 Well, so it is 10 a.m. now, so I won't quite start the talk yet, but I will just say to everybody. Hello. Welcome to Science Circle. I recognize many of the names here, so I know that most people here are regulars. Is anyone here? Is there anybody here who hasn't been to a Science Circle talk before? I always wonder how good we are at picking up new people. Ah, good. Excellent. So we have at least one new person. So I know that next, not next weekend, tomorrow there's the Jess birthday party. Chantal or Jess, are there any more talks this year coming up for Science Center? You can say I could look at the calendar and find out for myself, but I figure I can be lazy and ask Chantal and Jess. Yeah. Yeah, there's the panel next week, which sadly I will not be able to be there for because I have a wedding in real life that I'm going to. And I think if memory serves that panel is what are the big outstanding questions in your field, basically. I think that's the panel more or less. Yes, a big unanswered questions, which is a cool topic. I would have a hard time picking just one. I have to be honest for astronomy and then various subsets of astronomy. There's several big questions that we have. But yes. Yeah, I don't know. Is there going to be a neuroscience person there? Anyway, yeah. I mean, it's like so depending on who you ask, some people would probably say the biggest question is the whole are we alone thing? Is there life elsewhere in the galaxy? But if you ask me, I might say, well, what's the nature of dark energy? And that's on the completely different scale. So yeah, all kinds of crazy stuff out there. On a more prosaic level, there's the whole tension in the Hubble constant going on, which I gave a talk about here a year or two ago, and it's only gotten more firm that there is a discrepancy in measuring the Hubble constant. Yeah, the Fermi paradox is a good one. This fear that we're answering the Fermi paradox experimentally right now on earth by showing that the technological civilization self-destructs in short order. But we'll see. That's too depressing. Anyway, I will get started here. So hello everybody. Welcome to the science circle. I am Professor Knapp currently of Westminster College, although it turns out that Westminster College, like a lot of small liberal arts colleges in the US is having financial problems. So after next year, they're going to eliminate my position and I'm going to be looking for jobs next year, which is kind of frustrating. But there you go. Anyway, so, but for now, I'm still at Westminster College. And today I am going to talk about the first direct image of a black hole. And there it is. You see it. Okay. Any questions? I'm done. Not really. So yes, there's a lot to say about this image of a black hole. And of course I like the title staring into the abyss because there's the classic Nietzsche quote that if you stare into the abyss, it'll stare back at you. So the black hole is watching you and just keep that in mind while you while you say things because the black hole is watching. Well, all right, so to start with, I'm going to talk about two different things. Well, two related things. One is the nature of black holes at the center of galaxies because that's we're looking at and two, how do we actually, what is, you know, how did we actually see this black hole? So we have, we, for 20 years now, we've been pretty confident that most, you know, approximately all but probably, you know, you don't want to say all that most big galaxies have a supermassive black hole at their core. And when we say supermassive, we mean million or more times the mass of the sun. Excuse me, I have a the tail end of a cough. So I'm going to apologize. I'll cough occasionally. I'll try to mute when I cough, but if I fail, you'll hear it. So there's black holes come in various different sizes. In fact, black hole demographics I think is a talk that given here, but the supermassive ones are at cores of galaxies. Before last month, the best evidence we had for a supermassive black hole at the core of a galaxy was in our own galaxy. And we had good evidence in lots of galaxies. But in our own galaxy, two different groups. So one group here is the UCLA Galactic Center group led by Andrea Gez is a group also led by Genzel that have tracked over the course. And you can see here it's over the course of 20 years now have tracked the positions of stars right at the center of our galaxy. And for context here, this little line here shows you the scale it says 0.1 arc seconds I'll talk about an arc second a little later, but more to the point it's 0.04 parsecs. For comparison, the distance from the Sun to Alpha Centauri is 1.3 parsecs. So that's like a factor of 30 bigger than this line here is the distance from the Sun to Alpha Centauri. So these stars are packed way closer together than our stars in our neighborhood at the galaxy. But this is right at the center of the galaxy. Also context 800 astronomical units. Earth's orbit is one AU that's what an AU is around the sun and Neptune the farthest planet. Don't give me that Pluto stuff. Neptune's orbit is about 30 AU. Well, alright, so over 20 years they have tracked the positions of several stars near the center of our galaxy. It's a tour de force of observational technique. There's various challenges that include dust in the way, trying to get enough resolution to see it. But using infrared light they have tracked the orbits of a bunch of these stars and each one of these ellipses here the various spots are different observations taken at different times over the last 20 years. And what they have done is they've noticed that all of these stars are orbiting in ellipses around a point right there. Maybe if I make my leaves are green it'll be easier to see. Yeah, whatever. But you can tell where it is I think I'll blink it between red and green and you'll see it. A point right there they're all orbiting right around that just like planets and comets orbit around the sun that is the orbits are almost completely dominated by a single massive object. Now this is different from orbits of stars around the center of our galaxy where all the stars affect each other but then the galaxy as a whole affects it it's not a single point mass object. But at the center of our galaxy there is something there that we can't see. There's nothing glowing in the infrared at least appreciably. I mean it's almost certainly glowing a little bit but there's nothing glowing in the infrared appreciably where there is something and by fitting these orbits and figuring out based on how fast they are and how big they are. It's four million times the mass of the sun. There is a very compact mass, a very small mass that's four million times of the mass of the sun and all these stars are orbiting around it. And you can see all of these stars have very nice fits for their orbits. Perhaps one of the best ones is this green one over here which made a really close pass around the center of it. And when that one made its pass around the center it was one of the best things for centralizing exactly where this black hole is. So just looking at the dynamics of the star orbiting it we can conclude there is a really massive dark object right at the center of our galaxy and that's the supermassive black hole in our own galaxy. It's four million times the mass of the sun. So we've got that at the center of our sun. We haven't imaged it directly. What we've done is we've looked at the motions of stars at the center of our galaxy and based on those motions been able to conclude that there has to be something there that's not glowing and the only thing that we know that it could be is a black hole. Now there are other questions though it's possible and lots of theorists have worked on this that it's a thing that's like what we call a traditional black hole, but not exactly what we call a traditional black hole. So when we say black hole, at least from a theoretical point of view we're talking about stuff that Einstein's theory of general relativity predicts and includes things like event horizons and all kinds of fun stuff. And general relativity predicts all sorts of behavior for it, but it's possible that there are other dark objects that general relativity breaks down at these kinds of densities. There's other sorts of dark objects that aren't exactly those black holes although from an observational point of view they're still small and they're dark. So from an observational point of view you might just still call them a black hole but they might not actually be general relativistic black holes. But there's something there at the center of our galaxy. Again to put this in context so notice here just remember this scale here so the distance from about here to here, like the size of the orbit of this yellow ellipse here is about 0.04 parsecs. A parsec is 3.26 light years. Right so we're looking at scales of, I mean you have to go, you have to go like 30 of these. So basically the whole width of the image is like about a parsec. So a few light years across. In comparison our galaxy as a whole is a whole lot bigger than that. The distance from the sun to the center of the galaxy is 8000 parsecs. That means if you zoom in as close as you can on this image and you look at the center of the galaxy right here. Everything that was on the previous page on the previous slide all fits within one pixel of this image. Basically no matter how much you zoom it in because it's 0.04 parsecs compared to 8000 parsecs. So all of those stars orbiting are right there right at the very center of our galaxy. There's several implications for this. One is you really have to look right at the center of the galaxy to see it. You can't look at the galaxy as a whole. This is of course an artist's conception because we haven't been outside our galaxy to look down on it and take a picture. Maybe someday but that's going to be thousands or millions of years from now. Just because of light travel time if nothing else. So the scale is very different. Now there's another thing when people find out that there is a supermassive black hole at the center of our galaxy. It seems very natural to suppose, oh so the whole galaxy is orbiting around that black hole. And while, yes it is orbiting around the point where that black hole is, it is not the black hole's gravity that causes us to orbit. Over here we have several numbers. So this little spot here that's supposed to be a black hole. The mass of the black hole is four million times the mass of the sun. But the stars in the galaxy mass about 50 billion times the mass of the sun. So that's a factor of 10,000 bigger. The mass of stars in our galaxy is way more, 10,000 more than the mass of the black hole. And then the dark matter is actually a trillion times the mass of the sun. That's actually what most of the mass of the galaxy is dark matter. But even the stars themselves are much, much more massive than the black hole. And what that means from a gravitational point of view, once you get even out to like here, just barely out of the center of the galaxy, the black hole is no longer gravitationally important. Even though, yes, it's a black hole, and even though, yes, it's four million times the mass of the sun, once you get even a little bit off the center of the galaxy, the mass of all the stars there become much more important than the mass of the black hole. So, yes, here we are. We go around, once every 200 million years, more or less, we go around the center of the galaxy. But that's not because of the black hole. The black hole just happens to be there. I mean, it's not quite that there's the way galaxies evolve. It's all tied together. But from the point of view of the gravity, it's the dark matter and stars that are holding us in our orbit and making us orbit the center. So even though the black hole is there, even though it's the most important thing for the very closest stars, it doesn't matter for most of the galaxy. So that's another thing to keep in mind that these black holes at centers of galaxies, they're not the only mass in the galaxy. In fact, they tend to be a very small fraction of the mass of the galaxy. So there's two different scales there. The distance scale is much bigger. The mass scale here, factor of 10,000, yeah, whatever. The distance scale is a couple orders of magnitude more than that if you compare this 8,000 parsecs. So when we're talking these galactic center black holes, we're talking really small things, at least on galaxy scales. They're really big compared to you and I, but they're very small compared to galaxies. Now, just one more picture of another artist's conception of our galaxy. The last one showed all the stars. This one actually tries to give an image of the dark matter halo. So that's what the blue haze around it is. It represents the dark matter and our galaxy is embedded in this halo as we call it of dark matter. It's just this continuous distribution, densest at the center and it drops off, but it extends well outside the disk of the stars. And that's where most of the mass of our galaxy is. So in fact, a good way to think of our galaxy is it's a little condensation of dark matter and the gravity of that dark matter has pulled in a bunch of gas and stars to its center where they all made the bright glowing parts that we call the galaxy. So that's our galaxy. Now, the image of the black hole was actually not in our galaxy, the event horizon telescope. So just a dark matter, a good question dark matter does not make a measurable perturbation to those innermost orbits. So even though the dark matter is most of the mass of the galaxy, it is spread out enough that when you get right next to the black hole, the dark matter really doesn't matter very much at all. It's, it's pretty much the black hole. So the event horizon telescope, which I'll tell you more about the observational techniques and a little bit here. They're, they have, they have made observations of two different things, including our galactic center black hole that has not been released yet. They're still working on that one. I have no idea where they are in it because I'm not part of the collaboration. But the one they did release was in the galaxy M87. So M87 is a galaxy that's rather different from ours. It's a giant elliptical galaxy. It's at the center of the Virgo cluster. So one thing that happens with galaxy clusters is often at their center, they get a really huge elliptical galaxy. And that's the result of a bunch of other galaxies that have collided together. Oops, I walked through my slides. A bunch of other galaxies that have collided together and collected there at the center of the cluster. And they, all those galaxies collide together and build up a big old elliptical galaxy. Yes, it sounds like a name of an ordinance. It does very much sound like that. But in fact, this M stands for Messier. Charles Messier was a comet hunter in France a couple hundred years ago who cataloged a bunch of fuzzy things that weren't comets. And that's not what he's remembered for is his catalog of stuff. And so M87 is an elliptical galaxy. Here's the thing about elliptical galaxies is they don't look as pretty as spiral galaxies. They're just kind of a big blob, right? There they are. But it's really massive. M87, yes, thank you. Very messy. If you zoom in on just this part of the center, so you look at the core of the galaxy. Well, look at that. It's still an elliptical blob. But there's something cool. There's this jet of material shooting out towards us. Right from the center of the galaxy. And this jet of material, we've known around this for decades, and it's been fairly well studied. But there is a relativistic, meaning stuff moving close to the speed of light, jet of plasma, shooting out from the center of M87. So you can see the scale here is such that you wouldn't really see it on this. And the other thing is it's easier to see the jet and wavelengths other than optical. But you can see it in optical wavelengths as well. And notice this scale here is 7 kiloparsec. So this scale here is pretty close to the distance the Earth is from the center of the galaxy. Meaning that this one, this galaxy is quite a bit bigger than our galaxy. Because our whole galaxy would fit within about this size here. And in fact, this galaxy extends further out than you can see, because the stars even extend out further than you can see. It's a really massive galaxy at the center of the Virgo cluster. So there's this jet coming out of the center of it. What causes that? Well, there's this thing right to my right here that gives the whole answer away. We expect jets like this to happen sometimes, not always, but sometimes when there are supermassive black holes at the cores of galaxies. So I'll talk about that again a little bit later. Well, all right. So this jet is evidence that there's something going on at the center of the galaxy. And nowadays when we see this jet, we say, oh, there's a black hole that's helping to do that. We've actually known for quite some time that there is a supermassive black hole at the core of M87. That's why the event Horizon Telescope said, hey, we're going to go and image that supermassive black hole. Because we already knew it was there. How did we know it was there there if we hadn't imaged it yet? Well, very similar, at least conceptually, to what we did at the center of our galaxy. At the center of our galaxy, we concluded the black hole was there by looking how stuff around it moved. Now in our galaxy, we're close enough to our galaxy, 8,000 parsecs, that we could track individual stars. M87 is 16.8 million parsecs away. So obviously that's a lot farther than 8,000 parsecs. So we cannot track the orbits of individual stars at the center of M87. But we still did look at the motions of stuff near the center of the galaxy. And in fact, we looked at the motions of stars, but not individual stars. We looked at the motions of whole big groups of stars orbiting around the center of the galaxy. Also, we looked at gas orbiting around the center of the galaxy. And that's what the images here have to do with gas. This is a paper from 2013. And what they did, here's the center of the galaxy. These five vertical lines indicate places where they took spectroscopy. So they were able to get, spectroscopy shows emission lines and stuff. But what is important about it is using the Doppler effect, they can figure out how is the gas moving towards or away from us along each of these rectangles, along each of these slits as it were. And then they had five of these slits. So off to the right, here are the velocities they show. Let's actually look at slit number three, because that's the one that goes to the center. Here is the velocity as a function of position along the slit. Now you'll notice as a whole, all of them are moving away from us. It's something like 1,400 kilometers per second. That's because of the expansion of the universe. So this dotted line is basically the motion of the galaxy as a whole. So what's important is what's moving relative to that. And you can see that on one side, here's the center of the slit right here. So right there is right where this galaxy is. On one side, the velocities are lower. That means it's moving towards us. On the other side, the velocities are higher. That means it's moving away from us compared to the galaxy as a whole. And what this tells us is in fact that there's this huge slope in the velocities right near the center. We can then fit the orbits of these and figure out that the dynamics of this gas is being affected both by the gas and stars, but also by the supermassive black hole there. And it allows us to make a measurement of the black hole. Now somebody pointed out that the slits look a little different. This is because from here to here is comparing the velocities from here to here. Whereas if you look at five, you go from here to here is comparing the velocities from here to here. So even at the center of the slit here, you're not right on the center. You don't get as steep of a slope there because you're looking sort of off to the side. You could imagine turning all these slits horizontally and then plotting the velocities in a different way to get the same information, but they actually tilted these slits in the way such that it would work best. All right, so this is what they did. They looked at the gas. They looked at the motion of the gas. They saw that from one side of the center to the other side, there's a big jump. So there's stuff orbiting coming towards us on one side moving away from us. On the other side, that's a big orbiting disk of gas. People have done the same thing with stars. And based on this, they've got measurements of the black hole mass and notice they're different by about a factor of two, which says, okay, these are hard observational techniques. And it's hard to process the data, right? And it's hard to take into account systematics, including the effects of all the stars and the other stuff. So we knew that there was a several billion solar mass black hole at the center of M87, but we didn't have a great mass measurement of it because we had these two ones that were fairly different from each other. But two different techniques did tell us stuff is orbiting such that it was a black hole at the center. So we were able to conclude that there's a black hole at the center of M87 or at least there is a condensed mass. It might not be a general relativistic black hole, but there's something that's not emitting enough light to stand out as a thing all by itself that is several billion times the mass of the Sun affecting the orbits of the stars right at the center of that galaxy. And as Sissy Guy is pointing out, yeah, these slits are about the size of the resolution, meaning that the telescopes that they were using, well, this is actually the Hubble Space Telescope. So the telescopes they were using, the Hubble Space Telescope, could anything closer than these two slits to each other would be blurred together. And it would be like reading a road sign from a great distance. You can't make out the letters if you're too far away. And so that's the resolution. And in fact, I will talk a fair bit about resolution starting on the next slide. So when we talk about resolution, what we really mean is the angle between things that we can teleport. So to try and explain that, here's a telescope that's looking. And you're looking at, suppose you're looking at two galaxies. Obviously, this is not to scale because galaxies are not that close if they were this telescope would be in trouble or this telescope would be huge. Also, galaxies, like I say, are not the same size as telescopes. But it's the diagram that matters. So you're looking at, here's a nearby galaxy, here's a distant galaxy. And suppose you want to be able to tell apart one side of the center of the galaxy from the other side. You don't want it to look like one blob, right? So this is looking at the street sign from a distance. You want to be able to tell the difference between, say, a B and an O. And to do that, you have to be able to resolve enough to see that there's a line in the middle of the B and it's not just a circle of an O. You need to be able to resolve it. Well, when you're closer, it's easier to resolve it. And what really matters is the angle at which the light is coming into the telescope or to your eye or whatever. Your resolution is there's some minimum angle that it can tell apart. I'm going to call that angle delta theta. That is the smallest angle that you can resolve. So notice with this delta theta here, suppose that this delta theta is the resolution of the telescope. Yes, look at that. I can tell this side from this side just barely. But out here, this side of the galaxy to this side, the angle is less than delta theta. The whole thing will be blurred together and I won't be able to separate it. So if you want to take images of things that actually separate different parts, if you want to read the street sign, you have to have enough resolution to be able to tell apart really small angles that correspond to the distance of the object and the physical separation of the things you're looking at. And for a telescope, there's a fundamental limit that just comes from optics that comes from light waves going through apertures of telescope called the diffraction limit. This is the smallest resolution you can ever get with a telescope whose the diameter of the opening aperture or the mirror of the telescope is capital D. So for the Hubble Space Telescope, that's 2.4 meters. For the Keck telescope in Hawaii, that's 10 meters. So various different telescopes have different diameters. And then lambda is the wavelength of the light that you would get. So to give you a sense for this, so this just tells you what's the smallest thing that you could see. I have a table with a whole bunch of numbers on it. So, okay, let's think about this for a moment. What I've done is I've given you several different telescopes. I start with an 8-inch telescope because the C8, the Celestron 8-inch or the Meade 8-inch telescopes are a common good amateur telescope. These are the ones that both Vanderbilt and Westminster we used in the lab. I actually have an 8-inch Celestron telescope myself. So this is a backyard telescope that you might put your eye on. 2.4 meters, that's the Hubble Space Telescope. 10 meters is the Keck Telescope. 100 meters, there are no optical telescopes that big, but there are radio telescopes that big. In fact, in Greed Bank, West Virginia, the radio telescope there is a single dish radio telescope that's 100 meters across. That's really big, right? And they can steer it and point it around. They take this gigantic football field and they steer and point it around at different parts of the sky. All right, so that's that. And then we have various different wavelengths. I've included both blue and red light so that both edges of what your eye can see. Also infrared light, which is important. 2 microns is the image I showed you of the center of the galaxy. They did that in infrared light. And then finally, radio waves. Why? Because, well, the Greed Bank radio telescope, but also the image of the black hole was done on radio waves. And so then what this table shows you is from the diffraction limit of the telescope, what is the smallest angle that you can resolve for various different wavelengths and various different telescopes? These resolutions are in arc seconds. There are 60 arc minutes in a degree and 60 arc seconds in an arc minute. So this is 1,3600th of a degree. That's a really small angle. But I'll put this in context on the next slide. And so if you look at these numbers, you will notice that with optical light, the resolution of an 8-inch telescope is close to 1 arc second, maybe half an arc second from blue light. Whereas for the Hubble Space Telescope, it's close to 1,20th of an arc second. So usually we say the resolution of the Hubble Space Telescope is about 1,20th of an arc second because that's what I can see in optical light. And yes, Izzy points out that the Green Bank telescope operates it. What wavelength does the Green Bank telescope operate at? You may just know that off the top of your head. I don't. You notice as the wavelength gets bigger, you can't resolve as well. So for the Hubble Space Telescope at 2 microns, it can only resolve down to about 1,5th of an arc second, something like that. So whereas radio waves, oh my goodness, a 10-meter radio dish can only resolve 33 arc seconds. That's pretty huge. So radio waves, it's harder to resolve, which you might wonder then, well, why do we look at things in radio waves? Well, for other reasons that I will come back to in a little bit. So these tell you the angles. Now there's one other thing. If you're on the ground, in the optical and infrared wavelengths at least, maybe some other wavelengths too, but it matters in optical and infrared wavelengths, the resolution is actually limited by the blurriness of the atmosphere, the twinkling of the stars. Now there are ways around this basically you shoot lasers into the sky. I'm not making this up. You shoot lasers into the sky and you can get better resolutions on your telescope. Basically what you do is you shoot lasers into the sky and look at how the laser image gets blurred and you use that to correct for the atmosphere. But thank you for that information there. The atmosphere blurs things out to about 1 arc second, which means even though the telescope could resolve to a 20th of an arc second or a 100th of an arc second without using adaptive optics, which they use, but if you don't have adaptive optics, they actually can only resolve to about an arc second because they're limited by the atmosphere, not the telescope itself. All right, so I want to put this in context. I want to change from angles to what if you were looking at M87, what is the size of the smallest structure that you could resolve? And now I'm going to ignore atmospheric seeing, but because again we'll be talking about radio wavelengths. What is the smallest structure that you could resolve? Well, let's look here with a 10 meter telescope, so that would be like the optical kick telescope. The smallest thing that we could solve in radio waves would be about 3 parsecs across. And remember that is bigger than the entire image of the stars orbiting the center of our galaxy and the black hole was not resolved in that image. It was smaller than a pixel in that image. So you're going to come nowhere close, even with if you had a 100 meter telescope, you're going to come nowhere close to being able to resolve the gas right outside the event horizon of the telescope. So we have to do something else. The telescope just directly looking at it. The resolution is not going to be good enough to see stuff small enough to resolve the black hole. The smallest thing it can resolve here is 0.27 parsecs, which is way too big. So what do we do? You can't just do it with the telescope. So we use this technique called interferometry. Interferometry is so called because we look at the interference of light waves coming into two different telescopes. And so the way it works is you have two different... Actually, you use more than two. You want to use as many as you can. But to simplify it, we'll just consider two to start with. You use two different telescopes, and then they look at light. And so I've got light coming from two slightly different directions. So the blue and the red, that's not supposed to be the color of the light. That's just so you can tell apart what is what. You have them coming at slightly different directions. You can see the angle between them is pretty small. But notice what's important about that is if you compare the time of when the light reaches this telescope versus when the light reaches this telescope, you'll notice, so start with the blue line. Actually, start with the red line. You'll notice that when the light reaches this telescope here, this light over here is about a wavelength and a half behind. Which means that it has to go a wavelength and a half, and then you can multiply that by this... or divide by the speed of light, really, to figure out the time difference. It's a tiny fraction of a second. The light to reach this telescope. And then, how do you actually time the individual light? That's really tough. What you then have to do is you do interference. You look at how do the light waves overlap with each other. And so notice here, this guy and this guy, this one is towards the right side, the bumping up and down of the light. It's in a bottom part here. It's a top part. So those would be out of phase. Whereas on the blue light at a different angle, they're in phase because they're both down. So you'll look at how in phase and out of phase, the light waves are. That's what the interference is. You'd see are the wavelengths lining up or not. And based on that, you can figure out what's the angle the light came in at. And then, using the angle that the light came in at, you can resolve based on now not the size of the telescope, but the distance between the telescopes. So interferometry is a technique where instead of being limited by the size of one telescope, you are limited by how far apart you can place your telescopes and still put the data together in a way that you can keep it all coherent with each other, which is a technical challenge all itself. Now there's actually two reasons why you want a telescope to be big. One is for resolution. The bigger the telescope, the smaller things you can see. But actually the main reason you want a telescope to be big is that we're looking at dim stuff in the sky. The bigger your telescope, the more light you collect. It's like a bucket collecting rainwater. The bigger the bucket, the more rainwater you're going to get. Put it through a funnel into a glass. The big bucket is going to fill up the glass faster than the small bucket. So telescopes are light buckets. So yes, this only has twice the area of one telescope because it's just two telescopes. But for purposes of resolution, yes, never mind. For purposes of resolution, the distance between the telescopes is what matters. And so this is a technique that allows us to resolve things much smaller than we would have been able to just with the telescope itself. And so that's why radio telescopes in particular often come in arrays rather than just a single telescope. This is the VLA as an aside. If you've ever seen the movie Contact, Jody Foster spends some time at the VLA. That's where she first gets the signal from the aliens. I saw Contact in theaters because I'm old and it came out in the 90s, but I saw it then. And my sister, who is a, she is now a middle school principal that at the time she had graduated with a degree in American studies. So she didn't do astronomy. She leaned over to me and says, what does VLA stand for? And I told her very large array. And with a disgusted look on her face, she said, really? Yep. Yeah, I don't think the VLA, as far as I know, Sisi, that's right. I don't think the VLA was ever really used for setting. It was in that movie, but not really. Era Sebo, which also showed up in that movie, was used for setting. Anyway, so they have this, and notice they're in different directions in that, so you can do interferometry in more than one direction. They have all of these arrays, and in fact they can move the telescope around based on how much resolution you want. There's other considerations that go into it for how easy it is to detect stuff. So if you imagine drawing a big circle around the outside of all of these, the VLA has the resolution of a telescope that big. And so even though you couldn't build very easily a big, steerable dish that is that huge, you can get resolutions of a disk that that's huge, and that's what the VLA does. And so this is something the VLA has done for a very long time. Yeah, I don't know if quantum computers will be used for something on this. I wouldn't anticipate that right away because quantum computers currently are in the, can we even demonstrate that they work stage rather than actually doing useful computation stage? Why radio telescopes are not optical telescopes? Well, because the way they do this is they detect the radio waves and they send the signals down wires, just like you do with your radio. Radio waves are light waves. There's nothing sound about radio waves. They're just signals. Send the signals down through wires and then they can do electrical interference, just of the electronics, to figure out what the light wave interference would have been between the two telescopes. So it's basically combining those. Now, it's much easier to do this in radio waves because the frequencies are much lower than they are with optical waves. For radio waves we're talking megahertz and gigahertz, millions to billions of cycles per second. For optical, it's like 10 to the 14, 10 to the 15 cycles per second. So you need very high speed electronics, even to do this with radio waves, much harder with optical waves to do this with electronics. And so that's why this technique, interferometry has been done in the infrared and optical now. It's easier there if you use optical fibers and actually combine the light itself together. But for radio waves it's a lot easier to do and that's why we've done that. So interferometry allows us to resolve things that are much smaller than we would have with just one telescope. Now, there's yet another technique. So this is in the VLA. Each one of these distances is 10 meters. As anyone remember, that gives you a sense of the size of this whole thing. But this is all just one 20 meters. Thank you, Suzuki. So it's 20 meters from here to here, which means that these things can be on sizes of hundreds of meters is how big or never 100 meters is how far apart all these telescopes are from each other. Something like that. All right, well, 700 meters. That's great. But there is another technique called VLBI for very long baseline interferometry. So the baseline is the distance from one telescope to the most distant telescope. That's the baseline is the jargon. Very long baseline is where, instead of combining everything together immediately electronically, what you do is you have separated radio telescopes that record their radio signal or something related, you know, basically it's correct to say that record their radio signal coming from space with very, very, very precise clocks. And again, extremely precise clocks. And then later combine together the recorded signals to calculate what would have been if they had been able to do interferometry in real time. They can't do the interferometry in real time as they're detecting the light. They're recording the signals with extremely precise timing so that they know exactly which part of the radio wave came to which telescope at which time. They can combine it together later. Very long baseline interferometry. And doing that, you can take radio telescopes separated on other sides of the planet. Well, not exactly other sides, but most of the way across the planet looking at the same object. And now you have the resolution of a telescope that's the size of the Earth. And what the event horizon telescope is. The event horizon telescope is actually a collaboration of a whole bunch of existing radio observatories that do stuff just by themselves including some things that are arrays like ALMA is one of the newest and most advanced radio telescope arrays, ALMA down here in Chile. It's an array itself, a whole bunch of telescopes. So it does interferometry itself, but for the event horizon telescope all of these various different radio telescopes all look at the same object at the same time and record very high precision timing. We need atomic clocks and they calibrate it using GPS signals. Extremely precise timing and they collect huge amounts of data. You may have seen the picture of the woman with the huge number of hard drives of all the data that you had to send to one place to process later. Huge amounts of data, they collect it all and then they send it off to be processed and it takes a really long time to process. This is how, look at this. This is basically the size of the earth apart from each other. You go all the way from Europe here out to Hawaii there, down to yes, in fact, Australia at the bottom. So, they have a telescope. It doesn't have the collecting area of the whole telescope. Yes, Barragame, that's right, the lady. She was one of the core authors of the algorithm or actually one of the algorithms processing the data. The data with multiple different algorithms so that they could test how robust it was to make sure that the results weren't artifacts of something wrong in the algorithm. So, they did have multiple algorithms who are doing it. So, they have a telescope. It doesn't collect all the light that hits the earth, but it has the resolution of a telescope that is the size of the earth. That's really big and that allows them to resolve really, really small stuff and here it is. How long of an optical interferon? I don't really know. Yeah, like it was kilometers and I would think an optical interferometer would be limited about to something like that and it would be really expensive to do. So, notice the resolution here is 0.000 not the resolution, but the size of this thing. The resolution is about a quarter of this. So, the resolution is something like 1, 2, 3, 4, 5, 5 or 10 milli arc seconds in radio waves, way smaller than what the VLA can do. This image here, and now if you look at the size of this is 0.003 parsecs from here to here is 0.003 parsecs or if you compare it to the size of the solar system from here to here is about 680 astronomical units. So, that is about 10 times the diameter of Neptune's orbit. Great. We have resolved a really small thing, but we still have what the heck are we looking at? So, when this image came out some of the chat I was on a chat with some random friends of mine and I said, hey this is really cool check out this image. And one guy says I've seen clearer pictures of Bigfoot but okay fine. So, what do you see? You see a furry blob that is brighter on one side. Why are people so excited about this? It's a donut. It's a donut that's brighter on one side than the other side. Why are we excited? Okay. We have to know what we're looking at to figure out why we should be excited by this. The image all by itself it's a fuzzy donut. Just look at a star with a telescope that's not properly collimated put it out of focus and you'll get something that looks like this. What are we looking at? First of all, just again to compare the sizes XKCD always good for telling us fun things in quick ways. Give us this little diagram of the image with the orbit of Pluto, the sun and in fact how far Voyager 1 is so you can see that we are looking at something about the size of the solar system at a distance of 6.8 megaparsecs. All right. Well, what are we looking at? Well, the first thing is we have to know a little bit about gravitational lensing which is basically light's path is bent by gravity. This is a case where we're looking at galaxies and quasars. So this is a background quasar. This star is a quasar. This is a galaxy or maybe another quasar if you're lucky but really a galaxy in between the background quasar and us, the gravity of this galaxy bends the path of light. So light coming vastly exaggerated the effect here so you can see what's going on. It's a really small effect of exaggerated it here. The light that goes leaves the quasar in this direction gets bent by this galaxy so it actually comes and reaches our eye here really a telescope. And likewise the light that leaves the quasar over here gets bent and comes towards our eye. Well, what do you see? We see light coming in this direction. So what that looks like is there was a quasar here because light coming in this direction, that's what it looks like to us. And likewise down here we see a quasar here. Well, so gravitational lensing distorts what you see. This image down here, this is called the Einstein cross, the thing in the middle is the middle galaxy. The four spots around the edge are four different images of exactly the same quasar that reached us through light paths that were bent by the galaxy in the middle. So gravity bends the path of light. And that's really important when you get really close to a black hole because really close to a black hole, gravity is really, really, really strong and now the size of the effect I've drawn here is actually underestimated. I actually talked about this once a couple years ago when I gave a talk about the science of interstellar. In interstellar the black hole looked like this. And what this is sort of is like this thing to my right here. So I've got a black hole in the center that's a little squashed sphere and the big disc around it is a big glowing disc of gas. Now you look at this and you look at the interstellar and you say, well, okay, so that's this disc here. What the heck is with this light around the top and the bottom of it? Well, what that is is this disc but gravitationally lens. So where you actually have stuff in space there's a disc around the black hole. The light that comes off going in that direction is actually bent so much by the gravity of the black hole that the light bends all the way around the black hole and we see stuff that's behind the black hole. And so what does this look like to us? It looks like glowing disc up here and that's why you see this stuff up here and there. So the image, the way the black hole looked in interstellar was actually based on realistic physics not just of where stuff is, but of how light is bent. So when you look at black holes, you very much don't see where stuff is. You see where stuff is highly modified by the fact that the black hole itself is bending light hugely around the black hole. So that's an important part of what's going on here when you look at this image from the event horizon telescope. You can find on the web some nice simulations of this. Here's a website. Don't go to this. I probably shouldn't give you this URL because now you're not going to pay attention to me for the rest of the talk. If you go to this website, there's this neat interactive little tool where you can sort of drag a black hole around in front of a background image. So this would be there's a black hole somewhere this whole thing isn't the black hole. This is the thing they call the shadow of the black hole, but somewhere inside here about here there is a rotating black hole and then far away there's our galaxy basically the black holes in front of our galaxy and then this distortion here is the background light of our galaxy being distorted as it goes around the black hole and you'll notice you see this circular ring around the whole thing. There's no galaxy if the black hole weren't here there'd be no galaxy right there, but you see light there because the light that was behind the black hole is bent so much that it gets turned back in our direction and there is a sort of characteristic circle size where lots of the light tends to collect. This is maybe a less pretty but more quantitative way of looking at it. The background sky here was a gigantic sphere that just had it had four quadrants green, red, yellow, blue and if the black hole weren't there you would just see this whole thing coming together where the four colors would all come together right here, but the black hole you can see totally warps where the light is coming through and you get this really messed up image. Now, as an aside, somebody asked could we use this to try and image planets in our galaxy? That's a hard question. I think in principle there's no reason why you wouldn't be able to but here's the problem is that planets tend not to be very bright in radio waves so I think it would be really hard to see anything trying to look at solar systems in our own galaxy because they're just not going to emit enough radio waves to really see things very well. Now I could be wrong about that because Jupiter is a radio source that you can see on the telescope but yeah, so then also could you do it on the moon? That's another issue on the moon because of course the moon is moving and your telescope has to be able to steer to look at it and the moon is close enough it might actually be tough to do. I'm not sure I don't know the details well enough. Anyway, so the black hole, so here's one key called tremendously, this image is the prettier one, tremendously modifies the light that you see. So when you take an image you're not seeing what is there you're seeing what is there hugely modified by the gravity of the black hole. The black hole itself is characterized by an event horizon this is an image I got off of wikimedia commons it's on the wikipedia page this is actually an animation that has black holes spinning at different rates so I've picked a black hole spinning it something like the m82 black hole this there's several lines here don't worry about what most of them are but this one I'm tracing out here the second most outermost line is the event horizon of the black hole this outermost line is the thing called the ergo sphere and it has to do with if you get that close to the black hole you cannot help but orbit it the gravity of the black hole will drag you around in an orbit and there's absolutely nothing you can do fire rockets in the opposite direction to stop from being dragged around by the gravity of the black hole it's kind of cool but this inner this second most outermost one that is the event horizon of the black hole that's what we usually think of this as the surface of the black hole and notice that the spot is way bigger than that why is that well it's because if you do backwards ray tracing you ask what point would light be coming from that would come at us such that looks like it's coming from this direction well that would actually be a point on the black hole so the shadow of the black hole as it were is where on the sky does light come towards us that would have had to originate at the black hole itself and of course the black hole itself doesn't emit light so you won't really see anything so the shadow of the black hole is way bigger than the black will not way bigger but bigger than the black hole itself right a few times bigger than the black hole itself the black hole itself is just this big the shadow you see is bigger so that would tell you on this image here the black hole itself would actually be something like here that's about the size of the event horizon in this image so you're seeing a shadow that's bigger than that so yeah so the shadow of the black hole is bigger oh is it representative of the surface area that's a good question I don't think it's that director relationship right so is the area of this the same as the surface area it's certainly going to be closer than the cross section but I don't think there's a direct simple relationship like that there certainly is a relationship right bigger black hole bigger shadow but I don't think there's a direct yeah okay so here's a good other planets may be bright enough oh yes so Vic makes an excellent point so if we start to see radio waves from a star that looks like radio waves of intelligent civilizations then I would say make a whole lot of sense to point interferometry at it see if you can figure out how far the planet is from the star but yes anyway so back to the black hole so yeah so the shadow is way bigger than that so when you look at oh yeah there's one other effect I need to tell you about and that is relativistic beaming or the searchlight effect if you have an object that's at rest and it's emitting light in all directions you know here it is it emits light in all directions now suppose instead of being at rest this object is moving to the right that's what this black arrow indicates and if it's moving pretty close to the speed of light this doesn't I mean it happens always but you will never notice this if things are not going close to the speed of light two things happen first of all there's the Doppler effect so the light in the direction it's going shifts towards bluer light the light away from the direction it's going shifts towards red light but there's a second thing that the light gets focused in the direction it's going this is a relativistic effect so what this means is that if you're looking at something coming towards you really fast it will be very much brighter than the thing moving away from you very fast because the light is focused in the forward direction so this is called relativistic beaming so remember this remember both I just jumped in the air I don't know why I did that remember both that the black hole is going to bend the light and relativistic beaming means that stuff that comes towards you is going to be brighter than stuff that's moving away from you pull those together and now we can explain this image of this black hole that we're seeing so here's the image of the black hole we're seeing here is a model from one of their papers this paper is from the event horizon telescope of what's going on inside so that's what my image to the right here is supposed to be not what you would see because my my 3D model here has not taken into account gravitational lensing this is where stuff is not what you would see so what you've got here I'll just drag this to the center so you can see it a little better what you've got at the center is a black hole with a big disk of gas around it the disk is orbiting really fast because the gravity of the black hole makes it go fast also if the black hole is rotating that drags the disk around really fast it gets really hot because the stuff moving so fast as it falls into the black hole rubs against each other the gas hits each other moving really fast that heats it up so it glows in x-rays gamma rays even it is so hot it's glowing like that and then you don't always get this if there's a disk but often you will get two jets of material shooting out along the poles shooting out it near the speed of light and those jets are collimated by magnetic fields how are they actually accelerated well there's different ideas about that but part of it is just the light is pushing light actually pushes on stuff pushes the plasma out close to the speed of light so that's where stuff is and so that's what this image here let me move this back out of the way that's what this image up here is a model of here's the black hole this shows you the direction of the stuff the accretion flow that's the disk of the stuff orbiting the black hole so the black hole is spinning in this direction the accretion stuff is spinning in this direction and then the jet is coming out like this alright so that's where stuff is but if you then start with this and put in both the effects of relativistic beaming so this stuff will be much brighter than this stuff it's all the same intrinsic temperature but the stuff that's coming towards us is going to be brighter because of relativistic beaming and you calculate put all that stuff in there and then calculate what you would see if you had perfect resolution this is what you get so this is grmhd that's gamma sorry general relativistic magneto hydrodynamics I'm sure you're very illuminated now I said that well whatever they did simulations of plasma emitting and radio waves and then simulations of general relativity bending that light to see what you would see and remember you see this this disk is not where the stuff is this is the bright stuff that is just like the bright circle around the black hole looking at the center of our galaxy collected at that characteristic radius the photon sphere it's called the characteristic radius where light just tends to be amplified the most as a result of the gravitational lensing so the disk is not face on the disk is actually closer to edge on than face on but we see this circle because of the gravitational lensing you see other stuff around it the disk is brighter in the direction coming towards us than away from us and you see this it's called the shadow of the black hole but really it is it's this you know the silhouette or the shadow of the black hole where because of gravitational lensing you don't actually see anything coming from behind the black hole and the stuff in front of the black hole has trouble struggling out as well so there's this big dark spot and then this is what you would see if you had perfect resolution you blur this out to the actual resolution and what you get over here this thing here is the reconstructed calculated image of what you would have seen given the plasma given that it looked like this plus the blurring and you notice hey look the thing they reconstruct from calculations looks basically the same as the image they took how old is this light you see 54 55 million years old is how old the light is that so 16.8 megapar 6 is the distance to M87 that is something like 55 million light years multiply 16.8 by 3.26 you'll get the number of millions of light years it's about 55 if I remember correctly they can also calculate the mass of the black hole based on the size of the image that they see and they get hey it's about 6.5 billion times the mass of the sun though what I've tried to do here is indicate as best I can assuming I did the calculation right where would the event horizon of the black hole actually be on this this is also very close to the resolution of the telescope so here's the big deal about this is that yes we have seen evidence for galactic center black holes before we've seen stars orbiting around the galaxy in the center of our galaxy we have seen stuff moving in the center of M87 this is the first time we have an image whose resolution is big enough that you can actually resolve the shadow of this black hole the gravitational lensing and that you can see this ring around it because of the gravitational lensing so we're really probing the black hole itself it's radio light that we're looking at we're not looking at optical light so this is not what your eyes would see if you had that resolution it's radio waves but radio waves are light and we are resolving structure that is similar in size to the size of the black hole itself which is this but more importantly to the size of where the light is and this allows us to actually check to make sure you're seeing the right stuff that you should have seen if it were a black hole and we did it so this is alright so what should you take away from this well one of this general relativity keeps working we probe general relativity in regimes like very close to the surface of a black hole that before a few years ago we couldn't really probe that at all general relativity's calculations are giving us the right answer the other way we have probed that is with gravitational waves which I've given a couple talks about that here with LIGO general relativity seems to be a really good theory next black holes really exist we've been sure of this for a long time but here is yet another very strong confirmation that black holes exist because we see light at the center of m87 behaving exactly as it should if there was a black hole and not just a black hole but a general relativistic predicted black hole the light is behaving exactly as it should have right around that black hole another thing m87 now has better evidence for a galactic center black hole than the milky way before last month the milky way had the best evidence for galactic center black hole I would argue that the evidence in m87 is now better because we have looked right around the event horizon of the black hole this also means the black hole powered model for active galactic nuclei so this is supermassive black hole at the core of a galaxy accrete stuff around it shoots out jets that's what we think quasars are well look we've looked into the galaxy with a jet and hey look right at the center there's a black hole that's very much behaving like a general relativistic black hole that's what's going on and then finally what next well the event horizon telescope is also looking at the black hole at the center of our galaxy now why didn't they do that one first it's closer well it's also smaller the black hole is about 1500 times smaller than the black hole at the center of m87 but it's 2000 times closer so it actually will be similar to the black hole at the center of our galaxy and it's going to be a lot of difficulty and to resolve and the event horizon telescope I would guess sometime in the next year but it'll happen when it happens should be releasing images of plasma around the center of our galaxy the other thing is although it's closer the plasma is not going to be glowing as bright as it is around m87 but it's closer so I don't know what it's going to look like but that's something to look forward to so alright so I'm going to stop there I hope we're actually looking at when you see this little lopsided donut that's supposed to be a direct image of a black hole I hope I give you a sense of what it is we're really looking at you know you might think well black holes are black they emit no light so therefore how can you make a direct image well really you can't but what we're doing is looking at the light right around the black hole we are resolving the gravitationally lens ring of light lensed by the black hole we are resolving on a scale similar in size to the event horizon of the black hole and that's the first time we've done that for any black hole anywhere and so we're looking right around the black hole and I hope I've given you a sense of you know why it looks like it does and what the observational techniques were so I'll stop there and take any residual questions people have thank you a lot of the interferometry has been done both on quasars because they're very bright and infrared but also on young stellar objects where they also have some radio waves emitting and so there are water masers are things that happen in discs around young stars and so there've been interferometry of that using VLBI as well the event horizon telescope is using this VLBI technique but specifically they're interested in black holes and so that's why it's called the event horizon telescope great well so show up tomorrow for the Tchaikovsky spectacular birthday party and the next week for the panel where several people several of the science circle regulars will be talking about what is the most exciting significant unanswered question in the field yeah we'll have paleontology chemistry and biology so there you go Mike Shaw who is here right now telling us are Alex and Steven or either of them here right now I don't think so and yes millimeter wave VLBI which is fairly new too so I get here's I have a question for you Mike in chemistry are all chemists really just cooking meth that's the question anyway yeah I don't know what the most important question in chemistry is I'll have to wait and see what Mike says yes I know but as opposed to Mike so when I was in a standard class in grad school physics is a math methods class which we call math meth so that's like math math but backwards all right well I'm going to head out I've actually blown my voice out a little bit over cold that I have so I'm going to head out maybe have a little bit of lunch stuff I'm sounding a little hoarse towards the end here and have fun everybody unfortunately I will not be able to be at the panel next week but I am hoping to drop by for the birthday party tomorrow alright I'm going to head out now see y'all later have fun everybody