The life and death of (double) stars

This is the contact with the test 1. Touchdown. Welcome to Space Cowboys episode 12. Hi, Thijs. Hey, Herbert. How's it going? It's great. Yeah. You too? Yeah, doing wonderfully, actually. Yeah, it's really great. And I love the topic that we're going to talk about today. Double stars? Well, and the life and death of stars. Life and death of stars. Oh, well. I love it. Plenty of drama there. Plenty of drama and the basis of many of the things we see around us. So that's wonderful. And we're going to talk about that with Selma de Mink. Selma, welcome. Hi, Thijs. Hi. You do many things and we're going to give you a large introduction later, but you're an assistant professor at the Anton Pannekoek Institute at the University of Amsterdam. Associate. Associate. Associate. Not assistant. Associate professor. That's subtle. That means that is a big difference. What is the difference? Assistant professor. Assistant professor doesn't have a permanent contract, so an associate professor can stay for life. And you can. I can. Congratulations. Good. Good for you. Yeah. And you've been winning so many things that you can do the research you want, right? Well, yes. The topic I work on has become very popular lately. Not just by our efforts. Sometimes luck is involved in astronomy, but big discoveries have been made and that helps to get money for the research you want to do. I'll bet. And your topic is, in your own words? Yes. I work on massive stars and especially I want to understand how they die, leave black holes. And the reason why this has become very popular is that black holes can also produce gravitational waves, if there's two of them, that collide and merge together. And we have discovered those. Well, not me, but... Not me. Not you. Definitely not me. Definitely not me. There's a large collaboration of amazing scientists in both the US and Europe and actually worldwide that build an incredibly, insanely sensitive detector. That can do such accurate measurements that it can measure ripples in space time. LIGO. LIGO and Virgo these days, but the first discovery was by LIGO. Yeah. Great. Great. Sounds interesting. Yeah, definitely. So we're going to talk about that this episode and it's great. But first we're going to go to our stories of the week to see what's been happening. Herbert, I still have no clue what your story of the week is. Well, I'm not going to give you one. Oh! Because I seem to remember that you were in the US. Oh! I seem to remember that you wanted to start off with Selma's story of the week, didn't you? Oh yeah. Well, yeah. Yeah, actually. You told me just now before I started recording. That's true. Before we started. Yeah, that's great. Yeah, yeah, yeah. So you're going to... Oh, this is suspense building over here. That's right. Yeah. So Selma, we always ask our guests, do you have a story of the week? It can be anything, you know, anything from pop culture to something from your field or something you read in the news. And yours? Well, it's going to show my obsession with my topic, I guess. When you asked me... I think the thing I'm most excited about, not exactly this week, but in the past few weeks, there's a group in Princeton, a group of scientists that have been searching very hard in the data of this LIGO detector that we will talk about for the next hour and briefly mentioned. And they searched very hard in this data and they found another black hole. So we knew already about 10 of them and they found number 11. And I'm incredibly excited because it's a very special binary black hole, two black holes that are probably spinning very fast. Spinning very fast. And so it's two black holes also in a cosmic dance. Yes. And colliding onto each other and shaking space-time. That's beautiful. I love that. It's crazy. And when you say spinning, is it spinning around one another or are they spinning themselves as well? Both. Both of it. Okay. There's a lot of spinning going on. But the excitement is that this big collaboration of several hundreds of astronomers have worked so hard and did amazing work and got another one. And I think it's a very good thing that we got this discovery trigger, the Nobel Prize for this. Well, at least three people got this discovery trigger, the Nobel Prize. But so many people worked so hard. And then there's a small group of people that go sit down, analyze the data again, and they find another one. So I like this kind of... And you can still do discoveries without actually being at the forefront. You can still go through old data basically and maybe discover new things. To be fair, I should say it's very likely a black hole. But we always talk in progress. We talk in probabilities. And the real detections by LIGO are very clear cases. This is a case that has, I forgot exactly the number, but something like 60% chance to be real. And so it's on this ad. I want it to be real. Let's put it this way. The edge of what's possible. Yeah, great. My story of the week is different. It's about WFIRST and it's more about politics, I think, than about the actual telescope. WFIRST? WFIRST. Yeah. Well, let me just get the acronym right. The Whitefield Infrared Survey Telescope. It's a infrared telescope that's supposed to launch in the 20s, somewhere in the mid-20s. And basically what it's going to look for is how dark energy works, what its influences are and how... So much more about this than I'm almost afraid to say anything wrong. And it's a telescope. Yeah. Yeah. And the thing is, it was sort of going to be in conjunction with the James Webb telescope as this sort of like new generation, large space observatories. The thing is, there was a new budget that came out by President Trump. And if you just basically look at the numbers that are being reserved for this field of scientific research, they've been cut. And it's the same as last year. So last year there was a similar budget that Trump introduced. Yeah. And so the American president introduces a budget, then Congress has to approve this budget eventually. So very often they put stuff back in or take stuff out that Congress does or does not agree with. And so they tried last year and now they're sort of trying again. But even Scientific American, the Scientific American is now running headlines like, is NASA's golden age of space telescopes ending? Because there's... The whole reason is because the James Webb telescope went over budget. So incredibly that basically they're looking like where the money should come from. So either they just increased the entire NASA budget. And it's bad PR as well, like over budget. Yeah, exactly. And so I think they're sort of trying to cut it elsewhere. And so it's now up to Congress to see if they just want to increase the entire budget for this whole field so that both of them can still go up or that indeed something like WFIRST is maybe not entirely canceled, but at least... Well, delayed for a few years until they got the money. So you have beautiful projects eating one another. Yeah, exactly. That's helpful. Yeah. They could also just pump more money into NASA. That will be a solution. Somehow I don't think that's going to happen. Just print some extra money. Do you? Well... Print some extra... Yeah, that's what they've been doing for... They do that all the time. If you can save banks, you can also support a space telescope. Yeah. Well, what is exciting I think is that space is so extremely cool that whether you're left or right or conservative or progressive... Hey, space is too big to fail, right? Well, but space is such an exciting thing. It's a moving forward science or it's moving whether this is for... We want to be the first to do so and so. It appeals to people across the political spectrum. And so that has put astronomy relatively safe. Science about global warming, of course, wasn't very safe lately. But astrophysics and space travel has been more safe. It's one of the few bipartisan issues. It's maybe the only... Especially if you look at the market. Yeah. I think money is the only issue that both sides of the aisle in America support and elsewhere. So yeah, it's one of the reasons why I love it so much. Yeah. I'm reminded now of a famous joke by Ronald Reagan. There was something about a budget deficit and he told Congress the budget deficit is so big now, I think it can take care of itself. Yeah. Well, yeah. Maybe. Maybe. We'll see. So now without further ado, Herbert, your story of the week. Yeah. I have two stories, both of you. My story is very much down to earth. Do you remember the super wolf blood moon? Yeah. Okay. That's what I think. And that's what I thought at the time. I thought it was quite ridiculous because it was just a regular moon eclipse, right? Yeah. And then I don't know if you noticed, I didn't, but I looked it up. In February, there was another thing. It was called the super snow moon. I think I heard it. And it was called the super snow moon. Right. And it was just another slightly bigger moon than usual, you know, and somebody decided we could call it the super snow moon because there's often snow in February. Depending on where you live. Yeah. Somebody else called it the super hunger moon because in old days food could be scarce in February. Yeah. Okay. So basically every full moon needs its own name now. Is that what we're talking about? Well, at least when the moon is full during perigee. Perigee. When it's closest to earth. Okay. You know, so then it's slightly bigger and you don't notice that with a naked eye. I mean, it's not that you look up and you shout, wow, the moon is so big tonight. No, it's not that. So it's just in the papers and in the headlines. And now it's March and the moon is still a bit in the neighborhood of perigee. Okay. So you get the picture. I mean, it was beautiful. I was looking, I was walking through Vienna yesterday. Yeah. I saw the almost full moon. It's been beautiful. It's beautiful. Yeah. It's beautiful. There's so many exciting things in science that we need so many hyperlative. Yeah. Isn't science good enough for you? Yeah. But now guess what they call it this month. I don't know. The Easter moon. I don't know. According to various websites, it's a super equinox worm moon. And I have no idea why. The worm moon? No comment. I think we'll discuss it. I think I'm a supernova in the moment. I think my field is also full of all this super duper. I decided to call it the super bullshit hype moon. Yeah. The super bullshit moon. Yeah. Is in the sky every night. But it gets some websites very much confused because one asked the question, will we be able to see it in Arizona? I mean, hope for clear skies and look up. Yeah, exactly. Especially in Arizona. Yeah. Yeah. So I'm going to go to one website. See if I can find it back. Which let me see. I mean, there will be so many names for the moon that at a certain point, I mean, I'm already losing track. It's just like, hey, it's a moon eclipse. That's awesome. Yeah. Yeah. Sure. But if you then brand it, I don't know. Plenty. Do we brand supernovas? I don't know. Well, you need to. Usually you need a telescope to see a supernova, but a moon you can see from any major city. So maybe that's some of the things we can experience, even if we don't live in the countryside. Yeah. Yeah. Yeah. Yeah. Yeah. Yeah. Yeah. Yeah. Yeah. Maybe that's some of the things we can experience, even if we don't live in the countryside and have a dark sky. Some sort of cosmic conscience. Yeah. A little bit. This silly stuff will be over now because I'm told it's the last supermoon of the year. Finally. Well, and with that. That's my story of the week. Yeah. Well, thank you, Herbert. Awesome. You're welcome. So we're going to go over to Selma and all your topics. So Selma, I'm going to do a proper introduction. Yeah. So, you're the associate professor at the Anton Bonnekoek Institute at the University of Amsterdam. You have a fellowship, and you've had a fellowship at NASA, Princeton, and the University of Bonn. And you won the Merrick Prize. You got a VD. You have to maybe explain what a VD is for non-Dutch people. It's a Dutch award to support research groups here, and it allows you to either start building a team. You can start with maybe two PhD students and a postdoc. So you can really start your research group. That's nice. And you are an Espacia laureate. And you also did both your BAs and your masters and your PhD cum laude, which is like, what the hell? And Selma, if I understand correctly, you are now in a position where you can basically do the research that you want. You can formulate your own questions and you're smiling ear to ear because- Well, yeah. I'm not distracted by an overload of emails and service tasks and teaching, which I really enjoy. But yes, we always want more time for research. Can I do the research I want? Usually I'm behind on all the things that I- Yeah, exactly. Yeah. So what are your main- But yes, I get paid for working on amazing things, stars that die in a computer. So I'm a theoretical astrophysicist. So people often ask me, do you look through a telescope? Well, no, I don't do that. But I send computer programs to- Well, sometimes on a small computer, but sometimes we send it to a supercomputer to compute and try to predict what these stars will do during their lives. And well, this is a pretty old field. And so this is one of the ways that we learned what the sun is likely going to do at some point. The sun now is relatively quiet. It's flaring a bit and maybe that gives some trouble with our mobile phones once in a while. But overall it's very, very stable. Mm-hmm. And it's been like that for so many years that life could actually develop on earth. And why is it so stable? That's because deep inside there's a nuclear reactor going on that's powering the sun, fusing hydrogen into helium. But one day it will run out of fuel, right? Nuclear energy is also not infinite. Yeah. When all the hydrogen is gone- When all the hydrogen in the center is gone, it needs to think of something else. And the center will consist of helium and will start to contract. And when the center of the star starts to contract- Yeah. Yeah. When the center starts to contract, the outside will respond to that by expanding. Mm-hmm. That's something I was teaching this morning to my students in class. So why that is, you can write down the equations. It's not so easy to understand. Mm-hmm. But so we know that stars will expand and become bigger and bigger and become what we call red giants eventually. That's so our sun will become a red giant. A red giant. How big will it become? It will be so big that we are not safe here at earth, right? It will be bigger than the earth's orbit. So we will- Elon Musk is right. Mm-hmm. We need to leave this place. We need to go. We need to leave this place. Well- How much time do we have left? We have a couple of billion years left. A couple of billion? In that time, the planet formed life started from basically nothing to what we have now. We can, I think we have time to evolve into something more sophisticated or- Yeah. We have time to kill ourselves. Or to kill ourselves or to leave. But I wonder if there was like 1 billion before it starts to run out of hydrogen. It's a few giga years are left. But it starts to slowly change- A giga year is a billion years? A billion years. 10 to the 9th. Yeah. Okay. Yeah. Yeah. In Dutch, we have different words for this, which are not mixing with the English ones. I like the word giga year. Yeah. I like that. I'm not that sure I do it right. So it's not within one giga year that the sun will start expanding. It's more than that. It slowly starts to expand over the next giga years and maybe that's already harmful for life. I don't quite know, but the real drama is in about four giga years. Okay. So basically halfway-ish concerning the earth. As far as earth goes, as far as human civilization goes, we have lots of time left because we're only there. We've only been there for a hundred thousand years or something. Yeah. Well, human life. Yeah, of course. So, okay. Well, give us some time and then we'll leave. That times 4,000, 40,000 or something. And you're in the giga year, your four giga year range. Yeah. Yeah. That's fine. I don't worry about that much on a daily basis. But what I do worry about is stars that are way more interesting than the sun. I mean, a red giant is kind of cool. Hey, no disrespect to our sun, eh? It's cool. But these stars are slow. I like stars that are at least 10 to 100 times more massive and they can be a thousand to a million times brighter than the sun. And they live much shorter lives. They're very bright. So they shine at a much higher rate. Mm-hmm. And when they're shining, that means losing energy. That also means in the center, it needs to burn much faster. And even though it has a bit more fuel, because more massive, it's burning at such a high rate that these lives of these stars are just millions of years. Right? Millions of years is very short. Can I ask you a question? Yeah. Can I ask you a question concerning cause and effect? You tell me it shines very intensely, so it needs to burn energy. I would say it's burning energy at a high rate and therefore it shines very intensely. No, that's a complicated one. That will be an exam question, I think. For my students. It shines because it's hot. Anything that is hot shines. Actually, we are shining as well. We're shining in- Yeah, infrared. Yeah. Infrared. You can see this with a camera that a fireman would use. That's true, yeah. So anybody that has a temperature shines, so do stars. Anything that shines loses energy. And while it loses energy, it has to respond to this and it slowly contracts. That heats up the star. And as it happens at those temperatures, it burns. But cause and effect is a very funny, curious thing. I love this. Yeah. Because a star basically exists because in the middle you got nuclear fusion going on that wants to go, that creates sort of an explosion that wants to go out, but then gravity keeps it together and that's what makes a star stable. Life of a star is one big struggle against gravity. But it shines because it's hot and it shines so long because it has nuclear fusion. That's why it can keep shining for so long. Okay, good. But you work on these super massive stars and so they're incredibly young, you say. They're very massive. We use super massive for something that we don't think exists anymore, but like a hundred times more massive than the sun. And something really peculiar about these stars is that they're not alone. Meaning if we look at our sun, it's just one star. It's not really alone. There's a lot of planets going around it. And actually Jupiter is such a big planet. If it had been a bit bigger, it would have kind of been a star. Yeah. It's a pretty wimpy star, but well. It's sort of a failed star, Jupiter. Jupiter is pretty far out. Massive stars, what you can imagine, so the closest planet is Mercury, right? So it's pretty close to the sun. If at the place of the sun you put a star that is 10 or 100 times more massive, typically such a star has a second one of those at roughly this place where Mercury is. Okay. That's very close. Very close. And so then you get these amazing pictures. I think, is there a Star Wars? Is there a Star Wars movie where you see a binary star sunset? Yeah. Oh yeah. It's one of the ones we use in public talk sometimes. Yeah. Well, the question is, can you have a planet around a massive star? Probably not. You could have a planet around a binary star, probably a low mass one, but. Yeah. If it's too big, then it's too, then it will devour anything that's close to it. It needs to keep its distance to the pair. Yeah. It's a bit more stable. The planet needs to be reasonably far away. Could you form life there would be a different question. Oh yeah. Yeah. But what I meant, interesting, if you put these stars so close together, what's, what's, what does it do to these stars? Do they have a normal life? If I put them separate far apart, do they have the same life as when I put them so close together? Well, no, because we just talked about the sun, that the sun will expand and become so big hundreds, a few hundred times bigger, as big as the orbit of earth. Well, imagine this very massive star becoming a few hundred times bigger, but there's a second star sitting at Mercury orbit, right? That's going to give trouble for sure. Crazy things will start to happen. Yeah. Yeah. First, before we start talking about these crazy things that can happen so I can get a little bit of a grasp of it. So I know that Beetlejuice is a really massive star, right? And then Eta Carina, Eta Carina is also a very big star, but that has this small little star that torments it, that goes around it, right? How did you, can you first talk about maybe about Beetlejuice, like how big is that and, and why is that one going supernova and how does that compare to something like Eta Carina, which is also a gigantic star? Yeah. Yeah. And so, I'm going to start with the Eta Carina. So you have a gigantic star, but then has one little star tormenting it. Do you have an inner encyclopedia of stars in your head? No, but I really always... I don't remember all the data, but I know a few stories... No, but I love these because they're so, they're so, they're so wild. Beetlejuice is, you can see it easily. It's in Orion. It's a top left on Orion. I know that one. Yeah. And you can really see it's red, right? It's one of the shoulders. You can truly see it. Yeah. So that is a red supergiant. That's even bigger than the sun will be. The sun will become a red giant. The sun will become a red giant. So I'll give you credit for your super duper moves. Exactly. And one second, because what I loved about them is I think because they're so, besides that they're so visible, they're also about to go supernova. So I'm sort of secretly waiting, like maybe in my lifetime... Watch in hand. Yeah. Is it exploding yet? Yeah. Is it exploding yet? Exactly. So that's, that's the reason why I sort of know about these two because I just, I just love them. Yeah. And you can, and you can point Beetlejuice out. Sorry. Yeah. Well, it might have been. So how do they, how do they, how does a supergiant star like Beetlejuice and, and to also just kind of talk about these two stars, how does one compare that does not have this tormenting little star that goes around it and how it compares with one that does? Well, you know, maybe Beetlejuice already ate its companion and it's a melted version of two of them. I forgot if Beetlejuice, some of these stars, they are moving around and I think that was the case with Beetlejuice as well. Was there a bow shock around Beetlejuice? Maybe I'm mixing up two stars now, so I have to be careful. You didn't prepare me for this question. So sometimes you can still see the after effect of, of maybe it as a star that's being devoured. So it's still wobbles or something. It's hard to see if it really has devoured the other star then it's tough to know that because the star will find a new equilibrium fighting against gravity. Yeah. Then the interior might be different, but do you see this in the outside? We don't quite know. Yeah. If it once had a companion and it kind of got rid of this companion. The system broke up, then this star can run away. Yeah. And I'm not remembering sharply now and I really should, but I think there is a bow shock near Beetlejuice. Meaning? But I'm hoping I'm not mixing up with another star. What would that mean if you see a bow shock? Well, when do you get a bow shock? That is when you move very fast compared to the medium that you're moving in. And so this red supergiant has a wind and this wind says particles coming off and flowing away from the star, but it's crashing into. Yeah. Yeah. Yeah. So it's a little bit of particles that are in space. Space is not fully empty. We call this the interstellar medium. It's very low density, it's almost nothing, but not fully nothing. And so if this wind blows into, it's a bit like a boat going through water, right? You also get a bow shock around it. Yeah, exactly. And maybe before we continue, it's good to know something like Beetlejuice will go supernova and what a supernova then is. What happens in a supernova? Ah, but first it might have already gone supernova. Oh, of course. It's so far away. Maybe the information is still traveling to us. That's true. That's true. Yeah. But okay. So what's a supernova? So the stars, they burn in their centers hydrogen first into helium. That's an heavier element. And what then can you do? The star can contract further and get hotter and hotter. And at some point you can burn helium into carbon and oxygen. And that's really the carbon and oxygen that's, well, you can take a deep breath. We are stardust. That is truly the oxygen that was once made in these stars. Yeah. And so the question is how does it get out of these stars, right? So we know stars make it, but how does it get out? And so it doesn't stop at oxygen. Oxygen can still burn further, but it does stop around iron or so. Iron is a pretty heavy element. If you remember your chemistry class on all the periodic table, there's many more massive elements, but they, you don't get any energy anymore. Iron is the most stable element and you cannot smash two iron atoms together, or you could, but then you will just break up and it will take energy. It will cost it. Yeah. It will cost it. Right. Yeah. So you, you basically stop at iron. Fusion stops at iron. Yeah. So the inside rapidly becomes almost like an iron ball. Yeah. Okay. It's super gigantic. Yeah. Can't collapse even further. Well, as it turns out, iron looks like something strong, but if you put enough of it together, the weight is so heavy that it cannot support its own weight and it will collapse under its own weight. And this is something, well, the technical term is a degenerate material. And so it's very hard for this ball of iron to have enough pressure to not collapse under its own weight. If it's more massive than a certain mass, which we call the Chandrasekhar mass, which is actually my lecture of this morning at the university. Oh, wow. We're just redoing your lecture of this morning. Well, without getting technical, it's, you can imagine that there's a certain mass that it cannot support itself. Chandrasekhar was an Indian scientist. A scientist who was 20 years old, traveling by boat from India to UK. And he worked this out. He has two books with him. Eddington's book on the internal constitution of stars and the second book on relativistic, well, on electrons. And that's the only two books he had. And he put these two together. And then it's a very, well, for university students, it's a relatively simple exercise to work out what is the maximum mass of such a star. And there's a very nice interview with him. Like, did you really understand how important it was? And he says, yeah, he understood, but he had a lot of criticism from the people around him. Because why would something collapse to, to what? To a point? Yeah. And so this is something, it's very profound, right? So you have material that is sort of things that we know, like iron, and it would collapse to something that we don't know, to densities that we have never thought of. And so now we know that it would collapse to something that we call a neutron star. Oh, I was waiting for this. Oh, yeah. Yeah. So it would collapse into a neutron star. Okay. Or, well, it could even collapse into a black hole or first into a neutron star, then into a black hole. But it will collapse to something so compact that is something that we have never seen on earth. We can theoretically imagine that some, well, smart people can imagine that something like that could exist, but it's not something that you, I don't know, find when you go out on the planet. Just make up. Yeah. But then, so when does it collapse into a, when does it become supernova? When does it become a neutron star? And when does it become a black hole? So, yeah. When does it become a black hole? So. We're slowly going through all this because we need to understand before we understand anything that you do. So the star has done all the burning it can do. Yeah. It has a very massive iron core that collapses under its own weight. It forms a neutron star and it was collapsing. And then the density gets so high that this neutron star bounces back. And this shockwave that creates the bounce travels through this star outwards. And well, actually there's a few things we don't know how this happens, but apparently this shockwave and maybe even neutrinos can help then. For the shockwave for the outer parts of the star to be expelled from the star. And that creates a lot of light. And that's what we call a supernova. Yeah. And that's an amazing amount of light because I read that the Crab supernova in what was 14 something, 500 years ago, was visible during day. Yeah. Wasn't it? Well, yeah. That was discovered with… Yeah. By day or that, I don't know. It was incredibly bright. Yeah. You can read a book. It's like a full moon, I always hear. Yeah. Yeah. Exactly. I don't know if you have a mental picture of what galaxies look like, but… Sort of, yeah. I don't know. This nice spiral structure. The spiral stuff. Yeah. When one of these stars goes supernova, it can be almost as bright as all the stars in that galaxy together. Holy crap. That's a lot. That's bright. Exactly. And then also new material is being formed, I always hear. Well, it's such a… It's such a hot explosion that at that moment you also have a lot of nuclear fusion going on and radioactive material being thrown out. Well, some disappears in this neutron star, but the layers above it, they were expelled into space. And part of this is the oxygen and carbon and iron in your blood and in your tissues and in your body, right? So we already mentioned this, but we are made of stardust. Well, there's a long step from this, but this supernova material will someday cool, form nice… Yeah. …like the Hubble clouds. Maybe you've once seen these pictures of Hubble of these clouds where stars are forming. Yeah. That's one of the pictures I saw as a kid because the… How old is Hubble? A few… It had its 25th birthday a few years ago. Yeah. I'm roughly of the generation that where as school kids, these pictures came into the newspapers and inspired me to go into science. Oh, wow. Yeah, I have them all over my house, Hubble pictures. Yeah, actually. And I have this fantastic book of Hubble. Hubble pictures. Yeah. and I give them away at birthdays as presents. And it's great because you just mentioned the Crab Nebula, Herbert. It's great because you can see the remnants of an actual supernova, which is beautiful. A lot of Hubble pictures is then a Photoshop job as well. They just take some of the visible light, then some of the infrared, right, UV, and then they put it together. It's true, but your photo camera does that as well. Yeah, yeah, okay, okay, okay. The colors are slightly different than you would see by eye. Fair point. Hubble was launched in 1990, so that's almost 30 years ago. Wow, it took some time before it took decent data. It needed some glasses and all that. Yeah, exactly, yeah. And it's slowly becoming older as well, right? Because Hubble taught us so much about the life and death of stars, right? But I've been reading more and more messages that it's aging, that the James Webb Telescope needs to go up. When will Hubble cease working? Will it someday run out of fuel for attitude control or something? What will be the limiting factor? Well, it's an old instrument, so many things, you know, an old car, something will break. You don't quite know what breaks first, right? There's many parts of your engine that can stop working. So in Hubble, the most risky parts of Hubble, it was just a few months ago, one of the gyroscopes, isn't working. Exactly. So a gyroscope is just basically a spinning wheel, and it helps you to orient Hubble. So if you want to point at a certain star, you better have a very good control over the orientation of the satellite. And... Somebody didn't mute there. I'm shutting my laptop off. And so it has multiple gyroscopes, and for some reason this is a very fragile instrument. Because it has moving parts. I think they had about six, but there's a few that are broken. Yeah. Or they had some spare ones that went online. So that's the sensitive part. There's something else sensitive that's very important for the type of research that I do. So Hubble is one satellite, but there's many cameras and instruments on it. Some make pictures, that's the ones you probably see in the newspapers. Others are what we call spectrographs. And that is instruments, that's basically, you know, the Pink Floyd t-shirt, right? So the prisma that's, if light comes in, it will be spread out into a rainbow. Well, that's basically what a spectrograph does. So you take the light of stars and you rip it apart in all the colors it has. And if you look in much detail, it's not just a rainbow, but you will see all kinds of dark lines and brighter lines in it. And these lines tell us a lot about the composition of stars. What winds they have, do they rotate? Do they have companions? Are they alone or is there something else? And that's how we know that these supernovas make all these different elements. Because we can just look at it and suddenly see what components they have. Just looking at the colors would not be enough. That helps a lot. That we can take space. And then we can look at the spectrum. Yeah. Not just with Hubble. Exactly. And so I'm going back to, I still have two questions open. So what's the difference between a regular normal star and one that has a companion? The other one is when does one go supernova? We just answered that. And so when does it go to a neutron star and when will it become a black hole? Oh, well, I wish we knew. Okay. So that's why I never understood. We don't know. Most popular books will tell you that the most massive stars or most massive cores make black holes. The most massive cores make neutron stars. Honestly, if you go to a conference now, we'll be fighting over what is really happening. And it's probably much more complicated. Really? Most textbooks still say if it's stars over, I don't know what they mentioned, like if it's 20 times the mass of the sun, it will make a black hole and below a neutron star. That's not what the simulations today show. But it's an active matter of debate and computation. So I don't know what the answer will be. Really? I was always so confused about it. I was like, nobody was ever able to give me a straight answer to this. It's probably two of the biggest questions in this, in that particular area. How do supernova explode? Because most computer simulations fail. Yeah. Apparently they do. We see them, but the computer simulations have trouble. We can do a few of the lighter-ish stars, but most of them, they don't explode in the computer. Are we missing physics or are these simulations so complicated that we need much more computing power to actually resolve all, everything that we're interested in? And the second question is, what makes a supernova? What makes a neutron star? And what makes a black hole? Yeah. And we don't know this. We don't know. Well, we know it's both massive stars, but what decides? It's good news. There's something left to be found out. Yeah, definitely. Definitely. So, and it's great because we know they're there. That's what I love about science. So you can see that they're there. So there's clearly an explanation. There's an open question. So there's a lot of, you know, there's somebody one day will run out. So no prizes to be won. Yeah. Somebody, yeah, exactly. Somebody will run out of their bathtub and yell Eureka and be like, oh my God, we failed. That's right. We found it. We finally found it. So. Well, the yell Eureka, that's an idealized version of science. Of course, you work very hard to watch this. I know. I know. But still, sometimes, sometimes it still clicks, right? Still, sometimes. Yeah, that's not a great idea, but it's usually, well, we shouldn't over-celebrate it because Eureka could be the start of an idea, but truly proving that something's true and doing the measurements, that's just hard work. So it's easy to think of scientists as geniuses that somehow magically do this. But something emerges. Yeah. Yeah. You have to concentrate on something. Exactly. It's a bit of a romantic picture. Yeah. I think it's also romantic, but. Yeah, you have large teams that gather a lot of data and then truth emerges. That's also a more collective thing. Well, my point is, science is not just for rare geniuses that are just born this way. If you're fascinated with this, then you should go for it. Yeah. And so what is a neutron star? Well, it looks a bit like a star. It's roughly round, but it's not made. Okay, that's the start. It's. It's not made of the same material. The sun is made, stars are made mostly of hydrogen and helium. And this one is made of neutrons. And it's crazy small, right? Yeah, about 10 kilometers in size. 10 kilometers. Really crazy small. It's like the size of Amsterdam. Asteroid size. Yeah. So you should really think of a core of a star that is more massive than the sun. So think of the sun. Yeah. Try to compress it into something that fits in the city of. Of Amsterdam. Yeah. Whoa. Yeah. That's some serious compression. Yeah. That's a good compression rate. And so as its name would give away, it's just neutrons. Well, maybe some tiny things at the surface. Yeah. Something else. Yeah. And these neutron stars, that's not my field. So where have the protons and electrons gone? Oh, the electrons were. Expelled during the. No, the electrons and the protons were pressed together to make neutrons. Ah. But there's a colleague of mine you should invite to talk about. Yeah. Okay. Okay. Okay. So what's the difference between a neutron star and a black hole? Black hole is if a neutron star is too massive. Yeah. So either the core of the star is so massive that directly it falls into a black hole or there's first a neutron star and then this neutron star is too massive. So we think that if you can at maximum make a neutron star of about, certainly not more than three times the mass of the sun. Okay. The most massive one we have seen is about two times the mass of the sun. And so we're fighting still where's the real maximum. Yeah. So three times the mass of the sun, there's a theoretical limits that we're all agreeing with and below that people are really trying to find. You still have a chance. Okay. Wow. Well, we can really learn something about the theory if you find neutron stars there. Wow. Okay. So we got a lot of ground covered here. So I'm happy. My understanding is, is, is. Yeah. I'm super happy. Like I'm finally have someone to ask all these questions to. It's great. So before you can answer my question about these double star systems, right? Maybe it's, maybe it's just good that if we get an understanding of the different types of stars that there are, there's this, there's always the great what's the word for it? The way to remember it. Oh, be a fine girl. Kiss me. The classification of stars that you have different types of stars. You know, that's a very sexist line in a time. Oh, be a fine guy. Kiss me. Hey, that's there. Is that also sexist? Hey, be fine. I don't know. Something else. Something else. Be a fine genderless being. Kiss me. Yeah. I don't know. So that's, I mean, that's just naming, right? And this naming came from a time while they started with the alphabet and later they understood that the order, logical, physical order was different. Oh really? Okay. But honestly, it's just names. So I'm, so there's, I don't really care how the butterflies are called and how you classified. I want to understand why they are the way they are. Yeah. But basically there's big stars, there's small stars, there's hot stars, there's cold stars, there's old stars, there's young stars. And this classification system gives us some guidance on, on where they all are. Right? Yeah. Yeah. Okay. Yeah. Yeah. So now Eta Carina, it's this double, if you know about this, if you know about this, it's this double star system with this one huge star and then this tiny little star that goes around it. You don't have to give me any specifics because maybe you didn't study the specific. Oh, we talk a lot about this one. This is the wildest star. We usually go to the gravitational waves, but on Eta Carina, it's one of the biggest monsters that we have nearby. Yeah. So Thijs has good reason to be obsessed about it. It's really a special thing. So fair. It's throwing off enormous amounts of mass. The pictures of this are beautiful. It's actually throwing out mass in sort of its north and south pole direction. Well, it doesn't even have poles, but it's sort of too, and homunculus is the name for it. Yeah. You have to put a picture on the website. Humongous? It's a little guy. Homunculus. Like a peanut size. Okay. And so it has thrown off many, many stars. It has thrown off many, many solar masses of mass. There's a big debate why it's doing this. Maybe the most massive stars are just very unstable things. Yes, there is a second star. Honestly, I think that was the third star, if you know where I'm going. So it's very hard to make such a massive star. And some of the ideas is that Eta Carina itself used to be two stars that melted together, became this crazy thing that is spinning and throwing off all this material. And that the third star that's still there, it probably played a role for these inner two stars to actually come together. But this third star, yes, they call it the binary star, but it's far out. It's not what I was talking about before. You know, I was talking about massive stars and the second star being as close as the orbit of Mercury. But that's very close. It would take a few days for these stars to go around each other. The companion of Eta Carina takes five years. Oh, okay. I don't even call that a companion. I mean, it happens to be there, but it doesn't. So that's about science. Yeah. And how far is Jupiter orbit? Well, the masses are different. So my capitalist law is not as good to do this, but it's relatively far. So you study binary star systems. What I actually love is that if you go to the Wikipedia page of a binary star, the first animation you see over there is an animation that comes from your research. Oh, really? That's... I'm really flattered. It's this one, right? This is the one. Oh, wow. Yeah, exactly. Well, yes. You didn't know. That's fine. That was... Yeah, exactly. So just, I don't know what to ask. Tell me about binary stars. Binary stars. They're everywhere. I don't know. Maybe the coolest... Well, the closest to bring it closer. We were talking about the moon. What can you see? It's hard to see these binary stars. But if you want to find one, most people can find the... I don't know many of the signs in the stars, but I can find a Big Dipper, right? Anyone can. Yeah. I mean, it's the pen and the handle. And the handle is three stars, right? And the pen is four stars. So the middle of the three in the handle, if you look very carefully, it's not one star, but it's actually two. And it used to... The story goes that for a while it was a test... I mean, you can see this with the naked eye. This you can see with the naked eye. Okay, yeah. And for a while, I don't know if this story is true, but it would be a test of how good your eyesight is. I can imagine. Yeah. Yeah. Well, you know... I heard that. I always fail. Yeah. Yeah. So they're not really close, but they're physically bound. So they're actually close together. Yeah. Not just an illusion. Relatively close. Not as close as I want them to be, to do all kinds of fun things, but they are what we call gravitationally bound. So they stay together because they are close enough to feel each other's gravity more than of all other stars in the galaxy. And so later with telescopes people zoomed in, and so I didn't prepare this either, so I haven't looked this up, but both of these stars, I think one is actually a binary star itself. You can't see this by eye, but you can see this with a telescope. For example, if you take this Pink Floyd Prisma thing and... Yeah, you can clearly see it. Yeah. Yeah. If these stars go around each other, you can see the Doppler effect of this, right? The same as a fire truck passes by. If it's coming, the pitch is higher. If it goes, the pitch is lower. And that same happens with lights and this Doppler effect in light, we can see that in color. So you would see the lines of the stars shifting to the red and the blue and the red and the blue. So one of these is a double star and the other is actually two double stars. So I thought there was six stars in total. I might be one off, but... Yeah, I was pretty surprised that a few years ago when I got into stargazing that every other star turned out to be a binary star system. It's like we always thought it was one, but actually it turned out there's two. So this is very common and we're not really used to this because we have this, what is it, this egocentric idea that where we live is normal and our sun is single. Mm-hmm. So most stars have a companion and these massive stars... Most stars. Yeah. Wow. Okay. Depending on how wide you would account for as a companion, massive stars have companions that are very, very close, so close that their lives will be influenced. Meaning the companion is so close that these stars don't have the space to become red giants. They will start to, I don't know, eat their companion of flow, have mass flows from... Presence of the companion. Yeah. And that influences the evolution of the stars. The life and how it will die. Yeah. Yeah. So for massive stars that is happening for the majority. For stars like the sun, binaries are also very common, but they're usually a bit farther out. So far enough to maybe harm their planets or something, but not necessarily to... And so how do they behave, these binary star systems? Well, they turn around each other for a long time. So very typical system would mean a few days. So every few days they would turn around each other. Every few days. Super fast. That's, yeah, pretty fast. Yeah. And then it will still take millions of years for the stars to start doing anything because they have nuclear fusion, right? We just talked about why is the star shining and why is it shining so long? Well, massive stars can shine for about a few million years before they also run out of fuel in the center. And so the center starts to contract. The envelope starts to expand, just like for the sun. And so what happens is there is this point. If you expand beyond this point, you can see the sun. Beyond that point, that's bad. So this is kind of the point. Imagine that we're a little astronaut going to the moon. At the moment, we are being attracted by the gravity of the Earth. But there's this point when the gravity of the moon is stronger, right? So there's this point between Earth and moon where gravity switches. Pulls on you equally or when you cross Lagrange points. Yeah. So this point is called the Lagrange point. It's a little bit more complicated because you have to include the rotation of the system. But conceptually, that's the easiest way to think about it. So this also happens between two stars in a binary system. So if a particle, a gas particle of one star is getting so far that it's beyond this Lagrange point, of the point where the attraction from both stars is equal, if it passes beyond that, it starts to flow towards the second star. So it's a fall towards it. Yeah. And then it starts to eat it. The other star starts to eat the other one. So the technical term. It's what we call rush-lope overflow. Someone called Rush was the one who had to compute this. The more funny term that we sometimes use in press releases is that such a system would be like a vampire. And so this second star is basically sucking the gas out of the other star. And the analogy is not so bad. So the second star gets all fresh gas from the outer layers of the first star. Life energy. And that is fresh fuel. Mass is fuel for the stars, right? E is mc squared. That is energy as mass. We're burning mass into energy. That's what nuclear fusion is. So getting extra mass is extra energy. Extra energy means you're getting younger for a star or you can live longer. Basically, you can prolong your life. Vampire stars. It is a really accurate term. You have to say that with that voice. Vampire stars. And I'm starting to wonder which star is eating which. And if I understand you correctly, the one that starts to explode. Expand first is the one being eaten. Yeah. Okay. Yeah. So that's sad. Yeah. The one that evolves fastest. So the aggressive star that starts to expand and gets close to the territory of the other is the one that is actually. Okay. The aggressive one. The aggressive one gets eaten. Is dead meat. That's great. That's very just. Yeah. Yeah. Yeah. Yeah. Cosmic justice. Yes. There's another nice headline coming up. Exactly. And so then what happens? At a certain point, I can imagine that. Well, first, what I find interesting is that you sometimes already know that like, well, I think it's actually the third star instead of the second star. So it seems like a lot of these binary star systems might have actually been three or maybe even four stars all eating each other. And now there's like two left. And then eventually, how will this continue? Will they then become one or what are the next steps? It depends on how far where these stars apart. Mm-hmm. So if they're further apart, it takes longer. The stars are a bit older by the time they start to bother each other. It also depends on the ratio in masses. If one is much more massive than the other one, there's a much bigger difference between the two stars. This is actually also open questions. That's really something we work on in my research group. Okay. So we're trying to understand. But to simplify this, maybe one of two things can happen. Either you start to flow mass to the other star and it is unstable. Yeah. Or you start to move the other star. Yeah. And then a runaway process will start and it will engulf the other star and basically eat it. And the two stars will merge into one. So either you merge. The second is, and I showed you a little movie of this, and that's the one I think is on the Wikipedia site. That's on Wikipedia. So go to Wikipedia for binary star. That's the better outcome. It's this couple. So this very massive, aggressive star, if you want, is giving its envelope to the second star. But what is left is the core of this star. And so the core of the star will keep turning circles. Or orbits around this complex. Because it's back inside this dangerous limit beyond which it will be eaten. But it retreats because it's sucked empty. Sucked dry. Yeah. The only thing that is left is the center of the star, which has been burned into helium. And helium is much more compact than hydrogen. And so... But doesn't that burn itself up then as well? Yes. In the center, this star will keep burning, depending a bit on its mass. But so, and helium will... Well, we talked about this. It will go into carbon. It will go into oxygen. And so someday, into iron, into too much iron, it will collapse. Supernova! Supernova. And will blast the second, the now younger star, out of existence? No. I think they usually... It sounds very dramatic, right? A last punch. If you're two stars close together and one explodes. Yeah. Sounds... Computer simulations, honestly, we have to see what nature does. But computer simulations say that it's not so dramatic for these stars. You can blow off a little bit of the material. Only when you happen to have them super, super close at this moment, it can be dramatic. But this star is relatively okay for this blast to pass by. But it forms a Newton star. This is the one that dies. And this Newton star is not going to sit still. Usually this explosion is a bit asymmetric. And so a bit of the material is thrown to the left. And so what this Newton star has to do is going to the right. Right? This is Newton's law. Yeah. And so if you throw material to one side, you have to respond. That's how rockets work, right? Yeah. And so that also happens in a supernova explosion. So these Newton stars are born with what we call, even in scientific terms, a kick. Just like a kick in a ball. Kickstarter. Yeah. Or a birth kick. Okay. And so they are born with high speeds. And so, yeah, I think there was a NASA release also this week on a speeding Newton star. Yeah. And so it was a Newton star violating all universe traffic violations. No, it wasn't. It was still below the speed of light, but these things go fast. Yeah. And so where do gravitational waves then come in? Because you have what I understood from when they were discovered, gravitational waves or detected, let's call it that. It was also about binary black holes, I believe, going around each other and then causing these ripples in space time. Is that... Do they... So if a star goes around a massive star, is it already creating these gravitational waves or is it only black holes that do it? Any object that turns around another object is emitting gravitational waves. Just small, small little ones. I wouldn't propose we do this, but if we would hold hands and start spinning like we were in kindergarten, then we would also emit gravitational waves. Just so little. Really? So little that that's not what we measure, right? But still, I can do it. So I can make my own gravitational waves. Yeah. So anything rotating that has an asymmetry does emit some gravitational waves. Yeah. And Earth and Moon do it also. Yeah. But it's so little, let's not talk about that because we'll confuse everyone. So when can we detect this? It's so, so hard to detect. But you need very, very strong gravitational waves. And that happens if two things rotate around each other that are very massive, like Newton stars or probably black holes, and do it incredibly fast. How can you be fast? Well, then you have to be very close, right? It's Kepler's law that the planets closer to the sun rotate faster around the sun. And the same holds if you put them closer and closer. While normal stars, we can't put them infinitely close because normal stars don't fit if you put them too close. But black holes, you know, it's black holes, whatever black holes may be, but you can put them extremely close. And so they can rotate around each other. And the last turn before they merge, they almost go with a fraction of the speed of light when they collide. And so if you want to do the kindergarten, you can do it. Yeah. If you want to do the kindergarten dance, and we would be as massive as 10 suns, and then we would go with the speed of light, then there's a chance that LIGO will detect what we're doing. Exactly. And so you study these. And what do you want to know about them? What are your big questions? I'll tell you what I want to know. Oh, okay. Yes, please. What do you want to know? We talk about this whole life and death of stars. How much time passes between the beginning and the end of the story? For massive stars? Not much for astronomers, meaning a few million of years. Okay. Yeah. I mean, that's a lot for humans, but for stars, that is little. That's the shortest time span that is relevant. That is the time from having a star to an explosion. But an explosion will give you one neutron star or one black hole. So now we still have to wait. Let's say they're lucky enough to be in a binary system. We still have to wait for this other star to die and explode. And we talked about this kick. We need this neutron star not to speed away from the other star. We need to stay close. And so roughly, I don't know, one out of a thousand massive stars manages to have this, it's like a stellar marriage. Do these stars stay together? Everything, something dramatic happens, one of these stars will take off and fly away and they basically divorce. But in one out of a thousand cases or so, this neutron star or black hole will stay close to the neutron star or black hole of the other star. They will start spinning around. And then we have to wait because the only way for these black holes or neutron stars to come close together is because they already emit a bit of gravitational waves, not much. But the closer they get, the stronger the gravitational waves are that they emit. And that takes away energy. That takes away energy. Come on, it takes energy to shake space-time, right? So that has to come from somewhere. And so this will slowly spiral in and slowly we go from millions of years for the stellar life to death, and then billions of years from having two neutron stars to actually spiral in. Actually, it could be much longer, but if it's much longer than billions of years, well, that's the age of our universe, right? So if it's much longer than that, maybe some way, way future generation can see the gravitational wave. That answers my question. What kind of timescales are we talking? So considering your research, that's now open-ended and you can ask any, try to dive into any question that you can ask. What are your questions? So the, well, there's so many questions. Yeah, I know. See you think. Well, what I'm most excited about, I think the first gravitational wave event came from two black holes that were about 30 times the mass of the sun. And that was very heavy. Most black holes, stellar mass black holes we knew were about 10-ish solar masses. So how did we suddenly get black holes three times more massive? And so, well, the first big surprise that we had. We had this event in the first place. Most people were very skeptical. We're never going to find anything. And then, and then it happens and you see two black holes colliding onto each other. We have never seen such black holes before in other types of systems. We had seen very few. And so these gravitational waves, they really probe these remnants of stars in such a different way than we have done before. Yes. Yeah. Maybe we shouldn't be surprised that we start to find different things that we knew about, right? If you're going to explore a new country, you shouldn't be surprised that there's different birds and different. So this is this exploratory part of science. So we suddenly have this new window on very different remnants of massive stars. And I want to know where did they come from? Did they come from these binary stars that I'm studying? How did they get this black hole so close? If these stars want to be red super giants, how can they avoid eating their companion star before actually, how can they make sure they don't eat each other too early? I want them to merge. But first I want to have them become two black holes, right? And so there's many people in the field studying this and having different ideas on how to solve this problem. Yeah. I know you researched this by doing simulations. So now that you're telling us this and I'm trying to picture this, you doing simulations, it starts to sound like a computer game. Is that sort of the idea? Is it your experience as well? Yeah. Yeah. Well, a computer game seems like it's a lot of luck and you try and you try it until you're right. You can be a bit smarter, right? So it's a computer game in the sense where you really start from the laws of physics, the things that you hope really are true. And then you hope your computer simulations follow these laws of physics well. And it's not just simulations. What I contribute to the field are mostly the theoretical simulations. But we always work together. We work together with people that do the observations. We briefly before talked about the Hubble Space Telescope. That's very close to my heart, both because as a kid I was inspired by it, but also as a postdoc, I was a fellow at the institute where all the data comes in from Hubble. And so how do we learn? It's by comparing our computer simulations with the data that comes from, for example, the Hubble Space Telescope or other telescopes. And also now with the data that comes from gravitational waves, right? Yeah. So you try to think of the answer and then eventually you try to match it to reality, so to speak, to see where you… So you're not like Einstein who is reported to have said, what if the observations don't fit your theory? He's reported to have said, well, that will be too bad for the observations. Well, so stars are very complicated things and we know that there's no complete theory. I mean, it's a bit like imagine being someone simulating the weather, right? What is the… It's not a complete theory of the weather. It's so complicated. There's so many variables. And so it's just a complex system with, well, the technical terms, there's a lot of microphysics. You know that even your best computer cannot cover all. And with all respect to Einstein, he was thinking about very simple things in a way. Some of the jokes is what is the simplest thing in physics? It's a black hole. Yeah, yeah. It becomes very messy. Neutron stars and stars are, I would say, a lot more complicated than black holes. It's just they're a bit closer to our imagination. Yeah. Because we know about the sun. We see the sun every day when, well, unless you live in Holland where it's very cloudy. And so whether we have intuition for something as mundane objects doesn't make them less complicated. No. The comparison to the weather gives me an idea because I know meteorologists use a bunch of models and they compare them and, well, sort of let them vote and do statistics on the models themselves. And then tell us, okay, there's this probability that it will be rainy a week from now because half the models say so. Is that an approach that you follow too? Yeah, sort of. Yeah? Maybe. Well, there's some differences but they don't really matter for me. Have a lot of models and compare them. There's two people in my group who are really focusing on the statistics of modeling. How can you make probabilistic predictions rather than, I don't know, deterministic. Yeah. The laws of physics should dictate it. Yeah. So if you're doing a lot of data analysis and you're just simulating, maybe you cannot say the answer is A, but it's sort of A plus or minus a little bit and this is the distribution. Yeah. So that's a bit like weather modeling. Yeah. I never realized it was so much about probability and not so much about, like you said, that deterministic observation sort of. Yeah. Well, another thing to learn. I mean, even observations, I mean- Well, you don't know how it is. If you measure the mass of a star, we say it's 10 times the mass of the sun, but there's always an arrow bar, right? Yeah. So it's likely to be 10 times the mass of the sun, but there's a chance that it is a little bit less massive or a little bit more massive. So even observations are basically a probability distribution. So if the weather forecast says so and so- Chance of rain. We just wait and see what happens and then, okay, we have something to check against the weather forecast. So how does this work in your case? You can just wait for a couple of billion years. Yeah, that's problematic. So what do you do? So there's, yeah. Oh, there's a- Yeah. So the time scales in astronomy are usually too long. Although supernovas, you can actually watch from day by day. You can- If you're lucky enough to- Yeah, you can follow the explosion for most supernovae, like, no, 30 days. Some of the weird ones will stay bright for a few months. We got a very weird one that after a year was still bright. But that's the explosion itself, right? The stars are much harder. And so maybe the analogy there is a bit... I forget. I stole this from someone and I don't know from who, but the analogy is a bit... Let's say you walk into a square in a major city and you're an alien species and you want to understand the evolution of humans, but you're a strange alien species and you live on a different time scale. Say you're there for a microsecond and you see, take observations and you leave. This is fun. So you basically have a picture of humans and you see small humans and you see larger, taller humans and you see humans- Story's long. Bent ones. You see humans with gray hair. And so maybe you start to think of the laws of physics and you start to think maybe these small humans will eventually evolve into taller humans and then turn gray later. And so you need a theory here and then make predictions for if that's true, how many small humans, how many tall humans, how many gray humans would you predict? And this is basically how we have figured out what stellar evolution is like. Okay. That's a very nice one. Yeah. So the original one is an analogy with the forest where we actually have this feeling, right? If you walk into a forest, we don't see the trees grow, but somehow you know that that little sprout- It's probably going to be bigger next year. Yeah. Okay. Are you more or less satisfied, Thijs? I can talk about this for hours. Yeah, I suppose. We have an hour's worth of podcast now. We can continue. Well, I have a question about the... and I'm sorry. I'm sorry. I'm sorry. I'm sorry. And then after that, we'll round up unless you have the things to say. Well, maybe. I'm sorry. Yeah. About the instruments that you use. Is it... So because at the beginning of this podcast, I talked a little bit about something like WFIRST maybe being postponed or even, God forbid, canceled. Which ones do you use and how is that going? What's important for you? Which ones? Stars have such diverse lives and go through so many stages that there's many different types of telescopes that are interesting for me. WFIRST can do a few things, but not the main. LIGO is very exciting for me. Yeah, maybe that's a nice way to end this. So LIGO is the gravitational wave detector that found these ripples in space-time of two merging black holes. And so any moment now, it's switching on again. It was in a sort of commission... What is the word for it? Not repair mode. They try to improve the instruments. Yeah. And so they're coming back online. I guess they're already taking some data, but any day now. And so they will take data for about a couple of months to a year. And so the hope is that we find another Newton star merging, maybe a few dozen more binary black holes. And hopefully, we actually hope that we find a Newton star and a black hole merging. So this will happen over the coming months. And so the most exciting things of this will certainly still hit the press. And that's something to watch out for. And think. If you hear that... It's not just ripples in space-time. There was at least one or two... There was at least two supernova before this. Exactly. So I hope we can welcome you back. Yeah. Yeah. Yeah. To come talk about what they found out. If you'd like to. So thank you so much, Selma. This was great. This is... Yeah. And so many questions that I had were answered finally. And especially if it turns out that so many of the questions I have, we simply don't have the answer to. That's also in a way very satisfying. It is. It's not my own ignorance. It's just... It's not your fault. It's human ignorance. Yeah. About all these things left to discover. Yeah. So good luck with your research. Thanks a lot. In the coming years. Selma de Menck. Yeah. Thank you very much. Herbert, thank you so much. Yeah. Well, it's been fun. Yeah. This was really fun. Who are you going to talk to next week? Good question. I don't think my laptop will be... Oh yeah. We will have... No. I thought I knew it and I don't. We'll cut this out because I have it here somewhere. Okay. It will be Michel van Baal. Michel van Baal. Of Technical University Delft. And we're going to talk about PR in space. PR in space. Michel is a fun guy. He's a space engineer. Yeah. First of all. And he works as the PR person of the Technical University. So he has a foot in both camps, so to speak. Yeah. And... So he can comment on the super wolf blood worm moon. Yeah. Yeah. Yeah. He knows all about that. We will have to wait and see. We will. We will. We will. We will. We will. We will. We will. We went full circle on that story as well. Great. Well, spaceflight is a very PR sensitive business. You know that. Because things can explode? No. Because budgets are very sensitive to publicity and stuff. Ah, yeah. Publicity, image, you know. So that's why space big shots can be very... Itchy when journalists ask critical questions. I've had some experience in that field. Oh, yeah? Yeah. And well, we'll be... And on the other hand... We're going to put the fire to his feet. On the other hand, yeah. Well, I think he can tell us some inside stories, but then again, I can do that too. But on the other hand, I was going to say, ESA and NASA, of course, are very generous when it comes to publishing results. I mean, all photographic materials. I mean, all the... All the photographic material, it's all available free of rights and stuff. So on the one hand, they give away a lot of information. On the other hand, they can be very difficult when the information that you want to have as a journalist is not the information they want to supply. Ah, yeah. Okay. Well, all about that next week. It can be very interesting. Yeah. Okay. Thank you so much. Thank you, Herbert. This has been Space Cowboys episode 12. Yeah. On to 13. Thanks, everybody. And we'll see you back next week. Bye-bye. Bye. Bye. Good-bye. Good-bye.