Emily Levesque Public Lecture: The Weirdest Stars in the Universe

[Music] [Applause] welcome welcome welcome to Perimeter Institute and welcome to perimeter Institute's public lecture series for those of you that don't know perimeter is located in Waterloo Ontario Canada my name is Greg dick I'm the director of educational outreach and it is a pleasure to welcome everyone here this evening both those of you here in the live studio audience and those of you watching online the lecture itself will last approximately one hour and will be followed by a question-and-answer session for those of you that are watching online dr. Kelly Foyle and a team of P I research errs are behind their keyboard ready to engage in in conversation and answer questions throughout the lecture and if you want to ask a question both during the lecture that way or ask a question to our guest speaker use hashtag P I live and if you have a question for the guest speaker get it in early so it has time to get all the way to my phone all right and now it's time to introduce tonight's very special guest speaker dr. Emily Levesque dr. Levesque is an assistant professor of astronomy at the University of Washington in Seattle she received her Bachelor degree in physics from MIT and completed her PhD in astronomy at the University of Hawaii and was both an Einstein and and Hubble postdoc postdoctoral fellow at the University of Colorado Emily is a rising star in astronomy research her accolades include a 2017 Alfred P Sloan fellowship and and a 2014 and jump cannon research prize from the American Astronomical Society dr. lebackes research focus is on massive stellar astrophysics and the use of massive stars as cosmological tools tonight she will discuss some of the strangest stellar phenomena in our universe and how these weird stars serve as a common thread for exploring our universes history evolution and extremes ladies and gentlemen please welcome dr. Emily Levesque well hello and welcome to tonight's lecture I'm extremely excited to be here and so happy to be sharing these very weird Stars with all of you I always like to start by putting up some pictures of some of the weirdest stars in the universe so every object that you see on the screen right now represents some sort of bizarre or unexplained or particularly puzzling type of star something that has surprised or confused at times astronomers as I go through the talk and I look at things that are particularly weird or surprising I'll be marking them with these little exclamation points I can also promise you that by the time we get to the end of this talk you'll be able to name every single thing on this screen you'll be able to explain what it is at least as well as astronomers can explain them and you'll recognize all of them if you ever happen to come across them again so to start off talking about weird stars we need to establish what is considered normal for an object like a star and to do that I actually need to start with a diagram so this is a very common diagram used in astronomy it's called the hertzsprung-russell diagram what we're doing here is plotting temperature on the x axis going from very hot on the left to very cold on the right and plotting brightness on the y axis going from dim at the bottom to very bright at the top what we can do with this is drop the collection of normal stars that we know about onto the diagram and see where they land you can kind of see that there are clear spots where normal stars tend to hang out I'll fill this in with a slightly more detailed version of the illustration and you may recognize the names of some of the stars on the plot I always like to point out where our son is so our son is right in the thick of things and our son is really a kind of depressingly normal and unremarkable type of star so the main thing that we use this diagram for in astronomy is explaining how stars evolve and this is something a lot of people don't necessarily realize stars do they're born the age and evolved with time and change and then eventually they die and you can plot out how a star is going to live and die by following its path on the hertzsprung-russell diagram over the course of its life you can see the Sun you can see that sort of diagonal of very normal-looking stars the stars that I'm interested in and the weird stars that we'll be focusing on tonight are at the very top of this diagram so these are the super Giants these are massive stars they're stars that are at least eight times the mass of our Sun or more and I want to start by taking a short tour through these stars on the hertzsprung-russell diagram and looking at how they evolve I like to use examples of stars that you can find in your own night sky so to begin with I want to look at Spica Spica is a star in the constellation Virgo it's an amazing example of a blue supergiant so this is a massive star in the first phase of its life it's fusing hydrogen into helium in its core it's very hot it's about 22 thousand degrees Celsius that's about that's much hotter than our Sun our Sun is 5,500 degrees Celsius it's about seven times the mass of our Sun and it's about ten times the mass of our Sun in about seven times the size a star like Spica will stay in this part of the HR diagram for maybe ten million years fusing hydrogen into helium eventually the star will run out of hydrogen and it needs to try fusing something else so it switches from fusing hydrogen to helium when that happens the stars actually go streaking across the top of this diagram from left to right very quickly after 10 million years fusing hydrogen they cross from the hot to the cool side of the plot in about a hundred thousand years along the way though they make a brief pitstop when we would consider them yellow supergiant's and we actually have an amazing example of yellow CLO supergiant that we all know really well our North Star Polaris is a yellow supergiant this is actually pretty surprising because stars like this are rare since their lifetimes are so short so it's pretty cool that our North Star is this relatively rare type of massive star once these stars have completed their trip across the diagram they wind up as something like this this is fatal juice it's in the constellation Orion a constellation that I'm sure many of you are familiar with it's very easy to find in the night sky if you look for those three stars that make up his belt and you can see baitul juice as his left shoulder it's a very bright star that is very obviously red fatal juice is an excellent example of a red supergiant which are one of my research specialties and a particularly fascinating type of massive star what's interesting about a star like baitul juice is that as it has cooled off and moved across the hertzsprung-russell diagram it's also button enormous Li big this star was born with maybe 15 or 20 times as much mass as the Sun but it's 900 times the sun's size so I want to try and put that into context this is the orbit of the earth that one dot in the center it shows up as a couple pixels on the on the projector is our Sun if we back up a little bit we lose sight of the Sun but you can see the size of Earth's orbit relative to things like Jupiter's orbit and Saturn's orbit if we were to put baitul juice where our Sun is it would stretch out to well past the orbit of Mars it would begin approaching the size of Jupiter's orbit so this is incredibly big and in its own right makes the star a bit weird there's a couple funny consequences of a star being this big and this cool and I want to again try and compare it to the Sun so this is an image of our Sun and if you were to zoom in on it very close you would see things like this happening on the surface of the Sun these are called granules what we're seeing are the very tips of a convective layer in the top near the surface of the Sun what we're seeing is gas that starts out hot rises to near the surface of the Sun cools off and then follows back it's not unlike watching bubbles boil in a pot of water so on the scale of the Sun these are tiny but stars like red supergiant's do this to in the effect is a good deal more dramatic so if I put the Sun away it is now a single pixel on the screen but I promise you it's still there we can to scale compare the Sun there it is to fatal juice this is what those same little cells look like on the surface of Betelgeuse the whole star is boiling and roiling and changing very dramatically when you look at how bright it is this is a consequence of how large and how cold it is and this is a normal red supergiant this is very typical for stars like this so it starts to establish why these stars are as interesting as they are we went through the hertzsprung-russell diagram and we followed stars starting as hydrogen fusing blue supergiant's crossing the diagram to briefly become yellow supergiant's and ending up as helium fusing red supergiant's we can actually draw a line to represent the journey that we just followed this is how a 15 times the mass of the sun star would move during the course of its lifetime on the hertzsprung-russell diagram we call something like this an evolutionary track and it's a great way to quickly and at a glance look at how a star is going to behave during its lifetime this is actually a really great tool for studying theories of how stars evolve this is an evolutionary track for a 15 solar mass star but we can take a bunch of evolutionary tracks like that and draw them on a hertzsprung-russell diagram we can look at what a 12 solar mass star will do what a 20 solar mass what a 40 solar mass star will do and to get a good sense of what normal massive star evolution looks like so there's something you might notice on this diagram and it has to do with how cold the stars get every one of these evolutionary tracks was computed using our understanding of stellar physics and every single one seems to stop at about the same temperature every one is not really getting any colder than about 3,000 degrees Celsius or so to the right is this region where we don't think stars should be able to stable exist everything we know about stellar physics suggests that stars should not sit in as part of the diagram now I mentioned red supergiant's and I mentioned that they're incredibly cold we think that those stars should sit right at the edge of these evolutionary tracks but for a long time if we observed red supergiant's if we measured their temperature and we measured their brightness and we tried to put them on this diagram the stars would land here in exactly the place that they don't belong this bothered us for a very long time we were trying to understand what was wrong with our stellar physics what was wrong with our theory of how these stars evolved that could explain this really bad match between red supergiant's and the predictions of evolutionary tracks what finally clued us in was when we started looking at where the temperatures of those stars were coming from and when we developed a very good way to measure those temperatures more accurately than we had before the way that will do this is to take light from a red supergiant and sort it out into something called a spectrum so in a spectrum you observe light from an object and you sort it out according to its wavelength so the very bluest light will be on the left side of the diagram and the very readily will be on the right the brightness is still represented on the y-axis so you can tell at a glance that this is sort of a spectrum of a reddish star because we're seeing more red light than blue this is a cartoon version of what a red supergiant spectrum would look like an actual red supergiant spectrum looks like this it's a lot Messier and something you notice right away is that there are these strange sort of bites taken out of the spectrum there's these little dips that show up periodically as we go from blue to red all of those dips represent light that has been taken out of the spectrum on its way to us that's light that's been absorbed by something in the atmosphere of the red supergiant in this case that is light being absorbed by titanium oxide molecules these stars are so cold that molecules are able to form in their atmospheres it makes the spectrum look interesting and as it turns out it's also a really good tool for measuring temperatures if you look at a simulated spectrum of a red supergiant and you cool the star off at 4000 Kelvin you really don't see that many titanium oxide absorption signs at all as you cool the star off they suddenly appear and they get stronger very quickly what it means is that we can use those dips in the spectrum as tools for measuring temperature if we observe a star and we see very strong dips that means the star is very cold if we see very small ones it means it's relatively warm we decided to check this out as a means of maybe improving our temperatures for red supergiant's and maybe fixing that problem that we'd come across on the hertzsprung-russell diagram this was actually my very first research project as an astronomy student I worked on this after my sophomore year at MIT I got to go to Kitt Peak National Observatory in southern Arizona I had my very first observing run you can't tell from this image but I'm unbelievably excited because they're letting me open the dome of the 2.1 meter telescope and I'm gazing up going ha ha we had five perfectly clear nights this was wonderful observers beginners like and this has never happened to me again and we got spectra of 75 red supergiant's in the Milky Way we used that technique looking at those titanium oxide bytes in the spectrum to measure their temperatures and then weari plotted them on this same diagram so when we remade this with our temperatures the red supergiant's moved from here to here we had completely fixed the problem this was enough that little shift on the diagram was enough to get us unbelievably excited yes we've done exactly what we set out to do physics isn't wrong these stars work this is excellent let's write the paper and along the way we wound up discovering something very cool literally and entirely by accident so on this plot we've depicted each stars temperature and each stars luminosity and there's a very handy equation this is the only equation that I use in the talk but it's a very important one to have there's an equation in astronomy that relates how luminous a star is and how cold or hot it is to how big it is and I can walk through what everything in this equation means L stands for the luminosity how bright the star it's well we already knew that we know how much for is we know how much pi is that's just a constant and we know how much Sigma is that's another constant we had measured temperatures so now all that was left was the radius we had everything at hand so we figured why not this is just an algebra problem if we move radius to the other side of the equation take the square root of everything we've measured radius so we went ahead and calculated the size of every star in our list and we put everything at a big table and we started moving on to try and publish the paper it took one of our research collaborators looking at this table and going hang on I don't know if you've noticed one of the numbers in this list but it's astonishing this is the largest radius I've ever seen measured we might have discovered the largest stars in the universe we went back and did everything again we checked everything twice but it turned out it was true as part of this project we had by surprise discovered the very largest stars that anyone had ever seen so for comparison I showed you where baitul juice sat if we put it where the Sun was and compared it to the orbits of the planets this is the size of our new record holder a star named KY Sigma it reaches out well past Jupiter it starts approaching the size of Saturn's orbit so this on its own hitting this extreme of stellar evolution most definitely marks KY Sigma as a weird type of star so we've gone through how stars move on the hertzsprung-russell diagram we've talked about these cold red supergiant's fusing helium and their cores and how they can get fascinatingly big but eventually those stars also run out of things to fuse in their corpse does anybody know what happens when we get to that point supernova yes so to understand why a supernova happens it helps to look at what's going on inside the star right before the supernova massive stars started out their lives fusing hydrogen into helium then they moved on and fused helium into carbon and they progressed fusing heavier and heavier elements by the time they reached the ends of their lives if you were to slice one of these stars in half it would look like the inside of an onion with layers of every single element that it's been using for fusion or as the product of fusion inside this star gets into trouble when it starts to try and fuse iron this fusion happening in the core of the star serves a very important purpose it helps the star maintain this very delicate balancing act between the inward press of gravity and the outward press of that fusion as long as that balance is maintained the star is going to be alive and it's going to be just fine using iron disrupts this process because fusing something like hydrogen or helium or carbon produces energy if you try to fuse iron you need energy so at this point that delicate balancing act has been disrupted and I have an animation of what happens once we do that so in this animation we're zooming into the center of a red supergiant and you'll see the colors in the center of the star change to represent different fusion processes that are occurring as we switch from fusing hydrogen to fusing helium as we switch from fusing helium to fusing something like carbon you'll see the color change again and the star will progress through different fusion sources until it attempts to fuse iron this goes terribly for it and then in less than a second that iron core implodes all of the material in the outer layers of the star tumbles down onto that imploded core and then bounces back out and that rebound bounce gives us this unbelievable explosion that we see as a core collapse supernova so this is an incredibly dramatic death for a star and supernovae are amazingly bright this picture here is from a cave dwelling in Chaco Canyon New Mexico it shows a few illustrations on the rock you can see what looks to be a daytime moon you can see a person's hand and then you see this this we believe is a depiction of supernova 1054 this supernova went off on July 4th 1054 and was in our own galaxy it was very nearby it was so bright that you could see it during the daytime sky for two weeks we have historical records of it from Arabic astronomers from chinese astronomers they called it a guest star because it appeared stayed for a little while and then left this actually left behind what we now know as the Crab Nebula the Crab Nebula is the remnant of that 1054 supernova all of that material that got blasted off of the star now dissipating into interstellar space and giving us what we call a supernova remnant that was an unbelievably dramatic supernova and it was extremely bright in part because it was so nearby it was in our own Milky Way we had a supernova like this in 1054 there was a supernova in 1572 one in 1604 and we haven't had one since every modern supernova that we've studied has been in another galaxy and it's a little bit less of a fireworks show so this is an image of m51 this is the Whirlpool Galaxy and it's an image from January of 2005 in July of 2005 a supernova went off in and there's actually a really great image of that supernova happening did you see it such a dramatic explosion let me do it again yep usually when I turn it off then I had oh so that was the dramatic supernova two thousand five Cs we named supernovae based on the year that they happen and how many we've seen in that year so this supernova happened in 2005 we started with supernovae ABCD and went through the lettering so these supernovae are fairly common you can tell if we got all the way down to C s there's quite a lot of them this was a pretty bright and still pretty dramatic by astronomy standard supernova we catalogued it and we watched it do what a normal supernova does it got incredibly bright and then over the course of about a year it faded away this is what an exploding star should do sometimes we see something a little bit different so this is the beautiful galaxy NGC 76049 and by galaxy I mean the little fuzzball in the middle of the picture as we get farther away the photos get a little bit less dramatic this galaxy hosted a supernova we thought in 2009 this little bright thing appeared we identified it and immediately said hey we found another supernova this is supernova 2009 IP it got that name we saw this thing get very bright we watched it fade away and we thought well perfect another supernova doing its supernova thing and then it reappeared in 2010 it reappeared again in 2011 in 2012 we finally saw a very dramatic eruption from this star and we think that this star might now be dead although people are still keeping an eye on it and looking here just in case this was an example of a star that from our perspective was just pretending to explode what supernova 2009 IP actually is is an example of something called a luminous blue variable we tend to name things really literally in astronomy we talk about you know red supergiant's or our telescopes are named fabulous things like the Very Large Telescope so luminous blue variable is very literally what these stars are they're luminous they're incredibly bright they're blue which means a lot of the time they're very hot and the key thing is that they are variable so they change with time a star like the one that produced supernova 2009 IP is variable because it's flinging off enormous amounts of mass that appear to us as something very akin to a stellar explosion what we're seeing instead is an eruption and we still have a very limited understanding of what causes eruptions like that we have an amazing example of this in our own Milky Way this is a photo of a de Carina it's about 7,500 light years away and if you look at that image it looks like you're looking at something that exploded it looks like the violent post death of a star what we're instead seeing is material that got flung off of the star during an eruption in 1843 when that eruption happened ADA Khurana got so bright to do is actually the second brightest star in the night sky for a few days it's faded away since then but incredibly the star is still in there the star survived this explosion and what we're left with is this very fascinating material from that eruption that we're still studying in the hopes of maybe trying to explain what luminous blue variables are up to so I want to go back to the Crab Nebula to this remnant of a supernova I explained how a super no that happens you have that collapsing core material tumbling down after it and then rebounding and giving us this explosion the exploded material winds up giving us something like a supernova remnant like the Crab Nebula but there's actually something else in here that's worth highlighting at the heart of the Crab Nebula is something called a neutron star so a neutron star is what is left over when the core of a massive star collapses neutron stars are absolutely fascinating they aren't working like the normal stars that I've described these stars that have to fuse something in their cores to maintain a balancing act with gravity these stars are actually supported by principles of quantum physics they're supported by something called neutron degeneracy pressure hence why they're called neutron stars and the basic principle behind this is that neutrons that are very similar to one another they have similar quantum properties they occupy a similar state cannot be squeezed too close together they will literally resist this to the extent that they're able to support themselves against gravitational collapse neutron stars are unbelievably dense and unbelievably small one of these stars is the size of the city of Waterloo but if you took just one teaspoon of it it would weigh more than a mountain we're talking about a very extreme scenario in terms of the matter in this star you also sometimes see something interesting from a neutron star this is an artist's rendition and you'll notice those lines sort of poking out of the star in opposite directions those are showing the magnetic field lines of the star and illustrating that some neutron stars can be what we call a pulsar in some cases these stars will emit light out of their magnetic poles now we know on earth that our geographical Pole the actual pole that the earth rotates around is different than our magnetic poles in an extreme case like our neutron star what you'll get is a beam of light flinging around as the star rotates and sort of causing a flash as it goes by the best analogy that I've been able to find is looking at something like an emergency light on top of a fire truck or a police car those are two beams of light pointing out in opposite directions and as you spin it it appears as though something is flashing that flash is what we detect when we see something like this a pulsar Pulsar were actually discovered in a pretty interesting manner they were detected by a woman named Jocelyn Bell Burnell in the 1960s in the radio she actually detected first one and then two and eventually got up to four objects like this their pulsations were perfect it sounded like you were almost hearing a heartbeat from these stars they temporarily nicknamed the objects LGM 1 2 3 and 4 and lgm was an abbreviation for little green men and they were they were mostly kidding but it was a sort of tongue-in-cheek nod to the fact that this was such a perfect and regular signal that maybe maybe somewhere little green men were making this it turned out that wasn't the case at all and instead it could be explained by a neutron star that was specifically emitting this light and detectable as a pulsar so I've talked about these neutron stars that can form when the core of a massive star collapses if that collapse goes one step further if we have more mass in the core or if that neutron star gains mass with time we instead produce something else we produce a black hole I apologize for the artist rendition you understand these stars will produce black holes as part of their deaths now the black holes themselves are utterly fascinating but what I'm particularly interested in are a subset of stars that actually do something very strange when they die and produce black holes these stars produce something that we know as gamma-ray bursts and I have an animation of what this looks like this is a massive star something like 40 or 50 times the mass of our Sun now you'll notice it's blue it's not red the outer layers of this star have actually been ripped off over the course of its life exposing some of the hot inner layers when this star dies its core collapses into a very rapidly rotating black hole that black hole starts consuming the star and almost shattering the star from the inside out and it ignites these unbelievably high energy Jets of material shooting out perpendicular to how that black hole is rotating it consumes the star collisions in those beams produce the gamma rays that we detect here on earth and eventually the death of the star ends with the same sort of supernova that we talked about before so that whole video took about 15 or 20 seconds that was in real time a 40 solar mass star will actually die and produce a gamma-ray burst in a comparable amount of time so this is an incredibly violent death for a star it's incredibly weird and that's an amazing timescale to work on for something that huge those flashes of gamma rays that we see from stars like this were actually discovered by accident so these are the vaillar satellites it's a sketch of these satellites that were launched in the mid 1960s following the signing of the nuclear test-ban treaty so the job of the satellites was to orbit the Earth monitor the planet and look for signs that somebody was violating the treaty and performing a nuclear test which would have shown up as a flash of gamma rays the satellites worked great and they detected many flashes of gamma rays and fortunately for world peace none of them were coming from Earth instead they were coming from all over the sky it took us a long time to try and explain what we were actually seeing when we saw these gamma-ray what we finally determined was that we were seeing flashes of these dying stars from other galaxies we've now put up dedicated telescopes whose job it is to look for gamma-ray bursts and to tell us when one has happened as quickly as possible so we can try and study them so this is the Swift spacecraft it's a tailored telescope for detecting these sorts of gamma-ray flashes that flat-panel that you see on the front is a gamma ray detector and then under what looks like a baseball cap but is actually a Sun shield our x-ray and ultraviolet and optical telescopes that try to observe these objects as fast as possible what Swift will do is it will sit there orbiting the earth waiting for a gamma-ray burst to go off somewhere in its field of vision it'll spot a gamma-ray burst off the corner of its eye ago oh my god turn and start taking data on the gamma-ray burst as quickly as possible when it does that it sends a notification down to earth to astronomers saying a gamma-ray burst has just happened to remember that flash of gamma rays lasts 20 seconds we see light from these events in other wavelengths but if they still don't last very long so there's a great reason to try and go after these events and study them as quickly as possible so this gets into a type of astronomy called time domain astronomy I love this discipline it focuses on trying to study things that are very fleeting and very quick it's the closest I think that we get to sort of movie style astronomy so I want to do a quick comparison between how a movie might depict time domain astronomy detecting a gamma-ray burst and having to chase it very quickly versus how it actually happens I would contend that I think the way that we actually study these could be more interesting than a Hollywood film but in Hollywood if you detected a gamma-ray burst and you wanted to do something very quickly with it the detection would be announced by the science siren going off for some reason this is always a very public and very easy thing to do astronomers would get this notification that something exciting had happened they would run to their telescopes wearing lab coats for inexplicable reasons they would look through the telescopes with their eyes and they would naturally see something like this they would see perfect beautiful colorful data they would realize that some that they'd observed would help them to save the world they would dash off to talk to aliens or stop an asteroid or find a new home to live on and that tends to be how the movie goes the reality is a little bit different but I think some of the things that we do are more fun so in reality a science siren does not go off when a gamma-ray burst is detected instead you get a notification on your phone you will see a text alert or an email there are astronomers who are signed up specifically to get notifications if something this exciting happens once that happens the astronomer holding the phone gets to go all right we have now triggered something called a target of opportunity there's something that's happened in the sky that we want to follow up as quickly as possible with the best telescopes possible they will have access to something like the Keck 10-meter telescopes which are on the summit of Mauna Kea in Hawaii they will contact these telescopes and say you have to stop whatever you're doing I'm sorry astronomer who is doing their own science you have to stop whatever you're doing and take a little bit of time to observe this object in the sky very quickly before our chance goes away I think that these telescopes are unarguably cooler than the lab coat in I've urgent that you might see in a cartoon or a movie to give you a scale of what a 10 meter telescope looks like that's a about 6 foot tall person standing in front of one of the two cap telescope domes so you'll call in you'll trigger this observation and you hope that the night looks like this you hope that it's beautiful and clear and you can get amazing data of whatever you're wanting to observe the night might look like this this is an actual photo that I took when I was trying to observe at Keck and when you can't see the building that's like 30 feet away your odds of detecting something in deep space or getting really bad you can't even open a telescope when it's this crummy out it's unsafe for the telescope and the instruments hopefully the weather is clear you take observations and you get gorgeous data this is beautiful data and by the way that's the thing you're looking at the bright object up top is something else in the way there's a lot that has to be done too data before it can be finalized you have to account for things like the background glow of the sky electronic noise from the instruments on the telescope so there's a lot of effort that goes into eventually turning this into science once you have a discovery you don't run off and like call the President and save the world you wind up posting your results in some form of scientific publication something might be pretty quick you might just want to say oh we got a little bit of data on a gamma-ray burst so you're on a supernova so you'll put it on something like the gamma-ray burst circulars Network on the upper left or the astronomers telegram which is now a website on the lower right you might write a research paper for something like the Astrophysical Journal you'll put those papers on a public paper repository this is how we tend to spread our results around well work on something we'll analyze the data will very carefully get to an end result and then we spread it around to the community astronomers can sometimes still be amazingly fast at doing this but it winds up being a much more controlled way to do the science and it ensures that a lot of what we wind up seeing is both incredible and accurate so I think my favorite recent example of target of opportunity and time domain astronomy was related to gravitational waves and I'll start by briefly explaining what gravitational waves are a lot of you probably recognize this animation this animation came out when the first discovery of gravitational waves was announced in early 2016 they had detected gravitational waves from two black holes that were colliding this animation was everywhere it's excellent but I like to use something a little bit different to understand what a gravitational wave actually is so I want you to imagine you're holding something like a slinky and if you look at the slinky between your hands there's at least two different ways that you can cause a wave one is the obvious one you take that slinky you lift one end and you watch the wave propagate from one end to the other gravitational waves aren't quite this these are waves traveling through space time and what they're doing is something more a compression wave so if you took the slinky and shortened one hand and kicked off something like this those compression waves travel through space-time and impact space-time along the way and when a gravitational wave reaches Earth we see something like this so this is a wildly exaggerated effect but you can see Earth sort of getting squeezed and then stretched as a gravitational wave propagates by and squeezes and stretches the space-time that Earth is in we take advantage of that squeezing and stretching effect to detect gravitational waves so this image is LIGO this is the laser interferometry gravitational observatory in Hanford Washington there's three of these in the world there's one in Washington one in Louisiana and one in Italy and they're all specifically designed to detect gravitational waves they consist of these two arms set at perfect right angles to one another so each of those arms is exactly four kilometres long there is a laser and a beam splitter in that central building and what you can do on a normal day on a day when there is not a gravitational wave is fire a laser beam using the beam splitter down both of those arms at once with each arm being exactly four kilometres long the laser will travel the length of the arm will be reflected off a mirror at the end come back and the two laser signals will have traveled the exact same distance in the exact same time they'll cancel each other out and you know okay there's no gravitational wave now imagine a gravitational wave actually happening in squeezing space-time and squeezing the detector what I've just done is squeezed the picture so that the arm on the left is now a little bit shorter now if you send lasers along those arms they will arrive at slightly different times the one on the Left had a slightly shorter trip than the one on the right because of the effects of gravitational waves we now see a signal and we can confirm that we've detected a gravitational wave this started out by detecting two colliding black holes but last year on August 17th we detected something else so these are two neutron stars the same stars that I talked about before they're orbiting one another in a very close binary they're spiraling in spiraling in getting ready to collide when they collide they emit a very short flash of gamma-rays even shorter than the kind I talked about before and they emit gravitational waves we thought that this was going to happen for quite a long time and on August 17th a gravitational wave signal from two colliding neutron stars was detected so now we had something else exciting to do when two black holes collide we don't think there should be any light emitted by that process but these neutron stars are emitting gamma rays they're emitting light throughout the magnetic spectrum so we had to move very very quickly to try and find the electromagnetic light counterpart to the gravitational wave so there was a team in Santa Cruz that was working on this they had very quick observations with one of their telescopes of nearby galaxies where they thought this could have originated from and they were frantically looking through them to try and see if one of them showed a sign of the flash of light coming from this event it's very hard to tell exactly where gravitational waves are from are coming from so they had a big list of images to look through and one of the researchers on the team had about the most understated response does this discovery ever he sends a message around to the team that just said found something in one of the images they saw the unmistakable sign of one of these events so this was time domain astronomy this was astronomy that had to happen quickly and also had to happen carefully but it resulted in us discovering for the first time gravitational waves and light coming from an object in space which was really just incredible I've been talking a lot about weird discoveries and surprising discoveries and fast or fleeting or unusual discoveries sometimes this means something amazing like detecting gravitational waves and light from two colliding neutron stars sometimes it's maybe a little less dramatic sometimes it can even be a little bit disappointing once you look at the real reason why one example that I like pointing to you our potassium flare stars so we know that our Sun will produce what we call solar flares it's this eruption of material from the surface of the star and it shows up to us like a little tiny brightening other stars will also behave this way stellar flares are fairly typical and at the distances of the stars that we're talking about the flare has to be very bright so for years studying stellar flares and understanding stellar flares was somewhat commonplace in the 60s at provence observatory in france some astronomers were observing and taking data on a bunch of stars and analyzing the data as it came in and they were extremely surprised by one of the results that they found they saw a star that in its spectrum appeared to show a stellar flare that was very strong in a specific element it was very strong in the element potassium nobody had ever seen this before this wasn't a prediction of normal stellar flares and they were really surprised they were going wow we found a new type of physics we found a new type of flare we're seeing potassium flares from these stars they wrote a research paper it was really fascinating and the community was really interested they were going okay how do you explain potassium flares from a star and it got better to more potassium flare stars were discovered in those discoveries that we started to see a little bit of a problem nobody else was finding potassium flare stars except for this team and they were only finding them at this telescope so another research group in California decided to look into this decided to see if maybe there was some other explanation for what was going on so to understand why it's good to look at how telescopes like this are built this is a very typical telescope design it's known as a Cassegrain light will come down onto the primary mirror depicted in the bottom it will bounce up to a secondary and then bounce from the secondary down to the detector that we're showing in blue this can be a photographic plate this can be a digital camera like we have now it's a fairly straightforward way of gathering light from a telescope the telescope that was being used in France was taking advantage of something called a coup de design in this case we're bouncing off a couple of other mirrors along the way and were actually sending light to a detector in a completely separate room there's good reasons for this that traveled that the light has to go through actually improves the quality of the image and sometimes it's nice to have the detector in a completely separate room in this case that separate room was a nice little place where you could maybe go and take a break partway through the night it's the 60s it's France maybe you're taking a break and you decide to have a smoke break and strike a match potassium is the strongest element in the spectrum of match so people at Berkeley figured out that this might be what was going on they had an amazing research paper where they tried to debunk this and it essentially involved running around the dome of one of the telescopes playing with matches and striking matches to see if they could reproduce a potassium flare they acknowledged in their paper George Preston who was the director at the time for authorizing their unorthodox use of the 120 inch code a spectrograph the paper is amazingly thorough by the way they check book matches they check kitchen matches safety matches they contacted the people in France who were you know perhaps a little surprised that this was the explanation but scientists at their core and they said hey let's try our matches there's a line in the paper explaining that there is no spectroscopic difference between French and American matches and we now have our research paper that includes data on you know the spectrum of a match I assume that that room in the telescope and France is now non-smoking and you would think that the potassium flare stars had then been debunked what's great is that a few years later another observer was observing a star and did see excess potassium in the spectrum and they took care to note in their paper that the explanation did not apply since the observer does not smoke so potassium flare stars really are out there but perhaps not in the manner that they were originally discovered another good example of this happened at Parkes Observatory which is a radio telescope in Australia and this has to do with phenomena called fast radio bursts and something called a parrot on so during observations with this radio tape telescope they did did a brief burst of radio emission this was surprising this was very interesting we've seen gamma-ray bursts but a radio work burst like this and especially one on that rapid time scale was really puzzling now when they put this out some responses started coming in going oh a flash of radio is out we see those all the time there's lots of these this is probably something really cool we should figure it out and they started digging into the data as a whole to see what these were no those other detection zhh were nicknamed perry tongs and it was a sort of tongue-in-cheek nickname saying maybe these aren't entirely celestial maybe we have some other explanation for this but we don't yet know what it is now the key came when you sort of step back and look at where the Parkes radio telescope is in the larger observatory there's a couple of other buildings there's a couple you know dorms or administrative buildings and in the paper that finally explained this they noted that perry tongs were clustering around the lunchtime hour of the day so everybody in here I assume has microwaved popcorn or dinner at some point and you know how that goes you're hungry you're waiting and you're looking at the microwave and it's going five four third fine and you just open the microwave door to stop it just a second or two before it's done in old microwaves doing that can sometimes cause a brief flash of radio waves that were being detected as Perry taunts so again there is a delightful research paper showing how this happened they tested all three microwaves on site there's a paragraph where they probably learned more about microwave design that I think they ever wanted to in their lives microwaving a ceramic mug full of water microwaving the same thing every time but ultimately determining that yes that was what these Perry tongs were all of those detection zhh were probably just flashes from microwaves right most of them were one of them wasn't fast radio bursts again are real phenomena they are fascinating phenomena that we're still trying to understand we are now detecting more of them we know how to separate them from something like being impatient with lunch and we're trying to figure out whether these are coming from stars from objects that we may be fully explained yet they're a great example of a weird object in space but one that was discovered in a slightly unorthodox manner so the last type of weird star that I want to talk about actually combines two types of stars that we've talked about before I've explained red supergiant's what they are how enormous they are how cold they are and how they work and I've talked about neutron stars these quantum physics supported stars tiny and sort of dead remnants of a collapsed massive star there is really only one way that you could possibly make these weirder and it's to stick them together so if you imagine a red supergiant and a neutron star in a binary system these are two stars that are orbiting one another and perhaps interacting with one another exchanging mass in spiraling closer and closer kind of like those two neutron stars that we saw making a gamma-ray burst there's a really fascinating thing that can happen in a system like this that neutron star can effectively be swallowed by the red super time it can spiral in settle into and eventually replace the core of the red supergiant and make something called a Thorne cough object I found out about these for the first time around I think the year 2010 I've been working on red supergiant's for years publishing papers on them and noticing some strange red supergiant's or red supergiant's that we couldn't perfectly explain and in response to one of those emails or one of those papers I got an email from anisette cough saying years ago Kip Thorne and myself invented these theoretical models of stars which is just fascinating all on its own and asking if we were interested in trying to look for them so Thor injective objects predict this neutron star core surrounded by a big cold puffy outer layer they had predicted these back in the 1970s but they'd never actually seen one we had this rough idea of how they should work you're imagining these two stars in a binary to normal massive stars to blue supergiant the more massive of those stars the one in the foreground will collapse undergo an incredible supernova and what's left behind after the dust settles from that supernova is a neutron star the companion of that star will start to expand cool off go from the blue super diet to the red supergiant stage and swallow the neutron star along the way it's a scenario that absolutely seems like it could happen and the physics saying that these stars should be stable seemed quite solid but detecting them was a really big challenge if I back out and look at this again for a second I remember a red supergiant is the size of Jupiter's orbit neutron star size of the city of Waterloo so that neutron star cannot simply be seen inside the star it's buried deep in the heart of the star and from the outside a Thoren jet gab object will look exactly like a red supergiant almost we can take advantage of the fact that there's a neutron star in the core of That star to search for it in a very subtle way so to explain this I want to first remind you of that boiling convection that we see in the in these very cold massive big stars if I were to take a slice through a star like that you can see the surface of the red supergiant you can see the helium fusing core and you can see that convective cell in the middle if I now change this from the cross-section of a red supergiant to the cross-section of a thorn jitka object you can see a couple differences one is that the core is now a neutron star the other is that this star is quite cold it's as cold as the coldest red supergiant's that we know about that means that that convective region is huge it actually takes up the entire outer portion of the star from almost out the surface to almost down where the neutron star is this means that we can see some really strange chemistry going on in the star so if you imagine a packet of material traveling through that convective layer it will get dragged down to that area right near the surface of the neutron star where the temperature and the pressure are really extreme in that region protons start getting rapidly shoved onto the nuclei of atoms in that packet of material and if you remember your periodic table that means that these objects are starting to climb up Yanik table every atom is slowly increasing an atomic number the thing is material only stays there for about a hundredth of a second so it'll be bombarded with protons for a little while drift back out into the cooler quieter parts of the stars outer layers and start to undergo something called beta decay it'll start moving back down the periodic table before it can finish that trip it gets dragged back down to that lower region and bombarded by protons and the whole thing happens over and over this is a type of reaction that we can't expect in any other type of star and it should produce a very distinctive chemical signature we should see huge excesses of things like molybdenum and rubidium and lithium things that we would not normally expect to see a lot of in a red supergiant atmosphere so we decided to use this odd predicted chemical signature to look for thorns at gob objects I showed you what the spectrum of a red supergiant looks like before this is a very nice spectrum but in order to look for these little individual elements we had to basically take observations that let us zoom in we could zoom in on very specific small regions of the spectrum and look for the exact color that you would expect to see absorbed by something like molybdenum or lithium or rubidium so you see again these little bites out of the spectrum coming from molybdenum atoms absorbing light at a very particular wavelength or lithium or rubidium this is what a normal red supergiant would look like zooming in on these three regions and trying to look for these three elements we observed about 70 stars thinking you know what nobody even knows how much molybdenum is in a normal red supergiant this is going to be step one of the project we'll look at what normal stars are like and then we'll start trying to move on we'll survey more red supergiant's and maybe one day we might find a thorne jet goth object so out of 70 stars 69 of them looked like this one of them looked like this now if you'll notice all those little dips just got a lot bigger that means there's much more molybdenum or much more lithium or much more rubidium absorbing light that means that we're seeing excesses of these exact three elements the elements that you would predict from a thorn jadhav object in the spectrum we were amazed by this we looked at every aspect of the spectrum we could possibly think of and we eventually had one of our collaborators say this looking at the star I don't know what it is but I know that I like it when we compared what we had to the predictions of thorns it got objects it fit beautifully so we now have what we think is the first candidate for detecting a foreign Jadhav object I'm very careful to use the word candidate here the existence of Thor injective objects would have really profound implications for stellar astronomy the fact that you can have a stable star with a neutron star for a core is really surprising it gives us a new understanding of how stable stellar interiors could work it came from a system like this these two stars in a binary that merged so it gives us a slightly better understanding of how binary stars can behave and it's a great tool for making things like molybdenum and lithium you'll hear this phrase that we are all made of starstuff and stars really are factories for producing most of the atoms that we see and most of the elements that we see in the universe so a new way of making some elements is always fascinating because of this we love to call our object a candidate extraordinary claims require extraordinary evidence we have three little bites out of a spectrum that got bigger it's extraordinary in its own right these are very difficult measurements to make and it fits perfectly with the predictions of theory but we're very eager to get more observations of this star to try and find others like it and to really try and piece together a more complete understanding of how something like a foreign Jet gab object could work so I want to wrap up by leaving you with one last thought I talked about supernovae tonight I talked about these exploding stars and how unbelievably bright they are and how we observe them nowadays we observe them by seeing those little dots that turn on in other galaxies these represent violent explosions from massive star and in other galaxies that's what we see I like thinking about this supernova from the Year 1054 the supernova that happened in our own galaxy that was so bright you could see it in the daytime sky for two weeks that you could read by it at night we have last seen a supernova in the Milky Way like this in the year 1604 because of how many stars we have in the Milky Way and how often we think they should die we think we should have seen a supernova like this about once every hundred years so by that measure were 300 ish years overdue and I love imagining what it would look like if we had a galactic supernova right here in our own Milky Way go off tonight if we walked out of the building and saw this in the night sky it's a really fun thought experiment to do I mean at first it might actually cause a little bit of panic you're seeing something bright in the sky it's slowly getting brighter and brighter I think depending on the current like deal with geopolitical situation you might get a little nervous but once we'd established that it was definitely a supernova and nothing else it would be really interesting it would immediately get a hashtag nighttime hosts on shows would be talking about it every cell phone in the hemisphere would probably have a photo of it that somebody snapped and I guarantee you that every stellar astronomer would just up and lose their minds including me I really hope that we get the chance to see something like this happen I participated in the Eclipse that happened last August and it was a wonderful chance to see people from all over the US and all over the world flocked to the path of that Eclipse in the pursuit of astronomy and in the first suit of loving something like astronomy I think supernovae like this would do something similar that very bright object appearing in the sky something that you couldn't help but notice and something that you couldn't help but get curious about would be a really interesting thing to study and oh my god the data we get will be amazing so on that note I'll go back to the slide that I had up at the very start of the talk remember I promised you that you could name everything on this slide and now you can and on that note I will say thank you so much for being here tonight and I'm happy to answer any of your questions thank you all right so let's open the floor to questions there's a microphone right there if you have any questions just form a queue behind it and well let's go to a question in the theater right off the bat where you go great presentation I actually have two questions if that's okay absolutely the first one is I was curious with the gamma-ray burst sort of forums that you have online I was wondering do you guys share the raw data in order to get the meta analysis in the medicine world we've been kind of forced to do that some curious if you guys are doing that you know what it sometimes depends on the type of data or the type of group we will usually post results so somebody will take the data and very quickly look and try to determine for example how far away it is and then write a post saying here's this object it's at this distance sometimes you'll have a couple groups sort of racing to be first but generally if you email someone and you say hey I'm curious about this data they'll either send you the data or they'll send you their analysis of it so there's very much an encouragement toward collaboration it just sometimes happens organically rather than as a default when the data come graph the second question is as she has to do with the gravitational waves and I thought the one that you guys found you guys got to observe the light as well as the gravity at the same time so I'm not a scientist oh sorry I'm not a physicist so I'm just curious which one would be faster because technically time just like goes through space-time but gravity is space-time so you know or is a fantastic question so it sort of has a two part answer in terms of which is faster they're both traveling at the speed of light and for something like this it sort of helps to I have a couple colleagues who are experts in this but the way that I like to think of it is that the speed of light is almost a property of space-time it's built in it's not an extra speed limit that things have it's actually part of our model of how space-time works so both white and gravitational waves will travel at the speed of light now will detect the gravitational waves first with the light following it not because they're moving faster but because that's the order in which the signals are produced that gravitational wave signal happens first as part of the gravitational disruption of the two neutron stars colliding and then the flashes that happen after the gamma rays and other light that comes later something called a kill anova and emission of other light will happen a little later because it's literally happening later in the event not because it was just too slow fair enough so warp drives are possible then right let's take an online question in the Thorne's it cow objects what happens to the original core of the of their giant when it's replaced by a neutron star this is a fantastic question and it's a question we first of all don't have a definitive answer to we're just starting to study Thuringia objects there was a resurgence of interest after we thought we had found one so we're still working on trying to model them and how they behave but what we think happens is that that neutron star will settle into the core of the original star which is starting out by fusing helium in the core by disrupting the core itself we go from fusing helium in the very heart of the star diffusing helium in sort of a shell around the new core the actual fusion itself will also be disrupted by being very near the neutron star and by other weird physics that's happening in the core so that old coal core we think will sort of run out of fuel and peter out but this is just one of several explanations for what we think might happen to it and we're still trying to suss that out for models excellent in the theater once there you talked about a taqueria is a star a our star system i should say that i have heard of before from my online earth and space science class that i'm taking this semester what I've heard about that star is that when it goes supernova and it will its brightness will rival that of the moon is that true and if so how long will that last I think that could absolutely be true the supernova that happened in 1054 was out showing everything except to the Sun and the moon so I could certainly see something like a decline of behaving that way you also mentioned an interesting thing that I want to make sure everybody else understand because you were very careful in calling it a star system and you're right there are actually two stars buried in there buried in that picture of the ejected material that we see both of those stars are tens of times the mass of our own Sun and we do think that a supernova from something like that should be very dramatic and very if it gets as bright as the moon it's hard to say exactly how long that would last but it would be on the order of like maybe a week or two weeks supernovae will get bright very quickly and then start to fade very quickly and there's actually a lot we can learn about the star and the chemistry of it by following how the supernova actually fades away but that really bright period will last a couple weeks thank you good here's the another online question Polaris Polaris is a rare star that won't last that long do we know how much longer it might last it sounds wild that the near relatively speaking future the North Star might not be there so the good news is that the star will be there for a while it's just changing evolutionary state and it's hard to actually say where the star is in its evolution because yellow supergiant's are so rare and because it's so difficult to study them as a result we don't have a great formula in place for saying Oh Polaris is gonna last this much longer before it turns into a red supergiant or it's exactly at this point in its evolution it would be really interesting to find more of these stars but what's hard is that without knowing the exact distance to a star it's very easy to confuse something bright and faraway like a red yellow supergiant across our galaxy with something dim but nearby like a star like our Sun a yellow dwarf so we're trying to study more of these and we'd love to be able to eventually answer that question but we don't know yet let's finish with one last question your excitement passion for astronomy is infectious when did you know that you wanted to study the Stars I I think I knew I wanted to be an astronomer and I was about to and I remember why I have a reason so I was two years old in 1986 which was the last time that Halley's Comet made a close pass of Earth I have an older brother Ben who was 12 when I was 2 and he had a school assignment to observe Halley's Comet so me and him and my parents all went tromping out into the backyard and I'm sure I was a slightly fussy two-year-old who was a bit bothered by the dark until they sort of pointed me up and apparently I was fascinated and from then on people would ask me what I wanted being when I grew up and the answer was always well I want to be a ballerina or an astronomer or I want to be a firefighter or an astronomer and later on a marine biologist or a paleontologist or an astronomer but astronomer was always there an astronomer stuck I read a wrinkle in time when I was about eight years old and it just absolutely fascinated me I was so amazed that we had this protagonist of a little girl who was into physics and into astronomy and that and other books like that and things like science activities in school really helped encourage this in me and then when I went to college I majored in physics knowing that that was the starting path to becoming an astronomer and did not look back from there ladies and gentlemen dr. Emily Levesque [Applause] [Music]

Channel: Perimeter Institute for Theoretical Physics

Views: 470,652

Rating: 4.8132877 out of 5

Keywords: Astronomy, Space, Cosmos, Astrophysics, Stars, Emily Levesque, Perimeter Institute, Physics

Id: YR-l0b2iYy0

Length: 68min 46sec (4126 seconds)

Published: Thu Mar 08 2018