 We are ready to begin our second talk. Now, you may not know this, but in Astronomy on Top, our speakers don't get pained. They do get pained in fear. This is the first time that we will not be able to pay our speaker with fear. Our speaker today is Dr. Meredith Rawls, who is forming a protostar at the moment. He therefore is incapable of perceiving proper pain. And so please join me in getting the warmest possible welcome to the thoroughly undercompensated Dr. Meredith Rawls. A few months in a revenue situation. So my name is Meredith. I'm a post-doc at the University of Washington, and I also study stars. You're getting a whole bunch of star stuff tonight because stars are the best. I also write software, so if you like software, that's cool too. So stars and software together, that's kind of my life story right now. So this, as you probably may have guessed, I think it stopped playing the movie, but this is the song. Have you guys seen that before? Like maybe every day this month. So this is actually a picture of the sun from earlier today, taken from a satellite up in space. And you can see all the different activity and cool stuff going on in the sun. And what you might not know is there's also a lot of interesting activity going on inside the sun. And oh, it's going to quit moving again. Well, that's cool. We can watch the sun again. So this is kind of the outer surface of the sun rotating. It's sped up a little bit. It doesn't actually rotate that fast, but you know, it would be really boring if I stood here and watched your video all the time. But inside the sun, there's also a whole bunch of activity happening. So this is not an actual crop that X-rayed the sun. I can't look inside the sun with my eyes. I wish I could because it would make my life really easy. But our sun actually rings like a bell. It has these oscillations that go inside it and not to this picture showing you. So not only do we have these cool solar flares and corral loops and lots of activity going on outside of our sun, we also have a lot of activity going on inside the sun. And what's really cool about this ringing of these oscillations is that you can use them to study how our sun is made from the inside out. Which is pretty awesome. So lots of things resonate in the ring, right? I said the sun rings like a bell. Well, it turns out other stars do too. So the sun's great, but it's like right there and that's boring. So I like other stars better. But they're farther away and so that makes it harder to see what they're doing up close. They also resonate. We can study them with this cool Starquake Resonation bell ringing thing. And so this is showing you that our sun has some characteristic ringing frequency like a medium-sized bell, if you will. And then bigger stars have different characteristic frequencies. They might sound like a lower bigger bell like one of those clock tower bells, but it's such a low set of frequencies that even if you could hear it, which you can't because space is a vacuum, it's harder. You wouldn't be able to hear it with your ears because it's too low frequency. And this graph goes all the way up to Viola because I played Viola and Viola's awesome. And they also have resonance frequencies. So you can go home and tell people you learned that stars are like Violas if you want to because that's not entirely wrong. So Starquakes are awesome and I hope that I can convince you of not only their awesomeness but also their utility. And I want to kind of take a step back and remind you like star lifetimes, right? So we learned a little bit about how stars form all different elements like everything, right? Like beer and everything. And that happens, you know, the two categories of things, beer and everything. And for massive stars in particular. So on the right hand side here we have kind of the massive star life cycle. It forms into this big old blue thing and doesn't live all that long and it blows up and makes all those heavy elements and it's really amazing. But for every one of those stars there's like a bajillion lower mass stars kind of like our song. It's a technical term. There's a lot. And they have a much longer life time and they don't end their life quite as excitingly. But they live a long time and they're important because they're like our sun. And even though I know I guess our sun earlier, I apologize because the sun is actually really important. And you know planets orbit, the sun and other stars also have planets. And you know there's cool stuff out there with some like stars. So the main difference in these two life cycle options is mass. And so the mass of a star is really linked to its fate. And so what we'd really like to be able to do is measure the mass of stars. If you look up at just guy at night you can't just say oh I know how much that star way is. I know how much that star way is right. But it's not something you can just tell. If it was then I could just go home and it'll be done now. So yeah it's a little difficult. So one way we can do it and this is a way that I actually like a lot is using when you have two stars. You can measure how massive a star is and learn maybe it'll blow up in a supernova or maybe it'll be more like our sun and become a white dwarf in the end of its life. So the way you do that is you look at when the stars pass in front of each other you measure how much light gets blocked. And then you also measure the Doppler shift of the star as it like moves around each other and you combine that and you can actually get a very reliable measure for how massive a star is. It's really pretty sweet. So I like this method a lot because it's pretty straightforward. I know how to do it. It's always helpful. You know I have some software that does this, right? Like if every star was this way mass measurable that would be really great. Also really good because we understand gravity, right? This is just using gravity. Something goes around something else and we give these back to figure out how massive it is. Which is great and it's a well-known technique. Unfortunately not all stars are binaries so it's not going to work for every star ever and we're only going to be able to figure out the fate of stars that have binary dance partners. And well those are the best stars in my opinion. They're stars too and we'd like to be able to measure their mass also. Also really slow to do this thing on the right. It takes like a lot of telescope time and it turns out that other people also want to use the telescopes for like galaxies and stuff. I don't know what that's about. You'll have to come back another month to hear about that. Okay so this is all leading up to me telling you that I have a cool way to measure star masses using those ringing oscillations, those starpakes. But how does that work, right? That's not a straightforward thing to say. Like we have a bell that's actually a star. It's actually a way to kind of weigh the star. So sure, fine, uh-huh, totally right. It's the oscillation bell. Alright so how does this work? Well here's another picture of kind of the inside of the star if you can see it having all these different oscillations. So the trick is that even though these ringing bell oscillations are happening inside the star, they make the stars brightness change a little bit and we can observe that. You have telescopes, you have telescopes. And so this is like a brightness changing over time thing. And because we like math, frequencies at which that happens, using a Fourier transform, who's scary. And maybe you get a nice graph with locations showing you all the different frequencies. And then you can say, hey, I can characterize how that star is oscillating. You know, is it having a lot of low frequencies because it's really big. Does it have a lot of high frequencies because it's small. Does it have a really weird combination through to these? I have no idea what's going on. All of these are options. We'll look at the star's properties. So this is what it really looks like. You know, I show you the pretty picture and that's great. But this is more what you have to do in real life. You fit a bunch of curves to a bunch of wiggles and you try to convince yourself you're not making it up. It's fine, trust me, it's fine. So what I like to pretend that graph looks like is this. But this is much nicer to look at, right? This is much more friendly. And so maybe you can convince yourself. Like if you look in the middle of this, there's like more stuff there in the gray. And if you just like zoom in on that and flatten out a bit and stretch it and poke it, then it looks, you can measure the middle of that and you can measure the spacing of those. And that actually tells you something about the star. All I had to do was measure the star's brightness a whole bunch. Turn it into this and then I can directly measure something about the star's surface gravity. So that's like, you know, you go to the moon, you can jump really high. Well, if you are all these different stars, you'd better never mind. But you could have different surface gravities depending on what star is temperature and also it's density, how fluffy it is, or if it's like super packed down on the white dwarf. So that's fun. Are hotter, more dense, have a higher surface gravity, and stars that are oscillate with lower frequencies are cooler, less dense, and have lower surface gravity. So okay, that's a lot of physics works. That's great, big stars. I like to study these big red giant stars that are, you know, it's what our sun will be when it runs out of hydrogen. It's not going to happen anytime soon, you don't have to worry about it. But eventually our sun will become a red giant like this and it is going to be a lot brighter so we can see it with a telescope, which is helpful if you have a limited amount of time on a telescope. And it also oscillates a little more slowly so maybe you don't have to like observe it every second because that is difficult. So we like to be able to study the big ones. So because we want to study the big ones, we're like, well, a evolved star that our sun will eventually be is just a big version of our sun right now because if we're trying to measure the mass, if we know our sun's mass and we can figure out the surface gravity and the temperature and the density and do some math, like if you stare at math you've been to yourself said if you have the gravity density you can get a mass, which is pretty sweet. Then that seems doable. So what we've been doing or what some of my colleagues that I've been doing is using Kepler, everybody's favorite exoplanet telescope, not just new planets, also new stars. You measure the brightness changes. You make these cool graphs that totally look like this and not like that other one. And then you do some math to turn your densities and your gravities into masses and also radii but we care about mass right now. And you can actually get the mass of the bigger star. So that's pretty sweet. And what's nice about Kepler is that maybe you guys know this because you're all experts on exoplanets so they talk about that a lot here. It stared at a lot of stars. It stared at them for like four years and still looking at other ones. And so it is ranking up a whole bunch of these bright big stars. And we can actually get masses for a whole bunch of big stars really quickly which is awesome because the other technique that I was telling you about with the binary stars not only do they have to come in pairs but it takes forever. And doing it this way is a lot faster. So that is pretty sweet. The good scientists here maybe convinced you that this could work but it'd be nice if we could like verify the numbers that we're getting aren't completely wrong. So masses. So I made a little class of some stars using starquakes. And these stars happen to also be in binaries. As of the stars measure with binaries the other axis and then I was like oh crap it's not one to one. I broke science. Oh no. 16% on average which was kind of bad if you want to measure masses. And we were like okay, okay this is fine. This is science, this is cool. Sorry. What? What's going on here? Turns out that what's going on here is that big red giant stars so simply just giant versions of our sign. I mean they are infection stuff going on. There's different stuff happening in different layers of the star that isn't quite the same as what happens inside our sun. And it's just complicated enough that you can't just compare them one to one. Even though it would be super handy if you could. So what we have to do is we have to apply empirical corrections in order to get accurate masses. We have to fudge it a little bit but it's consistent. So it's fine. It's fine. Totally works. This technique actually works really great for stars that are like our sun for these smaller stars. It's a little harder to observe them enough to see the starquakes because they oscillate more quickly. So eh, turn it off. So you now, believe it or not, have learned a little bit about astro-seismology which is your word of the week, aka starquakes. And it's actually really useful even though sometimes it doesn't work perfectly because you can measure a lot of stars' masses really fast. So thank you very much. We have plenty of time for questions. So do your work. Oh boy. Why is 16% good enough? Why is 16% wrong good enough? Well, it's not. It's just that it's correctable. So it was, we weren't necessarily assuming it was going to be a perfect one-to-one when we did this. And the fact that it was off by a certain amount was actually really interesting. Because it means there's some physics we don't really understand perfectly yet. So there's more work to be done but it's still a really useful technique. Who else got a question? Sure, back here. Sure, that's a great question. So the question was that I said that we use brightness variations to measure the oscillations but don't other things also cause the star to change brightness like exoplanets or other stuff? And then you absolutely yes. The fact that we were using binary stars, there's an eclipses of those with a lot like exoplanets so we had to cut that out and use the chunks of the light curve, the brightness changing that was not part of the eclipse in order to do this. So yeah, it's a little tricky. Lots of things make stars change brightness but the characteristic frequencies here are in a special spot in the frequency range so it's a little tricky but it's something you have to consider. What else we got? Very good. The question was did I make up this entire methodology? I wish I had and I'm living out of the low price but No, I just use it to I use it and then I tear it apart a little bit and then I use it some more and go into science. But I see a hand over there So do I use just visual astronomy or also radio astronomy is the question? I'm only in working with visible light so it's possible to do why would you know if you do the radio or not? I also think you really could because you need the time resolution you need to have that observation super regularly and I think radio is not really set up to see a set of frequencies What was the most exciting surprise during this process aside from the 16% offset? Oh man, that's a good question I think it was really cool just that we found this many stars to even test it on because we were like there's got to be binaries they're also oscillating like we're going to try to find them like they have to be there and then we found like enough to actually make a graph and make a good conclusion Alright, what does our star weigh? Well, the sun weighs one solar mass Yes, so well it's as much of a standard as anything we tend to measure stars in terms of how many times our sun they weigh just because it's fast didn't seem to talk about it but most of the stars in our study if you just look really closely at this it's really faint here this goes from like 0.8 to like 2.2 solar masses they're similar mass to our sun but some of them are twice as heavy and some are a little less what is the units of what now? oh, so it's the mass of the star measured using star plates compared to the mass of the star measured using binary star thing what physics is causing the star plates? what a fun question so it is these star plates are driven by convection so it's a it's a continually stochastically driven process that's happening in the outer layers of these stars because of a lot of turbulent convection going on and so any star that has a convective outer layer potentially will have cancellations good question so the question is so I have any idea why the starquake mass when I measure the mass of starquakes it comes out higher instead of like sometimes higher and sometimes lower and the answer is kind of complicated but the fact that it is systematically high or systematically low tells us that there's something in the physics that we're missing if it was just scattered everywhere, then it would be like why are we so imprecise? why do we suck at measuring mass? at least this way we know that we're doing it right both ways and there's not getting the same number that's my main takeaway and if you really want to think into some of those papers you can move around it gets dirty clean does the frequency of the star change with its age? the frequency of the stars changes as they age that's a really great question so it doesn't change so yes it does change as the star ages and gets there then the frequencies change but it won't change over the course of the year so in the star time scales are really long and a star like the little yellow sun will become a big star like the red giant and then over the course of that the frequency totally changes do I like the surface of the star? how do you define the surface of the star? how do you define the surface of the star? it's actually not an easy question stars have lots of layers and sometimes it gets kind of dicey up there near the edge where maybe there's some stuff coming out as my business is still going on as you get farther away I don't worry about the edges of stars lots in the sky they're far away it's fine what are we going to do with the masses of all these stars? we are going to know a lot more about stars no that's a very very good question it's actually really important in order to understand how our galaxy has evolved over time because a lot of different astronomy that you want to do assumes that you know the mass of the stars that are going into the picture so if you want to understand how our galaxy form, if you want to understand its future or other galaxies, how bright they are and how many stars they have and what they're going to do in the future you really kind of need to understand how much mass of different stars that you see that we don't how is it going to evolve as we would like a good question which factor in my model has the biggest effect on changing the result? well it's I try to keep equations off of my slides because I don't think you want to know living codes there's no one thing that dominates it really it's a combination of the surface gravity to the density and temperature they have different powers ones like the negative free house but it's really you can't just ignore anyone they're all important players oh man no pressure here by the time I retire what do I want to have accomplished oh basically I've got a little while I I think that we're going to have more and more missions that are going to be able to take this kind of measurement and I hope that the pool satellite comes out soon called TESS that Europe is going to launch pretty soon and it's going to help us measure more stars like this so honestly I don't know why personally I'm going to be able to do this but I think it would be really cool if we could just have a handle on the properties of all the stars in our galaxy like a much better handle on their specific details so that we can really get a accurate model of everything that's happening and how it's all moving are there other methods that we're using that kind of to better results and see if the data is one or some other method the short answer is not really because there's not a lot of ways to measure masses there is another way to measure the size of stars it's radius and all and that's a technique called interferometry and that was one of the closest stars where you can actually measure the angular size of the sky I'd say all stars with dots if you're really careful maybe they have a size on the sky and what I can tell you is that when you measure mass like this you also get radius now and those actually don't light up perfectly either and having another way to see if our radii are agreeing is really helpful we found a little discrepancy of radians as well but interferometry is great it's amazing alright it looks like we have exhausted audience's question about stability and how the star works thank you guys so much keep it going for every day