The Intricacies of Angular Momentum - What Happens Near Black Holes | Space Nuts: Astronomy...

[00:00:00] [SPEAKER_02] Hi there, thanks again for joining us. This is Space Nuts. It's a Q&A edition where we answer audience questions. And I think we've got our very first question from Yemen. Hussein has sent it a question asking about radial velocity. Martin, one of our regular contributors, has a dark matter he wants to discuss. Peter in Sweden is talking angular momentum. That is the angular momentum of matter falling into a black hole.

[00:00:30] [SPEAKER_02] And a real bummer of a question. We'll tell you all about it on this episode of Space Nuts.

[00:00:38] [SPEAKER_04] 15 seconds. Guidance is internal. 10, 9. Ignition sequence start. Space Nuts. 5, 4, 3, 2. 1, 2, 3, 4, 5, 5, 4, 3, 2, 1. Space Nuts. Astronauts report it feels good.

[00:00:53] [SPEAKER_02] And he's back again to solve all your riddles. It's Professor Fred Watson, astronomer at large. Hello, Fred.

[00:01:00] [SPEAKER_05] Hello, Andrew. Good to see you again. I always hoped we'd get back together again one day.

[00:01:05] [SPEAKER_02] Yeah. It's been ages. About two minutes. Yeah. Anyway, I love the Q&A program. I really do because it gives people a chance to dump on us and see how much we can mess it up. And that's always fun.

[00:01:25] [SPEAKER_02] We might get straight into it, Fred. 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 this one comes from Hussein who says, I'm a huge fan of the podcast calling in from Yemen. See, I was right. It was Yemen.

[00:01:46] [SPEAKER_02] 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. Your voices are incredibly soothing, though I promise I do actually listen to the science before I drift off. I appreciate that. My wife says I keep her awake because I snore, but I don't believe it. I've never heard me.

[00:02:11] [SPEAKER_02] 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. 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,

[00:02:39] [SPEAKER_02] would they actually be able to untangle that messy combined signal to identify individual planets and their specific characteristics? 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, Hussein.

[00:03:05] [SPEAKER_05] It's a great question. And the answer, Hussein. is both the two alternatives that Hussein's put forward. 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, so what kind of strength of signal you get

[00:03:34] [SPEAKER_05] in terms of measuring the velocity of the star itself by this Doppler wobble method to analyse for planets. But also it depends on the sizes of the planets and on their mix as well. So 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. Saturn comes next in terms of its size

[00:04:03] [SPEAKER_05] and then the other two gas giants, Uranus and Neptune. The terrestrial planets or rocky planets also have an effect, but because their masses are much lower, the effect is also much lower. It's mitigated slightly by the fact that they're nearer to the sun, but nevertheless, they're much, much weaker than the gas giants.

[00:04:29] [SPEAKER_05] So if you were, you know, an alien on a planet orbiting a star, maybe eight or nine light years away, something like that, which is the distance to Sirius, the brightest star in the sky, and you're looking back at the solar system, the first thing you would see would be the main motion, which would be due to Jupiter, because its mass is so much bigger than the other planets.

[00:04:56] [SPEAKER_05] However, if you had really highly accurate velocity measurements and you'd need them almost to centimetres per second accuracy, it can be done. There are ways of calibrating spectrographs to let you do this. But if you did have these really accurate readings and you could do your measurements almost 24-7, which you can't because certainly if you were anything like the Earth,

[00:05:25] [SPEAKER_05] you've got daylight coming in the way. But, you know, 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 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.

[00:05:53] [SPEAKER_05] And you can disentangle those. There is a technique called Fourier analysis. It uses things that we call fast Fourier transforms, which is a mathematical tool that 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.

[00:06:21] [SPEAKER_05] In other words, how many regular passages are there caused by individual planets, if I can put it that way. So you can tease out the effect of each individual planet because they all have different periods of revolution around the Sun, in the case of, you know, if you're looking at the solar system. So if you've got good enough data, you can, as Hussain suggests,

[00:06:48] [SPEAKER_05] identify the individual planets and their specific characteristics. But if your data aren't too 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.

[00:07:00] [SPEAKER_02] Yeah. Early on, when we started discovering 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?

[00:07:13] [SPEAKER_05] That's right. And in fact, it highlights 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. It was when the Kepler spacecraft and TESS, the other planet-finding spacecraft, when they started looking in detail

[00:07:41] [SPEAKER_05] at the way the brightness of stars changed as planets passed in front of their parent stars. That's when we started discovering the smaller ones, because the smaller ones are actually easier to discover that way.

[00:07:57] [SPEAKER_02] Here's a dumb question. Can we look with accuracy at the wobble of our own sun because of the planets surrounding it, including our own?

[00:08:13] [SPEAKER_05] Yeah. You can, yes. And you can actually find diagrams showing the way, it's what we call the barycentre, the barycentre of the solar system is its centre of gravity, which takes into account not just the sun, but the planets as well. And the barycentre does wander around. It's mostly, it's inside the sun.

[00:08:41] [SPEAKER_05] It does come outside the sun from time to time. But you can find charts showing exactly how that happens, you know, little maps of the way the barycentre of the solar system wanders around relative to the sun.

[00:08:56] [SPEAKER_02] Okay. I wondered. I didn't know if we could do it within our own sphere, so to speak. Not a dumb question at all. Absolutely not. There you go. I occasionally ask one that's adequate. And thank you to Hussain for sending that question in from Yemen. Lovely to hear from you. And you're listening to Space Nuts with Andrew Dunkley and Professor Fred Watson. Let's take a quick break from the show to tell you about our sponsor, NordVPN.

[00:09:26] [SPEAKER_02] 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. And that means when you're connecting from an airport, a hotel, a cafe or any public network for that matter, you can have a greater level of protection

[00:09:54] [SPEAKER_02] for your internet traffic. NordVPN also lets you secure up to 10 devices with a single account. So you can protect your phone, your computer, your tablet, your TV or any other compatible device. And it's not just about privacy. Depending on the plan you choose, NordVPN also offers security features, scam and phishing protection, ad and tracker blocker, malware protection, password management. That's the tool I love the most, actually,

[00:10:23] [SPEAKER_02] the password management system. I would die without it. It is so very handy. You don't have to remember anything except your one password to get in to the Nord tool that looks after everything else. There's a 30-day money-back guarantee as well, giving you the opportunity to try before you buy and see if it's right for you. And I really do think it will be. They're the best in the business and they're our sponsor. So go to nordvpn.com slash space nuts, a special URL for Space Nuts listeners

[00:10:53] [SPEAKER_02] to find out more. That's nordvpn.com slash space nuts. And don't forget the code word space nuts.

[00:11:01] [SPEAKER_01] I'm going to step off the lamp now. Space Nuts.

[00:11:15] [SPEAKER_02] Let's hit you with an audio question from one of our regular contributors.

[00:11:20] [SPEAKER_00] Hello, Space Nuts. Martin from Potomac, Maryland, USA. Writer extraordinaire in many genres with a slightly less silly, though still highly speculative, question. Since dark energy

[00:11:48] [SPEAKER_00] is thought to pervade the entire universe, would it be possible, at least in theory, to harness that energy to drive spaceflight? And if so, could you make a spacecraft go arbitrarily fast by that means? You know, 99.9%

[00:12:18] [SPEAKER_00] of the speed of light for that extra-relativistic flip so that when you step out at your destination, the universe has aged significantly, but you, the traveller, have not. Can't wait for the answer, which will probably involve

[00:12:46] [SPEAKER_00] Professor Watson shooting me down in flames as usual. Berman Gorvine over and out. Out.

[00:12:57] [SPEAKER_02] Thanks, Martin. Martin sent me a copy of two of his latest books, which I haven't had a chance to read. I did promise I would, but I was too busy writing my own. But I will get to them, Martin. Thanks for sending those in. Fire away, Fred. To shoot him

[00:13:17] [SPEAKER_05] down. I have to say, these questions do sound like the making of another of Martin's books. books. So, you know, putting the ingredients of science into the books is a great idea. If you're going to write science fiction, it's nice to have some science in it as well. That's what I do. Yes, you do. What Martin's question made me think about was the number

[00:13:47] [SPEAKER_05] of joules of energy contained, represented by dark energy per cubic meter of space. And I've no idea what that is, but I bet per cubic meter, it's actually quite small because we only see the effects of dark energy when we look at the universe on a very large scale. When we look billions of light years out, we start to see its effects. We can tell that the

[00:14:17] [SPEAKER_05] universe has been expanding more rapidly since the universe was about half its present age. So I guess, you know, if you imagine a tank full of dark energy on any kind of human scale, whether it's the size of the fuel tank on your car or the size of the average super tanker, my guess is that the amount of energy that that would contain would actually be quite small.

[00:14:47] [SPEAKER_05] I'm happy to be shut down on that, but I think it would, simply because you're looking at 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 how do you bottle it? Well, good question. 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, but you might find that if you

[00:15:17] [SPEAKER_05] 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 99.99999999999999% of the speed of light. So I hope that's a suitably satisfactory shooting down, Martin. And I don't always shoot your theories down. I think your ideas are lovely and well worth listening to. Yes.

[00:15:43] [SPEAKER_02] He's got a way of asking questions that is lots of fun. He does. Thank you, Martin. We've got some live listeners or viewers who messaged us. And remember James from Cincinnati? Haven't heard from James in ages. Well, he's just popped up to say hello. So hi, James. And a question without notice, which sort of goes back to our radial velocity method of searching for exoplanets. I'm wondering, so we already

[00:16:13] [SPEAKER_02] know other suns have planets, so why the extensive investigation to keep searching for more? What's the point?

[00:16:19] [SPEAKER_05] Oh, it's a good question. So it's all about, it's surveying, basically. Astronomers are 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, and that need explanation, and that sometimes defy science as we know it, and often result in physics being rewritten.

[00:16:50] [SPEAKER_05] So it's almost, it's like doing population census studies. It's why do you want to know how many people live in a country? and it's all about, 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 because we might find exactly what we've just been talking about, the water worlds, we might find habitable worlds, we might

[00:17:19] [SPEAKER_05] even find a SETI signal from one of them. So 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

[00:17:33] [SPEAKER_02] can. Yeah, and of course the most important reason, if we do a planetary census, we can then introduce an international tax system, or intergalactic tax system, more to the point. Yes. Okay, you are listening to a Q&A edition of Space Nuts with Andrew Dunkley and Professor Fred Watson. Our next question comes

[00:18:02] [SPEAKER_02] from Sviden. Can matter that falls into a black hole keep its angular momentum and sort of add it to the black hole's angular momentum? Or does matter fall into a black hole or does matter falling into a black hole need to shed its angular momentum or part of it through radiating energy out into space before it can fall down the hole? If so, why can't a black hole that can retain

[00:18:32] [SPEAKER_02] 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. It's one of those complicated questions that would have wiped me out at school based on some form of geometry.

[00:18:57] [SPEAKER_05] I am, so I don't know the answer to this question, but thinking what little I do know about black holes, I would guess, and I'll need to check this, Peter, so I apologise that this is an off-the-cuff answer, but I would guess that it is additive, 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

[00:19:26] [SPEAKER_05] speeds as the stuff crosses the event horizon and is subsumed into the black hole. I would guess that actually adds to the black hole's angular momentum, but I'll need to check and I will do that because that's a really good question. Okay, well, that was easy. Well, it wasn't because I don't know the answer, but I'm guessing, I think it probably would.

[00:19:53] [SPEAKER_02] Yeah, it actually reminds me, we had one, we had to do some homework on recently and I think we've, I don't know if we did it, anyway, I'll go through my notes.

[00:20:02] [SPEAKER_05] Yeah, I usually make notes on things like that as well. I think you're right too. Yeah, we might do a whole show on follow-ups.

[00:20:11] [SPEAKER_02] On things we've forgotten. Things we've forgotten to look up. Yeah. We might get back to you, Peter. Thanks for the question. This question, this question needs setting up because it's a question but it's not a question. And it comes from Dave. Now, I know people have accidentally called me Dave from time to time. It's nice to have a real Dave. Dave. And when I read your question, Dave, I thought I can't just

[00:20:41] [SPEAKER_02] let you go. I've got to preempt it with something that I thought was appropriate. Hello, Dave. You're looking well today.

[00:20:53] [SPEAKER_01] This is Dave. Greetings. This is Dave from Gilbert, Arizona with apologies in advance for my question. So anyway, I don't know if you heard about this but 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.

[00:21:23] [SPEAKER_01] So by the way, some people in the U.S. government have pooed this idea while others from the U.S. military such as Colin Powell and several rear admirals are calling for a probe so we can get to the bottom of this. 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. I also have a question about, dang it, I got to go, that's my landlord calling, I must be in arrears again on my rent. I'll have to call you back later

[00:21:53] [SPEAKER_01] with my question about supermassive dark matter. Although that may actually be more of a medical question. Anyway, I wanted to say that your podcast is a real asset to the astronomical community. No ifs, ands or buts about that. So cheers to you slash bottoms up.

[00:22:11] [SPEAKER_02] Oh dear. That's very clever, Dave. I don't think we've ever had, you ready for this one, Fred? I don't think we've ever had such an asinine question. Oh dear.

[00:22:23] [SPEAKER_05] Oh dear. Yeah, it's got every buzzword in the dictionary in there, hasn't it? It sure has. Especially the no ifs or buts. I like that. I loved it. I loved it. Well done, Dave.

[00:22:35] [SPEAKER_02] I like that he spent time thinking about that and come up

[00:22:39] [SPEAKER_05] with all those superlatives. It's very, very well done. My answer to it is yes, accreted material does add to the angular momentum of a black hole.

[00:22:53] [SPEAKER_03] Oh, you looked it up.

[00:22:54] [SPEAKER_05] I looked it up while I was enjoying Dave's question because I know having heard it before, I didn't have to provide an answer to that.

[00:23:04] [SPEAKER_02] Yeah, actually the live audience thought that was brilliant too. We've got some remarks about it. Very good. And another question without notice, Fred. When AI first came along, the questioner can remember that and I think we all can, but can Professor Watson say whether or not AI is being used by SETI. Didn't we get that question

[00:23:34] [SPEAKER_02] the other day or a similar question about the use of AI in astronomy? I don't know if we did it in regard to the search for extraterrestrials. Yeah.

[00:23:45] [SPEAKER_05] Yes, we did. We did. About the way it can be used to really tease out information that might otherwise go unnoticed because of the statistical methods that we use. So it's an intriguing thought though when you turn it the other way around in regard to SETI, whether the putative extraterrestrial intelligence itself is using AI and may

[00:24:14] [SPEAKER_05] even be AI. how would we disentangle that from a non-AI extraterrestrial entity? It leads us into all kinds of uncharted waters. That's quite an interesting question.

[00:24:30] [SPEAKER_02] It does indeed. And back to Dave's tongue-in-cheek question. 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 where he was coming from, he was being extra funny and the comments are still coming from people who thought it was. But in reality

[00:25:00] [SPEAKER_02] there is definitely a possibility of something out there that they haven't found but they know it exists whether it's a planet or a bunch of stuff that's affecting the outer solar system I suppose.

[00:25:19] [SPEAKER_05] Correct. And it's been in the news again recently actually I almost put it up as one of the topics we should cover that there have been more comments on the possibility of Planet Nine. The original researchers who highlighted this, Mike Brown and 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

[00:25:49] [SPEAKER_05] you've just said. But they are still very confident that we will unearth a very distant planet quite a massive one that is affecting the orbits of these trans-Neptunian objects which are in very elongated orbits. So the jury is still out on it. It's one of these questions that we'll talk about for some time to come Andrew.

[00:26:12] [SPEAKER_02] And the questions are coming but we can't keep, we can't, like we'll be here all day if we can. But back to the AI question, how else has AI been used in astronomy? I think the possibilities are endless, aren't they? Yeah, pretty well.

[00:26:30] [SPEAKER_05] It's, you know, I mean people, the main way is 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 AI to mark the papers as well. Oh, wow. He said...

[00:26:50] [SPEAKER_02] Looking for patterns of people who didn't think for themselves?

[00:26:55] [SPEAKER_05] I think looking for the whole hog. He presented a paper, this was at a conference, was it last year or the year before? I think it was the year before last, which he was very impressed with the... 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 very well. But just aside from that, I think the main use in advancing astronomy is very much

[00:27:24] [SPEAKER_05] in applying it to these very large data sets.

[00:27:27] [SPEAKER_02] Yeah. I have used it quite a bit in researching elements of my books when I write. I've already started a prequel to my new trilogy, which is going well, and thanks to everyone who bought a copy. And it's lots of fun. I actually have found a way of using AI that I really enjoy. it's not just about

[00:27:57] [SPEAKER_02] doing a search, but you can sit there and literally have a conversation and weed out information as you go. It's a lot of fun. My wife thought I was a bit beyond my station using AI because I'm not a young person. She went to the hairdresser the other day and the hairdresser said I'm going to redesign my salon. I asked ChatGPT to design it for me. Well, now she's using AI, isn't she? Yeah. Okay.

[00:28:27] [SPEAKER_02] Wouldn't do it if I suggested it. But the hairdresser, they know everything. Okay. Thanks to everybody who's sending questions and our live audience for contributing as well. It's been a lot of fun. And thank you, Fred. That brings us to the end of yet another episode.

[00:28:45] [SPEAKER_05] It does, doesn't it? Yeah. Well, I've learned something in that one that, yes, angular momentum does add from accreted material. So there you go.

[00:28:56] [SPEAKER_02] All right. We'll see you soon, Fred. Thank you. Cheers for now. Professor Fred Watson, 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. And thanks to Hugh in the studio. Although Hugh couldn't be

[00:29:26] [SPEAKER_02] with us today, we've been searching for Planet Nine, which is difficult to find, but I reckon we'll probably find it before we find Hugh. And from me, Andrew Dunkley, thanks for your company. We'll see you on the next episode of Space Nuts. Bye-bye.

[00:29:42] [SPEAKER_03] Space Nuts. You'll be listening to the Spacenuts podcast. Available at Apple Podcasts, Spotify, iHeartRadio, or your favourite podcast player. You can also stream on demand at Bites.com. This has been another quality podcast production from Bites.com.