Strange Stars and Bizarre Binaries

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Get matched with a therapist online based on your unique needs and get help with everyday struggles like anxiety or managing tough emotions. Visit betterhelp.com forward slash random podcast for 10% off your first month of online therapy and let life feel better. Music What causes a start a pulsate? There are some binaries rotating around each other as short as just a few minutes. It is the oldest star that we know of. They're so weird. Music Hello and welcome to the supermassive podcast from the Royal Astronomical Society with me, science journalist Izzy Clark and astrophysicist Dr Becky Smethurst. This month we're chatting all about weird and wonderful stars. What are the different types of stars in our universe? Crucially, what are the odd balls out there? That's always what everyone wants to know. Absolutely. None of that normal stuff. We want the extremes of the distributions, please. Yes, please. Thank you very much. As always, Dr Robert Massey, the deputy director of the Royal Astronomical Society is here. So Robert, let's go from the very beginning. How do stars form? Yeah, so if you look at the kind of contemporary universe, the contemporary galaxy, then you've got stars, obviously across the sky. And you'll also notice, particularly this time of year, actually, if you look for constellations like Orion, you see these nebulae dotted around as well. Now, if they're visible, they tend to be bright clouds of gas that's glowing because the stars inside them. But those are associated with denser, darker regions behind these clouds of hydrogen, mostly hydrogen, with dust interspersed inside them as well. And if inside those, those are the stellar factories or the stellar nurseries, the places where young stars are, and they're pulled together by gravity. So if you imagine if there's enough mass, if there's enough gas, and it gets a bit clumpy at all, if there's any structure in it, then that will tend over time to pull together. If you wait long enough, and sometimes also they get shocked by nearby supernovae, they get compressed that way too. If you wait long enough, as those things pull together, the gas heats up, the density increases, and I'm missing out a few steps and few details here, but it radiates heat, the temperature rises, and it gets to the point where it's hot enough for nuclear fusion to happen, and a star is born, if you like. We're missing out of more than a few details here, but that's the gist of it. So when you look at the night sky, if you look at something like the Orion Nebulae in the winter sky, you can know that you're looking at a place where there are very, very many young stars that have formed in this way. Yeah, thanks Robert. We'll catch up with you later in the show for some more questions, and this month's Stargazing Tips as well. Now we know how all the stars have formed. What can we see? So Robert has started us on how a star is born, but what different types of stars are out there? I spoke with Andrew Norton, Professor of Astrophysics Education at the Open University, and began by asking why we end up with massive stars or regular sized ones like our Sun. Short answer, I think we don't really know, which is a good answer. Some stars form that are very massive, very large, others that are very small, very low mass, and we think that the sort of most massive stars that can form are around about 100 times the mass of the Sun or so. Any bigger than that, they can blow themselves apart, they can never form in the first place. And the smallest stars that form are somewhat less than about 10% the mass of the Sun. Any smaller than that, they don't get hot enough in the core to begin that hydrogen fusion. And we don't really know why some stars form very large, some stars form very small, but what we do know is that the large stars are much rarer and the small stars are much more common. I forget the exact numbers, but let's say for every one star that's 10 times the mass of the Sun, you might get a million stars that are half the mass of the Sun or something like that. So it's a really big difference. There's so, so many more really small low mass stars. We also know that lots of stars form in clusters from one cloud of gas that collapses and fragments, and so all the stars in that cluster form at the same time from the same cloud. And we know that some stars form in pairs or multiple star systems. Certainly the most massive stars, 10, 20, 30 times the mass of the Sun, they seem to almost always form in binaries, two together or even more. Whereas the lower mass stars, they maybe seem to form more often individually, but we don't really know for sure. It may be that those low mass stars, many more of them do have companions, but they're actually too small to see. We know that stars form in different environments in different combinations. So let's talk through those different types of stars, maybe going from, you know, the most common and then we'll go off to some of the more unusual ones. Yeah, when we look out there at stars, you can notice two things really. First of all, different stars are different brightnesses. So that's partly ineffective how luminous they actually are, how much energy they're putting out and how far away they are. Obviously something that's really luminous, but a long way away might look a similar brightness to something that's rather less luminous, but nearby. The other thing you might notice is that stars are different colors, blue or red or colors in between sort of thing. And that's really an indication of the temperature of the outer layers of a star. So the cooler stars tend to be redder in color and the hotter stars tend to be sort of blue, bluish-white. So when we plot a graph of their luminosity against their temperature, you see what's called a Hertzbrum-Russell diagram, named after, again, the two astronomers that first came up with this a hundred or so years ago. And when you plot luminosity up the vertical axis, temperature on the horizontal axis, you see that most stars lie in this single band running from top left, which is very luminous, very hot, down to bottom right, which is low luminosity, very cool. And that's what we call the main sequence. The stars at the top of the main sequence, the luminous hot ones, are more massive and larger. The ones at the bottom of the main sequence, the ones that are less massive and cooler, they're also smaller mass and smaller in size. And what it turns out is that that main sequence where we find most of the stars is where stars live for most of their lives. The sun is a pretty average star. It sits round about the middle of that main sequence, halfway up. And that's why we talk about other stars in terms of their mass relative to the sun or their luminosity relative to the sun and so on. When they're in that main sequence phase of their life, what they're doing is converting hydrogen into helium in their cores. Hydrogen and helium are the two most abundant elements in the universe. The universe is really about 75% hydrogen, about 25% helium and less than 1% of everything else. And a star like the sun will spend maybe 10 billion years in that phase of its life. A higher mass star, one that's several times the mass of the sun, will spend much less time on the main sequence. Massive stars live fast and die young. OK, so that's the main sequence covered. What are the other star types that we might be less familiar with? We've got things like red giants and super giants. They are examples of stars in the later phase of their life. So once a star runs out of hydrogen in its core, first of all, it will tend to get more luminous and cooler, move off into the red giant branch. Stars expand and they eventually then begin converting helium into carbon and oxygen in their cores. The more massive stars, they have a much more rapid and more violent evolution, really. They undergo successive types of fusion, turning first helium into carbon and oxygen, then carbon and oxygen into neon and magnesium and silicon and ultimately iron. And they track backwards and forwards in the so-called super giant branch. But stars essentially move around changing in brightness, changing in temperature as they evolve through these different phases. And they're much shorter lived those phases, but the stars in those phases tend to be much more prominent because they're very luminous. So we see them more readily. Stars like Rigel and Betelgeuse and some of these bright stars we know. And then there's this type of stars that I feel like on this podcast, we perhaps may not have given them their time in the spotlight. And those are the dwarf stars. So can you talk me through the different types because there are a few and what sets them apart? Well, how are they different? Yeah. So a dwarf star simply just means a small star, physically small in size. And the low mass stars on the main sequence, we call those red dwarfs, they spend all their life just calmly burning hydrogen into helium. They don't do much. I don't think they're terribly interesting, but plenty of people do. But any low mass star like the sun or in fact anything less than about eight times the mass of the sun initially will end its life as a so-called white dwarf. So they end up with a carbon and oxygen core, but they're not massive enough to initiate any more fusion. So when they have a core made of carbon and oxygen, eventually the outer layers of the star will drift away into space causing what we call a planetary nebula. There's nothing to do with planets. It's just through telescopes hundreds of years ago, they looked like fuzzy planets. So this cloud of gas expands away from the star as a planetary nebula, leaving behind the dead core of the star just made of carbon and oxygen. And that's essentially what a white dwarf is. It starts off very hot, white hot, and that's why they were called white dwarfs. But with time, they will gradually cool down and fade from being white dwarfs to eventually black dwarfs, dead, cold stars that are just sitting there doing nothing at all. And that's the fate that's in store for every star that really starts off with less than about eight or 10 times the mass of the sun will end up as a white dwarf. What are some of the processes that are driving these stars? And you know, when we get some of the obscure ones, which we'll get on to later, what's going on in there? Okay, there's various things, I guess. If we think about individual stars, first of all, at certain times in their lives, some stars become unstable and can begin to pulsate, literally pulsate in and out, getting larger and smaller, brighter and fainter with a regular periodic cycle. Different types of pulsating star occur at different times in a star's life, depending on its mass. Some of the most famous types of pulsating star, I guess, are things called RR Lyrae stars, named after the prototype, and Cepheid variable stars. So that's one type of unusual behavior that a star can undergo. I think another sort, I mentioned earlier that many stars are born in binary systems, and sometimes the two stars in a binary system are so close together that as the stars evolve at different times in their life, they can transfer material from one to the other and back again. There's a thing called the Algold paradox. The star Algold, famous variable star, was observed and realized that it was a binary star. Presumably the two stars were born at the same time, but the less massive star appeared to be more evolved than the more massive star. And that's a complete paradox, because as I already said, the more massive stars live fast and die young, they should evolve quicker. And the solution was that during its life, matter has passed from one star to the other in Algold, in that binary star, so making one star appear to be more evolved than the other, when in fact it wasn't. It had just taken some material from the other. So we see lots of stars where this mass transfer occurs, and that can tell us an awful lot about the history of the star, what's happened in the past, as well as what's going to happen in the future. So that's just a couple of examples, I guess. And we're going to hear more from Andrew in a moment, but Becky, I wanted to pick up on those last two examples that Andrew spoke about. So what causes a star to pulsate? Because that is strange. Yeah, you've never really thought about this before, you're like, sorry, what? But you've got to remember that a star's life is basically a constant fight against gravity. There's so much stuff there once you've got a star that gravity is just trying to crush it in endlessly, which is helpful because it means that the core of the star that is dense enough and hot enough for nuclear fusion, so that it can power itself. But also, nuclear fusion then gives you a process that produces energy that pushes back outwards against gravity. And so you have this nice balance set up. Unless you don't quite have the balance. If you don't have a perfect balance, which, you know, most of the time you don't because it is just this like just so scenario. And so instead, what happens is you end up with like gravity just crushing in a little bit more so that there's sort of outer regions of the core where maybe, you know, you're on that boundary between whether it's actually hot enough and dense enough in the middle of the star to actually have fusion going on. Gravity crushes that just a little bit in a little bit more, you know? And that does make it dense enough to then ignite nuclear fusion in those regions. But then you've got, you know, a greater force pushing outwards back against the gravity. And so then you push outwards again, which makes everything less dense and not as hot. And so, and then you haven't got as much force pushing back against gravity again. And then gravity starts to win again and crushes it in and so on and so on. And so you end up with this sort of pulsing scenario as you go between this sort of balance between gravity crushing in and then energy from fusion pushing outwards again. That's one way that stars pulse and obviously when stars sort of reach towards the end of their life and they start running out of fuel that also becomes more common. And then also you can get stars pulsing if they're in a close binary as well, as Andrew talked about, right? Like you have two that are pulling on each other that disrupt that nice equilibrium. Yep. Okay. And as for the mass transfer between that Algor binary system, what kicks off that process? It's gravity. Again, gravity really doesn't have a lot to answer. It's always gravity. Okay, fine. Damn it. It's why we're all here. In a binary system, right? The two stars like both have this sort of region around them that we call the Roshlob. That's how I've heard people pronounce it before the Roshlob, but I really want to pronounce it like Ferrero Rocher. Rosh. Rosh. But it's the Roshlob. I think it's named after the French astronomer Edouard Roche or Rocher who lived during the 1800s. But it's the region around the star where any material that's there is going to be held by the gravity of that star. Right? So it could just be, you know, the actual surface of the star, but it could also just be like a compound material that might be an orbit around it, whatever it might be. So in an isolated star, like the Sun, right, that's a sphere around the Sun where stuff is contained and contained in orbit on the Sun. But if you've got two stars that you bring ever closer together in a binary system, that sphere distorts in shape and gets pulled towards the other star until you end up with kind of like a teardrop shape. And so as you bring two stars- I think of it as like an egg timer on its side. Yeah, sure. I can do that. Yeah, because as soon as you bring the two of them together, you've got two teardrops and yeah, that makes like a binary system. And so those two teardrops eventually touch if you bring the stars closer together. And that's where you start to get this mass transfer, right? Because if a star is maybe say reaching the end of its life and it's swollen up in size and it starts to fill what's known as the roach lobe, right? You're going to hit that teardrop shape and you're going to get to that point where those two teardrops have touched. And so you're going to get transfer from one of those roach lobes over to the other star that then like sort of slowly will add mass to the other star, maybe start orbiting around it and like what we call an accretion disk, right? As well, as I said, it's this mass transfer and you get different types of binaries. They're kind of like houses, you get semi-detached binaries and you get detached binaries. Like a semi-detached one is like the Angol binary system where you have one star that's filled its roach lobe and is transferring together. And a detached binary is when there's no mass transfer going on at all. And actually in part two of Andrew's interview, he talks about this really extreme, I guess it's a binary system, but we'll get onto that later on in the episode. Well, you're such a teases. And another type of star that we haven't touched on and probably they've done an entire episode about them are neutron stars. So in a couple of minutes, Becky, give us a quick intro to neutron stars, please. Okay, I think the easiest way to describe them are like they are the baby siblings of black holes, right? They're sort of the first stage of the evolution before you get to a black hole, right? So they are the very dense, super compact cores of dead stars. So stars that've lived, died, they've gone supernova, the cores been left behind. Now you don't really have any nuclear fusion giving you energy pushing back outwards against gravity. So that's how you end up with a super compact core because gravity just comes along and goes squish, crushes it down until all the space between the atoms is gone. You've forced protons to merge together with electrons to make neutrons, and then you've got neutrons as tightly packed as they can go and almost like a crystal like structure. Right. And so the only thing now resisting the crush of gravity down more is that you can't have like two neutrons in the same state, essentially, right? So they're held together in that like crystal. But if you keep adding more mass, like if you have the mass transfer from a binary, right, then eventually you're going to reach that point where the neutrons can't resist that crush of gravity down anymore. And that's when a neutron star would collapse to become a black hole. And the fun thing about neutron stars is that they are some of the most extreme objects out there in the universe because of the black holes. They're so weird. We can see them. Yeah. Yeah, they're so, so cool. Right. We get information from them in the form of light from all across like the different types of light across the spectrum. Right. They spin incredibly incredibly fast because they sort of inherit the spin of their star that lived and died. And like an ice skater that sort of has their arms out and then spins around and pulls their arms in to make themselves denser and they spin faster. Like neutron stars end up spinning incredibly incredibly fast. You get these beams of radio light from their poles that sweep around like lighthouses. That's what we call pulsars. Some of them have incredibly strong magnetic fields as well and they flare and that's what we call magnetars. And we get everything from like radio X-ray, gamma rays, like UV light, everything from neutron stars. And I sometimes think that the astronomers who study neutron stars think they're superior to the black hole people just because they can see them. And they get all the information and light from it and they're like, oh, look at this cool transient. We can discover, we can learn so much from it. And then as black hole people are in the corner like... Is someone jealous? No. When considering care for a loved one with dementia, you want peace of mind that they'll be in the very best hands. With care delivered by expert teams and supported to live life happily, comfortably, in a dedicated environment that supports independence. You can expect all of this and more with Southern Down Care Home. You're invited to our Open Day on Saturday the 20th of June to take a look around our home and discuss what support you need. Visit budgestor.com.com. There are a lot of unusual stars out there, but I asked Andrew Norton about some of his favourite weirdest ones. So we got talking about bizarre binary stars and I wanted to know just how close can two stars get? The answer is really, really close. Some binary stars we know may be composed initially, let's say, of just two red dwarf stars, so low mass main sequence stars. But we see a lot of those where the stars are so close that essentially they're touching. So when the two stars become close enough, they get distorted into a sort of pear shape by the mutual gravity between them with the sort of points of the pair pointing towards each other. And in some close binary stars, those pear shaped stars can actually get so close that they overlap. And in these, we see a continuous variation in brightness because as the two stars rotate around, we're seeing a different projected area of this sort of pear shape. And those can have orbital periods as short as a few hours, but that's not the smallest ones. There are some binaries where one of the two stars has already evolved to become a white dwarf and in the process of that evolution, the two stars have ended up even closer together. And they might have a period rotating around each other as short as just a few minutes. And what are sort of the stresses of two stars being in such a close binary system? You know, that feels like quite a turbulent dynamic to be in. Yeah, absolutely. I mean, in one way they're very well behaved because they're just going about their business, orbiting around each other. They're losing energy. They radiate gravitational wave radiation. And so they're getting ever closer and closer together. And ultimately, in many cases, the two stars will merge together. We've seen that in action just once as far as I'm aware in terms of normal stars doing that merger. And it was only sort of retrospectively realized that that was what had happened. A particular star was observed to flare up and in brightness and then virtually disappear. And when astronomers went back and looked at previous observations and archives, they found out that it was a binary star. And over the years, that binary period had been getting shorter and shorter and shorter. And presumably what had happened in this event was that the two stars had merged with each other and produced this sort of outburst. So we know that happens. And that, you know, could indeed be the end point of many of these close binary stars. And how complex can a system be? This is one I really wanted to tell you about. My favorite star that my colleague and I discovered some years ago, my PhD student at the time, Marcus Law, was looking through the archive from the SuperWASP project. SuperWASP was the wide angle search for planets. It was looking for planets orbiting other stars. But as a byproduct of that, it built up this huge archive of data spanning about 10 years, observations of about 30 million bright stars. So for each star, we had tens of thousands of brightness measurements to see how its brightness might vary with time. And we found this one object where when we looked at it, we saw, well, it's got two different periods of variability. It's varying every five and a half hours in a regular way, but it's also varying every 1.3 days in another regular way. When we look closely, we realized the 1.3 day variation was a detached eclipsing binary star. So two stars that are orbiting around each other passing in front of each other, giving narrow eclipses every 1.3 days. When we looked at the same light curve varying every five and a half hours, it looked like a contact eclipsing binary star. Two stars distorted into pear shaped orbiting around each other with a continuous variation. So we figured, OK, this is actually four stars, a contact eclipsing binary and a detached eclipsing binary. So we went and looked at it closer with a bigger telescope and measured the spectrum of these stars. And sure enough, the contact binary, we could see the spectral lines moving backwards and forwards every five and a half hours. That was fine. Then we looked at the other pair and we actually saw three sets of spectral lines indicating there were three stars there, not two. And what we figured out was that detached binary is actually a triple star with a third star orbiting around the two maybe every several years. So we didn't see that motion. And the triple star and the contact binary star are then orbiting around their common center of mass with a period of probably a few hundred years. So what we found then was a doubly eclipsing quintuple star system. And it's absolutely my favorite system to have ever discovered. That's quite a mouthful. Yeah. Yeah. And let's look at some stars with unusual cores as well because they do exist. So what are some of the strangest ones? Have you got any examples of those? Yeah. I mentioned earlier about white dwarfs and a white dwarf normally is made of carbon and oxygen. And then the core of the star is this dead inert carbon oxygen lump of material that cools down. But a few years ago, there was particularly strange white dwarf discovered where this particular white dwarf had cooled down so much that it has sort of crystallized this cold, dead core of the star. Had actually turned into diamond. So that would be a diamond, roughly the mass of the sun, a bit less maybe, but compressed into something the size of the earth. So yeah, quite remarkable. Oh my gosh. That is quite remarkable. So what happens to that? Are we just saying that we're going to have like this crystallized floating diamond in space for almost an infinite amount of time? A very long amount of time? Forever. Yeah. There's nothing else that would happen to it really. It would just sit there till the end of time. Diamonds in the sky. Yeah. Is that quite rare? How common is that? Well, it probably is quite common. The most common stars in the galaxy, the universe, are low mass stars. And we know that all low mass stars will eventually evolve into white dwarfs made of carbon and oxygen mostly. And all those white dwarfs will eventually cool down and probably will turn into these diamond cores. So it's the ultimate fate really of all the low mass stars in the galaxy, in the universe. The more massive stars tend to be more spectacular in the way they explode as supernovae and produce neutron stars and so on. And really for most stars and something like the sun, that's what fate has in store for it. It will turn into a carbon oxygen core white dwarf that will eventually cool down and may then crystallize to form a diamond core. That's the ultimate fate of most of the stars in the universe. Thank you to Professor Andrew Norton from the Open University. This is the Supermassive Podcast from the Royal Astronomical Society with me, astrophysicist Dr Becky Smith-Hurst and science journalist Izzy Cork. This month it's all about weird and wonderful stars and we've had some weird and wonderful questions. And so most of them were, what is the weirdest star? But I think this email from Sebastian in Oslo best sums it up. So I'd like both of you to answer this. Sebastian says, which stars in the northern hemisphere can we point at and think there is an object that we cannot explain with our current physics and models? Which stars can I see which are inexplicably too big, small, bright, dim, fast, blue, red, green, square or made of cheese? Where should I look to see a point beyond the frontier of physics? Thank you again and keep making us looking up. Yeah, Sebastian, that's a nice challenge, isn't it? I have to say, a half. Anyway, I'm struggling to think of naked-eye stars that are completely inexplicable. And when you look at most of these cases, it's not so much that just that there are challenges to the models. You know, very few cases where you'd say, oh, the physics isn't good enough for this. But there's quite a lot. We'll be not sure exactly what's happening with them. And one like that is a Boyajian star, which is too faint to see with the eye, but pretty easy to see with an emeter telescope. It's in Cygnus, so it's high in the northern hemisphere of the sky. And you can see it this time of year, certainly for a few more months. And it was watched by the Kepler telescope, which you might remember. The main job of that was to study a couple of thousand stars or more than that, looking at a patch of sky in Cygnus. There was a few tens of thousands, I think. Tens of thousands, a little patch of the sky. And it was the same was to look for where stars were fading because of planetary transits. And in the process of that, it generated a data set which was looked at actually by citizen scientists. I think it's part of the Zooniverse, the Planet Hunters one. And they found this star, which has these inexplicable... Well, I hesitate to use the word inexplicable, but not completely... I explained, didn't you? Unexpected, yeah. So it's red in colour. It's a bit bigger than hotter and brighter than sun, not dramatically so, but a bit bigger. But it just has these weird events. And in one case, it's brightness dropped by a whole 20%. So the explanations are things like, is there a big planet blocking the light? Is there some sort of debris from where a planet's been destroyed and all around it got too close? Or some weird uneven ring of dust? And the wackiest idea is this alien mega-stretch thing, which you'll probably see if you spend any time looking at this on YouTube or somewhere. But that's not really taking seriously, so I'm not going to take that one forward very far. It doesn't explain the data that one. Exactly, yeah. It doesn't make sense to play as much as we all want to, it doesn't make sense. It's absolutely wishful thinking, you know, Dyson's visual is stuff. But a more anodyne example of the weird object, not quite as weird. If you find the bright star Vega in Lyra, so not far away from the Boyerjian star, and it's one of the brightest stars in the sky, and that rotates so quickly that it bulges out and it's equator, but of course you can't really see that with your eye, you can just look at it and think, oh that's a, if you had access to a sophisticated observatory, you'd be able to detect that. Yeah, so it just looks a bit squished, doesn't it? Yeah, I mean, you wouldn't see anything with your eye, just like a star there, they're all so far away. And it's very, very difficult to detect, but with the best telescopes in the world, you can start to see these features, and certainly when you have networks of them interferometry, when you get several telescopes working together, and that's the kind of thing they can pick up. Yeah, Becky, what about you? So I mean, in terms of like the Runeterror of Physics and not being able to explain it, because the models aren't quite, can't quite get it. My first thought was HD 140283, or Methuselah star, as it's often called, which is in the constellation of Libra. So like can we see northern hemisphere or southern hemisphere? So, this is one for both of you. Just below the limit for naked eye in dark skies. I'm so sorry, Sebastian, it's about magnitude seven, so you would need binoculars, but it's a bit brighter than Boyd's star. It is the oldest star that we know of, so it's a star in our own Milky Way galaxy. And our models of stars and what we fit to what the star's light looks like in there for how old it must be, give us an age, an estimated age, that is older than the estimated age of the universe. Which again, is one of these things that on the internet, people really, really misinterpret, because no, it doesn't mean that there is actually a star older than the universe, because it's obviously not possible. There's so many uncertainties that go into our models of what star's light is like, for how old they are. There's also so many uncertainties that go into figuring out how old the universe is as well. And that could also be a whole podcast episode by itself. What it means is that there's something wrong with our models. So Sebastian, I think that fits your criteria the best in terms of like, there's something wrong with our current physics and models if we're getting an age that's older than the age of the universe. But I also thought of brown dwarfs as well, where something stops being a brown dwarf and becomes a gas giant planet. It's really not a very clear cut line. We don't understand them. They're very dim and visible light. They're very bright in the infrared. So come on, sit with the naked eye. But I've decided, I think, in the conditions that Sebastian gave me in the Northern Hemisphere, specifically a naked eye star that is like the one that if you wanted to go out and point out and be like, this is probably the one that we have the biggest argument for. We don't understand it. It's probably Beetlejuice. I wondered if this would come up. I'm like, Klaxon goes up. Beetlejuice. And it's this whole idea of like, when will it go supernova, right? Because we have so many different estimates from so many, again, different stellar models, modeling the star and how old it is and how much fuel it has left. We get so many different answers anywhere from like, within the next century to within the next millennia to tens of thousands of years, right? So in terms of like, how good you want your physics model to be of like, when the end of a star's life happens compared to its light that it's giving off, I think it's Beetlejuice. And the good news is it's autumn right now. So Orion is very visible in the evening sky. And you can go point at it tonight if it's clear. Hooray. Okay, Becky, Peter Worthington has a question about merging neutron stars. They say, I recently read that astronomers now think that most of the heavy metals such as platinum and gold are created by the merger of two neutron stars rather than supernovae. Since neutron stars are already composed of matter where the electrons and protons have been squeezed down into neutrons, how does gold and platinum come out of such a merger? And why don't neutron stars simply gather up all of that matter into a black hole? Great question, Peter. Like, first things first, right? When we're picturing neutron stars merging together because they're spiraling in as a binary system, right? And getting ever closer. We picture it in our head, right? As like two perfect spheres getting ever closer and closer and spiraling in before all of a sudden at one moment they touch and they become one sphere and they collapse down into a black hole. And that is so far from what it would probably look like, right? It's nowhere near as neat and pretty as that because as the two in spiral in and get closer and closer and that orbits around each other, like, the forces of gravity in that are going to be absolutely insane, right? So they're going to completely warp their shape even if they are ultra-compact. You're going to get tidal forces. You know how, like, we get tidal forces between the moon and the earth, the bulges on the earth, and we get the bulges in the ocean that give us the tides and things like that. Like, can you imagine neutron stars bulging because of tidal forces between the two of them? Like, you actually end up getting material thrown out and ejected away from the two neutron stars spiraling in. So you've ever been on a roundabout or you've sort of held your arms out in front of you and held hands with a friend and then spun around. You'll know that sort of force of, like, feeling like you're getting pushed outwards all the time, right? So in a neutron star merger, you're going to have that happening, right? You're going to have material that's almost ejected and forced out. So not all the material and two neutron stars merger together will actually stay for the final merger point where, yes, okay, anything left in the middle is going to collapse down into a black hole if you've got enough material there that's heavy enough to overcome, sort of like, what I described before, we call neutron degeneracy pressure, like, that two neutrons come in the same place, right? And so you still have this ejector material, which will, yes, have a lot of neutrons in it, which, you know, is protons and electrons that move forced to merge, as Peter said. But if you've got a lot of high energy neutrons that are going to collide a lot and clump together, they're going to go through something called the R process, which is essentially a really rapid clumping and collection of neutrons, which are really unstable when there's not a lot of them in one place. We're talking like, you know, making up an atom, numbers of neutrons. And then if they're unstable, they're going to start radioactivity decaying. And they can do that back into a proton, essentially. They can give spit back out the electron, become a proton. And if chance happens that enough of that happens to give you like a stable element that has like the right number of protons in it with the right number of neutrons to make it stable, then you're going to get something probably like gold and platinum because of how many neutrons are just there and readily available. You're going to get heavier elements as opposed to lighter elements. And yeah, all the other elements heavier than iron that, you know, in a supernova where you have got almost like runaway just fusion of, you know, lighter elements into heavier elements, it takes more energy to make something heavier than iron than you get out in the process of fusion. So we don't make heavier elements through fusion. It's in this sort of like runaway R process of clumpigive neutrons that they get made instead. Thanks, Becky. And Robert Gershept on Instagram asks, what is for you one of the most amazing results in astro seismology? So that's the study of a star's internal structure by analyzing its oscillations. So what we've also referred to in the past is star quakes. So over to you, Robert. Yeah, I mean, this is sometimes described as kind of the natural music of the stars. And as you say, it tells us it's a great, great expression, isn't it? I don't credit me for it. Bill Chaplin in Birmingham came up with this one, but I think he did anyway. He's quite a good saying it. But it's the same technique in a sense that you use to understand the interior of the earth by using earthquakes, you know, that they're kind of probes of what's happening inside, a place you obviously can't see directly. And as it happens, yeah, I mentioned that University of Birmingham is a good world leading group for that. It's a nice UK connection. But that precise information allows astronomers to pin down what a star is like, including its size, and then it makes it possible to get precise measurements of things like exoplanets, because if you have a planet transiting the star at a dip and you know how long that takes and you know how big the star is, it's much easier to find the size of the planet. It might also be possible to do things. I was reading some speculative papers about this, thinking about what they could do with it. Do things like find out what the stars have got dark matter inside them as well. Now, I don't know if this is a fair answer to the question, but I thought the most, you know, the craziest one I came across was all the most energetic, was that because the science relates to star quakes that you mentioned, is he, the most dramatic of those are where you get the surface of a neutron star or a magnetar violently distorted by its magnetic field. And in 2004, there was an example of that with the not very exciting name SGR 180620, and that emitted a big burst of gamma rays as a result. And these are described as soft gamma ray repeaters. They don't seem very soft to me. Soft and hard, basically means like low energy, high energy. That's all it means. I don't know why they went for soft and hard. It doesn't make any sense to me. No, it's like these are not things you want to get near and sure enough, had this been really near the earth, as in within a few light years, it would have been, it's the kind of thing that could lead to an extinction event. So I should be quite glad it was a long way off. And there are no candidates nearby for this, but if it had been that really close, it would have been in trouble. It was enough to do things like blind X-ray satellites that were in orbit. So this was not a trivial event. You know, if you want an example of why understanding how stars reshape themselves and how starquakes work, this is probably a good one. Don't have nightmares. There's a way to say. Exactly. And a final one for you, Becky. Orvalane on Instagram wants to know, do you think there are dark matter stars in the universe? Now? No. In the early universe? Maybe. She said confidently. I mean, so dark matter stars are hilariously, unlike the name suggests, mostly normal matter, actually. But with enough dark matter in there, so that it would be dense enough that the likelihood of two dark matter particles coming together and meeting and colliding and annihilating with each other would go up. So if you remember, annihilation is when a particle meets its antiparticle and they just turn back to energy. Apparently a dark matter's antiparticle is itself. That's what particle physicists tell us, right? In one of the most likely candidates for dark matter, it would be its own antiparticle. So the annihilation of two dark matter particles in this dark matter star would be enough energy released to heat up the surrounding material. It would stop all the normal matter in the big gas cloud from collapsing into a normal star. And there would be huge clouds of gas if that was the case. We're talking about 100,000 times heavier than the Sun. It would be the size of the solar system. And it would be tens of thousands of Kelvin, right? So in essence, a star because it's producing heat inside, preventing the gas from collapsing. You've got something resisting gravity, so you've got some sort of equilibrium set up, right? So in that respect, it's a star, but it's not really a star. But once you've exhausted all the dark matter there and you've annihilated it all in the center of this star, the cloud would collapse, this cloud of normal matter. And this could actually possibly be the seeds of supermassive black holes, right? You could start with something that was like 10,000 times the mass of Sun to grow it into like a million to a billion times the mass of Sun. If these dark stars could survive to the present day, i.e. they had enough dark matter in the center to power them for 13.8 billion years, right? Then we should be able to detect them with gamma rays, maybe even neutrino detectors, but there's been no evidence for them. Nothing has been spotted that looks like them. So I don't think that these exist today, at least. The early universe is a different story though, because if there's enough dark matter to power it, you think, okay, well, how long for, and maybe you could spot them in the early universe. And some people argue that there's some object spotted in J. DeGrasse T-Data that people have assumed are galaxies, very, very distant galaxies, 13 billion light years away. But people say that actually, instead of modeling the light from these things that we found as like an extended object, like a galaxy where you've got lots and lots of stars over, you know, big area, actually it's like you could model the light better as just a single point source of light, just a single dot, right? And if that would be the case, the only thing that would be bright enough to produce that much light from a single dot would be one of these supermassive, giant dark stars in the early universe. I don't think I really believe that claim or that interpretation of the data necessarily. I think there's still a lot of work ongoing. I think it would help if one of these things got lensed, you know, where you have like a foreground galaxy that brightens it, and you know, you can see the shape better and things like that, because I think at some point all things just look like dots, right? That is the best part. All things just look like dots. Oh, that's the whole field of astronomy. This is also going from someone who's very biased, because they look at very nearby galaxies where I can see the gorgeous shapes that I can see on the individual like spiral arms, and I look at my colleagues that do very sort of distant galaxy studies, and I'm like, they look so boring, they're all just done. There is still a lot of work ongoing on this, but I think, I mean, it is a very sort of tentative hypothesis at this stage. Oh, well, that's still very exciting. And so thank you to anyone who sent in questions. Do keep sending them in. We love reading them. So you can email us at podcast at res.ac.uk or find us on Instagram. It's at SupermassivePod. So, I mean, it's never more fitting than this episode to end with some stargazing. So, Robert, what can we see in the night sky this month? Bizarre or just fairly standard? I mean, you know, a blend of the two really defined bizarre, I guess. But I mean, yeah, no, the autumn sky is good. You know, we're moving into the winter, not quite there yet, but it's a really good time to look for groups like Taurus the Bull and the clusters of stars, the Hyades and the Pleiades are fantastic. They're good with your eye. You know, they really stand out, but they're really nice for beginners because you can pick up even a small pair of binoculars and you suddenly think, oh, wow, there's just so many more stars in them. There's all the ones that are just below what your eye can see on its own. And above that, the group of Riga, the Charity, has got more of the same, the clusters that look a bit more like Hases, Messages 36, 37, 38, the very bright star propeller. And then the Andromeda Galaxies still around. Very easy to pick out to the east of the square of Pegasus. If you want to see, I'm guessing, what, I don't know, about 500,000 million stars or so, it'll crush into a little squidge from our perspective here on Earth. Now, planet-wise, it's getting a bit more interesting as well. Venus, which has been sort of skirting along the horizon for the last couple of months at sunset. That, because of where it is in the sky, it'll become a lot easier by the end of November. It'll be, and December, January, February, it'll be really good. It'll be really high and obvious in the sky after sunset. So if you do see this very bright thing sitting there, I mean, you're welcome to write to saying, have I seen a UFO? And we're going to write back and say, no, you haven't. It's Venus, but that's a very standard thing, because people are surprisingly often haven't seen it, and they're just struck by, what is this enormous and bright thing over in the sky? Saturn's still good in the south with that really narrow ring that's getting towards being edge on, disappearing next year for a while. It'll be very, very hard to pick out when it does that, and then it'll open up again. Jupiter's getting better over in the eastern sky, and it'll be as best in early December, and that'll be when it's so-called opposition opposite the sun in the sky. So, really good time to see it closest to the Earth. Loads of details that perform moons around it are really exquisite as well. And if you've never seen it, then the 17th of November is the opposition of Uranus, which is obviously the planet out beyond Saturn, and that's not bright. It's something that you can just about see with your eye if you're in the right place, and it'll be in Taurus, so you probably need a chart to know where it is. If you have access to quite a good telescope, then it'll look like a tiny blue-green disk, and it is striking. It's nice to see it. You're not going to look at it and be blown away by it, but you will know that you're looking at the 7th planet, the one that was the first one to be discovered with the telescope. And finally, of course, we've had the Northern Lights as well. Keep an eye out for that, because we just don't know really what another display of the Northern Lights is like to happen, another auroral display, I should say, the Southern Lights as well. All you can do is keep an eye on things like spaceweather.com, use the Aurora Watch app, and just check when one of these ejections and material from the sun is hitting the Earth. We just don't know, but the sun is still very active. It's officially at Sunspot Maximum now, so this year, the remainder of this year, next year is a really good time to keep an eye out for that. I've still got my fingers crossed for getting up on a dark morning in December, 7am, throwing open the curtains, and being like, not like, can you inbough from the air or something? You know, like in the sun setting at 4am, and you're on the train, or you're walking back later on, and you're like, not like, that's what I'm hoping for, is that I don't even get the alert, or I've not seen it yet, and I just happen to be out when it's dark, in winter, and I just happen to see them. I feel like that is a very big hope in the South England, however. Yeah, you know, the producer and I, Richard, were talking about the 70s for different reasons, and in the 1980s, there would have been no internet alerts, so you just saw the Northern Lights, they just happened. Maybe someone phoned you if you were very, very lucky. I just want surprise Northern Lights, that's all. Yeah, they are amazing. Absolutely. Well, I think that's it for this episode. I was just about to read the next line of our running order, and it's like, we'll be back next time with an episode on, and it's blank. So, it's a surprise episode next time, but there will be a bonus episode in a few weeks. And contact us if you drive some astronomy at home, it's at SupermassivePod on Instagram, or you can email your questions to podcast.ris.ac.uk to keep the ever-growing Supermassive mailbox a greeting, yes, more emails, and we will try and cover them in a future episode. Until then, though, everybody, happy stargazing. When considering care for a loved one with dementia, you want peace of mind that they'll be in the very best hands, with care delivered by expert teams and supported to live life happily, comfortably, in a dedicated environment that supports independence. You can expect all of this and more with Southern Down Care Home. You're invited to our Open Day on Saturday, the 20th of June, to take a look around our home and discuss what support you need. Visit budgester.com. The future is unpredictable at times, but the Open University are the experts in online learning, allowing you to fit study around your life. 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