting a gravitational wave gun in one direction and
• 32:15
  Speaker 2: the black holes get pushed back in the other direction
• 32:18
  Speaker 2: by conservation of momentum.
• 32:20
  Speaker 1: So you're saying you can have a galaxy without a
• 32:22
  Speaker 1: black hole, but the ones we've seen so far that
• 32:25
  Speaker 1: are like that, there's evidence that it had a black
• 32:27
  Speaker 1: hole in the middle at some point.
• 32:29
  Speaker 2: Exactly, so it might be possible to have a galaxy
• 32:32
  Speaker 2: without a black hole by building a galaxy with a
• 32:35
  Speaker 2: black hole and then like ejecting it getting rid of
• 32:38
  Speaker 2: the black hole.
• 32:39
  Speaker 1: I guess one thing that maybe important to understand is
• 32:42
  Speaker 1: that even though a galaxy can have a super massive
• 32:45
  Speaker 1: black hole in the middle with the massive millions of
• 32:48
  Speaker 1: our suns, it's not like the black hole is anchoring
• 32:51
  Speaker 1: the galaxy, right, like to a galaxy with tondreds of
• 32:54
  Speaker 1: millions of stars, like one little black hole in the
• 32:57
  Speaker 1: middle is not super important in the same way that
• 33:00
  Speaker 1: the Sun is important in our Solar system.
• 33:02
  Speaker 2: Right, Yeah, you're absolutely right. The Sun is like ninety
• 33:05
  Speaker 2: nine percent of the mass of our solar system. But
• 33:07
  Speaker 2: the black holes the hearts of these galaxies are a
• 33:09
  Speaker 2: tiny fraction, much less than one percent of the mass
• 33:12
  Speaker 2: of the galaxy. Like in the Milky Way, we have
• 33:15
  Speaker 2: billions of stars and so billions of solar masses, and
• 33:18
  Speaker 2: our black hole is only five million solar masses. So
• 33:21
  Speaker 2: it's a tiny fraction of the mass of our galaxy.
• 33:24
  Speaker 2: Even though we're talking about really big objects. Galaxies themselves
• 33:28
  Speaker 2: are much much bigger. So it's more like if our
• 33:31
  Speaker 2: Solar system lost Jupiter, right, Jupiter is a big planet,
• 33:34
  Speaker 2: that'd be kind of a big deal personally, but it
• 33:36
  Speaker 2: wouldn't affect the dynamics of the Solar System the way
• 33:38
  Speaker 2: it would if we lost the Sun, Right, that would
• 33:41
  Speaker 2: be much more dramatic.
• 33:42
  Speaker 1: Right, These super massive black holes are really more like
• 33:45
  Speaker 1: little pimples kind of in the middle of galaxies. Right,
• 33:48
  Speaker 1: It's not like the galaxies there because of the mass
• 33:50
  Speaker 1: super massive black hole. It's more like maybe just a
• 33:53
  Speaker 1: feature that pops up when you're making a galaxy.
• 33:55
  Speaker 2: Yeah, I think we don't really understand that. I mean,
• 33:58
  Speaker 2: I think the causal relationship is probably complicated. It seems
• 34:01
  Speaker 2: like it's probably a necessary outcome when you form a
• 34:05
  Speaker 2: galaxy that you get a super massive black hole. So
• 34:07
  Speaker 2: in that sense, it kind of is necessary to have it.
• 34:10
  Speaker 2: But you're right, you can get rid of the black
• 34:12
  Speaker 2: hole and the galaxy can still hold itself together, so
• 34:14
  Speaker 2: in that sense, you don't need it anymore.
• 34:17
  Speaker 1: Like maybe the black hole needed the galaxy to form,
• 34:19
  Speaker 1: but maybe the galaxy didn't need the black hole to form.
• 34:23
  Speaker 2: Yeah, But then the black hole stays a black hole.
• 34:25
  Speaker 2: When it's been ejected, it's still a black hole out
• 34:27
  Speaker 2: there wandering an intergalactic space. WHOA. So one way to
• 34:31
  Speaker 2: get rid of your black holes to generate a bunch
• 34:33
  Speaker 2: of gravitational radiation in one direction to kick the black hole.
• 34:37
  Speaker 2: For that to happen, you typically have to have sort
• 34:39
  Speaker 2: of like a low mass black hole in order to
• 34:41
  Speaker 2: get enough acceleration to like get out of the galaxy.
• 34:44
  Speaker 2: Another scenario is to have sort of like a three
• 34:46
  Speaker 2: galaxy dance. Remember that when three objects interact, it's much
• 34:50
  Speaker 2: more chaotic, Like, the three body problem is not something
• 34:53
  Speaker 2: we know how to solve, whereas the two body problem
• 34:56
  Speaker 2: is simple. So if you have three galaxies that are
• 34:58
  Speaker 2: merging at the same time, then one of those black
• 35:01
  Speaker 2: holes can get kicked out instead of merging with the
• 35:04
  Speaker 2: other two. So that's another scenario that can create a
• 35:07
  Speaker 2: runaway black hole, essentially kicking a black hole out of
• 35:10
  Speaker 2: a galaxy.
• 35:11
  Speaker 1: Like if three solar systems similar to ours came together,
• 35:14
  Speaker 1: it would get so chaotic and so scrambled that it
• 35:18
  Speaker 1: could actually like shoot off the Sun or Jupiter out
• 35:21
  Speaker 1: into space.
• 35:21
  Speaker 2: Right, yeah, exactly. And because of conservation momentum. If you're
• 35:25
  Speaker 2: going to kick one black hole out in one direction,
• 35:27
  Speaker 2: then the other two are going to get kicked in
• 35:29
  Speaker 2: the other direction, and so the whole system might end
• 35:33
  Speaker 2: up without a black hole at its center.
• 35:35
  Speaker 1: All right, let's take a little bit more into what
• 35:37
  Speaker 1: this all means and maybe how dark matter plays into it.
• 35:41
  Speaker 1: But first let's take another quick break. All right, we
• 35:57
  Speaker 1: are asking the question does every galaxy have a black
• 35:59
  Speaker 1: hole at its center? And I guess we've figured out
• 36:02
  Speaker 1: the answers. No, right, some galaxies have a black hole
• 36:07
  Speaker 1: near its edge if it gets kicked out.
• 36:09
  Speaker 2: Yeah, we think that probably every galaxy has a black
• 36:12
  Speaker 2: hole at its center during its formation or at some
• 36:16
  Speaker 2: point in its history, because we think probably the process
• 36:19
  Speaker 2: that makes these galaxies, it gathers together all this mass
• 36:23
  Speaker 2: and funnels it into this gravitational well that remember, in
• 36:27
  Speaker 2: the end, is made by dark matter. Right, The reason
• 36:29
  Speaker 2: these galaxies exist is because there's a density of dark
• 36:32
  Speaker 2: matter there which is pulling in all this other matter
• 36:35
  Speaker 2: to make this dense stuff that we can make a galaxy.
• 36:38
  Speaker 2: Probably that process inevitably makes a black hole at the
• 36:41
  Speaker 2: same time as it makes a galaxy. But then you
• 36:44
  Speaker 2: can lose that black hole. During the life of these galaxies,
• 36:47
  Speaker 2: as they merge, as they come together, as they dance
• 36:49
  Speaker 2: around each other, those black holes can get ejected from
• 36:53
  Speaker 2: the hearts of those galaxies. So yeah, you could end
• 36:55
  Speaker 2: up with a galaxy without a black hole at its center.
• 37:00
  Speaker 1: Like we said earlier in the episode, that every GALLESSI
• 37:04
  Speaker 1: we've seen has the black hole at its center, But
• 37:05
  Speaker 1: it sounds like that's not really true. That there are
• 37:08
  Speaker 1: galaxies out there we've seen so we can measure it
• 37:10
  Speaker 1: that don't have one in the middle at all. Have
• 37:13
  Speaker 1: we seen any with no black hole at all.
• 37:15
  Speaker 2: We have not found a galaxy without any kind of
• 37:18
  Speaker 2: black hole. Either they have a black hole at their center,
• 37:20
  Speaker 2: or we've identified a black hole that's been ejected from
• 37:23
  Speaker 2: the center. That's a very small number of cases so far,
• 37:26
  Speaker 2: or they're too far away for us to tell what's
• 37:29
  Speaker 2: going on at the center. Then there's one particular galaxy
• 37:32
  Speaker 2: which is a bit of a mystery. Its called Able
• 37:34
  Speaker 2: two two six one. It is a really big galaxy
• 37:37
  Speaker 2: and we have not yet found the super massive black
• 37:40
  Speaker 2: hole there. We looked at it in the X ray
• 37:42
  Speaker 2: and not seen the sign of it. It's still sort
• 37:44
  Speaker 2: of an open question whether people are going to find
• 37:46
  Speaker 2: evidence of the black hole or not, but it's one
• 37:48
  Speaker 2: that has a question mark next to it. Remember, this
• 37:51
  Speaker 2: is like a recent and active field of research. People
• 37:54
  Speaker 2: are developing new techniques to try to study these galaxies
• 37:57
  Speaker 2: to try to see if they are black holes in them.
• 37:59
  Speaker 2: It's definitely a question a lot of people are working on,
• 38:02
  Speaker 2: so it's evolving rapidly. But either we've seen a black
• 38:05
  Speaker 2: hole at center, or we've seen a black hole like
• 38:07
  Speaker 2: leaving its center, or there's this one question mark galaxy
• 38:10
  Speaker 2: able two two six 's one, or we're just not
• 38:13
  Speaker 2: able to see it, because remember, the galaxies have to
• 38:15
  Speaker 2: be close enough for us to like study their centers
• 38:18
  Speaker 2: in order to be able to see these black holes,
• 38:21
  Speaker 2: or they have to be active enough for us to
• 38:24
  Speaker 2: see them emitting. Like another way to see these black
• 38:27
  Speaker 2: holes is to watch them like burp as they eat something.
• 38:30
  Speaker 1: But then you're only seeing the rude black hole.
• 38:33
  Speaker 2: That's right. But occasionally, even a quiet black hole, even
• 38:36
  Speaker 2: when it's not surrounded by a big disc of gas
• 38:38
  Speaker 2: and dust and emitting like constant beams of light, occasionally
• 38:42
  Speaker 2: a star might wander close to it and get eaten
• 38:45
  Speaker 2: and the tidal disruption there will give you a very
• 38:47
  Speaker 2: bright flare. So we've seen those kinds of things as well,
• 38:50
  Speaker 2: like otherwise quiet galactic centers that suddenly emit a big,
• 38:55
  Speaker 2: bright burst of light. We've even seen that from our
• 38:57
  Speaker 2: own galactic center. Sometimes the way you can observe supermassive black.
• 39:02
  Speaker 1: Holes, it's like the final scream of a star before
• 39:05
  Speaker 1: it gets eaten wo.
• 39:08
  Speaker 2: Exactly. Another thing people are doing is trying to identify
• 39:12
  Speaker 2: these super massive black holes out in intergalactic space. Like
• 39:16
  Speaker 2: people are curious how often do super massive black holes
• 39:19
  Speaker 2: get kicked out into space? Remember we talked about like
• 39:22
  Speaker 2: rogue planets before, planets that used to be orbiting a
• 39:25
  Speaker 2: solar system but then due to the gravitational chaos of
• 39:28
  Speaker 2: their system, get thrown out into space. And it turns
• 39:31
  Speaker 2: out there's a huge number of them out there. People
• 39:33
  Speaker 2: have discovered rogue planets by micro lensing, looking for moments
• 39:38
  Speaker 2: when these planets pass in front of a star in
• 39:40
  Speaker 2: the background and that star's light gets distorted by the
• 39:43
  Speaker 2: gravity of the planet, And by doing that we can
• 39:46
  Speaker 2: spot a bunch of these things and then extrapolate to
• 39:48
  Speaker 2: how many there are. The same way we can look
• 39:50
  Speaker 2: for super massive black holes in intergalactic space by looking
• 39:54
  Speaker 2: at for these micro lensing events.
• 39:57
  Speaker 1: M sounds kind of scary, the idea that there are
• 40:00
  Speaker 1: super massive black holes out there roaming space, possibly in
• 40:04
  Speaker 1: our direction.
• 40:05
  Speaker 2: Yeah, it's certainly possible that they're out there. We've seen
• 40:07
  Speaker 2: some of them getting ejected from their galaxies, but we
• 40:10
  Speaker 2: think that might be kind of rare, and when we're
• 40:12
  Speaker 2: talking about like a one percent level event based on
• 40:14
  Speaker 2: our recent observation, so of course with a big uncertainty.
• 40:18
  Speaker 2: And there are many fewer galaxies than there are stars
• 40:21
  Speaker 2: of course, so the number of rogues super massive black
• 40:24
  Speaker 2: holes out there could be big. But space is of
• 40:26
  Speaker 2: course really really vast, so these things would be pretty
• 40:29
  Speaker 2: hard to spot.
• 40:30
  Speaker 1: I guess it's hard for even a super massive black
• 40:33
  Speaker 1: hole to leave a galaxy, right Like, as we said before,
• 40:36
  Speaker 1: a galaxies huge, got billions and trillions of stars, it's
• 40:39
  Speaker 1: really massive. It's probably pretty hard for a black hole
• 40:43
  Speaker 1: to get the escape velocity needed to leave a galaxy
• 40:46
  Speaker 1: and come towards us exactly.
• 40:47
  Speaker 2: That's why it tends to happen mostly for lower mass
• 40:50
  Speaker 2: super massive black holes, not necessarily even teeny tiny ones,
• 40:54
  Speaker 2: just ones on the lower edge, because a lot of
• 40:56
  Speaker 2: them are going to have this asymmetric radiation from gravitational
• 40:59
  Speaker 2: waves or some sort of chaotic merger event that it's
• 41:03
  Speaker 2: not totally symmetric. But most of them are massive enough
• 41:06
  Speaker 2: that they get pulled back to the center of the
• 41:07
  Speaker 2: galaxy and eventually settle down. But the lower mass ones
• 41:10
  Speaker 2: can get going pretty fast, like this CID forty two galaxy.
• 41:14
  Speaker 2: They estimated the velocity of the galaxy to be half
• 41:17
  Speaker 2: a percent of the speed of light, which is like
• 41:20
  Speaker 2: very very fast moving black hole.
• 41:23
  Speaker 1: It's in a hurry.
• 41:25
  Speaker 2: To get out of there, really wants to go somewhere exactly.
• 41:29
  Speaker 1: I guess the question is how does this all tie
• 41:31
  Speaker 1: into dark matter? Because I know dark matter is very
• 41:34
  Speaker 1: important in the formation of galaxies. Right, It's almost like,
• 41:37
  Speaker 1: I know we've mentioned this before, the galaxies form around
• 41:40
  Speaker 1: where dark matter is. Does that effect sort of how
• 41:44
  Speaker 1: black holes might get formed.
• 41:45
  Speaker 2: It definitely affects where galaxies and black holes get formed. Right.
• 41:49
  Speaker 2: Galaxies basically trace out where the dark matter is in
• 41:52
  Speaker 2: the universe. If you look at the large scale structure
• 41:55
  Speaker 2: of the universe, you see these filaments of galaxies and
• 41:57
  Speaker 2: these sheets of galaxies and that's because that where the
• 42:00
  Speaker 2: dark matter is. We can't see the dark matter directly,
• 42:03
  Speaker 2: but we can see that it's gathered together all this
• 42:05
  Speaker 2: matter and made all of those galaxies. And so every
• 42:08
  Speaker 2: galaxy has a huge dark matter halo around it, Like
• 42:11
  Speaker 2: the Milky Way is about one hundred thousand light years across,
• 42:15
  Speaker 2: but there's a big blob of dark matter that's like
• 42:17
  Speaker 2: two hundred thousand light years across that the Milky Way
• 42:19
  Speaker 2: is embedded in. Now, if we shot our black hole
• 42:22
  Speaker 2: out of our galaxy, then it would pass through that
• 42:25
  Speaker 2: dark matter halo, and it would gobble up a lot
• 42:27
  Speaker 2: of dark matter along the way. And so as these
• 42:30
  Speaker 2: supermassive black holes leave the galaxies, they can increase their
• 42:35
  Speaker 2: dark matter fraction.
• 42:36
  Speaker 1: They can get even darker than black Yeah.
• 42:40
  Speaker 2: We think that these black holes already have some dark
• 42:42
  Speaker 2: matter in them because dark matter is everywhere. But dark
• 42:45
  Speaker 2: matter also isn't sticky, and so it's very easy for
• 42:47
  Speaker 2: dark matter to just like rotate in orbit forever around
• 42:51
  Speaker 2: the galaxy and not fall in. We think will probably
• 42:54
  Speaker 2: fall into the center of the galaxy because eventually it's
• 42:56
  Speaker 2: like dynamical friction. Our star will get pushed by others
• 42:59
  Speaker 2: stars on. All that jostling ends up kicking somebody towards
• 43:03
  Speaker 2: the center of the galaxy. But dark matter doesn't do that,
• 43:06
  Speaker 2: right because dark matter just passes right through itself. So
• 43:08
  Speaker 2: normally dark matter can swirl around the center of the
• 43:11
  Speaker 2: galaxy not getting eaten by the black hole. But if
• 43:13
  Speaker 2: the black hole like runs free, then it's basically like
• 43:16
  Speaker 2: plowing through a buffet of dark matter.
• 43:19
  Speaker 1: But maybe when as the galaxy was forming, maybe the
• 43:22
  Speaker 1: black hole did eat a lot of dark matter. Or
• 43:25
  Speaker 1: maybe I wonder if the black hole in the middle
• 43:27
  Speaker 1: of galaxies is maybe mostly made out of dark matter.
• 43:30
  Speaker 2: It's hard to know, right, And what does it mean
• 43:32
  Speaker 2: to be made of dark matter? Because once it goes
• 43:34
  Speaker 2: past the event horizon, who knows what happens? Everything's dark matter,
• 43:40
  Speaker 2: everything's something else, some black hole state of matter. Right,
• 43:43
  Speaker 2: we don't know if dark matter gets annihilated it turns
• 43:45
  Speaker 2: into something else, or if it retains something of its nature.
• 43:49
  Speaker 2: We just don't even know because we don't know the
• 43:50
  Speaker 2: particle properties of it. So, like, what are the conservation
• 43:53
  Speaker 2: laws for dark matter? The universe might like keep track
• 43:56
  Speaker 2: of how much dark matter there is and not allow
• 43:57
  Speaker 2: things to convert. We just don't know so clueless about it.
• 44:01
  Speaker 1: So some black holes might be darker than others.
• 44:03
  Speaker 2: Absolutely, some might be darker than others. We know that
• 44:05
  Speaker 2: some galaxies are darker than others, some galaxies have a
• 44:08
  Speaker 2: larger dark matter fraction than others. That's for sure, all right.
• 44:12
  Speaker 1: Well, what does it mean for our understanding of galaxies
• 44:15
  Speaker 1: and how they form?
• 44:16
  Speaker 2: It means that we're still the very beginning of the
• 44:18
  Speaker 2: journey of understanding how galaxies come together, which is sort
• 44:22
  Speaker 2: of shocking because we've been setting galaxies for so long,
• 44:25
  Speaker 2: but every few decades we'd learned something new and surprising
• 44:28
  Speaker 2: about what's going on with these galaxies, how they come together,
• 44:31
  Speaker 2: what their history is, and what their future fate is. Right,
• 44:35
  Speaker 2: and we know that the galaxies and sort of our
• 44:37
  Speaker 2: local group are gravitationally bound together and so eventually going
• 44:41
  Speaker 2: to end up falling together and probably forming one super
• 44:45
  Speaker 2: galaxy while they're being separated from the rest of the
• 44:47
  Speaker 2: universe by dark energy. And that super galaxy is going
• 44:50
  Speaker 2: to have a super duper massive black hole at its
• 44:53
  Speaker 2: center unless that gets kicked out and shot into intergalactic space.
• 44:58
  Speaker 2: So it tells us a lot about our our potential
• 45:00
  Speaker 2: future because as we orbit our galaxy and merge with
• 45:03
  Speaker 2: those other galaxies, we also eventually fall towards the center
• 45:07
  Speaker 2: of this blob. And if there's a giant black hole
• 45:09
  Speaker 2: waiting for us there, this is really only one way
• 45:11
  Speaker 2: for the story to end.
• 45:12
  Speaker 1: But even if we kick out that black hole, eventually
• 45:15
  Speaker 1: the galaxy is going to collapse anyways, right, and maybe
• 45:18
  Speaker 1: it will collapse into a new black hole.
• 45:19
  Speaker 2: Yeah, exactly, it could definitely form a new black hole
• 45:22
  Speaker 2: even if you kick out the original one. There's no
• 45:24
  Speaker 2: noncompete clause in galactic formation.
• 45:26
  Speaker 1: And when is this supposed to happen, like tomorrow or
• 45:30
  Speaker 1: trillions of years?
• 45:32
  Speaker 2: Oh, we're talking about billions and billions of years for sure,
• 45:35
  Speaker 2: So we are much more a threat of the Sun
• 45:37
  Speaker 2: expiring before our system collapses into the center of a
• 45:40
  Speaker 2: black hole. But if we want to continue on for
• 45:42
  Speaker 2: billions and billions of years, we definitely need to plan
• 45:45
  Speaker 2: deep into the future. And also, we're just curious about
• 45:47
  Speaker 2: how black holes work and how galaxies work, and we
• 45:50
  Speaker 2: want to understand it because it could be that there's
• 45:52
  Speaker 2: some other deep insight into the way the universe works
• 45:55
  Speaker 2: waiting for us. Every time. In science, we're like, don't
• 45:58
  Speaker 2: really understand how something works, and we deeper, we discover
• 46:01
  Speaker 2: something fascinating underneath that we didn't even expect to find,
• 46:05
  Speaker 2: so satisfying our curiosity and like trying to understand this
• 46:08
  Speaker 2: in great detail is good path to like opening up
• 46:11
  Speaker 2: some surprising new doors. So we're doing our best to
• 46:14
  Speaker 2: improve our future prospects for understanding these things.
• 46:17
  Speaker 1: Mmm, sounds like a problem for the AIS. You could
• 46:21
  Speaker 1: just kick back, let to figure it out.
• 46:23
  Speaker 2: Well. One of my favorite ways to study these things
• 46:25
  Speaker 2: in the future is with our space based gravitational Observatory
• 46:30
  Speaker 2: so LIGO is this gravitational wave observatory that has two
• 46:33
  Speaker 2: arms that are kilometers long filled with lasers, and they're
• 46:36
  Speaker 2: planning to build one in space called Lisa LSA mean
• 46:40
  Speaker 2: much much bigger, and so it's going to be able
• 46:42
  Speaker 2: to observe gravitational waves at lower frequencies, which is what's
• 46:46
  Speaker 2: generated by the collisions of super massive black holes. So
• 46:50
  Speaker 2: we might be able to observe gravitational waves from galactic
• 46:54
  Speaker 2: mergers and understand this process in more detail. What happens
• 46:58
  Speaker 2: when two super massive black holes really do come together?
• 47:01
  Speaker 1: WHOA, which is what happens when two galaxies collide right.
• 47:04
  Speaker 2: Exactly, yeah, yeah, and so we could see the signature
• 47:07
  Speaker 2: of black holes getting injected from the hearts of their.
• 47:10
  Speaker 1: Galaxies, ejected or smushed.
• 47:12
  Speaker 2: Smushed or ejected. We don't know both outcomes are possible.
• 47:16
  Speaker 1: But will we hear the black hole get injected?
• 47:19
  Speaker 2: Well, black hole injection comes with a very powerful, very
• 47:22
  Speaker 2: directional gravitational wave signature, and so they think they might
• 47:26
  Speaker 2: be able to distinguish that from just like a normal
• 47:29
  Speaker 2: combination of two black holes into one. But it all depends
• 47:32
  Speaker 2: on this crazy set of satellites in space shooting lasers
• 47:36
  Speaker 2: in each other, measuring tiny changes in their relative distances.
• 47:41
  Speaker 1: Well, it sounds like the future is all black hole.
• 47:45
  Speaker 1: So we bidters start to understand them and get used
• 47:48
  Speaker 1: to them and figure out how they form.
• 47:50
  Speaker 2: Right, absolutely something we'd like to understand, not just because
• 47:54
  Speaker 2: we're curious about the universe, but because they might control
• 47:56
  Speaker 2: a fate of our galaxy.
• 47:57
  Speaker 1: Yep. Or it might be just something for our AI
• 48:00
  Speaker 1: replacements to figure out. We might be long gone.
• 48:06
  Speaker 2: I'll read about it from my lounge chair at the
• 48:08
  Speaker 2: center of the black hole.
• 48:09
  Speaker 1: All right, we hope you enjoyed that. Thanks for joining us.
• 48:12
  Speaker 1: See you next time.
• 48:21
  Speaker 2: Thanks for listening, and remember that Daniel and Jorge Explain
• 48:24
  Speaker 2: the Universe is a production of iHeartRadio. For more podcasts
• 48:28
  Speaker 2: from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever
• 48:32
  Speaker 2: you listen to your favorite shows.