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Speaker 1: Hey, Daniel, have you started planning for your retirement retirement?

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Speaker 2: Why would I ever retire?

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Speaker 1: I mean, you're gonna be a physicist forever to you're

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Speaker 1: dying breath.

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Speaker 2: I don't see myself burning out of questions.

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Speaker 1: Well, I guess eventually the Sun is gonna expand blow

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Speaker 1: up and burn the Earth, right, so at some point you.

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Speaker 2: Have to stop. I guess so, And eventually the galaxy

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Speaker 2: will collapse into a black hole. But that doesn't mean

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Speaker 2: we have to stop.

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Speaker 1: You're gonna be doing physics inside of the black hole.

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Speaker 2: Absolutely, I'll be writing papers about the singularity that nobody

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Speaker 2: can ever read.

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Speaker 1: Oh, because you're inside the black hole, right, unless I'm

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Speaker 1: like closer to the center, in which case you could

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Speaker 1: still technically send me the paper.

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Speaker 2: Yeah, and I could never get your comments back. Hey,

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Speaker 2: that sounds pretty good.

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Speaker 1: Actually, it's a win win situation or a lose lose situation.

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Speaker 1: It's a wind lose wind loose situation.

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Speaker 2: I'll be waiting for pure you literally forever.

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Speaker 3: Hi.

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Speaker 1: I'm Jorge, cartoonist and the creator of PhD comics.

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Speaker 2: Hi. I'm Daniel. I'm a particle physicist and a professor

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Speaker 2: at UC Irvine, and I do plan on doing this.

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Speaker 1: Forever, forever, even after your death.

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Speaker 2: I'm hoping my ideas live on.

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Speaker 1: Are you going to program an AI to do research

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Speaker 1: for you and make your children feel guilty after you're gone.

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Speaker 2: I'm going to upload my intelligence into the cloud so

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Speaker 2: I can continue to live as some sort of weird

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Speaker 2: mixture between biological and mechanical intelligence. But even that eventually

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Speaker 2: will fall into the galactic center and be gobbled up

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Speaker 2: by the black hole.

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Speaker 1: M But I guess why wait? I mean we could

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Speaker 1: technically generate this podcast with AI right now.

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Speaker 2: Can How do you know we haven't already? Who do

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Speaker 2: you think he's writing these outlines? Oh? My god?

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Speaker 1: Am I talking to an AI right now?

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Speaker 2: Maybe I'm talking to an AI right now? Maybe AI

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Speaker 2: are listening to this podcast.

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Speaker 1: He did seem smarter than usual.

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Speaker 2: That's the real Daniel.

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Speaker 1: And the real Danger. But anyways, welcome to our podcast

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Speaker 1: Daniel and Jorge Explain the Universe, a production of our

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Speaker 1: Heart Radio.

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Speaker 2: In which we use are still limited biological intelligence to

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Speaker 2: try to understand how the universe works. We want to

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Speaker 2: know everything that's out there. We want to know how

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Speaker 2: it works on the microscopic scale, to weave itself together

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Speaker 2: into reality that we experience and that we want to understand.

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Speaker 2: We cast our minds out into the farthest reaches of

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Speaker 2: space and hope to understand what they might encounter out there.

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Speaker 1: That's right, because it is a very perplexing universe full

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Speaker 1: of interesting mysteries for us to go out there explore

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Speaker 1: and try to uncover, and try to understand and try

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Speaker 1: to explain to others.

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Speaker 2: Some mysteries have lasted for decades or centuries or millennia,

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Speaker 2: but others have succumbed to the onslaught of human intelligence.

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Speaker 2: We have sometimes actually managed to crack puzzles of the

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Speaker 2: universe and understand what's going on at the atomic scale

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Speaker 2: or the subatomic scale, or how space bends to form

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Speaker 2: black holes. So there are times when our limited intelligence

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Speaker 2: is enough.

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Speaker 1: Why I make it sound like we're masters of the universe?

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Speaker 1: How far along are we are? We up to like

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Speaker 1: one percent of the universe by now.

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Speaker 2: I think that's probably a pretty generous estimate. But it's promising.

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Speaker 2: You know, we are making progress and we are understanding things,

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Speaker 2: and the understanding is coming faster and faster. So far,

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Speaker 2: there's no evidence that we're going to hit some wall

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Speaker 2: of understanding.

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Speaker 1: Especially with the AIS. Could we train AIS or just

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Speaker 1: ask AIS to do research for us?

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Speaker 2: I use AIS in my research all the time. We

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Speaker 2: have AIS answering questions. The big challenge is understanding what

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Speaker 2: they're doing. Are they doing physics for themselves or are

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Speaker 2: they doing it for us?

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Speaker 1: What do you mean for themselves? Like for their own curiosity?

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Speaker 1: Oh my god, are yet that already?

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Speaker 2: Well? We have AIS generating YouTube videos that are mostly

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Speaker 2: watched by other AIS to generate response videos, and now

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Speaker 2: we have AIS generating physics research, and at some point

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Speaker 2: AIS are going to be reading that physics research and

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Speaker 2: summarizing it for themselves.

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Speaker 1: Huh. So I wonder if the AI science community is

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Speaker 1: going to have as much politics and drama as the

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Speaker 1: real physics community, or maybe even more right, more drama.

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Speaker 1: But it's all artificial drama.

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Speaker 2: So all drama is artificial, and.

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Speaker 1: It happens faster, I guess, which is good.

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Speaker 2: Though there might be some real drama going on at

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Speaker 2: the center of our galaxy, as the black hole there

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Speaker 2: keeps sucking things in that's swirling around it.

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Speaker 1: Yes, we discussed on this podcast. There's a lot going

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Speaker 1: on at the center of galaxies, including some very big mysteries.

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Speaker 2: That's right, as we peer towards the center of our

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Speaker 2: own galaxy, we notice a very very large black hole

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Speaker 2: sitting there, gobbling up anything that comes near it, and

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Speaker 2: while we are safely swirling around it at tens of

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Speaker 2: thousands of light years away, eventually we think that everything

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Speaker 2: might fall into that black hole, flush down, the gravitational.

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Speaker 1: Drain down physics toilet? Is that really the case? Eventually? Like,

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Speaker 1: there's no prediction where we don't get sucked into that

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Speaker 1: black hole.

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Speaker 2: There are some variations. If the universe keeps expanding at

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Speaker 2: a faster and faster rate and something called phantom energy

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Speaker 2: takes over and creates enough space between us and the

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Speaker 2: central black hole to distance us from it. But if

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Speaker 2: dark energy stays at the level that it is, the

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Speaker 2: prediction is that the universe ends up with a bunch

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Speaker 2: of isolated galaxies, each of which collapse into their own

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Speaker 2: black holes.

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Speaker 1: Wait wait, wait, did you just say phantom energy.

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Speaker 2: Phantom energy exactly like.

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Speaker 4: The Phantom Menace named after that movie exactly. Not a coincidence,

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Speaker 4: m I guess we'll have to dig into that in

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Speaker 4: another episode. But it is interesting how as you said

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Speaker 4: that every galaxy has a black hole.

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Speaker 2: It is pretty cool to have a black hole the

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Speaker 2: center of our galaxy, and it makes us wonder if

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Speaker 2: that required for every galaxy. Is that a necessary product

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Speaker 2: of a galaxy? Do you have to have a black

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Speaker 2: hole to form a galaxy? Do galaxies form black holes?

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Speaker 2: Do black holes create galaxies?

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Speaker 1: It's a deep question, and so today on the podcast

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Speaker 1: we'll be asking the question, does every galaxy have a

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Speaker 1: black hole at its center? You mean, like like a

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Speaker 1: tasty snack or something like are there any defective galaxies

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Speaker 1: that they didn't get a black hole in the middle?

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Speaker 2: You mean, like you'd be disappointed to bite into a

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Speaker 2: galaxy and be like, oh, I didn't get a black

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Speaker 2: hole in the middle.

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Speaker 1: I know, that's the tastiest part. It's got the richest flavor.

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Speaker 2: So deep. That's interesting because black holes have mass, but

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Speaker 2: I wonder if they actually have calories. Like if you

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Speaker 2: eat a black hole, do you lose weight?

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Speaker 1: Or is the secret to a new diet?

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Speaker 2: I guess really the black hole eats you and it

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Speaker 2: gains weight, so you become part of the black hole.

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Speaker 1: Something gets eaten and it's you, which I guess is

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Speaker 1: a diet in a way you lose a lot more

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Speaker 1: than weight.

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Speaker 2: Though, definitely do not take health advice from either of us.

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Speaker 1: That's right, from either physicist or cartoonists, not the healthiest

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Speaker 1: people in the world or the universe.

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Speaker 2: We are totally unqualified to dispense health advice. I know

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Speaker 2: that doesn't stop most podcasters, but it does give us pause.

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Speaker 1: So, yeah, this is an interesting question. Does every galaxy

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Speaker 1: have a black hole at its center? I guess a

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Speaker 1: lot of galaxies have black holes at their centers.

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Speaker 2: We certainly have seen a black hole in the center

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Speaker 2: of our galaxy and a few others. But it's a

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Speaker 2: really interesting question both about how black holes get formed

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Speaker 2: and how galaxies get formed. It seems like there's a

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Speaker 2: fascinating dance between the two.

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Speaker 1: I guess. Kind of the deeper question is like, do

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Speaker 1: you need to have a black hole at the center

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Speaker 1: to have a galaxy?

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Speaker 2: Yeah? Exactly does it count as a galaxy if it's

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Speaker 2: just a bunch of stars?

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Speaker 1: So, as usual, we were wondering how many people have

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Speaker 1: asked this question, whether every galaxy has a black hole?

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Speaker 1: So Daniel went out there into the wilds of the

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Speaker 1: internet to ask folks, does every galaxy a black hole

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Speaker 1: at its center.

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Speaker 2: Thanks very much, my enduring gratitude to everybody who participates

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Speaker 2: in this segment. But remember it's open to everyone. If

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Speaker 2: you've been listening to pod and learning for years and

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Speaker 2: feel ready to answer a random questions, please don't be shy.

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Speaker 2: Write to me two questions at Danielandjorge dot com. We

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Speaker 2: want to hear from you.

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Speaker 1: So think about it for a second. You think every

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Speaker 1: galaxy has a black hole. Here's what people had to say.

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Speaker 5: Man, who knows if black holes even exist? Like, what

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Speaker 5: if they're just all dark stars like you guys talked

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Speaker 5: about earlier on the show. There could be wormholes or

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Speaker 5: something that we haven't even thought of yet. So no,

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Speaker 5: not all galaxies.

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Speaker 6: A galaxy is a cluster of a bunch of objects

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Speaker 6: in space swirling around a massive object in the middle.

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Speaker 6: And the only massive object you can have is a

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Speaker 6: black hole or a store I guess, and you can't

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Speaker 6: have such a big star. So I think every galaxy

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Speaker 6: has to have a black hole in the middle.

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Speaker 3: Probably there's got to be something like holding it all together.

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Speaker 3: But sence space is really big. Maybe there's some galaxies

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Speaker 3: that don't and they're just like really dense packed like

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Speaker 3: stars spinning around each other.

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Speaker 2: I would guess that just because you're asking the question,

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Speaker 2: the answer is no, But I don't know. I would

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Speaker 2: for you guys to explain it to me.

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Speaker 1: All Right, some people we have some conspiracy theories, apparently

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Speaker 1: as listeners, some galactic conspiracy theorists.

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Speaker 2: Well, we are guilty of promoting those black hole conspiracy

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Speaker 2: theories right when we talk on the podcast about how

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Speaker 2: black holes might be dark stars or fuzzballs or something else.

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Speaker 2: Even weirder, are you seen?

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Speaker 1: We're ground Sero or the black hole ism movement.

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Speaker 2: Black hole truthers. Yeah, this is the dark Horse podcast

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Speaker 2: for black holes exactly.

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Speaker 1: Maybe if we switched our podcast name to like universal

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Speaker 1: conspiracies or conspiracies about everything, maybe our ranking will go up.

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Speaker 2: It might go up, we might get a bigger audience.

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Speaker 2: But I don't think we'd get a better audience.

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Speaker 1: I mean, isn't physics, after all, just like the Hunt

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Speaker 1: for the Conspiracy.

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Speaker 2: Of the Universe.

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Speaker 1: You're like, there's something going on here, There's some sort

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Speaker 1: of plan or structure. We got to find out what

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Speaker 1: it is. We got to find out the truth. Man,

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Speaker 1: Isn't that what physics is all about.

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Speaker 2: Yeah, but conspiracies are usually built on wild speculation and

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Speaker 2: a lack of evidence.

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Speaker 1: Isn't that every other episode we discussed on the podcast.

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Speaker 2: Yeah, but we don't trust strong conclusions based on our

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Speaker 2: lack of knowledge. We talk about what we don't know

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Speaker 2: and how we might actually figure it out. We're trying

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Speaker 2: to build evidence. We're looking for data when we're happy

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Speaker 2: to disprove our ideas if the universe shows us we're wrong.

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Speaker 1: It sounds like something someone involved in a conspiracy would say.

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Speaker 2: And you've just proven that you can make a conspiracy

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Speaker 2: about anything with no information.

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Speaker 1: But anyways, this is an interesting question. Does every galaxy

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Speaker 1: have a black hole at its center? And, as you said,

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Speaker 1: there is one at the center of our galaxy. The

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Speaker 1: last podcast were recorded talked about how there's a big

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Speaker 1: one at the center of our galaxy, along with a

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Speaker 1: whole bunch of other stuff going on down there.

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Speaker 2: We certainly think that there is a black hole at

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Speaker 2: the center of our galaxy.

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Speaker 1: What do you say, we think?

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Speaker 2: Yeah, we don't really ever know for sure. I mean,

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Speaker 2: our galactic center is the one that's closest to us,

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Speaker 2: so it's easiest to study. It's also shrouded in gas

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Speaker 2: and dust, so it's complicated to study, and in the end,

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Speaker 2: all of our evidence for black holes is always a

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Speaker 2: little bit indirect. Usually the observations tell us that there's

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Speaker 2: something there that's very massive, something that's very small and

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Speaker 2: also has a lot of gravity, but we've never actually

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Speaker 2: observed an event horizon directly. It's always a little bit indirect.

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Speaker 1: I guess it's kind of hard to see a black

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Speaker 1: hole because they don't emit light themselves.

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Speaker 2: They might emit light. There might be gentle hawking radiation

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Speaker 2: from black holes, which would be very powerful direct evidence

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Speaker 2: for black holes, but that's not something we've ever seen.

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Speaker 2: The story of black holes for the last few decades

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Speaker 2: is an increasing belief that black holes probably are real.

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Speaker 2: As we identify these very massive objects and we put

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Speaker 2: limits on how big they can be, we see things

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Speaker 2: approaching closer and closer to the black hole the center

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Speaker 2: of our galaxy, which tells us more and more about

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Speaker 2: how small it has to be. And there are only

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Speaker 2: a few things out there that could satisfy all of

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Speaker 2: those constraints that are that massive and that compact. Black

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Speaker 2: holes of course the most classic example. But now we

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Speaker 2: have a few other candidates, dark stars, fuzzballs, et cetera,

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Speaker 2: et cetera.

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Speaker 1: Yeah, it's still a big mystery talking about the ones

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Speaker 1: that are at the center of galaxies. Let's maybe break

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Speaker 1: it down for folks and talk about black holes a

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Speaker 1: little bit in general, and the different kinds of black

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Speaker 1: holes that are out there and that could be at

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Speaker 1: the center of different galaxies.

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Speaker 2: When we hear about black holes, we're often thinking about

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Speaker 2: stellar black holes. Like a star burns for billions of

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Speaker 2: years until eventually it's fusion peters out and it loses

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Speaker 2: the battle with gravity, so the gravity collapses the star

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Speaker 2: into a black hole, meaning that there's a region of

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Speaker 2: space where there's so much mass and energy that space

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Speaker 2: becomes so dramatically curved that every path within the event

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Speaker 2: horizon leads towards the center. That any particle that passes

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Speaker 2: into that event horizon will eventually find its way to

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Speaker 2: this center of that region. There are no paths out.

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Speaker 2: Space within the event horizon is so bent that every

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Speaker 2: timelike path for a particle leads towards the center. So

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Speaker 2: that's a stellar black hole. And those are awesome, which

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Speaker 2: is why we call them stellar, but also because they

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Speaker 2: collapse from individual stars, and they can be quite big,

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Speaker 2: like ten times the mass of our Sun, but they're

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Speaker 2: small compared to the kinds of black holes we're going

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Speaker 2: to talk about today.

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Speaker 1: Yeah, those are called super massive black holes.

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Speaker 2: Yeah, there's basically two categories of black holes. The stellar

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Speaker 2: mass black holes that are like a few tens of masses,

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Speaker 2: and then we jump up to really really really big

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Speaker 2: black holes, things like ten thousand or one hundred thousand

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Speaker 2: times the mass of our Sun in one huge black hole.

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Speaker 2: But they get much much bigger than that as well.

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Speaker 2: There are black holes that are millions or even billions

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Speaker 2: of times the mass of our Sun. And these are

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Speaker 2: the ones found at the hearts of galaxies.

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Speaker 1: Yeah, you can sort of see them even in distant,

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Speaker 1: faraway galaxies, right, Like when you look at little Fuzzz

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Speaker 1: out there in the night sky with special telescopes, you

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Speaker 1: can actually kind of see the black hole in the middle. Right.

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Speaker 2: Yeah, that's a really interesting and complicated question, like how

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Speaker 2: do we see these black holes in the milky way?

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Speaker 2: We have actually a lot of really interesting and cool

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Speaker 2: ways to look at the black hole because it's so close.

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Speaker 2: Like some of the best evidence we have is a

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Speaker 2: picture of the black hole released by the event Horizon telescope,

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Speaker 2: which is actually a picture of the accretion disk around

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Speaker 2: the black hole, the hot gas that's swirling very very

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Speaker 2: close to it and radiating light because it's so hot,

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Speaker 2: so we can see that. We can also see stars

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Speaker 2: orbiting very very close to the black hole the center

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Speaker 2: of our galaxy. There's this one star in particular S two,

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Speaker 2: with zooms super close to the black hole and whips

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Speaker 2: around it. We've actually seen an entire orbit of that

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Speaker 2: star all the way around the black hole, which won

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Speaker 2: a Nobel prize very recently. So the black hole the

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Speaker 2: center of our galaxy we've observed very closely. Black Holes

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Speaker 2: in other galaxies are harder to spot because those galaxies

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Speaker 2: are further away now.

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Speaker 1: For the one at the center of our galaxy. Even

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Speaker 1: that one, we're not one hundred percent sure it is

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Speaker 1: a black hole, right, It could still be something else

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Speaker 1: super massive there, or are we pretty sure it's a

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Speaker 1: super mass black hole.

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Speaker 2: I think both of those things are true. We don't

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Speaker 2: have direct evidence that it's a black hole. We know

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Speaker 2: that there's a lot of mass there because we see

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Speaker 2: the influence of that object on the nearby stars and

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Speaker 2: all the gas and dust. We know that it's not

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Speaker 2: emitting any light itself, so it's compact, it's dark, and

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Speaker 2: it's massive. So most physicists, I think, are pretty convinced

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Speaker 2: that it's a black hole. But that's just sort of

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Speaker 2: like the best idea we have. There are these alternative

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Speaker 2: theories that it could be a very rapidly collapsing region

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Speaker 2: of space which is going to bounce back and turn

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Speaker 2: into a white hole, for example. So there are other

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Speaker 2: theories there, but I think the mainstream physics community is

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Speaker 2: pretty convinced that it's a black.

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Speaker 1: Hole, all right, So then how do we see them

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Speaker 1: in other galaxies?

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Speaker 2: There's sort of two ways to see black holes in

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Speaker 2: other galaxies. One is when they're feeding. When black holes

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Speaker 2: are eating stuff, when they have like a lot of

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Speaker 2: gas swirling very close to them and falling in, it

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Speaker 2: tends to get hot and that gas radiates and they

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Speaker 2: can generate very very powerful beams of light. These are

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Speaker 2: things we call quasars, and we can see these from

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Speaker 2: like across the universe. There's some objects that are super

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Speaker 2: duper far away but incredibly bright, and when they were

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Speaker 2: discovered decades ago, people couldn't believe that they were actually

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Speaker 2: that far away because they look super bright already here

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Speaker 2: on Earth, and if they're also very very distant, that

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Speaker 2: means that at their source they're incredibly bright. And that's

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Speaker 2: exactly what's happening. The gas around in the black hole

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Speaker 2: is getting very very heated up, and as it falls in,

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Speaker 2: it radiates, and it radiation gets channeled by the magnetic

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Speaker 2: field of the black hole, and you get these very

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Speaker 2: powerful beams emitted from above and below the black hole,

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Speaker 2: and we can see those from very very far away.

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Speaker 2: So those are quasars. But we can only see that

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Speaker 2: for black holes that are like actively feeding and growing,

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Speaker 2: and that tends to happen sort of early in the

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Speaker 2: life cycle of the universe. Quasars peaked about ten billion

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Speaker 2: years ago, so that's good for seeing like young super

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Speaker 2: massive black holes very very far away.

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Speaker 1: So not every super massive black hole is a quasar, right,

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Speaker 1: There are some that could be out there just sitting

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Speaker 1: there being big.

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Speaker 2: Exactly most of the super massive black holes we think

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Speaker 2: are not quasars. We think that a lot of them

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Speaker 2: stop sort of quazing billions of years ago and are

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Speaker 2: now more like dark relics, huge black holes sitting at

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Speaker 2: the centers of galaxies but not being quasars anymore. But

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Speaker 2: we can still spot those by looking at the motion

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Speaker 2: of stars around them. So pick them nearby galaxy and

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Speaker 2: look at the stars that are near the center of it.

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Speaker 2: You can't resolve them individually. We don't have telescopes that

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Speaker 2: can say here's a star, there's a star, there's a star.

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Speaker 2: But we can look at stellar populations at the hearts

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Speaker 2: of other galaxies, and we can measure their velocities, we

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Speaker 2: can measure their brightness. It's really complicated and very computationally expensive,

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Speaker 2: but we can build a model of how fast those

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Speaker 2: stars are moving around the center of that galaxy, and

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Speaker 2: from that we can infer the mass of the black hole.

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Speaker 2: How heavy does the thing have to be at the

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Speaker 2: center of the galaxy to support this super fast radial

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Speaker 2: motion by those stars.

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Speaker 1: All right, well, let's get into whether every galaxy has

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Speaker 1: a black hole and what would it mean for a

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Speaker 1: galaxy to not have a black hole at its center.

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Speaker 1: But first let's take a quick break. All right, we're

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Speaker 1: asking the question does every galaxy have a black hole

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Speaker 1: at its center? Like, does every galaxy have a dark

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Speaker 1: soul or something?

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Speaker 2: I'll leave you the philosophical and moral implications of it.

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Speaker 2: But from a physics point of view, it's a trend

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Speaker 2: that we're noticing that galaxies have these black holes, and

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Speaker 2: so we wonder if it's a rule. You know, it's

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Speaker 2: basically our strategy in physics is like, look out of

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Speaker 2: the universe, find patterns, wonder if those patterns reflecting like

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Speaker 2: deep rules of the universe. Figure out what those rules

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Speaker 2: have to be. So, you know, we're still in like

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Speaker 2: step two here.

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Speaker 1: Hmmm, Now, I guess what is it to say, Like,

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Speaker 1: you know, we can see traillions of galaxies out there

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Speaker 1: in space, can we tell what percentage of them have

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Speaker 1: black holes? Or does every galaxy we've seen have a

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Speaker 1: black hole in it that we can tell?

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Speaker 2: Yeah, that's a great point. You're right that we can

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Speaker 2: see zillions and zillions of galaxies out there, like the

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Speaker 2: Hubble deep field or the James Web deep field. Whenever

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Speaker 2: it focuses on some random patch of space and resolves it,

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Speaker 2: you can see evidence for so many galaxies in every

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Speaker 2: tiny little corner of space. So we know there are

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Speaker 2: lots and lots of galaxies out there. Very few of those, however,

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Speaker 2: have we identified a super massive black hole, in a

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Speaker 2: few very distant ones that happen to be koasars where like, okay,

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Speaker 2: that's definitely a super massive black hole, and some nearby

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Speaker 2: ones where we can watch the stellar populations and infer

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Speaker 2: that there must be something very very heavy at the core.

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Speaker 2: But most of those we can't do either because they're

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Speaker 2: either too far away or too quiet. But every galaxy

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Speaker 2: that's close enough for us to watch the stars, we

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Speaker 2: have seen a super massive black hole at its center.

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Speaker 2: So there's lots of galaxies out there, only very small

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Speaker 2: number can we check for a black hole, And every

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Speaker 2: single time we've checked, we've found one.

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Speaker 5: Mmmm.

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Speaker 1: So, like Andromeda, isn't it? Andromeda the closest galaxy to us.

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Speaker 2: Andromeda is the closest galaxy to us, and we think

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Speaker 2: it has a huge black hole at its center, and

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Speaker 2: it's close enough that we can pretty well model the

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Speaker 2: velocities of the stars at the center of that galaxy,

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Speaker 2: and so we're pretty sure there has to be something

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Speaker 2: super massive and very dense at the heart of Andromeda,

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Speaker 2: very likely a black hole.

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Speaker 1: All right, So then the data kind of suggests that,

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Speaker 1: like if you look at the galaxies that we can't

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Speaker 1: look at we do see a black hole in the

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Speaker 1: middle there, or something that is probably a black hole,

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Speaker 1: but why else would we extrapolate that to every galaxy

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Speaker 1: in the universe.

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Speaker 2: Yeah, that's a good question. And to underscore sort of

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Speaker 2: our lack of knowledge here, we really identified black holes

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Speaker 2: in an approximately like one hundred to two hundred galaxies.

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Speaker 2: So of the zillions of galaxies that we've seen, only

443
00:20:55,800 --> 00:20:58,160
Speaker 2: a very small number have we been able to do

444
00:20:58,200 --> 00:21:01,760
Speaker 2: this check. And so you're tentative when you're extrapolating from

445
00:21:01,800 --> 00:21:05,480
Speaker 2: like a few hundred examples two trillions of objects out there.

446
00:21:05,840 --> 00:21:07,640
Speaker 2: On the other hand, it's every single one that we've

447
00:21:07,640 --> 00:21:10,000
Speaker 2: seen so far, right, so we wonder if it really

448
00:21:10,080 --> 00:21:10,760
Speaker 2: is a theory.

449
00:21:10,880 --> 00:21:13,200
Speaker 1: So there's no black hole nearby, then we can check

450
00:21:13,280 --> 00:21:15,119
Speaker 1: that they didn't have a black hole in it, or

451
00:21:15,119 --> 00:21:17,720
Speaker 1: would we know or I guess what are you saying.

452
00:21:17,960 --> 00:21:20,440
Speaker 2: I'm saying there's no galaxy nearby that we can check

453
00:21:20,640 --> 00:21:22,440
Speaker 2: that hasn't had a black hole in it, and that

454
00:21:22,520 --> 00:21:26,440
Speaker 2: includes really large galaxies like Andrameda, and also even dwarf

455
00:21:26,480 --> 00:21:30,320
Speaker 2: galaxies like there's a dwarf galaxy called RGG one one

456
00:21:30,400 --> 00:21:33,240
Speaker 2: eight and they recently found what they call a teeny

457
00:21:33,320 --> 00:21:35,280
Speaker 2: tiny super massive black hole in it.

458
00:21:35,320 --> 00:21:39,080
Speaker 1: Where is that the actual scientific name? Teeny tiny supermassive?

459
00:21:40,080 --> 00:21:41,920
Speaker 2: That was the title of the press release. I don't

460
00:21:41,960 --> 00:21:43,760
Speaker 2: know if that ended up in the paper or not.

461
00:21:44,040 --> 00:21:46,040
Speaker 1: Doesn't that just average to a small black hole.

462
00:21:46,680 --> 00:21:49,240
Speaker 2: It's only fifty thousand times the mass of the Sun,

463
00:21:49,560 --> 00:21:52,280
Speaker 2: So for a super massive black hole, it's pretty teeny

464
00:21:52,320 --> 00:21:55,159
Speaker 2: tiny compared to the Sun. It's pretty much a monster.

465
00:21:55,320 --> 00:21:57,920
Speaker 2: It depends on your perspective. But there's something else going

466
00:21:57,960 --> 00:22:01,159
Speaker 2: on here that makes us suspect that maybe every single

467
00:22:01,240 --> 00:22:04,199
Speaker 2: galaxy has a black hole in it. It's not just

468
00:22:04,280 --> 00:22:06,400
Speaker 2: that every single one we've seen has a black hole

469
00:22:06,440 --> 00:22:09,199
Speaker 2: in it, but we see this very tight pattern. We

470
00:22:09,320 --> 00:22:11,960
Speaker 2: notice this very close connection between the mass of the

471
00:22:11,960 --> 00:22:15,600
Speaker 2: super massive black hole and the mass of the galaxy.

472
00:22:16,160 --> 00:22:18,320
Speaker 2: And that might not be a surprise. You figure, like, look,

473
00:22:18,600 --> 00:22:22,160
Speaker 2: more stuff means a bigger galaxy, means more stars means

474
00:22:22,400 --> 00:22:25,199
Speaker 2: bigger black hole, right, And that's true. But if you

475
00:22:25,240 --> 00:22:27,359
Speaker 2: run those simulations, you get kind of a scatter like

476
00:22:27,400 --> 00:22:30,080
Speaker 2: you get some bigger black holes and some smaller black holes.

477
00:22:30,440 --> 00:22:32,560
Speaker 2: But what we notice when we plot, like the mass

478
00:22:32,560 --> 00:22:34,560
Speaker 2: of the black hole versus the mass of the galaxy

479
00:22:34,960 --> 00:22:38,719
Speaker 2: is a much tighter correlation than you would expect. Just

480
00:22:38,720 --> 00:22:41,600
Speaker 2: from like more stuff means bigger black hole, you get

481
00:22:41,600 --> 00:22:45,119
Speaker 2: this very very compact line that suggests that there's like

482
00:22:45,160 --> 00:22:48,240
Speaker 2: some feedback between the black hole and the galaxy.

483
00:22:48,359 --> 00:22:50,119
Speaker 1: So you mean, like when we look at a black

484
00:22:50,119 --> 00:22:52,760
Speaker 1: hole in another galaxy, we can tell its size first

485
00:22:52,760 --> 00:22:55,960
Speaker 1: of all, And if you compare the size of the

486
00:22:55,960 --> 00:22:58,000
Speaker 1: black hole to the size with the galaxy, it's like

487
00:22:58,160 --> 00:22:59,640
Speaker 1: it's like almost one to one.

488
00:22:59,720 --> 00:23:02,200
Speaker 2: Kind and if you're just made bigger and smaller galaxies

489
00:23:02,520 --> 00:23:04,920
Speaker 2: and guess how big the black holes would be, then

490
00:23:04,960 --> 00:23:07,400
Speaker 2: the same size galaxy shouldn't always give you the same

491
00:23:07,400 --> 00:23:09,760
Speaker 2: size black hole. Depends a little bit on like where

492
00:23:09,800 --> 00:23:12,359
Speaker 2: the stuff is and how much falls in, etc. But

493
00:23:12,400 --> 00:23:14,800
Speaker 2: what we notice is a very very close connection, as

494
00:23:14,800 --> 00:23:17,119
Speaker 2: you say, like one to one, that the mass of

495
00:23:17,160 --> 00:23:18,880
Speaker 2: the galaxy and the mass of the black hole track

496
00:23:19,160 --> 00:23:20,720
Speaker 2: very very closely.

497
00:23:20,720 --> 00:23:23,080
Speaker 1: Meaning that there's no small galaxy with a big black hole,

498
00:23:23,119 --> 00:23:25,160
Speaker 1: and there's no big galaxy with a small black.

499
00:23:25,000 --> 00:23:27,600
Speaker 2: Hole exactly, and two galaxies with the same size that

500
00:23:27,720 --> 00:23:31,240
Speaker 2: basically exactly the same size black hole at their heart.

501
00:23:31,280 --> 00:23:34,439
Speaker 2: There's almost no variation there, and that tells us that

502
00:23:34,440 --> 00:23:37,280
Speaker 2: there must be some sort of connection, that there's something

503
00:23:37,320 --> 00:23:39,359
Speaker 2: about how the black hole is forming and how the

504
00:23:39,400 --> 00:23:42,000
Speaker 2: galaxy is forming that connects these two things. I mean,

505
00:23:42,000 --> 00:23:43,720
Speaker 2: even from a spatial point of view, it's kind of

506
00:23:43,720 --> 00:23:46,080
Speaker 2: weird that like this dot at the very very center

507
00:23:46,119 --> 00:23:48,719
Speaker 2: of the galaxy. I remember, these things are very massive,

508
00:23:48,720 --> 00:23:51,560
Speaker 2: but they're also very very small, So it's weird that

509
00:23:51,640 --> 00:23:54,359
Speaker 2: this dot at the center of the galaxy is influenced

510
00:23:54,359 --> 00:23:57,320
Speaker 2: by like the mass of the whole huge galaxy that's

511
00:23:57,359 --> 00:24:01,000
Speaker 2: like one hundred thousand light years across. So there must

512
00:24:01,080 --> 00:24:03,840
Speaker 2: be some sort of connection between them, some information passing

513
00:24:03,880 --> 00:24:07,160
Speaker 2: back and forth, some process that's controlling both of them.

514
00:24:07,800 --> 00:24:09,879
Speaker 2: And if that's the case, and that makes us think, oh,

515
00:24:09,920 --> 00:24:12,239
Speaker 2: there must be a connection between the two. And so

516
00:24:12,320 --> 00:24:14,960
Speaker 2: probably every galaxy does have one of these.

517
00:24:14,800 --> 00:24:19,800
Speaker 1: Things, because, like you're saying, if it's sort of inevitable

518
00:24:19,880 --> 00:24:21,960
Speaker 1: for a galaxy to get a black hole in the

519
00:24:21,960 --> 00:24:25,880
Speaker 1: middle when it forms, then there probably isn't any galaxies

520
00:24:25,920 --> 00:24:26,640
Speaker 1: without black.

521
00:24:26,400 --> 00:24:30,639
Speaker 2: Holes, Yeah, exactly. And if there's some feedback mechanisms, something

522
00:24:30,680 --> 00:24:34,240
Speaker 2: which is controlling both of these things, then probably generated

523
00:24:34,320 --> 00:24:36,560
Speaker 2: both at the same time. It controls the stars that

524
00:24:36,640 --> 00:24:38,840
Speaker 2: form in the galaxy and also controls the mass of

525
00:24:38,880 --> 00:24:41,880
Speaker 2: the black hole. There must be some process tying these

526
00:24:41,920 --> 00:24:45,080
Speaker 2: things together, and being weirdly vague about that process because

527
00:24:45,160 --> 00:24:47,600
Speaker 2: we don't know what it is. There's a bunch of

528
00:24:47,640 --> 00:24:51,080
Speaker 2: theories about how the black hole might form and grow

529
00:24:51,160 --> 00:24:53,840
Speaker 2: and then the radiation from the black hole stops it

530
00:24:53,880 --> 00:24:56,919
Speaker 2: from growing, and the same process might control how stars

531
00:24:56,920 --> 00:24:59,320
Speaker 2: are formed and how they collapse from blobs of gas

532
00:24:59,320 --> 00:25:01,840
Speaker 2: and dust into stars. So there's a bunch of different

533
00:25:01,880 --> 00:25:04,399
Speaker 2: ideas out there, but they're all very vague and nobody

534
00:25:04,440 --> 00:25:06,240
Speaker 2: can really agree about it, or at the point where

535
00:25:06,280 --> 00:25:08,920
Speaker 2: we're just like, it seems like there's something going on here,

536
00:25:08,960 --> 00:25:10,280
Speaker 2: but we don't know what it is.

537
00:25:11,400 --> 00:25:14,280
Speaker 1: Although this relationship between the black hole and the galaxy

538
00:25:14,320 --> 00:25:18,520
Speaker 1: size comes from data of galaxies that we found that

539
00:25:18,640 --> 00:25:21,120
Speaker 1: have black holes, right, Like, maybe there's still the possibility

540
00:25:21,119 --> 00:25:23,800
Speaker 1: that won and in a thousand galaxies doesn't have a

541
00:25:23,800 --> 00:25:24,240
Speaker 1: black hole.

542
00:25:24,359 --> 00:25:26,199
Speaker 2: Yeah, it's certainly possible that that's the case. There's a

543
00:25:26,200 --> 00:25:29,800
Speaker 2: small number of galaxies here. Also, people might remember there

544
00:25:29,840 --> 00:25:33,600
Speaker 2: was recently this crazy idea that super massive black holes

545
00:25:33,680 --> 00:25:36,680
Speaker 2: or the hearts of galaxies are connected to the cosmic acceleration,

546
00:25:37,119 --> 00:25:40,040
Speaker 2: that they're really like bubbles of dark energy. And a

547
00:25:40,400 --> 00:25:43,280
Speaker 2: crucial thing that people notice that fueled that idea was

548
00:25:43,280 --> 00:25:46,160
Speaker 2: that there's a connection between the expansion of the universe

549
00:25:46,600 --> 00:25:49,280
Speaker 2: and the size of these black holes. That the black

550
00:25:49,280 --> 00:25:51,840
Speaker 2: holes seem to be more closely connected to the cosmic

551
00:25:51,880 --> 00:25:55,520
Speaker 2: expansion than their own galaxies. So that might seem like

552
00:25:55,560 --> 00:25:57,639
Speaker 2: it's in contradiction of what we're saying here today. Today

553
00:25:57,680 --> 00:25:59,520
Speaker 2: we're saying, oh, the black holes of the hearts of

554
00:25:59,560 --> 00:26:02,840
Speaker 2: galaxies are very closely connected to the size of their galaxies,

555
00:26:03,119 --> 00:26:04,919
Speaker 2: and a few weeks ago we said, no, they're not.

556
00:26:04,960 --> 00:26:07,400
Speaker 2: They're more closely connected to the universe. And the way

557
00:26:07,440 --> 00:26:09,440
Speaker 2: to untangle it is to remember that there's two different

558
00:26:09,520 --> 00:26:11,520
Speaker 2: kinds of black holes that we're seeing. We're talking about

559
00:26:11,720 --> 00:26:14,280
Speaker 2: black holes we see very very close to us, and

560
00:26:14,320 --> 00:26:17,240
Speaker 2: in those the black holes very tightly connected to the

561
00:26:17,280 --> 00:26:19,800
Speaker 2: mass of the galaxy, versus black holes that are very

562
00:26:19,840 --> 00:26:23,240
Speaker 2: far away, very old black holes those are from quasars,

563
00:26:23,840 --> 00:26:26,320
Speaker 2: So those are the ones that seem to be connected

564
00:26:26,359 --> 00:26:29,240
Speaker 2: to the cosmic expansion. So, long story short, there's a

565
00:26:29,280 --> 00:26:32,320
Speaker 2: lot we still don't understand about super massive black holes.

566
00:26:32,920 --> 00:26:36,000
Speaker 1: Even how they form, right, Like, that's still a big mystery.

567
00:26:36,200 --> 00:26:38,840
Speaker 2: Absolutely, we have no idea how these things even got

568
00:26:38,880 --> 00:26:40,720
Speaker 2: to exist. If you just start from like a big

569
00:26:40,760 --> 00:26:43,080
Speaker 2: blob of stuff and watch it form a galaxy, like

570
00:26:43,359 --> 00:26:46,119
Speaker 2: in simulation, you get a black hole at the center,

571
00:26:46,480 --> 00:26:49,199
Speaker 2: that's not a mystery, but it's not this big. Like

572
00:26:49,280 --> 00:26:51,480
Speaker 2: we look back in time by looking at old light

573
00:26:51,560 --> 00:26:54,600
Speaker 2: and looking at really early galaxies, and we notice that

574
00:26:54,640 --> 00:26:57,520
Speaker 2: they have huge black holes at their hearts, like already

575
00:26:57,880 --> 00:27:00,280
Speaker 2: billions of times the mass of the Sun, like the

576
00:27:00,280 --> 00:27:03,119
Speaker 2: first billion years of the universe. These are again the

577
00:27:03,240 --> 00:27:06,399
Speaker 2: very distant, very old black holes we see from quasars,

578
00:27:07,040 --> 00:27:10,320
Speaker 2: and we can't explain how that happens. In our simulations.

579
00:27:10,359 --> 00:27:13,080
Speaker 2: That just doesn't happen so quickly. It takes much longer

580
00:27:13,320 --> 00:27:15,920
Speaker 2: for these black holes to get so big. So there's

581
00:27:15,920 --> 00:27:18,119
Speaker 2: something else going on to form these black holes that

582
00:27:18,160 --> 00:27:19,159
Speaker 2: we don't understand.

583
00:27:19,400 --> 00:27:21,879
Speaker 1: So we really have no idea what could be going on.

584
00:27:21,960 --> 00:27:24,280
Speaker 1: I mean, it kind of seems like maybe there's a

585
00:27:24,320 --> 00:27:27,199
Speaker 1: simple explanation in there somehow, Like you know, if you

586
00:27:27,240 --> 00:27:29,359
Speaker 1: start with a big cloud of gas, and yeah, the

587
00:27:29,520 --> 00:27:31,440
Speaker 1: galaxy is going to be bigger, and the black hole

588
00:27:31,440 --> 00:27:33,080
Speaker 1: in the middle is going to be bigger, Like what's

589
00:27:33,160 --> 00:27:34,359
Speaker 1: the big mystery there?

590
00:27:34,520 --> 00:27:36,480
Speaker 2: Yeah, and that would give you a correlation that would

591
00:27:36,520 --> 00:27:40,040
Speaker 2: say that in general, masses of galaxies should be connected

592
00:27:40,080 --> 00:27:41,960
Speaker 2: to the masses of the black hole. And we see that.

593
00:27:42,320 --> 00:27:44,760
Speaker 2: But again we see a much tighter connection than you

594
00:27:44,760 --> 00:27:47,840
Speaker 2: would expect just from that simple explanation. We see that

595
00:27:48,040 --> 00:27:51,720
Speaker 2: galaxies with the same mass have basically exactly the same

596
00:27:52,119 --> 00:27:55,240
Speaker 2: mass black hole. There's like no variation there. So the

597
00:27:55,240 --> 00:27:57,920
Speaker 2: connection is just tighter than what you would expect from

598
00:27:57,920 --> 00:28:00,680
Speaker 2: that simple argument. So there must be something else going on.

599
00:28:00,840 --> 00:28:02,560
Speaker 2: Is it true that we have no idea? I mean,

600
00:28:02,600 --> 00:28:04,960
Speaker 2: people definitely have ideas, and I read like ten papers

601
00:28:05,000 --> 00:28:08,160
Speaker 2: about ten different ideas for what could be controlling it

602
00:28:08,200 --> 00:28:11,280
Speaker 2: complicated theories about how the gas gets blown in or out,

603
00:28:11,359 --> 00:28:13,720
Speaker 2: or gets heated up or cool down. We have lots

604
00:28:13,760 --> 00:28:16,520
Speaker 2: of ideas, we just don't know which one might represent reality.

605
00:28:17,280 --> 00:28:20,320
Speaker 1: Interesting And now, is it possible, I guess, for a

606
00:28:20,359 --> 00:28:23,360
Speaker 1: galaxy to not have a black hole? Like why couldn't

607
00:28:23,400 --> 00:28:23,879
Speaker 1: that happen?

608
00:28:23,960 --> 00:28:25,600
Speaker 2: Yeah, that's a great question. And there's sort of two

609
00:28:25,680 --> 00:28:28,560
Speaker 2: questions there, right, Like one is could you make a

610
00:28:28,600 --> 00:28:31,280
Speaker 2: galaxy without a black hole. Is it possible to pull

611
00:28:31,359 --> 00:28:34,440
Speaker 2: all those stars and all that dark matter together without

612
00:28:34,520 --> 00:28:37,080
Speaker 2: making a black hole? And we think the answer to

613
00:28:37,119 --> 00:28:40,600
Speaker 2: that is no, That every time you get enough stuff together,

614
00:28:41,000 --> 00:28:43,040
Speaker 2: whatever is pulling that together is going to form a

615
00:28:43,040 --> 00:28:45,400
Speaker 2: black hole at its center. That's just inevitable.

616
00:28:45,480 --> 00:28:46,680
Speaker 1: Why do we think it's inevitable?

617
00:28:46,760 --> 00:28:48,880
Speaker 2: Well, I guess for a couple of reasons. To summarize,

618
00:28:48,920 --> 00:28:52,080
Speaker 2: One is every galaxy we've seen so far has a

619
00:28:52,080 --> 00:28:54,360
Speaker 2: black hole at it's heart, right, We've never seen a

620
00:28:54,440 --> 00:28:57,400
Speaker 2: galaxy where we're able to check whether there's a black

621
00:28:57,400 --> 00:28:59,600
Speaker 2: hole and haven't found one, though there's an asterisk there

622
00:28:59,640 --> 00:29:01,320
Speaker 2: which will get to in just a minute. And number

623
00:29:01,360 --> 00:29:03,719
Speaker 2: two is this connection between the sizes of them that

624
00:29:03,760 --> 00:29:07,280
Speaker 2: tells us that there's probably some mechanism that's controlling both

625
00:29:07,320 --> 00:29:09,240
Speaker 2: the mass of the galaxy and the mass of the

626
00:29:09,240 --> 00:29:12,240
Speaker 2: black hole together. So back to the asterisk, there actually

627
00:29:12,280 --> 00:29:14,960
Speaker 2: are a couple of galaxies nearby that we've looked at

628
00:29:15,080 --> 00:29:17,680
Speaker 2: that don't have a black hole at the center. And

629
00:29:17,720 --> 00:29:21,560
Speaker 2: that points to another potentially fascinating story, which is whether

630
00:29:21,600 --> 00:29:23,760
Speaker 2: it's possible for a galaxy to form a black hole

631
00:29:24,120 --> 00:29:27,280
Speaker 2: and then eject it like can a galaxy form, make

632
00:29:27,320 --> 00:29:30,000
Speaker 2: its own black hole and then lose that black hole.

633
00:29:30,240 --> 00:29:32,560
Speaker 1: Wait, wait, wait, wait, we're seeing that there are galaxies

634
00:29:32,600 --> 00:29:34,720
Speaker 1: we've seen that don't have a black hole in them

635
00:29:34,960 --> 00:29:35,480
Speaker 1: in the middle.

636
00:29:35,560 --> 00:29:37,920
Speaker 2: There are a small number of galaxies we've seen that

637
00:29:38,000 --> 00:29:40,160
Speaker 2: have a black hole, but it's no longer at the

638
00:29:40,200 --> 00:29:41,520
Speaker 2: middle of the galaxy.

639
00:29:41,840 --> 00:29:44,560
Speaker 1: Wait, what where is it? Like at the edge or

640
00:29:44,640 --> 00:29:46,240
Speaker 1: really far away from it? What do you mean?

641
00:29:46,280 --> 00:29:48,680
Speaker 2: So there's a few variations. In one case, we've seen

642
00:29:48,680 --> 00:29:51,200
Speaker 2: a super massive black hole that's like displaced from the

643
00:29:51,240 --> 00:29:55,000
Speaker 2: center and has a pretty high speed away from the center.

644
00:29:55,640 --> 00:29:59,040
Speaker 2: So there's this possibility that galaxies could form make a

645
00:29:59,040 --> 00:30:02,320
Speaker 2: black hole the center, and then through some dynamical process,

646
00:30:02,320 --> 00:30:05,440
Speaker 2: some like interaction with other galaxies, their black hole could

647
00:30:05,480 --> 00:30:08,080
Speaker 2: get like kicked out of the center. And we've actually

648
00:30:08,080 --> 00:30:09,680
Speaker 2: seen this in a few galaxies.

649
00:30:09,840 --> 00:30:11,560
Speaker 1: What are the other ones like that don't have a

650
00:30:11,560 --> 00:30:12,400
Speaker 1: black hole in the middle.

651
00:30:12,480 --> 00:30:15,320
Speaker 2: So there's the one example called CID forty two, which

652
00:30:15,400 --> 00:30:17,640
Speaker 2: is about four billion light years away. It has a

653
00:30:17,680 --> 00:30:20,200
Speaker 2: super massive black hole, but it's near the center, but

654
00:30:20,240 --> 00:30:22,760
Speaker 2: it's sort of displaced from the center. And then there's

655
00:30:22,880 --> 00:30:26,400
Speaker 2: another observation just a few weeks ago where they see

656
00:30:26,440 --> 00:30:29,760
Speaker 2: a streak of light shooting out of the galaxy. The

657
00:30:29,800 --> 00:30:32,400
Speaker 2: streak of light is like two hundred thousand light years long,

658
00:30:32,440 --> 00:30:34,560
Speaker 2: and at the end of it there's a black hole.

659
00:30:34,960 --> 00:30:36,800
Speaker 2: And so it looks sort of like the black hole

660
00:30:36,920 --> 00:30:40,280
Speaker 2: was ejected from this galaxy. It's like a runaway black

661
00:30:40,280 --> 00:30:43,720
Speaker 2: hole and left this streak of stars in hot gas

662
00:30:43,920 --> 00:30:44,480
Speaker 2: in its wake.

663
00:30:44,720 --> 00:30:47,000
Speaker 1: Well, it can actually see like the skid marks of it.

664
00:30:47,200 --> 00:30:51,000
Speaker 2: Yeah, exactly, And so we think that this might happen

665
00:30:51,080 --> 00:30:54,560
Speaker 2: sometimes when galaxies merge. We know that galaxies merge, that

666
00:30:54,560 --> 00:30:56,600
Speaker 2: that's a very normal thing. We think the Milky Way

667
00:30:56,680 --> 00:30:59,120
Speaker 2: is formed by a bunch of galactic mergers. And Dromeda

668
00:30:59,240 --> 00:31:01,120
Speaker 2: is so big because because it's a combination of a

669
00:31:01,160 --> 00:31:04,240
Speaker 2: bunch of baby galaxies that all got merged together. And

670
00:31:04,280 --> 00:31:06,800
Speaker 2: the normal thing to happen when galaxies merge is that

671
00:31:06,840 --> 00:31:09,480
Speaker 2: the black holes also merge. I mean, you have two

672
00:31:09,640 --> 00:31:12,520
Speaker 2: clouds of stars, each with a black hole at their center.

673
00:31:12,920 --> 00:31:15,360
Speaker 2: They're all going to orbit each other. Eventually, the black

674
00:31:15,360 --> 00:31:17,320
Speaker 2: holes that their hearts are going to orbit each other,

675
00:31:17,440 --> 00:31:20,840
Speaker 2: and then because of friction and gravitational radiation, they'll eventually

676
00:31:20,840 --> 00:31:23,920
Speaker 2: collapse into a single black hole. That's like the normal

677
00:31:23,960 --> 00:31:26,959
Speaker 2: thing to happen, but there's some variations there. When two

678
00:31:27,040 --> 00:31:30,320
Speaker 2: black holes collapse into one, they also emit a lot

679
00:31:30,360 --> 00:31:33,200
Speaker 2: of radiation. Like the mass of the two black holes

680
00:31:33,240 --> 00:31:35,920
Speaker 2: doesn't one hundred percent go into the mass of the

681
00:31:35,920 --> 00:31:39,400
Speaker 2: final black hole. It loses some mass and it generates

682
00:31:39,440 --> 00:31:42,600
Speaker 2: a bunch of gravitational waves. That's how we see these

683
00:31:42,640 --> 00:31:45,120
Speaker 2: black hole mergers. We talked about Logo and Virga and

684
00:31:45,160 --> 00:31:48,200
Speaker 2: all these observations that see these ripples in space time

685
00:31:48,560 --> 00:31:51,880
Speaker 2: generated by these black hole collisions. You get those ripples

686
00:31:51,920 --> 00:31:54,600
Speaker 2: because the black holes are accelerating as they orbit each other,

687
00:31:54,920 --> 00:31:58,160
Speaker 2: and that radiates a way energy, so it loses some mass. Now,

688
00:31:58,200 --> 00:32:01,320
Speaker 2: sometimes that radiation is in every direct like it just

689
00:32:01,320 --> 00:32:05,760
Speaker 2: sprays gravitational waves everywhere, but sometimes in special circumstances that

690
00:32:05,840 --> 00:32:09,120
Speaker 2: gravitational radiation tends to be in one direction rather than another,

691
00:32:09,680 --> 00:32:11,880
Speaker 2: and then it acts sort of like a recoil. It's

692
00:32:11,920 --> 00:32:15,560
Speaker 2: like shooting a gravitational wave gun in one direction and

693
00:32:15,600 --> 00:32:18,560
Speaker 2: the black holes get pushed back in the other direction

694
00:32:18,720 --> 00:32:20,280
Speaker 2: by conservation of momentum.

695
00:32:20,400 --> 00:32:22,480
Speaker 1: So you're saying you can have a galaxy without a

696
00:32:22,480 --> 00:32:25,440
Speaker 1: black hole, but the ones we've seen so far that

697
00:32:25,520 --> 00:32:27,800
Speaker 1: are like that, there's evidence that it had a black

698
00:32:27,840 --> 00:32:29,600
Speaker 1: hole in the middle at some point.

699
00:32:29,640 --> 00:32:32,520
Speaker 2: Exactly, so it might be possible to have a galaxy

700
00:32:32,520 --> 00:32:35,040
Speaker 2: without a black hole by building a galaxy with a

701
00:32:35,080 --> 00:32:38,000
Speaker 2: black hole and then like ejecting it getting rid of

702
00:32:38,040 --> 00:32:38,680
Speaker 2: the black hole.

703
00:32:39,480 --> 00:32:41,960
Speaker 1: I guess one thing that maybe important to understand is

704
00:32:42,000 --> 00:32:45,200
Speaker 1: that even though a galaxy can have a super massive

705
00:32:45,200 --> 00:32:48,200
Speaker 1: black hole in the middle with the massive millions of

706
00:32:48,240 --> 00:32:51,560
Speaker 1: our suns, it's not like the black hole is anchoring

707
00:32:51,760 --> 00:32:54,320
Speaker 1: the galaxy, right, like to a galaxy with tondreds of

708
00:32:54,320 --> 00:32:57,160
Speaker 1: millions of stars, like one little black hole in the

709
00:32:57,200 --> 00:33:00,760
Speaker 1: middle is not super important in the same way that

710
00:33:00,760 --> 00:33:02,480
Speaker 1: the Sun is important in our Solar system.

711
00:33:02,600 --> 00:33:05,200
Speaker 2: Right, Yeah, you're absolutely right. The Sun is like ninety

712
00:33:05,280 --> 00:33:07,560
Speaker 2: nine percent of the mass of our solar system. But

713
00:33:07,560 --> 00:33:09,800
Speaker 2: the black holes the hearts of these galaxies are a

714
00:33:09,840 --> 00:33:12,760
Speaker 2: tiny fraction, much less than one percent of the mass

715
00:33:12,760 --> 00:33:15,040
Speaker 2: of the galaxy. Like in the Milky Way, we have

716
00:33:15,200 --> 00:33:18,200
Speaker 2: billions of stars and so billions of solar masses, and

717
00:33:18,320 --> 00:33:21,800
Speaker 2: our black hole is only five million solar masses. So

718
00:33:21,840 --> 00:33:24,440
Speaker 2: it's a tiny fraction of the mass of our galaxy.

719
00:33:24,720 --> 00:33:28,080
Speaker 2: Even though we're talking about really big objects. Galaxies themselves

720
00:33:28,360 --> 00:33:31,280
Speaker 2: are much much bigger. So it's more like if our

721
00:33:31,280 --> 00:33:34,240
Speaker 2: Solar system lost Jupiter, right, Jupiter is a big planet,

722
00:33:34,320 --> 00:33:36,280
Speaker 2: that'd be kind of a big deal personally, but it

723
00:33:36,320 --> 00:33:38,920
Speaker 2: wouldn't affect the dynamics of the Solar System the way

724
00:33:38,920 --> 00:33:41,200
Speaker 2: it would if we lost the Sun, Right, that would

725
00:33:41,240 --> 00:33:42,320
Speaker 2: be much more dramatic.

726
00:33:42,720 --> 00:33:45,000
Speaker 1: Right, These super massive black holes are really more like

727
00:33:45,080 --> 00:33:48,040
Speaker 1: little pimples kind of in the middle of galaxies. Right,

728
00:33:48,320 --> 00:33:50,760
Speaker 1: It's not like the galaxies there because of the mass

729
00:33:50,760 --> 00:33:53,040
Speaker 1: super massive black hole. It's more like maybe just a

730
00:33:53,080 --> 00:33:55,600
Speaker 1: feature that pops up when you're making a galaxy.

731
00:33:55,840 --> 00:33:58,440
Speaker 2: Yeah, I think we don't really understand that. I mean,

732
00:33:58,480 --> 00:34:01,360
Speaker 2: I think the causal relationship is probably complicated. It seems

733
00:34:01,560 --> 00:34:05,160
Speaker 2: like it's probably a necessary outcome when you form a

734
00:34:05,200 --> 00:34:07,840
Speaker 2: galaxy that you get a super massive black hole. So

735
00:34:07,880 --> 00:34:10,359
Speaker 2: in that sense, it kind of is necessary to have it.

736
00:34:10,560 --> 00:34:12,080
Speaker 2: But you're right, you can get rid of the black

737
00:34:12,080 --> 00:34:14,600
Speaker 2: hole and the galaxy can still hold itself together, so

738
00:34:14,640 --> 00:34:16,719
Speaker 2: in that sense, you don't need it anymore.

739
00:34:17,200 --> 00:34:19,720
Speaker 1: Like maybe the black hole needed the galaxy to form,

740
00:34:19,760 --> 00:34:22,759
Speaker 1: but maybe the galaxy didn't need the black hole to form.

741
00:34:23,239 --> 00:34:25,080
Speaker 2: Yeah, But then the black hole stays a black hole.

742
00:34:25,120 --> 00:34:27,279
Speaker 2: When it's been ejected, it's still a black hole out

743
00:34:27,280 --> 00:34:31,600
Speaker 2: there wandering an intergalactic space. WHOA. So one way to

744
00:34:31,600 --> 00:34:33,440
Speaker 2: get rid of your black holes to generate a bunch

745
00:34:33,440 --> 00:34:37,120
Speaker 2: of gravitational radiation in one direction to kick the black hole.

746
00:34:37,520 --> 00:34:39,279
Speaker 2: For that to happen, you typically have to have sort

747
00:34:39,280 --> 00:34:41,080
Speaker 2: of like a low mass black hole in order to

748
00:34:41,080 --> 00:34:43,800
Speaker 2: get enough acceleration to like get out of the galaxy.

749
00:34:44,000 --> 00:34:46,520
Speaker 2: Another scenario is to have sort of like a three

750
00:34:46,680 --> 00:34:50,640
Speaker 2: galaxy dance. Remember that when three objects interact, it's much

751
00:34:50,719 --> 00:34:53,879
Speaker 2: more chaotic, Like, the three body problem is not something

752
00:34:53,920 --> 00:34:56,360
Speaker 2: we know how to solve, whereas the two body problem

753
00:34:56,440 --> 00:34:58,799
Speaker 2: is simple. So if you have three galaxies that are

754
00:34:58,920 --> 00:35:01,920
Speaker 2: merging at the same time, then one of those black

755
00:35:01,920 --> 00:35:04,640
Speaker 2: holes can get kicked out instead of merging with the

756
00:35:04,680 --> 00:35:07,319
Speaker 2: other two. So that's another scenario that can create a

757
00:35:07,440 --> 00:35:10,600
Speaker 2: runaway black hole, essentially kicking a black hole out of

758
00:35:10,640 --> 00:35:11,239
Speaker 2: a galaxy.

759
00:35:11,480 --> 00:35:14,760
Speaker 1: Like if three solar systems similar to ours came together,

760
00:35:14,960 --> 00:35:17,960
Speaker 1: it would get so chaotic and so scrambled that it

761
00:35:18,000 --> 00:35:21,200
Speaker 1: could actually like shoot off the Sun or Jupiter out

762
00:35:21,200 --> 00:35:21,720
Speaker 1: into space.

763
00:35:21,800 --> 00:35:25,600
Speaker 2: Right, yeah, exactly. And because of conservation momentum. If you're

764
00:35:25,600 --> 00:35:27,840
Speaker 2: going to kick one black hole out in one direction,

765
00:35:27,920 --> 00:35:29,920
Speaker 2: then the other two are going to get kicked in

766
00:35:29,960 --> 00:35:33,120
Speaker 2: the other direction, and so the whole system might end

767
00:35:33,160 --> 00:35:35,160
Speaker 2: up without a black hole at its center.

768
00:35:35,280 --> 00:35:37,799
Speaker 1: All right, let's take a little bit more into what

769
00:35:37,880 --> 00:35:41,359
Speaker 1: this all means and maybe how dark matter plays into it.

770
00:35:41,880 --> 00:35:57,040
Speaker 1: But first let's take another quick break. All right, we

771
00:35:57,080 --> 00:35:59,799
Speaker 1: are asking the question does every galaxy have a black

772
00:35:59,800 --> 00:36:02,879
Speaker 1: hole at its center? And I guess we've figured out

773
00:36:02,880 --> 00:36:07,080
Speaker 1: the answers. No, right, some galaxies have a black hole

774
00:36:07,239 --> 00:36:09,520
Speaker 1: near its edge if it gets kicked out.

775
00:36:09,800 --> 00:36:12,800
Speaker 2: Yeah, we think that probably every galaxy has a black

776
00:36:12,840 --> 00:36:16,360
Speaker 2: hole at its center during its formation or at some

777
00:36:16,440 --> 00:36:19,840
Speaker 2: point in its history, because we think probably the process

778
00:36:19,920 --> 00:36:23,640
Speaker 2: that makes these galaxies, it gathers together all this mass

779
00:36:23,640 --> 00:36:27,160
Speaker 2: and funnels it into this gravitational well that remember, in

780
00:36:27,160 --> 00:36:29,720
Speaker 2: the end, is made by dark matter. Right, The reason

781
00:36:29,760 --> 00:36:32,640
Speaker 2: these galaxies exist is because there's a density of dark

782
00:36:32,719 --> 00:36:35,080
Speaker 2: matter there which is pulling in all this other matter

783
00:36:35,440 --> 00:36:37,800
Speaker 2: to make this dense stuff that we can make a galaxy.

784
00:36:38,160 --> 00:36:41,600
Speaker 2: Probably that process inevitably makes a black hole at the

785
00:36:41,640 --> 00:36:44,560
Speaker 2: same time as it makes a galaxy. But then you

786
00:36:44,600 --> 00:36:47,640
Speaker 2: can lose that black hole. During the life of these galaxies,

787
00:36:47,680 --> 00:36:49,799
Speaker 2: as they merge, as they come together, as they dance

788
00:36:49,840 --> 00:36:53,200
Speaker 2: around each other, those black holes can get ejected from

789
00:36:53,200 --> 00:36:55,759
Speaker 2: the hearts of those galaxies. So yeah, you could end

790
00:36:55,840 --> 00:36:58,600
Speaker 2: up with a galaxy without a black hole at its center.

791
00:37:00,080 --> 00:37:04,080
Speaker 1: Like we said earlier in the episode, that every GALLESSI

792
00:37:04,120 --> 00:37:05,719
Speaker 1: we've seen has the black hole at its center, But

793
00:37:05,760 --> 00:37:08,279
Speaker 1: it sounds like that's not really true. That there are

794
00:37:08,320 --> 00:37:10,640
Speaker 1: galaxies out there we've seen so we can measure it

795
00:37:10,640 --> 00:37:13,000
Speaker 1: that don't have one in the middle at all. Have

796
00:37:13,040 --> 00:37:15,279
Speaker 1: we seen any with no black hole at all.

797
00:37:15,360 --> 00:37:18,000
Speaker 2: We have not found a galaxy without any kind of

798
00:37:18,040 --> 00:37:20,080
Speaker 2: black hole. Either they have a black hole at their center,

799
00:37:20,400 --> 00:37:23,120
Speaker 2: or we've identified a black hole that's been ejected from

800
00:37:23,160 --> 00:37:26,000
Speaker 2: the center. That's a very small number of cases so far,

801
00:37:26,680 --> 00:37:29,120
Speaker 2: or they're too far away for us to tell what's

802
00:37:29,160 --> 00:37:32,120
Speaker 2: going on at the center. Then there's one particular galaxy

803
00:37:32,160 --> 00:37:34,120
Speaker 2: which is a bit of a mystery. Its called Able

804
00:37:34,200 --> 00:37:37,320
Speaker 2: two two six one. It is a really big galaxy

805
00:37:37,760 --> 00:37:40,480
Speaker 2: and we have not yet found the super massive black

806
00:37:40,480 --> 00:37:42,439
Speaker 2: hole there. We looked at it in the X ray

807
00:37:42,480 --> 00:37:44,480
Speaker 2: and not seen the sign of it. It's still sort

808
00:37:44,520 --> 00:37:46,480
Speaker 2: of an open question whether people are going to find

809
00:37:46,520 --> 00:37:48,640
Speaker 2: evidence of the black hole or not, but it's one

810
00:37:48,640 --> 00:37:50,920
Speaker 2: that has a question mark next to it. Remember, this

811
00:37:51,000 --> 00:37:54,640
Speaker 2: is like a recent and active field of research. People

812
00:37:54,640 --> 00:37:57,320
Speaker 2: are developing new techniques to try to study these galaxies

813
00:37:57,680 --> 00:37:59,480
Speaker 2: to try to see if they are black holes in them.

814
00:37:59,560 --> 00:38:02,359
Speaker 2: It's definitely a question a lot of people are working on,

815
00:38:02,520 --> 00:38:05,040
Speaker 2: so it's evolving rapidly. But either we've seen a black

816
00:38:05,040 --> 00:38:07,120
Speaker 2: hole at center, or we've seen a black hole like

817
00:38:07,280 --> 00:38:10,560
Speaker 2: leaving its center, or there's this one question mark galaxy

818
00:38:10,640 --> 00:38:13,000
Speaker 2: able two two six 's one, or we're just not

819
00:38:13,200 --> 00:38:15,600
Speaker 2: able to see it, because remember, the galaxies have to

820
00:38:15,600 --> 00:38:18,640
Speaker 2: be close enough for us to like study their centers

821
00:38:18,920 --> 00:38:20,960
Speaker 2: in order to be able to see these black holes,

822
00:38:21,440 --> 00:38:24,160
Speaker 2: or they have to be active enough for us to

823
00:38:24,200 --> 00:38:27,040
Speaker 2: see them emitting. Like another way to see these black

824
00:38:27,040 --> 00:38:30,520
Speaker 2: holes is to watch them like burp as they eat something.

825
00:38:30,880 --> 00:38:32,680
Speaker 1: But then you're only seeing the rude black hole.

826
00:38:33,239 --> 00:38:36,520
Speaker 2: That's right. But occasionally, even a quiet black hole, even

827
00:38:36,520 --> 00:38:38,760
Speaker 2: when it's not surrounded by a big disc of gas

828
00:38:38,800 --> 00:38:42,440
Speaker 2: and dust and emitting like constant beams of light, occasionally

829
00:38:42,440 --> 00:38:45,200
Speaker 2: a star might wander close to it and get eaten

830
00:38:45,600 --> 00:38:47,719
Speaker 2: and the tidal disruption there will give you a very

831
00:38:47,760 --> 00:38:50,760
Speaker 2: bright flare. So we've seen those kinds of things as well,

832
00:38:50,800 --> 00:38:54,919
Speaker 2: like otherwise quiet galactic centers that suddenly emit a big,

833
00:38:55,000 --> 00:38:57,399
Speaker 2: bright burst of light. We've even seen that from our

834
00:38:57,480 --> 00:39:02,640
Speaker 2: own galactic center. Sometimes the way you can observe supermassive black.

835
00:39:02,440 --> 00:39:05,200
Speaker 1: Holes, it's like the final scream of a star before

836
00:39:05,239 --> 00:39:06,760
Speaker 1: it gets eaten wo.

837
00:39:08,400 --> 00:39:11,960
Speaker 2: Exactly. Another thing people are doing is trying to identify

838
00:39:12,040 --> 00:39:16,000
Speaker 2: these super massive black holes out in intergalactic space. Like

839
00:39:16,000 --> 00:39:19,120
Speaker 2: people are curious how often do super massive black holes

840
00:39:19,160 --> 00:39:22,120
Speaker 2: get kicked out into space? Remember we talked about like

841
00:39:22,320 --> 00:39:25,480
Speaker 2: rogue planets before, planets that used to be orbiting a

842
00:39:25,480 --> 00:39:28,759
Speaker 2: solar system but then due to the gravitational chaos of

843
00:39:28,800 --> 00:39:31,520
Speaker 2: their system, get thrown out into space. And it turns

844
00:39:31,520 --> 00:39:33,839
Speaker 2: out there's a huge number of them out there. People

845
00:39:33,840 --> 00:39:38,240
Speaker 2: have discovered rogue planets by micro lensing, looking for moments

846
00:39:38,280 --> 00:39:40,680
Speaker 2: when these planets pass in front of a star in

847
00:39:40,719 --> 00:39:43,920
Speaker 2: the background and that star's light gets distorted by the

848
00:39:43,920 --> 00:39:45,960
Speaker 2: gravity of the planet, And by doing that we can

849
00:39:46,000 --> 00:39:48,080
Speaker 2: spot a bunch of these things and then extrapolate to

850
00:39:48,120 --> 00:39:50,839
Speaker 2: how many there are. The same way we can look

851
00:39:50,880 --> 00:39:54,879
Speaker 2: for super massive black holes in intergalactic space by looking

852
00:39:54,920 --> 00:39:56,760
Speaker 2: at for these micro lensing events.

853
00:39:57,200 --> 00:39:59,680
Speaker 1: M sounds kind of scary, the idea that there are

854
00:40:00,320 --> 00:40:04,200
Speaker 1: super massive black holes out there roaming space, possibly in

855
00:40:04,239 --> 00:40:04,760
Speaker 1: our direction.

856
00:40:05,000 --> 00:40:07,359
Speaker 2: Yeah, it's certainly possible that they're out there. We've seen

857
00:40:07,440 --> 00:40:10,319
Speaker 2: some of them getting ejected from their galaxies, but we

858
00:40:10,400 --> 00:40:12,080
Speaker 2: think that might be kind of rare, and when we're

859
00:40:12,120 --> 00:40:14,759
Speaker 2: talking about like a one percent level event based on

860
00:40:14,800 --> 00:40:17,879
Speaker 2: our recent observation, so of course with a big uncertainty.

861
00:40:18,000 --> 00:40:21,160
Speaker 2: And there are many fewer galaxies than there are stars

862
00:40:21,200 --> 00:40:24,000
Speaker 2: of course, so the number of rogues super massive black

863
00:40:24,000 --> 00:40:26,759
Speaker 2: holes out there could be big. But space is of

864
00:40:26,760 --> 00:40:29,360
Speaker 2: course really really vast, so these things would be pretty

865
00:40:29,400 --> 00:40:30,240
Speaker 2: hard to spot.

866
00:40:30,920 --> 00:40:33,120
Speaker 1: I guess it's hard for even a super massive black

867
00:40:33,120 --> 00:40:35,720
Speaker 1: hole to leave a galaxy, right Like, as we said before,

868
00:40:36,040 --> 00:40:39,759
Speaker 1: a galaxies huge, got billions and trillions of stars, it's

869
00:40:39,840 --> 00:40:42,919
Speaker 1: really massive. It's probably pretty hard for a black hole

870
00:40:43,000 --> 00:40:45,960
Speaker 1: to get the escape velocity needed to leave a galaxy

871
00:40:46,000 --> 00:40:47,640
Speaker 1: and come towards us exactly.

872
00:40:47,880 --> 00:40:50,800
Speaker 2: That's why it tends to happen mostly for lower mass

873
00:40:50,960 --> 00:40:54,400
Speaker 2: super massive black holes, not necessarily even teeny tiny ones,

874
00:40:54,440 --> 00:40:56,320
Speaker 2: just ones on the lower edge, because a lot of

875
00:40:56,400 --> 00:40:59,600
Speaker 2: them are going to have this asymmetric radiation from gravitational

876
00:40:59,640 --> 00:41:03,200
Speaker 2: waves or some sort of chaotic merger event that it's

877
00:41:03,239 --> 00:41:06,080
Speaker 2: not totally symmetric. But most of them are massive enough

878
00:41:06,120 --> 00:41:07,960
Speaker 2: that they get pulled back to the center of the

879
00:41:07,960 --> 00:41:10,959
Speaker 2: galaxy and eventually settle down. But the lower mass ones

880
00:41:10,960 --> 00:41:14,720
Speaker 2: can get going pretty fast, like this CID forty two galaxy.

881
00:41:14,920 --> 00:41:17,560
Speaker 2: They estimated the velocity of the galaxy to be half

882
00:41:17,640 --> 00:41:20,000
Speaker 2: a percent of the speed of light, which is like

883
00:41:20,360 --> 00:41:22,239
Speaker 2: very very fast moving black hole.

884
00:41:23,520 --> 00:41:24,560
Speaker 1: It's in a hurry.

885
00:41:25,960 --> 00:41:29,160
Speaker 2: To get out of there, really wants to go somewhere exactly.

886
00:41:29,520 --> 00:41:31,879
Speaker 1: I guess the question is how does this all tie

887
00:41:31,920 --> 00:41:34,600
Speaker 1: into dark matter? Because I know dark matter is very

888
00:41:34,640 --> 00:41:37,360
Speaker 1: important in the formation of galaxies. Right, It's almost like,

889
00:41:37,600 --> 00:41:40,800
Speaker 1: I know we've mentioned this before, the galaxies form around

890
00:41:40,800 --> 00:41:43,879
Speaker 1: where dark matter is. Does that effect sort of how

891
00:41:44,000 --> 00:41:45,480
Speaker 1: black holes might get formed.

892
00:41:45,640 --> 00:41:49,480
Speaker 2: It definitely affects where galaxies and black holes get formed. Right.

893
00:41:49,640 --> 00:41:52,680
Speaker 2: Galaxies basically trace out where the dark matter is in

894
00:41:52,719 --> 00:41:55,000
Speaker 2: the universe. If you look at the large scale structure

895
00:41:55,000 --> 00:41:57,840
Speaker 2: of the universe, you see these filaments of galaxies and

896
00:41:57,880 --> 00:42:00,400
Speaker 2: these sheets of galaxies and that's because that where the

897
00:42:00,480 --> 00:42:02,960
Speaker 2: dark matter is. We can't see the dark matter directly,

898
00:42:03,239 --> 00:42:05,200
Speaker 2: but we can see that it's gathered together all this

899
00:42:05,320 --> 00:42:08,080
Speaker 2: matter and made all of those galaxies. And so every

900
00:42:08,120 --> 00:42:11,680
Speaker 2: galaxy has a huge dark matter halo around it, Like

901
00:42:11,719 --> 00:42:14,719
Speaker 2: the Milky Way is about one hundred thousand light years across,

902
00:42:15,040 --> 00:42:17,080
Speaker 2: but there's a big blob of dark matter that's like

903
00:42:17,120 --> 00:42:19,920
Speaker 2: two hundred thousand light years across that the Milky Way

904
00:42:19,960 --> 00:42:22,359
Speaker 2: is embedded in. Now, if we shot our black hole

905
00:42:22,440 --> 00:42:24,920
Speaker 2: out of our galaxy, then it would pass through that

906
00:42:25,040 --> 00:42:27,480
Speaker 2: dark matter halo, and it would gobble up a lot

907
00:42:27,520 --> 00:42:30,719
Speaker 2: of dark matter along the way. And so as these

908
00:42:30,800 --> 00:42:35,040
Speaker 2: supermassive black holes leave the galaxies, they can increase their

909
00:42:35,120 --> 00:42:36,120
Speaker 2: dark matter fraction.

910
00:42:36,719 --> 00:42:40,160
Speaker 1: They can get even darker than black Yeah.

911
00:42:40,000 --> 00:42:42,879
Speaker 2: We think that these black holes already have some dark

912
00:42:42,960 --> 00:42:45,600
Speaker 2: matter in them because dark matter is everywhere. But dark

913
00:42:45,640 --> 00:42:47,840
Speaker 2: matter also isn't sticky, and so it's very easy for

914
00:42:47,960 --> 00:42:51,160
Speaker 2: dark matter to just like rotate in orbit forever around

915
00:42:51,200 --> 00:42:54,440
Speaker 2: the galaxy and not fall in. We think will probably

916
00:42:54,440 --> 00:42:56,600
Speaker 2: fall into the center of the galaxy because eventually it's

917
00:42:56,640 --> 00:42:59,759
Speaker 2: like dynamical friction. Our star will get pushed by others

918
00:42:59,760 --> 00:43:03,280
Speaker 2: stars on. All that jostling ends up kicking somebody towards

919
00:43:03,320 --> 00:43:06,000
Speaker 2: the center of the galaxy. But dark matter doesn't do that,

920
00:43:06,080 --> 00:43:08,719
Speaker 2: right because dark matter just passes right through itself. So

921
00:43:08,840 --> 00:43:11,160
Speaker 2: normally dark matter can swirl around the center of the

922
00:43:11,160 --> 00:43:13,680
Speaker 2: galaxy not getting eaten by the black hole. But if

923
00:43:13,680 --> 00:43:16,359
Speaker 2: the black hole like runs free, then it's basically like

924
00:43:16,600 --> 00:43:18,640
Speaker 2: plowing through a buffet of dark matter.

925
00:43:19,840 --> 00:43:22,920
Speaker 1: But maybe when as the galaxy was forming, maybe the

926
00:43:22,960 --> 00:43:25,120
Speaker 1: black hole did eat a lot of dark matter. Or

927
00:43:25,160 --> 00:43:27,799
Speaker 1: maybe I wonder if the black hole in the middle

928
00:43:27,800 --> 00:43:30,520
Speaker 1: of galaxies is maybe mostly made out of dark matter.

929
00:43:30,960 --> 00:43:32,920
Speaker 2: It's hard to know, right, And what does it mean

930
00:43:32,960 --> 00:43:34,839
Speaker 2: to be made of dark matter? Because once it goes

931
00:43:34,880 --> 00:43:38,280
Speaker 2: past the event horizon, who knows what happens? Everything's dark matter,

932
00:43:40,440 --> 00:43:43,480
Speaker 2: everything's something else, some black hole state of matter. Right,

933
00:43:43,560 --> 00:43:45,600
Speaker 2: we don't know if dark matter gets annihilated it turns

934
00:43:45,640 --> 00:43:49,120
Speaker 2: into something else, or if it retains something of its nature.

935
00:43:49,239 --> 00:43:50,640
Speaker 2: We just don't even know because we don't know the

936
00:43:50,640 --> 00:43:53,040
Speaker 2: particle properties of it. So, like, what are the conservation

937
00:43:53,200 --> 00:43:55,960
Speaker 2: laws for dark matter? The universe might like keep track

938
00:43:56,000 --> 00:43:57,879
Speaker 2: of how much dark matter there is and not allow

939
00:43:57,960 --> 00:44:01,040
Speaker 2: things to convert. We just don't know so clueless about it.

940
00:44:01,160 --> 00:44:03,200
Speaker 1: So some black holes might be darker than others.

941
00:44:03,360 --> 00:44:05,520
Speaker 2: Absolutely, some might be darker than others. We know that

942
00:44:05,640 --> 00:44:08,279
Speaker 2: some galaxies are darker than others, some galaxies have a

943
00:44:08,360 --> 00:44:12,040
Speaker 2: larger dark matter fraction than others. That's for sure, all right.

944
00:44:12,080 --> 00:44:15,400
Speaker 1: Well, what does it mean for our understanding of galaxies

945
00:44:15,400 --> 00:44:16,040
Speaker 1: and how they form?

946
00:44:16,560 --> 00:44:18,799
Speaker 2: It means that we're still the very beginning of the

947
00:44:18,880 --> 00:44:22,759
Speaker 2: journey of understanding how galaxies come together, which is sort

948
00:44:22,760 --> 00:44:25,560
Speaker 2: of shocking because we've been setting galaxies for so long,

949
00:44:25,719 --> 00:44:28,440
Speaker 2: but every few decades we'd learned something new and surprising

950
00:44:28,640 --> 00:44:31,440
Speaker 2: about what's going on with these galaxies, how they come together,

951
00:44:31,800 --> 00:44:35,279
Speaker 2: what their history is, and what their future fate is. Right,

952
00:44:35,680 --> 00:44:37,520
Speaker 2: and we know that the galaxies and sort of our

953
00:44:37,560 --> 00:44:41,359
Speaker 2: local group are gravitationally bound together and so eventually going

954
00:44:41,400 --> 00:44:45,040
Speaker 2: to end up falling together and probably forming one super

955
00:44:45,080 --> 00:44:47,719
Speaker 2: galaxy while they're being separated from the rest of the

956
00:44:47,800 --> 00:44:50,640
Speaker 2: universe by dark energy. And that super galaxy is going

957
00:44:50,719 --> 00:44:53,319
Speaker 2: to have a super duper massive black hole at its

958
00:44:53,320 --> 00:44:58,000
Speaker 2: center unless that gets kicked out and shot into intergalactic space.

959
00:44:58,600 --> 00:45:00,520
Speaker 2: So it tells us a lot about our our potential

960
00:45:00,600 --> 00:45:03,520
Speaker 2: future because as we orbit our galaxy and merge with

961
00:45:03,600 --> 00:45:06,960
Speaker 2: those other galaxies, we also eventually fall towards the center

962
00:45:07,040 --> 00:45:09,640
Speaker 2: of this blob. And if there's a giant black hole

963
00:45:09,680 --> 00:45:11,879
Speaker 2: waiting for us there, this is really only one way

964
00:45:11,920 --> 00:45:12,839
Speaker 2: for the story to end.

965
00:45:12,920 --> 00:45:15,680
Speaker 1: But even if we kick out that black hole, eventually

966
00:45:15,680 --> 00:45:18,120
Speaker 1: the galaxy is going to collapse anyways, right, and maybe

967
00:45:18,200 --> 00:45:19,799
Speaker 1: it will collapse into a new black hole.

968
00:45:19,880 --> 00:45:22,319
Speaker 2: Yeah, exactly, it could definitely form a new black hole

969
00:45:22,360 --> 00:45:24,399
Speaker 2: even if you kick out the original one. There's no

970
00:45:24,400 --> 00:45:26,360
Speaker 2: noncompete clause in galactic formation.

971
00:45:26,960 --> 00:45:30,040
Speaker 1: And when is this supposed to happen, like tomorrow or

972
00:45:30,880 --> 00:45:31,840
Speaker 1: trillions of years?

973
00:45:32,239 --> 00:45:34,960
Speaker 2: Oh, we're talking about billions and billions of years for sure,

974
00:45:35,400 --> 00:45:37,279
Speaker 2: So we are much more a threat of the Sun

975
00:45:37,360 --> 00:45:40,600
Speaker 2: expiring before our system collapses into the center of a

976
00:45:40,640 --> 00:45:42,400
Speaker 2: black hole. But if we want to continue on for

977
00:45:42,440 --> 00:45:44,680
Speaker 2: billions and billions of years, we definitely need to plan

978
00:45:45,040 --> 00:45:47,840
Speaker 2: deep into the future. And also, we're just curious about

979
00:45:47,840 --> 00:45:50,440
Speaker 2: how black holes work and how galaxies work, and we

980
00:45:50,480 --> 00:45:52,319
Speaker 2: want to understand it because it could be that there's

981
00:45:52,360 --> 00:45:55,080
Speaker 2: some other deep insight into the way the universe works

982
00:45:55,120 --> 00:45:58,120
Speaker 2: waiting for us. Every time. In science, we're like, don't

983
00:45:58,160 --> 00:46:01,640
Speaker 2: really understand how something works, and we deeper, we discover

984
00:46:01,760 --> 00:46:05,440
Speaker 2: something fascinating underneath that we didn't even expect to find,

985
00:46:05,600 --> 00:46:08,279
Speaker 2: so satisfying our curiosity and like trying to understand this

986
00:46:08,400 --> 00:46:11,239
Speaker 2: in great detail is good path to like opening up

987
00:46:11,280 --> 00:46:14,319
Speaker 2: some surprising new doors. So we're doing our best to

988
00:46:14,400 --> 00:46:17,320
Speaker 2: improve our future prospects for understanding these things.

989
00:46:17,520 --> 00:46:21,239
Speaker 1: Mmm, sounds like a problem for the AIS. You could

990
00:46:21,239 --> 00:46:23,120
Speaker 1: just kick back, let to figure it out.

991
00:46:23,120 --> 00:46:25,120
Speaker 2: Well. One of my favorite ways to study these things

992
00:46:25,120 --> 00:46:29,799
Speaker 2: in the future is with our space based gravitational Observatory

993
00:46:30,200 --> 00:46:33,600
Speaker 2: so LIGO is this gravitational wave observatory that has two

994
00:46:33,719 --> 00:46:36,799
Speaker 2: arms that are kilometers long filled with lasers, and they're

995
00:46:36,800 --> 00:46:40,759
Speaker 2: planning to build one in space called Lisa LSA mean

996
00:46:40,840 --> 00:46:42,800
Speaker 2: much much bigger, and so it's going to be able

997
00:46:42,800 --> 00:46:46,359
Speaker 2: to observe gravitational waves at lower frequencies, which is what's

998
00:46:46,440 --> 00:46:50,200
Speaker 2: generated by the collisions of super massive black holes. So

999
00:46:50,239 --> 00:46:54,320
Speaker 2: we might be able to observe gravitational waves from galactic

1000
00:46:54,360 --> 00:46:58,040
Speaker 2: mergers and understand this process in more detail. What happens

1001
00:46:58,080 --> 00:47:00,720
Speaker 2: when two super massive black holes really do come together?

1002
00:47:01,680 --> 00:47:05,000
Speaker 1: WHOA, which is what happens when two galaxies collide right.

1003
00:47:04,840 --> 00:47:07,680
Speaker 2: Exactly, yeah, yeah, and so we could see the signature

1004
00:47:07,800 --> 00:47:10,520
Speaker 2: of black holes getting injected from the hearts of their.

1005
00:47:10,400 --> 00:47:12,520
Speaker 1: Galaxies, ejected or smushed.

1006
00:47:12,880 --> 00:47:16,760
Speaker 2: Smushed or ejected. We don't know both outcomes are possible.

1007
00:47:16,800 --> 00:47:19,840
Speaker 1: But will we hear the black hole get injected?

1008
00:47:19,880 --> 00:47:22,560
Speaker 2: Well, black hole injection comes with a very powerful, very

1009
00:47:22,600 --> 00:47:26,480
Speaker 2: directional gravitational wave signature, and so they think they might

1010
00:47:26,520 --> 00:47:28,920
Speaker 2: be able to distinguish that from just like a normal

1011
00:47:29,000 --> 00:47:32,960
Speaker 2: combination of two black holes into one. But it all depends

1012
00:47:32,960 --> 00:47:36,080
Speaker 2: on this crazy set of satellites in space shooting lasers

1013
00:47:36,120 --> 00:47:41,040
Speaker 2: in each other, measuring tiny changes in their relative distances.

1014
00:47:41,880 --> 00:47:45,320
Speaker 1: Well, it sounds like the future is all black hole.

1015
00:47:45,520 --> 00:47:48,319
Speaker 1: So we bidters start to understand them and get used

1016
00:47:48,360 --> 00:47:50,319
Speaker 1: to them and figure out how they form.

1017
00:47:50,480 --> 00:47:53,959
Speaker 2: Right, absolutely something we'd like to understand, not just because

1018
00:47:54,000 --> 00:47:56,240
Speaker 2: we're curious about the universe, but because they might control

1019
00:47:56,280 --> 00:47:57,480
Speaker 2: a fate of our galaxy.

1020
00:47:57,920 --> 00:48:00,320
Speaker 1: Yep. Or it might be just something for our AI

1021
00:48:00,520 --> 00:48:03,759
Speaker 1: replacements to figure out. We might be long gone.

1022
00:48:06,080 --> 00:48:08,080
Speaker 2: I'll read about it from my lounge chair at the

1023
00:48:08,080 --> 00:48:09,040
Speaker 2: center of the black hole.

1024
00:48:09,239 --> 00:48:12,120
Speaker 1: All right, we hope you enjoyed that. Thanks for joining us.

1025
00:48:12,680 --> 00:48:13,439
Speaker 1: See you next time.

1026
00:48:21,280 --> 00:48:24,080
Speaker 2: Thanks for listening, and remember that Daniel and Jorge Explain

1027
00:48:24,160 --> 00:48:28,160
Speaker 2: the Universe is a production of iHeartRadio. For more podcasts

1028
00:48:28,160 --> 00:48:32,800
Speaker 2: from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever

1029
00:48:32,880 --> 00:48:34,600
Speaker 2: you listen to your favorite shows.