11:15:26 Get away can.
11:15:28 All right.
11:15:30 Excellent. Thanks for having me. I'm excited to tell you today about our work on supernova and the creation of hypervelocity stars.
11:15:39 Hopefully the previous three talks of what did your appetite for explosive revelations.
11:15:47 Okay, so I'm going to start by talking about supernovae, and if my thing would work. Okay, about supernova as Mike said, there's two main classes of supernovae, so there are the core clap supernovae, which refer to type two and type one B and C.
11:16:05 And these are the gravitational collapses of stars that were initially at least 10 times more massive than the Sun, very interesting but I'm not going to actually discuss those my focus of my research is on type one a supernova.
11:16:21 And, spoiler alert. We think that these are thermal nuclear explosions of white dwarfs.
11:16:26 But for the next few slides. We're gonna pretend we don't even know what they are, we just see these supernovae.
11:16:33 And so what does a supernova look like, what does it take when a supernova look like. This is a well studied example from 2011 2011 Effie, which happened in a lovely spiral galaxy.
11:16:45 And we'll see over the course of a few months, what happens.
11:16:48 So here you see this pinpoint of light, get brighter and something like a month and then decay way over another few months.
11:16:56 If you take the light of the supernova and make a plots of its brightness versus time, it looks something like this.
11:17:02 So the brightness is on the y axis and the time in days is on the x axis, and Tiffany supernovae look like this so these are a few different examples, they get brighter and something like 15 days and then decay away, and something like that 20 to 30 days.
11:17:20 Now you've almost certainly heard of Tiffany supernovae for their role to play in cosmology, and that's because they have this really great feature where they're not standard candles, so they do have a quite a dispersion how break they get their standardized.
11:17:34 double. And what that means is that the dimmer ones rise to their peak more rapidly than the brighter ones. So you can use this fact to standardize them you can say, you know, if I look at a time when the supernova I may not know how intrinsically bright
11:17:48 it is yet, but I do know how fast, how rapidly it took, how long it took to rise to its peak.
11:17:56 So then I do know its intrinsic brightness and can make a standard candle out of it.
11:18:01 And that's great because in astronomy, as we all know, it's very hard to get distances to things especially things that are outside of our own galaxy.
11:18:09 And if we know the intrinsic luminosity of the supernovae, we can use how bright the appear to be and get a distance measurement to very very far away galaxies this way.
11:18:19 It's like when a supernova great not only are they standardized well they also happen to be extremely bright, so we can see them something like halfway across the universe.
11:18:27 Okay so Tony Soprano they give us a chronological distance indicator. Okay, that's half the half the puzzle. I don't need to tell you this your physics teachers but things that come towards us of a blue shift and things that are moving away from us that
11:18:41 are redshift.
11:18:41 And so, galaxies we've known since the 1920s that galaxies that are far away from us are also receding away from us. Okay, so we can correlate the distance to a galaxy based on its 20 supernovae.
11:18:55 We can correlate that with the redshift of this galaxy how how rapidly it's receding away from us. We can make a plot of this.
11:19:02 And it looks something like this. This was done in the late 90s. And this plot shows that distance to a galaxy, and the redshift that galaxy, and the redshift you can just get by looking at the, the spectrum of the host galaxy the distance that requires
11:19:16 something like it's like when you supernova some distance indicator.
11:19:19 And so it wasn't until the 90s where we had a large enough sample, where we can actually make these measurements out to a high redshift say this is Richard the one which is roughly at the age of the universe, what the people found was that very interestingly
11:19:47 enough when a supernovae were showing that the universe is not expanding and just a regular old sort of naive way. Instead, the things that are further away from us are actually receiving away from us, even faster, and the further you look the faster these things are going in an accelerated way to expansion the universe is accelerating.
11:19:51 And you can see this by these blue lines these dashed lines are showing different cosmology is different make compositions of the universe. So this omega matter is how much matter, there is the universe in omega lambda, was this new thing this cosmological
11:20:05 constant.
11:20:07 You can see from these data points that the best fit line was somewhere around here. Okay.
11:20:12 And this has an Omega lambda, this again this component cosmological dark energy or cosmological constant of ground zero points.
11:20:22 that was done in the late 90s.
11:20:24 You might you know squint at this and say well this is kind of being driven by these data points here by just look at this stuff, you know it's not really statistically obvious that the best fit line can maybe be this one, which has no cosmological constants.
11:20:37 Don't worry, they were very careful the other team were very careful about this. But since then, in case that wasn't convincing enough.
11:20:44 Many hours have been spent looking at distant supernovae. And there are a ton more points out here and now.
11:20:51 And so now it's quite, quite clear that this dark energy this cosmological constant makes up something like three quarters of the universe. Okay, so only a quarter is matter, only a very small percentage of that is actually regular matter.
11:21:06 But what's happening supernovae were telling us is that three quarters of the universe is this dark energy this accelerate this this thing that causes the expansion of the universe to accelerate.
11:21:16 And so this led to the 2011, Nobel Prize, that was shared by these two teams that were using Tony supernovae as these as these cosmological distance indicators.
11:21:26 So this was really, this really led to revolution and how we understand our universe, and the prior to this, you know some people were kind of considering it but it wasn't until Tiffany supernovae really cemented it that we understood cosmological accelerated
11:21:41 expansion was it was a real thing.
11:21:45 Now I'm not a cosmologist.
11:21:48 I think Tony Soprano they are very useful but I enjoy studying them for their own sake because I'm astrophysicist.
11:21:54 And so I'd like to know what Tony supernovae are what actually needs to them and what this can tell us about stars.
11:22:03 And so we can use the observation that's happening supernovae not just broadly for their cosmological utility but we can also gain some insight into their progenitors from their observations.
11:22:13 So again, this is the Lakers epiphany supernovae very broadly they rise, their peak and something like a few weeks and indicate away in a few weeks.
11:22:22 And then immediately tells us something about the star that is exploding to cause them okay and that's because photons, the light from the supernova take some time to get to us through the supernova.
11:22:33 Next to go in and get absorbed and re emitted by all these nuclei that are in the way these atoms. And so it takes some time for them to random walk to diffuse their way out of the supernova ejecta and eventually get to us.
11:22:44 So that immediately tells us something about the amount of mass amount of material that's inside the supernova ejecta if they were really a lot of mass it would take longer for these photons to get to us and so the light curve would take longer to evolve.
11:22:59 So the fact that it takes something like a few weeks to for a tiny supernova to evolve tells us the amount of mass is roughly equivalent to the mass in the sun.
11:23:07 Okay, give or take, you know, a few tenths of a solar mass right so these are not 10 solar mass objects, these are not massive stars that are exploding.
11:23:15 And they're not, you know, 0.1 solar mass explosions they're not just tiny parts of stars.
11:23:21 There's something that's roughly the mass of the Sun.
11:23:26 So that's the light curves you know if you just take a telescope and gather all the light from it. What happens when you take a spectrum when you pass that light through basically a fancy prism and refract the light into its constituent components, you
11:23:39 get a spectrum, which other, other people have discussed already. And you're probably familiar with this a solar spectrum, which shows, lots of these absorption lines, and as we all know these absorption lines tell us the chemical composition, what's
11:23:52 inside.
11:23:54 And so for example if you have a hydrogen atom in a particular excited states that this one has an electronics first excited state, it's only going to be able to absorb very specific wavelength of light.
11:24:06 To change the energy state of that electron. So this particular example, the red light doesn't get absorbed with a hydrogen blue light doesn't either this particular should actually be a cyan kind of frequency.
11:24:18 To change this electron from the first excited state up to the third. So, for the aficionados that speech beta.
11:24:24 Okay and so that leads to a spectrum where the red light gets through the relic is through the blue that gets through but the green light gets absorbed.
11:24:31 So, what happens when you take a type one a supernova spectrum.
11:24:35 What does that tell us about the chemical composition.
11:24:37 So you get these kinds of signatures, so there's a bunch of different type of a supernova spectra.
11:24:43 And they all share a few Hallmark features. So one of these features it's very obvious is this silicon line absorption line around, roughly 6000 extremes, and it tells you that there is silicon in the, in the supernova.
11:24:59 You also see as broadly here is is calcium case there's calcium around this funny looking w thing is, sulfur double it so there's still for in the explosion.
11:25:07 And there's a bunch of these iron lines siren has a lot of transitions so it gives you a lot of lines.
11:25:13 Okay, so whatever is exploded, that's produced silicon and sulfur and calcium and iron and there's some oxygen around.
11:25:20 It's also these, these specs are also very interesting for what they don't show.
11:25:31 There's no hydrogen, there's also no helium. Okay. And these are very interesting because hydrogen and helium, as we all know makeup with the vast majority of the stuff that universe.
11:25:39 So, the 98% of the matter in the universe would be hydrogen or helium, and yet there's nothing in the spectrum.
11:25:45 Okay, so that's really important clue as to what has exploded. It can't just be a main sequence star, very obviously because those have a lot of hydrogen helium around.
11:25:54 So it has to be some involved star.
11:25:56 Okay, that has gotten rid of its hydrogen helium.
11:26:00 Now for these and other a lot of other reasons, we're pretty sure that the thing that is exploded was initially made of carbon oxygen is when you take carbon, oxygen, and you blow it up you want to undergo is went away thermal nuclear fusion produces
11:26:22 of silicon and sulfur and iron, nickel and calcium and the things that we see in this spectrum. And if you don't start with hydrogen helium, you don't get hydrogen helium in the spectrum.
11:26:28 For these and other reasons we're pretty sure that's what leads to one is supernova explosions of carbon oxygen and white dwarfs.
11:26:35 Right.
11:26:38 Very interesting.
11:26:47 That's great.
11:26:47 The previous three talks we heard about white dwarfs but we have not seen them explode. Right. And that's just because white dwarfs on their own. We expect to be very very stable.
11:26:50 Right. The sun is going to become a white dwarf, we do not expect it to explode it'll just be held up by electron degeneracy pressure. Oh cool off, it will eventually freeze it'll crystallized, and we'll just keep going off for the age of the universe.
11:27:05 Right, so the white doors on their own just don't explode would be almost all when I took my days to pivot researchers thing is that the waiter has to be in a binary system has to have some sort of companion that triggers an explosion.
11:27:20 There are a few different progenitors scenarios for these binaries that might lead to type on a supernova.
11:27:27 The one that I focus most of my energy on involves binaries where the other companion star is another white dwarf.
11:27:35 So there are other kinds of scenarios that people study and might be the progenitor.
11:27:41 But I have for various reasons to invest in most of my time and double white dwarf binaries.
11:27:48 around each other but not do anything. Okay. But there is a subset of double white dwarfs that are born close enough that when they will undergo an interaction.
11:28:06 And the reason this is, this happens is because they're spiraling around close enough that they that the orbit emits gravitational waves there.
11:28:17 They're bending the fabric of space time in such a way that their orbit releases gravitational waves, and these takeaway angular momentum and energy and cause the orbit to decay, until eventually the whiteboards get close enough to interact.
11:28:31 Now you sure heard of binary black holes and find it in the binder and neutron star being detected by Lego.
11:28:37 And so this is a very very announcing exactly the same process it's just two white dwarfs not two black holes or two neutron stars.
11:28:45 Because of the characteristics of this orbit, they're much further apart when they interact then binary black holes about her neutron stars are.
11:28:54 So as a result, they're not going to be a detective, and they hadn't been detected by like they won't be detected by Lego.
11:29:00 However, in hopefully the 2030s there will be a space based mission. That's akin to Lego called Lisa. So this is the Laser Interferometer space antenna.
11:29:11 Okay, Lisa. That will be launched that will function, much like Lego but on a vastly different scale. So Lego has arms or something like a few kilometers long.
11:29:27 Lisa will have these, these, these arms will be something like a few million kilometers long, so it'll grow probe a very different regime of gravitational waves.
11:29:33 That is suited to search for different things. And in particular, will be really really good at looking at finding double white dwarf systems.
11:29:39 So be able to see these decaying the white dwarfs as they get closer and closer together, and eventually interact.
11:29:48 So, what happens when double white dwarfs interact.
11:29:52 There are there are a few different things that can happen. But the one that I'm most interested in is what happened, the possibility that they will explode.
11:30:01 So this simulation will show is to white dwarfs that are undergoing an interaction, and eventually explode on the left panel will see density. So this is where the masses, and the right panel we will see temperature and the brighter points will get hotter
11:30:14 and hotter regions. And these are top down use of these two white dwarfs as Mike mentioned, white doors are backwards in the sense that the more massive one is smaller, or in a radio extent, so the smaller thing is the more massive weight or if it's larger
11:30:28 one is the less mass of white dwarf, and they're close enough together where the gravity of this more massive white dwarf is pulling material off of off of the lesson as the bookstore.
11:30:39 There it goes.
11:30:42 I'm sorry. You all your nice faces are in the way. Okay.
11:30:46 Sorry, you all your nice faces are in the way. Okay. Okay, good. So you see the less massive white dwarf is donating material onto the surface of the more massive like door.
11:30:53 And we're impacts the surface leads to a hotspot. Okay, it's just this material is converting its kinetic energy into thermal energy and so it gets hot there.
11:31:02 Keep going.
11:31:03 See the onset of an explosion.
11:31:08 So it's only happening the surface layers. Now, as Mike mentioned, in particular, these white doors are carbon oxygen. Through and Through in the core, the surfaces should have some helium.
11:31:19 So there's helium on the surface here. And there's helium on the surface of this donor, so it's donating helium that is interacting with this helium, and it leads to an explosion, what's known as a destination in the helium surface layers on top of this
11:31:32 white dwarf.
11:31:33 That will propagate around the surface, and as he gets on the surface, whoops I press the wrong button. That's too bad.
11:31:40 As it propagates around the surface, it sends a shockwave into the core that ignites the core.
11:31:48 So that happens there. Right. So there was a surface that nation, and then it triggered a carbon destination in the court. So these are.
11:31:57 I wish I could aim the mouse. These are known as double detonation scenarios, because of the surface detonation that triggers a core detonation.
11:32:06 Great. So this next simulation will be a zoom in of that process and you can see a little bit of what's happening. There's a cutaway through, through the white dwarf that's going to explode.
11:32:17 So this is the North Pole. This is the equator, is the South Pole. And this is the center of the white dwarf, just to make sure you can see my cursor right
11:32:29 now, nod anything. Yes. No.
11:32:35 Yes.
11:32:35 Okay, thank you.
11:32:37 I'm sorry the face so looking at with frozen and I was worried that the internet had put out and I've been talking to no one for 30 minutes.
11:32:44 So we'll see the, the shell ignition happened up here, and it's going to spread down to the equator and eventually the South Pole. And as it spreads it'll send a shockwave into the core.
11:32:55 The colors are the temperature so riders bluer star riders hotter.
11:33:00 And these white lines are ISO density contours so there are lines of constant density. Initially the white dwarf hysterical. So, all the lines are our circles circles.
11:33:09 but we'll see a shockwave that will change that.
11:33:14 Right, so here goes the helium shell detonation.
11:33:17 What's happening along the surface to the white dwarf spreading down from the north pole to the equator so right now it is covered the northern hemisphere.
11:33:26 You can see us going in and sending the shockwave into the core.
11:33:29 And that's changing its perturbing the ISO density contours, which you can see, as these changes to the circular aspect.
11:33:40 Eventually, the helium show that national reach the southern hemisphere.
11:33:45 Okay.
11:33:46 And it's certainly the helium saw that nation is finished, but the shockwave has not finished the shockwave from the northern hemisphere is only propagated to about here, and the southern hemisphere Shockwave is now coming up to meet it.
11:33:59 And as this shock wave converges on itself, it's putting a lot of energy into a smaller and smaller volume.
11:34:06 Until eventually its temperature intensity high enough to ignite that second detonation.
11:34:11 Right, so there it goes.
11:34:13 So that healing show that nation was putting all this energy into this little small volume, and that's what triggers the secondary carbon coordination.
11:34:22 So again, a double detonation scenario in a system with two white dwarfs.
11:34:28 This is a little bit convoluted I mean it's two detonation it's not just one, and you know you have to interesting geometry that's required. It's actually not that crazy of an idea, and it's something that has happened on Earth.
11:34:46 This is akin to how one of the parts of a hydrogen bomb works. I'm certainly no expert in that but there is some key aspect what a key, key stage where a bunch of energy is being focused into a small region to ignite fission fusion reaction.
11:34:53 A very obvious analogy is, if you know anything about nuclear weapons.
11:35:03 I were to me that's not the most interesting analogy on Earth. There's somewhat more strict analogy, but one that I think is so interesting that I always talk about it.
11:35:12 So this involves what's known as they snapping shrimp, there's only like a couple centimeters across it's it's pretty small shrimp.
11:35:18 But if you heard a right radio lab episode about snapping shrimp you'll know that they're actually one of the main sources of noise in the ocean.
11:35:25 And that's due to this giant claw. Okay.
11:35:28 There's one regular club but in this giant on this, on the shrimp.
11:35:32 Actually, you might think that that clause used for combat and it's, you know, powering this giant thing that will attack its prey and it's in its competitors with, but it's actually not the claws actually pretty small.
11:35:43 It's, it's over here in a silhouette. All this clause and change the muscle to make this part, close really fast.
11:35:53 And when it closes it has this really interesting shape, where there's this protuberance on one side and a hole on the other side. And when it closes, close it really fascinated squirts out a jet of water moving so fast that it hits its prey, and it's
11:36:06 done it.
11:36:08 But it's moving so fast that it actually cavities, so we'll see this in this movie.
11:36:14 Right there goes the jet, but the jet is moving so fast that turns into vapor right it, the pressure in the stream dropped below the vapor pressure of water, the water surrounding it, and it turns from liquid to gas, that's the process known as competition,
11:36:29 Which, you know ships are always trying to avoid because it's damaging to the propellers but this particular case, there is using it, using this jet to stun its prey.
11:36:39 It develops this paper bubble.
11:36:41 But because it's a bubble underwater.
11:36:43 The pressure of the water surrounding it collapses it. Right.
11:36:47 And it collapses it boom.
11:36:50 However, it's the water is doing all this work, and it's concentrating into very small volume.
11:36:55 And it's actually so much energy in such a small volume that it raises the temperature high enough to emit light. So this is a process known as Sonic bloom in essence.
11:37:04 It also generates a shockwave that is the source of the snap that that submarines and you know sonar hearing.
11:37:11 So it's a really, I think, interesting case where nature is figured out a way to turn water into vapor under, you know deep at the bottom of the ocean and concentrate so much energy into a small volume that it generates light from this, which I think
11:37:26 is just amazing.
11:37:27 Highly listened, I recommend listening to that radio lab episode if you can find it.
11:37:33 Alright, so back to Whitehorse this is, you know, sort of, analogous to what's happening in this white dwarf. This helium detonation is sending in a whole bunch of energy into a small volume, and it's triggering the secondary detonation.
11:37:49 Now we've done a lot of work recently, trying to figure out what this kind of explosion would look like. And indeed We think it looks like a typo on a supernova.
11:37:56 The more and more work we do on it, the closer you know the better, the better able to disable the better it is able to look like it's opened a supernova so the more work we do on it, the more convinced.
11:38:07 At least I am that this is the mechanism that leads to type any supernovae.
11:38:14 So that's one aspect of the research I've been working on.
11:38:19 Another aspect that I think is really interesting is what happens to this other star.
11:38:23 Okay, so in this particular simulation.
11:38:25 As you can see the star still here right this this donor stars still here when explosion happens, it's not anywhere near being blown up itself or being disrupted the explosion from this star is not is not a percent energetic enough to undermine the star,
11:38:41 the star could survive.
11:38:44 If it works is arrived, what would it look like, um, this would be like a smoking gun that this explosion happened because there's no other way to, you know, this will be a very unique star.
11:38:56 And it's unique because of its proximity to the supernova explosion. Right, so the supernova explosion converted all this carbon and oxygen into the things we saw inside the spectrum where you thought silicon and sulfur and calcium, iron, all that materials
11:39:09 and we spread across the surface of the star in a very unique way that will be very different from all other stars that we see right old, you know create this unique fingerprints, when we see all the silicon and sulfur and etc on the surface of the star.
11:39:21 No other stars like this. So this would be a very unique thing. If we could see if we could take a spectrum of such stars and be a very nice way to fingerprint them.
11:39:32 I like to use this analogy that surviving stars something like this cake pop right and it's the cake is the regular Victoria, and on top of it, you have the sprinkles is thermonuclear ash, that is very obvious way to identify them.
11:39:48 The question is, how do we know which stars to look at, you know, how do we know which stars take a spectrum of and look for this thermonuclear ash. It's not like we can at least yet, it's not like we can go into a look at every single star in the galaxy
11:40:01 and look for these. These fingerprints.
11:40:05 However, this scenario has another, another very nice feature, which is its speed.
11:40:11 Okay, so remember this was a double wiper system. this was in a relatively tight orbit, white dwarfs again or roughly the size of the Earth, but they have the mass of something like the sun.
11:40:22 So you can imagine that they're moving quite rapidly. something like thousands of kilometers a second.
11:40:29 As the orbit each other.
11:40:31 So when when the equator, the more massive start explosive type when a supernova. What happened to the other star, well the gravitational potential that was holding this binder together is no longer there.
11:40:41 Right. So when one star disappears, the other star will be flung out.
11:40:46 Very much like a slingshot okay so when David let's go with a slingshot this rock will be let loose at the speed, it was traveling act in a straight line.
11:40:55 And for the case of these, the white refineries that surviving white dwarf will be moving up to 2500 kilometers a second. Okay, so it's only 1% the speed of light, Pollstar has been accelerated to 1% speed of light, which is pretty remarkable.
11:41:10 You can get in Berkeley you know across the US and under two seconds, and get to the moon It's enough minutes. Very importantly on the cosmological scale you can actually the star will be ejected from the Milky Way.
11:41:21 So, these speeds are high enough where they are above the escape speed of galaxies in the case the Milky Way, it would leave the Milky Way's influence in something like a few million years, which is sort of long time but I want an eclectic are on the
11:41:39 scale scale it's actually pretty short. It's actually fast enough to reach our nearest larger neighbor and under a Giga year. So, just a few hundred million years.
11:41:46 He's hypervelocity stars could reach into the galaxy.
11:41:51 Alright so this is the way to look for them right they're moving much much faster than regular stars regular stars.
11:41:57 You know usually 10s of kilometers a second maybe up to 100 kilometers a second 2500 kilometers second is you know just unheard of. So if we could figure out a way to get the actual velocities of stars, provide this mechanism we provide a very unique
11:42:10 way, a very easy way to identify which stars to expect rather than look for those thermonuclear ash signatures.
11:42:17 So this is indeed what we're able to do.
11:42:22 A few years ago, thanks to the help of guy Oh, she has been mentioned before this unit satellite that gave us distances to stars and US was able to give us absolute velocities of stars.
11:42:29 And so it was a relatively easy exercise just find the fastest stars that we could using Gaia, and then take specter of them.
11:42:36 So, um, and whole bunch of colleagues were able to do this, we found three stars that were indeed moving really really fast, so they were the fastest by far in the guy data and the fastest stars that are unbound from the galaxy.
11:42:51 And then we expect them and indeed we found what we'd hope to see which was that they're covered in thermonuclear ash that very strong signatures of silicon and calcium and iron, magnesium and all the things we hope to see if they were right next to a
11:43:05 supernova explosion, and even better when actually pointed back to the remnant of a supernova supernova explode, their material hangs around for a while we can still see it.
11:43:16 And if you trace the position, interesting trajectory one of the stars back, back you pointed right to a supernova remnants. So that was really even more confirmation that the stars happened because of supernova.
11:43:29 So that was great. That definitely made us happy.
11:43:32 But we're still pursuing a few big questions. So one of them is to all type when a supernova happen this way.
11:43:40 I mentioned there are other progenitors scenarios that definitely could be taking place.
11:43:45 We know that, at least for these three stars they happen this particular way with double white dwarfs.
11:43:51 We'd like to know if all tech when it's gonna happen this way if we can say that this is the main or maybe the only progenitor scenario that we definitely supernovae.
11:44:01 And as we're doing this work we're modeling explosions and seeing what they would actually look like.
11:44:07 As we do this we can figure out if they're very very subtle things that are happening say the Laker was very subtly different or the spectra look a certain way.
11:44:17 Are there things that might happen as the populations as these galaxies are aging and cosmological time that change the way Tony supernovae look.
11:44:26 So, that's important because. To do this, cosmology to do these inferences of the makeup of the universe relies on knowing the properties of the supernova they're very far away, and very far away means at a young age, so it's a different population of
11:44:43 stars that are exploding than the ones in the present day.
11:44:47 Now to zero order. It's just a whiteboard. We think it's just a way to have exploding. But if there are very subtle things that are changing the Lakers that'll change subtly the cosmological inferences we have.
11:44:59 And so if we're trying to get you know the value of cosmological constant too many decimal points. These kinds of effects might be important.
11:45:09 And with that, I will stop because some time. But, yeah, this is, I think one of the very interesting applications of white dwarf astrophysics, and I'm happy to take questions.
11:45:22 Thanks.
11:45:24 Great. Thank you so much can.
11:45:29 All right, we have plenty of time for entering a discussion before the breakout sessions, know.
11:45:42 Okay, so there is a sense.
11:45:48 Yeah, I was wondering how the detonation scenario might be different if the donor star was not a white dwarf but a red giant or something like that.
11:45:59 Yeah, so this is a whole class of progenitor scenarios I did not discuss at all.
11:46:04 And it's actually the one that was sort of the standard for many, many years.
11:46:11 And it's probably still the standard in most textbooks.
11:46:13 And again, I'm sorry I didn't have any time to talk about it but that's like an entirely different explosion mechanism where the idea is to make the white dwarf and that system, a crease gain enough mass to grow up close to the change of sacred mass this
11:46:28 limit that has been mentioned this morning at that limits, which is roughly 1.4 solar masses. As you approach that limit the white dwarf is growing, smaller in size, so its density is getting higher and higher, and eventually the density gets high enough
11:46:45 that's carbon nuclei the center can just start interacting to start fusing right so as you approach the train your sacred mass, you ignites.
11:46:55 Not you, the white dwarf ignites carbon fusion and a center that eventually through a whole chain of events leads to an explosion. So leads to a flood ration, which is sub Sonic slower than the speed of sound, and that definitely ration is then then possibly
11:47:13 possibly transitions to a destination, a supersonic plane. So eventually you get to that destination. It's just a very different way of doing it.
11:47:28 Okay next we have Sean.
11:47:47 more likely to be white or white or air. And that's just to be clear, just be clear, that's my thoughts. Okay. There are definitely people that think it's not who refineries.
11:47:59 I would say that very few.
11:48:03 I don't want to put numbers on it but most people don't think it's a red giants anymore, because there are other issues with red giants having to do with what happens when the supernova.
11:48:13 When the exploding white dwarf interacts with the red giant on its way out.
11:48:18 That leads to visible things, so most people I think would say it's not red giants, but there are people that think it could still be main sequence stars or slightly evolved beings, you can stars.
11:48:29 So, is it possible that the white dwarves actually make contact with each other or is it forces are just too strong, they're going to be repaired.
11:48:38 Yeah, so there isn't.
11:48:40 Let's see. Let me say two things. One is that I'm going to simulations I was showing the, the more massive white dwarf is a desert order it's not really impacted at all it's not affected at all.
11:48:52 I mean obviously it's affected and materials coming down upon it, but the bulk of the material is still basically a sphere, the less massive white dwarf is being totally disrupted.
11:49:02 But it happens over many, many orbital periods. So it's, you know, massive being pulled off it first. In a relatively gradual way. And it's only when this goes on for a long time that eventually would get totally disrupted.
11:49:16 if the solution didn't happen first.
11:49:19 So, it's on its way to total disruption the explosion might happen before then. Okay, so that's one part. The other part is, yes there is a class of scenarios where they're actually, they don't interact title The before they collide.
11:49:34 So instead of being an Orbitz maybe you have a system where they actually end up colliding head on.
11:49:40 That's a different scenario, that's not the one I'm talking about but yes so that is also a progenitor scenario. There are lots of progenitor scenarios.
11:49:51 Great.
11:49:52 Cliff.
11:49:54 Okay, thank you for a wonderful talk I really appreciate it and enjoyed it. And my question is, I'm assuming we have this wonderful explosion.
11:50:03 What kind of force and or energy, are we releasing. And is there any potential and part of me being a little sci fi but any potential for using that energy to human benefit.
11:50:17 I can answer the second one first,
11:50:22 we would want to not any b2b anywhere near this thing. It's really just somebody generally that it's
11:50:39 an inconceivable human civilization and timescale I don't think we're ever going to get close enough to tap into the actual kinetic energy of this explosion. So releases of order tend to the 51 burns, which is tend to the 44 jewels are tend to and seven
11:50:49 to 730 Central, I forget exactly, but anyway it's a tremendous amount of energy.
11:50:54 Central, I forget exactly, but anyway it's a tremendous amount of energy. And if we were anywhere near its, I think we would definitely be in trouble.
11:51:07 Yeah, it's like you. Whatever you do when you collect energy you want to be in a position where you can regulate the amount of energy that you're, you're capturing this is likely not the case.
11:51:22 I'm immediately immediate next.
11:51:25 Oh, thank you Dr Shin of a possible scenario, then what would could something possibly happen between serious, and it's white dwarf companion and if so we're only 8.6 light years away from that.
11:51:42 Um, let's see.
11:51:43 So I don't remember the exact orbital parameters of that system, I don't know if it will form a double A CP system that's close enough to interact on a useful timescale.
11:51:56 So I can't answer the specifics.
11:51:59 If it were to eventually happen, it would happen again on, you know, a cosmological timescales because the main star in Syria, or the bright star and Sirius is still, I mean sequence star.
11:52:13 So, you know, it's not going to involve another.
11:52:18 Certainly to solar masses right so it'll take order a couple of Giga years before it does, you know, it starts to become a white dwarf.
11:52:28 But yeah I don't actually remember if what kind of system that system will become.
11:52:33 it will become a doctor system, because.
11:52:39 Seriously, is it a anyway the main sequence started serious is low enough mass to become a white dwarf so we'll be comfortable with your system I just don't remember if it will be close enough to to interact on a cosmological timescale.
11:52:51 And so, Jay.
11:52:54 Jay Jay suggested orbit is about 50 years, or period.
11:52:59 Yeah.
11:53:02 Yeah. Oh, let's see. So when this is embarrassing I'm sure someone else can help me out, um, when, when the main sequence to evolve as it expands. And so I'm pretty sure it will interact with his white dwarf, as it expands becomes a red giants.
11:53:19 I don't remember reading, natural evolution then because interesting things happen when the white dwarf will interact with that, expanding star, things like, what's known as the common envelope, where a lot of the expanding star gets ejected out of the
11:53:34 system and you end up with a much closer orbit. Then you started with. So I don't remember if that is what's going to happen or if it will end up merging the four serious a forms of white dwarf.
11:53:47 Yeah, maybe someone else can help me, help someone help.
11:53:52 Sorry.
11:53:55 Yeah, I can look that up also I'm sure a paper has been written about this and get back to you.
11:54:01 I mean we were talking earlier about we don't really know the fate of the earth and the earth son system because tides from the sun are going to be competing with orbital expansion.
11:54:10 And here it's a similar situation tides from the white dwarf will be interacting with the drag from the eventual red giant of serious a. And so anybody that tells you the future of that system is probably lying to you because it's hard to simulate.
11:54:28 So, it's unclear how close they'll get together eventually but
11:54:33 they will definitely get closer together.
11:54:35 But the question is, how much closer.
11:54:41 Meaning Does that answer your question or at least partially yes I'm sorry I put dr Shin on the spot is a boy what a point six light years be too close, would be dangerous.
11:54:56 Another good question. I, I think so. I think that's not great for our atmosphere.
11:55:03 Yeah.
11:55:05 I'm not positive, because, yeah. Definitely a gamma ray burst I think would be bad.
11:55:12 I'm not sure there's enough energy in the radiation of one a at that distance.
11:55:18 Another thing to look up and get that sorry again.
11:55:22 We're fallible we don't know everything that's for sure.
11:55:28 Yeah I know the distance of, which we were saved from a GOP 500, light years.
11:55:37 I guess if you can convert that if you know the angle Carnaval.
11:55:44 I would say that.
11:55:53 Probably it's a little too close for comfort Yes, I wouldn't want that very exciting to see, that's for sure it'd be very bright. Yeah.
11:55:56 Yeah.
11:55:59 Okay, the call.
11:56:06 Hello. I have two questions. One is about the in your model then are we are there different possibilities for the mass of the white dwarf white dwarfs that are exploding in which case, there would be possibly different brightness is if I understood what
11:56:22 you were saying, and then the second question is something I read about crystallization of uranium.
11:56:28 During cooling as a possible way for this.
11:56:46 Okay, well, these are very detailed questions.
11:56:51 So for the first question, yes, the answer is yes, we do expect different masses for the word door center go explosion in the other presenters scenario that had to do with the sacred mass that, you know, was a certain mass, a mass limit and so all the
11:57:06 networks are exploding and roughly the same mass, but in this particular scenario, as you definitely know data, there's no reason that the mass would matter.
11:57:13 Right.
11:57:14 I mean there are some reasons that the mass of matter but there should indeed the range of masses and so we expect something like roughly 90% of the mass of the sun up to something like 110% of the mass of the sun to explode and produce the range of luminosity
11:57:30 that we see in type one a supernovae.
11:57:33 As I said before, they're not standard candles are standardized. And that's because there is a pretty large range, something like a factor of 10 in luminosity is at peak for these supernova and so we think that's because of the different masses of the
11:57:49 The second question.
11:57:50 That's a very recent paper.
11:57:54 And so I think people like me are still digesting the answer, or the outcomes. The basic idea was that, for reasons and molecular dynamics that I don't fully understand its way outside my purview.
11:58:10 Uranium nuclei at the center of the white dwarf could start getting together and preferentially find each other. And for me, freedom crystals. So, like, what Mike was talking about crystallization you know this freezing of the whole carbon oxygen white
11:58:22 dwarf.
11:58:23 This could take place, or just the uranium part of it.
11:58:27 And they form these little crystals and eventually possibly form super critical masses uranium is radioactive it's fissionable. And so as it decays a release and neutrons.
11:58:37 Once you get enough of this uranium together, the neutrons can start causing a chain reaction right they find another uranium that causes it to release, it's actually several neutrons, and so they, you know, causes chain reaction and released a bunch
11:58:51 of energy, which then in this paper was suggested that could then ignite a little sort of spark that would ignite the white dwarf and cause it to explode.
11:59:05 The question of how much uranium is a tremendously small amount. So just throughout the universe there is uranium, that's been produced in other kinds of explosions, and so it just pollutes the universe, and it has a fairly long half life so there's still
11:59:21 a lot of it around, you know not all that is decayed, and so on the way to our forms as a star and it goes through all the stages of evolution eventually comes to like Dorf theory there again a very very trace amounts, but there is still uranium.
11:59:35 And so the idea was that this uranium could then find each other and for these little uranium crystals and then explode.
11:59:43 Yeah. Does that answer your question.
11:59:46 Yes, thank you.
11:59:49 Okay, Natasha.
11:59:52 Thank you, Ken super interesting. I'm just wondering what your next steps are like, what, what instrument Are you hoping to use what what are you looking for next to try and really make this, this idea,
12:00:09 more, more real.
12:00:14 I think the idea is real as it is nice.
12:00:17 So there are a few different things that meet up my colleagues and I are looking at. One is through a theoretical.
12:00:25 As I mentioned, looking at the explosion models and seeing what they look like and seeing all the various details and seeing if they look like 20 supernovae, but I think what you're referring to is finding more of these hypervelocity stars.
12:00:37 So we did our best I think that we can do with Gaia Gaia was amazing. And so so revolutionary in many fields. But one thing that would have been nice.
12:00:50 In some fantastical world where we didn't have to care about trade offs is, if it could have gone deeper in the sense that it could have been fainter stars.
12:01:10 So, you know, the stars we discovered her sort of near the limit where Gaia can see they're almost faint enough that guy wouldn't have detected them. And I would have liked to see more than three because if indeed type when a supernova all come from this
12:01:18 mechanism and they always leave a survivor, that we should have seen many more, not just three but something like 100 or a couple hundred.
12:01:23 But I'm thinking, or I'm hoping is that the other stars that you think to see, we found the three greatest ones but the rest are to fantasy with Gaia.
12:01:31 And so I've been trying to think of ways to look for these hypervelocity stars using other instruments that go much faster, but one of the problems and you want to know guy was amazing because it gave you absolute distances to stars and without the distances.
12:01:46 That gives you an empty velocity. If you don't have that all you can say is that the stars moving fast across the sky, but I don't know how far away is it, it is and so I don't know in an absolute sense how fast it's moving.
12:01:58 So then you have to think of other ways to get at the distances to the stars, which are more difficult but I think will be necessary. If we want to find more than just these three.
12:02:09 So that's the main thing is using optical telescopes on the ground and trying to figure out how to get distances to the stars that way
12:02:23 onto that, you know, you don't have to explain fully but so we could technically then see stars that were rejected from Andromeda traveling through our galaxy.
12:02:34 Yeah.
12:02:36 Yeah. Possibly. So, you know, I gave Andromeda as an example just because I think it's interesting that you could actually send stars to the galaxies.
12:02:48 For us, looking at the drama and drama looking at us, the amount of the sky that's the galaxy covers is quite small. So, you know, the stars are going off all over the place that the chance that one of them will be pointed right at us from Andromeda is
12:03:03 actually pretty small. That said, there is evidence for at least one or two stars that we think.
12:03:18 But there is evidence for stars coming from another intact galaxy do to hypervelocity injection. So it is definitely possible.
12:03:35 It's great.
12:03:38 Okay.
12:03:40 Sean, last question and then we'll move to the breakout rooms. Yeah, I was just gonna say would be really awesome if Lego was able to detect these mergers and I imagine that, then looking forward to that that would be a really great confirmation of what
12:03:54 you're saying is that, you know, you could you could get the gravitational waves estimate the distance that way. And then also show with your models that you know that the the type one a supernova is not necessarily that at one point for solar mass phenomena
12:04:09 that would be really quite remarkable I'm not I just wanted to make a comment I just, I'm excited for you I think the future is bright.
12:04:17 Yeah, I think so too. So to be clear, Lego won't be able to check these, it'll have to be the space space one Lisa. And even though Lisa will be the text, a whole bunch of Deloitte or binaries.
12:04:30 They're all inside the galaxy, just because at the separations the amount of gravitational wave of mission is actually relatively small compared to the things that like I was able to see, so as a result we don't, we won't be able to see these and other
12:04:42 galaxies, or at least not far away galaxies. And so, since we're confined to our own galaxy the chance that one day will happen, is actually relatively small and a human timescale, maybe every couple hundred years.
12:04:56 So there is a chance that one goes off, and in the time that Lisa is up.
12:05:02 You know actually functioning in the sky but it would be amazing. I agree with that. I think the chances are pretty slim though.
12:05:12 Alright, thanks again can.
12:05:14 And thanks again to all the speakers.