 The astronomy on tap, if you participated in our very beautiful supernova trivia, please bring your trivia sheets up to our trivia czar here, holding his hand up and waving. We like to recycle and reuse them. We try to keep it green here at astronomy on tap. Oh, to the gentleman with the fancy new haircut. Most of our trivia goers have brought those up. I'd like to introduce our first speaker of the night. She is a research scientist at the University of Washington in the astronomy department. Please welcome Dr. Melissa Graham. Here back to astronomy on tap to give another top. Today, I want to tell you all about messy siblings in the universe. Supernovae that happened in binary systems. First, I want to start off by showing you exactly what it looks like when we discover a supernova. This is an image of M82, the Sakura galaxy, which is fairly close to the Milky Way. It's an image on the left taken on January 4th, 2014. And then an image on the left taken on January 22nd, 2014, which just so happens to be my birthday. This is my birthday gift from the universe, the supernova. And you can see the supernova up there in the corner with the little white lines pointing to it. And it's just a spot of light on an otherwise sort of diffused background of starlight and dust and gas from the M82 galaxy. This is what the images look like. So you'll notice that in this image of M82, we can't see any individual stars of the galaxy. So we don't know which star exactly exploded to make this particular supernova. And that's the case with most of the supernovae that we discover in the universe. But when we can see a resolved stellar population, this is what it looks like. There's many different types of stars, blue stars and red stars, young and old, hot and cooler stars. And so the question that my research focuses on is which kind of stars make which kind of supernovae. So today I'm going to tell you a little bit about the different kinds of supernovae, the characteristics we can measure for them, and then tell you how we figure out what kind of stars become those kinds of supernovae when we can almost never see it directly. It's a gift of a supernova exploding in a galaxy, which again is an unresolved stellar population. You see the light from that supernova rise and fall over time. So this is a time lapse of about two months that show you the light from the supernova getting brighter and then fading again. When we take this kind of data, usually we make something called a light curve out of it. So this is just a plot of the brightness of the function of time. In this case, it's about a six month time span. And if we do this for many supernovae, we can put them in different categories and then plot the different types of light curves that we see. So you can see the black line gets very bright, but then it declines rather rapidly compared to, for example, the heavy blue line that sort of gets not as bright, but it stays bright for a really long time. So these are supernova light curves. And we can tell by collecting many of them that supernovae come in different types. They're brightness varies in different ways. The other thing that we can measure for a supernova is its spectrum. So we use spectroscopy to reveal absorption lines which correspond to certain elements. This is how that works. Over here, there's a spectrum distance of sun. But these dark bands that occur across the spectrum are caused by absorption of very particular elements that are between the sun and us, mostly in the solar atmosphere. So here, these lines are caused by calcium and then iron. This one over here is sodium and then you have hydrogen and oxygen. We can take spectra in the same way of supernovae and figure out what kind of elements there are in the star that's exploding. When we do this, I mean spectra, the rainbows are very pretty, but we don't usually work with spectra like that. We make a plot of the intensity as a function of the wavelength or the color of the light. And look for these dips that tell us that there are certain elements that are present. So when we do do this for supernovae, this is what it looks like. So here are four different types of supernova spectra. And each of them have these dips in their brightness that tell you about the different kinds of elements that are present in the star that's exploding. So sulfur, silicon, iron, helium and hydrogen are all typically seen, some more so in some types like this one has lots of helium, this one has none. So these light curbs in the spectra are two ways that we can categorize different types of supernovae in these. The third thing that we can measure about supernovae and that's looking at their different types of host galaxies. So on the left you have an elliptical galaxy that's mostly older stars, older, cooler stars that have evolved for a long time. And on the right you have a beautiful spiral galaxy that has lots of blue stars. These are hotter, younger stars. So we can take a look at many different kinds of supernovae, look at the kind of host galaxies that they explode in, and then infer what kind of stars it must be that's doing the exploding. We put all this information together. We find that the types of supernovae with light curves that are fainter but fade more slippery. The kinds of supernovae that show iron, helium and hydrogen in their spectrum. And the kinds of supernovae that are found in these beautiful spiral galaxies that have lots of young stars are the explosions of high-mass stars. These are stars that start off as 8 to 25 times the solar mass. What's happening here? Why would a massive star even explode in the first place? For this we need a little bit of stellar revolution. So this is a picture, a graphic of a massive star. And a star that's like more massive than our sun will burn hydrogen to helium in the regions inside the star where it's hot enough to do so. The regions inside the helium where it's hot enough to burn the helium into carbon will make that burning process. Like that where it's hot enough to burn the carbon into neon and we do that process and so on. So you have this onion layer of burned elements inside the star which ends that iron in the center there. So once you can burn all the way to iron in the core of your star, that's kind of it. Iron doesn't burn. It just sits there accumulating until eventually the star has such a large iron core that it's not doing anything more in its center and the center will eventually collapse in on itself. The outer layers explode and that makes a very typical type of supernova. This is a very natural endpoint for massive stars, very natural stellar death for these massive stars. On the other hand, there were those other kinds of supernovae that I was telling you about that have a light curve like the black line that they get very bright but they fade much more quickly. Their spectra show iron, sulfur and silicon and do not show any hydrogen and helium and they are found in older stellar populations like the soliptical galaxy. These on the other hand are the explosions of carbon oxygen white dwarf stars which in that's a graphic of a carbon oxygen white dwarf star that I made myself. So what are these carbon oxygen white dwarf stars? That sounds like an unreal thing. So what happens in this case is it's a star that wasn't mass enough to fuse anything else inside the carbon layer. So it wasn't massive enough, it's interior didn't get hot enough or dense enough to burn that carbon into anything else. So it creates this carbon oxygen interior and stars that are about two days in the nebula phase where the carbon oxygen white dwarf core star just sort of hangs out there and starts to cool. It loses its outer layers of hydrogen and helium which is why we don't see any when that star explodes and just sort of ends its life as this new kind of star. Carbon oxygen white dwarf stars are very compact, very dense about the size of the earth but they can be up to 1.4 times the solar mass of the sun. And the thing is that this is, so long as they're under that mass limit, very stable. So this kind of star will just hang out, chill, live its life, not bother anyone and would not under normal circumstances explode. So when we do see these kinds of supernovae that are clearly the explosions of carbon oxygen white dwarf stars we have to wonder why? What happened to this poor thing that was happily living its life that made it explode? So we look to its closer environments and see what might be nearby. And in this case we're talking about siblings or a binary companion star that's in the same system as the exploding white dwarf. In this case there's kind of two scenarios for the different kind of siblings that this white dwarf star could have. The first one is that it's another white dwarf and the two spiraling word over time and eventually merge and explode. The other scenario is that the companion is a more regular star, a hydrogen or helium rich star like our sun or like a more massive star. And in this case the companion star can feed material onto this carbon-oxygen white dwarf star, might make it go over 1.4 solar masses, become unstable and then explode. So these are two scenarios for these kinds of supernovae. And a lot of my time is spent trying to figure out which of them happened and if both happened then how frequent the two scenarios are. And so generally we think this scenario where it's another carbon-oxygen white dwarf star is pretty common but this scenario where it's a more of a regular hydrogen rich star does occur sometimes. It's just kind of rare. And in this case we need some sort of extra evidence to prove that this particular supernova had this companion star. So this sibling over here that's sort of force feeding its older brother or sister is very messy. It's kind of like a celestial pigpen star that leaves a lot of material lying around. Maybe you have siblings and you know exactly what this feels like. I have two brothers and they both played hockey and there was always gear all over and it was very stinky. But it's lucky for me as an astronomer because these telltale signatures of a pink pen star are something I can now go and look for. So what am I going to look for? The situation is kind of like this up in this graphic here where you have a supernova that explodes and then eventually rams into this extra material that was left by the companion star. And this kind of thing we do see happens sometimes especially if that material is very close so that interaction happens almost right away. So when we're observing a supernova watching it get brighter and fainter we suddenly see signatures of hydrogen in the spectrum which shouldn't be there. And we see the supernova also have extra emission, extra luminosity from this interaction. The thing is that we see this very rarely, maybe one in five hundred to one in one thousand of this kind of supernova exhibit this. But we only really watch supernovae for about two months as they rise and fall. And if this pigpen leftover material was just a little bit further away and it got impacted sort of later after we stopped looking we would never see it. So I wanted to really try to figure out how often this scenario happens by waiting and looking at and watching supernovae say two to three years after they exploded to see if we could find the signatures of this extra material. To do this I used the Hubble Space Telescope and observed 65 carbon atom white dwarf star explosions about two to three years after their initial explosion. So I went in, do a little sort of check on them later to see if any of them got bright later on that would suggest that material was being impacted in the vicinity. Out of these 65 I very luckily found one. This is probably the least beautiful HST image you will ever see. But it's very dear to me. It's just one dot which is an ultraviolet source right at the location where the supernova was but 686 days later. So as soon as we saw this we called our friends who had time in the European very large telescope to try and confirm that there was hydrogen present in the spectrum. So the optical spectrum associated with this source looked like this and this is the hydrogen line that we now see in a mission that shows us a ha. There is pigmen material around this particular star so we know that it did not have its sibling was not another carbon oxygen white dwarf but it was a star that had hydrogen or helium in it. Altogether my whole survey do a statistical analysis on all of our 64 other non-detections. We can say that up to 5% of carbon oxygen white dwarf supernovae are caused by such messy siblings in the universe. And that was my main conclusion. If you want to find out... Oh thank you. Nobody whoos at science conferences. That's why I come here. If you would like to find out more you can just search for messy supernovae at University of Washington and you'll find these great articles that James Upton and Alan Boyle wrote There's two additional thoughts that I want to leave you with tonight. The first is as you have probably already figured out if you have siblings or roommates even that a massive twins can be messy too and so can massive only stars. And so here's a couple of examples of other messy things in the universe. The first one on the left is these are both very very massive stars. That's pretty much what Wolf-Ray-A means. It's a massive messy star. The one on the left is fortunately named Nasty One. Just because the acronym for the catalogue that it's in is NAST for reasons I don't know why. But it's a nasty situation, a nasty star. And the one over on the right is another kind of star. And this is all hydrogen that you're seeing coming off of this Wolf-Ray-A star and being blown around. And so these are both messy stars out there in the universe. In this one, in this case, it's two pig pens living together. And this one, it's a pig pen living on its own. And you can find out more information also about it. I think you just Google nasty supernova. This is what you get. So you can go find out more about that if you'd like. The second thought I want to leave you with is about the future. So this animated gift that's playing in the middle here shows you the sky location of supernovae that we've discovered since 1885. And it's about, average is about 100 supernova per year that we discover over time. Currently with this wiki transient facility, we're discovering about 500 supernovae per year. And I think Eric is going to tell you more about this wiki transient facility in the next talk. But it's not enough. I want more. And so I work for the Large Synoptic Survey Telescope, which is currently in construction in Chile. And it's going to survey the entire southern sky and find supernovae pretty much everywhere. That'll be 10 million supernovae in 10 years. So this marks a massive increase in our capability to both find and characterize supernovae. And so those 1 in 1,000, 1 in 500 events of these rare pig pen supernovae, I'll have a lot more than one to deal with and look at in the future. So that's what I've been up to. It's what I wanted to tell you about. Thanks for being here and laughing at my jokes. I really appreciate it. That's our question? Yes. Okay. Go over here. Okay, so a question about whether you could have two carbon-oxidant white dwarf stars that merge, which we think happens all the time. But then that supernovae inject interacts with some other material. That can absolutely happen. And the most dangerous thing sometimes with my studies like this is it just impacts interstellar material that's just there that wasn't actually related to the system in the first place. So I have to be kind of careful when I draw conclusions about where that material is. So yeah, it can happen. I think there was one here and then here. It's kind of a related question. How do you determine that the hydrogen from the sibling adopt from it? How do I know that the hydrogen was from a sibling star and not from just the interstellar medium that's out there? So in this case, there was just way too much. So you can do some estimates on how much material has to be there in order to make the luminosity that you see. And ISM densities are very low. So in this case, it was easy for me to say that this was definitely a messy sibling. But other cases are not so easy to do that. Why are there gaps on the sky where we can find supernovae? Is it because we're not searching there? Is it for another reason? Would you like to guess why first? Yeah, we don't usually look for supernovae there, but there's a reason why. There's something big in our sky that kind of blocks the milky way. So this inside of it shows you a nice map of where the milky way is on the sky. It's really hard to look through the milky way. So we don't find supernovae where the milky way is. Trevor and Nicole, should I do more questions? I could do one more question. So why would two stars become white dwarfs at the same time? This stellar evolution is mostly controlled by the stellar mass. So if you have two stars that form in a binary, there are the similar stellar mass to start with. They'll have similar evolutionary sequences, and so they'll sort of end up in the same end state at the same time. So it's pretty natural. Thanks again. Welcome back for our second talk of the evening. Please welcome a professor from the University of Washington Astronomy Department, Dr. Eric Bellum. How's everybody doing tonight? Alright, so I want to tell you how we used a very old telescope to do cutting-edge science. So we're going to start with a little bit of history, and then we'll talk about some technology, and then finally finish with some science. So I want to start with this guy, George Ellery Hale. He's an astronomer who was active around the turn of the last century and built the largest telescope in the world four different times, which I don't think will ever happen again. The first telescope he built was this one, the 40-inch refractor at Yerkes Observatory, named after the Chicago businessmen who paid for it. You can see some distinguished figures here, sort of a fuzzy-hair gentleman, for instance. The problem with this telescope is that it was located in Wisconsin, not usually the best place for an astronomical observatory. So after a few years, George Ellery Hale decided to head for Sonnier Climates on the west coast, and he moved to Pasadena, where he established the Mount Wilson Observatory up above the hills of Los Angeles. And there he built two giant telescopes, first the 60-inch, and then the 100-inch Hooker Telescope, named after the unfortunately named Los Angeles businessman who paid for it. So these increasingly large telescopes allowed Hale and the scientists who work with them to look farther and deeper into the past, look deeper into the night sky and further back in time and make groundbreaking discoveries like the expansion of the universe by Edwin Hubble. Unfortunately, even Mount Wilson was not perfect while it has really great seeing above the inversion layer of Los Angeles. Even back in the 1910s and 20s, increasing settlement meant there was more and more light pollution. So George Ellery Hale started thinking about a yet bigger telescope that would look even farther into the past, even deeper in the night sky. And so he looked south to Palomar Mountain outside of San Diego and established a new observatory there, the Palomar Observatory, which is the major telescope there is the 200-inch telescope, the big eye, the perfect machine. It was funded by the Rockefeller Foundation. Anybody want to guess the name of this telescope? Actually, it's the Hale Telescope. George Ellery Hale got the name for it. All right, so this is exactly the perfect machine. It's the biggest telescope in the world for more than 50 years. It helps bring Caltech to international prominence and astronomy. This is a really fun book describing all of this if you're curious. Here's another piece of old technology. Those of you who are my age or maybe older will remember before we all had GPS-enabled pocket supercomputers. If you wanted to figure out where you're going, you needed a match, the 48-inch telescope. This is a very different style of telescope. It has a very wide field of view. This is an old pencil drawing of this telescope, and this is the old telescope I'm going to tell you more about today that we are making new tricks. The light comes in, you can see through this corrector lens at the top. It bounces off the primary mirror and is recorded on a photographic plate that's in the middle of the telescope tube. And this gentleman in this era, in this picture, is sitting there staring through the guide or scope for an hour or more trying to keep the telescope on target while he's exposing this photographic plate. This is Jean Mueller, who was one of the observers for there's two sky surveys that the 48-inch did, one back in the 1950s and another in the 1980s and she's showing here some of the plates on a light box. This is the cartridge that the photographic plates went in and this is the plate-bending machine that made them sort of slightly curved so they would be in focus. And so she did all the observing back in the 1980s. So these sky surveys took a couple exposures of every spot in the northern hemisphere sky. It took several years to do that. And then for half a century, every place that did astronomy, every department, every observatory had paper copies of these photographic plates so that you could figure out where you were looking. Just for context, here's what the imaging area that the 200-inch sees. You can see where you need this big map so you can figure out where you're going. So again, it takes a couple years to cover the whole sky. That's photographic plates a couple times. But if you look at just a smaller area, you can do that a bunch of times and find things that are changing. And so scientists did this from the beginning. This gentleman is Fritz Zwicky, Caltech professor, kind of a jerk, I'm forced to admit. He likes to call his colleagues spherical bastards because they're bastards, whichever way you look at them. One of the things he's famous for is discovering the difference between novi and supernovae. And Melissa told you about supernovae. Novi are similar. They're explosions on white dwarfs instead of explosions of white dwarfs. So if you put these on a plot where the axis here is how long we can see the transient and this is how bright it is. You see there's a big space between these explosions on the surface of the white dwarf and the supernovae up here. And Melissa told you about the two kinds of supernovae, the core collapse that are exploding massive stars and the thermonuclear 1A supernova that either are two merging white dwarfs or a white dwarf with a big pin signalling sibling. And we still don't know totally again the breakdown of those two. But Zwicky was the one who discovered this gap. So other things that people use the 48 inch 4 through the years discovering asteroids. They took a multiple image of the same field separated by a few minutes and you can see these dots are moving objects. So they mapped asteroids through the solar system. Mike Brown used the 48 inch photographic plates to find dwarf planets in the outer solar system and killed Pluto. And then in the last since 2000 or so there's been a move from photographic plates to CCD cameras which are more sensitive and also to robotic operation moving away from having a human sitting at the telescope and plugging plates in and out all night. So this is an example survey that ran a few years ago called the Palomar Transit Factory where we got a second hand camera from some other telescope that they didn't want anymore and slapped it into the tube and used that to observe the sky. Pretty good we found the youngest supernova ever discovered at that time in 2011. And we found a bunch of weird stuff that fell in the gap between those Novi and Supernova that we didn't know about before. There's none on the plot here but Kilanova fit in the middle too. But the question is, is there something left? Are there things we don't know about yet? We need to survey faster and wider to find those things. So that leads us to the new tricks. The new idea we call this the Zwicky Transient Facility based around a new camera. I was the project scientist starting in 2011. I helped figure out what we would build and why. So again we have this PTF hand camera. A pretty good field of view. The moon would fit nicely here in this dead chip. Again it was a used camera. Got it out of eBay. But it was only using a little bit of that wide field we have on the 48 inch. Here's those photographic plates again. Look at all that empty space we're leaving. So the idea is fill it in with CCDs. So we did. 47 square degrees. It's not if you hold up a posted note and hold it at arm's length. That's about how much we can see in the sky at once. So you put it on the sky and compare it to some other big cameras and you can see that we're picking up a lot more sky at once. And so we can survey quickly, survey repeatedly, find things that are changing and things that are rare. Let me talk about the technology. It's only now that it's affordable to do this with CCDs. It takes a lot of CCDs. 16 of these dudes. Each one is about 4 inches on a side that's a lot bigger than the little chip that's behind the cell phone camera. And it's got to go inside the telescope. So we need this camera to be small. It's under vacuum. It's cool. The cryogenic temperatures. So we did a bunch of funny things that I'll describe to you and show you. So the camera, of course, it's very compact for how big it is. Pretty cool looking. Here it is in the lab. We have the world's largest astronomical shutter. It's at the top of the telescope tube. It's as big as a ping-pong and opens and closes in less than a second. We needed new optics. There's a big lens at the top of the telescope tube. So we ordered it from a vendor and they dropped it on the ground. Thankfully, we'd ordered a spare. So we put the camera in the tube. We got some big filters. Those are 100 grand a piece. Oh, and we needed a way to change the filters and we needed to stay out of the way of the camera. So we got a commercial robotic arm. Oops. All right, good. Got a commercial robotic arm. And so it goes and it will pick up the filter off the front of the camera and do some thinking to make sure it doesn't drop it. And then it's going to come and put it in this little slot here where other friends are waiting. So it goes and stows and there's a complicated system and mechanical and electromagnetic latches that make sure we don't drop this thing. So the primary mirror is the primary mirror and underneath us is the primary mirror which is even more expensive. So we got to be careful. But it hasn't broken yet. So here's first light. An image of the Orion Nebula and the Orion's belt. If you have seen Orion, you know it's a pretty big constellation. This is a big chunk of sky we're looking at all at once. So we started surveying in about March of last year and because of the sky that's visible in a given night, of course there's weather in downtime, you can see the seasons changing. The point is that for every point in the northern sky we're building up tens or hundreds or even thousands of images just in the last year and a half. That's letting us look for things that are rare, things that are changing quickly, things that are unusual. Let me give you a few examples. This is a funny looking light curve plot. It's folded at a period of the object which is only seven minutes long. You can see some big dips here. These are the two objects eclipsing each other. This big hump is then sort of shining on, the hotter one shining on the cooler one. These are two white dwarfs in a very tight orbit. There is a seven-minute orbit that's smaller than the radius of Saturn. These are spinning around each other very close. It probably will not merge in that sort of double degenerate scenario just because of the big mass gap that's going to evolve differently. They're very similar to that sort of double degenerate idea that Melissa was showing. Here's another cool thing. We've been observing this with PTF and ZTF for a while now. We can see the period changing. The dots are measurements of the period and the curve line is what's predicted by general relativity. We can see these decaying due to gravitational wave radiation as they orbit so close. Melissa talked about supernovae and how we're trying to understand what's happening around. It turns out discovering them young is one of the best ways to do that. These are some light curves. The more than 100 young type 1A supernova that ZTF has discovered all with early time colors and great temporal coverage early in the light curve. Finally here's a solar system object discovered in a twilight survey in four images you can see. The weird one because it turned out to be the one in the shortest year ever discovered. It orbits entirely within almost entirely within the orbit of Venus. That's the second of this rare family of asteroids that ZTF has discovered just in the last year. There's some technology we do too. We send out all of our events that we discover through Kafka. We send them out from UW to a bunch of partners and consumers around the world to allow other scientists to follow up in near real time. And we're hiring, so if you're experienced and you're interested in streaming platforms come talk to me. And all of this as Melissa said is helping us get ready for a big new survey large synoptic survey telescope which we expect to be taking data in just a couple of years. I think it's super cool we've got this more than 70 year old telescope that we're doing cutting edge science with thanks to the advances of technology. Thanks very much, I'm happy to take some questions. We ever found anomalies that we thought were astrophysical but we thought would be terrestrial. Yes we find stuff all the time that we think is and we discover it's some kind of glint inside the telescope. Yes there's all kinds of there's all kinds of junk in the images and when you look at them by the billions it's easy to find all of the artifacts. Yes. I mentioned the photos were a hundred grand at least how much was the camera itself and is there anything new technology in the camera that wasn't there? Yeah how much was the camera itself and is there any new technology in the camera? The camera is actually pretty I mean it's cutting edge but there's nothing really groundbreaking in terms of the technology it's standard CCBs standard Prius style mechanics but very well executed I think the whole project was about 20 grand sorry 20 million dollars 20 million dollars but that includes also data processing that includes the telescopes quite a bit of other stuff not just the camera. Alright thanks very much. Thank you tonight. We will see you again next month on September 25th but remember because the sun will be setting earlier and earlier we will see you at 7pm next month. Have a great September.