09:31:24 And next we have JJ Hermes 09:31:29 mentioned JJ is at Boston University. He's an expert on white dwarfs and today is going to tell us a little bit about what white dwarfs reveal about rocky exoplanets and exo-asteroids. 09:31:42 JJ take it away. 09:31:46 Okay, great. Thanks Mateo. Thanks to everyone for tuning in. 09:31:53 I will try to keep an eye on the chat. 09:31:56 But, as I mentioned, if you would like to ask a question feel free to just unmute yourself and interrupt me, or, or ask something in the chat I think one of the things I'm going to miss about teaching on zoom there's not much I'm going to miss about teaching 09:32:08 on zoom but one of the things I'm going to miss is the fact that many students who are reluctant to raise their hands can actually ask anonymous questions in the chat on zoom, and I would love for us to figure out a way to keep that alive. 09:32:22 When we start going back in person. 09:32:24 Because I know there are a lot of students that are reluctant to ask questions. 09:32:28 Anyway, um, I'm going to talk about something that's very specific that white dwarfs can help constrain Mike gave a great introduction to white dwarf stars, Mike was actually my co advisor for my PhD at the University of Texas, and I am fortunate enough 09:32:45 to have started a white dwarf group at Boston University, where I'm on the faculty now. And so if you'd like to check out some more that my group is working on, you can you can check us out here. 09:32:56 So I'm going to talk about an area of white dwarf research that I am relatively new to, but I'm growing an interest in, and hopefully by the end of this you'll understand why I am growing an interest in it because it white dwarfs can actually help us 09:33:11 constrain things about rocky exoplanets, and even exo-asteroids that is asteroids in solar systems, other than our own through relatively simple means. 09:33:24 And so this is a really interesting and growing field and astrophysics is using white dwarf stars to help us learn something about the actual rocky composition of material outside of our solar system. 09:33:38 And so, I'll motivate this by thinking about the, the dark future of the earth in our solar system. It's always great to start at home. 09:33:48 And so here is a cartoon of our solar system, I'm stealing this blatantly from Boris Gansicke, who's at the University of work and it's done a lot of work on planets around white dwarfs. 09:34:00 And so this is what our solar system looks like today. Our sun is nice happily burning hydrogen, helium and its core on the main sequence. it's about four and a half billion years old. 09:34:11 Here's our lovely solar system. 09:34:14 But over time, our sun will become more and more luminous. 09:34:32 So it's actually something that we don't have great expectations for Earth may actually be right on the outside, outside of survivability here. 09:34:42 But long before that all of our oceans will boil off earth will be a terrible place to go. Interestingly in this phase. 09:34:49 The, the amount of radiation that we get from the sun now in our orbit will exist around the moons of Jupiter. And so, there will be habitable moons in our solar system even during this phase and so, you know, we certainly have the technology to pick 09:35:07 up and move. 09:35:09 There are certain billionaires on our planet who who have this seeming desire to move us all to Mars. 09:35:18 But, you know, at some point billions of years from now, we, we will need to make this this great migration. 09:35:26 At least within our solar system. But that's far off into the future, we're talking hundreds of millions of years before things really, really get dire. 09:35:35 I also think it's worth mentioning that when you bring this up to to students or people in the community. A lot of times people have a sense of fatalism about climate change and global warming because eventually the sun will make our planet. 09:35:51 But all of the temperature rise that's happening right now on our planet is not because of a change in solar flux or solar output. So, we have very good, get good data now to say that that global warming, that's happening right now is is happening because 09:36:07 of increases in greenhouse gases on our planet. 09:36:12 But 5 billion years from now are some will evolve, it'll expand in size and as it does that it starts to lose more and more of its outer layers, and we will end up with a white dwarf star in our solar system that this, our sun will lose more than half 09:36:25 of its mass and all that will be leftover is a dense core, a white dwarf. 09:36:33 And that star will have lost a lot of mass which means everything that survives that phase, Mars will will almost certainly survive that phase Jupiter will certainly survive that phase, and lots of the asteroids in the asteroid belt, which are shown here 09:36:48 on this diagram will also survive, but if I go back in time you'll notice that their orbits have changed, they've expanded and anytime those orbits change, they get destabilized our mass distribution in our solar system will have changed. 09:37:05 That's not just true for the asteroids in our asteroid belt but that's true for commets Kuiper Belt Objects, or cloud objects things that are much much farther away and the outskirts of our solar system and so they're going to get destabilize, and they 09:37:20 will likely fall onto the remaining star the remaining white dwarf and that's what I'm going to talk about today is what we can learn about those surviving objects when they actually fall on to the white dwarf stars, so nothing is ever as simple as a 09:37:35 cartoon. 09:37:37 But if I kind of jump back. This is how we view white dwarf stars so if you were to, to have an extremely powerful telescope, this would, this is what a white dwarf would look like through about a three meter telescope. 09:37:53 With a relatively wide field of view. Maybe 20 minutes on each side. 09:38:00 This is how stars look to most astronomers. They are just points of light. 09:38:07 And so a lot of times we have to get creative about how we learned about those points of light, and I may be the only person talking about spectroscopy today so I just want to mention that we can pass that star light through a prism. 09:38:21 So I want to be inspired by the dark side of the moon. 09:38:25 So the album cover for for Pink Floyd's album really, really helps bring to home. If you pass Star light through a prism, you can break that light up into its constituent colors and study the intensity of that light as a function of wavelength. 09:38:41 So that can tell us a lot about stars I can tell us a lot about white door so everything I'm going to talk about in this talk will be using spectroscopy to analyze white dwarf starlight. 09:38:56 So the other important key thing to remember here is that every element in the periodic table from hydrogen and helium all the way down to uranium and plutonium. 09:39:09 They all have their own fingerprint in light. That is the electrons in those atoms, all have distinct energy level transitions that correspond to certain wavelength. 09:39:25 And so, when you look at the spectrum of a star when you pass that star light through a prism, or a diffraction grading and you cause that light to interfere with itself, and that causes the light to spread out, where you can measure the intensity as 09:39:40 a function of wavelength, you can learn what chemical elements are actually in those those stars. 09:39:46 And so I love this, you can actually buy this as a poster, it's actually kind of expensive it's like $40 for a poster, but I definitely I'm not getting a cut of this but I love this poster because it, it shows you that each, each element has its own fingerprint 09:40:03 in light sodium is usually a great thing to to refer folks to street lamps glow, orange, if they're sodium street lamps because they're just sodium in the tube that's getting lit up. 09:40:21 And that's why they look orange. 09:40:24 That is not going to be irrelevant reference in five years because all of our street lamps are getting replaced by LED lights and so they will no longer glow naturally glow that that orange but but that's why sodium street lamps glow orange. 09:40:40 So Mike gave a nice introduction about white dwarf structure and how white dwarfs are carbon oxygen core objects with, with these nice layers of helium and hydrogen on top of them. 09:40:53 And I'll remind you that hydrogen just like all other elements, has specific transitions. We call these the bomber series. They have specific transitions at specific wavelengths. 09:41:06 And so when you go out and you pass white dwarf light through a prism. 09:41:11 This is what you see. 09:41:13 You see very broad features. 09:41:16 Only at wavelengths, where you see hydrogen. And so if you were to look at a hydrogen lamp with your eyes in up at optical wavelengths, you would see the bomber series you would see bomber transitions you would see what we call each alpha in the red ah 09:41:35 and so on, higher and higher order series. And so here are sort of the bluer lines that you would see here's h beta. These are some of the lines Mike was showing with his laboratory experience experiments at Sandia. 09:41:49 But you, you really only see hydrogen in the spectrum at this resolution on this white dwarf. 09:42:03 That's because the hydrogen has effectively bubbled up all of the heavier elements have sunk down. 09:42:05 This is a great diffusion problem this is just like if you have some apple cider. All of the sediments sink down. 09:42:13 And all you're left with is just this hydrogen at the surface. So the settling time for metals, other than hydrogen settle out of that atmosphere of the white dwarf on a timescale shorter than yours. 09:42:28 For most white dwarfs that we find in surveys. 09:42:33 And so we expect to just see hydrogen, because most of those heavy elements has sunk down so white dwarfs have extremely strong surface gravity's they're extremely dense. 09:42:41 So the surface gravity on a white dwarf is about 100,000 times stronger than here on Earth. So imagine what Apple Cider would look like on the surface of a white dwarf, I mean things sink out very quickly. 09:42:53 That's why you get these nice strong segregated layers. But when we go out and we actually measure the spectrum of lots and lots of white dwarfs. We don't just see hydrogen in their atmospheres. 09:43:04 Many of these white dwarfs show transitions from lots of other metals in their atmospheres, so here you're seeing a white dwarf. Here's its name Gd 362, you see the hydrogen, but you also see calcium and iron, magnesium, you see lots of transitions from 09:43:23 other elements in the atmosphere. And what we are very likely seeing is pollution of what should be a pristine white dwarf from surviving rocky material around that star. 09:43:38 So, here is the, here's the the nutshell story here, we're arguing that the pollution and these white dwarfs reveals the future of planetary systems around stars just like our Sun. 09:43:51 So we know planets are extremely common around other stars thanks to missions like Kepler now tests are finding tons and tons of exoplanets we have thousands of confirmed active exoplanets now. 09:44:04 So we know stars like our Sun have planets, as that star evolves the orbits of everything that survives whether it's asteroids are planets are moons, all of those orbits are going to expand because that stars last mass, and that's going to cause those 09:44:23 to become destabilized in some cases, and so some of that material is going to scatter in. And so that those ancient solar systems are going to have some leftover debris. And if that debris, get scattered close enough to the white dwarf, it'll get ripped 09:44:30 apart by the strong tides of the star. And then all that material will form a disk and eventually fall onto the leftover star. 09:44:39 So Mark Garlick is a. 09:44:42 He's an author he's an illustrator he makes a lot of great illustrations of these these white dwarf systems. So, I give him credit for a lot of these, these great illustrations but this picture has really been confirmed and a lot of different observational 09:44:57 avenues, over the last few decades. So this is really put forward. 09:45:03 Early on several decades ago by several researchers at UCLA and around the world. And eventually, now we've, we've gotten enough evidence, where not only do we see photos field pollution. 09:45:16 So if we take a spectrum of a white dwarf and measure its intensity as a function of wavelength. We see calcium and iron, and magnesium that should not exist in these stars but it is there. 09:45:28 And so it has to be raining onto those stars. 09:45:32 And so that's the strongest line of evidence but we also see infrared accesses around the stars, which we think is explained by there being dust discs. 09:45:43 Not only do we see big clouds of dust. In fact, we've actually taken spectra of some of these infrared features, and they match bumps at about 10 microns, which is where we would expect all of you. 09:45:59 These are silicon oxy like like silicon oxides, so just like the green sand beaches in Hawaii, we can actually see spectral evidence of some of this dust around these white dwarfs that's getting ground apart from from these bigger parent bodies. 09:46:14 But even closer into the white dwarfs, we can see some of this material, as, as gas emission. And this material is not just existing at one wavelength, some of that material is in a desk in that material is coming towards and away from us. 09:46:30 And it's causing these Doppler features where we have some of that gas moving towards us and some of it moving away from us so we see that in these, these three different lines of calcium. 09:46:43 Right. 09:46:45 So I just want to focus on, on these two dust and gas disk lines of evidence. 09:46:52 Here's a cartoon showing Saturn and a white dwarf to scale and so these disks have ripped apart rocky material around white dwarfs is on a very similar scale to the rings of Saturn. 09:47:06 And so, I have here, to really nice reviews that were written in 2016 by Jay Farihi and Dimitri Veras and Dimitri is actually on the call. And so Dimitri is, I would argue the world expert on planets that survive main sequence evolution, and he is a 09:47:28 fountain of information about all this so if you find yourself in a breakout room with Dimitri, make sure you pepper him with lots of questions because he is, he's very prolific he writes several papers a year about this field so these white dwarfs show 09:47:43 all these different lines of evidence. So what can we learn from from these lines of evidence. 09:47:51 The first thing I want to I want to mention is that just by measuring the abundances of this material, we can actually learn something about what is the bulk abundance of these rocks that are falling on white dwarf so if we look at different white dwarfs, 09:48:06 we can compare their atmosphere compositions, we can assume that what is falling onto those stars is representative of of the rocks that have been ripped apart. 09:48:18 Remember we only expect to see hydrogen and these white dwarf so all of the metals we see have to be coming from, from the rocks that are falling onto them. 09:48:30 Sean I'm going to save your question about how the rocks get there for a little while. 09:48:35 This is what the book Earth composition looks like, and it's dominated by four main elements. If you were to break apart, our planet. 09:48:45 The average composition of our planet. It would really be dominated by oxygen magnesium silicon, an iron. 09:48:52 That's not true for comets, like Halley's comet. 09:48:55 That's mostly volatile rich you see mostly oxygen and carbon, and then iron and silicon of magnesium. 09:49:03 But here are the here are pie charts of the abundances of 10 different rocks that are falling on 10 different white dwarfs as we speak. This is from a paper by see shoe. 09:49:16 I'm showing on the bottom left, just to show you that there's a big diversity in the types of rocks that fall onto white dwarfs, but these rocks look a lot like both the meteors, and the bulk Earth composition here in our solar system. 09:49:39 I'm not sure if this musics coming through I hope it's not because it's kind of silly. 09:49:44 Comets crashing to our sun, all the time. So this this destabilization of orbits, is, is not uncommon. 09:49:52 This happens in our solar system. 09:49:55 Comets can come and approach the sun from really high eccentricities. And so comets do crash into the sun all the time but we can't really learn anything about the composition of those comets because they contribute so little to the overall composition 09:50:09 of the sun, that when a comet falls onto the sun it really doesn't change the composition of the sun, the boat composition of the sun, very much. 09:50:20 I like to think of white dwarfs more like freshly laid snow, where, When these rocks are falling onto these, these white dwarfs were actually able to trace the footprints of that one rock because everything else will have sunk out of the atmosphere of 09:50:44 that white dwarf very quickly and so when we see those those elements on the surface of the white dwarf. They are telling us that they are being put there in the moment they are from it. 09:50:49 In an asteroid or rocky body. 09:50:53 So, so unlike you know a trail in the woods that's been tried many times you can't really you know trace footprints on one of those trails, with white dwarfs, that's what it would be like first star like the Sun we really can't learn about rocky material 09:51:06 around normal sunlight stars. So we really need to look for places where it's kind of like a blank canvas. 09:51:13 Where, where we can actually learn something about that rocky material. 09:51:17 And so that's the big power we have here with white dwarfs is, we can actually constrain the abundances of the rocks that are falling onto those stars, by looking but by taking a spectrum, we can we can pass that white dwarf light through a prism, and 09:51:35 compare the abundances, and they can tell us something about the diversity of rocks around these objects but they can also tell us that the rocks around these objects are really no different than the rocks in our solar system. 09:51:48 So a lot of these rocks that are falling onto white dwarfs they look a lot like our bowl Earth composition. 09:51:55 They look a lot like contracts and other meteorites in our solar system. 09:52:01 So what else can we do let's get even more exciting. 09:52:05 Let's think about all of the different 09:52:10 molecules that could exist on a rocky body. So, almost all of the rocks we know here on Earth are oxides metal oxides, magnesium oxide aluminum oxide silicon oxide. 09:52:25 That is how most of the rocks exist on on our planet on other planets in the solar system. 09:52:33 So those are some molecules that are relevant volatiles are also relevant like I mentioned with with Halley's comet. You've carbon dioxide, you could have carbon dioxide in ice form, so you could have co2 ice. 09:52:46 You could have water ice. 09:52:49 And I hope you see where I'm going with this. If we start to think about the budgets for oxygen specifically if we assume that all of these other elements are metal oxides, so the iron comes as iron oxide, the silicon comes in silicon oxide the magnesium 09:53:09 comes as magnesium oxide, we can build up in a budget for how much oxygen we expect. 09:53:16 And I want to just pick out one of these stars. And you'll notice that the pie for oxygen is pretty big. 09:53:23 It's much bigger than many of these other oxygen pies and around this specific white dwarf, if we add up all of the oxygen that we'd expect to come from magnesium oxide or aluminum or silicon or calcium from those elements that we see in that star. 09:53:45 That makes up less than 50% of the oxygen budget that we see in this white dwarf. 09:53:55 And so we can actually use these observations to say that there is so much oxygen, the abundance of oxygen compared to calcium silicon aluminum magnesium and all the other elements that all the other atomic elements that we see in this white dwarf. 09:54:14 It has so little carbon that all of this excess oxygen is likely coming from water. 09:54:23 And we can further estimate that that parent body was originally composed of at least 26% water biomass. So we're actually able to constrain the water mass fraction of some of these rocks that are falling on this white dwarf so this was first done by 09:54:40 Jay Farihi in 2013 it's been done for a few other white dwarfs. So it's not just a one off a small fraction of these white dwarfs look like the material falling onto them is very water rich, just really cool. 09:54:56 The earth is relatively water poor for things in our solar system right our oceans or makeup a very very small fraction of the the bulk mass here on Earth. 09:55:08 Right. 09:55:11 So that's, that's really, really cool. So, we can say something about water on rocks outside of our solar system, and this is really one of the only ways we can, we can learn about what is the actual water mass fraction of things outside of our solar 09:55:30 system. 09:55:34 So, I've highlighted a few of the elements in the periodic table I've been talking about just because they make the strongest transition at optical wavelengths where our instruments are most sensitive to make these measurements. 09:55:47 But there's a whole periodic table of things that must exist in these rocks, but they probably exist in small enough concentrations that they just don't really stick out in our spectra. 09:55:58 But it's amazing to think that, you know, we assume that these white dwarfs have hydrogen on the surface sometimes they have helium on the surface but we're beginning to see carbon, oxygen, silicon sulfur, iron, magnesium and higher and higher concentrations 09:56:13 and really these four elements which are the same four elements that make up bulk Earth. That's what dominates the abundances of rocks around other stars and other solar systems. 09:56:29 So I want to finish up talking about these two elements lithium and beryllium because over the last few years. 09:56:38 These are I say over the last few years are really over the last few months. 09:56:42 These two elements have been detected for the first time in white dwarfs, and they may say two really interesting things. So I'll start with lithium, and just this year in a science paper led by a grad student at UNC Ben Kaiser, Ben used the the four 09:57:01 meter sore telescope in July. 09:57:03 And he identified this lithium line. For the first time in a white dwarf now lithium is really cool because lithium is not created in stars. 09:57:13 So its abundance is set around the Universe by the Big Bang. 09:57:20 And so these white dwarfs that show lithium been found several. 09:57:27 They are very cool therefore they are very old white dwarfs, and the hope is at some point these lithium abundances can say something about lithium concentrations around stars that were formed at different ages so our sun form four and a half billion 09:57:41 years ago. 09:57:44 And over the next few years, hopefully we will start to study these lithium abundances and learn more about how lithium is distributed among stars, and rocks around, around our galaxy. 09:57:59 So that's not just true for lithium, there's another element I'll get to, but I want to talk about one other paper that that very very recently talked about lithium abundances and white dwarf so you'll notice in this star not only was lithium detected 09:58:15 but so is sodium, so is potassium. 09:58:19 So as magnesium, so is calcium, so there were other elements observed in this spectrum. 09:58:26 And another group independently first found also found lithium, and a handful of white dwarfs. So that's this this line right here. 09:58:38 But what this group did was compare that lithium abundance. 09:58:43 And you have to scale it to something because we don't see hydrogen in these specific white dwarfs they scaled it to sodium. 09:58:50 And so they compared lithium to calcium and lithium to potassium. 09:58:57 And so you can see the potassium line here and you can measure how abundant that line is by the depth of these absorption features and so they basically compared the depth of these potassium features to the depth of the lithium features to the depth 09:59:12 of the sodium features. 09:59:15 And what they found is that the abundance of lithium the calcium and these rocks around these old white dwarfs looks very much like continental crust here on earth. 09:59:28 And so they made an argument. like a lot of things in science. 09:59:33 People will will argue about this argument I know of several experts in the field who are skeptical of this argument, but I know of other experts in the field who are less skeptical of the argument that the lithium abundances in this white dwarf maybe 09:59:49 saying something about how how these rocks came about and, and it may be that they're the ripped off parts of large planets that had crusts. 10:00:05 And we're seeing just the crystal part of one of those large planets. 10:00:10 So, just by measuring these abundances we're, we're, we're trying to piece together, where these rocks came from, and they may not just be normal asteroids they may be fragments of larger planets. 10:00:24 And I, I saw some questions about orbit expansion and I want to get into that in the questions but it's very likely that a very large rock collided with Earth and our history, and the fragments of that created our moon. 10:00:41 And so it's very likely that if there is another phase of destabilized orbits in solar systems like our own, there will be planet to planet collisions, or moon to Planet collisions, as these things get destabilized, and so it's not outside the realm of 10:00:57 possibility to think that, you know, big bits of crust from these, these planets could get liberated and eventually find their ways to the white dwarfs. 10:01:07 Okay, last slide, beryllium is another element that was just this year published for the first time. 10:01:16 First in a paper by Beth Klein at UCLA, and then followed up theoretically by a grad student at UCLA and beryllium is another one of those elements that is actually quite rare and stars it's usually destroyed and stars and the simplest way to form beryllium 10:01:36 is actually through a process called speculation, which is taking heavier elements like oxygen and bombarding them with cosmic rays and causing that oxygen to actually fission. 10:01:49 So you normally think of uranium, or really really heavy elements that confusion and break apart to make smaller elements on the periodic table. 10:02:00 If you hit oxygen or nitrogen with cosmic rays, so high energy protons. 10:02:08 that can cause the oxygen to efficient and form beryllium. 10:02:15 And this very recent theoretical paper by Doyle at all in 2021 argues that perhaps the beryllium we're seeing in the rocks that are falling onto this polluted white dwarf are from rocks that existed around, former giant planets, and maybe those rocks 10:02:36 were even moons, and maybe that speculation occurred at a very high rate because of the strong magnetic field of those giant planets. So some of the abundances and some of the moon's dice moons around Jupiter and Saturn have high beryllium abundances 10:03:01 so maybe this is evidence that the rocks we're seeing that are falling onto this white dwarf are from an icy moon from around a former giant planet. Cool. So the bottom line here is that, that these alien rocks are just like rocks in our solar system. 10:03:09 They're mostly composed of iron, oxygen, silicon and magnesium. 10:03:13 Maybe some of you, some of them even show evidence of an oxygen excess from from water. 10:03:22 I am involved in in research studies to try to find more and more white dwarfs that so transiting debris in front of these white dwarfs, this was found for the first time in 2015, and for the interest of time because I really prefer to take some questions, 10:03:36 although I can come back to this if you have if you'd like, like to talk about it, we are finding more and more white, white dwarfs that are showing periodic dinning from big clouds of debris from rocks that are actively being ripped apart around the 10:03:50 white dwarf in real time. And so we're seeing these white dwarfs dim on relatively short like a few hour or even relatively long like a few hundred day timescale so this was from a paper lead BY ZACH Vanderbosch UT Austin last year. 10:04:07 But then another student at UT Austin Joseph Guidry has found many more white dwarfs that show periodic transits from this this ripped apart debris so that adds even more evidence to this idea that we're actually seeing rocks getting ripped apart in real 10:04:24 time around, these white dwarfs. 10:04:28 The last thing I'll mention is that James Webb Space Telescope, the successor to Hubble, much bigger mostly infrared will launch Halloween of this year, hopefully, fingers crossed. 10:04:41 And more than a day of JWST time was recently awarded to Susan Mullally to look out for white dwarfs to try to find evidence of wide surviving planets around these white dwarf so stay tuned hopefully will actually see some of these wide 10:04:59 planets that survived stellar evolution and are actually kicking in the rocks that we see that pollute the white dwarfs now so I'll leave up my conclusions, and I would love to take questions. 10:05:13 Thank you, JJ. Thank you so much. Very, very cool. 10:05:17 Um, okay so questions for JJ destroyer of worlds, Hermes. 10:05:28 We had the few questions on the chat, very interesting conversation. 10:05:35 That maybe can continue here. Most people are interested on. 10:05:42 So maybe I should start on the chat I saw there were maybe bring up a couple of pointers so there's definitely discussion about the evolution of the orbits of the planets and the effect of both tides, and the expansion. 10:06:04 Yeah. 10:06:04 Yeah, I just end up here, 10:06:12 wherever you want to go ahead. 10:06:14 I was wondering what happens to the magnetic field energy of the planets that get ripped apart. 10:06:22 You know, I realized that when I played my movie I muted myself and I didn't hear any of your question just then, and if there were questions over the last minute 10:06:30 I did not hear them, so I apologize if there was like this weird. 10:06:36 So sorry, good. 10:06:38 I was wondering, what happens to the magnetic field energy of the planets to get ripped up. 10:06:45 Yeah, that's a great question. So, presumably, it is it is relatively small compared to the scales involved. 10:06:58 But yeah, I mean, they're there as far as I know, there haven't been a lot of in depth studies about what how the magnetic field of whatever surviving object that makes it onto the white dwarf could impart more energy to that white dwarf. 10:07:18 I think the important thing that's to say here is that we think, based on a few different lines of evidence that the mass of the objects involved in the accretion of the rocks that we see are relatively small so probably have masses of things smaller 10:07:32 than the moon, and most most objects, like our moon is not magnetic not strongly magnetic it just doesn't have a big, you know, molten core to generate a dynamo to generate a big global magnetic field. 10:07:49 And so, odds are most of the things that we see that make their way into the white dwarf, probably don't have very strong magnetic fields, they're probably pretty small. 10:08:02 Um, so we have Robert just asked and we have Sean and then Vince, Sean. Thank you so much, that was really exciting. I'm just wondering, can you tell me do the white dwarfs have press. 10:08:11 Okay. 10:08:15 Are they going to have like geological processes that are happening is any of the material that you see in the surface, coming from inside or is it just you there's no mechanism that you can think of for that. 10:08:29 No So, so there's there's two things happening here. So, this material that's that's raining on to the star will set up, we pick white dwarfs specifically that do not have convection zones at their surface, because as those convictions zone so just like 10:08:47 our Sun. 10:08:48 There's a large region at the surface of the star where convection is doing the energy transport. 10:08:55 And if a convection zone on a white dwarf star gets deep enough, it can start to dredge up material heavier elements like carbon, and in fact we definitely see that in some cool white dwarfs, but that's at temperatures surface temperatures below six or 10:09:10 10:09:22 So, we, we specifically try to pick white dwarfs that are in the temperature range where we know those convection zones are not really relevant to bringing up material. 10:09:32 Great, thank you, thank you, that's very exciting to see the water though that's really amazing. Cool. 10:09:41 And, Vince. 10:09:42 Oh, yeah. 10:09:44 I was wondering if you can see the sort of the history of planet formation. 10:09:59 By looking at how old the white dwarves are and the oldest ones wouldn't have had planets because there wouldn't earliest not rocky planets, because those elements didn't exist yet. 10:10:00 Yeah, newer newer ones would. 10:10:03 So as this star loses mass. These orbits, expand to conserve angular momentum because the central masses is now less. 10:10:27 Over time, these orbits the star no longer loses mass and so they should start to relatively stabilize. 10:10:33 But 10:10:36 they're, they're still dynamical processes, and it's all about the dynamics that's kicking this stuff in over time. 10:10:43 And so you have an expectation that over time, there will be less and less material to kick in. over time so there's some evolving timescale where the dynamics dictate how fast stuff gets kicked in and that's actually been constrained by looking at what 10:11:00 is the fraction of white dwarfs as a function of temperature that show metal pollution and the evolving timescale is a little more than a billion years but it's probably less than 2 billion years. 10:11:10 And so just from from from that that that's what's really driving, why the older and cooler white dwarfs 10:11:19 tend to show less pollution, because more of that material has been scattered out. So that's the complicating factor but but you know at some level there is signal there were perhaps the oldest stars in our galaxy have a much lower planet occurrence rate 10:11:36 rate and therefore should have lower pollution rates. 10:11:39 So it'd be really cool if we could constrain it that way. But, yeah, like, like a lot of things in science, there's some, there's some complicating factor in the way that's that's affecting that signal. 10:11:53 Right, you call it. 10:11:57 Well, I'm wondering about the planetary nebula formed after the red giant phase, how large that is, and like what's the difference on the impact of things inside of that versus outside of the planetary nebula. 10:12:10 Yeah, that's a great question. The the planetary, the material that makes up the planetary nebula, as you go further and further away from the central star, the less and less dense it gets and less dense it is, the less it really matters in the grand 10:12:25 scheme of things, so right now our sun is actually losing a lot of material, there is a solar wind. We heard a little bit about the question to Mike in the first session about a gyro chronology and how stars spin down. 10:12:39 That's exactly why star spin down is because they have this slow wind, and the magnetic field, X to break on that wind. 10:12:48 But the solar winds. 10:12:51 Well fortunately for us, our planet has a nice magnetic field that protects us from that wind but you know the further and further away you get from the sun, the less that solar wind matters. 10:13:01 It's a lot like that with the planetary nebula so this planetary nebula can extend out, and I love how I'm extending my arms here like it really matters to really really huge distances far outside of Pluto's orbit in our solar system, but the material 10:13:14 is just so it's just so under dense that it really doesn't affect any sort of planetary orbits but yeah so that's why we think things like planets like Jupiter will will be relatively unaffected by the sun's eventual evolution, not just into a red giant 10:13:35 phase but but into any other planetary nebula faces faces like that where the, the outer layers are shed, and then get get lit up by the very very hot exposed core of the star, so that's effectively what's happening in that planetary nebula phases. 10:13:51 You get a lot of high energy radiation from that 200,000 degree exposed core of the star and so it lights up all of that that mass that's last. 10:14:03 Great. 10:14:06 Okay. 10:14:09 It seems like there are no more questions so I think it's also a good time to transition to our next speaker.