 It is my great pleasure now to introduce an outstanding scientist who believes that regardless of when and where you were born, how you were raised or your gender, science is something that is transcendent and ingrained in our culture much like art. A woman who has never been comfortable being siloed, she started her career in philosophy and came later to science fascinated by the undeniable and universal truths it carries. She's the Clare Toe Professor of Physics and Astronomy at Barnard College of Columbia University. Yay! She's also the chair and founding director of the science studios at Pioneer Works and editor-in-chief of the broadcast. A Guggenheim fellow, she's contributed to an understanding of black holes, the cosmology of extra dimensions and gravitational waves in the shape of space-time. She's the presenter of the Nova feature Black Hole Apocalypse, which aired on PBS and in fact she was the first female presenter on Nova in over 35 years. A winner of a pen prize for her first work of fiction, her latest book is entitled Black Hole Survival Guide to bring us on an exciting journey through black holes and the expanding cosmos. It is my great pleasure to welcome to the stage, Jana Levin. Merci beaucoup pour l'invitation. Je suis si heureuse d'être là. That's the extent of my French. I practiced that. It is truly a privilege to be here to honor Maryland and if you don't know Maryland personally, she's not just brilliant, she's buoyant. She's really been a great inspiration to me and I'm delighted to be here. I'm here to give you a 15 minute tour of black holes in the universe and I'm going to start, there's a lot of them, spoiler alert. I'm going to start with a little bit of context. This is not a cartoon. This is actual data that we assess of our galaxy, the Milky Way and right now we're going to move into the Milky Way and I want to try to plant us a little bit about where we live. So our Milky Way galaxy has 300 billion stars and we now have learned and quite recently that most of them have multiple planets. That means that there are more planets than there are stars in the Milky Way galaxy. And here we are invigorated by the search for life. This is our ordinary star and if you look at our own solar system, it's pretty obvious that the planets are varied in ways that are astounding. You know, we have sulfur rains on Venus and we have a Jupiter-like gas planet and we have a rocky earth, our little pleasant little haven. And the exoplanets seem to be the same as though nature has tried every possibility and continues to try every possibility. I think at this point it's impossible to imagine that only here on earth has life emerged. Yet, as far as we know to date, we're the only one scanning the sky. And here we are scanning the sky. I've been scanning it for hundreds of years since Galileo invented the telescope and what we've compiled is basically a silent movie of the universe and it's gorgeous and it's stunning and it's a testament to who we are. I know there's this sense of dread that we're insignificant but that is a testament to who we are from this little rock. That is not a cartoon. That's all real data observations that we place as accurately as we can. And if you have the privilege to go to the American Museum of Natural History on a private tour, you can ask them to go anywhere. You can be like, can we go to Elvis and Tari and they'll take you there. It's pretty fabulous. Now it was exciting to me to think that in this silent movie of the universe the way that we understand the universe is through light and yet some of the most interesting phenomena are completely dark. And my favorite are black holes. They are utterly dark and they are nearly unobservable. And it was about 100 years ago, more than 100 years ago when Einstein first discussed and began imagining space-time and his general theory of relativity. It was proposed to him that there was this mathematical solution which only decades later earned the title of black holes. And Einstein thought, nature will protect us from their formation. He thought the math was beautiful but they weren't real. And nature finds a way just as nature is exploring all the possibilities for planets. Nature figured out a way how to make black holes. And it's by killing off a few stars. The way that nature makes black holes is by finding incredibly massive stars. Stars are buoyant and luminous and because they're churning up a lot of thermonuclear fuel and when they run out they collapse under their own weight. And if the core is heavy enough it might explode in a supernova, some stunning event. But the remnant, if it's heavy, has no choice but to continue to collapse catastrophically. And it's this beautiful phenomenon in which the object becomes so dense that it creates like a waterfall and space-time is what you should really imagine. As though the space-time is raining down into this deformation of the geometry. And the star itself can no more sit there than it can race outward at the speed of light. The star itself is forced to continue to collapse. What happens to it after that we don't know. It's a mystery. But we know that the star is gone. There is nothing there. It leaves behind an archaeological record on the shape of space-time that we call the event horizon. What it really is is it's an empty shadow. You should not think of a black hole as a dense object. You should think of it as nothing. You should think of it as a place. It's not a thing. There's nothing there. And that's crazy, but it's real. But we had not until this century really observed black holes. I know you might think we have, but what we have is really only inadvertently observed black holes. And here's a little, by the way, I should say I'm always queuing you if these are mathematical or cartoons. Nothing in here is a cartoon. It's either an observation or it's formal mathematics. This is a formal mathematical simulation of what it would be like. If you were an astronaut who had not paid attention when I told you not to go near that big shadow. And you would see, like, this astronaut is actually orbiting. What I want you to understand is this astronaut has now crossed the event horizon, is inside the black hole, and it is no more dramatic than stepping into the shadow of a tree because there's nothing there. They're just crossing into a dark, empty space. But I also want to impress upon you not just that the black hole is nothing, but that it's dark on the outside and not necessarily dark on the inside. Because all the light from the galaxy rains down on you and can catch up to you as you're facing your imminent death. And you can see the evolution of the future of the entire galaxy raining down at you. You can find out what happens with the climate crisis. You can watch civilizations come and go. You can see stars born and die. And all of that in the flash of a second for you, what might be microseconds or a flash of a second. The way I like to show this little visual, which is, again, a very mathematical model, all the light gets concentrated as you go towards the center of a black hole. So you see this, like, bright flash of light, like the near-death experience, the light at the end of the tunnel, only it's an absolutely total death experience. Now, black holes are nothing. They're a place they're not a thing. They're bright on the inside, dark on the outside. They're also small. And this is one of the misunderstandings about black holes, that there are these weapons of mass destruction. But actually, black holes are tiny. If you were to look at a black hole 60 times the mass of our sun, imagine how big that is. It would be about, I was going to, okay, let me rephrase. Let's say 10 times the mass of the sun. That would be about 60 kilometers across the shadow of the event horizon. That's sprawling city-sized, okay? Now, imagine trying to observe a dark, empty nothingness, 60 kilometers across thousands of light-years away. It's impossible. We have never directly observed a dead star in the form of a black hole. It's never happened. When we talk that we've seen black holes, what we've really seen is the mayhem that they cause around them and we indirectly deduce that they exist. But we have never seen one of those, laid our eyes on the shadow. You need to illuminate something to see the shadow, just like you need the sun to shine to see the shadow of a tree, right? The shadow doesn't exist in darkness. So lots of these black holes against dark background, they're just completely imperceptible. There was this very clever idea that dated back to Einstein right after he announced his finally, when he finally got it right, that buffoon kept getting it wrong. So he publishes his general theory of relativity. It's gorgeous. It's stunning. And Einstein often said he was not afraid to get things wrong, and that's something that I really miss in science. People would say, Einstein, your famous name is going to be in these papers. You have to be very careful, and he would laugh. He said, my name is on a lot of wrong papers. Couldn't care. But he did propose the existence of what we now call gravitational waves. I'm actually going to back this up and show this again. So the idea that Einstein proposed immediately after publishing his general theory of relativity, he said this is the most important thing next. They're called gravitational waves. And the idea was, let's say you have something like two black holes in orbit around each other. They're going to be like mallets on a drum, and the drum is space-time. And space-time is going to ring like a drum when these mallets move, and it's going to ring in response to the motion, the shape, the size of the mallets. Literally, if you were the same astronaut who didn't pay attention when they approached the big event horizon and you were nearby the collision of two black holes, the squeezing and stretching of the shape of space could actually ignite your auditory mechanism. You could hear it conceivably, even in the absence of air. So this is very much like hearing the universe for the first time. And this was proposed. It was 1915, 1916. And a few ambitious observers decided to go out and have a listen. It took them 50 years in the centenary of the year Einstein published, The General Theory of Relativity. I don't know how. Ray Weiss, who now has a Nobel Prize, said to me just, I want it to be the centenary. That's what I want. And this is what happened. About a billion point three years ago, two black holes were in the final throes of their lives together. This is, in fact, a mathematical model. It's not a cartoon. And they were, it's drastically slowed down. This is about 20 milliseconds in their final orbits together. They might have been together a billion years. But it's only in the final stage of their orbits that they're ringing space-time strongly enough that there's any aspiration for us to hear it at our great distance, 1.3 billion light years away. When that gravitational wave signal, this ringing in the shape of space-time, left those colliding black holes, multicellular organisms were differentiating on the Earth. By the time it entered a nearby solar system, Einstein was born. By the time it entered our solar system, a group of experimentalists were on a 50-year project to try to make the centenary out of homage to Ray Weiss. And they were messing with the instrument, which they decided wasn't ready. And at the final hour, they put their instruments down and they went home exhausted, mercifully leaving the instrument locked in observing mode. Within the span of an hour, the signal that had traveled 1.3 billion years washed over the Earth. It went past the antenna in Louisiana, which I haven't really told you the details about, but it's quite an extraordinary story. And at the speed of light, washed over Washington State where the second instrument recorded it. 8.30 in the morning, Ray Weiss, who's then in his 80s started this as a young man, woke up, looked at the red alarm and said, what the hell is this? And they studied the data and they realized for the first time they have detected black holes. No light from anything else around them. They're completely dark. That event happened in complete darkness. 100% of the energy came out in the ringing of space time. It was the most powerful event human beings have ever detected since the Big Bang. And none of it came out in light. It's the soundtrack to the universe. Now I want all of you to imagine what this sounds like. And then I want all of you to be really disappointed when I play it for you. Are you ready? And this is drastically slowed down. It goes on for just a handful of milliseconds, okay? It's in the human auditory range, which is just a coincidence that black holes roughly, these were about 30 times the mass of the sun, they ring space time in the frequency range of the piano. It's in the human auditory range. But we can't hear it because it's so fast. So this is drastically slowed down. Okay, are you ready to be disappointed? Here we go. Who wants to hear that again? I don't know if I got back. Oh, no, not that far back. That's it. Now I want to mention that there's a very famous renowned French physicist, Professor Thibaud Demour who is at the IHES, who did some of the most foundational work in predicting the sounds of black holes colliding. I was very much a student of his work from afar, and it's just this coincidence that he happens to be a very prominent IHES professor. But he was doing this decades before the detection. Then a couple of years later, so this is 2015, Nobel Prizes are awarded, there's fanfare, it's on the cover of the New York Times. Then in 2019, humanity takes its first ever picture of a black hole. It is not a dead star. This thing is humongous, okay? We have a black hole, which we call a supermassive black hole, the center of our galaxy. It's 26,000 light years away. It's called Sagittarius A star because the star indicates the black hole because it's in the direction of the constellation, Sagittarius, from our perspective. It weighs over four million times the mass of the sun, but it's less than 20 times the width of the sun across. So I imagine 20 times the width of the sun, and you're jamming over four million times the mass in that tiny space. And it's 26,000 light years away. Imagine how tiny that thing is. To try to take a picture of it is equivalent to resolving a piece of fruit on the moon. Or as the experimentalist, the Event Horizon Telescope Project that announced this result put it. It's equivalent to reading the date on a quarter in San Francisco from New York City. And what they had to do to resolve that was build basically a network of telescopes as big as the entire Earth. And the main candidate was Sagittarius A star, our supermassive black hole. We don't know how it got there. We don't know what it's doing there. It's big. It's not a dead star. But what they actually took a picture of, and this was very exciting. It was at the National Press Club in DC. And when they made the announcement, over a billion people around the globe watched this together. It was this transcendent moment, which is what's so beautiful about science. It was true for everybody under the sun, literally. And what they actually took a picture of was the only other possible candidate in the universe that could have taken a picture of, which was called the M87 star. It's a black hole in the center of a nearby galaxy named M87 because it's the 87th object in the Messier catalog. Messier was a French astronomer who made a list of objects that were so boring you should avoid looking at them. And this was the 87th. M87 star has a black hole 6.5 billion times the mass of the sun. I would say it's about solar system sized in extent in terms of its shadow. It's 55 million light years away. And if you compare our black hole, Sagittarius A star, are super massive to this one, they're about the same size in the sky. That one's bigger, but further. And that was the one they actually captured a picture of. What you're looking at is the bright light that's just allowing us to see the shadow cast just like without a blazing sun, you can't see the shadow of a tree. And this is the century of black hole discoveries. This is the first time we have ever as a human species laid eyes on black holes. I don't wanna speak for other species. I don't know what they're looking at. There might be planets around black holes. Now to put this in context, these are real galaxies. This is from the Hubble satellite mission. There are as many galaxies in the observable universe as there are stars in the Milky Way. That's hundreds of billions. And very nearly every single one of them has a super massive black hole at its center. That's hundreds of billions of super massive black holes. They're not dead stars. We don't know how they got there. We don't know how they formed. But we do know more and more that they are responsible for sculpting the galaxies, for shaping the history, for instance of the Milky Way, for creating an environment hospitable for life because they blow out a lot of gas and dust and they modulate the galaxy. We are here because that black hole is in our past. And that black hole is also in our future because in a billion years or so we're gonna collide with Andromeda. Andromeda has a massive black hole at its center. Our black holes will merge. The entire solar system will be kicked about together though. We won't break apart, likely, very unlikely. We'll probably be held together and just be on some crazy orbit around a new super massive black hole. And unless the expansion of the universe rips us apart, that's our ultimate fate. We are orbiting a black hole. We are falling into a black hole. And we will eventually fall into that black hole. So black holes are our past, they're our future. By then, we'll be gone. But maybe there will be some species in our solar system that we'll be able to experience, maybe unwillingly, with a terrible sense of existential dread. Exactly what happens inside a black hole. Thank you so much. Thank you. Thank you.