Dr. Lindsey Kwok -- The Forensic Science of Supernovae

Welcome to the Astrophysics Podcast. When you think about it, it's just incredible how much an astrophysicist can do with a seemingly tiny amount of data. Take a supernova, for example. At face value, all a supernova is, is a point of light that appears in the sky, gets brighter and brighter, then gets dimmer again until you can't see it anymore. From this seemingly small amount of information, an astrophysicist can conclude all kinds of things about what happened. Not only that a star exploded, but what type of star, and what caused the explosion. What was it doing just before exploding and how much energy was imparted? Now, we can't always answer all of these questions for every single supernova, but the fact that we can ever do this at all is simply incredible. It just goes to show there's a whole lot of information carried in that little point of light. I sometimes like to imagine astronomers as sort of like detectives trying to solve a murder case, but with very few clues, they have to get out their most advanced forensic technology, search for fingerprints and DNA, and pull every tiny piece of data they can from the crime scene if they want to figure out what happened. Today, we will be talking with one such supernova detective, Dr. Lindsey Kwok. Dr. Kwok is a post-doctoral research fellow at the Center for Interdisciplinary Education and Research and Astrophysics at Northwestern University, and she's going to tell us about our latest piece of forensic technology that James Webb Space Telescope poured JWST. Dr. Kwok uses JWST to do forensic science on supernovae to learn things that we have never had the technology to figure out before. She's going to tell us about all the new things JWST can teach us about these crazy exploding stars. I'm Paul Duffel, and this is the Astrophysics Podcast. Oh, what did you think? I loved it. I want to read. I want to listen to the other ones. That's nice. Let me see. I'm just playing with the levels here. You have the voice for a podcast. Yeah, I like it. Thank you. Okay, everything I think that's, I don't know, is probably not, but we'll figure it out. And when we go. Okay. Here we go. Are you ready? I hope so. Okay, good. I'm Paul Duffel. And my guest today is Dr. Lindsay Kwok. She's a postdoctoral researcher at Northwestern University. Dr. Kwok, thank you for being here. Thank you so much for having me. So this, you were the first guest. We just met this morning. This is the first, you're the first guest that that's true about. I usually just get my friends to do. So normally, yeah, I'm normally last questions. I already know the answer to, but this will be a little different. Okay, great. So we start by just talking about, you know, you and where, how you got to be where you are. And so let me start by asking, where did you grow up? I grew up in Grand Junction, Colorado. It's typically people know it. If you've driven from Salt Lake through to Denver, it's like right on the Utah border. And it's beautiful, clear skies, a little bit rural, not like super rural, but yeah. It's kind of the biggest thing between Salt Lake and Denver. Okay, okay. So, and so I'd be used to clear skies, is that it hintes to what got you excited about space? I think you definitely play the pretty big role. It was funny is ever since I went to college to start studying space, I have lived in places where you can't see the stars anymore. So I'm coming down to here to Purdue. I looked out my window last night and I said, wow, I can see the stars again. So that was nice. Yeah, my, I had a friend who had a daughter. She lives in New York City and her daughter one night looked up and said, mom, I see the star. And she's like, okay, I gotta get my kids out of the city. But anyway, yeah. So, um, so that's, so you grew up, so, um, and what was, I mean, I guess what was, you said it was kind of rural, what was it like for you growing up in that area? Like, do you have, do you have any memories of like, what about like the first time you got into science or thought, first memory you could think of that made you that you were going to get excited about science. Yeah, so, uh, Grand Trashon's got a lot of really amazing nature around, but I would say, um, it's not super science-minded as a, as a town. I would, I think my science, um, first, like interest in it really stemmed from my grandpa. Uh, he's a nuclear physicist. Oh, okay. And he worked at Los Alamos National Laboratories. And I always thought that he was the smartest person, coolest person I knew, and I wanted to be like him. So growing up, um, I just enjoyed math and science. And so, um, maybe partially to like please my grandpa, I said, I wanted to be an engineer when I was little, and then that kind of evolved in middle school too. All right, I'm going to be a nuclear physicist like my grandpa, because now I understand the difference between physicist and engineer. So, wait, when you're really little, like, how old when you wanted to be an engineer? Oh, probably like eight. Like eight? I can't think of an eight-year-old who wanted to be an engineer unless they meant like Scotty from Star Trek or something, right? Like, I think it does depend on if you have people in your life that are like if that's their profession. Yeah, yeah, right, right. So it wasn't so much, it wasn't so much you even knew exactly what he did all day. Oh, definitely not. No, it was just you wanted to be like him. Exactly. Okay. Um, but that, but that was part at least some part of what fueled your excitement about science. Yeah. And you, and you did a lot of math and you like, it's got head fun with math and science. Yeah, it helped that I enjoyed and excelled at my math and science classes. So, so you, so that was your grandpa, your parents? I mean, were they influences at all? Yeah, I think so. I mean, they were all, they've always been very supportive. And my dad, he's a physical therapist, but he just is love science stuff. He'll like listen to podcasts about, okay, it wasn't that it was one more listener. That's good. I need all the ones I can get, but he's also very like, um, fixes stuff around our house. So he would always, whenever the lawnmower broke, which was very frequently, he would say, let's say you want to come out and see how this works. And I sometimes felt obligated because I was like, oh, I want to be an engineer, but I wasn't that interested in the lawnmowers. You want to be an engineer, you better learn how to fix the lawnmower. So that's good. So, um, so that's it. So that's what that's that you thought I'm going to be a nuclear engineer. So when did that transition to astrophysics? Like what about space? Got you excited? Or, um, I think I've always been interested and fascinated in space, especially things like, um, the high energy, like black holes, exploding stuff. Um, I always thought that was cool. And so I'd say in eighth grade, I was like, yes, I'm going to be a nuclear physicist just like my grandpa. And then in ninth grade, I took an astronomy class and I was like, I love this stuff. I'm going to be an astrophysicist. And so I think that kind of changed, um, after that course. And for some reason, it has always stuck ever since. So, but I would say also some of my interest in astronomy, I think stems from just not a very practically minded person. My head is in the, I see, yes. Yeah, it's in the clouds and the stars. And so, oh yeah, nuclear physicist is too practical. It's too useful. Yes. It's too much like you're doing something for specific and means or and to like rather than just for the general knowledge of humanity. Yeah. Astrophysics is like very philosophical. You're getting concrete answers to questions, whether much like big like just we want to know broadly what's this, what's this whole universe doing? Yes. And it doesn't like my findings don't impact my daily life. Right. Yeah. Not usually. But so you considered that a plus. Uh, it just works for me. Yeah. I don't know why. Tell family members that I do the Astrophysics. I say, yeah, what do you do with that? I've got my question for my mother several times. Right. Yeah. But that's doesn't that doesn't hinder you at all. You want that's what you want. Yeah. Okay. Um, so then all right. So when then what, uh, at what point do you feel like you like learn how to be a scientist? You know, I would say that's only happened in the last couple of years. Okay. Um, so in graduate school, I started working on projects where it's real research. And then, um, particularly in the second half of grad school, we started getting new data from JWST. Yeah. And for me, that was when I was like, oh my goodness, I'm doing science that has never been done before. Now I actually feel like a scientist. I would say in my mind, my identity as like, okay, I'm a legit scientist. It's really only solidified in the last maybe even year. I got my PhD and I got a JWST proposal accepted as myself being the principal investigator. And I was like, oh my gosh, I thought of an idea. And someone else thought it was a good idea. And now I'm pursuing this new idea, discovering new things. And so that's what made me feel like a real scientist. - I would say that definitely a good validation is that somebody's willing to like say, we're willing to put this much because it's a dollar amount and they're testing it, right? Just thinking towards the side. - Yes, someone's actually giving me money for it, which is crazy. - Now you have this identity as I am a scientist, but like what do you think, like is there a pattern of thought or something that distinguishes that, that you've gotten, you've learned how to do something that, yeah. - I think I've been developing that for a very long time. And I think that I probably should have felt like I was a legit scientist much earlier. I think for me, it's just partly, I don't know, maybe a little bit of like the imposter syndrome sort of like, am I really good enough yet? - Right. - But I think, yeah, the patterns of thought, types of problem solving, all the skills that I've been building throughout research projects and undergraduate and graduate school, it's all been part of that process. It's just been more like myself recognizing it now. - So you don't think there's like some point like between your second or third year of grad school you suddenly like know how to do this or something. It's more like you are, have sort of, you're building those skills over time and then maybe the realization that you actually know how to do it, you're making realization. - I think it's a self realization, at least for me. - Yeah, yeah. - Okay, that makes sense. Okay, well, so now you're an astrophysicist. What would you say you like the most about your job? - Well, I love that someone pays me to think about space. Like, that's so fun. I get to think about big questions. But in terms of my day to day job, I really like being an observational astrophysicist or astronomer. Astrophysicist kind of makes me think of like theory and I would not really consider myself a theoretician. - So we use astrophysics to, wait, it is often used to describe both theory and observation, but by putting the physics, it was sticking physics with it makes it feel like more like you would be doing theory. So, but you, okay, so. - So I really like working with the data and I did some projects previously in undergrad where I realized, okay, only doing computer simulations is not really, for me, I like getting my hands dirty with the observations a little bit. - It's a wait, okay, you did computer, you did some kind of computer simulating stuff and I get excited because I'm a theorist. I'm like, what did tell me about that? Now, what did you do in undergrad? - So I had a lot of opportunities in undergrad, which I was very fortunate about. So I was at the California Institute of Technology or Caltech and they just have very few students per faculty. So I got to try several different research projects. So the first time I tried something at NASA's Jet Propulsion Laboratory, mostly because I wanted to work at JPL. - Yeah. - And the project was more on like trying to find signatures of molecules and titans at my sphere. Titan is one of Saturn's moons. And so that's, it was really just me trying to get my foot in the door. - Yes. - And then the next project was, I was really interested in black holes. - Yeah. - They're so cool. I still think they're so cool. And so LIGO, it's the laser interferometer gravitational wave observatory. And they try to observe these gravitational wave signatures. And so actually the summer before the big LIGO discoveries of the first detections of gravitational waves, I was doing a little summer internship running basically computer simulations that merge black holes and give them like a super kick and they fly off because they've got these, the ones I was doing had super high spins. But anyway, I realized that I didn't want to just be running these numerical simulation codes partially 'cause I honestly had no idea what was going on inside of the physics inside of the simulation. - You didn't write the code, you were just running somebody else's code basically. - Yes. And then I also just realized, you know, LIGO's a huge collaboration. - Right. - And I wanted to do something where I had kind of a bigger sliver of the pie. - That's right, right. So you could have been on the paper with the LIGO discovery paper or whatever, but you would have been like 400 thought or something. - Well, I think that's more like 1000. - Okay, so yes. - You know better than me, I guess, but I don't, yes, but it was, I remember it's a very large. It's like one of the biggest author lists. - It was really okay. - I realized that the day-to-day work was actually important, even in terms of the ideas as well. And so then I, there was a new assistant professor at the time or she's much more established now, names Moncy Cosleywell and she does observational, strongly on supernovae. And I was like, I like exploding stars, that's cool too. And I tried it and I really liked how, like working with the data, how, you know, in the field of supernovae, you can find one weirdo object you've never seen before and all of a sudden, boom, you can write a paper on one object. And I also like how the field moves quickly. And because of the nature of these transient sources, right, the supernova explodes and fades away on very human time scales of like weeks, hours, weeks, months, days, years, I guess up to years, but you have to respond to them and you go up to quickly. Yeah, I find that exciting. - You don't have all, you don't have years to just go, but I'll look at that at some point. - Yes. - And I'll put it in a provahose the next year to, like I think it helps me get things done, to be honest. - Yeah, you have, you have some deadline I have to work towards. - Like a newspaper reporter. - Yeah. - You don't look at it, you won't see it. - So it's interesting you mentioned that, you know, like it's easy to, you know, when you ask what do you like about doing astrophysics, it's easy to basically talk about all of the like broad big picture things, like, oh, black holes are really cool. But then like the big thing is day to day, you know, you have to actually enjoy the work that's not as like fun. - Right. - Right, the work there, you're like, you know, for me, it's where, why isn't my code compile? - That's actually another big reason with the computational theory side. I have less tolerance for the debugging. - Yes. - Yeah, yeah, I've developed a tolerance for it. But yeah, it is, you have to be willing to do that. And so, yeah, you have to learn what day to day work, you're actually willing to tolerate. Okay, so, did we get to what you like about your job? I asked you this question, then I'm not sure we answered. - I must not have answered it very well. (laughing) - That's all right. - I enjoy working with the data. I enjoy that I get to talk to people, collaborators about like exploding stuff in space. I think the ideas are really cool and really fun. I also kind of like that at least so far, I have not become a professor yet. - Right. - I am kind of just in charge of myself. - Yeah. - And I also don't have like clients or like-- - Yeah, or telling you like you have to get this to me on at this time. - Well, sometimes I have that a little bit. I mean, definitely I drive my own research for like in grad school. My head, I felt like I needed to have something to show my advisor. - That's true. - Of course, sure there's a little bit of that accountability. But I don't have someone that's relying on me to like make a product that actually works for that. (laughing) - I can use this factor, it's true. - I also enjoy like writing the proposals. - No really? - Yeah, I do want to know when, no one yet has answered that is the thing they look at. - Maybe it's 'cause I'm new to this. (laughing) My good old really soon. - I don't personally enjoy being the government for money, but I guess I'm kind of like writing about it so that it kind of reminds me why I want to do this. - I do like writing. - And I like the communication aspect in terms of presenting my work at conferences and things. Yeah, I think I get a lot of energy from talking to people about my, what I'm doing and what we're discovering and why it might be cool and what the data could mean. so when I get to do this, that I guess it kind of fills my bucket, makes me excited. - Yeah, it makes sense. And so yeah, I was gonna say, I don't remember what I was gonna say, it doesn't matter. So then, okay, so that's what you like. What is there anything you don't like about your job? - Sometimes I don't like that. There are days when it feels a little isolating. Like sometimes I'm the only, well, I enjoy that I'm like leading my projects, but I've had projects where it feels like I'm the only one working on it and maybe even the only one that cares about it. - No, don't be like that. (laughing) - Yeah. - So yeah, and especially as a graduate school, as a graduate student, like COVID happened during my graduate student years. And so there were definitely times where I felt like, I was a little isolated. - Yeah, it's very hard. You know, it can be, you can feel like you're just talking to a lawyer, writing into a lawyer, and you put up supposed to paper and you're not sure if anyone cares. - Right, so in the last few years, I've definitely started going to a lot more conferences. Part of that is that the world has opened back up again. - Right. - And so, you know, every so often, going to those, talking to people, reconnecting with peers, I think the social aspect is important for me and like connecting to other scientists definitely makes me stay excited about the work I'm doing. (upbeat music) - Now I remember what I was gonna say. You were saying something about how you weren't sure whether that would continue. When you said, you know, kind of, we've got to be your own, drive your own research or be your own boss or that sort of thing. And you said, I'm not sure if that continues in your professor. I was gonna say, it does, but it's, I mean, you're also other people's bosses. - Right. - So it's a little different. - Yes, I'll be in charge of people. - Yeah. - I was a high school teacher, actually. - Oh really? - Between undergrad and grad school for two years. - It's very bad. - And I would say that that felt a lot more stressful to me because every day I was in charge of like, a lot, yeah, at least 60. I was working in the private schools and so I was pretty fortunate that that part was easier. But I was just in charge of a lot of people and a lot of people depended on me every day to have a new material to learn and things like that. So, - That's true. Every day you gotta come with a material with a new material. - Yeah. So that was a little stressful. - With the little, that's a crazy thing, right? - It was also fun. Like I really enjoyed the people interactions in terms of teaching. So yeah, hoping to become a professor where I can do both the research and the teaching. - I love the teaching aspect, but I only have to prepare like a couple hours of material per week, right? - Yes. - I can't imagine being a high school teacher and having to do basically what is it like eight hours today? Something like that? - Depends on how many preps you have. - Yeah. - Yeah. - And I was doing my only two years teaching. So I think it gets a little easier once you have all the materials. But when you're still building material every day, it's like every single day, you need more material. Yeah. So. - Okay. - So now what would you say was, what do you think, like what are some of the challenges you feel in academia? Like what was the most challenging aspect of getting to where you are? - I think just the day to day work is in its own nature, challenging. Sometimes there's this feeling and academia of needing to be good enough and needing to be good enough being like getting enough papers published. - Yes. - You know, it's easy to compare yourself to all these other people who are doing extraordinarily well and have 12 papers out of grad school. Oh my goodness, that's insanity. So there's a little bit of a feeling that you never really get to turn your work off. Like occasionally I feel, you know, I should be working in the evening or need to get some stuff done on the weekend in order to like meet all these deadlamps and things that I have going on. - Well, I think also if you're working on supernovae, there's a lot of, there's inherently competitive nature to it, because there is some of that pressure. - Yeah, 'cause I mean, you know, you'll be looking at the same object that someone else probably is looking at, right? And so you have to be like, am I gonna get my paper out before they are? - Yeah. - That is my paper, like what kind of date is there a date of better than mine? (laughs) - Yes. - So anyway. - So I would say that's a challenging aspect just having high expectations in myself and try, like, knowing that there's so few spots in like the profession that I want to go into. - Right. - So I, you know, when I started graduate school, the hope has always been to be a professor. And so I'm very excited that I was able to get a post-doctoral position to continue doing what I'm doing. It has made me a little more hopeful to be able to get that professor ship somewhere someday. But there is a little bit of that fear of not very many spots in academia, - Right. - You kind of have to either be a little bit lucky or just exceptionally hard working and all of this stuff to get that spot. - Yeah. - So that's a little stressful sometimes. - All right, now we're actually gonna talk about the science you work on. You already mentioned you were an observer. So but here's the question I asked to start this off, which is when you meet a new grad student or a fellow scientist, what do you tell them and they ask you what you work on? What do you tell them? - I tell them that I work on JWST spectroscopy of type 1A supernovae or exploding white warfs. - Okay, so JWST is this new space telescope that hopefully people who listen to my podcast know about, but it's the James Webb Space Telescope, JWST, we're all calling it JWST in like night right now, just like the Hubble telescope we called HST. And I'm sure if we said HST, most of my listeners wouldn't know necessarily what they were saying. So I just like to clarify that. And then you said spectroscopy. - Right, so for a supernova, there's kind of two ways to get observational data or two main ways. One of them is called photometry. And it's basically just taking an image of the supernova and tracking, measuring in each of those images over time, how bright it is. - Okay. - And you can do photometry in different filters. So you could put a filter over a certain wavelength range of light. So maybe you just wanna get the red color of the supernova. So you put the R filter on or the blue, this is a wavelength range of the supernova light and you get the B filter and there's B, G for green and all these and it goes up into the near infrared. And so photometry, well actually into the mid infrared tube. So photometry is a measure of the brightness of the supernova and you take photometry over time to track the supernova's brightness rising and falling. So the other type of observation you can do is getting spectra and that's where you take the light that comes to your telescope but you pass it through a prism or a grading and it disperses the light into its constituent wavelengths. So you're getting kind of like a rainbow in the optical but then certain parts of the rainbow are gonna be more intense. They'll have more pixel counts there and certain will be less because there are absorption and emission lines from different elements and so you can use spectroscopy to get additional information that you can't get from photometry alone. - That was a very detailed explanation of spectroscopy. So basically breaking it into a sort of a rainbow of wavelengths and seeing how bright is it at each wavelength and you've not even mentioned that you can use that for example to figure out what stuff is there, what different elements are in there because different elements absorb a different wavelength. - Right and you can learn things about the temperature as well. Density, speed, the stat things are going at. Yeah, there's a lot of information that's kind of packed into spectra if you can. - Right, and so then you say, okay, JWST spectroscopy of type 1A supernova and you did say what a type 1A supernova is but we might as well say it again, it's been said exploding white dwarfs. So as you mentioned, you said you listened to Abby's podcast. in the way over. So we already, we did talk about type 1 A supernovae in there. So I don't know where you're going to complete detail, but right. The point is there are different types of supernovae stars can explode in different ways. Right, and particularly the kind that I've been studying most recently are not the kind where you have a massive star of that explodes due to like gravitationally collapsing. And so I like to say white dwarf supernovae to remind people that it's a white dwarf that exploding. And then the opposite channel of supernovae would be massive star supernova where you have the core collapse of a massive star. Yes, because astronomers like to come up with a whole bunch of classifications that like to regular people doesn't have any meaning kind of type 1 A or type 2 B. Well, if I can defend that just a little bit, there's a reason for that. And part of it is because we see different signatures in the spectra, but we don't always know what it means yet. So our names for things are not always physically meaningful because we don't always know the meaning yet. That's right. Although astronomers have a terrible like tendency not to go back and rename things. That's right. They kind of figure it about. The naming like we still have our star naming conventions from like a century ago or a little longer. Oh, you've been longer than that. Yeah, terrible. So, but yeah, so we like to we just stick with the end, yeah, we can get it. We use the magnitude system that the ancient Greeks came up with. And for brightness. It's horribly confusing. But yeah, so but that's an excellent point, which is why sometimes these things seem to have weird names that don't seem to explain what they are. And that's because we didn't have an explanation when they were discovered. Yes. So good. So that was tight set. So JWC spectroscopy of these type 1 A supernovae or white dwarf explosions. All right. And so specifically we we look at them, you know, we can look at them with any telescope in the world, right? Why JWC? So JWC is NASA's new really exciting telescope that's super powerful. And the really awesome thing about JWC is that it's looking at infrared wavelengths. And so infrared wavelengths are very difficult to observe from the ground because there's a lot of atmosphere that gets in the way. So there's things like carbon dioxide and water and the atmosphere that will absorb certain wavelength ranges of light. And so we can't observe some wavelength ranges unless we have a space telescope where, you know, there is no atmospheric interference. So JWC goes from like the near infrared, which is at the end of the optical, which might be meaningful for some people, but my not for others. That's like 10,000 angstroms or one micron wavelength of light. And then it goes all the way out to the mid infrared, which the farthest that JWC is observing is about 28 microns. So near infrared we mean just beyond red basically. Yeah. It goes from like one to like well ground based near infrared gets to 2.5 microns, but JWC they say near infrared goes to five microns. And then five to 28 is mid infrared. All right, I shouldn't have asked for clarification. So the important thing about JWC and the mid infrared for supernovae is that there are additional lines from elements and ions that we can't see in the optical and the near infrared from the ground. And so there are also a lot more isolated in the optical. There's a lot of different transition like lines that arise from transitions in the iron group elements like iron, cobalt, and nickel that arise from or that are very close by to each other. And so they overlap. In supernovae these speeds are very high. They get up to like upwards of 10,000 kilometers per second. And so if you're familiar with the Doppler shift basically as things are at higher velocities, the lines will broaden. Okay, let me let me let me let me I'm trying to break down everything you're saying here. So the the first thing is you know the I guess we're trying to explain why infrared right why what do we learn the infrared with you don't do we don't learn an optical and you're saying an optical you know they're certain elements that you can see in the infrared that you could also see in the optical but it's a little bit hard to interpret them in the optical because basically they're absorbing in all these different wavelengths and in the optical they have there's a bunch of different elements that absorb all close to the same way they're doing so it's hard to tell the difference between them and then moreover these things this supernova moving so fast that they cause the they basically smear out the absorption features from different from different elements and then they just and so you can't tell what's what in the particular. Yeah so each line is kind of smeared out with the high velocities and then there's a whole ton of lines right next to each other. Right. Then they all overlap and they all blend together and you basically need models to be able to pick them apart but in the the mid infrared there's lines that are isolated enough that it's you know dominantly just one line and you can see the the shape of the line you can measure velocities you can actually directly get the ejected geometry from the profile shape of the of the basically from the shape of the emission line and there's also emission from elements like argon and calcium and that's important because those are what we term intermediate mass elements they're not as heavy as iron nickel and cobalt so they were nucleosynthesized or like fused and created in the supernova explosion in a different way at a different density the lower density material is going to fuse into the lower mass elements things like argon and calcium. Okay so let me let me back up a little bit you so you have you've mentioned a whole bunch of elements and we're not going to get probably not going to get too well but like there's there's iron group elements and there's other elements like calcium argon so some of these like a lot of these basically are are forged just during this very brief process when the supernova explodes. Yes. And so if you can say how much there is of each element you can learn things about this explosion mechanism itself like how hot it got and so it got to burn a whole bunch of this particular material or something you can yeah you can learn about how complete the burning was that sort of thing. Right but you can also learn about where the elements are located in the ejecta and back and inform you about your explosion mechanism. So when you say the ejecta you mean the stuff that's got flung out this the end the it's basically the supernova that and when it explodes and it's become this ball of gas that's flying outwards we call that the ejecta and so that has all those elements in it that it forged during the explosion and you can say where in that explosion where they're located. Yeah so for one of the the things that we see very clearly in the JWST observations that we've gotten of normal type 1a supernovae the argon and the calcium those intermediate mass lower mass elements are located on the outside whereas the inner the iron group elements are located in the inside and that's because the white dwarf the densities are really high in the center and so the high densities fuse the iron group elements whereas the lower density outer layers fuse to the intermediate mass elements because they're they're lower mass and lower it came from lower densities. Okay so then basically if I'm picturing the explosion it starts maybe the these normal say quote unquote normal type 1a supernovae you imagine they could start from the explosion starts from the center and it's very hot and dense and it forten it burns to these iron group elements but then the explosion propagates out and it goes to lower densities maybe it's not quite as hot as it gets out or something like that and then it and then it burns to maybe maybe only produces intermediate mass elements like calcium not just only of course all of these statements have millions of copy of some I'm not getting to but like calcium and argon these intermediate mass elements and you can say if you can say where those elements are in the final out outflow you can say what you can talk about that that process that how you can constrain. Right so in particular because we see this layered structure where the iron the intermediate mass elements and iron group elements are kind of separated that tells us that it's the explosion had to involve some type of detonation. So detonation means that the nuclear burning is super sonic, is going very fast. So the explosion proceeds so fast that the start doesn't have time to react and those layers just burn kind of similar to like the densities that they're at and they don't have time to mix around. So that's in contrast to say, for example, an explosion mechanism called a death flagration, which is the opposite. It's subsonic burning where it's slower and the star has time to react and as it burns and gets hotter, it puffs up to lower densities and then there's convection that takes those hot burning ashes and rises those to the surface and other unburnt material falls down. And everything gets mixed together. And so that's part of why, you know, in the observations if we can see where in the eject of these things are located, it helps us understand how it exploded. Right, okay, that's very impressive. So there's a very good argument for J.A.R. we have to see there. So like, if we, I guess the claim then is that in the infrared, we can, because things are so isolated, we can actually constrain different explosion, how we can actually constrain the process that it exploded with. Right, and in the optical and the infrared, there aren't lines from these intermediate mass elements, except for like, there's a calcium two line in the optical that's a singly ionized calcium. But it's very difficult because it is sitting straight on top of like a really strong iron and strong nickel line. So it's really hard to distinguish, well, what's the contribution from calcium versus what's the contribution from nickel and iron? And what are those different shapes when they're all right on top of each other? It's hard to deduce. So in the mid infrared, it makes it so much clearer. - Okay, wow. And so that's kind of incredible. So you know, for decades, we've had these understanding that white type 1 A supernovae are these exploding white dwarfs, but the details of exactly what caused, like what that explosion looks like, we've kind of just mostly argued about for those decades. And we may be able to get answers, like concrete answers, if we can say where the different elements are located and expanding out flow. - Yeah, so I think it's amazing that JWST is opening this new window because each of these new wavelength regimes is reveals different kinds of physics. And it's also cool 'cause like the mid infrared, you can see signatures of dust. You can't see those in optical and in the air infrared. And so there's all sorts of things to be probed here, low hanging fruit that we've just never, like we just haven't seen what's out there before at these wavelength ranges. So there's a lot to learn. (upbeat music) (upbeat music) - Yeah, I was like a lot of the motivation for putting a new telescope up there is, if you can look in just a new band or in a new way that we haven't looked before, you always find things. - Yes, and we're definitely discovering exciting things with every new supernova that we're observing with JWST. - That's cool. So let me ask about your sort of data or day research. So what is it, you know, you say you work with JWST data. So that means presumably part of that has been writing proposals to point JWST at things. But like what else is, you know, I guess what it would, what does your work look like? - So there one aspect is the data reduction. Once you get the data, you have to, you know, clean up the image and then extract the spectrum so it's like the useful information. So reducing the data is part of what I do. And then we want to, you know, identify which lines there are. We're actually seeing a lot of lines that we've never seen before. And so part of it is saying, what is that thing I'm seeing? (laughs) That was not expected. And sometimes it's a line that you didn't even expect from the model. And so trying to figure out what am I actually seeing? And then another part of what I do is like measuring, trying to measure physical properties from the observations. So potentially measuring things like temperatures or a lot of what I do is fitting lines to measure velocities. And those velocities tell us about the, like wet materials located in the supernova expansion. - Right, how fast is going also to tell us where it is? - Supernova is, it expands, is this word called homologously, but it just means like it expands so that the radius equals the velocity times the time. So if you measure the velocities, you're actually getting the radius of structure. And so, yeah, measuring the velocities is directly measuring where things are in the ejecta. - But the fast moving stuff is on the outside, the slow moving stuff is on the inside. - Yep. - And so, like a lot, okay. So then just looking at data reduction and like looking at it, sometimes seeing new things that we didn't expect to see there, but a lot of it is just identifying what all the different features are. - Yeah. - And analyzing lots of plots, writing papers, yeah. - Okay, and so, I mean, now what would you say would be the sort of the big result that you'd be interested in talking about, like with these new Javistee one A's that you've looked at, is there, or what would you say is the big result that I guess A big result that you have been a part of recently? - So, I would say that we have a lot of new results that I haven't been able to get time to publish quite yet. So we can't talk about that. - Most exciting for me right now. But I really enjoyed a project from last year where we got the first Javistee spectrum of this peculiar kind of white dwarf supernova that's actually like over luminous compared to normal type one A's. And they have this maybe slightly misleading but exciting name is called Super Chandra Seikar Mass, white dwarfs and supernova one A. And the idea is that the Chandra Seikar Mass is like this limit for how big a white dwarf can get before it explodes. But these have properties that would imply that maybe the thing that's exploding is super. - It's a one point above that. - It's bigger than that, man. - And so our Javistee observations pointed a very strong evidence for the violent merger of two white dwarfs. So both of these white dwarfs are subchandra seikar mass instead of the one point four, they're like 0.7, 0.9, something like that. So if you get two of them together, that combined mass can exceed the Chandra Seikar mass. - Okay. - Yeah. - Okay. So well that's the idea anyway that's the working theory. - Yeah. - Is that it's a merger of two white dwarfs when the combined mass is above the Chandra Seikar mass. And so they're allowed to beat this criterion that they're allowed to go above that. - Yeah. - So I really enjoy looking at the weirdos and the oddballs and this one is definitely one of those. And it was exciting because our data did point quite definitively towards that particular model. - Okay. It's very cool. Okay. Well let me ask you this. In your opinion, we get touched about this like near the beginning, but when your opinion, why should we care about astrophysics? - Um, my highlight top of my head answer is because it's cool. Which is probably not a very convincing answer for most people. It works for me. I think we care about astrophysics really in large part because abses understand like where we fit in in the universe. What is this universe around us? And then where is our place in it? I think that studying astrophysics for me definitely kind of expands my mind. And there's so much crazy stuff out there. You know, on earth, sometimes I get bogged down by the mundane things or cleaning dishes all the time. And I like fold into laundry. But there's stuff out there that like, literally explodes with crazy energies. And like stars are born and die. And things get sucked into black holes. Like, I don't know, I just feel like that is inspirational sort of. - Yeah. - Yeah. - I agree. - And then I guess there's also the more practical answers. Like, you know, a lot of the technology that has been developed to make incredible telescopes like JWST actually has applications towards advancing technology and technology. other sectors. But that's not why you study astrophysics. No, I study astrophysics because I think it's cool. Okay, good. So I guess what's, you know, what's the next big thing you're hoping to do? I mean, you don't have to be specific if you want to, if it, what are you? Oh, sure. No, I'm happy to talk about it. So I feel extremely fortunate that I'm a postdoctoral fellow, which means that I get to drive my research direction as a postdoc, rather than being like tied to one particular grant where I have to do one project. So we have a lot of data that we've collected from the JWST program that I worked on in my thesis work. And there's a lot more work that I have to do to understand what's going on with all these different kind of, there's some observational observations of other normal type 1As where we're seeing like variations. So try to understand the model is that produce normal type 1As. But then also there's a lot of different peculiar things in what we call the thermonuclear supernova zoo. And I want to understand like what different ways you can explode a white dwarf that come up with these odd balls. And so lots of existing JWST data to continue working with. But I also have my own program. I'm now the PI of a JWST program that's looking at these mid-infrared spectra at early times, whereas in the other program that I was working on in my thesis work it's like later times. I don't know if we want to go ahead and help that. Anyway, at the early time we've never seen before and we're seeing we want to watch how it evolves over time and that we're hoping is going to help us figure out additional additional evidence for different models. So the idea is you're catching the supernova really early. Is that the idea? Earlier. Earlier. Yeah, this program is not super super early where you have to be really disruptive on the JWST schedule. I see. But what time scale in? This is like tens of days after the supernova's maximum light. Which is basically at 20 days for the explosion time. So we're talking about after it explodes like 30 to 70 days after it explodes. Yeah, and these earlier times you see changing lines, strengths, different changing shapes, different elements and I/O minds emerge at different times. And we're hoping that this can help us constrain like densities of the material and help us kind of piece apart additional evidence for which model fits each thing because each model predicts that they'll evolve and change over time in different ways too. So you mentioned the thermonuclear supernova zoo or I don't remember what you called exactly. But basically the idea being like over the past, I think I mentioned already over the past several decades like we've seen these type 1A supernovae and we had this idea that it was an exploding white dwarf. But then all these different theories of exactly what happened, right? Does it merge with a companion or does it get mass created from a companion? And what is the companion? All these different questions you can ask, is it like a violent thing or is it something that slowly gets just above some mass level and then explodes? And there's all these different theories as to how it goes and maybe all of those things might happen. But first of all we're still piecing together what the normal ones are. But then beyond that, it's where's the rest of the zoo? What are these weird ones? And what are these weird ones? And all these ideas are presentially things that could be happening and maybe things that we've already seen but we just need to look at them with new instruments and understand them. So that's very cool. Thank you. Okay, well thank you very much Dr. Quack for joining me. I had a great time talking science with you and I hope you'll join me again sometime. Thanks so much for having me. Amazing, just how much information we can pull out of a little point of light. Not to mention just how much new there is to learn about supernovae using JWST. So thank you so much to Dr. Quack and thank you to our listeners. We will see you next time. The Astrophysics podcast is supported in part by the National Science Foundation under grant number AAG-20629. If you want to connect more or if you have astronomy or astrophysics questions, follow me on bluesky at PaulDuffel.bsky.social. The music you hear on the astrophysics podcast was written and recorded by Britain Ashford. They are instrumental versions of songs from her album "Trader". All songs are used with permission from the artist and producer. Look up "Britain Ashford" if you enjoyed the music. This podcast is produced in beautiful Lafayette, Indiana by me, Aldefl, professor of physics and astronomy at Purdue University.