The Intricacies of Angular Momentum - What Happens Near Black Holes

0:00Andrew Dunkley Hi there. Thanks again for joining us. This

0:02 is Space Nuts. It's a Q and A edition where we answer audience questions. And, uh, we. I think we've got our very first question from Yemen. Uh, Hussein has sent, uh, it a question asking about radial velocity. Uh, Martin, one of our regular contributors, has a dark matter he wants to discuss. Uh, Peter in Sweden is talking angular momentum.

0:26 Uh, that is the angular momentum of matter falling into a black hole. And a real bummer of a question. We'll tell you all about it on this episode of space nuts.

0:38Professor Fred Watson 15 seconds. Guidance is internal.

0:40 10, 9. Ignition sequence start. Space nuts.

0:45Berman Gorvine 5, 4, 3, 2.

0:46Professor Fred Watson 1, 2, 3, 4, 5, 5, 4, 3,

0:49 2, 1.

0:50Andrew Dunkley Space nuts.

0:51Professor Fred Watson Astronauts report it feels good.

0:54Andrew Dunkley And he's back again to solve all your

0:56 riddles. It's Professor Fred Watson Watson, astronomer at large. Hello, Fred Watson.

1:01Professor Fred Watson Hello, Andrew. Good to see you again. I

1:03 always hoped we'd get back together again one day and here we've been ages.

1:09Andrew Dunkley About two minutes. Uh, yeah.

1:12 Um, anyway, I love the Q and A programme, I really do, because it gives people a chance to, um, dump on us and see how much we can mess it up. And that's always fun. Um, we might get straight into it. Fred Watson and I was very excited to see that. We've got a question from Yemen. I never thought we. I didn't even know we were heard in Yemen, so that's really fantastic. And, um, this one comes from Hussain, who says, I'm a huge fan of the podcast Calling in from Yemen. See, I was right. It was Yemen. Ah, First, a quick confession. I hope you're not offended, but Space Nuts is my absolute favourite show to listen to when I'm falling asleep.

1:57 Your voices are incredibly soothing. Uh, though I promise I do actually listen to the science before I drift off. I appreciate that. Um, my wife says I keep her awake, um, because I snore, but I don't believe it. I've never heard me. Uh, my question is about the radial velocity method for detecting exoplanets. I understand that a star wobbles because of the gravitational pull of its orbiting planets.

2:22 However, how do astronomers use this method to isolate individual planets? For example, our sun must wobble because Mercury, Venus, Earth, Mars, Jupiter and the rest pull in different directions at the same time. If an alien astronomer were looking at our sun's wobble from across the galaxy, would they actually be able to untangle that messy combined signal to identify individual planets and their specific characteristics?

2:50 Or does the wobble method just tell us, hey, there are planets here, without giving away the exact Details of who's who. Love the show. Keep up the fantastic work, Hussein. That's a really well crafted question. Thank you, Hussain.

3:05Professor Fred Watson It is a great question as well. Uh, and

3:08 the answer in a way is both. Um, the two alternatives that Hussein's put forward, uh, can you disentangle them or does the wobble method just tell us, hey, there are planets there, without giving away the exact details and what differentiates between them is first of all how bright the star is, how near it is.

3:32 So what kind of strength of signal you get in terms of measuring the velocity of the star itself by this Doppler wobble method, uh, to analyse for planets. But also it depends on the sizes of the planets and on their mix, uh, as well. Um, so, uh, just thinking about the solar system, we've got the biggest planet, Jupiter. That's the one that has by far the biggest effect on the sun.

4:00 Saturn comes next, uh, in terms of its size. And then the other two, uh, gas giants, uh, uh, Uranus and Neptune, uh, the terrestrial planets or rocky planets also have an effect. Uh, but because their masses are much lower, the effect is also much lower. It's mitigated slightly by by the fact that they're nearer to the sun, uh, but nevertheless they're much, much weaker than the gas giants. So if you were, uh, uh, an alien on a planet, uh, orbiting a star maybe eight or nine light years away, something like that, which is the distance to Sirius, uh, the brightest star in the sky, and you're looking back at the solar system, uh, the first thing you would see would be, uh, the main motion which would be due

4:51 to Jupiter because its mass is so much bigger. The other planets, however, if you had really highly accurate velocity measurements and you'd need them almost to centimetres per second accuracy, uh, it can be done. Uh, there are ways of calibrating spectrographs to let you do this. Uh, but if you did have these really accurate readings and you could do your measurements almost 24 7, which you can't because, uh, certainly if we're anything like the Earth, you've got daylight coming in the way. Uh, but what you want to do is fill in the time domain as full as you can to get as many data points as you can, then what you would do, you'd build up a picture which would be dominated by Jupiter. But the

5:43 graph of the speed of the star, the wobble of the star would have little ups and downs in it caused by the other planets. Uh, and you can disentangle those. There is a technique called Fourier analysis, uh, it uses, uh, things that we call fast Fourier transforms, which is a mathematical tool that um, kind of dates from the early days of computing, in fact, well before that when people did their calculations by hand. But for this, it's a way of disentangling just how many, what we might call periodicities, in other words, how many regular, um, passages are there, ah, caused by individual planets, if I can put it that way.

6:30 So you can tease out the effect of each individual planet because they all have different periods of revolution, uh, around the sun. In the case of, if you're looking at the solar system. So, um, if you've got good enough data, you can uh, as Hussein suggests, uh, identify the individual planets and their specific characteristics. But if your data aren't so good, then you're basically just seeing the biggest ones of them. And that's just telling you that there's at least one planet there.

7:01Andrew Dunkley Yeah, early on when we started discovering

7:04 uh, exoplanets, we were only finding the big ones, weren't we? We assumed there were small ones, but it took us a long time to find the first one, didn't it?

7:13Professor Fred Watson That's right. And in fact, um,

7:16 it highlights the uh, the deficiencies of the Doppler wobble method, what Hussain was talking about as a way to discover planets, because it's really, that's most sensitive to the biggest ones. Uh, it was when the Kepler spacecraft, uh, and uh, Tess, the other, um, planet finding spacecraft, when they started looking in detail at the way the brightness of stars changed, uh, as planets passed in front of their parent stars. Uh, that's when we started discovering the smaller ones because the smaller ones are actually, uh, easier to discover that way.

7:57Andrew Dunkley Um, here's a dumb question.

8:01 Can we, can, can we look with accuracy at the wobble of our own sun because of the planets surrounding it, including our own?

8:13Professor Fred Watson Yeah, uh, you can, yes.

8:16 Um, and um, you can actually find, um, uh, diagrams showing the way. It's what we call the barycenter. The barycenter of the solar system is its centre of gravity, which takes into account not just the sun, uh, but the planets as well. And the barycenter does wander around. Uh, mostly it's inside the sun. It does come outside the sun from time to time. Uh, but uh, you can find charts showing exactly how that happens.

8:50 Uh, you know, little maps of the way the barycentra of the solar system wanders around relative to the sun.

8:57Berman Gorvine Okay.

8:57Andrew Dunkley I wondered, I didn't know if we

9:00 could do it within our own sphere. So to speak.

9:04Professor Fred Watson Not a dumb question at all. Absolutely.

9:05Andrew Dunkley There you go. I occasionally ask one that's

9:08 adequate. Uh, and uh, thank you to Hussain for sending that question in from Yemen. Lovely to hear from you. And you're listening to SpaceNuts with Andrew Dunkley and Professor Fred Watson Watson. Let's take a quick break from the show to tell you about our sponsor, NordVPN. Now, if you travel, work remotely or regularly use public WI fi, having a VPN service can be a very useful layer of online security. NORDVPN encrypts your Internet connection and helps keep your online activity private by hiding your IP address and your location. That means when your connecting from an airport, a hotel, a cafe, uh, or any public network for that matter, you can have a greater level of protection for your Internet traffic. NORDVPN

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11:02Professor Fred Watson I'm going to step off the land now.

11:06 That's one small step for man.

11:11Berman Gorvine One Space Nuts.

11:16Andrew Dunkley Let's hit uh, you with an audio question from

11:18 one of our regular contributors.

11:21Berman Gorvine Hello, Space Nuts.

11:24 Martin Berman Gorvine here from Potomac, Maryland, usa, writer extraordinaire in many genres. With a slightly less silly, though still highly speculative question. Since dark energy is thought to pervade the entire universe, would it be possible, at least in theory, to harness that energy to drive space flight? And if so, uh, could you make a spacecraft go arbitrarily fast? By that means, you know, 99 point a whole bunch of nines percent of uh, the Speed of light for that extra relativistic Philip. So that when you step out at your destination, the uh, universe has aged significantly, but you, the traveller, have not.

12:41 Can't wait for the answer. Which will probably involve Professor Watson shooting me down in flames as usual. Berman Gorvine, over and out.

12:57Andrew Dunkley Thanks, Martin. Martin sent me a couple

13:00 copy, uh, of uh, two of his latest books which I haven't had a chance to, to read and I did promise I would but um, uh, I was too busy writing my own. So, uh, um, but I will get to the. Martin, thanks for sending those in. Uh, fire away, Fred Watson.

13:17Professor Fred Watson To shoot him down. Uh, I have to say these

13:20 um, these questions do sound like the making of another of Martin's books. Uh, so, uh, you know, putting the ingredients uh, of um, science into the books. It's a great idea if you're going to write science fiction. It's nice to have some science in it as well. Um, yes you do. Um, what Martin's question made me think about was, um, the number of joules of energy contained, represented by dark energy per cubic metre of space.

13:57 And I've no idea what that is, but I bet per cubic metre it's actually quite small, uh, because um, we only see the effect of dark energy when we look at the universe on a very large scale. When we look, you know, billions of light years out, we start to see its effects. We can tell that the universe has been expanding more rapidly, uh, since the universe was about half its present age. Uh, so I guess, you know, if you imagine a tank full of dark energy, uh, on any kind of human scale, whether it's the size of a, I don't know, you know, the size of the fuel tank on your car or the size of the average supertanker, um, my guess is that the amount of energy that, that would cont would actually be

14:45 quite small. Um, I'm um, happy to be shot down on that, but I think it would simply because you're looking at uh, um, almost an infinitesimally small volume compared with the volumes that we think about when we're talking about the expansion of the universe and the accelerated expansion of the universe. So, um, how do you bottle it? Well, good question. Uh, that's the first thing you've got to do is find a way of extracting dark energy from space, putting it in a tank.

15:15 But you might that if you do that on any kind of conceivable scale, you don't have enough to make any difference whatsoever to your spacecraft, let alone accelerate it to 99.99999999% of the speed of light. So, um, I hope that's, uh, suitably satisfactory. Shooting down, Martin. Uh, I don't always shoot your theories down.

15:37 I think your, uh, ideas are uh, lovely and well worth listening to.

15:42Andrew Dunkley Yes, he's got a way, he's got a way of asking

15:45 questions that he does. Lots of, Lots of fun. Lots of fun.

15:48Professor Fred Watson He does.

15:49Andrew Dunkley Uh, thank you, Martin. Um, we've got some

15:52 live listeners, uh, uh, or viewers, um, who messaged us. And remember, uh, James from Cincinnati. Haven't heard from James in ages. Well, he's just popped up to say hello.

16:02Professor Fred Watson So.

16:02Andrew Dunkley Hi James. And uh, a question without

16:04 notice, um, which sort of goes back to our radial velocity message method of searching for exoplanets. Um, I'm wondering, um, so we already know other suns have planets, so why the extensive investigation to keep searching for more? What's the point?

16:20Professor Fred Watson Oh, it's a good question. Um, so it's all

16:23 about, it's surveying. Um, basically, uh, astronomers are, uh, inveterate surveyors. It's how we discover the large scale characteristics of the universe. And it's also how we find the outliers, the things that are really peculiar, uh, and that need explanation and that sometimes defy science as we know it and um, often result in physics being rewritten. Uh, so, uh, it's like doing population census studies. It's.

16:57 Why do you want to know how many people, uh, live in a country? And it's all about, um. Well, in the case of humans, it's all about providing the right resources for them. But in the case of. Why do you want to know how many different kinds of exoplanets there are? It's uh, because we might find exactly what we've just been talking about. The water worlds. Uh, we might find habitable worlds. We might even find a SETI signal from one of them. So, uh, this is very much an important part of the astronomers understanding of the universe. To explore and investigate as many of these things as we can.

17:34Andrew Dunkley Yeah. And of course, the most important

17:35 reason, if we do a planetary census, we can then introduce an international tax system system or intergalactic tax system, more to the point. Yes. Okay. Uh, you are listening to a Q and A edition of Space Nuts with Andrew Dunkley and Professor Fred Watson Watson.

17:57Professor Fred Watson Three, two, one.

18:00Andrew Dunkley Space Nuts. Our next question comes from

18:03 Svedon. Uh, can matter that falls into a black hole keep its angular momentum and sort of add it to the black hole's angular momentum? Uh, or does matter Fall into a black hole. Um, or does matter falling into a black hole need to shed its angular momentum, or part of it through radiating, uh, energy out into space before it can fall down the hole? If so, why can't a black hole that can retain light and spaghettify things pull things in despite their angular momentum and just add the incoming momentum to itself? That comes from Peter in Sweden.

18:45 Uh, it's one of those complicated questions that would have wiped me out at school based on some form of geometry.

18:56Professor Fred Watson Uh, I am, um. So I

18:59 don't know the answer to this question. Um, but thinking what little I do know about black holes, I would guess. Um, and I'll need to cheque this, Peter. So I apologise that this is an off the cuff answer. But I would guess that the angular momentum does. That it is additive. Uh, that you would add the angular momentum of incoming accreted material which will have it because it's whizzing around the black hole at very high speeds. Um, uh, as the black hole collapse, as the stuff crosses the event horizon and is subsumed into the black hole, uh, I would guess that actually adds to the, to the black hole's angular momentum. But I'll need to cheque. Uh, and I will do that because that's a really good question.

19:44Andrew Dunkley Okay. Well, that was easy.

19:46Professor Fred Watson Yeah, well, it wasn't because I don't know

19:48 the answer, but. But I'm guessing I, uh, I think it probably would. Yeah.

19:53Andrew Dunkley Actually reminds me, we had one we had to do

19:56 some homework on recently and I think we've. I don't know if we did it. Anyway, I'll go.

20:01Professor Fred Watson I usually make it. Yeah, I usually make notes

20:04 on things like that as well. I think you're right too.

20:07Andrew Dunkley Yeah. I might do a whole show on

20:11Professor Fred Watson things we've forgotten.

20:13Andrew Dunkley Things we've forgotten to look up.

20:15Professor Fred Watson Yeah, yeah.

20:16Andrew Dunkley Um, we might get back to you, Peter.

20:19 Uh, thanks for the question. Um, this question. This question needs setting up because, uh, it's a question, but it's not a question. Uh, and it comes from, uh, Dave. Now, I know people have accidentally called me Dave from time to time. It's nice to have a real Dave. And when I read your question, Dave, I thought, I can't just let you go. I've got to, um, preempt it with something that I thought was appropriate.

20:48Professor Fred Watson Hello, Dave. You're looking well

20:51 today.

20:53Andrew Dunkley Um, this is Dave.

20:56Berman Gorvine Greetings. This is Dave from Gilbert,

20:58 Arizona, with apologies in advance for my question. So anyway, I don't know if you, uh, heard about this, but, um, it's been reported that there's something strange in the region of our solar system somewhere between Saturn and Neptune. And I wanted to hear your opinion on the notion that it could be a black hole or a brown dwarf, or possibly a black dwarf or a brown hole out near the orbit of Uranus. So, by the way, uh, some people in the US Government have pooh, poohed this idea, while others from the US Military, such as Colin Powell and several rear admirals, are calling for a probe so we can get to the bottom of this.

21:36 Now, I was wondering if you can get behind this notion or if you care to rebut it. In either case, I'm looking forward to hearing your posterior analysis. Uh, I also have a question about. Dang it, I gotta go. That's my landlord calling. I must be in arrears again on my rent. I'll have to call you back later with my question, super massive dark matter. Although that may actually be more of a medical question.

21:59 Anyway, I wanted to say that your podcast is a real asset to the astronomical community. No ifs, ifs, ands, or buts about that. So cheers to you. Slash. Bottoms up.

22:11Andrew Dunkley Ah, that's very clever, Dave. Um, I

22:14 don't think we've ever had. You ready for this one, Fred Watson? I don't think we've ever had such an asinine question.

22:23Professor Fred Watson Uh, yeah, it's, um. It's got

22:26 every buzzword in the dictionary in there, hasn't it?

22:29Andrew Dunkley It sure has.

22:30Professor Fred Watson Especially the no if so. But I like that. I

22:32 loved it. I loved it.

22:34Andrew Dunkley Well done, Dave. I like that he spent

22:37 time thinking about that and. And come up with. Yeah, all those superlatives.

22:43Professor Fred Watson It's very, very well done. Um, my

22:46 answer to it is, uh, yes, accreted material does add to the angular momentum of a black hole.

22:53Andrew Dunkley Oh, you looked it up?

22:55Professor Fred Watson I looked it up well, while I was enjoying

22:57 Dave's question, because I know, having heard it before, that I didn't have to provide an answer to that.

23:04Andrew Dunkley Yeah, actually, the live audience thought

23:06 that was brilliant, too. We've got some very good remarks about it.

23:10Professor Fred Watson So. Yeah.

23:10Andrew Dunkley And another question, without notice,

23:12 Fred Watson, when AI first came along, um, the. The questioner can remember that, and. Well, I think we all can. But can Professor Watson say, um, whether or not AI is being used by seti? Didn't we get that question the other day? Or a similar question about the use of AI in, um. In, uh, in astronomy? I don't know if we did it in regard to the search for extraterrestrials yeah.

23:45Professor Fred Watson Yes, we did, we did. About the way it can be

23:48 used to really tease out information that might otherwise, uh, go unnoticed because of the statistical methods that we use. So, um, uh, it's an intriguing thought though, uh, when you turn it the other way around in regard to seti, whether the putative extraterrestrial intelligence itself is using AI and may even be AI, um, how would we disentangle that from, um, a non AI, um, uh, extraterrestrial entity?

24:25 It leads us into all kinds of uncharted waters. Does. That's quite an interesting question.

24:30Andrew Dunkley It does indeed.

24:32 Um, and back to Dave's, uh, tongue in cheek question. Uh, of course there is an object that they think is out there somewhere that we haven't yet found, and that's called Planet Nine. So even though I know, I know where he was coming from, he was, he was being extra funny and the comments are still coming from people who thought it was. Um, but in reality there, there is definitely a possibility of something out there that they haven't found, but they, they know it exists, whether it's a planet or a bunch of stuff, um, that's affecting the outer solar system, I suppose.

25:19Professor Fred Watson Correct. And it's been in the news again

25:21 recently. Actually. I almost, uh, put it up as one of the topics we should cover that, um, there have been more comments on the possibility of Planet Nine. The original researchers who highlighted this, um, Mike Brown and uh, one of his colleagues, they have basically said that if it's not Planet Nine, there is still something that needs explained, which is more or less what you've just said. Ah, but, um, they are still very confident that we will, uh, unearth a very distant planet, quite a massive one, that is affecting the orbits of these, um, trans neptunian objects, which are, ah, in very elongated orbits.

26:05 So the jury's still out on it. It's one of these, I think it's one of these questions that we'll talk about for some time to come, Andrew.

26:12Andrew Dunkley And like, the questions are coming, but we

26:14 can't keep. We can't. Like, we'll be here all day if we go. But, um, back to the AI question. How else has AI been used in astronomy? Uh, I think the possibilities, uh, are endless, aren't they?

26:28Professor Fred Watson Yeah, pretty. Well, um, uh, it's,

26:30 it's, you know, I mean, people, the main ways, the way I've just described in terms of actually using it to advance astronomy, people use AI, I'm sure, for writing their papers. And I do know one of my colleagues in Arizona uses, uh, AI to mark the papers as well. Oh, uh, wow.

26:50Andrew Dunkley Looking for patterns of people who didn't

26:53 think for themselves.

26:55Professor Fred Watson I think looking for the whole hug. Um, he

26:58 presented a paper. This was at a conference. Was it last year or the year before? I think it was the year before last. Uh, which, um, he was very impressed with, um, the, uh, I don't know which breed of AI he was using, but he was very impressed with the outcomes from that and said they actually matched the human marking results, uh, very well. But just aside from that, I think, um, the main use in advancing astronomy is very much in applying it to these very large data sets.

27:28Andrew Dunkley Yeah, I have used it quite a

27:31 bit, uh, in researching elements of my books when I write. Um, I've already started a prequel to my latest to my new trilogy, which is, um, going well and thanks to everyone who's, who's bought a copy. Uh, and it's lots of fun. I actually, uh, have found a way of using AI, um, that I, uh, really enjoy. It's not just about doing a search, but you can sit there and literally have a conversation and, and weed out information as you go. It's, It's a lot of fun. Um, my wife thought I was, you know, a bit, um, beyond my station using AI because I'm, I'm not a young person. Um, she went to the hairdresser the other day and, um, the hairdresser said, I'm going to redesign my salon. I asked Chat GPT to design it for me. Well, now she's using

28:25 AI, isn't she? Yeah. Okay. Wouldn't, wouldn't do it if I suggested a it. But the hairdresser, they know everything. Um, okay, thanks to everybody who's sending questions and, uh, our live audience for contributing as well. It's been a lot of fun and thank you, Fred Watson. Uh, that brings us to the end of yet another episode.

28:46Professor Fred Watson It does, doesn't it? Yeah, well, I've learned

28:48 something in that one. Um, that, uh, yes, angular momentum does, ah, add from accretive material. So there you go.

28:56Andrew Dunkley All right, uh, we'll see you soon,

28:58 Fred Watson. Thank you.

29:00Professor Fred Watson Cheers.

29:00Andrew Dunkley For now, Professor Fred Watson Watson,

29:02 astronomer at large. And if you've got questions for us, please jump on our website, spacenutspodcast.com or spacenuts IO if you're a lazy typist. And click on the AMA tab at the top and send us your text or audio questions. Don't forget to tell us who you are and where you're from. We just like to know so that we can spam you later. Uh, and, uh, thanks to Huw in the studio. Um, although Huw couldn't be with us today. Uh, you know, we've been, um, searching for. For Planet nine, which is difficult to find, but I reckon we'll probably find it before we find Huw.

29:36 And from me, Andrew Dunkley, thanks for your company. We'll see you on the next episode of Space Nuts. Bye.

29:42Professor Fred Watson Bye.

29:43Andrew Dunkley You've been listening to the Space Nuts

29:45 podcast, available at Apple Podcasts, Spotify, iHeartRadio or your favourite podcast player. You can also stream on demand@bytes.com.

29:57Professor Fred Watson this has been another quality podcast

29:59 production from bytes.com.

30:01Berman Gorvine um,