NASA’s Universe Of Learning: Black Holes, Out of the Shadows 12.3.20

Amelia Chapman: Welcome, everybody. This is Amelia and thanks for joining us today for Museum Alliance and Solar System Ambassador professional development conversation on NASA's Universe of Learning, on Black Holes: Out of the Shadows. I'm going to turn it over to Chris Britt to introduce himself and our speakers, and we'll get into it. Chris?

Chris Britt: Thanks. Hello, this is Chris Britt from the Space Telescope Science Institute, with NASA's Universe of Learning. Welcome to today's science briefing. Thank you to everyone for joining us and for anyone listening to the recordings of this in the future. For this December science briefing, we're talking about something that always generates lots of questions from the public: Black holes. Probably one of the number one subjects that astronomers get asked about interacting with the public, and I do, too, when talking about astronomy. Questions like how do we know they're real? And what impact do they have on us? Or the universe is large? Slides for today's presentation can be found at the Museum Alliance and NASA Nationwide sites as well as NASA's Universe of Learning site. All of the recordings from previous talks should be up on those websites as well, which you are more than welcome to peruse at your leisure. As always, if you have any issues or questions, now or in the future, you can email Amelia Chapman at [email protected] or Museum Alliance members can contact her through the team chat app. Their info for that is on the Museum Alliance website. As a final reminder, for anyone who's calling in on phone lines, please do not put us on hold even if you have to step away because some phones will play holding music which can disrupt the talk.

We have a panel of impressive speakers today. So I'll introduce them briefly as they come up to talk. But you can and should read their bios in full on their website as well. Please hold all your questions until all of the speakers have had a chance to present, and then we'll have a panel Q&A about black holes afterwards.

Our first speaker for this briefing is Professor Tuan Do, who is the Deputy Director of the Galactic Center Group at UCLA. He received his PhD in astronomy from UCLA in 2010. He was a TMT Fellow at UC Irvine and a Dunlop Fellow at the University of Toronto. He's currently an assistant professor at UCLA, UCLA's Galactic Center Group, of course, was part of the Nobel Prize that was awarded this year for proving the existence of the black hole in center of our own galaxy, the Milky Way. So welcome, Dr. Do, and please take it away.

Dr. Tuan Do: Great, thanks. Thanks, everyone for coming to this talk. I'm Tuan Do and I'm from UCLA. Today, I'd like to talk about how we can use the discovery of the supermassive black hole at the center of our galaxy as an example of how science works. I found that a lot of people are really fascinated by supermassive black holes from all ages and backgrounds. So it's a great topic to engage in discussions about how we know what we know about astronomy. We can't touch black holes, and we probably don't want to, but we can still learn amazing things about them. Next slide.

This year, the Nobel Prize for Physics was awarded to three scientists: Roger Penrose, Reinhardt Genzel and Andrea Ghez. Roger Penrose won for his theoretical contributions to black holes, while Reinhard Genzel and Andrea Ghez won for showing that there was a supermassive black hole at the center of our Milky Way galaxy. So today, I'd like to talk about how this black hole was detected, how we were able to measure its mass, and what the future brings in this work. I'm concentrating the story from the perspective of Professor Ghez's work, since that's what I'm most familiar with. But the general framework will also apply to Reinhard Genzel's work as well. Next slide, please.

One of the central aspects of the scientific process is hypothesis testing, and a lot of the discussion about this centers around the idea of proposing a hypothesis and then doing observations or experiments to see if it's consistent with the hypothesis. What I'm interested in is that it's a little bit more complicated than that. We're really never satisfied because one class we're continuously posing new questions in a really interesting feedback loop. So the story I want to tell today is about that feedback loop of hypothesis and observations. Next slide.

So here's a picture of Professor Andrea Ghez very early in the morning after she got the call from the Nobel Committee about winning the prize. But let's start at the beginning of how this work began. So in the early '90s, there was starting to be evidence that the centers of galaxies can harbor supermassive black holes. These black holes have masses that are equivalent to millions of times that of our Sun, but they're pretty exciting objects. And there wasn't a lot known about them. But one of the best places to test for the existence of a supermassive black hole is in our very own backyard, at the center of our Milky Way galaxy. It has the highest concentration of stars anywhere in the galaxy. And there were suggestions and observations of radio wavelengths that there was maybe a massive object at the very center. So the initial hypothesis that Professor Ghez started with was that if there's a supermassive black hole at the center of our galaxy, its strong gravity should make the stars move really quickly around it. But there were a number of challenges, including Can you see enough stars? Can you see them move quickly enough to make these measurements. Next slide, please.

This hypothesis requires a large telescope. And luckily, at the time, the largest optical and near infrared telescope at the time was just built in Hawaii. So this picture shows the two Keck telescopes. The mirror is about 10 meters. Next slide.

And in the next slide, we see a picture of Professor Ghez next to the telescope in the background. She's standing in front of an astronomical instrument here. In this case, you can think of these instruments as giant digital cameras that can see infrared light. Next slide.

This picture is now from the mid '90s, in a control room of a telescope. So this is kind of how astronomers do their work, Professor Ghez is in the blue sweater in the middle, this is still a pretty accurate view what we do at night. But computers are much fancier. But when we take the data and interact with the telescope in this way. Next slide, please.

Using these first images, what do we see? In the top left is an actual image in the early '90s, of the center of the galaxy. The image has been inverted, so actually, the dark spots are the bright stars. And zoomed in, you can see a zoomed in portion of the middle with the stars are. And on the right is a plot showing the locations of these stars in 1995, 1996, and 1997. So really remarkably, the stars move, they're in different places each year. So it does indeed look like it starts moving quickly. So this is exactly what he predicted. There was a supermassive black hole. Next slide.

Is our hypothesis test done? Well, we passed one test, but we'd like to be constrained to the black hole better. If there's a supermassive black hole, it should be very compact in size with a lot of mass in it. So that means a star should actually orbit it like the planets orbit our Sun. So we revise our hypothesis. If there's a supermassive black hole, that there should be a large amount of mass in a very small volume. Next slide.

We need better technology to do this. Next slide.

The first with of the development of adaptive optics on very large telescopes. Adaptive optics is this technology that lets us correct for the blurring effect on the atmosphere. This is why stars twinkle, for example. But it makes images blurry for telescopes on the ground. In this picture of two telescopes, two telescopes have lasers pointing at the center of a galaxy. This is an actual picture taken next to the telescope. Lasers kind of look like a Death Star from Star Wars, but really, all it does is it creates a spot of light at 90 kilometers up in the atmosphere. This creates an artificial star. So by observing how this artificial star changes a thousand times a second, we can measure the effect of the atmosphere and correct for it using sophisticated mirrors that can change shape to match the variations in the atmosphere. So this creates really sharp images as if the atmosphere wasn't there.

Here's a picture of the center of the galaxy with adaptive optics. Oh, sorry, next slide.

This whole image covers just a very tiny portion of the sky. So if you hold a strand of hair at arm's length, it would cover more of the sky than this picture. Next slide, please.

And the next technological improvement was the development of spectroscopy that can take advantage of adaptive optics. These spectrographs allow us to measure the motions of stars along our line of sight. So with images alone, we can only see how stars move in 2D, but spectrographs really let us add a third dimensional approach, which is a crucial ingredient when measuring the orbits of stars around a black hole. And so these spectrographs are pretty big, about human size. Here's a picture of me next to a spectrograph at Keck. And so I joined this project about 14 years ago now, and in my work really specialized trying to use these spectrographs to understand the nature of stars next to the supermassive black hole. Next slide.

So by combining the new technology of adaptive optics and spectroscopy, along with imaging, we can now start tracking how the stars move around the black hole. It started becoming clear by the year 2000 that the stars move in curves all around a similar spot. So by 2008, though, we can measure full orbits and some of these stars such as the one in yellow in the bottom right. And it's very important star. It's called S0-2. Next slide.

This star, S0-2, orbits the black hole once every 16 years. This is really fast for a star. And by applying Kepler's laws and Newton's laws of gravity, we can measure how much mass is inside of S0-2's orbit. The plot on the right shows how well we can measure the massive black hole and the distance to the galactic center. So the takeaway from that plot is that this experiment was able to show that there is 4 million times the mass of the Sun confined in a region that's smaller than the size of our solar system. So this measurement really shows beyond reasonable doubt that there is a supermassive black hole at the center of our galaxy. Next slide.

Now that we know that there's existence balance, I go black hole though, where do we go from here? Well, having a supermassive black hole in our own backyard is really interesting, because we can now ask questions about physics we can't before, for example, is Einstein's General Relativity a good description of supermassive black holes? So Einstein didn't know about supermassive black holes when he first proposed this theory, so we can test to see if his predictions still hold, because if it does, it should apply everywhere, right? And so the test that we're going to try to do with that general relativity predicts that the star, S0-2, should become slightly redder when it gets close to the black hole. Next slide.

According to general relativity, gravity should affect light. So this series of frames show how the star S0-2, which is this yellow ball, in this drawing, and as it gets close to the black hole, it should get slightly redder than when it's far from the black hole. So the reason for this is that the strong gravity in the black hole causes light leaving the star to lose energy. So this loss of energy makes the light look redder than it should be. And we call this the gravitational redshift. So by observing S0-2 as it moves around a black hole, we can test this effect. And this happened in 2015. Next slide.

So this also required better technology, and a lot of observations of group closest approach. Next slide.

So for this project, we needed to use all of the data that had been gathered since 1995. And also a lot of data in 2018, as the star went through closest approach. So in fact, we use data from all four eight to 10 meter telescopes on Mauna Kea on the ground where Keck is deployed. The picture shows are all equipment, laser guides, our adaptive optic system and it just happened on this night, that they were all looking at the same part of the sky. Next slide, please.

And the other thing is that the team has grown a lot over the years. Next slide.

Here's an example of what it looks like to look over the shoulders of folks observing the night. Here we have a postdoc and grad student taking data. Next slide.

Occasionally, the black hole brightens up when stuff falls onto the black hole. And we get really excited. And you'll hear more about this, why this happens with black hole accretion from Professor Markoff. Next slide.

Here's a photo of the computer screen when the night of the closest approach actually, when S0- 2 went around. Next slide.

Here's a picture of our team really excited about getting the data. We were very nervous about whether the weather was going to be good, because you miss this chance you can come again for another 16 years. Next slide.

This effort really requires a lot of people working together towards this common goal. Here's a team of graduate students, postdocs, researchers and faculty on top of Mauna Kea with the Keck telescopes in the background. Our group spans multiple institutions, both here in the US as well as Canada and France. Next slide.

So in the end, what did our experiments show? So here's a plot showing the measurements we made in 2018. That's what these black dots are. The x axis shows time, and then the y axis shows how much the star S0-2 shifted. So the dotted line shows the prediction from general relativity and the solid line on the bottom at zero shows what Newton would have predicted. And so you can see that indeed, our measurements are pretty close to what General Relativity predicted. Next slide, please.

What's really exciting is now we're entering this era that we can use supermassive black holes to test theories, general relativity and trying to understand gravity from these tests. Next slide, please.

And I'll just leave you here with the latest measurements so far we have from 1995 to 2020 for tracking evermore stars, and each store has a really interesting story to tell about their environment around the black hole. So stay tuned for more. Thanks so much for listening.

Chris Britt: Thank you so much, Dr. Do. That was great. We'll have all question periods coming at the end. For now. Our next speaker is Dr. Kristen Dage. She's a postdoctoral fellow at the McGill Space Institute. In the McGill Extreme Gravity and Accretion Group. She received her bachelor's degree from the University of Michigan Dearborn and her PhD in astrophysics from Michigan State University. Please take it away, Kristen.

Dr. Kristen Dage: Thanks, Chris. Um, so I wanted to talk about these things called intermediate mass black holes. So you can kind of think of them as the baby bears of black holes. They're not too big. They're not too small. They're just right.

But the problem is, we haven't found any yet. So I'm just going to talk about where we think they might be, and how we could take them how to go to the next slide, please.

So, as you've seen, we've gotten really good at measuring supermassive black holes. This plot on the right here shows all the supermassive black holes that we have measurements of so far, so we're talking millions or a billion times the mass of the Sun. We've also imaged the accretion disk around a supermassive black hole, which is the image on the left, which I think you're going to hear about more in the next talk. If you could go to the next slide, please.

So we've also found stellar mass black holes. So they are black holes that are tens to hundreds of times the mass of the Sun. And we found a few of them. The most massive one we found, is about 160 solar masses. So if you go the next slide, please.

So as you can see, we're missing black holes that are in the order of thousands of solar masses. It is perplexing. Next slide, please.

There's one place they might be hiding, which is in globular clusters. So I really love globular clusters. They are these big clusters of tens of thousands of stars. The image on the right is an example of one of the clusters in our galaxy. These are dynamic places. And I feel like I never appreciated how dynamic they were until I got bees that summer. And I spent all summer watching my bees, you know, like tens of thousands of bees all interacting and crowding around each other and just reminded me of a globular cluster so much. So these are really, really special environments. And what's interesting is that, you know, a galaxy is comprised of millions and millions of stars, whereas globular clusters are only tens of thousands of stars. So there's a lot of differences between these environments. Next slide, please.

So one of the sources we're interested in following up on it's called an ultraluminous. x-ray source, or I'm going to refer to it as ULXs for the rest of the talk. And these are weird x-ray binary sources. So remember that black holes don't give off light. So that means that we can only watch them by how they interact with other stars. So as you saw on the last talk, one of the ways they interact with other stars was pulling them around. The second way the interact with stars is through accretion. And the picture on the right is a really good example of it. So it's close enough to a star where they orbit each other. And it sucks material off the star in such a way that it forms a disc of stolen material from the star, and then it gives off light and x-rays. And now the amount of light that that can give off in x-rays is governed by the mass of the black hole. So that means that if you are a black hole of a certain mass, you can only get so bright. But as it turns out, that's what's called the Eddington Limit, but the Eddington Limit is more like a speed limit. So there are objects, which maybe they aren't supposed to get that bright, but we definitely see them going that fast. So as you can see, I have a speed limit sign in kilometers per hour, because I live in Canada now. And I’ve got to get used to those units. Next slide, please.

Oh, okay, what makes them so great? So we have a couple of scenarios. So I'm putting this picture on the right of an accretion disk, just to remind you, what's happening is we have a black hole sucking off material. And so there's two options. One is that we could have a less massive black hole that's pulling material, you know, past the speed limit, so to speak. So it's happening in some weird regime of physics we don't understand. But the other option is that it could be a more massive black hole that is pulling material from the same way. So it could be the same physics we understand, just something really more massive than we were expecting. And I put these pictures, these are my chickens. And to remind you that either we have a normal sized chicken that's like a small chicken that's eating really, really fast, or we have a big chicken that's eating normally. Like those were kind of our two scenarios here. Next slide, please.

So this is kind of what I do to look for these, in principle. So these really bright sources only exist in galaxies really far outside of our own. And so what we do is we look for bright x-ray sources, and then we check to see if they align with globular clusters or not. The bright x-ray sources that align with globular clusters, we're interested in. And this is exciting because we can study them in both optical and an in x-ray. You know, these sources are super, super rare. And like we've studied about 10 galaxies so far, and we've looked at tens of thousands of globular clusters. And we've only found about 17 of these, so they're pretty fine. Next slide, please.

So one of the ways we can study them in optical is using spectroscopy. In the upper right corner, you'll see I put the little image from the Pink Floyd album cover. And so spectroscopy is basically a fancy version of this, where the light goes in through our instrument, and it splits it out into all the constituent light.

So this image here is a spectrum of one of our favorite sources, and it's a little bit like a histogram. So we have an intensity on the y axis. On the x axis, we have the wavelength of light, in angstroms. And when it kind of builds up like this pattern that you're seeing here, this is an emission line feature that's actually changing over time, which is really weird. But more importantly, because we can identify what elements gives this off, we know that there is oxygen in the system. So we know that for some reason, there's a something weird and like an unknown physicality happening here that puts a lot of oxygen in the system where it disrupts oxygen molecules. So that means that there are outflows happening in the system. And outflows are something we don't understand well, so this is evidence of weird physics happening in these systems. Next slide, please.

So this is some of the x-ray data we've looked at. And I know it's a lot, and I'm very sorry, but I promise that we can try to make it painless. So what you're looking at here is a comparison of the source brightness to the accretion disk temperature. So the temperature of the accretion disk tells us a lot about the physics of the system. So one of the things that we care about is to look at general trends here. So what you'll notice, especially if you compare the purple source on the left, and the black source on the right, the overall trends behave very differently. Next slide, please.

And so you can see that we can actually split up into two different trends: the sources with the lower temperature and the sources with the higher temperature. So this is really interesting. If we go to optical and compare the optical properties of these sources, it gets even more interesting. Next slide, please.

So as it turns out, the sources with the low temperatures have emission. Now the sources with higher temperatures don't have emission. Remember that having emission means that they have some kind of weird physics we don't understand. And the other thing that's interesting is that the sources with the higher temperature behave in physics we do understand. Next slide, please.

So what does this mean for intermediate mass black holes? So we think that the sources with the low temperature that have emission are probably smaller mass black holes that have weird physics, we don't understand. But the sources that don't have emission are actually our best candidates for intermediate mass black holes, or more massive black holes, that are accreting with normal physics. The problem is to understand if something's a black hole or not, you need to measure mass, which is really difficult to do. So, yeah, it'd be nice to find these. They could tell us so much about everything. But we just can't seem to find the darn things.

Chris Britt: Thank you so much, Kristen. It's great. So our final speaker is Professor Sera Markoff. Following her PhD in theoretical astrophysics from the University of Arizona in 2000, she held a Humboldt Research Fellowship at the Max Planck Institute for Radio Astronomy in Germany, and an NSF postdoctoral fellowship at MIT. She's now a full professor at the University of Amsterdam, where she runs a research group focusing on observing as well as modeling the data from black holes. She's a member of the Event Horizon Telescope collaboration, where she currently serves as the vice chair of its science council. Welcome, Professor Markoff.

Dr. Sera Markoff: Hey, hi, everyone. Well thanks a lot for having me here. I'm at 10 o'clock at night in Amsterdam. So hopefully, I'll be coherent for this. And I'm following up on the other great talks, because you now know that there are black holes in all different sizes, but I want to talk a little bit kind of generally about what black holes do, what their role is in the universe. And that basically holds for all black holes. But I'm going to be showing you examples from supermassive black holes, mostly just because those are the biggest ones and they sort of pack the biggest punch. But just keep in mind that all black holes at all scales, even the ones we can't see like the intermediate ones that Kristen was talking about probably are doing this sort of stuff. And it's interesting, right? Because if you think about black holes and what you're told in the media, or what usually is focused on, people think about this kind of sinkhole, right? Like a vacuum where stuff is just basically falling in, and nothing can get out. And so how can it have any sort of influence, right? But what's happening is you heard from Kristen, of course, that the material that's around the black hole is basically doing a lot of energetic stuff. And that means that material that's accreting or falling onto the black hole, but also being ejected, has a lot of energy. And that energy is actually coming from skirting the black hole, so not falling directly in. But stuff is kind of coming in on orbits. And it's basically gaining gravitational potential energy and converting it into other forms. And things like magnetic fields get involved, but it's emitting across the entire electromagnetic spectrum. So we see light from radio, all the way up to gamma rays. And there's also material being shot out from near the black hole, at near the speed of light. And that can really wreak a lot of havoc on the black hole's environment. So that's kind of why I call them the cosmic influencers, because they really have a lot of influence. And it sounds a little crazy, but the best way that we can understand this is to actually directly see it. So what I want to do is show you first some images of black holes in action, supermassive black hole and how this influence comes out, then, I want to talk a bit about how we measure this and then show you a couple slides that are connected to this movie that's in the extra slides about how we actually go about doing the modeling. So if you can go to the next slide, please.

So this is an image from the famous NASA Hubble Space Telescope. So it's an optical image of what's called a cluster of galaxies. So all of the points that you see are actually galaxies, and they're held together by their mutual gravity. This is basically the largest gravitationally bound structures in the universe. And you can think of this as kind of the birthing place. And the nursery of galaxies is where they form and they grow together with their black holes. And in the center, there's a really whopping big galaxy there. And it has a big, supermassive black hole that's contributing to some of the optical light that you see. But to really understand how much energy is coming out, we need to look in other frequencies, because as I said, black holes are radiating from across the entire electromagnetic spectrum. So if we go to the next slide, please...

We're going to see the exact same field. But now we're looking in the radio waves. So this is taken with a radio telescope, this is a frequency your eyes can't see. So we translate this into fake colors. So the blue is completely meaningless here, it's just pretty. But what you see is something completely different. And radio waves are tracing very hot, magnetized material. And it's what we call a plasma form, because it's completely ionized. And these are basically huge jets like magnetic fire hoses being shot out from the black hole on crazy big scales. So if you can jump to the next slide.

These these jets are basically 800,000 light years across from one black hole. And that's about a billion times bigger than the black hole that's launching it. And if you want to understand more about the energetics, we actually want to look at all the different frequencies that we can. So for instance, and this is by the way, not taken from space, this is taken from the ground with a very large array. Now, if you go to the next slide, please.

Now here we're looking in the x-ray with NASA's Chandra X-ray Observatory, and x-rays trace really hot gas. So this is basically gas that's millions of degrees, kind of like the solar corona. And it's basically trapped in between all of those galaxies that you saw by the gravity. And, and if we put this all together, and now look at the next slide, please.

This is sort of a composite image now, you can start to trace all the energy coming out of this black hole. And for instance, the x-ray gas is a bit denser, and we can calculate how much energy took for those big jets to punch through. And we find out that it's something like the black holes depositing on the order of 10 to 100 billion supernovas worth of energy into the environment. And all that heat and energy basically influences all the galaxies that are in this cluster and can heat them up and stop their growth. So if we want to understand all of this, we have to really try to work our way down to the source of the energy, which is the black hole, basically, its gravitational pull is what's being used to convert, it's sort of like a gravitational assist if you think about it, how you use the gravity, energy to turns to other forms. And if you jump to the next slide, please.

One of the ways that we can look this way is we start to build better telescopes with new technology and higher frequency to work our way down to the black hole. And so this is an image of, we're going in the radio frequencies again, this is actually the galaxy that hosts the black hole that we took a picture of last year, M87. "This image is about 200,000 light years across, as you can see all sorts of stuff that this is basically tracers of prior events in the past when the black hole had a different jet that was more active. But now if we move to higher frequencies, and we build bigger telescopes, can you move to the next slide, please?

What we see here is kind of a zoom in of several images from the top to the bottom. We're going to from 1.5 gigahertz down to basically the millimeter or 230 gigahertz. So higher frequency means getting closer to the black hole in terms of what we can see, or zooming in from scales, the original image was 200,000 light years across. And now we're coming down to 0.003 light years across, so it's a scale of like 100 million times zoom in. And that means that we have the capacity now with our telescopes to basically see the entire system and try to model it. If you jump to the next slide.

I won't say too much about the Event Horizon Telescope, which is how we made that image. But just to say, this is a Google Earth image of the telescope. So obviously, we didn't build a new telescope the size of the Earth, but we sort of cheated, and we borrowed telescopes across the globe. And this is just showing you where those telescopes sit. And if you show the next build, please.

We actually didn't have that top one when we took that image in 2017, which is in Greenland. But in 2018, we did add that telescope. And in the last few years, we've added a few more telescopes. And unfortunately, because of COVID, we actually couldn't observe this past year, but we're hoping in 2021, COVID allowing, that we will observe and we'll have even sharper images of black holes, especially the one M87, and also the one that Tuan was talking about that we're working on data for at the moment. So what do we do with all this data? I mean, once we have it, we want to try to make models and understand the black hole. So if you jump to the next slide...

What I'm going to show here is a bit about the technique. And you can see a movie. So these are just like snapshots from the movie that's in the extra slides. But I thought it might be cool for you to see that also for your students. We're using GPUs more in these are gaming chips in our computers to model these. So these are the chips that people use for video games. And they're really good for doing parallel processing, because they can do many, many processes in parallel, which is great, because that's kind of what we have to do when we try to make models of black holes. And so we take basically a computer and we put a black hole in the center, we do all the calculations with Einstein's gravity. And we start with a donut of material wrapped around it. And this is what you see in the left panel. And the color scale shows you sort of a slice through this donut. The color scale shows you the density. So red is high density and blue is low density. And then what we're going to do is jump through time, over six panels have seen the evolution of how these black holes accrete and how the jets are launched, and the black lines there show you the magnetic fields. So going from the left to the right panel, we're sort of zooming in closer to the black hole, as the system is allowed to start accreting. And you see that the magnetic fields are sort of falling in towards the black hole as well as the material. And if you jump to the next slide, please.

Then we move forward in time. And what you start to see is that basically, these lines of magnetic fields coming up and down our magnetic field lines that have come very close to the black hole, but basically didn't fall in, and were sort of shot out almost like centrifugally shot out like a bead on a wire, and the matter falls with it. And they channel the matter outwards. And if you look to the right, we've moved forward in time in the simulation, but we've also moved to larger scales, you start to see these jets are basically tumbling out away from the black hole and carrying material outwards. And if you move to the next slide, please.

Then you can start to see we move further in time and also further away from the black hole. And it's hard to see the scale here. But the scale is in units of what we call gravitational radius, which is basically the size of the black hole. So we're now able to simulate by the time you look at that further slide, we've managed to launch jets that are 100,000 times bigger than the black hole. So we're getting close to actually being able to model complete physical systems from the inside out. And we use these simulations to try to compare to our Event Horizon Telescope data to our other multi wavelength data from x-rays and optical and all the things that you've heard about from Tuan and Kristen, and try to see if our models are correct. So if you move to the next slide, please.

So just sort of tying it up. You've heard that they're black holes in a huge range of size, from basically they range the size of billions from stellar mass to supermassive. But they act very similarly. We see this process of stuff falling onto black holes and launching of outflows and jets on all scales. And if you actually could jump two slides forward, please Sorry, I'm just kind of skipping over the build.

What the real difference is is the timescale on which they change. And so basically the little black holes change much faster, they're doing all the same things, but they do it much faster than big black holes. You can kind of think about it, like the fruit flies that, you know, live and die in 24 hours. And so we can use the small black holes, like Kristen was talking about to watch jets being launched. And actually sort of quench and go away within days and weeks, whereas that process would happen in supermassive black holes over timescales of millions of years. But in the big black holes, we can actually zoom in and see the black hole area, like we did with the Event Horizon Telescope, which we can't do in the small one. So we learn different things from the different scales. And you jump to the last slide.

We're really interested in this whole process of stuff falling onto things and using gravitational energy to turn into other forums and launching jets. Because we see this all over. It's not just black holes, actually. This happens with young stellar objects forming stars, planetary nebula, supernova, and neutron stars, you name it. And so it's kind of a universal process. But black holes, basically the power source is gravity. So black holes give you the biggest punch. And that's why I call them the biggest influencers. But it's important for us to understand this process in a generic way. And if you jump to the last build...

Some of you might have heard about the gravitational wave detections in the last few years. And when two neutron stars merge, basically, they eventually form a black hole and a jet gets launched. So we see all sorts of cool stuff with gravity and light and matter happening all at once. So these are kind of the ultimate goal for us to try to understand. And that's it. Thank you very much.

Chris Britt: Thank you very much, Professor Markoff, great job of tying everything together. So we'll go ahead and answer some of the questions that were in the chat. And if you have any other questions, please feel free to drop them in the chat as well. So first off, I think this was a question for Kristen. What will make it easier to find intermediate mass black holes? Basically, what technologies would be needed?

Dr. Kristen Dage: So I think for the ones that are in globular clusters, we would need like a lot higher resolution. So I think one of the best techniques to measure the mass of the black hole is kind of the techniques that Tuan talked about, so we would need a spaceship that would be able to resolve like a little beehive stars really far away. And I think that'd be difficult, but JWST (the James Webb Space Telescope) might be able to do some of that, actually.

Chris Britt: Another question here, about the Event Horizon Telescope? When can we expect to see the Event Horizon Telescope used next?

Dr. Sera Markoff: Well, it's been used quite a bit, actually, we still have quite a lot of data, for even from the first year in 2017. It's just this was the first time this was ever done to string all of these telescopes together. It's extremely complicated. And we have to, you know, when you do something, for the first time in science, you have to be really sure. So you have to do a lot of work to analyze your results. We're actually working now on the images from 2017 for the supermassive black hole, that Tuan was talking about. Our own private, supermassive black hole in our galaxy, Sag. A star. And we're hoping to get those kind of out in the next year, so that you'll start to see them. But there's actually some other images already published, you might have missed from another black hole, but just you can't see the whole event horizon with this black hole. But you can see these jets that I'm talking about, very, very close in. And that was a system called 3C279. So that's actually available to see. And there are some new papers coming out on M87 soon, which talk about the magnetic field orientation. So there is quite a lot of work coming out. It just does take time to get things right and do things carefully.

Unknown Speaker Thank you very much.

Chris Britt: Black holes at the center. Why or why not?

Dr. Sera Markoff: Should I take this one?

Chris Britt: Sure. They didn't specify any one specific.

Dr. Sera Markoff: Tuan and always, and Kristen can break in, but basically, we're not entirely sure how black holes form. But we do think that they form very early in the universe and sort of, together with their galaxy, so that maybe when you have this condensation of galaxies forming and basically a galaxy starts as a ball of dust and gas that eventually will clump down and form stars and a big concentration will happen in the center. One idea is that maybe it turns into something like a crazy huge star that then will collapse and form like a really big intermediate mass black hole exactly what Kristen was talking about and then over time as the galaxy grows, the black hole grows with it. Maybe early stars in general were really big and form these immediate mass black holes that became seed black holes and grew the black hole so there's kind of competing theories at the beginning but as far as we can tell, pretty much every galaxy has a black hole in the center and some galaxies have more than one supermassive black hole and that's because galaxies also grow by merging, and sometimes you catch them in the act when the two central black holes haven't gotten together and formed a really big one yet. And so, there's quite a few possibilities out there.

Chris Britt: Thank you. This was kind of a fun question: Any examples of science fiction that gets the science of black holes right?

Dr. Sera Markoff: I'm waiting because I've talked too much. Tuan and Kristen, I have an idea but if you guys have something.

Dr. Tuan Do: Um, I guess, like Interstellar has a lot of interesting black hole physics as part of it, right? Make it as the simulations for what you would see if you were next to the black hole I really interesting. And then like this idea of time dilation and you're in the black hole that's a really bizarre consequence of like the warping of space time that black holes have is you're really close to the black hole time seems to be moving more slowly for a person there than if you are far away from a black hole. But I think that a lot of things are unknown about black holes which makes them good fodder for science fiction, because one of the interesting things about black holes is we don't know what's inside of a black hole so you can have all sorts of theories about like, do they lead to another universe, or are they bridges to different places in our universe? Those things it's very difficult to test, basically,

Chris Britt: Thanks very much. So here's another good question. Can gravitational lensing be used to study and find black holes?

Dr. Sera Markoff: I can take this one if you guys. Yeah. So actually, it's interesting. There's, there's a lot of ideas that there's primordial black holes these early black holes that form that are just sort of floating around. And one way that you might see them is that basically they would gravitationally lens. Light of a star that would pass behind them, and then make that star brighten up temporarily. And so, this has been seen. But then usually this is used to look at very distant galaxies, but you can find smaller objects and this is called microlensing and it's difficult to know what the lens is, but people have hypothesized that some of these microlenses are black holes, so that actually is one way that you could detect them.

Chris Britt: So what are the speeds of the jets coming out of the black hole, or coming from near the black hole? Are speeds different, depending on the black hole size?

Dr. Sera Markoff: I guess this is one also. Yeah, that's a great question. Basically, anything that happens near a black hole is going to be moving very close to the speed of light, and that's because the escape velocity to get out of a black hole is already pretty much the speed of light. So you're talking about percentages of speed of light, whether it's a fraction of 10% or more like 90% is the kind of thing that we discuss. So it's extremely what we call relativistic so you have to deal with special relativity, and the size of the black hole plays a role and also the strength of the magnetic fields, and that can vary from black hole to black hole, so kind of the amount of magnetic pressure that's sort of channeling the material can play a role in the speed.

Chris Britt: Let's see, I recently heard Dr. Mike Brown say in a presentation that if the hypothesized Planet Nine was really a black hole, you'd have seen it already. So it says that if there is a Planet Nine object, it's not a black hole. Does that make sense. Sounds like he's trying to start some drama with Mike Brown.

Dr. Sera Markoff: Tuan, do you know? I'm not so sure about Planet Nine.

Dr. Tuan Do: Me either actually. Yeah I'm not actually sure what he is referring to, I don't know, I guess if you had a black hole in the solar system. Would you see microlensing. By now, you would probably see strong lensing, even.

Dr. Sera Markoff: Someone says Pluto was planet nine. Yeah. I think what maybe they're getting at is that it would be kind of hard to hide a black hole because there's quite a lot of stuff around in the solar system and as Kristen was talking about, maybe she wants to say something, but when a black hole is accreting, a lot of light comes out so they get hard to hide. Maybe that's what he's getting at, but I'm not familiar with this discussion.

Chris Britt: Yeah, I think that's fair. Let's see, so how does dark matter figure into the formation and behavior of black holes? How much Dark Matter may actually be inside a black hole?

Dr. Tuan Do: That's an interesting question, I think, and probably. It depends on how the density of dark matter in the centers of galaxies, is kind of the answer, because we know dark matter on really large scales. That's how we kind of measure dark matter. So let's just take our galaxy. We know that our galaxy 90% of the galaxy's mass is dark matter, but we don't know how concentrated it is when it gets to the center of our galaxy. So a lot of the mass in the center of our galaxy we think is probably from stars. But if there's a large concentration of dark matter, it could be part of the black hole. The black hole doesn't care what kind of matter it is, as long as its gravity can affect it, it will absorb it. So it's hard to know exactly what fraction, but probably not as much as ordinary matter, I would say. That seems to be the dominant amount of stuff in the center of our galaxy.

Dr. Sera Markoff: And I guess it's important to say that once it's in the black hole we have no way of knowing, right? Because we can't - I mean you could throw a black hole in a black hole, you can throw a person in a black hole, a chair, you know, a neutron star or whatever or dark matter and we don't have any way of knowing that, so we can only measure the mass and the spin, basically.

Dr. Tuan Do: Yeah. It's also worth saying there's this hypothesis that maybe dark matter are primordial black holes. That's a branch that folks are thinking about these days.

Chris Britt: Here's another question about the jets. Are the jets coming from inside of the black hole or material coming from the accretion disk. What is the ejection mechanism?

Dr. Sera Markoff: So this is really at the heart of what a lot of us are trying to understand and the questions and if you look at that movie, you'll start to get a bit of insight. The colors tell you where the matter is. Basically, what happens is you need to have the material near the black hole to create the magnetic fields that pull the material out of the black hole in some sense, not out of the black hole but from away from falling into the black hole. Now you cannot technically pull anything out of the black hole. But what's happening is when you have these magnetic fields thrust onto what's called the ergosphere which is the region of space time, which is basically more - you see the movie, and you can watch this in your spare time and sort of track things and slow and see what happens frame by frame. But what we think is happening is that the magnetic fields are effectively pressing on to what's called the working surface of the black hole, which is a strange region where you're not inside the event horizon yet, you're just outside, but you're close enough that spacetime is rotating basically almost at the speed of light. And so you're kind of twisting up the magnetic fields and that, torsionally, it's like a spring that's been twisted up. It has a lot of energy. So, what happens is, in this movie, you're looking at it unspun, but actually if you looked at it when it was spinning you'd see that the lines were all like a slinky. Were all twisted up, and that carries a lot of energy and we think that these jets are actually tapping the spin of the black hole. So, in that sense, you're pulling energy out of the black hole. It's a quantum process. And it's kind of related to things you might have heard of by Stephen Hawking. It's a very subtle question and we're not entirely sure of the exact balance of energy of how much is coming from inside and how much - mostly we think that the material from outside the black hole is pulling all these magnetic fields in, and some of it is getting sucked into the black hole and some of it is getting dredged up along inside these jets and sort of pulled along for the ride. I'm sorry that's sort of complicated. It's a complicated question.

Chris Britt: I think we have time for one more question and we'll get into some of the resources we've got for people to use. See I know that Dr. Dage is focused on globular clusters but are there other potential hiding places for intermediate black holes?

Dr. Kristen Dage: This is a really good question and I was thinking about this when I was writing my talk and so there's a couple of things to it. And the first is, we like globular clusters as a place for hosting intermediate mass black holes, because it has to do with black hole formation. But also, there's not a lot of other options because remember that for us to find black holes we need it to interact with other stars, and the only other candidate I can think of is a source called HLX-1 (Hyper- Luminous X-ray source 1), So this source is in a spiral galaxy. I think it's kind of the edges of it, but it exceeds the Eddington limit, like hundreds of times more than most sources do, and because it gets so bright. It's one of our best candidates for an intermediate mass black hole so far. But it has to do with mostly that we're running out of options to find them in other galaxies.

Chris Britt: Thanks very much. I want to thank all of our speakers again before we move on to some of the resources we've collected. And I would ask that, if we have time to stick around at the end for the second set of questions. If everyone has time, but I know we're slated to end at 4:30, so we may not. Let's see. So for the resources that we've gathered, those can all be found on our website, UniverseofLearning.org. The link is there to our site for you to follow from the slides. There are also some extra slides there, along with some videos that Dr, Markoff provided. So what you just saw at the end there, showing the launching material jets. We go on to the next slide, 63.

I also wanted to direct your attention to the ViewSpace video library, which some of you may already be using. This video library is kind of an improvement that was made to ViewSpace over the last year or two, where it is now possible to find a set of videos based on subject keyword rather than just playing through at random. So you can actually go into the ViewSpace video library, search for black holes, and find all of the black hole videos that ViewSpace has to offer. On to the next slide.

ViewSpace has also continued to add interactive elements in the form of these sliders. And one of those new interactive sliders is based on some of the work that Tuan Do just presented, showing the motion of stars in the galactic center. And by allowing people to kind of slide that bar across the bottom you can actually track the stars at each given point in time to see how they move relative to the center of the galaxy there. That is not the only interactive there on the interactive page on ViewSpace. It is the one most closely related to the talks today. Move on to the next slide please. 65.

And as always, since black holes give off a lot of x-rays, this Chandra X-ray Observatory has a host of black hole products available through the Chandra mission. Those can be found at the websites listed there in the presentation. This includes illustrations and animations for you to browse through and find something that might suit your needs, or answer your questions. Chandra also provides this principal black hole infographic, which answers common questions about black holes with engaging visuals, so this is the kind of thing that might be handy to hang up on a door somewhere for people to look at it their leisure. We go on to this next slide please, 67.

We also have some articles about black holes through other missions, such as through WebbTelescope.org articles that discuss some of the work of the Galactic Center. How do we know there are black holes, which also talks some about how Webb will study black holes in the future. We also have some resources on Hubble site and the article on black holes there, HubbleSite.org. Go on to the next slide, please.

Other missions that include a lot of resources about black holes are Fermi, which is a gamma ray telescope that NASA operates. Its black hole resource area is linked there on the slide, and it includes things like a PBS Nova special on black holes, a Denver Museum of Nature and Science planetarium show, Black Holes: The Other Side of Infinity, an educator workshop, From Here to Infinity, of black holes. Black Hole activities for the classroom and some games about black holes for all ages. And please check out EventHorizonTelescope.org too, for resources related to black holes. There's also an active galaxy education unit that Fermi telescope has working at their templates, specifically for educators. Next slide please.

There's also a set of simulations which have been around for a little while now that have a lot of fun, which shows the perspective, what it looks like if someone is falling into a black hole down with relativistic ray tracing. So, if you're kind of curious to answer that question, What would it look like if I fell into a black hole? These videos kind of give you that perspective. Move on to the next slide, please.

I think that concludes it. Great. So thank you, everyone. Please check out our resources. I think we do have a few minutes left, so if anyone has any other questions to ask our speakers here I know that we didn't quite get to all of them. Before I jump over the resources, maybe have time for a couple more at the end. I hated to interrupt the Q&A earlier.

There's a question about citizen science programs related to black holes. I'm not aware of any personally but I don't know if any of our speakers are.

Dr. Sera Markoff: There's one in development, but it's not ready yet, so I'm not sure when it's going to be ready, and it's not only about black holes, but it's about these little when little black holes, but also neutron stars and other sorts of compact objects flare on the sky they're called transients. And they're very difficult to find. Sort of what Kristen was talking about, you have to look through these huge maps. And so there's a plan to use citizen science to start trying to identify these, because we're going to have more and more of these telescopes looking at the sky all the time, and it's quite difficult to find them. So it's not exactly black holes, but it will turn up some black holes, I don't know if that's interesting for people but you might have to wait a little while.

Chris Britt: There was one question that we skipped over last time and had to cut short. Someone was asking about primordial black holes, since they heard it in the offing but were away from their computer at the time. The question is, What is a primordial black hole, and how is it different from a non-primare black hole?

Dr. Tuan Do: Primordial black holes we think are black holes that were formed during the Big Bang. They tend to be very small in mass, compared to the black holes we see today, so even maybe smaller than the mass of the Sun, so we know that from our ideas of black hole formation that black holes are about a stellar mass black holes are formed from supernovae, from really massive stars, and those black holes tend to be about three solar masses, or more. And then we get into this regime of intermediate mass black holes we talked about and then these like very supermassive black holes but below three solar masses are black holes that we think could only be formed during the beginning of the universe. We don't know if these primordial black holes exist, that's a big topic at the moment, but theoretically they can. That's what makes it really interesting.

Chris Britt: Does anyone who's calling in. Want to unmute and ask a question verbally? [Long pause.]

Okay. Well, I suppose, barring that, then it sounds like we're about tapped out as far as questions go. So thank you to all of our speakers. We really appreciate your time coming and chatting with all of us to tell us all about your work, and the amazing things that are happening in astronomy today. Thank you so much for everyone and thank you for all of our attendees for coming and learning about it. All of this material will be available on our website and on the Museum Alliance afterwards, recorded and transcript. So, thank you for coming, and have a wonderful evening.

Amelia Chapman And I'd just like to second that and invite everybody back next week on Tuesday, December 8 (2020) for our next professional development telecon, which is going to be about smartphone astrophotography. I don't think you can get a black hole on your phone yet, but you can take some really great photos, so tune in to learn how. Thank you, everybody.

Dr. Tuan Do: Thanks, Bye

Dr. Sera Markoff: Bye everyone.