The Updated Physics of Black Holes with Steve Balbus & Andrew Mummery

What’s happening just outside a black hole? Neil deGrasse Tyson and co-host Gary O’Reilly travel to Oxford University to explore the mysterious universe of black holes, their accretion disks, and the impact they have on the world around them with astrophysicist Steve Balbus and theoretical physicist Andy Mummery.

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Neil deGrasse Tyson?

  He's in a different gravitational field from the ones who went down to the planet, which was near the black hole. They'd lived fifteen minutes or something, and the guy up there went ten years or some.

• 0:10Speaker 01

  Yeah, I think they should have been more.

• 0:11Neil deGrasse Tyson?

  But yeah, yeah, crazy ratio of time.

• 0:14Speaker 01

  Time dilation.

• 0:14Neil deGrasse Tyson?

  Time dilation, crazy time dilation. So I was going to try to calculate how close that orbit had to be, and then I said, no, I'm not gonna, I will wait till I get somebody else to do this. It sounds like you're the guy for that.

• 0:28Neil deGrasse Tyson?

  Welcome to StarTalk, your place in the universe where science and pop culture collide. StarTalk begins right now.

• 0:42Neil deGrasse Tyson?

  Gary, we're in the UK now.

• 0:44Speaker 01

  Good.

• 0:44Neil deGrasse Tyson?

  This is your place.

• 0:45Speaker 01

  It is. I'm here as your interpreter.

• 0:48Neil deGrasse Tyson?

  We're in the town of Oxford.

• 0:50Speaker 01

  Is it city or town?

• 0:52Neil deGrasse Tyson?

  Oh, I don't know, but I.

• 0:53Speaker 01

  We'll give it city sake.

• 0:54Neil deGrasse Tyson?

  All I care is that there's a university here, and I have colleagues. My people.

• 0:58Speaker 01

  You've got peeps.

• 0:58Neil deGrasse Tyson?

  I got people.

• 0:59Speaker 01

  All right.

• 0:59Neil deGrasse Tyson?

  I got people.

• 1:00Speaker 01

  Okay.

• 1:00Neil deGrasse Tyson?

  All right, very good.

• 1:02Speaker 01

  We're gonna meet any?

• 1:03Neil deGrasse Tyson?

  Yeah, and, and by the way, like, where's Chuck?

• 1:05Speaker 01

  Chuck is otherwise disposed.

• 1:07Neil deGrasse Tyson?

  Okay, and I figure I'll, I'll settle for a Brit.

• 1:10Speaker 01

  Okay.

• 1:10Neil deGrasse Tyson?

  As my co-host.

• 1:11Speaker 01

  I am not the new Chuck.

• 1:13Neil deGrasse Tyson?

  Episode, okay. I have a colleague who I met many, many years ago.

• 1:17Speaker 01

  All right.

• 1:17Neil deGrasse Tyson?

  Like decades ago.

• 1:18Speaker 01

  All right, he still wants to know you?

• 1:22Neil deGrasse Tyson?

  And I found him and I called him and said, I'm in town, and he like invited me to come chill with him.

• 1:27Speaker 01

  Nice.

• 1:27Neil deGrasse Tyson?

  Sitting right here.

• 1:29Speaker 01

  Is that who he is?

• 1:31Neil deGrasse Tyson?

  Steve Balbus, Steve. Hello, Neil, good to see you again. Welcome to StarTalk. Thank you, pleasure to be here. Dude, you're a fellow astrophysicist? Yes. And, you know, he has astrophysical phenomenon named after him.

• 1:45Speaker 01

  Did you know? Are we having a phenomenon envy?

• 1:50Speaker 01

  Are we, are we, are we having a little bit of phenomenon envy at all?

• 1:53Neil deGrasse Tyson?

  Is that a thing? I didn't know.

• 1:54Speaker 01

  It is now.

• 1:54Neil deGrasse Tyson?

  The psychologists haven't gotten to that one yet.

• 1:56Speaker 01

  I see, I see, if I've just invented it, I'm claiming it.

• 1:59Neil deGrasse Tyson?

  No, so, uh, tell me about this thing that carries your name in our field.

• 2:05Speaker 02

  So, uh, it's work, based on work-

• 2:07Neil deGrasse Tyson?

  You're a theorist.

• 2:09Speaker 02

  Yeah, well, I do theory.

• 2:10Neil deGrasse Tyson?

  Yeah.

• 2:10Speaker 02

  A pencil, a lot of pencil and paper, and of course nowadays, computational work.

• 2:14Neil deGrasse Tyson?

  Yeah.

• 2:15Speaker 02

  And in particular, back in the 90s, I did some work with a colleague named John Hawley.

• 2:21Neil deGrasse Tyson?

  Uh huh.

• 2:22Speaker 02

  And-

• 2:22Neil deGrasse Tyson?

  The late John Hawley.

• 2:23Speaker 02

  The late John Hawley. So he, yeah, he passed away a few years ago, unfortunately. And, um, at the time, we were trying to figure out how you make black holes.

• 2:36Neil deGrasse Tyson?

  Oh.

• 2:36Speaker 02

  And the hard part of doing that, gravity is present, and of course, gravity ultimately is the reason that things make compact objects.

• 2:47Neil deGrasse Tyson?

  Wait, wait, you're, you go so far back to a time before we knew how to make black holes? That's how old you were?

• 2:53Speaker 02

  That's how old I am.

• 2:54Neil deGrasse Tyson?

  Okay.

• 2:54Speaker 02

  I would go back to a time when black holes were controversial.

• 2:58Neil deGrasse Tyson?

  Oh, okay.

• 2:59Speaker 02

  You know, that polite astrophysicist-

• 3:01Neil deGrasse Tyson?

  And since then, Nobel prizes have been given for black holes.

• 3:04Speaker 02

  We take pictures of them and put them on our iPhones. But there was a time when respectable astrophysicists didn't talk about it in mixed company.

• 3:13Neil deGrasse Tyson?

  Okay.

• 3:14Speaker 02

  Yeah, you know, if you read it, you put a fake cover on it.

• 3:16Neil deGrasse Tyson?

  Oh, alright.

• 3:18Speaker 02

  People wouldn't know. But the hard part was, if you have a black hole forming, the last stages, stuff is going around in a disk, a little bit like the planets go around the solar system. Our solar system was once a disk, that's probably how the sun was made. But the planets in the solar system just go around in orbits. Whereas, the gas in a disk around the black hole, or any other type of sort of compact object that's being made, has to get out of those orbits and down into the center. So how does it do that? And people talk about friction now.

• 4:02Speaker 02

  The gas rubs against itself, planets don't do that. But when you put in the numbers to see whether that would work or not, it would fail by orders of magnitude.

• 4:13Neil deGrasse Tyson?

  The powers of 10.

• 4:14Speaker 02

  Yeah, powers of 10, yeah. Yeah, millions, it was millions of times too inefficient.

• 4:21Neil deGrasse Tyson?

  Which is a fun state of mind of research to be in. Where you think you're on top of the physics or something. You calculate it out and you're off by factors of thousands.

• 4:31Speaker 02

  Yeah.

• 4:31Neil deGrasse Tyson?

  And then, but you still go to work the next day.

• 4:36Speaker 02

  Exactly. You don't let that kind of thing bother you. Or, or you should find another line of work.

• 4:41Speaker 01

  It's a stimulation to seek.

• 4:43Speaker 02

  You know that you're almost, that you're on to something, but there's an important piece that you're missing.

• 4:48Neil deGrasse Tyson?

  Evidently. Yeah, okay.

• 4:50Speaker 02

  So, what people suspected, and with good reason, is the reason that the discs work the way they do is it's not just friction, but the gas itself is turbulent. So it's a little bit like the, what you see in your sink when you turn on the faucet. There's a lot of, or in a river, there's a lot of churning and bubbling. And under those circumstances, the friction in the flow can indeed be thousands or tens of thousands, millions of times.

• 5:24Neil deGrasse Tyson?

  Higher.

• 5:25Speaker 02

  Higher, more efficient.

• 5:26Speaker 01

  So you say you can get like an eddy?

• 5:29Speaker 02

  You get lots of eddies.

• 5:30Speaker 01

  So that random thing spinning and spearing up?

• 5:34Speaker 02

  Exactly. Exactly. They, they rub against each other. That's exactly what the professionals call them.

• 5:41Neil deGrasse Tyson?

  I knew a turbulent eddy.

• 5:42Speaker 01

  I think we all do. Probably, probably not the same guy, but there's always a turbulent eddy.

• 5:47Neil deGrasse Tyson?

  Actually, I got that from Al Roker. I, I mentioned the phrase turbulent eddy. And, and he said, I knew a turbulent eddy. And I, I felt, I walked right into it. I said, what's he doing now? He said, five to 10.

• 6:01Speaker 02

  You're the straight man.

• 6:02Neil deGrasse Tyson?

  I didn't know I walked into the straight man.

• 6:05Speaker 01

  Torneville, we're here all week.

• 6:06Neil deGrasse Tyson?

  That was with Al Roker a few years ago.

• 6:08Speaker 02

  Al Roker's turbulent eddies, that's what we're talking about. So the, but you want to understand why they're there. Um, because when you actually write down the mathematical equations for the flow and you analyze whether it should break down into this kind of structure, the answer is no.

• 6:26Speaker 01

  Interesting.

• 6:27Speaker 02

  There just wasn't any way that you could do that. So it occurred to me that there was one thing that people were leaving out, which seemed kind of inconsequential. But because of other work I had done, I wondered whether it might be a good idea to put it back in. And that is that every magnet, every disk in astrophysics.

• 6:48Neil deGrasse Tyson?

  This is the accretion disk.

• 6:50Speaker 02

  This is the accretion disk around.

• 6:52Neil deGrasse Tyson?

  Circulating toilet bowl style.

• 6:54Speaker 02

  Exactly, the whirlpool. Any kind of a disk or even any astrophysical gas, wherever it might be, has some kind of a magnetic field in it. There's magnetic field in this room.

• 7:08Neil deGrasse Tyson?

  Yep.

• 7:09Speaker 02

  And if there are enough charged particles to make a current, then the magnetic field can affect the way that that gas flows. And you don't need very much. Even a very little bit will work quite well for that gas to act as though it's magnetized.

• 7:29Neil deGrasse Tyson?

  So you published this, Balbus and Hawley.

• 7:31Speaker 02

  Mm-hmm.

• 7:32Neil deGrasse Tyson?

  And then, the polite way is you just publish it and let other people say, "The Balbus and Hawley paper talked about this instability." "Oh, the Balbus and Hawley instability." And then it just becomes part of our lexicon. Is that how that happened? Or did you have a campaign?

• 7:49Speaker 02

  No, I can't say that I had a conscious campaign. Yes, he did. Look at that face. Yeah. And in fact, it's known by a few names. It's not known, I should say, exclusively by Balbus. It's also called magnetorotational instability. Because that describes why, what breaks, what it actually, it's a combination of the magnetic field and the rotation that renders the gas unstable and makes it break down into these kind of turbulent eddies. And what John was able to do, John Hawley, my colleague, at the time, which nobody, very few people in the world could do, was to set up a computer program.

• 8:33Speaker 02

  Which could actually follow the equations at a level of detail that we could actually see not just the breakdown of the circular orbits, but the emergence of turbulence itself and actually visualize that.

• 8:48Speaker 01

  Was it able to predict emergence?

• 8:51Speaker 02

  So that's an interesting question. So yes, it was able to predict if you put a magnetic field which is this strong in this kind of a disk, then there won't be a breakdown. If you put a magnetic field which is this strong, then there will be, and that could be tested.

• 9:09Neil deGrasse Tyson?

  And without that, you're just pushing pencil, right, at that level.

• 9:13Speaker 01

  Yeah, but you're getting more clues. You said there was something missing in your puzzle.

• 9:17Speaker 02

  So it was clear that that was what was missing. And the amazing thing is, is that even a very weak magnetic field would be enough to completely disrupt the stability properties of the gas. And that's what a lot of people had a hard time getting their head around. That something that seems so weak could have such an important effect.

• 9:40Neil deGrasse Tyson?

  So this was an astrophysical instability, not an emotional instability?

• 9:44Speaker 02

  Well, I had those as well, but what I'm talking about, right, the astrophysical side of things.

• 9:49Speaker 01

  So you mentioned like a whirlpool effect?

• 9:53Speaker 02

  Yes.

• 9:54Speaker 01

  Would it have been any use to study whirlpools and maybe construct the computational element of that to see if there was anything that you could learn?

• 10:03Speaker 02

  Well, yes and no, in the sense that the whirlpools in your kitchen sink or something like that won't be sort of run by a magnetic field.

• 10:11Speaker 01

  No, I was just thinking, the sort of things you could see in nature.

• 10:14Speaker 02

  Absolutely. In terms of what people, people can do rather detailed studies now of turbulence, its statistical properties and so forth, and absolutely those kinds of studies would be of interest and are of interest to the people who do this kind of turbulence in accretion disks.

• 10:32Neil deGrasse Tyson?

  So I think what's fun about this is, the great thing about physics, when you break it down, is physical principles are transplantable to multiple different questions in search of various answers. So the power of physics, it knows no bounds.

• 10:49Speaker 01

  Yes. What is it you said to me earlier on today?

• 10:52Neil deGrasse Tyson?

  I don't remember.

• 10:53Speaker 01

  That I'm gonna get the T-shirt, "Physics is my god."

• 10:57Neil deGrasse Tyson?

  Okay, you're gonna get that T-shirt?

• 10:59Speaker 01

  No, I'm gonna get it for start off. We're gonna have it made up, we're gonna murk and make money.

• 11:03Neil deGrasse Tyson?

  Okay, alright. So let's fast forward, and I understand, uh, recently that, uh, this year, uh, twenty twenty-four, uh, you have a textbook coming out on Einstein's general theory of relativity.

• 11:16Speaker 02

  That's right, I've taught a course here at Oxford for several years, and had a set of notes, and then I've been encouraged, because people liked it, to turn it on to, into a textbook on general relativity. And the timing was very good, because the very first year that I taught the course was the year that gravitational radiation was discovered.

• 11:40Neil deGrasse Tyson?

  That would have been two thousand sixteen.

• 11:42Speaker 02

  Two thousand sixteen, that's exactly right.

• 11:44Speaker 01

  Is that the same as Hawking's?

• 11:45Speaker 02

  No, that's a different kind of radiation.

• 11:47Neil deGrasse Tyson?

  This one was like a-

• 11:48Speaker 01

  Then I won't blur the lines here, sorry.

• 11:51Speaker 02

  Yeah.

• 11:51Neil deGrasse Tyson?

  Get your radiation straight, dude.

• 11:53Speaker 01

  Sorry, dude.

• 11:54Neil deGrasse Tyson?

  Last time I bite you on this program.

• 11:56Speaker 02

  Yeah, no, this is, this is the force of gravity itself being radiated, in a way which is some rather similar to the way that electromagnetic radiation is being radiated. An effect predicted by Einstein a hundred years ago, but so small and so difficult to measure. It was only in the last few years that the technology was there to do that. And so, the book covers that.

• 12:22Neil deGrasse Tyson?

  It's an update.

• 12:24Speaker 02

  It's very, there are a lot has been going on on the observational side. And so I'm fortunate, because the textbook can, discusses that as well.

• 12:32Neil deGrasse Tyson?

  Alright, so it's a textbook, so is there like a general relativity for dummies that you can, uh, is there like the, the crib, crib notes version of the textbook? Have you considered that?

• 12:45Speaker 02

  I haven't considered it, but talking to you now makes me think perhaps I should consider that a little bit more, that's a thought. There are good, very good books.

• 12:53Neil deGrasse Tyson?

  So it'll be general relativity for non-Oxford physics majors?

• 12:56Speaker 02

  Yeah, you know what a very good book is? One that I love, and, I mean, you know, but, but it's meant for, you know, the layman, because it's written very clearly. There's a book from the nineteen nineties by Kip Thorne. Probably the most famous relativist in the world, but also very gifted for writing and for making things very, very clear. So yeah, the book is called Black Holes and Time Warps: Einstein's Outrageous Legacy.

• 13:24Neil deGrasse Tyson?

  That's Kip Thorne.

• 13:25Speaker 02

  And that's Kip Thorne.

• 13:26Neil deGrasse Tyson?

  That's our book guy, Kip Thorne.

• 13:27Speaker 02

  That's your guy?

• 13:28Neil deGrasse Tyson?

  We all live love Kip Thorne.

• 13:29Speaker 02

  Kip Thorne is-

• 13:30Neil deGrasse Tyson?

  Co-executive producer of the film Interstellar.

• 13:34Speaker 02

  Absolutely.

• 13:35Neil deGrasse Tyson?

  Yes.

• 13:36Speaker 02

  And he's the man who knows all there is to know about general relativity.

• 13:41Neil deGrasse Tyson?

  He's one of the co-winners of the Nobel Prize for LIGO and the discovery of gravitational radiation.

• 13:46Speaker 02

  He did a lot of the heavy lifting on the theory side of that.

• 13:49Speaker 01

  Okay.

• 13:50Speaker 02

  Yeah, yeah. And he writes brilliantly and very, very clearly.

• 13:53Neil deGrasse Tyson?

  For The Laman, okay, good.

• 13:54Speaker 02

  Yes, and so that's an excellent book. And he makes predictions about what he thought was going to happen in the years after 1992.

• 14:03Speaker 01

  How'd he do?

• 14:05Speaker 02

  He did okay. He predicted-

• 14:09Speaker 01

  You're just damned if by faint praise.

• 14:12Speaker 02

  Well, that's very hard.

• 14:14Neil deGrasse Tyson?

  I'm just impressed that we live in a time where okay means not so well.

• 14:20Neil deGrasse Tyson?

  How'd he do? Okay.

• 14:22Speaker 01

  I mean, I can't, I can't throw shade on a Nobel Prize winner. Really, just can't do it.

• 14:26Speaker 02

  And look, to give him credit, he was being optimistic. So at that point, gravitational radiation was still two decades in the future. Um, and, or more, and he predicted that. That that would happen. And at about roughly the right time scale. On the more theoretical side of things, theories that would combine quantum mechanics with general relativity, he was much too optimistic. So he didn't get quite those right.

• 14:56Speaker 01

  So you made me think, where are we now with what we don't know? And, and what is it we think we need to know? And sort of move on from-

• 15:05Neil deGrasse Tyson?

  Yeah, let me, let me add punctuation to that. Einstein in 1915 or 16 publishes The General Theory of Relativity.

• 15:14Speaker 02

  Yes.

• 15:14Neil deGrasse Tyson?

  Right, and, um, we've been working with it for more than 100 years.

• 15:19Speaker 02

  That's right.

• 15:20Neil deGrasse Tyson?

  And so what I ask of you, and I'm picking up his question.

• 15:24Speaker 02

  Yeah.

• 15:25Neil deGrasse Tyson?

  Are there still loose ends today? We're a quarter of the way into the 21st century. Are there still loose ends, not only in general relativity, but in those fields? Are there still parts of black holes we don't know or understand?

• 15:41Speaker 02

  That's an interesting question, so...

• 15:44Neil deGrasse Tyson?

  Because he laid it out

• 15:45Speaker 02

  Yeah.

• 15:45Neil deGrasse Tyson?

  More than 100 years ago.

• 15:46Speaker 02

  Well, he gave us the equations for it. And that's, of course, a very big step because you can't begin to do anything.

• 15:53Neil deGrasse Tyson?

  Right.

• 15:54Speaker 02

  But it's only the beginning step because unless you know the content of the equations and are able to understand their implications, you only know relatively little.

• 16:06Neil deGrasse Tyson?

  I think he just said you have to know the power of the equations. Is that another?

• 16:11Speaker 02

  Well, I would say...

• 16:13Neil deGrasse Tyson?

  You said context, that how powerful...

• 16:16Speaker 02

  Not context, content.

• 16:18Neil deGrasse Tyson?

  The content of the equation.

• 16:20Speaker 01

  I'm here to translate, that was definitely content.

• 16:22Speaker 02

  Content.

• 16:22Neil deGrasse Tyson?

  The content of the equation. You want to know what's sort of hidden in there?

• 16:27Speaker 02

  What do the solutions to the equations actually look like? For example, we now know that the most general kind of black...

• 16:37Neil deGrasse Tyson?

  Wait, you're telling me he gave us equations but not solutions? That's not, that ain't right.

• 16:45Neil deGrasse Tyson?

  Leave us hanging?

• 16:47Speaker 02

  Any great physicist will do that.

• 16:50Speaker 01

  They just left homework.

• 16:51Speaker 02

  Right.

• 16:52Neil deGrasse Tyson?

  Homework.

• 16:52Speaker 02

  Isaac Newton didn't solve all the equations of gravity.

• 16:57Neil deGrasse Tyson?

  Okay.

• 16:57Speaker 02

  Maxwell didn't solve all...

• 16:59Neil deGrasse Tyson?

  There have been at least a half dozen Nobel Prizes given to people working on Einstein's equations.

• 17:05Speaker 02

  Absolutely, very much.

• 17:06Neil deGrasse Tyson?

  That's crazy, crazy fact.

• 17:08Speaker 02

  Yeah.

• 17:09Neil deGrasse Tyson?

  Okay.

• 17:09Speaker 02

  And in fact, we didn't even really know what a black hole was in terms of solving Einstein's equations in a relatively simple context. Just what they call the vacuum solutions. The solutions to Einstein's equations when there's nothing there but some kind of a little point mass, the black hole. So the solution to that really didn't come until the 1960s, when the mathematician Roy Kerr... Published his solution to what a rotating black hole looks like.

• 17:46Neil deGrasse Tyson?

  And everything of yours rotates.

• 17:47Speaker 02

  And everything rotates. So that's a very, very important solution.

• 17:50Neil deGrasse Tyson?

  That's the care black hole. That's its own kind of black hole.

• 17:52Speaker 02

  That's right. It has his name. There's a Schwarzschild black hole. That came pretty quickly. That came within a month of when Einstein published his theory. But that's no rotating at all. And that's a little too simple for nature. That's an important solution and we learn a lot from it. Yeah. But it's not really a practical solution as we learn later. Because most black holes have a lot of rotation. And that makes a big difference in terms of how they behave.

• 18:39Speaker 03

  I'm Kais from Bangladesh and I support StarTalk on Patreon. This is StarTalk with Neil deGrasse Tyson.

• 18:56Neil deGrasse Tyson?

  All right, so today, what are some unsolved problems?

• 19:00Speaker 02

  Well, so there are different kinds of unsolved problems. So one problem which is still not really well understood is what happens? How do you see a black hole? Because the black hole itself is just empty space. You see a black hole because of the effect of the, that the black hole has on the surrounding gas.

• 19:26Neil deGrasse Tyson?

  Or anything surrounding it.

• 19:27Speaker 02

  Surrounding anything. But this gas is usually what you have at hand.

• 19:31Neil deGrasse Tyson?

  Mm-hmm.

• 19:33Speaker 02

  And yeah, under some circumstances, if there are a lot of stars, you can see how the stars are concentrated near the black hole and learn something from that. But most of the time, you get most of your information from the gas, which is around the black hole. So it was important to learn, for example, in my earlier work, that the gas is turbulent and to make use of that. But there was still things to learn about the orbits that are very, very close to the, what they call the singularity, to the real point mass, which is the black hole. That's where the effects of relativity become very important.

• 20:13Neil deGrasse Tyson?

  So just to be clear, you know, a black hole is not some giant sucking machine, right? So if you have a stable orbit around a black hole, you're cool. The sun could become a black hole today, we'll get very cold, but we'll just keep orbiting it like it was not, like, we're fine.

• 20:29Speaker 02

  Well, even more than that, there would be absolutely, if the sun were perfectly spherical as it is, versus a sun which was a black hole, there would be no difference whatsoever in terms of what it's doing to the, to the, to the entire space around it.

• 20:46Neil deGrasse Tyson?

  Right.

• 20:46Speaker 02

  That's right.

• 20:47Neil deGrasse Tyson?

  You would get very cold, but other than that, and we free suggest, but otherwise, but ignoring that complication, we'd be fine.

• 20:54Speaker 02

  Right.

• 20:54Neil deGrasse Tyson?

  Right, okay.

• 20:55Speaker 02

  Just the gravitational part.

• 20:56Speaker 01

  Do they rotate the same direction every single time?

• 21:01Speaker 02

  The black holes?

• 21:02Speaker 01

  Yeah.

• 21:02Neil deGrasse Tyson?

  No.

• 21:03Speaker 01

  Interesting.

• 21:04Speaker 02

  They can rotate however they like.

• 21:06Speaker 01

  All right.

• 21:07Neil deGrasse Tyson?

  Like the 900-pound gorilla.

• 21:08Speaker 01

  I don't think so.

• 21:10Neil deGrasse Tyson?

  It sits where it wants.

• 21:11Speaker 02

  Yep.

• 21:12Neil deGrasse Tyson?

  These orbits, it seems to me they'd be easy to calculate.

• 21:17Speaker 02

  Well, no, because the equations themselves, I mean, they are easy to calculate in some sense, if you put it all on a computer, but it's often very hard to understand what the results mean. The hard part is to be able to calculate orbits, say, the same way that Isaac Newton was able to prove that the orbits in his theory of gravity would be exactly ellipses. So that's very useful to know. So can you do the same thing around black holes?

• 21:51Neil deGrasse Tyson?

  Pull a Newton on a black hole.

• 21:53Speaker 02

  Pull a Newton on a black hole. And the answer is...

• 21:57Neil deGrasse Tyson?

  Newton is your guy.

• 21:58Speaker 01

  I know.

• 21:59Neil deGrasse Tyson?

  But he's not, he's not from Oxford, he's from Cambridge.

• 22:01Speaker 01

  Okay, well, that's okay, yeah.

• 22:03Neil deGrasse Tyson?

  You'll take it, you'll take it.

• 22:04Speaker 01

  Oh, yeah, we're big fans of Newton.

• 22:06Neil deGrasse Tyson?

  Okay.

• 22:07Speaker 02

  And so, when you're dealing with orbits around Kerr black holes, the equations are so daunting. They, just to write down the equation takes up a page of your notes. Not just to write it, let alone find a solution, that most people were put off by that task. But it turns out, when you study black holes, there are some simplifications that you can bring to bear that people were not really aware of, that people didn't fully appreciate. And you can exploit those, and then it turns out, you can kind of pull a Newton

• 22:51Speaker 02

  for some of the orbits which are not just, you know, kind of mathematical curiosities, but which actually have some practical interest as well. And so, I have a student who is actually able to do precisely that. And so, that, I think, has been able to advance the field significantly.

• 23:14Neil deGrasse Tyson?

  Interesting. So this would be a fresh advance on our understanding of black holes' effect on their environment that we haven't really had in a while. Is that a fair statement?

• 23:24Speaker 02

  I think that's a very fair statement.

• 23:26Neil deGrasse Tyson?

  Okay.

• 23:26Speaker 02

  I think it's a very fair statement. Contrary to sort of, you know, popular impressions, physicists don't really love complexity. If they have to deal with it, they'll muster the fortitude, and they will do so. But if they can find something...

• 23:44Neil deGrasse Tyson?

  Muster the fortitude, what does that mean? That sounds very British. No fun to wait to get it done.

• 23:50Speaker 02

  Thank you.

• 23:51Neil deGrasse Tyson?

  Thank you for the translation. Told you, that's why I'm here. Muster the fortitude. Thank you, William Shakespeare.

• 23:59Speaker 02

  But if they can find a simple way to, that is really the holy grail. That's really what they're after. And so that, I think, is where we're heading with that. We really do have a much simpler way of understanding what is going on with the orbits which are quite close to the black hole. And those are the ones of also not just kind of mathematical interest, but astronomical interest, observational interest.

• 24:26Neil deGrasse Tyson?

  Observational consequences.

• 24:28Speaker 02

  With observational consequences, very much so.

• 24:30Neil deGrasse Tyson?

  Okay, so you have a student who did this?

• 24:32Speaker 02

  I do.

• 24:33Neil deGrasse Tyson?

  So why am I still talking to you?

• 24:35Speaker 02

  Well, I don't know, Neil. I didn't arrange the schedule.

• 24:37Neil deGrasse Tyson?

  Okay, all right, Gary, let's get him out of here. Okay, ready, on three, on three. One, two, three. There you go.

• 24:45Speaker 04

  There you go.

• 24:45Neil deGrasse Tyson?

  Hello.

• 24:46Speaker 04

  Hello.

• 24:46Neil deGrasse Tyson?

  Your name?

• 24:47Speaker 04

  I'm Andy.

• 24:48Neil deGrasse Tyson?

  Andy, pleased to meet you.

• 24:49Speaker 04

  Nice to meet you.

• 24:50Neil deGrasse Tyson?

  Welcome. You sound like this guy. Yes, how about that? You're a Brit.

• 24:54Speaker 04

  I am a Brit.

• 24:55Neil deGrasse Tyson?

  What gave it away?

• 24:58Neil deGrasse Tyson?

  Okay, you'll help me translate. Of course, yeah. May not tell the truth, but I'll translate. So you're not literally a student, you're a postdoc.

• 25:07Speaker 04

  I'm a postdoc.

• 25:08Neil deGrasse Tyson?

  Postdoc.

• 25:08Speaker 04

  So I was Steve's student 2014 to 20, no, 2018 to 2022.

• 25:15Neil deGrasse Tyson?

  Okay.

• 25:16Speaker 04

  And then I've been a research fellow here since then.

• 25:18Neil deGrasse Tyson?

  Here at Oxford.

• 25:20Speaker 04

  In Oxford.

• 25:20Neil deGrasse Tyson?

  Oxford.

• 25:21Speaker 04

  Oxford.

• 25:24Neil deGrasse Tyson?

  So you picked up some of Einstein's mantle here.

• 25:29Speaker 04

  That's very generous.

• 25:31Neil deGrasse Tyson?

  To the mantle of Einstein.

• 25:32Speaker 04

  Yeah, yeah, yeah.

• 25:33Neil deGrasse Tyson?

  So what exactly did you do? And let me tell you our angle into this, all right? The public's, the public's angle is everyone has seen the movie Interstellar. All right, and Kip Thorne. Yes. Had a hand in that, helped write a lot of the physics that was in it. And one of the more intriguing scenes was This visit to this black hole planet, the gargantuan, I think, was the name of it. And it left one of their astronauts up in the orbiting spacecraft. And so he's in a different gravitational field from the ones who went down to the planet, which was near the black hole. And I forgot what the ratio was, but they lived 15 minutes or something,

• 26:18Neil deGrasse Tyson?

  and the guy up there went 10 years or some...

• 26:21Speaker 04

  Yeah, I think they even more.

• 26:22Neil deGrasse Tyson?

  But yeah, crazy ratio of time.

• 26:25Speaker 04

  Time dilation.

• 26:25Neil deGrasse Tyson?

  Time dilation, crazy time dilation. So I was going to try to calculate how close that orbit had to be. And then I said, "No, I'm not gonna, I will wait till I get somebody else to do this." It sounds like you're the guy for that.

• 26:37Speaker 04

  Yes, that's, yeah, I'm orbiting near to a black hole, that's my, that's the danger.

• 26:41Neil deGrasse Tyson?

  He's the guy.

• 26:42Speaker 04

  That's the danger.

• 26:42Speaker 01

  How many people do we bump into? How many of our audience...

• 26:46Neil deGrasse Tyson?

  This was not an accidental bump into the...

• 26:47Speaker 01

  No, no, no, I'm not bumping into Andy, but how many people in our StarTalk realm and universe want to know, "How close can I orbit to a black hole?" Because that's what they do. Before I get or...

• 27:00Neil deGrasse Tyson?

  We have very curious people who watch this.

• 27:02Speaker 04

  Yeah, I'm sure they ask that question frequently.

• 27:04Neil deGrasse Tyson?

  Because you'll see it, and they're not just gonna receive it, assuming it just can happen. Give me some answers there.

• 27:09Speaker 04

  So you can get pretty close. So for your simplest Schwarzschild black hole?

• 27:14Neil deGrasse Tyson?

  Schwarzschild, so that's the non-rotating black hole.

• 27:16Speaker 04

  Non-rotating, so let's make the event horizon one.

• 27:19Neil deGrasse Tyson?

  Okay, we all know what the event horizon is. The point of no return that we all know about.

• 27:24Speaker 04

  So the edge of the black hole, that's one. Then you can stably orbit on a circular orbit down to three.

• 27:31Neil deGrasse Tyson?

  But not less than three?

• 27:33Speaker 04

  Not less than three. So, yeah, I mean, it's, you know, it's the roundabout force. When you drive around a roundabout, you get pushed out. Okay, so that's what an orbit is, you balance that with gravity.

• 27:42Neil deGrasse Tyson?

  A roundabout would be a traffic circle.

• 27:44Speaker 04

  Yes, sorry.

• 27:46Speaker 01

  It's a roundabout.

• 27:48Speaker 04

  Yeah.

• 27:48Speaker 01

  When you're here, you're roundabout. When you're back home, traffic circle yourself silly.

• 27:54Neil deGrasse Tyson?

  This, so the planet Gargantuan, to have that much time dilation difference, because, I think most of our audience knows, as you get to a stronger and stronger gravitational field, your time slows down relative to others.

• 28:10Speaker 04

  Absolutely.

• 28:11Neil deGrasse Tyson?

  So, so how close was the Gargantuan planet? I don't remember them saying so. Do you?

• 28:18Speaker 04

  It has to be really, I mean fantastically close. In fact, I'm not-

• 28:21Neil deGrasse Tyson?

  Closer than three?

• 28:23Speaker 04

  I'm pretty sure it's gonna be closer than three.

• 28:25Neil deGrasse Tyson?

  Uh-oh. Uh-oh. Uh-oh.

• 28:31Neil deGrasse Tyson?

  Okay, so this would mean Kip? Kip, oh boy. Kip Thorne. You're calling him out. We're calling out Kip Thorne. Kip Thorne.

• 28:40Speaker 04

  Yeah, so them landing on the planet, that would have been unstable. That little kick would have sent it spiraling in.

• 28:45Neil deGrasse Tyson?

  Wow. So, so what happens? Why can't you just orbit right above the event horizon?

• 28:52Speaker 04

  In Newtonian gravity, so the Earth going around the Sun, you have to balance two forces. You've got gravity coming in and revolution pushing you out.

• 29:00Neil deGrasse Tyson?

  So that keeps you at the same distance from the big red?

• 29:03Speaker 04

  Absolutely.

• 29:04Neil deGrasse Tyson?

  Your urge to fly off is a balance. Okay, so now what?

• 29:08Speaker 04

  And then you write down the same problem in Einstein's equation, and you find that there's a new force effectively. Or there's a new-

• 29:15Neil deGrasse Tyson?

  A new force?

• 29:15Speaker 04

  Well, no. Okay, so the force is gravity. That's the only force. But there's something, an effective force effectively, which is gravity times rotation. So that's what the equation looks like.

• 29:25Neil deGrasse Tyson?

  So this is a new term?

• 29:27Speaker 04

  It's a new term in the energy equation.

• 29:29Neil deGrasse Tyson?

  That operates on the stability of the system.

• 29:32Speaker 04

  Yeah, and that points in. Okay? So the faster you go around-

• 29:36Neil deGrasse Tyson?

  So that term is not there in Newton's equations?

• 29:38Speaker 04

  No, no, no.

• 29:39Neil deGrasse Tyson?

  So as you get closer and closer to a black hole, this other term shows up that prevents you from sustaining a balance.

• 29:45Speaker 04

  So this is one of the things that we didn't know, that we need to know, because this is helping solve why this happens the way it does.

• 29:53Neil deGrasse Tyson?

  Yes.

• 29:54Speaker 04

  So you get closer, you have to go faster and faster and faster-

• 29:57Neil deGrasse Tyson?

  In order to stabilize that extra term.

• 29:59Speaker 04

  To stay in orbit, but that just makes this third term even bigger. Because it's gravity times rotation. And that eventually destabilizes the orbit.

• 30:08Speaker 01

  So the faster you go.

• 30:09Speaker 04

  Yeah.

• 30:10Speaker 01

  It starts to work against you.

• 30:11Speaker 04

  Yeah, exactly. And eventually.

• 30:12Neil deGrasse Tyson?

  That ain't right.

• 30:13Speaker 01

  Diminishing returns.

• 30:14Speaker 04

  Exactly.

• 30:15Neil deGrasse Tyson?

  That ain't right. That's wrong. That's just wrong. Why did you come up with that?

• 30:20Speaker 04

  I mean, that's the universe.

• 30:21Neil deGrasse Tyson?

  Are you telling me no one figured this out before you?

• 30:24Speaker 04

  So this was known. We knew the orbits became unstable. Okay, but the point was, how simply can you describe the plunge effectively? So you get flicked off the circular orbit and you dive in towards the black hole. And the question is, how do you describe that?

• 30:40Neil deGrasse Tyson?

  And by the way, as I understand it, if you dive into the black hole, your orbital speed increases, which would further increase the term. Is that correct? So it's catastrophically unstable.

• 30:52Speaker 04

  Yeah, exactly. So it's unstable in that you perturb it and you're gone.

• 30:56Neil deGrasse Tyson?

  And it gets even more and you're in.

• 30:59Speaker 04

  Yeah, you're not.

• 31:00Speaker 01

  So you speed up to try and break the orbit and you just end up making it way worse.

• 31:05Neil deGrasse Tyson?

  Worse, okay.

• 31:05Speaker 04

  And you're gone. And you plunge into across the event horizon and you're doomed. Yeah, absolutely.

• 31:09Speaker 01

  Say goodbye.

• 31:10Neil deGrasse Tyson?

  Damn, dude.

• 31:12Speaker 04

  Yeah, and so, you know, this is a prediction.

• 31:14Neil deGrasse Tyson?

  You're bumming us out here.

• 31:15Speaker 04

  Yeah, yeah, I'm sorry. It's the universe's fault.

• 31:19Neil deGrasse Tyson?

  Yeah, it's not your fault. The universe revealed it. Right, so let's get the understanding, just so we learn how science works. Some of this was known before your work.

• 31:27Speaker 04

  Yes, we knew this happened.

• 31:29Neil deGrasse Tyson?

  Okay, but so how did you contribute to that problem? So just to make it clear, so much of what's out there, people have little bits of solutions to it. Right? And we're all sort of touching the elephant, trying to understand it.

• 31:43Speaker 04

  Well, it's like a piece of paper that someone's ripped into tiny little bits and then scattered.

• 31:47Neil deGrasse Tyson?

  Okay.

• 31:48Speaker 04

  And then you're now trying to bring it all back.

• 31:49Neil deGrasse Tyson?

  Well, the papers, it's a pre-existing how the universe works.

• 31:52Speaker 04

  So then trying to piece it back together to say, oh, no, that goes there, this goes here.

• 31:57Neil deGrasse Tyson?

  Right.

• 31:57Speaker 04

  And then we're getting there. So this is what I think Andy's kind of.

• 32:00Neil deGrasse Tyson?

  Okay, so how did you come in on this?

• 32:02Speaker 04

  So we knew this should happen. Okay? And I mean, you know something should happen, you want to go see it effectively. Okay, so you want to go see it out in nature. You want to observe it in a real physical system. Now, to know.

• 32:14Neil deGrasse Tyson?

  You want to observe the unstable world.

• 32:17Speaker 04

  Yeah, the plunge. You want to see this gas that's plunging. That's what you want to do. Because then you know it's there, you know. And so before you can tell. That you've seen this, you need to know what to look for. Okay, so you've got to build a model of this plunging gas.

• 32:30Neil deGrasse Tyson?

  So build a model, this on a computer.

• 32:32Speaker 04

  Yeah, pen and paper, computer.

• 32:33Neil deGrasse Tyson?

  What did you use?

• 32:34Speaker 04

  I used pen and paper.

• 32:35Neil deGrasse Tyson?

  Old school. Oh, oh chalkboard. Oh, oh. These are like the cheapest scientists to keep around.

• 32:45Speaker 04

  No, they're not.

• 32:46Neil deGrasse Tyson?

  Yes, they are.

• 32:47Speaker 04

  No, they're not.

• 32:47Neil deGrasse Tyson?

  They're totally cheap. There's no computer, there's no telescope, there's no particle accelerator.

• 32:51Speaker 04

  Have you seen the price of graphite lately? Go through pencils. I need the best chalk.

• 32:57Neil deGrasse Tyson?

  And then he'll be busy and come out later. Okay, so go on.

• 33:01Speaker 04

  So you want to simplify these equations down to make them useful? So that you can make predictions and then you can go and look in the data and see if there's any black hole sources out there that we just can't understand without this plunging gas.

• 33:13Neil deGrasse Tyson?

  So you have to predict what unstable spiraling gas would look like?

• 33:20Speaker 04

  Exactly, yeah.

• 33:21Neil deGrasse Tyson?

  So what does it look like?

• 33:22Speaker 04

  Well, essentially, it's hot and small is the...

• 33:25Neil deGrasse Tyson?

  I just said that.

• 33:26Speaker 04

  Yeah.

• 33:27Speaker 01

  You didn't.

• 33:27Neil deGrasse Tyson?

  But I said stop.

• 33:29Speaker 01

  You didn't, and you didn't go for swirling and unstable either.

• 33:33Neil deGrasse Tyson?

  Okay.

• 33:34Speaker 04

  Precisely how hot, precisely how small, that's for the money.

• 33:37Neil deGrasse Tyson?

  You got it, you got it.

• 33:39Speaker 04

  So, yeah, so we have these theories that Steve worked on, you know, since the 70s.

• 33:45Neil deGrasse Tyson?

  Your advisor, Steve Bobbys?

• 33:46Speaker 04

  Yeah, absolutely.

• 33:47Neil deGrasse Tyson?

  Who snapped him out of existence.

• 33:48Speaker 04

  Yeah, he did work on it. And, you know, they had these models and they just stopped at this stable, last stable orbit because then it plunges, it gets difficult and we'll just, we'll ignore it, basically. And so you stop there, that's what I would have done, okay, you know? And then eventually we started getting data that they couldn't explain with these models.

• 34:25Neil deGrasse Tyson?

  Okay, so now that you have insights, right down to the orbits at the event horizon, non-orbits at the event horizon, tell me now where you think Gargantuan had to have been to give you that stark difference in time dilation? I think it's well inside. Inside your unstable orbit. Absolutely, yeah. So that planet just would have not been hanging out? No, absolutely not. It would have been gone eons ago? Gone, eons. Okay, why didn't Kip Thorne know this? I'm sure Kip Thorne did know this. I'm sure it was just very inconvenient for the plot. That may well have more than a grain of truth in it. Oh, okay, so you're being very kind here.

• 35:08Neil deGrasse Tyson?

  What you're saying, let me reword what you're saying. Okay, you're saying, apart from the extra detail that you have provided, all of us inside those unstable orbits, we knew they were unstable orbits. He certainly would have known there's unstable orbits, because his middle name is General Relativity. Okay. He's co-author of like the most famous relativity book there ever was. Okay. It's called Gravitation. It has the proportions of a Manhattan Yellow Pages phone book, okay? Well, he certainly simplified the title, didn't he? Well, it's the only book you learn all about just by carrying it around, right? Yeah, I get that, yeah, see what you did. So it says three authors, Misner, Thorne, and Wheeler, and Kip Thorne is the middle

• 35:53Neil deGrasse Tyson?

  author there. So we all have it in my generation. It's too old for you. No, I've got it on. You do have the book, okay? It's a pencil and paper, he'll have a book. All right, so what you're suggesting is that he wanted that degree of time dilation difference. And took some cinematic liberties to get it.

• 36:15Speaker 04

  I mean, the man's got an overall prize, he's, you know.

• 36:18Speaker 01

  It might not have been him, he might have been overridden by producers and directors.

• 36:22Neil deGrasse Tyson?

  Yeah, okay.

• 36:23Speaker 01

  Because that does, that does happen.

• 36:25Neil deGrasse Tyson?

  Okay, I cut people's slack in movies.

• 36:27Speaker 01

  I know.

• 36:28Neil deGrasse Tyson?

  If the idea is kind of right.

• 36:30Speaker 01

  Okay.

• 36:31Neil deGrasse Tyson?

  Even if in detail is wrong.

• 36:32Speaker 04

  That, that orbit exists. That orbit exists that the planet's on, it's just unstable. So it just won't exist for long, but, but, but it.

• 36:38Neil deGrasse Tyson?

  It wouldn't exist for long enough for them to do anything they were doing.

• 36:40Speaker 04

  But it exists, it's a solution that's, that's valid, it just won't, just won't.

• 36:44Speaker 01

  All right, we'll, we'll take the thorn out of your side for the moment.

• 36:46Neil deGrasse Tyson?

  The kit thorn out of my side?

• 36:48Speaker 01

  Yes, thank you. You talked about we're finding new data coming in. Now, if you're a forensic accountant, follow the money, stupid, you're gonna find what's all about. This, for me, is you being forensic for the data. So what kind of data is coming in and what are you able to kind of?

• 37:08Neil deGrasse Tyson?

  And what kind of telescopes? Yeah, coming to you as an astronomer, I want to know what I should point my telescope.

• 37:14Speaker 01

  So what are your data sources? Is it telescopes? Is it computational? Where are we headed?

• 37:18Speaker 04

  So these are, these are X-ray telescopes, so, so they're satellites in orbit?

• 37:21Neil deGrasse Tyson?

  X-ray telescopes.

• 37:22Speaker 04

  Yeah, yeah, yeah.

• 37:23Neil deGrasse Tyson?

  And we're about to lose our last X-ray telescope, the Chandra Great Observatory.

• 37:27Speaker 04

  That's, that's gonna be a real, a real.

• 37:29Neil deGrasse Tyson?

  It's gonna get de-orbited very soon, I think, last I heard.

• 37:32Speaker 04

  There will be, there will be others, but, but Chandra is a wonderful instrument.

• 37:35Neil deGrasse Tyson?

  Yes.

• 37:35Speaker 04

  So it's, you know, it.

• 37:36Neil deGrasse Tyson?

  Named for?

• 37:37Speaker 04

  Chandra Seharkar.

• 37:38Neil deGrasse Tyson?

  Chandra Seharkar, very good.

• 37:40Speaker 01

  He knows.

• 37:40Neil deGrasse Tyson?

  I'm just checking, he knows. I'm still a student.

• 37:43Speaker 01

  Make him dance.

• 37:43Neil deGrasse Tyson?

  I'm allowed to be my professor Neo every now and then, okay?

• 37:49Neil deGrasse Tyson?

  Uh, and, uh, as I remember, he was a great astrophysics theorist and good tradition in the steps you're following.

• 37:57Speaker 04

  If I have half the success of Chandra Seharkar, I'd take that, yeah.

• 38:01Neil deGrasse Tyson?

  So you publish this.

• 38:02Speaker 04

  Yeah, yeah, so, so it's X-ray data, so these, these discs are super hot. They're incredibly hot and they produce X-rays and they, they, you know, they, they are detected by satellites.

• 38:11Neil deGrasse Tyson?

  They're so hot, they radiate X-rays.

• 38:13Speaker 04

  Absolutely.

• 38:13Neil deGrasse Tyson?

  As opposed to being so hot like your electric stove, it radiates infrared.

• 38:19Speaker 04

  Yeah.

• 38:20Neil deGrasse Tyson?

  Then you can radiate like ultraviolet if you get like hotter and then. And then X-rays, you keep radiating up the spectrum.

• 38:26Speaker 01

  What goes hot, what, how hot do you have to radiate to get worse than X-rays?

• 38:30Speaker 04

  Millions of, millions of degrees.

• 38:32Speaker 01

  So why would it get even hotter?

• 38:33Speaker 04

  And it's gamma rays.

• 38:34Speaker 01

  And then what's gonna say like, we're in Hulk territory.

• 38:37Neil deGrasse Tyson?

  That's very hot, whereas your stove is a thousand degrees, you know? Yeah.

• 38:42Speaker 01

  We're talking millions.

• 38:44Speaker 04

  We're talking millions of degrees and, and, and so we, yeah, yeah. And it's, and it's, and it's, you know, tens of kilometers from the edge of a black hole, millions of degrees, X-ray photons are coming across the galaxy, 10,000 light years.

• 38:58Neil deGrasse Tyson?

  Okay, so you, so you published, did you publish your theoretical predictions and found some data that explained?

• 39:06Speaker 04

  So, yeah, yeah, so we, we did.

• 39:07Neil deGrasse Tyson?

  That's the best way to do that, right?

• 39:08Speaker 04

  We, we did, exactly, yeah, yeah. We, we had a bit of a, we had a bit of a heads up. We knew that there were mysteries out there and, and we thought we had the answer.

• 39:17Speaker 01

  As they do us all, my friend.

• 39:19Speaker 04

  Yeah, and, and we were able to show, yes, you have this, this data, it's beautiful data, and you just can't explain it without this, this plunge, this gas on the planet.

• 39:26Neil deGrasse Tyson?

  And where did that appear?

• 39:27Speaker 04

  It was in the monthly notices of the Royal Astronomical Society, a very, a very British journal, yeah.

• 39:33Neil deGrasse Tyson?

  Kept it bred. You know, we have journals too in America.

• 39:36Speaker 01

  Yeah, but they're not royal.

• 39:37Speaker 04

  Yeah, they don't have the king's approval.

• 39:40Speaker 01

  Okay, here we go.

• 39:41Neil deGrasse Tyson?

  I gotta get used to this, not the queen's approval, the king's approval, King Charles, okay. So this is, this is a leading journal in our field, yes, so congratulations on that.

• 39:51Speaker 04

  Yeah, thank you.

• 39:52Neil deGrasse Tyson?

  And if I understand correctly, that, that got some media attention.

• 39:57Speaker 04

  Yeah, it caused a bit of a stir, yeah, yeah, it was, it was good fun.

• 40:00Speaker 01

  Classic British understatement.

• 40:04Neil deGrasse Tyson?

  Which means people went ape shit.

• 40:07Speaker 01

  A couple of heads blew out.

• 40:10Speaker 01

  So. Before we let Andy go, what is your top unsolved problem?

• 40:15Neil deGrasse Tyson?

  And at this point in your career, surely you have some ambitions.

• 40:18Speaker 04

  So I, I wanna know how fast black holes are rotating, the black holes we have out in the galaxy, I wanna know how fast they're spinning.

• 40:24Neil deGrasse Tyson?

  Dude, think bigger than that, come on.

• 40:26Speaker 04

  Oh, no, this, this tells us, this tells us how they're formed, so this tells us.

• 40:30Speaker 01

  There you go, that's why I want.

• 40:31Speaker 04

  So, okay, the, the question you answer is how fast they're spinning, but the, the long term, but that, you know, that's, that's one question, but the real, the real answer is how, how do they form and how do they evolve over the age of the universe?

• 40:42Neil deGrasse Tyson?

  Okay, and, and this includes supermassive black holes?

• 40:45Speaker 04

  Absolutely, yeah, yeah, supermassive.

• 40:46Neil deGrasse Tyson?

  The big ones, isn't it?

• 40:47Speaker 01

  I got the hint.

• 40:50Neil deGrasse Tyson?

  Supermassive, the big ones, yeah. So, you think you can have a general understanding that can apply to all the regimes of black holes that we know?

• 40:57Speaker 04

  That's the plan.

• 40:58Neil deGrasse Tyson?

  So you're gonna be the black hole guy?

• 40:59Speaker 04

  Yeah, absolutely.

• 41:00Neil deGrasse Tyson?

  I'm a black hole go-to guy. Go-to black hole guy. Well, so, good luck with that. Sometimes you need a little bit of that, of course. Yeah. My little island leading the way now, how about that? So, so tell me, why must everything circle a black hole to go in? Why can't it just fall straight in?

• 41:19Speaker 04

  It's got angular momentum, basically, and angular momentum's hard to lose.

• 41:23Neil deGrasse Tyson?

  Hard to lose?

• 41:23Speaker 04

  Yeah.

• 41:25Neil deGrasse Tyson?

  Why?

• 41:26Speaker 04

  Stuff that's spinning.

• 41:27Neil deGrasse Tyson?

  Why can't I just?

• 41:29Speaker 04

  It's conserved, it's conserved quantity.

• 41:32Neil deGrasse Tyson?

  What about a black hole that doesn't spin? What do you call those? That's a Schwarzschild black hole. How about that one? No, but we're talking about stuff that falls in. Yeah, that's what I'm thinking. If it's not rotating, is it? If you're not gonna have a little disky thing, somehow it has to have been exactly pointed at it.

• 41:49Speaker 04

  And in these systems, we're peeling off the outer edge of a star. That's where this gas is coming from. So you've got a star in an orbit around a black hole, and you're peeling off the outside.

• 41:56Neil deGrasse Tyson?

  I learned what word that says that. The star's getting flayed. Is that a good word? Oh. That's a good word. It's skinned alive, it's to be flayed. Okay. Did I teach a Brit a word? That's not, I'm an American, we're not supposed to. I think we'd actually tell you.

• 42:17Neil deGrasse Tyson?

  So, but okay, so we have these discs, but suppose other material comes the other way? Doesn't it all cancel out?

• 42:23Speaker 04

  We've got one source of matter, that's the problem.

• 42:26Neil deGrasse Tyson?

  Oh.

• 42:27Speaker 04

  So you've got, it's all coming in from the same direction.

• 42:29Neil deGrasse Tyson?

  From one thing that's circulating that way.

• 42:31Speaker 04

  So you're peeling, so you inherit this angular momentum.

• 42:34Neil deGrasse Tyson?

  It would be odd to have two things simultaneously.

• 42:36Speaker 04

  Absolutely.

• 42:37Neil deGrasse Tyson?

  Doing that, okay. So that, that's what gives you a job, thinking about the spiraling material.

• 42:43Speaker 04

  Yeah, yeah.

• 42:43Neil deGrasse Tyson?

  If everything just fell straight in, you'd be out of job.

• 42:45Speaker 04

  Yeah, exactly.

• 42:47Neil deGrasse Tyson?

  And what about really, really big black holes? Where? They wouldn't necessarily have a disk.

• 42:54Speaker 01

  Not always, no.

• 42:55Speaker 04

  Oh.

• 42:56Neil deGrasse Tyson?

  Because it's just really, really big. And how are you going to coherently create a disk around it? You just fall in.

• 43:02Speaker 01

  Within a supermassive black hole, does it not spawn its own little miniature?

• 43:07Speaker 04

  Sometimes there's, you know, gas in the middle of the galaxy. It comes nearby. You switch on, you switch on the effect of a supermassive black hole.

• 43:15Neil deGrasse Tyson?

  I like that phrase. Because the black hole is lurking.

• 43:19Speaker 01

  Yep.

• 43:20Neil deGrasse Tyson?

  Right? And only when it has something to dine upon, does the mechanism turn on. Very good. I like this.

• 43:28Speaker 04

  Those are the interesting ones.

• 43:29Neil deGrasse Tyson?

  Yes, of course. Actually, physically. Well, this is great. Well, thank you.

• 43:33Speaker 01

  Yeah.

• 43:33Neil deGrasse Tyson?

  For sharing us your expertise. And we'll look for great things. And I still want you to be more ambitious. I just want to know how black holes form. Dude, it's a big universe. Okay?

• 43:44Speaker 01

  Give him one thing to do at a time.

• 43:46Neil deGrasse Tyson?

  No, no.

• 43:47Speaker 01

  One thing to do at a time.

• 43:49Neil deGrasse Tyson?

  I learned to not, I'm pick, I'm.

• 43:51Speaker 01

  All right, okay.

• 43:52Neil deGrasse Tyson?

  Can I be wise here?

• 43:53Speaker 01

  Go ahead.

• 43:54Neil deGrasse Tyson?

  The wise elder?

• 43:54Speaker 01

  Mm-hmm.

• 43:55Neil deGrasse Tyson?

  In my day, people said, I just want to know the value of the Hubble constant. I just want to know the rate of the universe. I just want to know. And then we discover that and we're on to other questions. Because it's not so much, I want to know the answer to these questions I posed. I want to know the answers to questions I have yet to think of. And that's your future.

• 44:24Neil deGrasse Tyson?

  Whether you like it or not.

• 44:25Speaker 04

  Absolutely.

• 44:26Neil deGrasse Tyson?

  All right, dude. Thanks for being on StarTalk.

• 44:28Speaker 04

  Thank you.

• 44:29Neil deGrasse Tyson?

  You got it.

• 44:29Speaker 04

  Cheers.

• 44:30Neil deGrasse Tyson?

  You have one last Brit thing you want to say before we sign off?

• 44:33Speaker 01

  Hop on the last thing, just ignore him.

• 44:37Neil deGrasse Tyson?

  What is science if not this eternal quest to decode the operations of nature? Isaac Newton once said, if I can see farther than others, it's because I've stood on the shoulders of giants that have come before me. Now, I don't really believe him because he was completely brilliant. But for most of us, that's true. And, but what does that mean? Those who come before you, they put together part of that cosmic puzzle. But no, it's not completely solved.

• 45:09Neil deGrasse Tyson?

  And there are parts of the puzzle we don't even know exist yet that will need to be assembled. And this, the act of asking questions, probing the universe and finding answers, is the passing of a torch. I think of like the Olympic torch. It goes from one group to another, from one generation to the next. And is the sum of all of this that is responsible for our understanding of the world as we know it. And in this little slice of theoretical physics, in the Beecroft Building on the campus of Oxford University, we got a little taste of that.

• 45:52Neil deGrasse Tyson?

  And I'm delighted to have brought you a slice of how science works. And that is a cosmic perspective. Until next time, as always, keep looking up.