Cosmic Queries – Starquakes with Conny Aerts

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StarTalk Cosmic Queries

2:04Hey StarTalkians, Neil here. You're about to listen to an episode specially drawn from our archives to serve your cosmic curiosities. The archives run deep. If you enjoy this, take a peek at the full catalogue on your favourite podcast platform. There's a lot there to tickle your geek underbelly. Check it out. Welcome to StarTalk, your place in the universe where science and pop culture collide.

2:38StarTalk begins right now. This is StarTalk Cosmic Queries Edition. This one is titled Starquakes. I've got as a co-host here Matt Kirshen. Matt, welcome back to StarTalk. Thank you so much for having me. It's nice to be back. Yeah, so you solicited questions about like stars and starquakes from... I'm very excited about this topic and so are the listeners. There's been a lot of... A lot of your Patreon patrons have responded to this one.

3:08And we're going to try and get through as many of these as possible, but... Well, I don't know a damn thing about... I can't promise all of them. I will try. I don't know a damn thing about starquakes, so... Yeah, I know. I'm excited. I live in California where earthquakes are a problem, so I know how to deal with those. But if you're involved in a starquake, is getting under a table still enough, or how do we deal with it? Yeah, we're going to find out for sure. So our guest, with the expertise we need, is Connie Arts. I think I pronounced that right, Connie. Welcome to StarTalk. Hi. Glad to be here.

3:40Excellent. Now, you're in from Belgium and the Netherlands. You have a dual appointment. One as the professor of astrophysics at... Let me get this straight. In Leuven, Belgium. And it's KU. It's Catholic University. It's like Catholic University in Leuven. Is that correct? Yeah. KU Leuven. Just don't worry about it.

4:05KU Leuven. Leuven is a small college town in Belgium. So that's where I'm from. Excellent. And in the Netherlands, you're a professor of astroseismology at Radboud University in the Netherlands. And so the fact that that's even a title to hold, astroseismology, says how far we've come in just the specification within the broader field of astrophysics. And I think this is just delightful. And your expertise is stellar astrophysics, stellar structure and evolution.

4:38These are two favorites of mine. Professionally. But I never really thought about seismology in anything other than Earth. And so first, tell us, what is astroseismology? Well, it's the study of the seismology of stars. Now, as you say... You have to do better than that. Yeah, I know, I know, give me a chance, right? Give me a chance. So we all know earthquakes, that the Earth has a whole crust, you know.

5:11Well, it's not pleasant to have earthquakes, but it's fantastic to have starquakes. Now, stars are hot, caches, fierce, and they also move up and down. And we can use these starquakes to learn what's inside the star. It's the only way to know how to look inside the star. And that's just like seismologists of the Earth, you know. They are the only happy people when the Earth is quaking, let's say. Why? Because the earthquakes create waves.

5:41They travel into the planet, they bounce back at the iron core, and seismographs detect it. And then we can do all sorts of fun physics and chemistry of our planet. And we do the same, but then for stars. Okay, Matt, I think Connie just said that while cities are burning and everyone is dying, geologists are delighted that they have earthquakes. Absolutely, yeah. I'm hiding under a table while my pets are going crazy, and seismologists like the data. What beautiful data we're getting right now.

6:12The data. So, but I'm confused, though, because when I think of an earthquake, I have a very simple understanding of it, that you have a rigid crust that is under pressure and under tension, and then it spontaneously gives way. And then you get an abrupt shift, and that's an earthquake. But when I think of stars, they're fluids. They're gaseous fluids. So, what could possibly be quaking if you don't have anything solid to build up the tension

6:44that then gets released? Yeah, so that's a bit different, because the starquakes are happening all the time, because it's a gas. And so you have motions, right? Up and down motions, but also more complex motions. And if you, you know, press a gas and then release it, it creates sound waves. That's a bit like music in a theater hall. So, for me, stars are three-dimensional musical halls, concert halls, right?

7:17Wow. And so, the nice thing is that starquakes are always there. Luckily for us humans, the earthquakes die out quickly, right? And they're rare, relative. I mean, they're rare in the sense of the ones that do serious damage are rare. But as I understand it, there are actually earthquakes of even very small magnitude almost all the time. I think that's correct. Yeah, that's correct, because anybody in nature vibrates, yeah? And so, yeah, stars do that all the time, and they do it permanently, which for us astrophysicists

7:50is great, because we can measure the up and down motion. Why? Because it gives changes in the temperature of the star. And so, the brightness of the star changes as a function of time. And then we have our seismographs that measure these changes as a function of time. And your seismographs are also, you implied there, that they're sensitive to those boundaries where temperature changes, right? That's right. Because your sound would get reflected, or your pressure wave, which we're calling sound,

8:23would get reflected or bent in a different way, and you use that to model the total interior structure of the star. Is that correct? Yeah, that's correct. But, yeah, like, we cannot hear these sound waves with our ears. So, we see the brightness variations, because the sound is only propagating there where there is gas, and between us and the star, you know, there's nothing. It's empty, right? So, we can't literally hear the frequencies of the waves, but we see the up and down motion.

8:53And so, that is actually connected. The frequency of the sound waves created by these up and down motions is connected to the physics, and also the chemical composition of the star in its interior. So, we can't literally dive into the stellar concert hall, but we can measure the frequencies from a distance, let's say. But if you could, you would hear all of these sounds. Yeah, yeah, yeah, yeah. That's fantastic. Sometimes I give lectures for musical artists, and then they are all totally fascinated about

9:25these sounds, like, you know... Let me test this on Matt. So, Matt, NASA's going to plan a mission to send astronauts to the sun to listen to these sounds. But it's dangerous, obviously, so they're going to go at night. Right.

9:42You'd need your earplugs as well. You know, I go to loud concerts sometimes. I don't take any chances now. I'm getting old, and my hearing's going. That, by the way, I know we haven't got into the questions yet, but that actually is one of our questions from Lucas, from listening to Lucas, was actually about whether you can make that the heartbeat of stars into music. Yes. Yes. So, you're saying yes, that you can absolutely do that. Oh, my goodness. So, have people done... So, you have a portfolio of frequencies going on at different times in different locations, and so you've got a clever musician to sort of take all of that base material and figure

10:17out a way to listen to it. That would be interesting. Yeah, yeah. So, we actually just shift... I mean, each star has its own symphony, right? Depending on how big it is, how much mass it has, how old it is, it has its own symphony. But then we shift that global symphony into the audible range of humans. That's called sonification. It's a whole field by itself. And actually, it allows blind people to be astronomers. I find that I'm a very...

10:48For me, inclusion is very important. So, in this way, we can reach people who can't see, but they can hear the stars. But we have to help them a little bit by shifting to the audible range. We have finally achieved the goals of the ancients by celebrating the music of the spheres. Yeah, yeah, exactly. That's true. Oh, man. Okay. So, that question already got asked, Matt. So, that was... Who asked that? That was Lucas from New West who asked that question. What is New West? What is that? I don't know.

11:18It just says New West. I'm not sure exactly. But Lucas also proceeds it by saying, I have a geek kind of question, which I don't think you need to proceed any questions to start off with that. This is a geek safe space here, everybody.

11:30You don't have to preface it. But New West, I mean, I live in New York. And, you know, there's... Formerly New Amsterdam. Just south of New England. I've never heard of New West. I don't know what that is. Maybe that's California after it breaks away from the San Andreas Fault. Just floating off. Just floating off into the Pacific.

11:50So, why don't we get some more questions here? This is great. Now that we have some foundation for what... Yeah, we've got some awesome ones. Some of them have already... Some of them you've already kind of answered. And I'm sure that'll happen as we go along. But I'll try and get as many ones in. So, James Smith from Indianapolis says, What is the largest recorded quake not found here on Earth? And also, do all planets have plates that shift like Earth? A couple of people have asked that question as well, whether all other planets have plates. Interesting. So, let's start there first. You know, we know Earth is geologically active, because there's like volcanoes and plate tectonics. So, where else in the solar system might do that before we get back to the sun?

12:25Oh, well, you know, all planets will have quakes. I mean, any body in nature quakes. I was banging... I was about to bang the table here, but I will not do that. But the table would also have, you know, quakes. So, they damp out quickly, depending on whether you have a gaseous planet or a crust-like planet like Earth. So, Jupiter, Saturn, all the big gaseous planets in our solar system, they also have quakes. Wait a minute, Connie.

12:55Planetary quakes. You're saying every sound anywhere is a quake to you. Yeah. Okay. That's true. You do. So, a guitarist, what we're doing right now is kind of causing the tiniest of tiniest quakes by making sound... We're quaking through Earth's atmosphere. Of course. You're creating sound waves. Oh, my God. Listener Woody also asked, by the way, on this same topic, what difference... Would the ice giants experience quakes? I guess you've said the answer is yes. And what possible differences would there be between Earth, water, ice, frozen, methane, and nitrogen quakes? Yeah. So, the...

13:26Right. That's a bit... Wait. Just a quick thing. So, we've got ice in Uranus-Neptune, the ice giants, and we've got sort of gases in Jupiter-Saturn. We've got Earth's crust here. Mm-hmm. And so, presumably, you've... Connie, you've got some portfolio of who makes what kind of sound under what conditions... Yes. ...so that you can decode what you hear. Is that correct?

13:56That's correct. And so, the frequency of the sound waves of all these heavenly bodies is really determined by the density of the object. Right? And so, stars are gases, and their density is very different from the density here on Earth. They're very low, yeah. Or in Jupiter, yeah? So, by measuring the frequencies of the quakes, we know quite directly how big the object is and what its density is.

14:27And if you know these two, then you know the mass. So, that's the basic tools, right? You said that on the sun, you measure the quakes because some parts of the sun get brighter relative to others because they're hotter. How do you do that with just a planet sitting out there in space? Yeah, we need to send some space mission... Oh! ...there to come closer and to be able to see this. And so, for stars, we also... I mean, this is a booming research field in astrophysics.

14:57Why? Because we recently had the luck of being able to measure the brightness variations with satellites. Yeah, we don't have a seismograph that we can put there, literally, like for the Earth, but we sent instruments that measure these tiny variations in the gas, you know? Okay, so I'm an old-world astrophysicist. So, when you say, we make these measurements by going there, that's cheating, okay?

15:27That's cheating, yeah, yeah. We can't go there. That's tabletop science at that level. Yes, yeah. If you get to go there. Yeah. But you're saying it's the same kind of features in a gaseous planet. Some parts will be a little warmer or cooler than others on the surface, and that'll tell you... that'll give you seismic information about what's going on inside. Yeah, as soon as the density changes, for whatever reason, density changes give pressure waves, and these are sound waves, right? Oh, okay.

15:58And so, the follow-up part from James, what's the largest recorded quake not found on Earth? Oh, well, we have the slowest quake in a star. Like, it can take several, several months in period. Well, for the sun, it's five minutes, by the way. For those who don't know, yeah, the solar quakes go up and down, create sound waves with periods of about a few minutes, five minutes at their strongest. So, for a very big blue supergiant star,

16:30it takes months before the quake went up and down. So, just to be clear, the normal frequencies we listen to are hundreds and thousands of cycles per second, and that's what our eardrum and brain will record. And you're saying these are cycles every five minutes. Yes, and that's even fast. Or even every month. So, that's why you have to shift it back to our audio range. Yeah. Otherwise, we would never even know it was happening. That's right. These are slow waves

17:01to human standards. Right. You'd vaporize first, but while you were vaporized, you would not know you were in the middle of a star quake. That's right. That's wild for me. So, incredibly slow, but presumably hugely energetic. Yes, that's true. Yeah. So, the energy of each wave can be quite tremendous, but that also depends on the type of waves that you're dealing with. Okay. Wow. All right. Well, let's take a quick break, and we're going to come back

17:31to more star quakes. Something was like, what?

17:38But, Tukani, everything's a quake. Yes. So, we'll get more into that in this episode of StarTalk Cosmic Queries when we return.

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Star Quakes Discussion

22:00We're back. Star Talk, Cosmic Queries. We're talking about Star Quakes. And my co-host, Matt Kirshen. Matt, where can I find you on the internet? Well, you can find my podcast, Probably Science. I start with the Neil episode. That's always a nice place to start. I was a guest once on your Probably Science. I just thought by now it would have been called Certainly Science. I just thought it was evolutionary

22:31but apparently not. The longer we do the show, the more probably it gets. It's going to descend through possibly to Ah, Science. Probably not. And then I'm on Twitter at Matt Kirshen and technically on Instagram but I'm very rarely there. Okay, Kirshen, K-A-R-S-H-E-N. And we have as our in-house expert right now on Star Quakes, professor of astroseismology in the Netherlands but right now

23:01Connie Arts, I think I pronounced that right, is visiting New York City at a place called the Flat Iron Institute which is in the Flat Iron section of Manhattan and very cool science is happening there. All manner of science. It started with sort of math and astrophysics but it's spilling into biology and computer science where very deep problems that need high performance computing and clever people to solve them

23:31are invited to then gather their talents and try to solve the secrets of the universe and Connie Arts is on sabbatical this year so Connie we're delighted to have you as part of this podcast. Very grateful to be here. Thank you. Yeah, so we've got some more questions but before we do that I just want to be clear that most people's understanding of the word quake is I think built in

24:02is that it's abrupt and short lived that's kind of built into our life experience with a quake and but we're now hearing about quakes on completely different time scales. Should you have invented another word to describe a quake that moves on the scale of days or months rather than seconds or minutes? Sure and I use the term starquakes for popular lectures but actually in our professional life

24:33we speak of stellar oscillations so they're global oscillations they're smooth they're properly behaved so for stars it's a bit less abrupt than for earthquakes let's say. okay okay so if on earth they were earth oscillations then Matt maybe you wouldn't have to hide under a desk or in the structural beams of the house I would just ride it out just ride it out surf it out keep the knees

25:03flexed keep your core stable that's all you need but you would get seasick all the time you know because they would always be there you know yeah lies on the horizon that's the secret always look out the window don't try and look at the fixed objects inside take me surfing one day out in Los Angeles and teach me oh I'm a terrible surfer but oh okay so Matt what else do we have for Connie we've got some great questions by the way just side note I love when we have topics like this when it's something that is close to Neil's wheelhouse but just outside it when it's like in your field of

25:33astrophysics but something that you've never really encountered they're my favorite episodes because because you like looking how much of an idiot I am that's what you're saying I love it when you're just just at the edge of Neil's knowledge it's my favorite it's the best well those are my favorite episodes where I learn stuff so absolutely this is good this is good so I'm going to combine these two questions I like to do this because I want to hear their names anyway absolutely Dylan and from NAU in Flagstaff and Alejandro Reynoso from Monterrey

26:04have both asked about what we can actually learn from the oscillation of stars Dylan says can we predict its age and or understand the core and also do all stars oscillate or just dying stars supermassive stars main sequence stars and then Alejandro says what have you learned from analyzing star quakes that you couldn't learn with other methods so basically they're both asking what specifically is it that we can learn from these quakes I'm going to tighten that question and say what are you learning that we didn't otherwise figure out through other means

26:35okay if there's one word that I have to ask to that question it is rotation of stars that's more than one word but internal rotation of stars you know and why is that let me give the analogy with music again so we have sound waves that are happening inside a star but the gas in the star is rotating around right and what do you get when you put a musician in a theater play and you make the podium rotate just for the fun of it as a surprise to the musician

27:06you get pissed off musicians that's what you get exactly I like that experiment actually you can really hear that but the symphony is destroyed that's what the audience would say now for me as an astro seismologist the frequencies of the waves get shifted right the Doppler shift yeah they get shifted because of the extra motion you're to the rotation and we can measure that and we're not measuring that at the surface

27:37of the star but inside the star where the starquake has its strongest energy right and so what we have come to realize is that the theory of how stars evolve relying on how they rotate in their interior is quite off it's not very good and that's not surprising right because we could only measure before we had starquakes we could only measure the rotation of the star at its external layer like for the sun

28:07you see the you see the tiny little dark spots of the sun rotating around if you're patient every 26 days you see them back in your line of sight but so the sun rotates with a period of about 26 days but that's just the outer layers it doesn't say at all how it rotates in its interior so if you have no information what can you do well you think well it won't be that different you just assume it's the same right you assume it's the same everything else rotates as a kind of a unified object why would I even think

28:39some lower level would rotate at a different rate well the stars have many more surprises than us astrophysicists have imagination what a smack did you hear Matt did I just hear this woman correctly here I stand by it I'm on team star on this one that was a smack down right there I always say the stars are right the theory is wrong if it doesn't match with each other right

29:09so thanks to the frequency shifts of these waves we can now measure how stars rotate around and why is that important well if they rotate faster or slower then their material gets mixed in a different way yeah that's also something you can imagine if you take the analogy with coffee drinkers you know if you if you like coffee with milk you pour milk into your coffee you don't wait until you know until everything is mixed because then the coffee is cold and it doesn't

29:41taste well anymore no you take a spoon and you rotate your coffee in my terminology that is saying you bring angular momentum to the coffee cup and what why do you do that that's what everyone says when they're having coffee that's what everybody does without saying it and that's because everybody prefers well mixed coffee with milk and so I'm assuming at the Flatiron Institute that just the coffee station there has angular momentum implements how much angular momentum

30:13would you like on your coffee this morning do you want do you want a metal angular momentum implement or one of the wooden straight ones well we could do an experiment of how people do that but you know the diversity of human beings taking their spoons will be large and in stars there's a whole range of internal rotation frequencies that we have measured in we have about 2,000 stars now for which this has been measured

30:43by many groups in the world with astrothesmologists and so the life of the stars is really going slower if I look at the measurements you mean our estimates for their life expectancy need to be updated to have them live longer than we originally thought is that what you're saying yeah particularly for the big massive stars is that because they're mixing more material into their core giving them a little more lease on life and they get more material into their

31:13inner part and in the inner part of the stars is actually