Understanding the Unseen Universe

Let. Me thank, our speak are, those. Individuals that make these. These. Lectures, free, for all of us last, week I thank research, discovery, innovation the VP for research at, the University of Arizona and T, P they've been so. The flagship, folks. That have been paying, for, for. Most of the costs here but, in addition to that there's. A list of individuals, and organizations. That have been supporting, this for many years and today. I'd like to just point out two of them one. Of them is a Marshall, Foundation, and the other one is hello Aloha, hello. Aloha, investment, the. Person, that's the president, of hollow hollow is Michael Kassar I don't know how many of you know Michael, Michael. Is incredible. We have a theater, in here that I think in large part is due, to Michaels. Funding. And, and. Not only funding but pushing hard for that thing to be successful, he's, given, money so that we have amazing. Athletics. At the University of Arizona and he, supported. The College of Science and other in other entities, of the university, with. Great. Gusto, as he would say he. Believes in, Arts. And Sciences, greatly, he. Is probably, the most extraordinary, individual, I know you know like like seven languages, and I hate him for it and and. He, got a PhD, from in chemical, engineering and, a master's from. Harvard, and an MBA so, anyway he's one of those individuals, that make you feel small, every. Time you talk to him but, not really because he is he. Is always the same Michael Kassar in his Hawaiian shirt, he, is really. All Tucson, and the Marshall. Foundation, many, of you have been here for a long time and know, that if. You go, from Park, Avenue, -. Let's say fourth Street and even less, that. Place, was not very nice ten, years ago the, Marshall, Foundation, has created, an environment around, the University, of Arizona that, has made it well coming that, has supported, the university's. Mission and in, addition to that supports. The university's. Mission by giving funds, for. Fellowships, and scholarships and. Endowments, for faculty and, I want to thank both hello Aloha and the Marshall foundation, for, all that they do for our community, thank you. So. Today we're we're, in for, a, treat. You're. Gonna hear for y'all or o sell, let. Me let me just say what my job is about I mostly. Hang around and. Tell. People that, things. Are all great but one of the things that I do which. Makes my job really, extraordinary. Is that when people come, to the University, of Arizona and they apply, for the job or we're trying to bring them to the U of A I get, to chat with them. More. Or less right off the bat, and. When I met for y'all it's one of those things. That, you sit there in front of. Intelligence. And Grace and quality, and you go holy smokes, if I, had to compete with fer y'all for a job anywhere, I'd. Be, screwed. That's, a scientific term by the way. So. For y'all is, in, astronomy, when, I first chatted. With her yah she was chatting. About a job in physics, but. She's comfortable, in in. The field of physics and astronomy astrophysics, is. Is, probably. The best way of talking. About that she's. An absolute expert in black holes and neutron stars. She. Is wanted, by every, committee. International. That is out there for. Her for. Her intelligence. And, for her advice and, and where astrophysics. Should go. Her. The details of. Her. Degrees, are, really. Irrelevant because you're gonna hear her today and you're gonna say wow this. Is something really, extraordinary, but, just, so you know that I do know it, she. Did get her bachelor's degree from Columbia she, got. The job the degree with Cooma Sam Lauda and, she. Went to Niels Bohr where she got a master's she was, and she, got her PhD at Harvard. She, came to us because we're. As good as she is. And. And, it is time for me to remind you that every time that NSF. Shows. The rankings, of. The. Quality, of programs. Astronomy. Always ranks number one in the country, so. For, y'all is one of the reasons, why that's the case. So. Please please, welcome, for, yellow cell who's going to tell us Oh before I do that because I think it's important, it is important, to just say the following today's. Lecture, is a second, of what, we would more or less called a scientific, method the, first lecture, for those of you that were here pointed. Out the importance. Of. Double-blind. Experiments. The statistics. Of, doing. Work with. Randomized. Tests, and how. In the end you, can only approach. Certainty. I think. The lecture was extraordinary and, it very clearly pointed, out the, importance, of the generation.

Of Statistics, now, just to make it clear to all of you. Double-blind. Experiments. And. Randomized. Experiments. Are not only the purview of biology, I was, talking to my fellow Dean. At the College of Science, Elliot Shu who's, a particle. Physicist who pointed out that, in particle physics blind, experiments. Have been used for a long time to get rid of bias of physicists, so it comes in all, flavors. But, today, we're, going to talk about what, in science, we call laws and. Even. Though we may not know why these laws exist these, are these, are issues in science that we take that. We can use to try to understand, the parts of the universe that we cannot see and, I. Will leave it at that and I will let Professor, ozell described, what she's going to talk about thank you. Thank. You very much for that gracious introduction. Indeed. Degrees don't matter what is fun is exploring. The universe and that's what I'm hoping to do with you tonight, so. We're. Continuing, on our journey, on. Searching. For certainty last. Week indeed, we we heard about experimenting. And this. Week I want to tell you about how, as astronomers. And astrophysicists, we. Can say things about the parts of the universe that we can't directly see but. Before I tell you how and are we certain and, what is the search for certainty, how what does it involve I want, to begin with a few facts, about our universe. First. Is the, fact that our. Observations. With, many telescopes in, many different wavelengths, of many. Different types of objects, have told us that, the. Universe by. And large is. Occupied. By things. We don't see so, to. Be more precise, we. Now say that 68%, of, the universe is is, made. Up of dark energy, so when we count up all the sources, of matter and energy in the universe. 68%. Of it turns out to be a form of energy that we don't have direct understanding. Of this. Is the energy. That makes our universe. Expand, faster than it should and. We. Have many different observations. That point to that of. The. Type that is more matter like, what we've, found out is that. 27%. So. About, a factor, of five more, than, normal matter is dark, matter dark matter. Is, the. Type of matter that we can feel through its gravitational, interaction. It doesn't. Emit light at, all in fact it doesn't have any interactions. Magnetic. Electromagnetic. Trickle or any. Other type of interaction. Apart. From its gravitational, interaction. That we can directly. Observe with our telescopes. Of. Everything. We look at 5%. Or, 4.8%. To, be more precise is, things. That we have tested, meaning. Stuff. That makes up our bodies, our planet. Stars. The. Stuff between stars, gas clouds, and. Anything. Else in the universe that we can that shines, and. Whose. Light reaches our telescopes. Now. All this, four-and-a-half, percent even. Among, the things that we say, are normal, matter, there. Is a class of objects, that we don't see directly and this, is the black holes, so.

What, Are black holes well black, holes are collapsed, dead objects. They. Can be formed from collapsed, stars like, things that are maybe 20 times mass more, massive than our Sun or. They. Can be at the Centers of galaxies. In fact when we look around us, in our, galaxy there are dozens of, black, holes that are more like this small, type what we call stellar mass and. Around. Us when we look at each and every galaxy, at, its center there is there are black holes whose, masses, reach 10, billion. Times the mass of our Sun. Ok. So. Different. Types of unseen, things dark energy, dark matter black holes and I said let me just begin with a few facts about the universe now. Let's stop and take stock for a second. How. Many of you and please don't, be shy about this think, that I'm downright CRAZY. Show. Of hands please. Okay. At least one person, is honest. Okay. How many of you think this is more like a Star, Trek kind, of thing that I'm, not crazy but maybe it's science fiction as opposed to science that this is not astronomy okay. There are there are some who, are admitting, to that well, at the very least when I said, all of this none, of you walked out at least I couldn't see anybody walking out. None. Of you laughed so. You, probably, thought to yourself hmm. There. Must be a way of knowing, things that we don't see directly. And she. Must know that probably. That's what you thought. Indeed. There, are some rules, of the game and we, apply these rules, pretty. Diligently, in order, to gain. An understanding of, the universe whether or not light. From these objects, reach our telescopes, directly. What. I would call rule number one is the. Exploration. Phase, we. Do our best to, build bigger better. And different. Types, of telescopes, in, order, to look far in order to look all over and. In. Order to gain all bits, and pieces of information that, we can we. Don't just build optical, telescopes, we also build radio telescopes, we also build x-ray telescopes, because there are things, in the universe that are at different temperatures, that that, shine differently. We. Also put, telescopes in. Orbit. Around. The, Earth for, example, this image right here is. A piece, of what is called the Hubble Ultra Deep Field. Meaning. This is from the Hubble Space Telescope and it. Is from a patch of sky that, Hubble stared, at for a very, very long period, of time and. What. We saw work. Were. Thousands. Of galaxies. You. Might say hmm, how far is this are we really looking as far as we should well. This was a patch of sky. That. To. Our naked I would, look like nothing. In fact it was chosen to be one of the emptiest. Parts, of the sky so. Far away that. It. Would look like a. Nothing. God in the distance. Completely. Empty so, we. Are in the doing our best in terms of looking, far looking deep and exploring. In every, way that we can but. There is a second, principle that we follow which, is not exploration. But it is more, about our. Methodology. And, I would say this is even more important. Than the, exploration. One and. I'm. Going to call it do, try it at home. Understand. How it works, and then. Apply it to the other parts, of the universe so. If I can make a tabletop, experiment. In a laboratory and, understand, how objects, move out or how forces, between them behave. I can. For sure apply. This to objects, in the sky or if I can now look, at things, in the solar system and. Understand. How. Stars. Behave in my galaxy, for. Sure I can assume not just my neighboring galaxy but, a galaxy halfway. Across the universe is, also going to behave the same way okay. So. Unlike. The usual warning. That we hear kids don't try it at home we, actually do want to try it at home okay. So. One. Of this, one. Of these ideas is that motion. In the universe is deterministic. I should, be able to understand, why, a particular. Phenomenon. Happened, okay. I'll, give you an example. Everything. That we have done every experiment, that we've done and this is not even a new idea in fact it's one of the pillars stones of modern science, tells, us that objects. Left, to their own devices. Travel. In a straight line okay. If there is no force on them no, influence of another body on them in in whichever, way that. They will travel in a straight line, if. I now take the same object.

And. It. Does this I. Know. For a fact that. There, is another object that, curved, its path. Otherwise. It would have traveled in a straight line do. I know exactly. What the nature of the interaction, between, this. And this is not, really but, I can tell you that there is one and in, fact it's even more powerful than that if this, is some bright, shiny object. Versus. Something quite, dim that I can't directly see I know. I can still tell that it's there in fact this is the whole, idea, behind Planet. 9 not. Pluto, Pluto is you know it's. Still kind of demoted. The. Real, planet. 9 in our solar system, believe. It or not when. We look at the motions. Of the outer solar system objects. They, are pointing, to the presence, of a body a, planet. 9 that is most, likely twice, the mass of the earth and, quite. Far away farther, than Pluto's, orbit. That. Must be, influencing. The those bodies, have, we seen it directly, no are we trying to yes there are now two separate, observational. Campaigns, searching. The outer solar, system. Mosaicing. Where where it where we think it should be and trying. To get direct evidence for it but, this has happened before. Neptune. Was predicted, before it was seen and in, fact it's the it's, just the backbone of our understanding, so, since, I talked about the solar system, let, me tell you a little bit more about how motion. In the solar system, forms. Our understanding. Of how gravity works and, how I'm now going to use it to. Tell you more about dark, matter and more about black holes. So. This. Is a view, of the solar system, we usually don't have we, are actually in the plane with all these orbiting. Planets, so, we get more, partial. Views, of their orbits, but if we could see it from the top, you. Would see the inner four planets, orbiting. Fairly rapidly, and the speed, diminishing. As you go farther, and farther out okay. Now. It's. The observations. Of planetary. Motion that. Started, but. What I would call physical, sciences. Or at, the very least observational. Astronomy, started, by understanding how. Objects. In the or and planets in the solar system move, okay, so. What. Do you see they are moving in nearly circular orbits. With. An object move, around, if it, was left to its own devices no. There has got to be a central, body that, is keeping it in place so. This. Was in fact the it's, it's so monumental, that, it is considered, to be the launching. Point of the scientific, revolution it. Was the, Copernican. View of the, solar system, that said the, Sun must be at the center okay, this. Is the first level of understanding in, building, a theory but, I what I would call an observational. Model simply. Finding, a pattern that explains, the data it, might not be quantitative. It might not be the most basic, understanding. But, certainly, putting the Sun at the center explains. All of that. Now. Let's look at it a little bit more closely, now. The Sun is at the center but. As data. Accumulated, over, time and more. And more planetary. Orbits, were determined. Now. Scientists. Could not, only look at where, they are but. How, the Peary, how their period, which is the amount of time a planet. Takes to complete an orbit around the Sun and their. Distance, from the Sun relate. To one another okay. For. Circular, orbits this is just the radius the distance from the Sun but, in principle, orbits can be elliptical so. When we plot these data what. We show. Cube. Of the semi-major axis. Semi-major, axis, is the distance from the Sun and square. Of the orbital period, and these. Are all, the. Planets. In the solar system you see that they lie on a straight. Line ok. So. Now. We, are starting to build empirical. Evidence and this, is indeed what now, Kepler, used, to. Build his laws of planetary motion. This, is what I would call the second stage I, don't. Understand. Why, the square of the period is related. To the, cube. Of the of the, radius or the distance, but. I know that they are and not, just that but, I know, what. Mass, should, be holding, these orbits, in place I know what is holding these planets, in place and that, is the mass of the Sun so now simply. By plotting, these data on a straight. Line, we, can measure the mass of the Sun we. Never have to go with a scale and weigh it I mean. We are right I mean this is going with a scale and and weighing it in in a way.

Kepler's. Laws are really, fundamental in, our understanding of the universe in universe, I'm going to keep coming back to this again and again, now. As. A mini, detour, I'm going to also take you through the next two stages which. Is going, from Kepler, to a physical, law and that, we owe to Newton. Newton. Was the one who formulated. The specific, force on bodies, and not. Just that but the force between. Objects. That are interacting, through the gravitational force, he, formulated. It he said that, force is going to be as big, as de as the. One that is a plot the two basically, that are applying this force on each other separated. By their distance squared the, formula doesn't matter its but, what, is very interesting, is that he's. Now thinking about the interaction. Between two bodies how it affects each one of them, and now going from an empirical, law to a physical, law, oh I, understand. Where it's coming from moment, okay. So. This is also a big, revolution, in. Astronomy. But. Are, we certainly, not, Newton is right are we, now have. We now completed. Our full. Understanding. Of how we are exploring, the universe and how gravity works, no. Certainly not in, fact, physical. Laws are there to be revised in our search for certainty. We. Get, to an understanding, where we can formulate, a physical, law then. We make predictions of, how. It should work in situations, that we understand. Go. Make measurements, and then. They, either, corroborate. Or, they. Refute, our theories, okay. So. What, happened to Newton well Newton's law certainly, work on certain scales but. They're. Not there to be. To, be the final, word on this in, fact they, were broken, when I spine came around. Now. This. Is Einstein's. Law of gravity, it. Looks nothing like Newton's, right so. What. Einstein said, is that, actually. All this, thing about forces. And, objects. Pulling and pushing on each other this is all wrong he, came up with a completely, different formulation. A geometrical. Theory which. We call general. Relativity, he. Said that. Masses. Of all. All sizes. Even. The smallest ones to black holes to entire. Galaxies. Warp. The space-time, around them so, that other, objects. That are simply, help around them follow. What, they think are straight lines on this warped space-time so. Think, of a sheet four people holding every corner you put a mass at the center it bends, that that sheet so, now if I take a letter.

Little, Ball and roll, it on the sheet, is it going to do it's just going to go and follow, the curvature of that sheet right so, a size formulation. Is completely, different why, did he do that what was wrong with Newton's, laws. Two. Things one. Is the. Practical. Reason, Newton's. Laws worked, on predicting. The, orbits, of all. Planets. Except. The procession of mercury, mercury. Is the innermost planet, it is elliptical and that, ellipse rotates. A little bit as time goes on. Newton's. Law predicted. The precession, but not not, the right magnitude, and I sign you about this but. That really wasn't his motivation, he wasn't trying to fix it when he came out with this theory if he was trying to fix that he would have added a little term to Newton's equation, and be like I'm, done. That's. Not what he did he, was actually working, in the Patent Office in Switzerland. And, it. Was the time when precise clocks, were becoming available in, Switzerland, and trains were. Becoming. More and more common. He. Reviewed. A lot of patents for synchronization, of, clocks across, different, train stations, how, do you know that the clock at this train station in Bern, is this, is showing the same time as in, this train station in Zurich, he. Kept thinking about synchronization. Of clocks he - he kept thinking about relativity, of time he. Formulated. His theory, of special relativity and. Then. He realized that's. Not compatible, with Newton's, law of gravity. So. One. Of the most fruitful, endeavors, we can embark on as scientists. Is when we have two well-established theories. And we, find a place, where they contradict, one another that's. Where we should go. So. So. That's physical. Laws can be revised in light of new data in, light of contradicting. Theories, and we, keep doing that in our search for a certainty. Okay. Let's. Go back to dark, matter, black holes I promised, you some of that and I said we, have tools we can apply them and. One. Of those tools is going, to be Kepler's, laws. So. Where. Do we know the. Existence of dark matter from, we. Know it from what, we call the, rotation. Curves of galaxies, what. Does that mean, there. Is a type. Of galaxy that's commonly, seen in the universe called a spiral galaxy so. This is a face on view we can see it's, not a it's not the closest, one but I like, it because you can see the spiral, arms here and, you. Can also imagine, this, galaxy. Rotating, about its center right, here and the. Whole galaxy. Actually. Wrote spins, around this, axis. Okay, all spiral, galaxies, do that without, an exception, so, just. Like planets. Orbiting, the Sun or other stars. Entire. Galaxies. Spin. Around their own axis, okay, so. This. Is now our neighbor, Andromeda it's. A slightly more edge-on view and I. Want. To show you how. We actually rotate. The obtain. These rotation. Curves, so. This. Is due to the. Famous, astronomer, Vera, Rubin, of the. Last century. One. Of the things she noticed, is that as as. We. Look further, and further out in the galaxy so. Smaller. Orbits, near, the center larger. Orbits, where the the, stellar, disk ends, and all the, way out here, where there seems to be a lot less matter certainly, a lot less light, a lot less stars. The. Speed. With, which these. Objects. Rotate these stars rotate very. So. If, we. Make, a prediction, using. Kepler's laws, about, how. How, fast. This should this should turn. There. Isn't very there, isn't a lot of mass interior. To it so it, should be pretty slow but, as you go further and further out as you get more and more mass holding. All these stars in place. Then. The speed should increase but. As you go farther out just, like the outer planets. Are now rotating, more slowly. And, the, inner planets. Kepler's. Laws tell us that the speed should, decrease, okay, so this red line here is the Keplerian, prediction. Interestingly. If, you are paying attention to, what this y axis, is this, is the rotation, speed in kilometers. Per second, so. The. Sun is. Well. This is not our galaxy, but it's about, somewhere, here, in, our own galaxy the Milky Way which also is a spiral galaxy so. Right. Now as we speak we are being hurled around at 200, kilometers, per second, isn't. That fun. Anyway. The numbers don't matter what, matters, is that the. Data that they collected, Vera Rubin and her colleagues, collected. Said. Something. Completely, different. Indeed. The, speed increased, at first but. Then it stayed there as if. More, and more and more mass, was, holding. This galaxy, in place and allowing, it to rotate in, this with. These huge speeds without breaking, apart or matter flying, off so. Very. Simple. Application of, Kepler's, laws either. Option. A I have, more mass, there, than I can see there, is some form of matter there, that, it's not stars it's not yes it's not dust it, doesn't, shine but. It is there and I can see it I mean, and and I can feel.

It In the rotation, Europe chirps capillary. In prediction, dark, matter, or. What. Is option D. What. Happened to Newton his, law was wrong so. What if now. The. Galaxy, is all there is to it. And this, is Kepler and this. Is a new law of gravity, that's possible, right we. Have to weigh both possibilities. And in. Fact we do. Just. Like we, have revised, even. Einstein's, equations, over time we, look for different modifications, that could explain this phenomenon. Without, resorting. To things that we don't see so. The top equation is what I showed you first what is I'm formulated, first it, was in his first trial, he, actually, tried many different forms and at, some point he, put in an equation which we, now call a, term, in the equation which we now call the cosmological constant, here. And then. He went on to call it his biggest blunder he. Said that is absolutely, not there but, now with the accelerated. Expansion of, the universe we know that term is there the cosmological constant, or something, like it exists, so. Why stop here what. If there are other terms in the equation, that that, simply weren't discovered, before or that, weren't motivated by, data before this. Is only one form among many that I could have written. So. What. Do we do now. We have a framework we. Apply Kepler's laws, something's. Got to give either there is dark matter or there. Is modification. To our law. Of gravity. We. Turn elsewhere we, say okay if it is dark matter we're, going to have to see it in not just individual. Galaxies, and their rotation, curves but, in clusters, of galaxies. Huge. Bodies, in the universe that, contain, hundreds, of galaxies, and. This is a gallery this, is. These. Are all individual. Clusters, some of them are, named. Up here so. What, do we do we, go count up the lights that they have in, terms. Of everything that emits then. We go away them. Through. Their gravitational, interactions. And we compare, the two is. Their dark matter or is there not there, is now overwhelming. Evidence that, there, is far, more five. To one in fact, more. Dark matter or more, matter in the universe than, the standard. Luminous, matter that we're that. We are used, to. We. Didn't stop there we, started, devising, experiments. To, tell the difference, between the, option a dark matter and option, B the, revised law of gravity. This. Is a famous example, called the bullet cluster we. Didn't make this happen but, once, we saw that it was there and your. Way scientists, were involved, in this in, this observation we. Certainly knew what to do with it this is a very interesting, case these are now two clusters, of galaxies. That have collided, with one another in fact they have collided and have, gone past each other, dark. Matter doesn't, have any interaction. Other than gravitational, so, it can light through more easily, normal. Matter has. Other interactions. Electromagnetic. For example, so it's more viscous, there is more friction so, it moves through a little bit more slowly if, this. Is dark matter then. What, we expect to see is that, more, mass, should. Go through one another and less, light should go through one another is that. What happened. So. This. Is a, Chandra. X-ray image, showing. You where the majority of the emitting. Gases because, they ran into one another this, is a shocked, gasp and there's, a lot of light coming out of here let's. Compare, it to the mass map of the bullet cluster. The. Mass is further. Away so there is one Center, belonging, to the smaller cluster, here and one, Center belonging. To the bigger cluster, here so, if I now overlay them. You. See that, most. Of the mass, has. Gone farther apart and the, light is interior, to it. Ha. Is, this, the smoking, gun is that why we call it the bullet cluster. Not. Really. There. Is a way to explain, this with modified, gravity but. It looks, a little bit different than explaining, it with dark matter, so. Even. Though this was a very. Big. Evidence, I would say in in. Favor of dark matter even, this didn't settle the debate so, the search goes on so the search for certainty, goes. On and we. Devise, different.

Experiments, Of course in the mean time we also set, up. Experiments. Where we can detect dark matter particles. Directly we look for what it could be at CERN, at the LHC we. Do, tabletop, experiments. We do Dark, Matter interactions. If it has any sort, of interaction, can we see it with with, other devices so. That's. That's how we're going to keep, on looking for more and more and more evidence. For a dark matter and at some point either be completely convinced, or. Find. An alternative, which we are happy with. Ok. Switching gears I want. To tell you about the other unseen in the universe. Which. Are black holes let. Me introduce you to one that I love. In particular. It's. The one at the center of our own galaxy. It's called Sagittarius, a star because. It's toward the constellation. Sagittarius. And it, was initially discovered, as a radio, source in the sky, which. Is this, this, object right here it, looks a little bright in this in this picture but actually, it's kind of wimpy, it's. Not a particularly. Bright, source like, we've, we've seen many brighter, sources, across. Our galaxy, but this is the dead center. Of our galaxy so, this, is a dynamical. Center and this, is this. Is that radio source. Now. Like. Good scientists, we want to take a closer look at the center of our galaxy so over, time we've built bigger telescopes, better, technologies. Like adaptive, optics, and. We. Have gathered, lots. And lots and lots of data, on, stars. That. Are in the vicinity. Of, our galactic center okay. The star cluster is called s I know it is super imaginative. And. The. Stars are called 101-102, on, etc, etc it's. But. What. I'm going to show you now is real data even. Though it has been turned, into a time-lapse movie. These. Data were collected, over 23. Years the. Time we'll be running here, and each, time you see a dot here, let. Me run it for you it. Is. Real, data, so these are, individual. Stars. At. The center of our galaxy. 26,000. Light-years away, and. We. Just, like our. Forefathers. The. Early scientists. Followed. Mars's. Orbit and, Juke, Jupiter's, orbit we. Are now following, these, Celler orbits, that are very, far away very dim we, switch to infrared light so we can see a little bit further we use adaptive optics, and. At. The end you. Probably saw, that, this. Diligent. Repeated. Observation. Of the same field again, and again and again to, trace out the orbits, have. Given us two very fruitful, results. Which. Is that the closest. Two stars have completed, a full orbit over these 23, years. What. Are they orbiting, hmm. I don't know I, don't. See anything deal. But. Maybe just maybe. By. Using their orbits, I can get some information about, how. Big the thing they're orbiting is. What. Would I use any, ideas. Kepler's. Laws, yeah.

Kepler's, Laws I I know if. Something. Is orbiting something, else how, big the math should be that holds it in place okay. It. Is four, million, times. The mass of the Sun what, is holding, these orbits, in place and. Yet these orbits, are tiny and. They. Are very far away but. If. The. Object, that is four million times the mass of the Sun was. Anything, like normal, stars that we see that. Object, would shine brighter, than our Sun and, I don't mean at the distance of the Sun I mean from. The center of our galaxy it. Would look brighter it would overwhelm the, amount. Of light that we get from our own Sun. Certainly. That's not happening, instead, it's a relatively. Wimpy, radio source okay. So. Are, we convinced. Yay, black, holes. Certainly. A lot of mass it's. Not shining. It. It. Looks black and Einstein's. Theory. Predicts. The existence of, these objects, that that collapse to nothing and at the end of their lives so. Are we done not, really, because. We are searching for a certainty we, actually, go, the next step if these are black holes not, only, should they contain. A lot of mass in a small volume and look dark but, they should have a very peculiar. Property, called an event horizon it, is the point of no return that's, basically. The definition of, a black hole, not. Every massive object, that is not emitting a lot of light is a black hole it, needs to be compact, enough its gravitational, pull on its environment, should be strong. Enough that at, some distance, from the black hole even. Light cannot. Make it out so, there is a complete, absorption. Of light, into. The interior. Therefore. The center, of such a thing should look black, okay. This. Is an animation, that's showing, you what would happen if, I was shining light on a black hole if. The light, rays were. Sufficiently. Far from the black hole. Would be bent a little bit just, like that those. Motions. In the bent space-time. The fabric, but, they would go on their way if, they're. Coming too close see. What happens, they get bent so much that they end up in this circle, of no return, and that. Leaves, that that, signature, that, should, be the. Signature, of the black hole okay. Now. This, is the very basics, of the theory but, we want to put. This into practice we, want to see if black holes are for aizen's so, what. We discovered, in the recent year, long not that recent I was, actually doing my PhD one when I first calculated. This but. Not, only horizons. Should, exist, but, at with the right wavelength of light we should be able to see them so. What. We what I calculated, this isn't in year 2000. Is that, if. You look at long radio, wavelengths there.

Is A lot of opaque material around. The black hole but. If you start looking at shorter, and shorter wavelengths at, around a millimeter, that, gas turns transparent, and. The. Hole in the middle should appear, so. If we could take an actual. Picture of a black hole not in visible wavelengths, but, at one millimeter. Our. Theories. Predict, that. A, we. Should be able to see down to the horizon and, to if. It, is a black hole with an event horizon there. Should be a hole in that image okay. This, is year 2000. Since. Then, we've. Built many, many different. Sophisticated. Computer, simulations. Of black. Holes and their environments. Trying, to understand, how black holes behave, how the gas around it behaves so. As gas gets trapped in this, well. Potential. While going down to the black, hole for. A while it heats, up and it emits light and that light is able to get away we've, built computer, models, of exactly. How this light shines how much of it can we see and, this. Right. Here is a compilation, from, many. Groups around the world six different types, of simulations six, different types of. Algorithms. Physical. Models, and these. Are all very expensive, simulations, each. One of them has been run on a supercomputer. Upper-left, one is is, ours, right here at the U of A my groups work. And you. Can see many different predictions. Why. Is this important. It's important, because if, we're going to go on this, huge. Fishing, expedition. Taking. A picture of a black hole and seeing if it has a hole in the center we want to know what we're looking for right, we. Want to be able to interpret, our data we. Didn't stop at this at, the U of A using, our computer, cluster, out Elgato which. Was supported by the, National. Science Foundation as, well as the VPR's office. We. Looked, at how this image could change over time so, not just the still but, if we did, subsequent. Shots. Of like images. Of the black hole at the center of our galaxy or. In nearby, galaxies. Like in m87. We. Basically made movies, of how, these images would change okay. So these. Are our predictions. It. Turns out that, predicting. Something, and actually measuring, it turns out to be quite different especially. In this case, because. The, images, that we were predicting, turned out to be so small, in the sky that. It would be the equivalent of putting a doughnut on the moon and asking, us to take a picture, of it with cameras, from here on earth okay. Like literally. As a size of a doughnut at the distance of the moon. It. Also turns, out that the telescope, that has sufficient. Resolution to, carry, out this experiment, is as big as the earth. We. Went to funding agencies, we said can we build a big telescope. They. Said no. No. We didn't, we didn't, even try but we said huh okay, given. We can't build a telescope literally. As big as the earth how about figuratively. As big as the earth and that, that, is a concept, called interferometry. What. You do is you, put a telescope here you put a telescope there, you'll, look at the sky at the same time you record the data you record it very faithfully. Time. Targets, so you know exactly when your signal arrived then. You bring the these two data pieces together, you. Combine it and it. Is, as if you looked, at the source with a telescope, as big, as the separation, between the two in, terms. Of collecting, power of course you don't have it your dishes your dish but, in terms of angular, resolution how. Big a telescope. You have how, fine, a scale, you can resolve in the sky it serves, that purpose, okay. So. This. Is just a graphic, that explains, it if I want to take a picture of this black hole I put, one radio telescope, here remember, millimeter is the is the magic number millimeter. Wavelength, of light I, put. One here. Light. Arrives. At these telescopes at slightly different times, I record. It and then I, correlated. After the fact and. Hopefully. I have an image that looks like a hole in the sky. Or. Looks like one of those images, from the image library that I showed you just a couple of minutes ago okay.

So. We've. Been working on this for, about 15. Years we've. Been working on building, a global. Telescope. An earth. Sight what we call an earth-sized, array for, those of you who were in my talk a couple, years ago maybe, you heard some of the. Ongoing. Efforts. In building this array and we, were just getting, ready in, 2017. To make the first, round, of observations. That involved, all these, telescopes across, the globe, what. Did we do well. We're using our own telescope, on Mount Graham SMT, and this year actually we're working on putting a second, dish on Kitt Peak so. This. Year's observations. Are going to have to, Arizona telescopes. We. Also outfitted. The, telescope, in the South Pole so we can literally span, the, the size of the earth. This. Is the Greenland telescope. Our northernmost, point, and our southernmost point, -, in the Atacama, Desert in, Chile Alma, and apex, Alma itself is an array it's a big, powerful, telescope. That that, we are lucky, enough to use for this experiment. And. A bunch of others LMT. In Mexico, is a very important, site you can see how it's connected to all these other sites so. We can have all these pairs that. Are connecting. The information. And giving, us more and more of that image that we're looking for this. Took many years and, it, took a lot of effort so just just, one of those that I really, like my. Colleague, Dan. Maroney here at the University, of Arizona this. Is from one of his trips to the South Pole he's actually there right now with two of his graduate students, this. Is a couple years ago this is the South Pole telescope and. On. A sunny. Wonderfully. Warm. Day what. They did was put this receiver, you can barely make it out in purple. Into. The telescope, so that they were able to record, the right kind of data and and do this experiment, you might, also see, his grad student, right here John Hahn. It. Is so much fun to be a graduate, student in our department. It. Took years, of effort, so for those of you who are at the lecture last. Week, Joanna, talked about these. Control. Trials, and double-blind, experiments. In astronomy, we don't have the luxury of controlling, the phenomenon, but we certainly have the luxury, of designing. Our experiments. Here. Is my prediction here.

Is The right, place to look the right type of data to get and if it's option, a I will know and if it's option B I will know so. It is a it's certainly an. Experimental. Science not, just an observational. Science when you spend so much time building, the right type of telescopes. Equipment, experiments. In order to answer questions. So. In. 2017. We did our first full, array observations. Even, though the array keeps growing, like I said Kitt Peak is coming online this year. What. We mean by full array is having, both the east west and the north, south large. Coverage, that will give us enough resolution and. You. Can see from the happy faces, in these pictures that weather was good on seven. Different sites, and. We. Need good weather because. Millimeter, wavelength, gets absorbed by moisture, in the atmosphere so. We. Were lucky enough to get five nights of data and. At. Least I'm bringing, you up to speed a little bit on what, happened, in the intervening two years this is April of 2017. We. Collected, three and a half petabytes, of data over, those five nights. It's. An extraordinary, amount, and. Since. Then what. Have we been doing well we've been first. We, literally, had to physically, ship the data, because. It's, so much data that you, can't actually transfer. It over. The internet. From. Location. A to location B, remember we, have to collect all of these data centrally, from the South Pole from Greenland, from everywhere, and, combine, it and search, for where, they match up, it's. So much data FedEx, took, it to different places for us, so. These, are some. Of those hard drives being created, and. Being shipped and this, is the one of the correlation, centers, one of the two correlation, centers with disc, after disc after, disc of data okay. We. Did combine it, we. Calibrated. It we, wanted, to make sure that. Each. Telescope, behaved, as we expected, that it didn't get, too little light for whatever technical. Problem, that. Calibration, step is is very important, and. In the intervening, year, and a half we've been working, super hard on. Interpreting. The data so. As. I said correlate, calibrate. Interpret. And we. Are very close unfortunately. I won't be able to show you what, we see tonight. But. We're close I can tell you that, later. The spring, we. Will be able to release our first set of data with, some results about black. Holes and and what their environments, look like, so. I'm excited about that but, I'm. Just going to leave you with this my, daughter is here in the audience tonight, and she, can tell you the the past year and a half is looking. More and more like searching, for serenity, as in. Let's, just be done with this, I'm working around the clock as, opposed. To searching, for a certainty but really. The question is. Do. Two black holes look anything like we predicted, is, it going to be one of these images is it, going to be anything that is. Similar. To it, is. Einstein, right in this particular, prediction, or is. There a place where Einstein's, theory of gravity also breaks down because it's incompatible, with our understanding, of the microscopic, world hopefully. We'll. Find something, interesting that. I can share with you but. I have to say, failing. Is not a bad option because. It's job security, if, we. If. We say we. Understand, everything, about the universe let's, go home that, that is not going to be fun so we're, just gonna keep on searching, for more and more evidence. For. Our theories, and hopefully. Some will fail thank, you. You. You.

2019-02-03 21:22

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