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How did we discover black holes? · Daniel and Kelly’s Extraordinary Universe

0:08
Speaker 1: Hey, Jorge, do you still have that pet black hole
0:11
Speaker 1: in your backyard? Well, you know, my physics lawyer tells
0:14
Speaker 1: me as you'd neither confirm nor deny that that's good advice.
0:19
Speaker 1: So in that case, I have a question for your
0:22
Speaker 1: physics lawyer. He charges a lot better be good. All right,
0:26
Speaker 1: is my question. How do you actually know that it's
0:30
Speaker 1: a black hole? Well, it's either a black hole or
0:32
Speaker 1: something else that eats a lot of bananas. All right,
0:35
Speaker 1: So you either have a black hole or King Kong
0:38
Speaker 1: living in your backyard. Either way, I definitely need more bananas.
0:56
Speaker 1: I am or handmade cartoonist and the creator of PhD comic. Hi.
1:00
Speaker 1: I'm Daniel. I'm a particle physicist, and I think the
1:03
Speaker 1: universe is kind of bananas. Welcome to our podcast. Daniel
1:06
Speaker 1: and Jorge explained the university production of I Heart Radio,
1:09
Speaker 1: in which we take you on a tour of everything
1:12
Speaker 1: that's crazy and amazing about our universe, which turns out
1:15
Speaker 1: to be most of it. We talk to you about
1:17
Speaker 1: the things that we do know and about the things
1:19
Speaker 1: that we don't know, the things that scientists are trying
1:21
Speaker 1: to figure out, and the things that you are wondering about.
1:25
Speaker 1: This incredible, glittering cosmos we find ourselves in. Yeah, all
1:28
Speaker 1: the amazing stuff out there that's mysterious and interesting and
1:32
Speaker 1: intriguing and potentially mind blowing. And sometimes we also like
1:36
Speaker 1: to talk about how we discover things, because you know,
1:39
Speaker 1: I think that how we discover things sometimes it's almost
1:42
Speaker 1: as important as knowing the thing itself, because that's how
1:44
Speaker 1: we know it's there and tells us a little bit
1:47
Speaker 1: about how science works. Yeah, as an experimentalist, I always
1:50
Speaker 1: want to know, like, how do we know that's true?
1:53
Speaker 1: You're telling me this thing exists in the universe. How
1:56
Speaker 1: do we really know? What is the evidence that convinced people?
1:59
Speaker 1: Because there was a moment in science when we didn't
2:01
Speaker 1: think it existed, and then all of a sudden things
2:03
Speaker 1: shifted and everybody was convinced. What were the pieces of
2:06
Speaker 1: evidence that came together in people's minds that made them
2:09
Speaker 1: believe something new and wacky and unbelievable was real. Daniel,
2:14
Speaker 1: is there the equivalent of like a behind the scenes
2:17
Speaker 1: clip for physics? You know, like when you publish a paper,
2:20
Speaker 1: do you also publish the commentary or behind the scenes
2:23
Speaker 1: or bloopers? You know, sometimes people accidentally leave little comments
2:29
Speaker 1: in their paper. I mean they're not visible in the
2:32
Speaker 1: final product, but they're sort of hidden inside the text
2:34
Speaker 1: that creates the paper, and you can scan through and
2:37
Speaker 1: you can see people authors arguing about what they should
2:40
Speaker 1: put in the paper, like this next line is hot garbage,
2:43
Speaker 1: we should cut it out. Stuff like that. Yeah, no kidding.
2:47
Speaker 1: It's the equivalent of like leaving little comments in your
2:49
Speaker 1: Microsoft word document. We usually write our stuff in l tech,
2:53
Speaker 1: and you can put comments inside the source and sometimes
2:55
Speaker 1: people forget to pull that stuff out, and so you
2:58
Speaker 1: can get some pretty hilarious insights into how the paper
3:01
Speaker 1: was Does anyone ever say we totally made this up?
3:04
Speaker 1: But don't tell anybody no? And it's not usually a
3:08
Speaker 1: dramatic It's not like you know, the Last Dance that
3:11
Speaker 1: documentary about Michael Jordan's We don't have you know, that
3:14
Speaker 1: much drama in physics. Usually if you're writing papers with people,
3:17
Speaker 1: then you mostly agree. Most of the drama is between papers,
3:20
Speaker 1: like you know, this paper says the other paper was wrong,
3:23
Speaker 1: and those folks over there in that university don't know
3:25
Speaker 1: what they're talking about. That's where most of the conflict
3:28
Speaker 1: with you. That's right, Hey, the stakes are high. You know,
3:31
Speaker 1: we are trying to figure out the nature of the
3:33
Speaker 1: universe itself. Here, man, it's not just basketball. You can't
3:37
Speaker 1: get catty enough when it comes to the universe. So
3:40
Speaker 1: to be on the program, we'll be talking about the
3:41
Speaker 1: discovery of something that I guess most people have heard
3:44
Speaker 1: of this. You know, everyone who's interested in science and
3:48
Speaker 1: space probably has heard of these, but I've been not
3:50
Speaker 1: a lot of people know how they were discovered. That's right.
3:53
Speaker 1: It's something that's extra weird and fascinating in the universe,
3:56
Speaker 1: and it took science a long time to come to
3:59
Speaker 1: grips with the idea that they could actually be out there,
4:02
Speaker 1: that they could really be a real weird thing in
4:05
Speaker 1: our universe. And this is something that happens a lot
4:08
Speaker 1: sort of in physics, that we have an idea for
4:10
Speaker 1: something weird and strange, we think, well, that's just like
4:12
Speaker 1: some mathematical artifact that's not actually real, it doesn't really
4:16
Speaker 1: happen out there, and then we discover, wow, the universe
4:19
Speaker 1: actually is that weird. Quantum mechanics is real, Electrons really
4:24
Speaker 1: are determined by weird probabilities. And so we're sort of
4:27
Speaker 1: coming to grips with we're waking up to realize that
4:30
Speaker 1: the universe is stranger than we ever imagined. Yeah, and
4:33
Speaker 1: this thing is extra strange and extra weird. It's one
4:37
Speaker 1: of the maybe a true like pockets of mystery in
4:40
Speaker 1: the universe that we may never even discover what's inside
4:43
Speaker 1: of him. So to be on the podcast, we'll be
4:45
Speaker 1: asking the question how do we discover black holes? So, Daniel,
4:54
Speaker 1: I assume we didn't just fall into one by accident.
4:57
Speaker 1: We're inside one right now. Welcome to the podcast Why
5:00
Speaker 1: inside the black Hole that notity will ever hear? We
5:05
Speaker 1: are literally screaming into the void. There's an idea that
5:08
Speaker 1: maybe we are inside of a black hole. Isn't that possibility? Yeah,
5:11
Speaker 1: that's a possibility. It's theoretically possible that our entire universe
5:15
Speaker 1: is inside another black hole. We had the Loop quantum
5:19
Speaker 1: gravity theorist come on. We asked her what's inside a
5:21
Speaker 1: black hole? And she actually said maybe an entire universe,
5:25
Speaker 1: And so that's fun to think about. But you know
5:27
Speaker 1: the problem with black holes is that we can't see
5:30
Speaker 1: inside them, so we don't know what's inside them. And
5:33
Speaker 1: anybody who does survive the journey into a black hole
5:36
Speaker 1: can't then shout to us about what they find. So,
5:39
Speaker 1: as you said, they may be eternal pockets of missing.
5:43
Speaker 1: So we might be live inside of a black hole
5:45
Speaker 1: right now along with everybody else. That's right, along with
5:49
Speaker 1: all those socks you've lost that probably went into a
5:51
Speaker 1: black hole somewhere. That's an extra black hole, that's like
5:54
Speaker 1: a laundry hole. Yeah, it's a big question, like how
5:58
Speaker 1: do we know that black holes really exist? What's the evidence?
6:02
Speaker 1: And more kind of maybe interesting is how do we
6:04
Speaker 1: come to think of them and how do people become
6:06
Speaker 1: convinced that they exist even before we had ever seen
6:09
Speaker 1: And so, as usual, I pulled our listeners and I
6:13
Speaker 1: asked them if they knew about the history of the
6:15
Speaker 1: discovery of the black hole, what was the crucial piece
6:17
Speaker 1: of evidence that moved it from the category of like
6:20
Speaker 1: crazy bonkers theoretical idea to crazy bonkers real actual facts.
6:25
Speaker 1: Let's think about it for a second. How do you
6:27
Speaker 1: think we discovered black holes? Here's what people had to say.
6:30
Speaker 1: There was a star found that was turning red and blue,
6:33
Speaker 1: but it didn't but there was no recognizable binary pair
6:37
Speaker 1: or another star for it. So that's how they knew
6:40
Speaker 1: that it must be a binary pair with a black hole.
6:44
Speaker 1: I would say that this is true. Somebody observing the
6:47
Speaker 1: space and and has seen some sort of gravitational lensing
6:51
Speaker 1: happening that black hole has gone in between a observed
6:56
Speaker 1: star and a observer. I believe that they were initially
7:01
Speaker 1: discovered by in more of a theoretical sense, by not
7:07
Speaker 1: being able to explain the gravity that was missing due
7:12
Speaker 1: to the rotation universe and was holding it together. They
7:16
Speaker 1: were officially discovered by the gravitational lensing, I believe. I
7:21
Speaker 1: think black holes were predicted by Einstein um, but how
7:26
Speaker 1: they were discovered was by seeing lensing in stars. An
7:30
Speaker 1: idea in which I rather believe is that when two
7:34
Speaker 1: black holes, Clyde or black hole is like born, so
7:39
Speaker 1: when a star collapse isn't a singularity that these occurrences
7:45
Speaker 1: leads like this leads to an emission of race, maybe
7:49
Speaker 1: like X rays or gramma rays, I'm not sure. And
7:53
Speaker 1: these race were like measured on Earth. I'm not sure,
7:56
Speaker 1: but I would guess some gravitational lens effect from what
7:59
Speaker 1: I can remember. Instantly, we're the one that figured out
8:02
Speaker 1: the black holes were a thing. Was just equations and stuff,
8:05
Speaker 1: and then it took years and years and years until
8:08
Speaker 1: until I finally found actual evidence of it in real life.
8:11
Speaker 1: The only way I contain the black holes were discovered
8:14
Speaker 1: were maybe because of their gravitational effect on the surroundings,
8:18
Speaker 1: and assume that it was probably a mathematical possibility for
8:23
Speaker 1: the existence of such a body which had such strong
8:27
Speaker 1: gravitational pull that even light cannot escape, and maybe later
8:31
Speaker 1: on they finally found it. All right, pretty interesting answers. Yeah,
8:35
Speaker 1: people do have an idea that black holes were first
8:38
Speaker 1: thought of and then later discovered, which is pretty cool.
8:42
Speaker 1: But the consensus tends to be here some gravitational lensing
8:45
Speaker 1: that you could like see a black hole passing in
8:48
Speaker 1: front of a star and distorting it, And that's true
8:51
Speaker 1: in theory that if that happened, you might be able
8:53
Speaker 1: to see it, but that's definitely not how black holes
8:56
Speaker 1: were discovered, so not through gravitational lensing. But maybe there's
8:58
Speaker 1: some other gravitation means. Yeah, and this actually has a
9:01
Speaker 1: lot of parallels to other big mysteries of the universe,
9:05
Speaker 1: like dark matter. We've talked about dark matter on this
9:07
Speaker 1: podcast a lot. It's something we know is there, but
9:10
Speaker 1: only have sort of indirect hints of its existence, and
9:13
Speaker 1: all those hints are gravitational. And in a very similar way,
9:17
Speaker 1: black holes are very strong, very powerful, very important to
9:21
Speaker 1: the universe, but also very hard to see directly because
9:25
Speaker 1: they're mostly gravitational objects and gravity is very weak. I
9:29
Speaker 1: guess it's hard. How do you see something that's dark
9:31
Speaker 1: in space? Especially, it's the perfect camouflage, well done, black holes.
9:37
Speaker 1: It's hiding what but what is it hiding from? It's
9:40
Speaker 1: hiding from us. I guess, alright, well, step us through here, Daniel,
9:44
Speaker 1: Because black holes are sort of interesting in that they
9:46
Speaker 1: were thought of theoretically first, or there was sort of
9:50
Speaker 1: discovered theoretically first, probably a long time, almost hundred years
9:53
Speaker 1: before we actually ever saw one. Yeah, and you might
9:56
Speaker 1: be wondering, like, what does it mean to discover something theoretically? Right?
10:00
Speaker 1: After all, for things to exist, they have to be
10:02
Speaker 1: in our universe, and so experimentally in things that can
10:05
Speaker 1: really discover something right, Well, you can actually make discoveries theoretically.
10:10
Speaker 1: You can say, here the laws of the universe as
10:12
Speaker 1: we think we understand them, what are the consequences of them?
10:15
Speaker 1: What are some predictions we can make from these laws
10:18
Speaker 1: that would maybe be surprising and so if you like
10:21
Speaker 1: look in the corners of the space and say, oh,
10:23
Speaker 1: if these laws do this and these laws do that,
10:25
Speaker 1: is there something that we hadn't anticipated that these laws
10:28
Speaker 1: can do. And that's precisely what happened with black holes.
10:31
Speaker 1: We came to some new understanding of the way gravity
10:34
Speaker 1: worked and then started to look at the consequences that
10:36
Speaker 1: what does that mean? What possible weird stuff can gravity do?
10:40
Speaker 1: And people almost literally stumbled over this weird, bizarre prediction
10:45
Speaker 1: for what gravity could do. Yeah, I guess you can
10:47
Speaker 1: theoretically discover things theoretically. It's kind of what you're saying, yeah,
10:50
Speaker 1: And that's exactly what was done, for example, with the
10:53
Speaker 1: Higgs boson. The Higgs boson was an idea which first
10:56
Speaker 1: came about theoretically. People looked at the pattern of the
10:58
Speaker 1: particles and they thought, you know, this would make more
11:01
Speaker 1: sense if there was this other thing that existed, and
11:03
Speaker 1: then we found it. Very much in contrast to dark matter,
11:06
Speaker 1: dark matter is something that was seeing experimental. It was
11:09
Speaker 1: like a puzzle in the universe. We didn't understand what
11:11
Speaker 1: we were seeing until later we came up with an
11:14
Speaker 1: idea to explain it. But black holes were found theoretically,
11:17
Speaker 1: and it really, as you said, goes back to the
11:20
Speaker 1: genesis of general relativity back in nineteen fifteen when Einstein
11:24
Speaker 1: published his final paper on the field equations for general
11:28
Speaker 1: relative and then he dropped the mic. He's like, I'm out.
11:32
Speaker 1: He sort of did. And the thing to understand about
11:35
Speaker 1: his field equations is that they are nasty and complicated,
11:38
Speaker 1: like he discovered sort of how space and time talk
11:41
Speaker 1: to matter, you know, And what he discovered is that
11:44
Speaker 1: space isn't just like an empty backdrop, but it's something
11:47
Speaker 1: that's dynamical and that it responds to matter. So matter
11:51
Speaker 1: tells space how to curve, how to bend, how to shape,
11:55
Speaker 1: and then space tells matter how to move. So it's
11:57
Speaker 1: like a complex system, a thing with a lot of feedback,
12:00
Speaker 1: and that makes it very difficult to know, like, well,
12:03
Speaker 1: what is the solution would actually happened in various circumstances,
12:07
Speaker 1: and for a long time, the only thing people could
12:09
Speaker 1: ever figure out in terms of the Einstein field equations
12:12
Speaker 1: were super simplified universe like the universe field with homogeneous
12:15
Speaker 1: dust or totally empty universe like. Nobody's ever solved the
12:19
Speaker 1: Einstein field equations for our actual universe. I guess you
12:23
Speaker 1: can sort of explore with the equations, right, like if
12:25
Speaker 1: you find that the things around you obey as certain
12:28
Speaker 1: law or equations like f equals and make and then
12:31
Speaker 1: kind of tweaked the numbers and the parameters to kind
12:34
Speaker 1: of explore more extreme conditions than what you have around you. Right,
12:38
Speaker 1: you could add like what happens if the mask coast
12:40
Speaker 1: to zero, or what happens if the force coast to zero,
12:43
Speaker 1: and the equations would tell you that's right, and that's
12:46
Speaker 1: exactly what happened. So Einstein published these equations in nineteen fifteen,
12:50
Speaker 1: and then he sent them to his friend and colleague,
12:52
Speaker 1: Short Stild, and short Stile looked at these and he
12:56
Speaker 1: played around with him, and he actually found a solution.
12:58
Speaker 1: Just a few months later. He found what's one of
13:01
Speaker 1: the first exact solutions to the field equations, like a
13:04
Speaker 1: configuration of matter and the definition of space that satisfied
13:08
Speaker 1: those equations that could be real in the universe. So
13:11
Speaker 1: he found this solution, and he found some things about
13:14
Speaker 1: it that were kind of weird. Well, I guess to
13:15
Speaker 1: step us through a little bit, what did what did
13:17
Speaker 1: you mean by a solution to the equations like the
13:19
Speaker 1: equations kind of related space and matter, and then you
13:25
Speaker 1: have to find a solution for them, and the solutions
13:27
Speaker 1: what do the solutions tell you? The solutions tell you
13:29
Speaker 1: how space curves. So if you have a configuration of matter,
13:32
Speaker 1: if you say I'm going to put a big blob
13:34
Speaker 1: of stuff right here in the middle of the universe,
13:36
Speaker 1: then the solutions tell you how space curves all the
13:39
Speaker 1: way through that universe. And so that's a solution meaning
13:43
Speaker 1: how space bends, or like how things move around it.
13:45
Speaker 1: How space bends, and then how space bends determines how
13:48
Speaker 1: things move right, Like we know that having the Sun
13:51
Speaker 1: in the center of our Solar system bends the space
13:54
Speaker 1: in its vicinity, so that therefore the Earth moves in
13:57
Speaker 1: an orbit around the Sun rather than just lying off
14:00
Speaker 1: in what otherwise looks like a straight line. So you
14:03
Speaker 1: start with the mass. You said, I'm gonna put this
14:05
Speaker 1: mass into the universe. That tells you the shape of space,
14:09
Speaker 1: and then that lets you determine the equations of motion
14:12
Speaker 1: how something would actually move through that space. So he
14:15
Speaker 1: was the first one to figure out if you put
14:17
Speaker 1: a really massive object in the universe that's spherically symmetric
14:20
Speaker 1: what is the shape of space around it? And what
14:24
Speaker 1: he found was really weird. He found that if you
14:26
Speaker 1: put in a really heavy mass, enough mass that there's
14:30
Speaker 1: this sort of edge to it, that there's this point
14:32
Speaker 1: where the curvature space sort of becomes infinite, right, like
14:36
Speaker 1: space is curved like it is around the Sun. But
14:39
Speaker 1: if the mass gets large enough, then you have this threshold,
14:42
Speaker 1: this point which we now call the short styles radius,
14:45
Speaker 1: where the curvature of space gets a singularity, or like
14:48
Speaker 1: the field equations have this infinity in them. And it's
14:51
Speaker 1: not something that he understood at the time the way
14:54
Speaker 1: that we understand it now. He didn't say, oh, this
14:56
Speaker 1: is the event horizon of a black hole. He was like,
14:58
Speaker 1: all right, I found a salut, but it has some
15:01
Speaker 1: weirdness at a certain distance from this audition, I see.
15:03
Speaker 1: He just sort of like turned the knob on the
15:05
Speaker 1: mass and then he found that the equations suddenly kind
15:08
Speaker 1: of got wonk. Yeah, they got wonky, And people were like, huh,
15:11
Speaker 1: that's weird, and you know that happens a lot in
15:13
Speaker 1: theoretical physics. You're like, I found a solution to this
15:15
Speaker 1: set of equations. It makes sense over here, I don't
15:18
Speaker 1: really understand what's going on in that part, but let's
15:20
Speaker 1: just put that aside for now. And people studied it
15:23
Speaker 1: for you know, ten years, twenty years, forty years before
15:27
Speaker 1: they really had an understanding for what that meant. Initially,
15:30
Speaker 1: they only looked at it as well, the curvature of
15:33
Speaker 1: space gets really strong here, so time slows down in
15:37
Speaker 1: the vicinity of a lot of curvature, and so it
15:40
Speaker 1: might be something like a frozen star. They thought, if
15:44
Speaker 1: time slows down as you approach this heavy, heavy mass,
15:47
Speaker 1: then you'll see time slow down as things approach this thing,
15:50
Speaker 1: and it's sort of like time stops when you get
15:53
Speaker 1: to that point. So they didn't call it a black
15:55
Speaker 1: hole back then. They called it a frozen star. Wow,
15:58
Speaker 1: that's almost a little better. Yeah, well, and I think
16:01
Speaker 1: that they thought that if you saw one of these
16:03
Speaker 1: things in nature, it wouldn't be a black emptiness. It
16:07
Speaker 1: would be like a star, but just like frozen in time.
16:09
Speaker 1: You know, like if a star grew so massive that
16:12
Speaker 1: it passed this threshold, it would just like freeze in whatever,
16:16
Speaker 1: like crazy flaming moment it happened to be in, right,
16:19
Speaker 1: but it would stop emitting photons in which case it
16:22
Speaker 1: might be black. Yeah, well that's not something that they
16:23
Speaker 1: understood until much much later, all right, So then it
16:26
Speaker 1: was kind of wonkey, And didn't they think that maybe
16:28
Speaker 1: the equation was wrong, like like, this is a weird
16:32
Speaker 1: result and predict something that seems that would make time stop.
16:36
Speaker 1: Maybe our equations are not meant to work in these extremes. Yes, definitely.
16:40
Speaker 1: For a long time people thought, well, this is an
16:42
Speaker 1: interesting sort of mathematical curiosity, but they thought it couldn't
16:45
Speaker 1: be real. They thought instead that it only happened under
16:48
Speaker 1: a certain very special, perfectly symmetric conditions that you could
16:52
Speaker 1: achieve sort of on the page, but would never actually
16:54
Speaker 1: happen in reality. Then in reality something else would interfere,
16:58
Speaker 1: would muck it up, so you wouldn't get this weird behavior.
17:01
Speaker 1: So for a long time it was like, hey, look
17:03
Speaker 1: at this cute, little weird mathematical effect. Of course that's
17:06
Speaker 1: not real, like that would never really exist. The universe
17:09
Speaker 1: is not that insane. But they had to give it
17:14
Speaker 1: some second thoughts later, and then later there were big
17:16
Speaker 1: discoveries about him. So let's get into those. But first
17:19
Speaker 1: let's take a quick break, all right, Daniel, So what
17:34
Speaker 1: do I do about the pet black hole in my backyard?
17:36
Speaker 1: Should I call the physics vet or I feel like
17:40
Speaker 1: this is a legal trapping no matter what advice I
17:42
Speaker 1: give you, I mean, the complicit in your death or
17:46
Speaker 1: the death of your neighbors somehow, Well, may it's just
17:48
Speaker 1: a theoretical black hole that I have in my theoretical yard. Alright,
17:52
Speaker 1: So we're talking about the discovery of black holes, and
17:54
Speaker 1: so they were sort of this weird mathematical kind of
17:58
Speaker 1: oddity in the equations, and maybe the equations were wrong,
18:01
Speaker 1: or maybe these things were real, but people didn't know.
18:04
Speaker 1: So what kind of pushed people to think that maybe
18:05
Speaker 1: they were real? There was a period in the late
18:08
Speaker 1: nineteen fifties when there was a lot of theoretical activity
18:11
Speaker 1: because people finally understood theoretically what this might mean. There's
18:15
Speaker 1: a guy named David Finkelstein, and he was actually working
18:17
Speaker 1: on something totally different. He was trying to understand quantum gravity,
18:21
Speaker 1: was trying to bring together quantum mechanics and gravity, and
18:24
Speaker 1: he cooked up a really weird system that had some
18:26
Speaker 1: gravitational kink in it. And it was a weird system,
18:29
Speaker 1: but it gave him an idea. He was like, you
18:31
Speaker 1: know what, in my weird system, I had this concept
18:34
Speaker 1: of an event horizon where information can go in one
18:37
Speaker 1: direction but not the other. And he was looking at
18:39
Speaker 1: his weird theory and he thought, you know what, this
18:42
Speaker 1: might be what we're talking about in short stiles theory.
18:45
Speaker 1: And he went back and he looked at these frozen
18:48
Speaker 1: stars and the short siled radius and the singularity in
18:51
Speaker 1: the gravitation equations and he said, you know what, that's
18:53
Speaker 1: what's happening here. He like theoretically reinterpreted this and said
18:58
Speaker 1: this is what an event horizon is. He came at
19:00
Speaker 1: it from a different direction. Yeah, he just had like
19:03
Speaker 1: a moment of insight, like how to look at these equations.
19:05
Speaker 1: But still people thought, all right, well that's cool. This
19:09
Speaker 1: makes this weird mathematical curiosity more interesting, Like how weird
19:13
Speaker 1: would that be if information it could only flow in
19:15
Speaker 1: one direction across a threshold in space? Right? But then
19:19
Speaker 1: they started seeing weird stuff out there in the universe
19:22
Speaker 1: that slowly built up the evidence that these things could
19:25
Speaker 1: be real. And the first thing was the discovery not
19:28
Speaker 1: of black holes, but actually of pulsings. These are like
19:31
Speaker 1: special stars, right, yeah, these are special stars. There are
19:35
Speaker 1: neutron stars. These are stars that are at the end
19:37
Speaker 1: of their life, and this is the leftover chord, and
19:39
Speaker 1: it's so dense that all the protons and electrons have
19:42
Speaker 1: merged together to form neutrons. It's a very dense kind
19:46
Speaker 1: of object. But again it was a theoretical object. People thought, well, potentially,
19:50
Speaker 1: if you had enough stuff together, collapse into a neutron star,
19:54
Speaker 1: but nobody really believed that existed until they were discovered
19:57
Speaker 1: in nineteen sixty seven a special version and of them pulsars,
20:01
Speaker 1: which rotate and have a very strong beam coming at
20:04
Speaker 1: the top of them. We're discovering people thought, oh, my gosh,
20:07
Speaker 1: maybe these very massive, gravitationally collapsed objects really do exist
20:12
Speaker 1: in the universe, and people started to take these mathematical
20:15
Speaker 1: solutions a little bit more seriously. Pulsars are not sort
20:18
Speaker 1: of related to black holes, but they are sort of
20:21
Speaker 1: extreme and crazy and maybe also kind of like a
20:24
Speaker 1: weird equation oddity, and so when they find it, they're like, hey,
20:28
Speaker 1: maybe need that applies to black holes too. Yeah, maybe
20:31
Speaker 1: we should start taking these gravitational oddities that are theoretical,
20:34
Speaker 1: we should start taking them more seriously, because you know,
20:37
Speaker 1: if neutron stars are real, maybe black holes are also.
20:41
Speaker 1: It's like, hey, he got a Nobel price, I want
20:43
Speaker 1: one to Let's dig into this and it's a fascinating
20:46
Speaker 1: store because there's a lot of different threads. At the
20:47
Speaker 1: same time. You have this theory thread where people are
20:50
Speaker 1: finally starting to understand what these equations mean. Then you
20:53
Speaker 1: have this thread from the neutron stars where people discovered pulsars,
20:57
Speaker 1: and then totally separately, people were launching rockets into the
21:01
Speaker 1: atmosphere to try to study X rays, and in White
21:04
Speaker 1: Sands Missile based in New Mexico, a couple of folks
21:07
Speaker 1: outfitted a rocket with this X ray detector because they
21:11
Speaker 1: wanted to see, like what does the sky look like
21:13
Speaker 1: in the X ray Because the atmosphere stops a lot
21:16
Speaker 1: of X rays from coming down to Earth. So if
21:19
Speaker 1: you want to see X rays, you can. I have
21:20
Speaker 1: to go out into space, that's right, and it's a
21:22
Speaker 1: great opportunity to see something new. It's just to look
21:24
Speaker 1: at the universe in a new way. Like we've looked
21:27
Speaker 1: at the universe using our eyeballs, and we build telescopes
21:31
Speaker 1: that are more powerful to look invisible light. But we
21:33
Speaker 1: also like to look at the universe in invisible light,
21:36
Speaker 1: you know, infrared or radio waves or X rays, and
21:40
Speaker 1: X rays are extra powerful because they come from gas
21:43
Speaker 1: that's at millions and millions of degrees. There are things
21:47
Speaker 1: out there that emit only in the X rays and
21:49
Speaker 1: you can only see their X rays. They don't emit
21:52
Speaker 1: visible light. So people thought, well, let's take a look
21:55
Speaker 1: at the universe using a new set of eyeballs. So
21:58
Speaker 1: they flew these rockets up to the top of the
22:00
Speaker 1: atmosphere and outfit of them with X ray detectors. And
22:03
Speaker 1: this is not like you know, in orbit. It just
22:05
Speaker 1: like goes up. It's sort of suborbital picture. It takes
22:09
Speaker 1: selfie and drop takes the university sort of scans the
22:13
Speaker 1: sky for like eight degrees and then it comes back.
22:17
Speaker 1: I like that. And they saw some really weird stuff.
22:20
Speaker 1: They found eight new very bright sources of X rays
22:23
Speaker 1: that nobody had ever seen before, like spiked, and they
22:27
Speaker 1: could tell where it was coming from. Yeah, they could
22:29
Speaker 1: tell where it was coming from. They were like points
22:30
Speaker 1: in space. It was like, you know, you develop your
22:33
Speaker 1: picture and you see these bright dots in the sky
22:35
Speaker 1: and this one sickness X one which turns out to
22:38
Speaker 1: historically be the most important was the brightest one. And
22:41
Speaker 1: if you look up in the sky, there's nothing there,
22:44
Speaker 1: like you don't see anything in the optical. Your eyes
22:47
Speaker 1: don't tell you there's anything, But there's an incredible source
22:50
Speaker 1: of X rays coming at you from this dot in
22:52
Speaker 1: the sky. Interesting, and that's weird. So it's it's not
22:56
Speaker 1: emitting visible light, but it's emitting X rays. Yes, And
22:59
Speaker 1: that was really weird. So people thought, well, what's there.
23:02
Speaker 1: So then these same folks that are like, well, let's
23:04
Speaker 1: follow up on this, and they built a satellite with
23:06
Speaker 1: NASA and they put it up in space to orbit,
23:08
Speaker 1: and this gave them more data and more precision, and
23:11
Speaker 1: they were able to figure out exactly where it was
23:13
Speaker 1: coming from. This is now nineteen seventy, and they learned
23:17
Speaker 1: something else really fascinating about this source was that it
23:20
Speaker 1: was variable, Like it wasn't just emitting X rays. It
23:23
Speaker 1: would admit a bunch of X rays and then not
23:25
Speaker 1: very much, and then a bunch of BAST rays and
23:26
Speaker 1: then not very much. It was highly variable, and it
23:29
Speaker 1: was variable on a really short time scale. It's not
23:32
Speaker 1: like it would take a year to change. It could
23:34
Speaker 1: go like on and off in less than a second.
23:36
Speaker 1: What and was it consistent or was it sort of random?
23:39
Speaker 1: It was sort of random and sporadic. But the fact
23:42
Speaker 1: that it would go on and off in like less
23:43
Speaker 1: than a second gave them a really, really valuable clue
23:46
Speaker 1: about how big it is. Because something that turns on
23:49
Speaker 1: and off in less than a second can't actually be
23:53
Speaker 1: that large. Why not because of the speed of light.
23:56
Speaker 1: Like if this is all caused by a single event,
23:59
Speaker 1: you have some event which is causing this thing to
24:01
Speaker 1: flare up, then there's a certain amount of time that
24:04
Speaker 1: the information has to travel across an object. So that
24:07
Speaker 1: limits how big that object can be if it's going
24:09
Speaker 1: to sort of operate coherent, Like if it's too big,
24:13
Speaker 1: then you would see it fade in and out kind of.
24:16
Speaker 1: If it's too big, then they would have like lots
24:17
Speaker 1: of different pockets, Right, they have a little pocket over
24:19
Speaker 1: here that's doing something, a little pocket over there that's
24:21
Speaker 1: doing something. But for an object to act like as one,
24:24
Speaker 1: like one coherent source turning on and off, means it
24:28
Speaker 1: has to be pretty small because all that stuff has
24:31
Speaker 1: to sort of be in communication within light speed, in sync. Right, Yeah,
24:35
Speaker 1: it has to be in sync exactly, just like the
24:37
Speaker 1: boy band. It has to move in one direction, if
24:39
Speaker 1: you know what I'm talking about. Yeah, totally. I'm a
24:43
Speaker 1: big fan of black Hole Street Boys. They were the
24:49
Speaker 1: best anyway. So they knew that this thing was very powerful,
24:52
Speaker 1: and then it had to be smaller than the sun,
24:54
Speaker 1: like the time variability of it. Given the clue that
24:57
Speaker 1: this thing was like smaller than about ten p the Sun,
25:00
Speaker 1: So then that was really interesting because now you know
25:03
Speaker 1: you have something They're very bright in the X ray
25:06
Speaker 1: and very very small, I see. And it couldn't be
25:08
Speaker 1: one of these crazy like neutron stars or did they
25:11
Speaker 1: think it was a new kind of star. That was
25:12
Speaker 1: the next thing. It's like, well, maybe it's a neutron star.
25:15
Speaker 1: And so to figure out whether or not it was
25:16
Speaker 1: a neutron star, they had to figure out how heavy
25:19
Speaker 1: is it? Because neutron stars have a maximum mass, like
25:22
Speaker 1: you can't get a neutron star more than like three
25:24
Speaker 1: or four times the mass of the Sun. If they
25:26
Speaker 1: get that big, they should collapse to a black hole.
25:29
Speaker 1: So the next thing was to figure out like, well
25:31
Speaker 1: how heavy is this? And the good news is that
25:35
Speaker 1: this X ray source had a star nearby there was
25:38
Speaker 1: another a really big star as blue supergiant that was
25:41
Speaker 1: near it, that was orbiting around that one was bright
25:45
Speaker 1: and that when you can see in the visible and
25:47
Speaker 1: so this object, whatever it was that was making the
25:50
Speaker 1: X rays, was orbiting around this blue supergiant star. Really
25:54
Speaker 1: they're orbiting each other. It's like a binary system. And
25:57
Speaker 1: you knew that the X rays were not coming from
25:59
Speaker 1: that other star because stars like that can't make X
26:02
Speaker 1: rays they're not hot enough. You could tell like their
26:04
Speaker 1: X rays coming from this separate thing that's orbiting the star.
26:08
Speaker 1: And based on how fast the star and this new
26:10
Speaker 1: mystery object we're orbiting each other, you could figure out
26:13
Speaker 1: the mass of that mystery Interesting what did they find?
26:15
Speaker 1: How massive was it? It was really pretty big. It
26:18
Speaker 1: was like fifteen times the mass of our Sun. And
26:21
Speaker 1: this new object was orbiting this super giant star like
26:24
Speaker 1: every five days. Like this is not you know, a
26:28
Speaker 1: year long orbit or something pretty close to each other. Yeah,
26:32
Speaker 1: this is like cosmically very violent. And so you knew
26:36
Speaker 1: it was very massive but not very large, and you
26:39
Speaker 1: knew that it was really dense, and you knew that
26:41
Speaker 1: it was dark. And in the end, all of the
26:44
Speaker 1: evidence for The observation of black holes basically comes down
26:47
Speaker 1: to an argument like that, like, you have a huge
26:50
Speaker 1: amount of mass in a small amount of space and
26:52
Speaker 1: it's not radiating, so therefore it must be a black hole.
26:56
Speaker 1: But the thing itself had to be a black hole,
26:59
Speaker 1: because what nutrons rs can't be that heavy. Neutron stars
27:02
Speaker 1: cannot be that heavy. If they get any heavier, they
27:04
Speaker 1: should collapse gravitationally to being a black hole. Theoretically though, Like,
27:09
Speaker 1: but at the time, they didn't know black holes were real,
27:11
Speaker 1: so couldn't they just have assumed that it was a
27:14
Speaker 1: super duper dense neutron star. Yeah, well, you could rule
27:17
Speaker 1: out neutron stars because neutron stars actually do make visible light.
27:21
Speaker 1: I mean, they have a surface, and when stuff falls
27:24
Speaker 1: under the surface of a neutron star, you can see
27:26
Speaker 1: it radiates, right, so neutron stars can be visualized. But
27:30
Speaker 1: you're right, you could say, well, how do we know
27:31
Speaker 1: it's actually a black hole? How do we know it's
27:33
Speaker 1: not something else? If it's just really massive and really small,
27:37
Speaker 1: how do you know it is a black hole, not
27:39
Speaker 1: some like weird preon star or a quark star or
27:43
Speaker 1: some other new kind of non black hole matter, right,
27:47
Speaker 1: But the theories back then predicted black holes emitted X rays.
27:51
Speaker 1: So the X rays don't actually come from the black
27:53
Speaker 1: hole itself. It comes from the gas that's swirling around
27:57
Speaker 1: the black hole, the accretion disk. And so what we're
27:59
Speaker 1: seeing are not X rays from the black hole, but
28:02
Speaker 1: from the gas that's about to go in the black hole.
28:05
Speaker 1: The black hole was slurping out gas from this super
28:08
Speaker 1: giant blue star that was near it, and there was
28:10
Speaker 1: this like stream of gas and there would swirl around
28:13
Speaker 1: the black hole, and as it was swirling around, the
28:15
Speaker 1: black hole gets rubbed against each other, a lot of
28:18
Speaker 1: friction there, and that's when the gas is then emitting
28:21
Speaker 1: in these millions of degree situations, is emitting these X rays.
28:24
Speaker 1: But did they know that back then? Did they know
28:26
Speaker 1: that about the equation discs, that that was all part
28:29
Speaker 1: of their model of black holes, That was all part
28:31
Speaker 1: of the model of black holes. Yeah, but you know,
28:33
Speaker 1: it's still it's a little bit indirect, like how do
28:35
Speaker 1: you really know that it's a black hole? Even to
28:38
Speaker 1: this day, Like our evidence is limited to basically that
28:41
Speaker 1: kind of argument. It's like there's nothing else that we
28:44
Speaker 1: can think of that could describe this nothing else that
28:47
Speaker 1: could be this dense and this massive and radiate in
28:51
Speaker 1: these certain ways and in no other ways. Black holes
28:54
Speaker 1: sort of the only candidate we have to me. That's
28:57
Speaker 1: not like total slam dunk evidence. You know, it's about
29:01
Speaker 1: as good as I think we can get. I'm not criticizing,
29:03
Speaker 1: but there's still there's a level of indirection there. It's like, yeah,
29:07
Speaker 1: I don't really solved the murder until you've seen the body, right,
29:10
Speaker 1: but you can still maybe find a person guilty, the
29:14
Speaker 1: stellar object guilty. And you know, there was a lot
29:17
Speaker 1: of debate and discussion in the community like is this
29:20
Speaker 1: thing real? And you know, like in the early seventies,
29:23
Speaker 1: I think most people were convinced in the astrophysics community
29:27
Speaker 1: that this was a black hole. But there was one holdout,
29:30
Speaker 1: very notable holdout. Who was it well, Stephen Hawking. Stephen
29:34
Speaker 1: Hawking in the nineteen seventy four, and he had just
29:36
Speaker 1: come up with his theory of like black hole thermodynamics
29:39
Speaker 1: and Hawking radiation, and he really moved the whole like
29:43
Speaker 1: theoretical field of black hoology I suppose forward, But he
29:47
Speaker 1: wasn't sure that it was a black hole, and he
29:49
Speaker 1: made sort of a famous bet with Kip Thorne. Hawking
29:52
Speaker 1: bet Kip Thorne that it wasn't a black hole? Really,
29:54
Speaker 1: what made him think it wasn't What was he skeptical about.
29:57
Speaker 1: I'm not sure he was actually skeptical, lay he when
30:00
Speaker 1: he finally conceded it, he said that he was just
30:02
Speaker 1: hedging his best. But this way either it was a
30:05
Speaker 1: black hole, which is awesome for him, or he wont
30:08
Speaker 1: to bet against Kip Thorne, which was also awesome for him,
30:11
Speaker 1: And so this way he got something. He's playing all
30:14
Speaker 1: the angles, Yeah, sort of like Pascal's wager with black holes.
30:18
Speaker 1: Maybe he's superstitious. He's like, if I bet against myself,
30:20
Speaker 1: maybe he'll come through and then I'll get a Nobel price. Yeah.
30:24
Speaker 1: And so that's the early seventies, and we have this
30:27
Speaker 1: evidence for a source, you know, that's very intense mass
30:30
Speaker 1: and a small space has the right radiation profile. And
30:33
Speaker 1: then this one last thread, which is quasars. Quasars are
30:38
Speaker 1: these very very bright source of radiation from very deep
30:42
Speaker 1: in the universe, and for a long time nobody really
30:44
Speaker 1: understood they seemed to be coming from really far away,
30:48
Speaker 1: yet they were still really bright, which meant that whatever
30:51
Speaker 1: was making them was extraordinarily bright. For a long time,
30:54
Speaker 1: nobody really believed They didn't believe that they were black holes.
30:57
Speaker 1: That was actually like a coded black hole. No nobody
31:00
Speaker 1: even even thought it was black holes. For a while,
31:02
Speaker 1: people just didn't even really believe that the data was right.
31:05
Speaker 1: They thought, you know, how could something be this bright
31:08
Speaker 1: and so far away, because then it had to be
31:10
Speaker 1: riduculously bright at its source. But people eventually believed these
31:14
Speaker 1: really are super bright sources, and then finally came to
31:17
Speaker 1: understand them as supermassive black holes at the centers of galaxies.
31:23
Speaker 1: And so this thread of quasars was sort of helped
31:25
Speaker 1: along by the discovery of black holes as a real thing.
31:28
Speaker 1: People like, oh, well, black holes are real, Maybe we
31:31
Speaker 1: can use that to explain quasars. Also, because we seem quasars,
31:36
Speaker 1: we just didn't know what could be making that much energy. Yeah,
31:40
Speaker 1: and this could explain it. A really dense, compact gravitational
31:44
Speaker 1: mass capable of squeezing the gas in its environment enough
31:48
Speaker 1: to generate this incredible radiation. And now we know that
31:52
Speaker 1: we have one. For example, at the center of our galaxy,
31:55
Speaker 1: center of the Milky Way is a huge black hole
31:57
Speaker 1: four million times the mass of the Sun. It's called
32:00
Speaker 1: Sagittarius a star. It's funny it's called a star there
32:04
Speaker 1: because the guy who named it was so excited and
32:06
Speaker 1: he thought star made something exciting. What really, Yeah, he
32:11
Speaker 1: didn't think of putting an asterix would make people somehow
32:14
Speaker 1: suspicious of it. I know in the sports world an
32:16
Speaker 1: asterisk means like, well maybe not right, but in chemistry,
32:20
Speaker 1: star means excited state. For him, it's like an exclamation mark,
32:24
Speaker 1: exclamation yeah, like a smiley face at the end, I
32:27
Speaker 1: discovered Sagittarius, a smiley phase, emoji, star emoji, telescope star night.
32:36
Speaker 1: So you have all these threads coming together, this theoretical
32:39
Speaker 1: understanding of it as an event horizon beyond which no
32:42
Speaker 1: information can pass, and then the discovery these X ray
32:45
Speaker 1: sources which had no corresponding optical signature, and then come
32:49
Speaker 1: together with this line of thinking about quasars, what are
32:52
Speaker 1: these weird emitters at the centers of these galaxies? Plus
32:55
Speaker 1: trying to prove Stephen hawkingrong. I mean, that's that's some
32:59
Speaker 1: motivation right there. Alright, but all of this is still
33:01
Speaker 1: sort of circumstantial evidence, And so let's get into how
33:05
Speaker 1: we actually see them today. But first let's take another
33:08
Speaker 1: quick break, all right, Daniel, So we're we're I guess
33:24
Speaker 1: we're in the seventies and the eighties, and we have
33:26
Speaker 1: all this evidence for black holes, and there's a lot
33:29
Speaker 1: of stuff that we're seeing that could be or would
33:32
Speaker 1: be explained by black holes. And also everyone wants Stephen
33:35
Speaker 1: Hawking to be wrong. Um, so what sort of sealed
33:38
Speaker 1: the deal for black holes? Like, was it us seeing
33:41
Speaker 1: them or tend taking a picture last year for the
33:43
Speaker 1: first time, or did were we pretty convinced before? Well,
33:46
Speaker 1: it's been a sort of slow accumulation of evidence. And
33:49
Speaker 1: the best way to convince yourself that something weird is
33:52
Speaker 1: real is to see it in lots of different ways,
33:54
Speaker 1: because that prevents you from having made one particular mistake
33:58
Speaker 1: or misunderstanding one kind of data, or screwing up your
34:01
Speaker 1: lenses or something. And so the first piece of evidence
34:04
Speaker 1: was you know, this sickness X one, this X ray
34:07
Speaker 1: source from a very compact object. But now we have
34:10
Speaker 1: several ways, also still indirect, to point to these black holes.
34:14
Speaker 1: All right, so what are what are some of these ways?
34:17
Speaker 1: Can we lose something out there in space? Or Number
34:19
Speaker 1: one is that we started seeing a lot of quasars,
34:21
Speaker 1: and by now we've seen like a hundred thousand galactic quaisars.
34:26
Speaker 1: And so each of these, yeah, each of these are
34:29
Speaker 1: probably a supermassive black hole the center of a galaxy,
34:33
Speaker 1: and so we see the radiation from them. You can
34:36
Speaker 1: see the accretion disk around some of them if they're
34:38
Speaker 1: close enough, really, and so this is pretty strong evidence
34:41
Speaker 1: that those black holes exist. You can actually see the
34:43
Speaker 1: accretion disk, or you can just see something really bright,
34:46
Speaker 1: but you can see something really bright coming from the
34:48
Speaker 1: center of the galaxy. And we're talking in a minute
34:50
Speaker 1: about the direct imaging of a black hole that came
34:53
Speaker 1: up much later. But this is pretty strong evidence for
34:56
Speaker 1: sort of black holes to exist in the universe. But
34:58
Speaker 1: you know, there's two linds the black holes. There's these
35:01
Speaker 1: supermassive black holes at the center of galaxies that are
35:04
Speaker 1: very powerful and crazy. And then there's the kind of
35:06
Speaker 1: black hole that I think most people think about, like
35:08
Speaker 1: a star at the end of its life that collapses
35:11
Speaker 1: and turns into a black hole. Those are like the
35:13
Speaker 1: pet black holes. Yeah, that's right. Those are the kinds
35:15
Speaker 1: you can pick up at the local mall. And we
35:17
Speaker 1: think that there are a lot of those, but we've
35:19
Speaker 1: only actually ever seen a few because they're much harder
35:22
Speaker 1: to spot. So while we've seen like a hundred thousand
35:25
Speaker 1: galactic quasars, we only have a few dozen stellar mass
35:29
Speaker 1: black holes that we've actually observed. But don't we see
35:31
Speaker 1: stars training into black holes a lot, like you know
35:34
Speaker 1: these supernova? Don't we see those pretty often? We see
35:37
Speaker 1: supernova I mean not that often, but not every supernova
35:40
Speaker 1: turns into a black hole. Some of them turn into
35:43
Speaker 1: a neutron stars or something else. And so it has
35:46
Speaker 1: to be particular sized to turn into a black hole.
35:49
Speaker 1: And also you see a supernova, the black hole doesn't
35:51
Speaker 1: necessarily form immediately and isn't visible immediately. It's surrounded by
35:55
Speaker 1: this huge cloud of stuff still for a while, and
35:58
Speaker 1: so it's gonna take a long time for accretion disk
36:01
Speaker 1: to sort of gathered together and make the black hole visible.
36:04
Speaker 1: I hadn't realized that we have seen many more super
36:07
Speaker 1: massive black holes and than the smaller black holes. Yeah,
36:10
Speaker 1: these stellar mass black holes are harder to spot, all right,
36:13
Speaker 1: So that's one growing body of evidence. What else is there?
36:17
Speaker 1: Another indirect way to see a black hole is to
36:19
Speaker 1: look at the stars around them. Like if you see
36:22
Speaker 1: nothing in the sky, but then you see things swirling
36:26
Speaker 1: around it as if there was a very strong amount
36:29
Speaker 1: of gravity there, then you can make sort of the
36:31
Speaker 1: same argument. You can say, well, there has to be
36:33
Speaker 1: a big blob of stuff there that's providing the gravity.
36:36
Speaker 1: And we see this, for example again at the center
36:39
Speaker 1: of our own galaxy. We can watch the path of
36:42
Speaker 1: stars as they near the center of the galaxy and
36:44
Speaker 1: we can tell that they are bent in a curve
36:47
Speaker 1: as if there was an incredibly strong gravitational source there.
36:50
Speaker 1: We can't see the black hole directly, of course, but
36:53
Speaker 1: we can see the motion of stars around it, right,
36:55
Speaker 1: And you can find movies of this online probably right.
36:58
Speaker 1: It's like a take a picture basically a black screen,
37:01
Speaker 1: but you see stars kind of moving and going really
37:04
Speaker 1: fast around nothingness. Yeah, there's a group at U c
37:07
Speaker 1: l A that's been watching the center of our galaxy
37:09
Speaker 1: for like two decades now and plotting the motion of
37:12
Speaker 1: these stars. And there's one star in particular, it's called
37:14
Speaker 1: S two, which passes really close to the center of
37:17
Speaker 1: the galaxy and then whips around who has sort of
37:20
Speaker 1: a shorter period And because they've been watching for two decades.
37:24
Speaker 1: You can see like complete orbits of some of these stars,
37:26
Speaker 1: and then you can do the calculation and you can
37:28
Speaker 1: tell how much mass there is, and because the star
37:31
Speaker 1: has passed so close to the center, you can get
37:34
Speaker 1: a sense for how small it has to be right there.
37:37
Speaker 1: The stars trajectory limits the size of this thing, and
37:40
Speaker 1: so at some point you're like, well, there's a huge
37:42
Speaker 1: amount of gravity and a small amount of space boom
37:44
Speaker 1: black right, and so wow, we can actually point a
37:47
Speaker 1: telescope at the center of our galaxy and get a
37:49
Speaker 1: picture like that. Yeah, you can. You can see these stars.
37:51
Speaker 1: It's difficult because there's so much gas and dust and
37:54
Speaker 1: so you have to sort of see through that and
37:56
Speaker 1: look in the near infrared light and also use like
38:00
Speaker 1: fancy adaptive optics. But you can actually see that. So
38:04
Speaker 1: we do have kind of a pet black hole inner
38:05
Speaker 1: back yard. Yeah. Yeah, it's a tens of thousands of
38:09
Speaker 1: light years away. So if your backyard is that big,
38:11
Speaker 1: then yes, you have a black hole inside, or maybe
38:14
Speaker 1: we're the pets of the black hole. And then recently
38:18
Speaker 1: we have a total different kind of evidence for black holes,
38:22
Speaker 1: and that's the gravitational waves that come when they collide
38:25
Speaker 1: with each other. Right, that's what Lego discovered recently, right,
38:27
Speaker 1: a couple of years ago. That's right. If black holes
38:29
Speaker 1: get close enough to each other, then they slurp each
38:31
Speaker 1: other in. But usually they have some like angular momentum
38:34
Speaker 1: around each other, so they can't just like approach head on.
38:37
Speaker 1: It's like a near miss. And then they swing around
38:39
Speaker 1: and they come back around and they swirl a little bit,
38:42
Speaker 1: just like stuff going down the toilet bowl. It swirls
38:45
Speaker 1: a little bit until eventually it finally collapses into a
38:48
Speaker 1: single black hole. And in those last moments when they're
38:51
Speaker 1: swirling around each other really really fast, then the gravity
38:55
Speaker 1: is changing really really quickly. So the gravitational field goes
38:57
Speaker 1: up and down and up and down, up and down
39:00
Speaker 1: as the black hole swirls around. And that's what we
39:02
Speaker 1: call a gravitational way. Right. It's kind of pulling and
39:05
Speaker 1: pulling and pushing really quickly and making waves in the
39:09
Speaker 1: fabric of spacetime. That's right, because if you think about
39:11
Speaker 1: gravity not as like a gravitational field, but instead curving space,
39:16
Speaker 1: which is what general relativity tells us, then what happens
39:19
Speaker 1: is you're seeing these ripples in space time, and that's
39:22
Speaker 1: what we saw here on Earth using Lego, and we
39:24
Speaker 1: have a whole episode about that. But the point is
39:26
Speaker 1: that there's a signature there in this shaking of space.
39:29
Speaker 1: It starts, then it goes faster and faster and faster
39:31
Speaker 1: and faster, boom, until the black holes collide. And that
39:34
Speaker 1: looks a certain way, and you expect it to look
39:37
Speaker 1: a certain way if you see two black holes, and
39:39
Speaker 1: it looks different if you see like a black hole
39:41
Speaker 1: eating a neutron star. And so this is really pretty
39:44
Speaker 1: good evidence that those black holes are real, that they're
39:46
Speaker 1: out right, and so that's pretty recent. And then even
39:49
Speaker 1: more recently, we actually took a picture of a black hole. Yeah,
39:52
Speaker 1: we did this direct image from the event horizon telescope.
39:56
Speaker 1: It looked a black hole the center of a nearby
39:59
Speaker 1: galaxy M eighty seven, which has a really super duper
40:03
Speaker 1: black hole at its center, and they try to like
40:05
Speaker 1: focus in and they try to separate the part of
40:08
Speaker 1: the black hole that's the very center of the actual
40:10
Speaker 1: event horizon from the gas that's around it, and we
40:13
Speaker 1: got a picture, like there's an image you can look
40:15
Speaker 1: up online and see it, which sort of proves all
40:19
Speaker 1: these theories. Yeah, you have a picture. It looks sort
40:21
Speaker 1: of like, you know, a fuzzy donut or something. It's
40:24
Speaker 1: not too spectacular unless you like really understand the context
40:27
Speaker 1: of it, which is what you're seeing is the gas
40:29
Speaker 1: swirling around the black hole. And then at the very
40:32
Speaker 1: center you see the shadow. You see nothing, right, there's
40:36
Speaker 1: nothing there. I mean, you see the hole, you see
40:38
Speaker 1: the whole, and it's black. Yeah, you see the whole
40:40
Speaker 1: and it's black. And you know what's different about that blackness,
40:44
Speaker 1: And just like the random blackness of a patch of space,
40:46
Speaker 1: it's really the stuff around it. It's this incredibly hot
40:50
Speaker 1: gas that's swirling around and it looks exactly the way
40:53
Speaker 1: you would expect. And it's impossible to get that configuration
40:56
Speaker 1: of high speed gas emitting X rays without huge gravitational mass.
41:01
Speaker 1: So we know there's a gravitational mass right in the
41:04
Speaker 1: center of that picture where the black part is right,
41:07
Speaker 1: but there's no light being admitted. So again it's a
41:10
Speaker 1: direct picture of what a black hole would look like.
41:13
Speaker 1: Is it actually a black hole or something else that
41:15
Speaker 1: doesn't admit light? You know, then you get into semantics
41:18
Speaker 1: about what is and is not a black hole. It's
41:20
Speaker 1: something very dense, very compact, very strong gravitationally that does
41:25
Speaker 1: not admit any visible light. Well, I'm gonna make a
41:27
Speaker 1: bed with you, Daniel, just like Stephen Hawkins made a bit.
41:29
Speaker 1: We'll bid you that it is actually a giant, fuzzy doughnut. Okay,
41:33
Speaker 1: And how are you going to prove that you're gonna
41:35
Speaker 1: take a trip out there and take a bite. Well,
41:39
Speaker 1: we may never set a lot of When that image
41:42
Speaker 1: came out, I saw people online taking pictures of Crispy
41:45
Speaker 1: Kreams and saying, hey, look my picture of Krispy Kreme
41:48
Speaker 1: looks just like this crazy discovery. How come I'm not
41:51
Speaker 1: getting any press by the Science News. But it's fun
41:55
Speaker 1: to actually look at that picture and to think about,
41:57
Speaker 1: like what am I seeing? And you know, if you
41:59
Speaker 1: look at the very sent tour of it, you're looking
42:01
Speaker 1: at the event horizon itself. Right, There's no photons come
42:05
Speaker 1: to your eyeballs from the very center because any photon
42:08
Speaker 1: that could would have had to come out of the
42:10
Speaker 1: black hole. And so that's impossible, right, So it is
42:13
Speaker 1: like a black hole, and and it does, and in
42:17
Speaker 1: subtle ways too. I heard that it really confirms a
42:20
Speaker 1: lot of our theories about what's happening around a black hole,
42:22
Speaker 1: like one side of it is brighter than the other
42:25
Speaker 1: side of the doughnut because the light is going faster
42:27
Speaker 1: when one side and not the other. So it really
42:30
Speaker 1: does sort of confirm and and look like what we predicted.
42:34
Speaker 1: Like in the movies Interstellar, they sort of simulated black
42:38
Speaker 1: holes and they made up pictures of it, and it's
42:41
Speaker 1: the real one sort of looks like that. Yeah, and
42:42
Speaker 1: it's amazing. And remember that what you're seeing is not
42:45
Speaker 1: what's there. You're looking at an image. Just like when
42:47
Speaker 1: you look through distorted glass outside the trees look all
42:51
Speaker 1: wibbly and wobbly and whatever. That's not what's actually happening.
42:54
Speaker 1: That's the image you're seeing. So that's what's happening here.
42:57
Speaker 1: And the reason you're seeing an image enough, just you
42:59
Speaker 1: know what's there is that space is being bent, right,
43:02
Speaker 1: the environment around a black hole. Space is curved and
43:05
Speaker 1: so light doesn't travel in straight lines. And so they
43:08
Speaker 1: predicted this image, as you're saying, they predicted, if you
43:11
Speaker 1: have a black hole with an acretion disc around it,
43:13
Speaker 1: what would you see, what would it look like? And
43:16
Speaker 1: they predicted all these distortions by retracing all those photons,
43:19
Speaker 1: and as you said, what we see is what they expected,
43:23
Speaker 1: and so that's pretty good confirmation that they understand the
43:25
Speaker 1: physics of what's happening there. So do you feel like
43:27
Speaker 1: the picture was kind of the nail in the coffin
43:30
Speaker 1: that people finally said, yes, now we can rest easy
43:34
Speaker 1: and know for sure that black holes are real? Or
43:37
Speaker 1: were people pretty convinced before we saw the picture. People
43:39
Speaker 1: were pretty convinced the black holes were real before we
43:41
Speaker 1: saw the picture. The picture is like an even more
43:44
Speaker 1: stringent test in a new, fascinating and frankly visually appealing
43:48
Speaker 1: way of the black hole theory. So I think, you know,
43:51
Speaker 1: since the mid nineteventies, black holes have been generally accepted
43:55
Speaker 1: as real, but they just get cooler and cooler as
43:57
Speaker 1: we learn more and more about them. Kind of guess
44:00
Speaker 1: it's you know, it's really amazing to think not just
44:03
Speaker 1: the kind of the long path that we've taken here,
44:05
Speaker 1: like seeing it in the equations, coming up with solutions,
44:09
Speaker 1: finding circumstantial evidence, but just to think that, you know,
44:13
Speaker 1: these crazy ideas are real. You know that space really
44:17
Speaker 1: does kind of form these pockets where nothing can come out,
44:21
Speaker 1: and that they can exist, and that you can actually
44:24
Speaker 1: kind of go out there and touching them, be around them. Yeah,
44:27
Speaker 1: and it makes you wonder about the sort of primacy
44:30
Speaker 1: of mathematics, because you know, all these ideas came from
44:33
Speaker 1: just following the mathematics. We expressed our physical laws in
44:37
Speaker 1: terms of math, and we followed the consequences, and we
44:39
Speaker 1: got this weird result and then it turns out to
44:41
Speaker 1: be real. It makes you wonder, like, is math just
44:43
Speaker 1: something in our heads or is it like fundamental to
44:46
Speaker 1: the universe itself, because it seems like the universe is
44:50
Speaker 1: following these mathematical rules regardless of their absurtainty. Are you
44:54
Speaker 1: thinking math is better than physics, Doyle, I know that
44:57
Speaker 1: all of my colleagues in the math department find to
45:00
Speaker 1: be more fundamental than physics. But we all know love
45:04
Speaker 1: is the true fundamental power in the universe, according to
45:09
Speaker 1: all according to the original boy band the Beatles, I
45:14
Speaker 1: was just about to say the same thing. And remember
45:16
Speaker 1: a lot of the listeners suggested that we could see
45:18
Speaker 1: black holes by seeing their lensing, Like if a black
45:21
Speaker 1: hole past in front of another star, you would see
45:23
Speaker 1: it distorting. And that's true. Theoretically, we just haven't observed
45:27
Speaker 1: that yet, and so that's a possibility something we might
45:30
Speaker 1: get to see in the future, and that would be
45:31
Speaker 1: a very nice additional piece of evidence. But there haven't
45:34
Speaker 1: been any micro lensing events observed yet. Okay, but we've
45:38
Speaker 1: seen it in other ways for sure. Yeah, we've seen
45:41
Speaker 1: it in lots of ways. Yeah, But that's just something
45:43
Speaker 1: to look forward to. That's something you the listener out there,
45:46
Speaker 1: might be the first person to ever come right, So
45:49
Speaker 1: keep looking up at the stars and don't look away.
45:53
Speaker 1: All right. Well, we hope you enjoyed that. Thanks for
45:56
Speaker 1: joining us, Thanks for tuning in, and thanks for sending
45:58
Speaker 1: us your questions and sharing your curiosity with us, even
46:01
Speaker 1: if we do sometimes go down a black hole. See
46:04
Speaker 1: you next time. Thanks for listening, and remember that. Daniel
46:14
Speaker 1: and Jorge Explain the Universe is a production of I
46:17
Speaker 1: Heart Radio. For more podcast from my Heart Radio, visit
46:20
Speaker 1: the I Heart Radio Apple Apple Podcasts, or wherever you
46:24
Speaker 1: listen to your favorite shows.