 Okay, so this is the highlight of our three-day celebration. It's my great pleasure to introduce today's speaker, Professor Andrea Gays. She's a professor at the University of California in Los Angeles, where she heads the UCLA Galactic Center Group, which she created, in fact. And of course she has many awards to her credit, but the most important perhaps is in 1920-20. She shared the Nobel Prize in Physics with Roger Penrose and Reinhard Genzel for their discoveries relating to black holes. And in particular, the citation reads about for the discovery of a supermassive compact object. At the center of our galaxy, that's a cautious way of calling a black hole. And her work has been in infrared astronomy with the Keck telescope, basically imaging the galactic center to see through the dust and to see the stars that are going around the black hole at the center of the galaxy, Sagittarius A star. And it's one of the conclusions is that it has a mass of four million solar masses so it's a very impressive achievement in observational astronomy. But in addition, I should add that she's only the fourth woman scientist to win the Physics Nobel Prize. And I should say something about black holes since not everybody in this audience is familiar with it. And it's also something that is close to my own research because black holes have now come to play a very central role in the recent explorations of quantum gravity and string theory, leading to very deep new concepts like holography. And it may be now hard to imagine that the reality of black holes was in question for a very long time. And it makes for a really fascinating study in the history of science. In fact, the Schwarzschild solution which describes the black hole was one of the simplest solutions of Einstein's equations which was found almost immediately. But there was enormous resistance to accepting what the solution was telling you. In fact, Einstein himself in 1939 published a paper and the purpose of that paper was to show that the essential result of this investigation is a clear understanding as to why the Schwarzschild singularity is by which we mean the horizon of the black hole. And it does not exist in physical reality. And this conclusion of Einstein was actually based on an incorrect argument. So it shows that the road in science is not always linear. It takes many twists and turns and it has taken several decades to establish the reality of black holes and incontrovertibly. And the work of Professor Gates is what has been central to this establishing observationally that a black hole actually does exist. And so sometimes easy to forget that it's now accepted wisdom. What is now accepted wisdom was really a matter of great intellectual raging debate for several decades. And I would say that it's a truly marvelous tribute to both to the sophistication and sensitivity of the observational tools, but also the remarkable power of our theoretical understanding of nature, which seemed very outlandish just a few few years ago, even to the leading figures in our field. So anyway, I think I would leave Professor Gates to explain to us all this impressive and dedicated work in observational astronomy. And apart from her, of course, achievements in science, she is I'm told that she's also swimming enthusiast and a master swimmer, and she also has an Italian connection. So we were in fact hoping to hold this ceremony in person and I was hoping that she could visit us in in person. So I hope she will visit ICTP sometime in the future for good Italian coffee and dinner and a swim in the Adriatic. But for now, we look forward to an inspiring talk from her about her personal journey to the black hole at the center of our galaxy. And I'm sure it will be a great inspiration for all of us to hear about her experiences and also about her science. So thank you. Thank you for that introduction. It's a pleasure to be with you this evening and to congratulate you on your accomplishments. You've worked incredibly hard and persevered in very unusual and trying times and earned diplomas and fields that are expanding our understanding of the world in which we live. At this moment you stand ready to begin your next chapter and you have a tremendous opportunity to reflect on your path forward. And the older I become the more I appreciate those moments in life when you can reflect on our purpose, our opportunities and our responsibilities. And it turns out that most organizations do some sort of self reflections to lay out a strategic plan for the next five years every five years or so. And early in life we have an obvious and and very common opportunities to do the same as we graduate from high school as we graduate from college and other advanced degrees. I'd like to suggest to you that finding opportunities for self reflection might be a useful way to think about going forward. We rarely understand what life holds in store for us too far in the future, but we can assess ourselves in our context along the way to better understand which roads we want to take next. So I've come to think that it's useful to ask three very specific questions every five years or so. First, what it is, what is it at this point in my life that I truly enjoy doing. In other words, what are my authentic passions and the pursuits that I'm really passionate enough to overcome the bumps in the road that are inevitable along the way. Two, what is it that I'd like to explore that's new that might require me to take some risks in my level of comfort and that might expand my understanding of what I don't know about that I might enjoy in the future. And then last but not least, how can I give back in a particular how can I help others in their journey in life. So many people help us along the way. So as we become more secure in our own journey it seems appropriate to think about how we can help others and theirs. I thought I would take this opportunity to share some of my own journey, a journey that now includes a Nobel Prize. And I think it's really appropriate to start off by saying I did not know at the beginning of my own journey what I wanted to do in life. I was fortunate to grow up in a family that valued education, so I never questioned that I would go to college and I was strongly encouraged to pursue my passions. But I had parents who are who were from very different backgrounds. My father was a European Jew who escaped persecution and World War II through immigration, who was highly educated and spent most of his most of his youth in big cities actually as it was introduced he was born in Rome, but actually spent most, most of his youth growing up in Geneva with a small foray to New York City during the war. In contrast, my mother grew up in a tiny blue collar town on the east coast of the United States was Catholic, didn't go to college and achieved much through very very hard work. Their differences meant that home was a very lively place full of passion around the things that they loved in common and friction around the differences in their background. And today I'm very great. I'm really grateful for having grown up in a household that shared a commitment to education of their children for the arts and creativity, but I'm equally grateful for the disagreements as they taught me an important early lesson about being comfortable with disagreement, being comfortable with discomfort effectively. And I was not one of those kids who knew exactly what they wanted to do but I today I can find the seeds of what led me to where I am today. For me, I find them in three early pieces at age for the first moon landings were happening and I according to the family legend announced that I wanted to be the first woman on the moon. And evidently the job is still open. But these events led me to be very curious about the universe, and in particular about questions of boundaries. What is the beginning and end of time. What is the edge of the universe. These questions fascinated me, but they also kept me up at night, because I couldn't resolve them as a young girl. At the same time I wanted to become a ballerina, but I soon learned that I didn't have the talent for the latter and got interested in choreography actually, all along the way, it was clear that I loved a good puzzle, as well as a good mystery. So putting together the pieces is clearly what scientists do, and it's also what choreographers do. Today, science has become my profession and appreciating dance has become my hobby. As I headed to college, it seemed to me that solving the mysteries of the universe was a math problem. So I actually began college as a math major. But I soon learned that the language of math was far more esoteric than I liked, and it was the language of physics that resonated with me. Today, that sounds like an easy switch, but like many of you, there were semesters or so of complete angst about what to major in. And this gave me a wonderful opportunity to explore topics and classes I hadn't before considered organic chemistry and philosophy or two that stick in my mind today. When I graduated from college I knew I wanted to become a scientist but I also knew that one of my greatest fears was that of public speaking. I could not introduce myself without my voice shaking. So in choosing graduate school I thought about schools that would give me access to the world's largest telescopes. But I also thought about places that I would not have to be a teaching assistant. In other words, I wouldn't have to stand up and speak in front of big audiences. Caltech offered me that chance, the chance to enter graduate school as a research assistance, which is what I thought I wanted. I enjoyed the rigor of classes and excitement of a new research group, but in my second year I was asked to give a lunch talk about my project, and I shook from my head to my toes throughout the whole presentation. I can guarantee you was absolutely awful. And my PhD advisor insisted at that point that it would be good for me to teach. And this is what exactly what I wanted to avoid. But I had gone to the point in my studies that I understood that speaking was not just about teaching, but an important thing for us to do as scientists. Now comes the interesting part in reflecting back on this. At Caltech, only professors at that time taught discussion sections and I had decided that if I was going to teach that I really wanted to teach freshman physics, or at least a discussion section for freshman physics. At the time I believe there were no female physics professors there. But I found that I could overcome my fears of teaching by bringing a passion or a desire to encourage young women into the sciences. I got to the point in my own career where there were very few women and I could see the importance of having teachers who look like you in the classroom. I succeeded in convincing the power that be to allow me to do this, and in doing so I discovered my own passion for teaching, one that quite frankly I had not anticipated and a lesson that I'm so grateful for. And scientifically what brought me to graduate school was an interest in black holes and an interest in developing new technique for observing the universe. For me black holes were an extension of my early ponderings about the universe, those early childhood questions about the beginning and end of time, and the edge of the universe. Black holes are on the one hand incredibly simple and then the other hand very complex. You can think actually as it was already mentioned you can think of a black hole as an object that has mass, but no finite size. And in fact, they're incredibly simple in the sense that they only have the three characteristics that you can describe mass spin and charge. So if you compare that to the complex set of characteristics that you can describe your family members with say black holes are very simple. And if you think about density, which is mass divided by volume, the density of these objects is infinite, because you've got something divided by zero. And in physics, whenever you have a number going to infinity. That's described as a singularity or effectively a giant red arrow that says that you do not have your description of the physical world correct there. So in this way, black holes are complex. And in fact black holes represent a fundamental frontier of our knowledge of the physical world. This interest in black holes led me at the beginning of graduate school to join a group that proposed to develop new ways of using large telescopes specifically ways that remove the blurring effects of the Earth's atmosphere to get very precise or sharp images. The scientific promise was that this technique would allow studies of galaxies that were thought to host very large and active black holes at their centers, what are known today as active galactic nearly I Unfortunately, the technique was over promised our technology wasn't where people thought it was today so I was faced with yet another interesting dilemma which was to pursue the technique or the science. I really was beginning to understand that I had a passion for opening new windows to study the universe I really thought that that was an interesting way to make progress with our knowledge. So I study, I chose the direction of the technology rather than the science, keeping an eye always on the progress that the technology was brain progressing to get back to my passion for black holes. I thought I was really making a left hand turn scientifically, I chose to understand how stars form and under what conditions they might not or might not form planetary systems. So I was understanding how stars like our sun form. And specifically I was interested in finding out whether or not they were formed in twins and pairs of stars binary stars. And so this was a fascinating topic but it really did feel like a left hand turn. This time, Keck Observatory, which is the largest observatory in the world was coming online. It's a collaboration between Caltech and the University of California. And I really, and it was just in the early phases, as I was finishing graduate school. So what I knew at that point is that what I wanted was a job that would give me access to this formidable instrument. And in fact, as I moved into my postgraduate work, I turned down two faculty jobs to get to a university that would allow me to have access to this facility. Today, recognizing how hard it is to get faculty jobs, I don't know what got into me to be willing to take that risk to be able to get to the University of California. Plus, UCLA in particular was interested in developing infrared detectors, which is key to doing some of the work. So at this point, actually, if it's okay, I'm going to share some some slides. So to just share some of this work directly. Okay, so at this, these are the telescopes, they're they're phenomenal instruments, they're up on the top of monarchy. And you can see lasers pointing out of that and that's really related to this development of no techniques. So at the, just as I got to UCLA, the technology had gotten to the point where you could observe the center of the galaxy. And what we asked that question is, is there a super massive black hole at the center of our own galaxy. And that I did with a small team in the beginning, we actually thought it would be only three, a three year program. And so it's rather remarkable to think that 25 years later we'll we're still doing this. And it's a team that's now grown from a small set of three to a team of roughly 20, 20 people at the core and a broader collaboration of 100 people. I'll come back to that later. In, there's actually two big picture perspectives on why this question was interesting. One is, you know, can we prove that really massive black holes exist in the universe. And here it's useful to comment that the concept of black holes really came from a theoretical pursuit. So that's what I see TP so good at is the theoretical piece. And from theory, we understood that stellar mass black holes form from the evolution of very massive stars. So observations that suggested that a much larger much more massive counterpart could exist in the universe. So rather than being roughly 10 times the mass of the sun these were a million to a billion times the mass of the sun and it was thought these were thought to exist at the center of galaxies and our galaxies a wonderful place to ask that question because it's the closest center of a galaxy that will ever have to examine the next closest galaxy is 100 times further away. So in this work, we're looking for proving the existence of supermassive black holes and ultimately testing our theories of gravity. But we're also interested in a more astronomy based rather than a more physics based perspective, which is what role do black holes play in the formation and evolution of galaxies. So if you guys have not understood that these things were so closely connected. People would ask would phrase the relationship between supermassive black holes and their host galaxy is which came first the black hole or the galaxy, sort of like the chicken or the egg question which came first. And today we understand that that's actually even the wrong framework that they seem to form together, because the mass of the black hole and the mass to the host galaxy seems to be related. It's sort of feedback mechanism that we can explore. So our galaxy is the best place to look. If you look up on a clear and dark night if you get away from the city lights you can see the plane of our Milky Way. And all the light is the are the stars in our galaxy and what runs through the middle is a dark lane that's created by dust in our galaxy. Dust is very good at absorbing light that our eyes can detect optical light. But it turns out if you go to longer wavelengths wavelengths where TV remote control work, you can actually penetrate through this in this dust and actually see the center of our galaxy. So this is why infrared astronomy and astrophysics is so important to the studies really the development of infrared detectors that were part of the key of doing this experiment. Another part, which I already alluded to was the techniques for overcoming the blurring effects of the Earth's atmosphere and in fact I remember when I was graduating from Caltech my advisor, you know that what what I had learned to do was take the twinkle out of stars. And this is a technology that has advanced tremendously over the last two, two decades. So our ability to see the universe by overcoming the Earth's atmosphere has has really radically changed moving from very simple techniques to much more sophisticated, much more expensive but much more powerful techniques. So we see that we've enabled our ability to see what's going on in the center of the box. One thing that I wanted to share with you about this work. If you were calling that I come to UCLA to get access to this telescope and to do these kinds of experiments. But when I propose the first experiment back in 1994 when I was beginning my faculty position and I put my first proposal to get telescope time it was actually turned down. I mean, one it was only a three year proposal. So here we're doing it 25 years later but we had a very simple and very straightforward approach to beginning this work and it was turned down because people didn't believe that this technology would work on the Keck telescope the Keck telescope had new architecture it's a segmented mirror so people didn't believe that these techniques would work so I would say that was one of the very first and major bumps along the road to where we are today. It took us a year to convince the August time allocation committee that this technique would actually work and and we've come back and we've come back actually with quite a vengeance. So we become quite a big user of Keck and and it's gone so much further than anything we could possibly have imagined. The goal of this work was to measure how the black hole affects the stars around it because you can't see black holes directly so you have to look for their presence indirectly so the objective was to see how these stars moved on the plane of the sky. And this is a quarter of the real estate I have to say this is one of my favorite movies in the world. And it shows that you can actually see these individual stars and while our original project was just to see line segments, you can see that they make complete orbits. The orbits are the most fundamental way of measuring the presence of mass, these stars move around the black hole for the same reason that planets orbit the sun. So using the same sort of physics and some senses from a physics perspective this experiment is actually quite straightforward, you're trying to use basic laws of gravity is to prove how much mass is located at the center of these orbits, and then the size of the orbit show you how small a volume so how small a region you've confined that mass to what this work has done has shown that there's 4 million times the mass of the sun inside a very small region. So before this work started we knew that there was a lot of mass inside a very large circle and in fact the circle so big that you just couldn't claim that it was a black hole. So this work has done has been to show that that 4 million times the mass the sun is confined to a region or a volume that's a factor of 10 million times smaller, a region that corresponds to roughly the size of our solar system. And if you think about this I mean to get a sense of scale our solar system is dominated dominated by the sun. So that's one times the mass the sun, and we've shown that within the same region that there's 4 million times more mass inside this volume. And this is advanced the evidence for the presence of these really massive, or as we call them the supermassive black holes by a factor of 10 million. So think about anything that you want increase in your own personal life be it your paycheck or I don't know some other example that you would like more of, and being able to advance it by a factor of 10 million. So this is a truly, this is a truly large step forward. Our initial objective that we wanted to do in the three years which was just to measure the line segments got us the first factor of 1000. And at that point, you know that was good, but there were still lots of questions and lots of critiques of the work or the idea that it could be a black hole and this is where science I think is so wonderful in terms of the way. It's constructed because I think that's what really pushed us to go further and it's also at that point what that we realized that the tech, the techniques that we were proposing actually worked far better than we could possibly have imagined and the technology that we were developing was continue to advance and we got to the next phase of measuring individual orbits which gave us yet another factor of 10,000 getting to this 10 million at the end of the day. So this has given us the best evidence that we have today for the existence of a super massive black hole, not only in our own galaxy, you know the words in our own backyard but anywhere in the universe. So today, you know the question is no longer do we have a super massive black hole but really now the. Now we've demonstrated the existence of this object we have a wonderful laboratory for understanding the, the role of black holes. Now, this, this is the result that the Nobel Prize was given for because the Nobel Prize wasn't celebrated in person I don't have the picture but I have one from the Crawford Prize and the reason I wanted to show this picture was to acknowledge that there's been two groups involved in this project independently for the last two decades and to really call out the importance of competition. The importance of diversity of viewpoints. It has been phenomenal to have these two groups in my opinion, working on these, these projects for the last 25 years or so. The, the work, although it's conceptually simple in actuality there are a lot of ways to go wrong. And the two groups have had different ideas about how to proceed. And while we're independent, the way science works of course is that we're constantly publishing or presenting our works at conference conferences so we're learning from one another. And there's nothing like a competitor to both keep you on your toes. And find your mistakes, and also get most effectively and, and fastest to the ultimate truth, which is what we're after as scientists. So I really wanted to, to recognize the real benefit of having competition in the field of science. In this project, one of the wonderful things about advances in technology is that we've actually uncovered more questions than answers. We've found at the center of the galaxy, an environment that's unlike any theory that's been predicted for what we should see. We have lots of ideas about the role that black holes should play in the growth and the environment around it. This animation shows just some of the stars that we've discovered it's color coded the kinds of stars and I'll just give you three quick examples of what's been so fun about this and I have to say when you find these regions, or these areas where you don't expect the answer for me that's the most interesting situation as a scientist to find these things that actually don't work. I've, I've often been surprised, or actually I should say that one of the things that fascinates me is that people outside of science are often surprised to understand that as a scientist, we're most interested in when things don't work. That that's they that this is the problem that actually these are the problems that drive forward our understanding is actually when things break down. So what's breaking down here is one of the, one of the predictions of really big black holes at center of galaxies is that there should be no young stars. And here I just wanted to recall that as a graduate student I got very interested in studying black holes and what we discovered at the center of the galaxy is that the most dominant population at the center of the galaxy are young stars. And to me this was also personally fascinating because it was a moment in which an earlier left what seemed to be a left hand turn for me in terms of my interest in black holes came back and was actually quite helpful in understanding the statistics that I had spent a large number of years studying how stars form. And it turns out that one of the things that you'll notice in this animation as it pulls back pulls back are that many of these young stars which are color coded green or awkward, awkward blue depending on how you is that there's these stars form a plane. So in fact, many of the ideas that we think are relevant today can be borrowed from from understanding how planets form around central stars because this looks like a scaled up solar system. So that's an interesting moment when we when it was really useful to have explored other ideas, other than what we would I thought was my primary mainline passion. There are other mysteries that I think I will not delve into unless people are interested in other afterwards, except to say that this has been a really gratifying experiment because there have been so many questions that have been that have come from these studies. So it's what I call technology driven discovery. And it really is like being a kid in a candy shop when these sorts of things happen. Now let me come back to a final some final just short remarks. Today, I find doing research in the university context incredibly gratifying as I have the opportunity to do cutting edge research that creates new knowledge about how the universe works, and at the same time I get to do. I get to create new knowledge in a completely different way through training the next generation of scientists. I love my job and while I've been a professor for 27 years my job is constantly evolving as I move from being a junior faculty to a more senior faculty. While my science has been very focused over this time period on a single spot at the center of our galaxy, one that is no wider than the width than a hair width at arms length. Our ability to see this region has changed radically over the last three decades. Over this time I've had to learn to go from doing my own coding to do the analysis to managing a large and international team. I've come to love and embrace the expression every challenges and opportunity and I hope that I have many more ahead of me. You are at the beginning of your professional lives and you are doing so at an incredibly unusual time. You face the challenges of coven. Hopefully this is given you strength and a perspective that is different from past graduates. Take advantage of the opportunities that lie ahead, learn from the challenges that you face, and take the time to self reflect on where you were going along the road that lies ahead. And I suggest once again these three fundamental questions. What is it that you enjoy. How can you take risks to explore new things and lastly, where are the opportunities for you to give back and help others along their journeys. So congratulations once again, may your futures be extraordinary and may you embody the changes our world needs. Thanks. Okay. Thank you very much for this wonderful talk. Both inspiring talk for also for the students to see how how major career in science like yours develops through this sentence and and leading to major discoveries in science. So I, we have time for questions now, please raise your raise your hand. There is a question from the audience here. Hello. Thank you for your nice presentation. I want to know, I want to know more about this telescope. Because as I understood you are illuminating the objects with the two different laser and you're using the information, information three techniques to capture the image. But first the center of a galaxy is a very far from us, and the laser can arrive this distance. And it will be nice for me to know more about this. Thank you. Thanks for the question. The center of the galaxy just to give some context is what we call 26,000 light years away from us. So in other words light takes 26,000 years to get from the center of the galaxy to us. And in fact, if you put this on a human context, it's quite profound. So if you think about what's happened, what was happening when light was halfway to us, the first human cave paintings were being made. We're seeing a history lesson. So you're absolutely correct, the laser itself is not reaching the center of the galaxy. And the current technique of adaptive optics, what you want to do is you want since we can we don't have bright stars that are near the center of the galaxy to tell us how to move a mirror to counteract the effects of the atmosphere. That mirror is called a deformable mirror. The way you can think about the problem and the solution is that if you think about the atmosphere being like a circus funhouse mirror so those circus funhouse mirrors warp your your your image. The solution is to put a second mirror in that can counteract to be the conjugate form to flatten out your image again. So we need to look at something bright to tell us how to move the mirror. And since there are no stars that are bright enough, what we do is we shine a laser up into the atmosphere and there's a fluke of nature that up at 90 kilometers. So nowhere near the distance of the galaxy this is just high in our own the Earth's there's a thin layer of sodium atoms that just happens that's deposited there through meteorites so when you go out, I don't know camping and you see the shooting star the shooting stars those are actually meteorites that are breaking up and depositing sodium atoms that because of the atmospheric structure gets trapped at 90 kilometers and this four kilometer wide so very narrow layer. So we take a these pictures behind me lasers that are tuned to a transition electronic transition in the sodium atom and force those sodium atoms to shine. So that's called that creates what's called a later laser artificial guide star. So we can look at this local very bright star to help us understand the blurring effects of the Earth's atmosphere is that that effect is very local so you're correcting what's underneath 90 kilometers which is the primary distortion for our view of the universe. Andrea, can you hear me. Yes, I'm being connected from Los Angeles neighbor. That's fabulous. I have some quick question, have some quick question, and probably two or three. And so, when two black holes much together do the single that it is remains separate or they also much together. They also merge so black holes merging create a new black hole and in fact, that's one of the ways in which we think black holes become more massive over time is through the merger process, both from in the case of the small black holes what we call the stellar mass black holes so pairs. I mean most stars actually start their lives off as twins. They're close enough and in particular if you have a third body you can drive these pairs of stars to merge and they'll, they'll form a larger black hole. Same thing with galaxies is that most galaxies build up their master collisions so two galaxies that have big central black holes in the middle. So will the galaxies will merge form a new galaxy, and the black to black holes will spiral into a center and form a slightly larger supermassive black hole. So two single that it is become one. Right. Yes, and in doing so they send out gravitational waves so there's been a lot of work that's been in the press and the last few years about the detection of gravitational waves. So those arise when these compact objects are are spiraling in and then ultimately merged that there's this ringing effect that we can detect here on earth. And is the first radius of Sagittarius A star constant or does it vary that it's first radius of Sagittarius A star is it constant or does it vary. So the constant just so everybody under understands the question that concept of the short shield radius is an abstract radius associated with black holes. And it's a very, it's actually a very important radius for a number of reasons. It's the last point that light can escape from the black hole. And it's also the point at which, if you compress mass to its short shield radius that gravity will overcome other all other known forces and force the object to become the black hole so actually it's a it's a point that I glossed over in the description of our work so if you want to show that there's mass inside a small volume there's actually a goal of getting to within that short shield radius. So if you want to be a skeptic you're still allowed to because we're not quite at the short shield radius. Okay, but the short shield radius to answer your question is tied only to the mass of the object. Mass is the only variable that determines the short shield radius. Masses are being engulfed by the black hole. So do you think it's a constant radius or does. Well so if your mass goes up your radius your short shield radius will go up. Okay, and my last question. My last question is this, in case of a planetary formation only 0.5% of the masses being converted to energy. In the case of a galaxy formation with a supermassive black hole like the Milky Way we have a dissent or suggested to be assessed. In the case of a galaxy act galactic formation with an active galactic new play the mass to radiation conversion is 11%. So in case of a planetary formation on the point 5% of the masses being converted to energy. In the case of a galaxy formation. 11% of the masses being converted to energy that is a ratio of one is to 22. Why this huge discrepancy you think. Okay, so. Let me also introduce some concepts to everybody else so you've asked about sagittarius Sagittarius, which is the constellation of the tea cups if you go out camping you look for the teapot it pours into the center of the galaxy. So that's why the name Sagittarius comes up in the discussion of the center of the galaxy. The Sagittarius a star is a source that's located at the center of the galaxy. It's a radio source. So seen at wavelengths even longer than what we're working at the infrared. It was discovered. Roughly a half a century ago. We all thought that this emission radio emission is associated with matter falling into the black hole through the event horizon. Okay, so this question about the energy that's coming out in a particular associated with this radio source, sagittarius. Sagittarius a star, actually very unfortunate name. It's actually sagittarius star asterisk, because people who discovered it come. We're borrowing the language from nuclear physics where asterisk means excited state. So what they were trying to say is that the gas wasn't an excited state that didn't look like a star so we should really call it sagittarius not a star, but our language has evolved to this unfortunate point where we're referring to an object that is absolutely not a star as sagittarius star. So it's been so striking about sagittarius star, if we really associate it with the black hole and it is spot on so in that animation of, of orbits, the location of the, the asterisk or star where the dynamical center is the focus of those three dimensional ellipses is absolutely on this radio source so we can associate the emission, the non gas like emission with material falling onto the black hole. And what's puzzled people as you're referring to for a very long time is that it's really faint. It doesn't, it doesn't behave in a way that you might expect for mass falling on to, or through the or at the location of the event horizon and this is this is really puzzled people for, for a very long time. It's what people call it under an under luminous version of these active galactic nuclei. And so it read ultimately comes to the question is how does matter fall through or towards the event horizon and radiate its emission. It's thought today that in the center of our galaxy and presumably in the center of most galaxies that compared to the range of galaxies were kind of a wimpy black hole simply because or the center of the galaxy has a wimpy black hole or on the scale of galaxies a low mass black hole simply because our galaxies also the central pieces is also relatively small. And so the solution to this today's thought, although I think there's still a big question mark here to have to do with the structure of the flow and the active galactic galaxies and many others like the stellar mass cases. There's a really clear accretion disk. So the flow is very confined, whereas in our own galaxy, it's a much more distributed amorphous or not quite spherical but sort of blown up. It allows the galactic the black hole to accrete in a much quieter way. So that's, that's, I mean, very, very, very broad terms, some of the thinking but it is still a very active area of research to understand the amount of energy that's emitted from matter falling in just outside the black hole. We had a question from from the president of the students. So let's give the priority to the graduates, please. Hello, it's, it's an honor to virtually meet you. My question is about the event horizon telescope collaboration. So, when we have a supermassive black hole in our own galaxy, why did we choose to image the one in 87. And do you plan to image the one in our own galaxy and what can that image potentially tell us. Thanks for asking this question. I mean we're really living in an extraordinary moment in terms of both astrophysical research but also black hole research where we have so many new experiments that are giving us insight. So this work that you're referring to from the event horizon telescope. It's, it's work that these are radio telescopes a moment ago we were talking about Sagittarius star being detected at radio wavelengths. And the way these techniques work is that you have to radio telescopes all around the world. So I work with telescopes that are one big piece of continuous means segmented but it's a it's a it's a single telescope at radio wavelengths, which are much longer wavelengths, you can actually combine the light from separate telescopes. So you can combine the telescopes that are all around the world. So you make this network. Okay. And in fact, this event horizon telescope originally was targeting the center of our galaxy, they wanted to image Sagittarius star that was the primary target. And then it was realized that one of the challenges with our own galaxy is that radio source is variable. It varies on short time scales. And it comes back to the size of the event horizon. So the, you can calculate the time it takes matter to go around just outside the event horizon that gives you sort of a time scale for variation and it turns out it's roughly half an hour. And a half an hour is much shorter than the time scale for the earth to rotate. So these radio techniques assume that the object is constant in brightness or structure over the time scale that the various telescopes see the object. So if you want to do this radio experiment you have to assume that the object is static or stationary or non variable on a 24 hour cycle, and that's simply not true for the center of our own galaxy. Actually, we've done the questions in a very nice way because we've already talked about the event horizon, and the event horizon is a scale and abstract size that depends only on mass. The more massive the black hole, the larger the event horizon. So it turns out that M87, a different galaxy, has a much more, is much more mat the black hole is much more massive. And so the radius is larger, and that corresponds to a time scale for getting all the way down, being longer. So it's on order of months rather than a half an hour. And now months is longer than the 24 hour period. So you can actually image it. So it's further away, but it's larger so the angle is about the same, but the time scales are longer. And that's really the heart so it was recognized just a few years ago that M87 from an imaging perspective was was easier. There are observations made with the event horizon telescope of our the center of our own galaxy just becomes a much harder imaging problem because you have to account for the this variation that at present has no clear structure. So it's really hard on it. I think that we will hear more from them over time. And in fact, it's one of the ways in which we have a collaboration with them is that you'd like to do this experiment when the activity from matter accreting onto through the event horizon is low, so that the gravitational measurements can be seen more clearly, because otherwise this accretion emission can swamp. So in fact you can use the infrared measurements to tell you when the black hole is active and not use those measurements, or at least use them in a in an informed way. So it's harder, but it doesn't mean that we won't be hearing from them. And let's take two more questions that is one from from the audience here. Hi. Nice to meet you virtually. Thank you for this great talk. It's really an honor to ask my questions as any physicist I as many physicists I would say I turned to physics by reading about black holes so fascinating subject. I'd like to know a bit more about the mechanism behind the formation of such supermassive black holes. So that's another area in which there's been a lot of progress. So as I very briefly alluded to people used to frame this as which came first did did the black hole form, and then seed the galaxy, or did the galaxy form and through collisions form the black holes. But this relationship that we now see today where the mass of the black hole seems to be very correlated with the mass of the central component of the galaxy known as the bulge suggests that they had to form together synergistically. So the thinking today is that in the early universe. At the time when we're when we're thinking about something that's very simple and that you're looking at just small fluctuations that give rise to the formation of galaxies that that process forms both the central core being which turns into the black hole as well as the galaxy that this forms together. So that is, that is the current thinking, although again, it's still an active area of research to really understand that process and detail, and that and and how that relationship is maintained over time so it's not just in the formation that that relationship where the black hole is roughly point one percent of the mass of the central component of the galaxy known as the bulge, but it's maintained over its evolution. Nuschia maybe you can you send your question maybe you can ask online Nuschia is next diploma student she's an astrophysicist so Hi, Andrea. Professor thank you so much for your talk it was really great to hear from you. So yeah I'm one of the organizers of the reunion that actually led into this ceremony where we're celebrating the diploma graduates. So my question is sort of themed with the reunion but also kind of looking forward based on all the wonderful questions you started with for the graduates. So, you know in my home country which is Sri Lanka, and in also many other countries, parents they often would like their children to either work or become something that has direct impact, or a more visible social impact as an example to be a doctor or an engineer. And I would like to ask you how would you suggest how we can convince our communities that subjects like astrophysics and astronomy, or generally physics can actually fundamentally impactful and can actually make a social impact. I have two answers for this from very different perspectives. One is that fields like astronomy and astrophysics playing incredibly important role. I often view them as what I would call gateway science. We live in a society that depends on science and technology on stem fields in general. And yet we also have a society that's incredibly phobic of math and science. And astronomy has this interesting opportunity of being sort of the kinder and gentler the one that where kids have always looked up and gotten curious so it's the hook. It's the way of engaging and educating a really broad array of students about science and technology and beyond you know how to be critical about information so given that we're living in the age of misinformation. We're having introductory courses on astronomy, very powerful UCLA as is as the cases in many other universities. Astronomy is actually the most popular way of satisfying the general education requirements, I think, 20 to 25% of all our students take an astronomy class before they graduate. And that societal role of educating people about stem I think this this arena is incredibly important in terms of science education. There's another perspective on this so if you look at what we train our students to do. There was an alert there was a little discussion of this just before I came online in terms of what our students do. Certainly not, you know, not all of our students become professors, it's not reasonable to assume that they would but we actually train our students for an incredibly wide range of fields. That find our students desirable and extremely well trained. I find my students these days often going off into big data analytics, our data sets are enormous and complicated so the skill the tool sets that we use are very desirable by the fields of big data, big data analytics. Our students are very well trained in techniques that are of desire to the military, you know, techniques that you want to look up and down are certainly of use to multiple fields not only astronomy but communication that these the depth of optics techniques are actually used in vision communications the military so our students go off into those fields. As well as finance, actually we've had a brilliant collaboration with a professor in finance, because they care about that modeling the stock market as it varies and sad J star has such erratic variability that we can borrowed techniques from the business world so I've now had several students use be hired in in the financial world simply because of their time very time analysis tools. So I think that's an independent argument that in fact is a great training and a very solid training for a large and interesting swath of industry. Thank you very much. So we have the last question, ancient funny. Now, thank you professor guess for your nice talk. I actually had a couple of questions but I'm just speaking two of them are in the observational points of the viewer hearing the point that to test general activity near these super massive black hole because you know that the new Tony mechanics works very well at this point. And also, can we say that we are seeing just one black hole is just always binary black hole. Thank you so much. Thanks for the questions there. This is definitely really where we are today in terms of the quest scientific questions that we're probing. Roughly a decade ago it became clear that the measurements were precise enough that other people started to predict that we should be able to get into this arena that we should be able to get into the these tests of how gravity works near a super massive black hole. And there are a couple that are within reach. So the first one is what's known as the gravitational redshift so looking at the impact of the mixing of space and time that occurs near a black hole on how photons light packets make it from the star itself to us. So those those photons lose energy as they climb out of the gravitational well so you should be able to see these that loss in our spectroscopic measurements. So it was predicted. Oh, I should say one more thing which is to get a seat at the table to do this kind of work. You have to be you have to have a clean measurement all the way around of the orbit. And the best one is so to I mentioned so to I think when I was showing that movie. It's, it's orbital period is 16 years so you need imaging measurements that give you the, the, the location of the star and the plane of the sky as well as spectroscopic measurements that allow you to measure the speed along your line of sight over the whole orbit. So that's 16 years so it's already a 16 year investment. And then the next time it goes through closest approach because this is on a quite eccentric orbit, then you're in a position to measure this gravitational redshift. So that occurred in 2018. So 2018 for us was an incredibly exciting year. And there were three critical measurements that we had to make within a six month period. To me, you actually was a really interesting moment and the experiment where here you are you're looking at light that's been traveling to you for 26,000 years and you're excited about a six month period, where you get to make these critical measurements. And you could see it clear as day this deviation from the Newtonian expectation and see the effects of this gravitational redshift in in 2018. So that was actually that was an interesting year from the point of view of competition as well, I have to say because there were three points that you had to measure. The other team went early, tried to convince us to publish together, we chose to wait and get all the measurements in the papers do people want to read on one thing so that was an interesting moment in terms of what really coming to to ask yourself what is your scientific style, and are you willing to wait to get it to collect all the data to really see it at that risk. It's sort of the, the put your science ahead of your desire to be first moment. And I'm glad we did because these measurements are these measurements are hard. With that done, the next thing that you can look for is the procession what's known as the procession of the periapse which is really looking at how the object itself moves through space time as opposed to the journey of the photon from the object to us. And what's so exciting about what we're seeing today is the prediction is that the orbit should precess in the direction of the orbit. In other words, if you think about like a kid spiral graph toy where they make orbits but the whole thing just rotates like a flower pattern. It goes and there's a very clear prediction in one direction and in what one rate. And, and that you should start to see as it comes out of closest approach and heads towards furthest approach. So furthest approach happens in 2026. So you kind of predict that you should start to see it and then the signal just gets stronger and stronger as time progresses. And in the last year or two we've begun to see a signal, but what's so surprising about what we've seen in the early days is that it seems to be going in the opposite direction at twice the rate. Okay, so we haven't published this because this is the interesting phase where you have to convince yourself that this is physics, and not the accumulation of small errors. But if you think about this experiment, you have to put 2526 years of data, all in the same reference frame frame or coordinate system. And if you had asked me 25 years ago if I thought that was an exciting topic I would have told you, absolutely not. But it's the thing that limits us or our ability to understand whether or not this is physics or a inaccuracy in your methodology. To go on, we can make more and more precise measurement but it also makes more and more demands that your framework your methodology is absolutely right to if you go back and reanalyze all the assumptions the underlying assumptions to make sure that any of these rotations aren't from your approach or the visual I have of this which is really strong is like it's going around your car and kicking the tires to make sure that everything your house is in order. And I find this a really interesting phase of science where you have an interesting signal and you really have to ask yourself, is this physics, or is this something that you could, you know, you could improve on. So if you take this seriously. And I say, with a huge grain of salt. That would mean that you've detected dark matter at the center of the galaxy. Now there are predictions that there should be dark matter surrounding the central black hole, and even reasons to believe that the amount that this rotation or procession suggests. There will be lots of reasons to believe that underlying assumptions can create such a signal. So, like I say I find, I find this. Yeah, one of the most this this moment and this kind of moment has happened a lot in this experiment where you really have to think deeply about your results is really thrilling. So there's more to come. Okay, and I think we're coming to close. Maybe I can ask you a couple of questions. First of all, how close is the closest approach in terms of the social radius of the black hole that you have 500 times the commercial radius. And what are the prospects of measuring the spin of this black hole. With check there's not a chance. So this is potentially the realm of this next generation of telescopes, or any other technique that would get you to orbits of stars that are on shorter periods, you really need to get closer both to introduce a stronger signal, but also because you want the time scales to be shorter so that you can measure these effects on more than one orbit to make sure again that you haven't gone awry. So one of the fundamental goals that we've been aiming at with the development of the 30 meter telescope, but you could equivalently talk about the European extremely large telescope or the giant Magellan telescope. Yeah, so there is a lot of exciting science waiting in the future. Okay, so I think we are coming to an end I should perhaps you're not able to see the people who are sitting in this audience. You only see the people who are on zoom. I should just tell you that we have students from something like 3040 countries. And some of them quite underrepresented in, let's say an American University. And we are very happy that in this particular year in ICTP, about 50% are women so we are really doing well in terms of stem training for gender balance instead. Fabulous. Yes, go ahead please. Oh fabulous and maybe actually on that note I should have mentioned in this, you know along the orbit of SO2 I can often think about plotting my career but I can also plot the personal events that have happened in my life. I'm at the birth of my two kids so throughout this I've actually had I have two sons one who's a sophomore in high school and one who's entering his junior year in college, and I think like many women I've worried about how one balances, or does both having a family and having a son and I would say this is another place in my life where I've learned in unexpected corners. I think what one learns from being a parent, you really benefits you in terms of being an advisor and being an empathetic mentor to other people. And the other way in which I have to say that I've really appreciated having kids is through putting them in daycare UCLA as many universities have has a great daycare system so it enabled me to meet people in other fields, which has helped me, both personally and professionally. So I'm delighted to hear that you have such a diverse student body in so many ways and I hope many of you will consider applying to UCLA in your future years should you be interested. That would be great. Okay, so thank you very much, Professor. Yes, this was really wonderful to have you here. Thank you very much for your time. And as I said, you have a long come to visit us next time you're in Italy or in Europe. And thank you.