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Get matched with a qualified therapist and start clearing your mental inbox today at BetterHelp. Visit BetterHelp.com slash random podcast for 10% of your first month of online therapy. Ready to launch your business? Get started with the commerce platform made for entrepreneurs. Shopify is specially designed to help you start, run and grow your business with easy customizable themes that let you build your brand, marketing tools that get your products out there, integrated shipping solutions that actually save you time from startups to scale up online, in person and on the go. Shopify is made for entrepreneurs like you. Sign up for your $1 a month trial at Shopify.com slash setup. Hello and welcome to another bonus episode of the supermassive podcast from the Royal Astronomical Society. With me science journalist Izzy Clark, astrophysicist Dr Becky Smithers and the society's deputy director Dr Robert Massey. We've had a lot of questions and I've always enjoyed them. I feel like it's been a while since we've all been on this call. So Becky, Sean O'Rourke has a question about rogue black holes. So before we dive into that, can you actually explain what is a rogue black hole? Yeah, rogue basically means it's wandering into stellar or into galactic space. So in between stars or in between galaxies, it's not bound in orbit to anything else, whether that's another star that it might be orbiting round or a star cluster or even the center of the galaxy. It is just freely roaming. And that feels like we should do a whole episode on them. Rogue anything is we should go rogue one. Supermassive gone rogue. Rogue stars, rogue planets, rogue black holes. Okay. Right. So on to Sean's question, who says, Hey gang, greetings from New Hampshire, thanks for the engaging content and continued success with the podcast. Well, thank you. Very nice. Nice part of the world as well, especially at this time of year. Yeah, definitely. He says, been reading more about rogue black holes. So Sean has sent in a few questions here, Becky. First one, is beetle juice large enough to produce a black hole when it goes supernova or will its remnant be something of another type of by-product? Unknown, really. It's right on the boundary, beetle juice of around about 15 times heavier than the sun, which is kind of like the boundary of where things like that tend to become neutron stars and things heavier than that tend to become black holes. So it all sort of depends what happens when beetle juice goes supernova and what its exact mass is because we also, we can't measure it that precisely either to know exactly which side of the boundary it will fall on. And it also depends how heavy its core is as well. And that's really the crucial thing because if the supernova is very energetic, so the actual part where the supernova is, it happens because there's no process in the center of the star anymore that can actually produce energy to resist the crush of gravity downwards. So everything starts to collapse inwards and then all the outer layers of the star rebound off the core. So if that rebound is very energetic and it takes more of the material outwards with it, then you've got less material left in the core. And therefore you're probably going to collapse down into a neutron star. You're not going to be heavy enough to make a black hole, which is when you've squished all the space out of atoms, right? And all you've got is neutrons as tightly packed together as they can be. Or if less than the material is rebounded, you've got more left in the core, which means, you know, you're going to have a heavier core, which when it does collapse under gravity, you might end up with something where the escape velocity is then faster than light and you'll get an event horizon and a black hole forming. And we don't know what those ones are made of. So in terms of beetle juice, not only do we not really know when it's going to go supernova, but we think it might be soon, at least astrophysically, soon, the next few hundred years. And we don't really know what it's going to make at the end, either. Okay. And then the next part of Sean's question is, how close would a decent-sized rogue black hole have to get to the solar system to affect the sun and planet's gravitational effects? I will caveat this question by saying, we don't think there's a rogue black hole. I know the solar system before I start to freak people out. But first thing I'm going to do, this is where I remind people, it doesn't matter if it's a black hole or a star of the same mass, right? If it's heavy, gravity only cares about mass and distance. It doesn't care about how dense the thing is, right? So everything I'm about to say would also be true if you had like a rogue star coming close to the solar system as well. This is not black hole fear mongering. We're nothing to fear from black holes. Black holes are our friends, okay? So let's say that we've got something like, I mean, you said a decent-sized rogue black hole, Sean. Let's say we've got a black hole 10 times heavier than the sun, just for nice numbers, right? That's typical as well, what you'd get when you have a supernova formed a black hole as well from a very massive star. So let's say we start with this rogue black hole a light year away, which is well closer than any of the nearest star, the nearest star is four light years away. So already we're getting quite close to the solar system. Nothing to worry about with only a light year away. The sun's gravity is still always going to be dominant when you have still something at that distance. But as it would get closer, the objects obviously furthest out from the sun in the sort of aught cloud and the Kuiper Belt, they're the things that are obviously going to have their orbits influenced first because they're further away from the sun, they're not as tightly held. And so you might get some distant comets or asteroids maybe ejected from the solar system or maybe even drawn into orbit around this rogue black hole if it did get close enough to them. If you're talking about, I want pure chaos. I want to disrupt the orbits of the major planets. Obviously, if we start with Neptune furthest out from the sun, that's like 30 times the Earth's sun distance. So I did some back of the envelope calculations for like Sean. We love it when you do that. And if you work through the maths, you're looking at a rogue black hole being at a distance of around 9500 times the Earth's sun distance before the pull of gravity to this rogue black hole about 10 times heavier than the sun is stronger for Neptune than the pull from the sun is. Now, you're obviously going to get some tugging from the black hole before that some perturbance because you're going to have like a three body problem of like some Neptune black hole before it gets to the point where the black hole's gravity is even stronger. So let's say 200 times the Earth's sun distance is where you start to really like notice something might be further out than that. But that's sort of like a ballpark figure for you Sean, if you will. That's when you start to notice less than 100 times the Earth's sun distance is where chaos starts. And once you know you're anywhere near like 10 times Earth's sun distance from us is when it starts to get absolutely catastrophic for the solar system and for us here on Earth as well. Again, not happening, not that we know of. And if this would be true, not just for a black hole, but for any rogue object that came close to the solar system too. Oh gosh, I really enjoyed that. Thank you Sean. Thank you Becky. And so for this next batch of questions, I think it seems to be the theme of this episode is the next questions are from someone called Nicole Boisvert. Now she's clearly been binging our shows and sending us questions as she's gone. So she sent us 12 brilliant questions while she was listening through our back catalog, which is amazing. One for each month is. So I picked one for both of you. So Robert, let's start with this one. With JWST, are we able to see satellites natural or made orbiting exoplanets when they transit their sun or with other telescopes or could we eventually do this to detect intelligent life? Yeah, well Nicole, what you're talking about her is finding things called exo moons, which mean moons around exoplanets. And exoplanets are, you know, we've got a lot better at detecting them. There's been an awful lot detected by transits where they move in front of a star and we see the light drop down a little bit. And then we assume there's an exoplanet there, measure its properties, etc, etc. And then other techniques like it pulls on its star back and forth and we measure that tiny, tiny change in the light, the tiny redshift and blueshift that results with a moon, because the moons are small and definitely smaller than the planets, they go around, you know, by definition, and they're lighter than both of those techniques are going to be a lot harder. And they don't, as far as I know, there are no definitive discoveries of these yet, not even with JWST. I have a lot of colleagues trying to do this. Yeah. They desperately want to find exo moons and you're just looking for that extra little blip on a transit or something. Yeah. Yeah, I really wanted to find it, but they're all struggling. It's so much noise, basically, I guess. Exactly. Yeah, it's really difficult to do. I mean, you look at tiny, tiny to bits, a bit of a signal. But the question is timely, because it turns out there's a paper in our own journal, Monthly Notices, the RES, where they were discussing a candidate and there are two examples of hot Jupiter planets. And these are planets which are big gas giants that are close to their star. And the first one of these wasp 39b, which was one of the ones that was named in a competition a few years ago, Bocaparans, I think it's pronounced, is a giant planet 700 light years away and it orbits its star every four days. It races around and it's scorched. And previously astronomers had found sulfur dioxide in its atmosphere and the new work suggests instead that there's a certain variation in this, that they attribute to having an exo moon origin. And the analogy is something like Io, the moon that goes around Jupiter, which has a, you know, churns out stuff from volcanic activity. So there's a suggestion it might be that. Obviously, no one knows the short. It's really hard to definitively answer this. And the same team also talk about an exo moon around a different planet wasp 49b, you know, he could be way out in space again. As for other telescopes, well, things like the extremely large telescope will help see more exoplanets when that comes. That's the one being built in Chile, be the biggest telescope in the world, nearly a 40 meter wide mirror. When it comes on stream, that's one of its jobs is to find Earth like planets around the nearest stars if they're there. Seeing the moon will still be really tough. Their moons will be really hard, but it might get us a bit closer along that. And as for the thing about detecting intelligent life, I imagine what you're referring to when you talk about maybe made satellites or things like these techno signatures idea. So the idea you have these very large structures that sometimes are suggested for the way that the property of some stars vary, the light of some stars varies. So they're looking at this dip down, maybe there's this huge death star there or some Dyson sphere or these these big structures that people speculate about. They're pretty controversial. There aren't very many people who actually say there's any evidence whatsoever of those things being there. So if you want to find intelligent life around another star and definitely intelligent life, beyond doing things like finding signals, I think it's going to be pretty tough. Maybe you could do things like detect certain pollutants that can only be made in artificial manufacturing processes, which would be quite hard, but maybe you could do that other than that. It's going to be the signals. You're not going to get a telescope that's good enough to see not just the presence of a planet, but actually see such detail on its surface that you could confirm that intelligent life had made it. I think that would be next level really. You'd basically have to send a space probe to that system to find those things. And that's going to be really hard too. Tens of thousands or hundreds of thousands of years of that. So definitely a legacy project there. Yeah. I mean, I was at the European Space Agency recently and there was a panel talk about studying exoplanets. We've got three missions upcoming and all at various different phases, but collectively, if they could all look at exoplanets and understand them more, it would be so amazing to know if this is something that they could look into in terms of exomoons as well, because there's Keopsis one, there's Ariel, and there's also Plato, so they're all having different functions. Plato. Well, this is what I said. I called it Plato, but they were all calling it Plato. I've never heard anyone call it Plato. Exactly. So I introduced it on stage as Plato and they were all talking about Plato and I was like, have I just announced the wrong mission for the entire room? But anyway, the panel itself was amazing. But imagine if you had three missions that were all collectively looking at this and working on this together. That would be amazing. Right, back onto Nicole's questions. Becky, we've had this one as well, which is, is there a theoretical upper limit to the density of black holes? I don't understand how they can just keep absorbing more mass. So this is a weird one, actually, because as black holes grow in mass, their density drops. It's bizarre because actually, I mean, really, if we're sort of being mathematical about this, if we think about a black hole and how we describe it, we say that all the mass is actually condensed into the singularity, like into an infinitely small, infinitely tiny space, which doesn't really have a definable anything, including a volume. So it doesn't have a density. But if you were going to define the black hole as everything just inside the event horizon, which really is kind of what we define as the black hole in the first place, the point where you're not getting any more light from that region of space, that sphere in space, then that does have a set radius. So then you can work out a volume and you can work out a density as mass divided by volume, whether that has any physical meaning that was debatable. And that's what I was talking about before where I was like, if the mass goes up, the density goes down. So the reason for that is if you think about it as a black hole grows in mass, the event horizon actually pushes outwards. So the radius gets bigger. And the radius gets bigger, sort of, quite proportional to the mass. But density is mass divided by volume and volume is proportional to radius cubed. So if you up the mass and the radius proportionally, then you really drop the density. So while stellar mass black holes, like we were talking about with the rogue black holes, they can be densities, denser than atomic nucleus, incredibly dense. Whereas when you get up to like supermassive black holes, like 100 million times heavier than the sun, they're less dense than water, which is 1,000 kilogram meter cubed density. So, Nicole, if we were going to find the maximum density that we could have for a black hole, we'd have to find the least massive black hole. Now, we can get a sort of like a lower limit of where we think that border is when something goes supernova of whether we get neutron star or black hole. That's known as the Tolman-Oppenheimer-Volkov limit and it's around about 2.17 times the mass of the sun. The jury is kind of still out on where exactly that is. So I thought instead we'll go for the lowest mass black hole that we've ever found, at least, which is 3.04 times the mass of the sun. That gives a density, if you say that it's mass, right? You assume that everything is inside the event horizon. That gives a density, and I'm using density in like quotes there, of 2 million trillion kilograms per meter cubed. And again, for context, water is 1,000 kilograms per meter cubed. So that I think is interesting that we could say, okay, that's our upper limit in terms of observational upper limit. But you did ask for a theoretical upper limit call. Okay, here we go. Here comes that envelope again. So hypothetically, there is also something that we think called primordial black holes, which form in the early universe from the sort of quantum fluctuations that are going off, where you could just have like random little clumps of mass that come together that happen to then give you a density that would collapse you down into a black hole. And so if you think about, okay, well, what's the dearest, tiniest primordial black hole that you could possibly make, then that would be a plank mass, is what it's called for all the quantum physicists out there. 0.00001 grams, I'm sure you were expecting more notes there, but in terms of grams, a plank mass is sort of like almost like a normal amount. That would give you a density, though, of 7 times 10 to the 95 grams to meters cubed, which is a 7 with 95 zeros after it. It's just in terms of like the radius you would have, and therefore like if you were never head and horizon, and then what the density would be. As I said, I don't think these numbers actually mean anything. But it's a very strange concept to wrap your head around, is that if you increase the mass, the density drops. Yeah, I'm going to be thinking about that all day. I just know that that's going to be a good It comes back to sort of, it actually does make sense. If you think about Einstein's theory of general relativity and like what gravity, how we describe gravity as like big objects curving space, right? And we think, I always explain this to people and people think it's very strange, but like if you think about like a stellar mass black hole 10 times heavier than the sun versus a supermassive black hole a billion times heavier than the sun, yes, okay, the sort of well of curvature that it makes will be deeper, but the gradient is less steep. So you think about it in terms of mountains, like a stellar mass black hole is like, it's a not very high mountain, it's like say 200 meters, but it's like a cliff side. Whereas a supermassive black hole is like, you know, Everest, but with a really shallow, well it's Snowden, right? It's a really shallow gradient, so it's really easy to climb almost, you know? So it's one of those, it's sort of the inverse of that when it comes to black holes, is that actually it's almost easier to escape from a supermassive black hole as long as you don't get obviously event horizon wise than it is sometimes from a stellar mass black hole, because of the gradient, which is all comes back to like, if you think about it as density, you know, if you think about it as spread, yeah. Yeah. Oh, thanks for tackling that Becky, and thank you Nicole for all of your questions and for listening to the entirety of our back catalog. It gold star for you. And so Robert, we've got this final question from Mark in Chroma, one of my favorite places in the UK actually, love that part of the world. It's so good. I had to Google where it was, I didn't know where it was. I had to Chroma, I've just discovered you. I've never been, I need to go. We love it. Oh my gosh guys, come on. Anyway, Mark says, hi and hello to all at my favorite podcast by far, brilliant and fun. So his question is, with news of a possible gas giant in the nearest star system to Earth, Alpha Centauri, being four light years distant and often described as in our neighborhood, just how big is our neighborhood? So if the co-moving distance from Earth to the edge of the observable universe is about 14.26 giga par six or 46.5 billion light years according to Wiki, in brackets, I had to look that up. And wouldn't it be more accurate to say in our front garden? Can't wait for the next episode, Mark. Yeah. Over to you Robert. Mark, yes it would, I guess. I mean, astronomers, we love using words like nearby star to talk about Alpha Centauri, four light years away, 40 trillion kilometers and some, so 40 million, million kilometers away, a vast distance. Take tens of thousands of years to get there. So it's crazy far away, but it's obviously so much nearer than all the other stars in our galaxy, let alone other galaxies. And then we talk about things like the local group for the nearest galaxies, which implies like a trip to the shop or something, but actually Andromeda, for example, two and a half million light years away. So again, unimaginably distant in everyday terms. So describing what is our neighborhood is a bit tricky. It really depends probably on what kind of astronomy you are, what sort of objects you're looking at, because a solar system scientist might describe the moon as being our neighboring world. I mean, even that is a 400,000 kilometers away, much further away than anywhere on earth. So once you get to the whole observable universe with that huge distance, 46 billion light years as a co-moving distance, then you're right, these distances, these things to the nearest star is not just in our garden, it's like the other side of the room or maybe the other side of the table you're sitting at in comparison. So the sensor scale is really variable. I suspect depending on what kind of scientist you are. And also maybe it's just a way of making it seem a bit more familiar, you know, after the Sun Alpha Centauri and Proxima Centauri, the nearest stars to us. So we've got to think of them as neighboring at least, even if they're not exactly in our neighborhood. And I think it tends up meaning, well, it's easy to see and study. It's not about sort of how easy it is to get to it. You know, this isn't something you can just stroll down the street when we tend to think about neighborhoods on earth. So that I think is the difference. And that's why we tend to lapse into these things, because it just makes it familiar and easier to handle. And we know that they're easier to study as a result. It is funny the way you say that. Like, I think one of the things that me and my colleagues have said so much in the past five years since JDGrest tea launch is define high redshift. Because when you get to more distant galaxies, we start instead of, you know, talking about giga power sex and distance, we start referring to a redshift factor, because it's what we measure when we know how far away galaxies are. The things with the light more redshifted off further away. And so, and it's an easy number. It's like one, two, three foot, right? It's one to 14, basically. And a bit higher now. But the funny thing is, like, I cast myself as a low redshift galaxy person. And that's like less than 0.3 away. And somebody who says, Oh, they're a high redshift person, like usually might have been more than redshift two in the past before JDGrest tea. But now if someone says they're a high redshift person, it's like, I'm like redshift 10 and above, you know, and like redshift 10 and above in like Hubble era would have been like nothing. So it's really interesting now is the amount of people who are like, Oh, yeah, we're talking about this high redshift. And somebody goes, I don't know. Like, that doesn't make any sense. And you realize it's because they've now everyone's got different definitions of what high redshift means. So I guess this is just sort of like another question about we need to come up with actual definitions of what we mean when we talk about these things. Yeah, absolutely. Well, thank you so much for everyone who sent in their questions. Do keep them coming. It's at Super MassivePod on Instagram. You can email your questions to podcasts at ris.ac.uk. And we'll try and cover them in a future episode. And if you like an ad free version of the podcast, and we talked about other things, I'm like, Yeah, maybe some rants as well. Yeah, just make sure you sign up to the Supermassive Club. I'll put a link in the show notes. But thank you to everyone who's already on there because it helps us keep making this show. We'll be back in a few weeks time with an episode about quiet and dark skies, Robert and I are all like, I'm holding back to you. Robert even more so than me. So I'm excited this is what I'm saying. There might be a ramp turning up on the Supermassive Club that just got cut from the previous episode. But until then, everybody happy start gazing. Hi, this is Joe from Vanta. In today's digital world, compliance regulations are changing constantly and earning customer trust has never mattered more. Vanta helps companies get compliant fast and stay secure with the most advanced AI automation and continuous monitoring out there. 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