WSU Master Class: The Monster at the Heart of our Galaxy with Andrea Ghez

all right it is such a pleasure to be here at the world science festival this week is uh for scientists is just uh so much fun so we're going to start today with a question which is how do you observe something you can't see and this is a key question if you want to find and study black holes because black holes are objects whose pull of gravity is so intense that nothing can escape them not even light so we can't see them directly uh the story i would like to share with you this morning or this afternoon is how we've been able to find a supermassive black hole at the center of our galaxy and this has provided us with the best evidence to date that these exotic objects truly do exist which gives us a wonderful laboratory for understanding the physics of these objects how they warp space-time and the astrophysics of these objects what role they play in the formation and evolution of galaxies so to begin with we all have to agree on what a black hole is so it seemed very appropriate to put up a blank slide so while black holes require relatively exotic and complex physics to describe the way i i would like you to think about a black hole is the way i actually think about a black hole on an everyday basis so black hole is mass is an object with mass but this mass is confined to an infinitesimally small volume so if we think about density which is mass divided by volume the density goes to infinity and in physics any time we have the number infinity that's known as a singularity which is like a big red arrow that says you do not have your description of the physical world right here and of course in uh physics that means that we don't actually know how to make the world of general relativity which is the study of gravity in its most extreme form and black holes definitely have a lot of gravity work with the study of quantum mechanics which is a study of things that are very small of course black holes are infinitesimally small so they qualify so when we figure out how to make these two aspects of physics work together we will understand what a black hole actually is but today we don't but fortunately for me there is a size that we can associate with the black hole so it's a virtual size it's not a surface of the of the black hole because the black hole has um no finite size and this is known as the short shield radius it's popularized by star trek it's the event horizon it's the point of no return so light the last point that light can escape from the gravitational field of the black hole is this event horizon or schwarzschild radius it's also important because every object of a given mass has a short child radius associated with it and it simply depends on the mass and why is this radius important it's important because if you can figure out how to squeeze that mass down to its short child radius gravity will overcome all other known forces and the object will collapse to the infinite potentially small object so if you want to prove that there is a black hole out there in the universe that these objects really do exist your job is to show that there is a mass inside a very small volume and the volume that's set by this short shell radius and it depends only on mass so the more massive the object is um the larger this the scale is or the size so if we were to take the earth and squeeze it down to the size of a sugar cube it would be forced to become a black hole if we were to scale up and consider the sun and squeeze it on down and of course i had to put ucla in there because that's where i'm from but take any college campus pretty much uh and the sun would become a black hole okay so now we have what is a black hole and how do you prove that these things exist so now let's talk about where black holes appear and the black holes that i'm fascinated by are the supermassive black holes and i'll get back to what that means but in astrophysics there are two classes of super of black holes uh the ordinary black holes as if there could be such a thing as an ordinary black hole um and these were uh thought of from theoretical studies first so theorists who were contemplating how stars the most massive stars in our galaxy would go through would evolve throughout their lives understood that at the end of their life the inner parts of the star would collapse to form a black hole the outer parts would explode and expand in an explosive way and form a supernova so that's what we're actually seeing here this is a supernova remnant so it's the outer layers of a very massive star a star that started its life off with roughly 30 times the mass the sun ending its life in this explosive way and the thinking was it would form a black hole of roughly 10 times the mass of the sun so thought of from a theoretical perspective and then observations have come along to prove that these objects truly do exist and that's been known for a long time and ligo the gravitational wave detector put the evidence for the stellar mass black hole in a whole other regime so we're that is the final point on the stellar mass black holes now the story about supermassive black holes is very different the story of supermassive black holes come from the study of galaxies so galaxies there are a lot of galaxies actually if we look at the next one this is a picture from hubble space telescope and everything in this picture is a galaxy except one object in the middle which is a star in our own galaxy and the scale here is uh you can understand is different because each galaxy has roughly um a hundred billion stars in the last picture we were looking at a single star within our own galaxy and what we're looking at is a picture at optical wavelengths which is what your eye detects and you see the light from the stars the stars that are like our sun and there's nothing um unusual about um this this picture to lead us to conclude that there was a super there are supermassive black holes but roughly 10 of all galaxies if you look at them in radio wavelengths long wavelengths where your cell phone works roughly you see something truly um spectacular at the center of the galaxy the starlight is now no longer visible and you see a mission coming out these jets and the jets are moving tremendously fast so you know that there's something powerful at the center at the heart of these galaxies and at the heart we also see a dot in the middle and that dot has emission or light characteristics that look nothing like starlight and it was thought or speculated when these objects were discovered that what we're seeing here is the dining habits of really massive black holes so matter is falling onto this black hole and powering these jets so you can think of these as black holes which are roughly a million to a billion times the mass of the sun so much more massive than the stellar mass black holes that are having a thanksgiving feast you know they're they're definitely indulging and we see the light of the feast because remember you can't see light inside um the event horizon okay now those are you could call them maybe the prima donnas of the extra galactic world they're kind of show-offs they're only a small fraction but it did lead to the question roughly uh 40 years ago do all galaxies harbor supermassive black holes at their centers and if we uh are going to entertain that notion then our galaxy is certainly the best place to look because it's the closest center of a galaxy that we'll ever have to study so this is a picture of of one of those galaxies that would presumably look pretty much what like what our own galaxy would look like if we could get outside it and look back at it galaxies for the most part are flattened disk-like structures in our own galaxy we have these beautiful spiral arms but of course we're not looking at it from the outside we're looking from it from the inside and from an inside vantage our solar system is about halfway out in the galaxy so if we look in the night sky what we're seeing in terms of this flattened disc-like structure is we're seeing the plane of the galaxy so this is a picture of the milky way seen from hawaii um and you see the um the light the the and in fact this is why it was called the milky way the greeks uh the word galaxy comes from gala which is milky way so we see a path that looks kind of milky from all the starlight but we also might notice that in the uh in this milky band um that there's a lack of light and that lack of light comes from dust in the plane of our our galaxy i'm from los angeles i have a very good feeling for um what dust in the air how it does to you it's like smog so our galaxy's kind of smoggy and um what you know from visiting a smoggy city is it if you look with your eye your eye can't see very far through uh the smog so in los angeles you don't see the local mountains very clearly on a on a smoggy day uh so in the center of our galaxy there's light coming out and only roughly one out of every 10 billion light packets or photons makes it to us so that's why the center of the galaxy is not observable at wavelengths at your eye detects now if we go to the infrared which is just longward of where your eye detects light or where your tv remote control works you get one out of every 10 photons coming to you so you can actually see the center of the galaxy so a key aspect of the work that i'm sharing with you today is the advancements that have been made in infrared technology your ability to see this kind of light now if i want to show that there's a black hole at the center of the galaxy the key way to do this or a direct way to do this is to look for the stars that are as close to the center of the galaxy as possible and to watch or measure how these stars orbit around the center this is tracing or seeing the black hole through the gra the gravitational influence on the stars in the very same way that we could actually measure the mass of the sun by measuring how the planets go around the sun so what i need to measure is how long it takes that star to go around and i need to measure the size of the orbit that gives me the mass so that's number one and once i know the mass i know the short child radius and uh and each orbit gives me a size as well so i have a mass and a size by approaching the problem this way now what does this mean this means that i'm inward bound what i want is to see the stars that are as close to the center as possible so that i can confine the mass to a smaller region as possible okay this tells you why i wanted more than anything else to have the job that i have today i have my dream job i feel incredibly fortunate the university of california and kel-tec co-owned the largest telescope in the world so why is this important it's important because large telescopes come with two campaign promises one is that you build a big telescope and we describe how big a telescope is by the size of the mirror the collecting mirror and if you have a big collecting mirror you can see things that are very faint it's uh you can uh because it's like a light bucket you're collecting the photons that are coming reigning in so the bigger your light bucket the more photons you can collect in a certain amount of time which means you can see things that are very faint and in astronomy faint means distance so mo um there's a most astronomers really care uh historically about this aspect of being able to see the most distant universe to be able to see the earliest moments in the universe because light takes a finite amount of time to get from distant objects to us it's like getting a history lesson so it's a really important aspect of large telescope what i care about is actually the second campaign promise which is the larger your telescope the bigger your diameter of the mirror the smaller the detail that you can see and the way i like to describe this aspect your ability to get high angular resolution is to make the analogy to the um the painting style of pointillism so pointillism is made with a bunch of dots and the closer you get to that painting the better your ability to see or resolve the dots if you stand further away it all blurs together and it makes for a beautiful painting so i want to see the dots if i want to see the dots that are as close to the center of the galaxy as possible so i want to get my hands on as big a telescope as possible and to develop techniques that really take advantage of this aspect of telescopes so this is why i love working at ucla to work with this fabulous facility now you might ask where is this facility this is like asking where is my lab well you might say los angeles but i'm going to tell you actually it's hawaii my lab is in hawaii uh hawaii on the big island so actually the big island has been in the news quite a bit recently because of the volcano so it's useful to remember hawaii is a volcano and i'll explain why the astronomers still think that hawaii is the best place in the world to build big telescopes so we're on the top of uh mauna kea on the big island and the reason why mauna kea is such a fabulous place to build telescopes is that it's uh for one reason it's a very uh high peak so we're up at 14 000 feet so if you want to build a telescope you want to get it on as high a peak as possible because you want to see through the atmosphere and this is a picture that i actually took on the first time my first trip up to the top back in 1994 and you can see the clouds below you so that's uh useful because if you're like me and think of hawaii i usually think of a tropical place with lots of rain that's not good for astronomers and the reason why this makes sense is all of that is below you now it's also true that 14 000 feet is a very challenging place to work in terms of human physiology uh turns out your brain doesn't function particularly well up at 14 000 feet which is an interesting challenge so you have astronomers astrophysicists who desperately want to use this facility the typical uc astronomer might get two nights a year the operational cost of this telescope is evaluated at roughly a hundred thousand a night so you do not want to be at suboptimal during your night of observing and there are classic stories like the astronomers who will write down the list of everything they should remember and then forget the list or in my case the first time i went up with a graduate student my first graduate student we had a an interesting debate up at the top which was what's 128 divided by two so these are the in one one of the aspects that make doing astronomy challenging so the way we do astronomy today has evolved quite a bit um we now no longer go to the summit for many years in this experiment we did we did go to the summit which was an exciting adventure and i loved going up there but then it became possible to observe from the headquarters which are in uh waimea uh there's about a hundred people a hundred staff that are responsible for the operations of this facility down there and and it turns out you think much better at a thousand feet uh so that's wonderful and now uh since uh since roughly the last uh 10 years it's possible to control these facilities from campus so now we can work we work in concert with those people who are operating the telescope but as the scientists we can do this from campus so every place comes with pros and cons this is always the way it is with advancing technology you get something and you uh but though you also lose something so the things that we gain are better thinking and certainly better uh educational opportunities uh by bringing the observations uh back to the the campus all right now let's come to the volcano aspect of this so um the big island is composed of five volcanoes one of them is active that's kilauea that's the one in the news and fortunately it's uh it's a volcano all the volcanic activity in hawaii is a uh is for the most part pretty calm and not extremely explosive uh in this you have seen in the news plumes but you haven't seen anything that throws the dust up into the higher levels of the atmosphere which would really be a problem for astronomers but mauna kea uh kilauea is a diff a different kind of a volcano this is a picture of kilauea from 1994 when it was in a similar state where you could actually see surface flows so it is an interesting and exciting place but we can we can carry out our observations uh during this in fact we had a night the other night uh where we could actually see uh an eruption that appeared on the front page of the los angeles times the next morning so it's it's exciting but it does not uh disrupt mauna kea is a dormant volcano which means according to this geologist it's not going to do anything for another million years now i have to trust them because i'm married to one so we hope they got that right now the other reason why the big island is such a great place in a particular mauna kea to build telescopes is that you want not only a high sight that gets you through most of the atmosphere but the atmosphere that you have left you want the airflow to be very smooth what the scientists call laminar and to get very smooth air flows you need to you want to be around a large body of water so to be on an island actually optimizes this so if you look at the forefront facilities that are built today around the world you'll notice they're on high peaks near big bodies of water so the andes in chile the canary islands and the hawaiian islands and that's the reason you're getting this very smooth air flow for for going to a high peak near a big body of water now the next thing you want for a large telescope is a dark site you work very hard to collect these precious photons from across the universe or across our galaxy and they've been traveling to us for a very long time in the case of the galactic center the center of our own galaxy those light packets those photons have been traveling to us for 26 000 years so the last thing you want to do is have them messed up in any way or contaminated so a dark site where you don't have local light is incredibly important so this introduces a very interesting tension in the world of astrophysics because you want to be both in a very dark place and you're trying to build incredibly advanced technological buildings and facilities and instruments so you want access to high-tech industry that tends not to be in den dark places so you're trying to optimize this this trade so hawaii is one of the few places in the world that provides you with relatively good access to high tech both in terms of the industry and the people it gets satisfied nicely in hawaii so you want it high tech and you want it dark so that's that's the piece about the darkness okay so now we have a telescope we have it in hawaii we've explained why we want it in hawaii let's come back to the problem or the promise of getting very high resolution uh information the second campaign promise so um the problem is while it's high you're still looking through quite a bit of atmosphere and it's smooth but still not that smooth and you can see that by looking at this picture these are data that we took uh when this experiment started back in 1995 it was the original data type and the trick there was just to take lots of short exposures and you freeze the interfering effects of the earth's atmosphere and if there were no atmosphere each of the five stars that we're looking at here prominently would be the size of the smallest structures that you're seeing and rock solid that's not what you're seeing you're not seeing this because these photons that have been coming into us for 26 000 years hits the top of the atmosphere 30 micro seconds before it hits your telescope so they say accidents hope happen close to home and that's true in the case of these photons okay so i'm super interested in how do you overcome this problem how do you beat the atmosphere oh and i should also say another analogy for how to think about the problem with the earth's atmosphere is think of us of a river moving by you and you're trying to look at a pebble on the at the bottom of the of the river and if it's moving and turbulent it's very difficult to get a picture of the pebble that's what's happening here i'm trying to see through a stream of atmosphere that's turbulent so the analogy works fairly well the other analogy that i like to make in terms of what's happening and what we're trying to accomplish is to think of a circus funhouse mirror and um it distorts you so that's what's happening to the starlight it's it's getting distorted and i want to figure out a way of putting a second mirror in there or some process that makes me look flat again okay so astronomers have looked and thought about this for a long time so if you want to beat the atmosphere one very straightforward and effective way of doing this is you get above the atmosphere and that is the solution of the hubble space telescope it is a incredibly powerful telescope that is not affected by the earth's atmosphere so we use this for our our work but the reason why for the work that i'm going to just share with you today that i'm sharing with you today that keck is the choice instrument is because it's bigger so the diameter of the hubble space telescope is 2.4 meters the diameter of cac is 10 meters you want to kind of visualize that that's like the width of a tennis court and the power of the diameter for the kind of work that i do goes as the diameter to the fourth power so i've got a telescope that's four times bigger so that's four times four times four times four and because i'm not at the summing of mono k i actually can do that math and that's a factor of 100 better in principle if i can figure out how to make that uh to take the blurring effects out so as you might imagine if you're being offered the opportunity to do something 100 times better you're probably going to work pretty hard at it so that's what i've spent a large part of my career thinking about which is what what techniques can we use and develop to beat the atmosphere one of my advisors said when i was a grad student you know andrea you just take the twinkle out of stars that's my job so this is an animation that shows uh some of the work that we've done it captures what happens if you take a very long exposure in time on the center of the galaxy so you can see the five bright stars that we were seeing the bug splat patterns for a moment ago and those were short exposures those were a tenth of a second and they're at two microns that's the wavelength that we do our primary work at and if we use these techniques we can get to the highest resolution afforded by the telescope which is about the resolution is about a factor of 20 times better okay now the technology that we've been using and developing has changed radically over the last 20 years so this project is a is very much technology driven discovery so at each phase that where we are in our technological development has sort of dictated um how much science we can do and i have to i have to share this has been incredibly exciting journey when i first started this project uh 25-ish years ago i wrote my first proposal i was a brand new assistant professor i thought i had such a good idea for how to use this telescope in a new and different way and you have to apply for telescope time and this committee this group of people said well um this idea that you have for how to collect the data uh probably won't work and even if you do you probably won't see stars under the galaxy and even if you do uh or that are close enough and even if you do you won't see them move okay so that's a lot of no no no's um to get at the beginning but fortunately uh i'm kind of i'm used to being told you can't do something as a woman in physics so i said okay fine i've heard that a lot i've heard that before let's keep going and i also work in a department that is um i'd say very supportive um so these are colleagues and i think this is a comment on how science works you can't do it in isolation you actually need the support of others to be successful i think there was a comment in the gala about that that just so resonated with me so i had a colleague who lent me his telescope time which is you can't give it back so enabled us to show that this technique would work and um this is just a picture showing uh the original instrument so it was a facility it was an instrument that was designed for the facility and we just uh built this is in collaboration with my colleagues um a little uh uh adaptation that allowed the uh instrument to see ver uh on a smaller scale than it was designed to do and i think this is also an interesting comment this is a you know 100 200 million dollars scale facility that they're letting an assistant professor come and add a little tweak to it that that is also a rather amazing comment about this this particular facility in terms of its willingness to engage in doing something different or outside the box okay so the way this was what we did for the first 20 years it was hardware simple which means not very expensive computationally complex so you basically take a little bit of data back and you spend a lot of time developing software and algorithms to figure out what did the atmosphere do versus what did the what's the true underlying object and there are a lot of people out there who care about that yeah it's not just the astronomers who think a lot about seeing through the atmosphere both up and down uh and and working out the image uh that's the military if you hadn't figured that one out um there is all there is also the whole medical industry that's interested in imaging through um tissues either through your eye or various parts of your body and want to figure out what's actually what you're trying to see underlying some distorting media so from a technique perspective there's a lot of um reasons um to think about uh about this outside of astronomy uh it's not why we do it and and and uh but we want to see the universe okay um the way this uh story evolves now is that there's a hardware solution to this and this is a solution that was developed by the uh by the military um and as the uh astrophysics community was making progress in figuring out much more sophisticated hardware solutions uh the military basically said oh and i should say um the funding for astronomy and astrophysics is nothing compared to funding in the military so as we were starting to ask for funding to do this the military said basically we know how to do this and declassified it so in the mid to late 90s there was this huge thrust forward because of a declassification and this was really exciting and i was really excited uh because i knew this would be a completely revolutionized what we were doing at the center of the galaxy now this animation shows both a couple of miracles like the dome going away but it also is designed to help us talk about how does adaptive optics which is this new technology work so we see a beam of light coming to the telescope the the mirror was the uh the thing it bounced off of and then it goes into an instrument bay and the instrument bay is where all the magic happens for correcting or taking the blurring effects out so we're going to see both the beam of light and in a minute it's also going to be shown in a second way you can talk about light which is a wave front and if there were no atmosphere each wave front would be um a flattened pancake so you can see in this the beam going through bouncing off various mirrors and if you don't do anything it's that bug splat pattern again and the this it's going to show you a very important element this is called the deformable mirror this is the second circus fun house mirror that um that takes out the distorting effects so rather than pancakes coming in we have pringles potato chips and then you have the second mirror that when it's not on uh it doesn't do anything but if it starts to look at what the past wave fronts look like then it bounces off into these flat pancakes so if the if the system works uh fully understands or can fully probe the atmosphere um it is a perfect image at the end of the day so it gets nice and tight and for the first time in our work at the center of the galaxy we can take an exposure that's longer than a tenth of a second so the kind of work that we can do is so much more powerful with this technology okay and now you might ask how do you know how to move that deformable mirror and a key aspect of that is that we shine lasers into the atmosphere and we do this because up at about 90 kilometers there's a very thin layer of sodium atoms just a fluke of nature so i love uh shooting stars or making a wish on shooting stars because those are not really stars those are meteorites or meteors coming through the atmosphere and burning up and the sodium atoms in those uh meteorites or meteors are get trapped at 90 kilometers in this very thin layer that's about four kilometers thick so you can take a laser that's tuned to a transition uh in the sodium atom and stimulate those atoms to shine so that's an artificial star and we can then look at that artificial star we can create it in any direction we want and use the light from that artificial star to inform us about how to change uh the deformable mirror for me this was an amazing night we actually got telescope time on both telescopes so we you only need one laser per telescope but it's like two laser pointers showing you the road map to the center of the galaxy uh if you want to look up at the center of the galaxy it's up this time of year you find the constellation of sagittarius which is the teapot and it pours into the center of the galaxy okay so we now have this much more advanced way of correcting for the earth's atmosphere and we can see the stars at the center now we're going to look at a little animation here that shows a much smaller box than we were looking at before remember the on off picture blur not blur and there was a little inset this is about the fourth of the size of the little inset this is a ridiculously small uh field uh field of view according for most astronomers but nonetheless it shows the stars that we want to see and it shows how they've moved over the last 24 years so we've been very very patient i'm going to play this again actually because i just love watching it to give you a sense now there's all sorts of information color coded in here or coded in here um when you see the star with images it's trailed by a solid line so from the very beginning we could take pictures but the pictures got better which meant we could see stars that we couldn't see in the beginning so you'll see stars pop up that you didn't see before okay so that's image progression and imaging but images only show me how something's moving on the plane of the sky two dimensions and these are these these are moving in space in three dimensions um and we pick up the third dimension by uh taking uh spectra uh which allow us to measure the motion along the line of sight and that was only possible uh when uh adaptive optics came online and i'm realizing i think i misspoke so when things have an image behind uh are picked up by an image uh it's trailed by a dotted line let's watch this one more time yeah and when it's uh got the third dimension it's turned into a solid line and the whole thing ends highlighting my favorite star in the universe its name is so2 why is it my favorite star in the universe it's because it taught us that there was a supermassive black hole at the center of our galaxy it did that because we can measure that it took 16 years for it to go around and we can measure the size of the orbit and in particular we can measure the size compared to its motion its path how close it gets to the mass that drives the motion okay so what does that tell us oh i can do this now this tells us that while we knew there was 4 million times the mass of the sun located at the center of the galaxy inside a very large circle we didn't know at the outset of this experiment that that was a black hole what this experiment has done has to show has been to show us in fact if you look at a volume that's 10 million times smaller you still see 4 million times the mass of the sun another way of saying that is that you've moved the case forward by a factor of 10 million for the existence of a supermassive black hole and that's true not only at the center of our galaxy but anywhere in our universe so that's why this is so exciting and to give you a sense of scale we've confined it to a region that corresponds to roughly the size of our solar system so again think about it we have four million times the mass of the sun inside a region that in our that we experience as having just one sun's worth of mass there so that's incredible concentration of mass and therefore a case for a super mass black hole so we now have this wonderful case and we say fantastic so you might ask do you keep going with this and i'm going to tell you well of course you keep going with this this just gets better and better and better and better in a way that we couldn't have even predicted given that we couldn't we could barely convince the the folks in the beginning to let us do a three-year project never mind a 24-year project and the reason why this has gotten so interesting is that now you have a laboratory for understanding supermassive black holes it's the closest supermassive black hole you'll ever have to study and you can study it in a way that you cannot study anywhere else in our universe it's the only galaxy for which you could measure the orbits of stars so you have now effectively through this opened up a new approach to studying the physics and astrophysics of supermassive black holes it's also i think a great demonstration here of how science is both driven by questions you know to ask and sometimes by technology that shows you views of things that leads to questions you didn't even think to ask okay so uh let's talk let's start from the point of view of the astrophysics the astrophysics uh as time has gone on the story the astrophysics story has evolved a lot when we first announced the result of the supermassive black hole people used to ask well which came first the black hole of the galaxy it's kind of like the chicken um or the egg and of course we had all sorts of uh answers for why one would happen versus the other but today we realize that's not even the right question to ask because if you look in other galaxies today we're able to show that the mass of black holes that are in those galaxies seem to correlate very well with the mass of the central part of the galaxy and the scale of that is so different that that leads us to the conclusion that whatever process formed the black hole had to form the galaxy and that there's some feedback loop that keeps the growth of these two very different scale entities in lockstep okay so this is this correlation so this is the thinking over the last roughly um 10 years so at the center of the galaxy we have this unique opportunity to look at what kind of processes might be ongoing that keep the galaxy uh well actually let me put it this way that enable us to understand the role that black holes play in shaping their hose galaxies okay so uh there were a couple of ideas that were out there about what we should find near this uh a black hole at the center of the galaxy based on the notion that there was this connection and one was that for old stars old stars have been around for a long time they've had a lot of time to interact and they know where the life of the party is so they like to congregate there so the life of the party is the black hole so things tend to sink or what we call by dynamical friction towards the most massive thing in the system so you expect a very large concentration of old stars at the center of galaxies and in fact we even use that theoretical notion to find black holes in other galaxies because we look for the concentration of old star light to tell us that maybe there's a black hole okay so that was prediction number one for the old stars then there's a prediction for the young stars um and and for the young stars oh and i should qualify what i mean by old and young so old in astronomy means a billion years and young means a million years and and the analogy um with human time scales uh is uh you can make the following analogy if you compare all the age of old stars to a human lifetime then the age of these babies these baby stars are the human gestation time scale okay so these really you really can think of them as baby stars and you're looking at stellar nurseries and you're trying to figure out how they form and the analogy works really well because you need these things that begin as very fragile objects they begin as big balls of gas and dust that are fragile and you need these objects to collapse under their own self-gravity to form stars okay now the problem with black hole is black holes are not nice to that process you do not want your stellar nursery near a black hole and that's because black holes have what's known as tidal forces so if you've seen the movie interstellar with those giant tidal waves that get created on the planet close to the black hole that's what happens to young stars is they get pulled apart and that's because the tidal force means that if you fall in feet first there's a larger amount of gravity on your feet than your head so you get torn apart and astrophysicists like to call this um process or popularize it to call it spaghettification like a spaghetti okay these are two young stars i'm particularly fond of they're my little my little young stars they're a little older these days but i would not want them near a black hole okay now what do we see so we've got two predictions lots of old stars no young stars so let's look at what the observations show and what i love is it's the exact opposite okay so the color coding here and this is now a three-dimensional picture is the old stars are orange the young stars are blue aqua blue and then the pink stars we didn't even think to make predictions for so that's three new mysteries so again wow questions we didn't even think to think to to to consider and that means that that drives both both theoretical work so the theorists go to work in terms of coming up with new ideas how do you get the young stars there how do you get the old stars there and what in the world are those pink stars which i'll get to in a minute so lots of lots of work from a theoretical perspective and as an observer or somebody who uses a telescope my perspective on this is what other observations can i make that gives us new insight into what's going on the key one of the key things that we can do is just keep going time really helps the longer you go the longer you the the further you are from the black hole the longer it takes for stars to go around so if i measure for a longer and longer amount of time i can actually learn about the orbits that are more distant from the black hole so i start with a really kind of myopic view of what's going on at the center of the galaxy and over time i get a more expansive view and it's been fascinating what's dropped out of this and again totally unexpected so you can see hopefully in this animation as we pull back from the center and and look at the kinds of orbits that we're measuring you see a set of young stars that form a disc it actually looks completely like a scaled up version of the solar system and this and and it works perfectly well the the ratio of masses between planets and the central host star in our solar system is almost the same as these massive stars compared to the black hole so that's exciting and we're going to use insight from how solar systems form to understand what's going on here so we think that what happened is that when these stars were being formed there was a disc of gas and dust that created both the stars that then orbit in that plane but also probably provided a lot more gas at the center of the galaxy and that suggests that our galaxy was probably much more active in the past it was probably a much more akin to those active galactic nuclei those prima donna galaxies that we showed in the beginning our galaxy was actually probably more like that than it is today today we are completely ordinary garden variety nothing special about us state and that's because that gas has now been locked up in the stars okay so that's idea number one for the young stars so i kind of like that idea we're still working on it but that's starting to i think it's really gelling in terms of both the theory and the observations old stars don't know i'll just say don't have a clean answer lots of ideas don't know but i what i'm most recently most excited well sorry second most excited about are the magenta stars we think those are star are probably pairs of stars that the black hole drove to merge so in other words this is an interaction that people didn't think about and when they merge they become really fat when they're really fat really big just really enormous then the tidal forces are bigger so they get pulled apart and that's what we see the magenta stars are the stars that we see the process of being disrupted the surfaces are being pulled apart so really exciting and probably uh connected in a way that i could not have anticipated to the ligo results okay that's fun okay now what am i really excited about this year we are excited because so2 is going through its closest approach right now and i cannot and again i cannot believe i'm here right now um but this event this so2 goes around every 16 years and there's an event that basically lasts six months so admittedly it's hard to be here it's a very special time but it's it's all the season and what are we trying to do we're trying to understand the curvature of space time how space and time get co-mingled or mixed when you get close to the black hole so there's that classic picture of what happens near black hole the funnel you see in science museums and that's what you're seeing here it's two dimensions of space and one dimension of time and we want to see how both light is affected by having to make its way out of that well what we call the potential well and how the star's orbit is affected okay i'm going to skip that because that's really crappy actually no i'm not i'm going to go back a little tacky but we're gonna do it uh you can see here actually what you're also seeing is how new this is the graphics are different and that's because we're in the middle of this so we um don't have the clean so you're getting the first look i'm not gonna show you the answer i can't i'm strictly sworn to secrecy but i want to show you this is a blown up version of what so2 might do it's going through this curvature of spacetime that closest approach the forms are most extreme to test you need to know the shape of the orbit so you basically need the history of having already seen it go once around and the next time it goes through closest approach is your opportunity to do this unique test so you can think of it as the wild west there are four theories of four fundamental forces gravity is one it's the least tested and nobody has ever tested it this near a supermassive black hole so you're just you're exploring an unknown frontier have no idea what's going to happen this is a little bit more detail red is the line of sight measurements green is the images and you have to measure when it's at a maximum and a minimum and i'm just going to say the shaded part is our galactic center season you can see it from six months roughly because the earth goes around the sun and so i'm just breathing a sigh of relief of thanks goodness all three events happened in that window and uh we'll probably be sharing our results when we finish with this window so it's an exciting exciting time for us all right you

Channel: World Science Festival

Views: 42,311

Rating: 4.8950438 out of 5

Keywords: Andrea Ghez, Nobel Prize, Nobel Prize in Physics 2020, Nobel Prize in Physics, Black Hole, Keck Telescope, Galactic Center, Kepler's law, supermassive black hole, Astronomy, gravitational waves, Free online courses, Albert Einstein, Science lecture, World Science U, WSU, World, Science, Festival

Id: YcPPGVigvZk

Length: 49min 34sec (2974 seconds)

Published: Wed Oct 07 2020