Into the Impossible With Brian Keating - Is a rogue black hole lurking in the Milky Way? | Professor Jessica Lu (#237)

Episode Date: July 3, 2022

Today's guest, UC Berkeley Professor Jessica Lu, discusses the discovery of the first dark, isolated black hole or neutron star in the Milky Way using gravitational microlensing! This ‘ghost black hole’ is far from the center of the Milky Way. We also discussed: ⬛ dark matter and the future of multi-messenger astronomy w/ the Roman and James Webb Space telescope as well as the Vera Rubin Observatory. Finally, we answered your❓Questions -- you can always submit them on the "Community" tab for this channel. This work was led by UC Berkeley grad, Casey Lam, and details are in papers in The Astrophysical Journal (https://arxiv.org/abs/2202.01903). See Jessica's awesome Twitter thread on this discovery, and what it might mean: https://twitter.com/jlu_astro/status/1535292954180341760?s=20&t=ZFaQb9iG5SIsaQW3ijH7ZQ Please enjoy my black hole playlist for more on the theory and observation of these mysterious objects https://www.youtube.com/watch?v=FvGInn1efR8&list=PLJGKdZD30K_9Gx0SBRjFn_TNPBN-9t9md Learn more about your ad choices. Visit megaphone.fm/adchoices

Any sufficiently advanced technology is indistinguishable from magic. Open the pod bay doors, please help. Welcome everybody to another episode of the Into the Impossible podcast. This one is kind of like an office hours episode with your chance to talk to one of the renowned astronomers of our times. Someone who works on observation and works on the interface with new theories and on instrumentation. That's my colleague in the University of California, the world's best university, Dr. Jessica Liu, joining us from UC Berkeley's Astro Department. How are you, Jessica?

I'm doing great. Thanks for having you, Brian. Yeah, it's such a great pleasure. Yeah, as soon as I heard these results, I was immediately hoping that you would honor me by coming on the podcast, and you did. So I'm super grateful for that. and I'm hoping that we will get a chance to take questions from the audience, as we like to do. So we had recently Adam Reese, who's another observational astronomer of some note, and he was on live. We take questions from the audience. Some of them are pre-asked.

Some of them will be asked as we go along on this conversation. And you have some materials to show, but I think maybe first, kind of, set the scene. You, I always knew you as I said, as a renowned astronomer, observational astronomer with an interest in galaxies, if I remember correctly, and kind of traditional observational and instrumental methods. This may not be a departure for you, but in my recollections it is, so I could be the absent-minded professor effect. Can you tell me, where does this fit in the Jessica Lou brand portfolio? Where are black holes in that? Is this a new research endeavor? Is this something you've long been interested in?

Yeah, ever since I was an undergraduate at MIT, I've always been fascinated at this interface between astronomy and physics, particularly sort of exotic forms of matter or black holes. That's always been my interest. Where can we really push the boundaries of our physics knowledge by looking out into the universe? So when I was an undergrad, I actually studied neutron stars with Vicki Kaspi. And then I took a break and worked as a software engineer and industry in Silicon Valley for a little while. But as soon as I got back to grad school, my first interest at UCLA was working on the supermassive black hole

at the center of our galaxy. So that was a lot of my early work, because working on the galactic center, trying to understand how stars evolve and are formed and born and die all around that whopping big black hole at the center of our galaxy. Yeah. Yeah. So the stellar mass black holes work that we're talking about today

and that you've seen in the press, that's all using the same techniques, which is called astrometry. It's the ability to measure the positions of stars on the sky. So that's really where it was born. It was born because we were doing all this hard work on the center of our galaxy to watch stars orbit the black hole. And we can use the same exact techniques to look for these small baby black holes, the stellar math black holes.

And this particular black hole isn't necessarily at the very center of the Milky Way galaxy, is it? No, not at all. also turns out our big galaxy is swarming with black holes, at least we think, it should be swarming with stellar mass black holes. So we can look a lot closer to home. But the technique that we're using called gravitational lensing, which we'll talk about in a little while, really is done best towards where the galaxy is really crowded. So we'd like to look towards the center roughly, not right at the center, but a little bit off. and we're using the background field of really crowded stars as a screen to hunt for stellar mass black holes that are in the foreground.

And how does this work fit in with the recent guest we had on Shep Dolman in the Event Horizon Telescope? Is there any hope for black holes like the one you're going to describe today that Event Horizon could verify this, this, you know, amazing, startling discovery that you and your team have made? or is it hopeless because the mass levels are so small compared to the monster black hole that we always talk about? Right. I really wish we could, but there's two ingredients that are missing. One is on the universe side. In order to see black holes in the way that the event horizon telescope looks for them,

you have to have gas accruiting onto the black hole. You still need electromagnetic radiation coming from right around the event horizon to see it. So that's one ingredient that's missing. The second one is that the event horizon telescope, as large as it is, as big as it's spread out over the whole Earth, it's nowhere near big enough to resolve these tiny little stellar mass black hole event horizon. I always like to remind everyone, the stellar mass black hole event horizon is only about 30 kilometers in size. It's like the size of a city.

These things are so, so tiny. So, yeah, we would need, you know, solar system sized event horizon telescope. Right. Well, we can put in a request for NSF funding for that as we go on. So a reminder we're talking with Jessica Liu, colleague in the University of California system, a really incredibly productive. You know, I've always followed your career, had aspirations that you might be a colleague in San Diego, but that, you know, we'll talk about that later.

I have to talk to the dean. But at any rate, you're so creative, and what you do is use tools of astronomy to understand astrophysical processes and new objects. Talk about what this discovery meant. Maybe we can go to the screen share, and then I want to talk about, how did you realize that this discovery had the significance that we're just now realizing it does? So we can go to a screen share if you press that button, and then we'll remind folks that they can take. We'll take questions in just a bit. So let me add that.

I'm going to take myself, actually, hold on, I'm going to switch screens here. I've got this whole mobile command center here, Jessica. You'd be so impressed. but often it is a little more trouble technologically. Okay, so now we are seeing your Twitter feed, which is how the world discovered it first, and I immediately recognized my opportunity to finally get you on the show. So walk us through this.

First of all, everyone should follow Jessica Liu, at Jay Lou underscore Astro on Twitter, and her feed is phenomenal. only for the astronomy that we get into, Jess, but all the lifestyles of the rich, maybe, and famous professors. You share so much cool content that what it's like to be a professor. I want to get into academia, too, if you'll indulge me later. But anyway, everyone follow Jessica, please. And don't forget, you can submit questions on YouTube or on Twitter at either one of our feeds. So take it away with this magnificent Twitter storm.

Sure, yeah. So I set this up because, you know, a lot of times you read a press release, and it's great, you're really intrigued, you hop in, and you just want to know a little more, right? What does this discovery mean? Where did it come from? If you recall way back, if you ever took an astronomy class in college, maybe you sort of remembered something,

but you want a refresher. That's kind of what I've put this together for. So it's really to set the stage, what does it mean to be a black hole, to find a black hole, why are they interesting, why are they important? So I think maybe the first place to start is here. So when stars die,

If they're big stars, really massive stars, say 10 times heavier than our sun, we think they will collapse and leave behind either a black hole or a neutron star. What's funny is we teach all of our undergraduates. If you're eight times as massive as the sun, you'll turn into a neutron star. And if you're 20 or 30 times as massive as the sun, you'll turn into a black hole. The reality is we don't actually know those numbers very well. That's a big puzzle for us. And what we used to tell everyone, we think now might be wrong. So that's a lot of what motivates our work is which stars die and leave behind black hole ghosts and which ones die and leave behind neutron star ghosts.

Yeah, I'd say that's the first bit. So then we do know of black holes. We know they exist in the universe. And a lot of what we know comes from looking in our own galaxy at black holes that have companions. So this is a little swarm or family picture, family photo of all of the. the black holes with companions that we know about in our own Milky Way. See, it's pretty small. There's only about two dozen.

All of these have bright companions that are dumping gas onto the black hole. It's falling in, accreting, and then it glows in the x-rays. So this hot gas that varies with time is how we recognize these systems, these black hole systems exist in the first place. Then we monitor the star, watch it wander around, use that to measure the math and show whether it's a black hole or neutron star. So that's a, we know a couple dozen, but you see they're all in these binary systems, all with companions. These days, the black hole family picture is growing even larger.

These are all the black holes that have been found now with gravitational waves. These are the ripples in space time that are propagating through the universe from many distant galaxies. These are not in our own Milky Way galaxy. So each one of these combos of two blue points here is a binary black hole. that merged and sent out its gravitational wave siren that we're now able to detect. You see, there's now almost 100 black holes and even a few neutron stars where they've measured their masses, figured out where they came from, what they turned into. But this is a big family portrait.

The only problem is everything still in a binary system. So if we want to know where black holes came from, what kind of stars they died, originally had and then died from, the binaries are not enough. The binaries are really messy. They had only the close companions are the binaries we can probe today. Only these tight binary black holes are the ones we can see. What about the things that are far apart? What about the things that aren't in binaries at all that are all isolated and lonely black holes?

That's what we think most of them are. We think most of them are probably just floating around, isolated, not doing anything, not accruiting any gas, not growing. Something like 100 million in our own Milky Way, probably, of these free-floating ghost black holes. And so that's where this work comes in, is how do we go about sort of filling in the gap between these binary black holes

and their progenitor stars and find the free-floating isolated ones that are out there and that we think are so numerous. You said this place was steps from the water. We just haven't found the steps yet. How much did we save? Enough.

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It matters where you stay. Hilton for the stay. So that's where gravitational microlensing comes in. Brian, have you ever used microlensing in galaxies or cosmology? Well, we use it in, We use it quite frequently in the CMB, not to look at necessarily innards of galaxies or stars, but we are looking for the imprint of other massive objects, including neutrinos, on the clustering properties of galaxies, which are in the foreground for the CMB.

So we do use it, but not quite in this way. It's a ubiquitous tool in astronomy, though. You're absolutely right. Yeah, so gravitational lensing is pretty fun because gravity is just a property of matter. Everything is providing gravity and lensing all of the background objects behind it. So we just use that same, as Brian said, ubiquitous technique, but we're hunting for these isolated stellar mass black holes. This is a fun little animation that my postdoc Matthew Freeman put together where he just took a picture of the sun. This is not real.

We can't observe this, unfortunately. He took the picture of the sun and sent it behind a black hole and you see what the gravity of the black hole does to the light. that's coming from that background star, it warps it. So instead of seeing one picture, you actually see two pictures of the same thing, and then it warps it and turns it into these arcs very temporarily. What's really fun is you can do this experiment at home. If you go and take a wine glass and you hold it up in front of a light bulb or a candle, you can see the bottom of your wine glass produce the exact same effect.

It's really fun. The multiple images, the little arcs makes the candle brighter. The black hole is doing exactly the same thing to the background light. Is this comparable in mass to what the black hole is potentially that you've discovered, or is this just a more massive one? Yeah, this is not the right geometry. The star is really close to the black hole just behind it in this case, and we're way zoomed in. So unfortunately, all of our modern telescopes can't see these two images.

We can't see the arcs. So instead, yeah, our picture's a lot lower resolution. And of course, Einstein didn't think that it would be possible to detect this gravitational lensing. I love the paper, which is just like a letter. Can you imagine, Jessica, if we could just write to nature, just like on a cocktail napkin and say, I think he said, like, a while ago, my friend Mr. Mandel came by and asked me to do a little calculator. He basically derives gravitational lens in a, you know, in a napkin that he sends immediately gets published. Good for him. I mean, I'm looking forward to those days someday, Jessica.

I don't know the observational paper that confirmed the periap's procession of mercury, which was the validation of general relativity. That paper was a lot longer. Yeah, that's true. Yeah, so this is fun too. So this is a second view, but looking top down, again, to kind of give you a sense. So if we're here on Earth, let's see, I could probably blow this up here. Yeah, there we go. Can you still see it, Brian?

It says click. Is there, can you just like zoom in on the actual web page? Because now it's, I just see it says click to exit full screen. Ah, yeah. Okay, so it didn't, here, I'll just leave it here then. So let's say we're here out on Earth. Here's our Milky Way galaxy. We could never get this picture because you have to fly out of our galaxy to see it.

But we're looking towards the center and we see some random background star. And we're waiting for a black hole to just have a chance coincident alignment. And you can see when that does happen, the light raised from, that background star bend towards us. So that's kind of what we're looking for. That's exactly the signal that we're looking for is that chance alignment of the black hole in star temporarily. And as it moves in front, it bends the light rays

and makes the background star look brighter. And it also makes it take a little jaunt on the sky. It makes it wobble around a little bit. Yes. So that's kind of what we're doing is where, I won't go through all of these. The Twitter feeds up. You can definitely see it.

But here's kind of the actual data. So this is from a ground-based, telescope called Ogle. It's a survey. The telescope's located in Chile, and it's staring towards this very crowded star field all the time, just waiting to see a little popcorn like this, as you see in the middle. It brightens, and then it goes away. And then here's the measurements of what happens down on the bottom. It brightens with time for a very short period of time and then falls away. So that's the signal we're looking for. That's the signal of gravitational microlensing, but this alone doesn't tell you whether it's a black hole or just,

a foreground star or brown dwarf or exoplanet that might be doing the deputations. Right. So my colleague, Kim Greist, who coined the term macho, I believe, he, you know, he and his colleagues, I think some from Berkeley, searched for this effect in the halo of the Milkyway by looking at, I think, the small Magellanic cloud. And he used this to set limits on the amount, he and his team, to set limits of the amount of machos, massive, compact halo objects that it could be to potentially solve the dark matter crisis problem, which is a topic for another day.

But how can you be sure these aren't, you know, because they did find a lot of, you know, machos. There are tons and tons of these things. There's just not enough to make up enough dark matter to account for the missing gap between barionic dark matter and total dark matter. How do you know that these are black holes or not just ordinary Jupiters

or something less exotic. Yeah, so if I go back up to this picture, so in, let me see if it'll play, there we go. So if you look on the lower left and lower right here, you see that it gets brighter and fades away, but there's also a change, a wobble on the sky. And that wobble on the sky, if you can measure that with astrometry, as I mentioned earlier,

you can measure the lens mass. So you can tell is this thing a tiny Jupiter that's 100 Earth masses, a small fraction of a stellar mass? Is it a star that's one solar mass? Or is it a black hole that's 10 solar masses? So we use both the little wobble on the sky, which is the thing that's really hard to measure,

and we're only just now measuring the first astrometric microlensing signals. So that's really the key difference. And do you also get color information as well? You can show that the lensing event takes place for all wavelengths, or not yet? So you can do that. We do, in fact, have that because we observed with Ogle and two different filters, and we observe with Hubble, Space Telescope, and two different wavelength ranges. So that's all there, too, and that's an important piece of the puzzle to make sure that it's not.

This thing is, let's say it's three solar masses. It could be a three solar mass star. So we use the color information to tell us, hey, no, there's no starlight here. Both the color of it is wrong and just the overall brightness of the lens itself is wrong. So we can infer all of that. So it's the size of that astrometric wobble that you'll see going there, plus the color and brightness information. Those two things tell us the mass of the lens and whether it's bright or dark.

And that's the fake data. The real data is down here. So you can see the signal we're trying to measure is pretty tiny. Right. So we expect the star to move on the green. gray line and instead it moves on this red line right there. Yeah, so it's a pretty, pretty tiny measurement. It's about one milliarck second on the sky.

And that's kind of like measuring, if you could, take a picture with your camera of the surface of the moon, somebody standing up there. It's like the equivalently trying to watch their eyelashes blink. Wow. The kind of scale of the measurement we're trying to make. How big is the Ogle telescope diameter? So the Ogal telescope isn't able to measure this.

This is measured with Hubble. Oh, this is. Yeah, Ogle is still a decently. In fact, it's bigger than Hubble. It's a three meter telescope. But it's on the ground. So the Earth's atmosphere blurs everything out, makes your images very fuzzy,

and so you can't measure positions very well. The Hubble, because it's in space and doesn't have to contend with the Earth's atmosphere, gives us much sharper images, and we can measure this astrometric signal, the position of the star way better. Were you able to get the Hubble telescope time ahead of time? Was it based on the fact that you had done some measurements with other instruments?

Or did you, is it serendipitous? You know, and that you found this by accident. Walk us through the order of operations. Did you kind of suspect you could detect this guy but didn't know exactly where to look? Or how did you really zero in on this? It's fascinating. Yeah, so it's kind of funny. Way back when I was a postdoc at Caltech.

So I had just graduated. I've been working on the Glaxic Center, and I was looking for new projects and new ideas. And Caltech's a great place to be innovative, right? You can go and have coffee with colleagues, and they'll ask, hey, you know, I have this idea with this work. And I'm like, yeah, the technique works. We can do this astrometrically.

This would be really fun. And then we wrote a proposal and tried to do this at first with the Keck telescopes. So, yeah, so we thought we could do it. We proved to ourselves we could do it technologically. and that we think that there were enough signals out there, black holes swarming around to find them. And we put in our first proposals and started our first experiment. And we started with just three targets.

And two of them were really crappy weather, you know, just cloudy during the event. So it didn't work out so well. And then the other one, we didn't see a signal. It just kept following, you know, the expected line, the gray line, so to speak. But we proved to ourselves we could do it that, you know, The signal was, our ability to measure it was good enough that we could have seen a black hole if it was there. That's how we got started.

It wasn't very exciting work. And the result, you know, I wasn't on your show. Actually, the show didn't exist. But, you know, for a non-detection, you don't get much more press. Sorry about that. The lights going off. But, you know, that's how we started. And that's what we had to do, that hard work to show it was possible technologically wise.

Yeah. And then to connect Hubble in, so after we did that project, we started proposing to work with Keck again. And then our colleagues at Space Telescope, the team led by Kyle Ashahoo, who's on the competitor paper, they started using Hubble data. So we kind of went in parallel. We were working with Keck and they were working with Hubble to try and find these black holes. I see. Hold on. Give me just a minute.

There we go. trying to trick the lights to coming back on. All about saving energy in California. So if you don't move a muscle in your body, the governor shuts off our lights. It's rough. All right. Yeah, so I think then the Hubble data for this target,

the way we use two telescopes. So we use one telescope, which is a ground-based telescope, to just constantly be looking for possible microlensing events. That's what the Ogle survey and the Moa survey do. These are on-ground-based telescopes constantly staring and making images and movies like this. And then we have to pick out. There's maybe a thousand, 2,000 microlensing events every year. And of those, maybe a handful, five, might be black holes.

Right. So how do you pick out the needle in the haystack? So I think that's the fun part of the job is picking which targets you're going to look at. And we have to be really careful. We start observing them. We decide right about here. This one's going to be a good black hole candidate. We don't know, but we're going to try.

And then we point Keck or Hubble at the peak, right at the peak of the event, and then we have to follow it all the way down for several years. Ah. Mm-hmm. And right. So you're using the ground base to select it on the left side of the curve and then Hubble and then Ogle again? Or, I mean, you can't get five years of Hubble time dedicated, I'm sure, right? Not the whole time, no.

So we're constantly continuing to watch with Ogle or Moa. And then the Hubble data, we take, you know, one or two or three measurements in the first year, and then one measurement in year two, another one in three, four. But we're just taking one measurement, right? So that's why this astrometric curve is so sparse, right? It's not all filled in. There's just a point there, a point there, a year later, a year later, a year later. So it's a long-term program, for sure, a very patient one.

Yeah, my grad students aren't always happy about that, right? It's a project that takes longer than a grad career. I know. Well, I say it depends on how long a grad career half-life is in your group. but I say start complaining around the eighth year and then I start listening to when we can make red. No, I'm just kidding. I've never had someone take eight years. Seven, but not eight. No. So great. Okay, cool. So we've gotten over the right. So we're extrapoling down. And then what if you saw something strange, you know, at what point, I mean, do you want to really catch, how important

is it to catch that very most peak point, you know, because that seems like that could be pretty crucially relevant. Are you less sparsely sampling at that point and really densely trying to cover it? Yeah. So that's absolutely the case. So in the first year, you'd like to have more measurements. But actually, the peak of when the astrometry peak happens is not at the same time that the brightening peak happens. Let's see. I think I have in this paper, we have a fun figure here. Yeah. So this is the same event, that same black hole. neutron star candidate that we're talking about. And you can see that this is in timescales of days.

So this is 2,000 days for each tick mark. So the peak of the astrometry doesn't actually happen at time zero, which is close to this 56,000 there. It actually happens a little bit later, a lot later, in fact, like a year later, depending on the event. So that's kind of cool because we can catch it when it basically has almost no wobble and then catch the wobble and then watch it fade away. That's kind of what we're doing.

And we have the luxury of time with these black hole candidates. Oh, wow. Yeah. So then after that, once we've got both our brightness, photometry measurements and the position astrometry measurements, we put it all into a really complex modeling process to get out that lens mass and a bunch of other parameters too. And this is, we did this for five targets.

observed with Hubble. And this one, which is called OB-11-0462, is the last one that has the biggest masses. But the hard work is that you can see there's two possible masses, two sort of solutions that might be allowed. At least that's what we find in our data. The competing team finds a one solution with a little bit higher mass. But no matter what, these are in the mass regime where there are more massive than stars, typically in the neutron star, black hole mass range. And that's the real, that's the photometry data that I was talking about there. So unless you have other questions, I can show, keep going down this or I can stop sharing. No, no, keep going.

Okay. People are loving it. Yeah. Yeah. Yeah. So the black holes, you know, and the mass is one thing. If it's bigger than a sun-like star, we know it could be a black hole. And then we have to show it's dark.

There's other figures in the paper that go into why we think it's dark. But we're pretty calm. Both teams are very confident about that. And so it's just really the masses that we're debating, whether it's definitely a black hole mass object or it's at the boundary between a black hole and neutron star. So that's fun. And then we can tell all kinds of cool things. We can tell how fast the black hole might be moving through the galaxy. You can see where, like which direction it's moving for the black hole in black and which direction the background star is moving and red.

So there's all kinds of fun things. And then my very favorite part is we can put together, you know, it's super exciting. You find a black hole. That's great. But then what? What do you do? Who cares? Why is it a big deal?

We put it all together. So with a big old computer model, a mock Milky Way in our computer, we say if we know the Milky Way, how many did we expect to detect versus how many did we actually detect. And so then we do this big old population synthesis where we say in some microcontextextive. microlensing parameter spaces, don't worry about the axes here. Where do we expect things to fall? That's all the tiny little points. Those are all mock simulations, not real.

And we expect the black holes to fall down here or down here. And what did we actually find? Well, we found a bunch of stuff ended up up here, but this one event, which is the black and purple contours, fell in this kind of in-between space. So then what's neat is we can use all of them, the detections, the non-detections, to say, is our picture of the Milky Way right? Is the number of black holes what we expected it to be? Is it too low?

Is it too high? Are they moving as fast as we thought they should? What are their mass distributions? Those are sort of the real astrophysics questions that we're trying to get at. So this is the first in the step where, you know, we have a sample of five or six targets. We need to build up the sample to really answer these population questions. Yep. So I think that's all I got.

Everything else is in the papers. There's more fun animations if you'd like to take a look. And I'm happy to answer questions. Yeah, that's really great. So we have a couple of questions so far. And then I'm reminding folks that we're talking with Professor Jessica Liu, is an astronomy professor at UC Berkeley and has been there for some time working with her team. Also, you mentioned quite a lot, the companion or competitor paper.

I guess people don't usually think of astronomy as really competitive and so forth. But can you talk about it? What was the sensation of, you know, kind of not wanting to get scooped or something like that? How did that figure into it? Or, you know, how competitive really is the search space? Yeah. So I think in science, it's always important to have someone checking independently, right? Doing independent work, especially for big results to make sure that everything is right.

And so I'm very used to working in situations where or on science. projects where there's another team also working on the same science project. That's pretty typical for a scientist. So when I worked on the Galactic Center, I worked at UCLA with Andrea Ghez and her group there. And of course, there was a competitive team in Germany led by Reinhardt Genzel. So we were always both colleagues, but always competing. And it's the same thing here. So my group and my graduate student, Casey Lamb, who led this work and just did a phenomenal job, We're always in competition and yet friendly, you know, collegial interactions with the competing team who's led by Kailash Sahou at Space Telescope Science Institute. So, yeah, it was really fun to see both papers coming out sort of at the same time together and really having that independent verification that, yeah, indeed, this is a free-floating ghost star, either a black hole or neutron star.

While we don't perfectly agree on every single thing, I think the main message is. we mainly agree on, and it just means we have lots more fun work to do going forward to figure out why there's differences. Right. So you mentioned one of the key enabling tools was the Hubble Space Telescope. Can you talk a little bit about upcoming measurements either with Hubble or could even the James Webb Space Telescope give us even more clues, more data, better data, how will that play in? So for this particular event, we have one more measurement coming with Hubble this fall in October.

So we're really hoping to fold that last measurement in and really, you know, see if we can definitely pin down the mass. Is it a black hole or is it a neutron star? So that's for this particular target. What I'm really excited about is we've launched a second campaign now that we've gone through this batch. We've launched another campaign we hope to start this fall where we'll, We'll start five more. Now it'll take a while. These each take, you know, four years to complete,

but we'll be able to pick out four or five brand new targets and work on those. And we've got targets we haven't published yet, too, another five from the Keck Observatory. So that population that I was talking about is going to just grow and grow and grow. So that's really exciting. And that's both Hubble and Keck are capable of making these measurements along with the VLT in Europe. Those are the only three telescopes in the world that can really do this.

JWST, will it help or not? Maybe. So I'm really excited about JWST, but we have no idea how it will do with astrometry, the ability to measure positions of stars, because it's a floppy telescope. Right? The primary mirror is segmented. The segments warp. They try to keep them aligned, but that might affect the astrometry. So we have a lot of groundwork to do to see how good JW is going to do at astrometry, both for this project and for the Galactic Center projects. to work on. In fact, I'm leading a JWST Galactic Center proposal. We're super excited to get pictures of the Galactic Center from JW this fall in August or so. Will that be

dedicated towards black hole physics or other astrophysics phenomena? So the JWST Galactic Center program is aimed at both. So you can get black hole science, watch the accretion onto the supermassive black hole. You can get stars science watching all the stars zip around, which ones are binaries, which ones look typical or unusual, and even what I'm super excited about, stellar mass black hole science. So we have some hints that we might be watching stars wobble around stellar mass black hole companions. They're not accreting.

They're still in binaries, but they're separated binaries compared to like those LIGO ones that I was showing earlier. So we're hoping to use JWST to confirm whether those are real or not. Oh, wow. And then we have a question from Ernesto. He's a friend of the show. I'll put it up there on my screen. Would we be able to detect the presence of black holes from similar types of effects,

but on incoming neutrinos? Do black holes affect neutrino gravitational lensing in the same way they do for light? Yeah, that's definitely tricky. I think there aren't, so this signal requires a lot of light to measure it. And so I would guess the neutrino streams are all too thin. There's not enough neutrinos coming in. that we can detect or our ability to detect them is not very good. So in principle, maybe, but you'd have to have a neutrino source lined up with the black hole,

and then you'd have to get enough neutrinos, and we'd have to have better detectors. So that's my take on it, but I am definitely no expert in the neutrinos, Brian. Neutrinos are still in the regime where they name the events after, you know, cartoon characters. And when they detect a neutrino at Ice Cube, they give it names like, Ernie and Bert. So if we did that with photons, we wouldn't have time for anything else.

That's a good question, though. Thank you. Next question comes from a person who actually stole the name that I was going to name for my second child. The name is Prometheus. Prometheus Unchained, who asks both of us, what happens to the space time

in the electromagnetic radiation around a black hole ring rotating near the speed of light. I guess this question maybe if I could reimagine it, reinterpret it from Aetheus. You know, what is the nature of space and time near these free-floating black holes versus the ones you see in interstellar

or even the ones the super, super-duper massive ones at the center of M-Av7 or even the Milky Way? How do they differ? Yeah, so the fun thing is that that gravitational warping of space time is in a sense scale-free. It can be a big black hole or a small black hole, but the space-time around it responds in the same way.

It's just how much curvature there is, and that's all related to the lens mass, the mass of the black hole. So you scale up, you get to a big supermassive black hole that's more massive. You get more warping at a fixed distance. You scale down, you get less warping at a fixed distance. But if you convert into event horizon steps, not meters or, you know, kilometers or miles.

You just convert into units of event horizons. Everything behaves the same around a big black hole and a small black hole. So that's kind of neat. And then for us, the stellar mass black holes that we're seeing in gravitational lensing, the light rays that are coming in from the background star, they're not actually perfectly aligned. They're offset just a little bit. And so the light rays are not passing necessarily super close to the event horizon.

They're approaching the black hole from a little bit further away. 10, 60, 100 event horizons away and then getting bent and warped back down. If they were going too close, they would actually do crazy things like wrap around the black hole and be sent far, far away from our telescopes. Someone whose name I won't pronounce, let's say, it ends in dreams, is asking, how do we know it's a black hole and not a black sphere? I guess my question to you, to reimagine that question, it would be, you know, you do kind of couch in appropriate terms that it could be a neutron star.

I don't think it would be any less excited. You know, it's like I called the show Ghost Black Hole, but, you know, ghost neutron star is pretty damn scary too. But anyway, how do you know, like, why did you use that specific languages? And, you know, I think it's a teachable thing for the audience, many of whom are grad students and say, how do you write a paper title and balance that, you know, kind of, you know, need to get the appropriate detention, but also to be cautious and couch things in the right terms. Why did you say could be a neutron star?

Yeah, so the data still allows for neutron star. We know this thing is dark, but not so dark that it has to be a black hole. Neutron stars are extremely dark too. Now, we're used to thinking about neutron stars as pulsars. These would be a subset, a small set of neutron stars that are very young. They may still have a lot of electromagnetic radiation coming to us in the form of these pulsars. Most neutron stars are cold. They're dead.

They have surfaces, but they're so cold that the light that they're emitting is really, really, really little. And so, you know, imagine a neutron star is smaller than Pluto. It's at times sizes of asteroids and think about how bright asteroids are. They're very, very dark by themselves unless they're reflecting sunlight. So if you put an asteroid out in space, it's not going to emit hardly anything. Same thing with a neutron star. So neutron stars are very dark, but they're not zero.

And black holes are very dark to the point where there's zero light coming out. So it's a really small difference between a black hole and neutron star in terms of brightness. And it's only the masses that we sort of think tell us which one is which. Exactly. Now I want a question, which isn't really fully fleshed out, but I'm going to kind of riff on it from T-Car. We might be related to Missy Carr. I'm not sure. but T-Car is asking or just mentioned spin, charge, and mass, which are the three properties.

You know, black holes are kind of like commodities. You know, they're fungible. You've seen one. You've seen them all. But I'm wondering, yeah, could you perhaps address the question of what other properties of black holes besides the mass? Could this technique enable, if any? And, you know, don't feel pressure to, to, you know, overreach on my behalf. But could you get at the spin and charge of a black hole?

from this type of new technique? I don't think so. So charge almost certainly not because it doesn't, well, we don't really know how it would affect the light rays that are coming in. We don't know that the charge would affect light at all, right?

So I don't think we could probe the charge at all if it even existed for astrophysical black holes. Spin is another game. So in principle, yes, but I don't think we have the ingredients nor the facilities to observe it. So the spin, if you had a perfectly lined up black hole and star, which is extremely rare to the point where it almost never happens.

Almost there's always a little bit of offset between the two. But if they were perfectly lined up, maybe there would be an impact where the Einstein ring, those arcs that I was showing, it turns into a full ring if they're perfectly lined up. That should shrink in or out depending on the spin of the black hole. But the effect is super small and we can't today resolve the ring. So I think we are a long, long way from being able to do that for stellar mass black holes. But of course, they're really excited to try this for the event horizon telescope for supermassive black holes, where the event horizon is big enough. We can actually see the ring.

Right. And maybe riffing on that, we'll pivot to the buzzword of the last decade old survey, which was multi-messinger astronomy. George Anderson is asking, what exactly is the mass of the ghost black hole you're observing? so I'm going to just cut and paste or read off the astramash. Has an inferred lens mass of between 1.6 to 4.4 solar masses. Is that right, Jessica? Yeah, that's our result. And then Kyle Ashahou's result paper has it around seven solar masses.

So, you know, there's still a decently uncertain mass. But as we find more of these and our measurements get better, we're hoping to find a bunch of black holes and know their masses really well. Let's see, Ernesto again is asking a question, could there be a unique topology for each black hole, considering that if all matters compressed, an order fell in plus hawking radiation? In other words, I guess does the topology of spacetime or geometry moreover, it really is only dependent on those three properties, right, mass spin and charts. So no, Ernesto, I think, Jessica, if you agree, there wouldn't be anything specifically unique topologically speaking. different, we have to disentangle topology from geometry.

So no, I don't think so. Jessica, am I wrong, all right? As far as I know, no, but, you know, there are a whole suite down the hall of sort of quantum mechanical gravitational, you know, people at that interface who are trying to prove whether that's the case or not. So someone I'm sure is working on it, but not that I know of. So in terms of multi-messinger astronomy, you mentioned multiple different instruments that you're working on. Where do you see, you know, the future, the next 10 years of

black holes, is more event horizon data combined with stuff like this on kind of outskirts of black holes in the galaxy, not at the galactic center? How do you see the portfolio of black hole astronomy improving with Gaia data perhaps and other things? What does the landscape look like? Yeah, I think it's a real revolution that starts with the, advent of LIGO and gravitational wave detections. I mean, we went from 20 years of knowing a handful 10, 20 black holes, all accreting from a companion to overnight in the space of three or four years, you know, multiplying that times a factor of five. And these are now dark black holes with just another black hole companion. So it really is a game changer, the detection of gravitational waves.

So there's 100 black holes today. Five years from now, there are probably going to be a thousand black holes known from LIGO gravitational wave and Virgo gravitational wave measurements. The black holes, the isolated ones that we're looking at, we have one maybe now, but we're looking at after the Roman space telescope launches, we predict there could be hundreds from that survey. So again, just rapid, rapid expansion of the black hole landscape. Gaia will find black holes in binaries that are with distant companions, not accreting gas. So we hope that number will be in the hundreds, if not thousands.

Yeah, I think it's like the early days of exoplanets where you were going from one or a few every few years to suddenly just an explosion of lots and lots and lots of exoplanets. And what's fun about black holes is then you get to do all kinds of cool astrophysics with it. Where did they come from? Connect them back to their stars. How do they influence their environments? That's really what we're looking forward to. Yeah, awesome. Channel Warhorse listener viewer is pointing out that we've only known black holes exist or predicted to existence the 1930s.

So they're not even 100 years old, and yet they've revolutionized not only our view of the galaxy, the universe, but also quantum mechanics and things like hawking radiation, wormholes, and so forth. What is most fascinating to you about black holes, Jessica, just on a personal to human level? What fascinates you about these objects? Your summer starts now with Memorial Day deals at the Home Depot. It's time to fire up summer cookouts with the next grill for burner gas grill on special buy for only $199. And entertain all season with the Hampton Bay West Grove seven-piece outdoor dining set for only $499. This Memorial Day get low prices guaranteed at the Home Depot. While supplies, price invalid May 14th or May 27th, U.S. only exclusions apply.

See Home Depot.com slash price match for details. Yeah, I think it is the mystery. It's not knowing what happens inside them and knowing you'll know. never know, but somehow still trying to figure out this puzzle, right? And I don't know if it'll be astronomy and astrophysics that helps answer those questions. I think it's going to take everyone to try and figure out what's happening in the inside of a black hole. But yeah, I really love this, you know, from the universe's perspective, trying to understand fundamental physics, this place where we, it really is a deep mystery and these things are more exotic than anything we can

ever hope to make on Earth. You mentioned black holes and dark matter and beer-ruban observatory and stuff like that. People often think that the black hole, the Milky Way, is somehow responsible for dark matter or the behavior of our galactic orbit, which is not. But I have a video about that somewhere else in the channel about maybe it was on the event horizon, Sajai star detection. But I guess one question I have is, if you, you know, how many of these things would be finding if they could seriously contribute to the dark matter gap, you know, between barionic

and non-barionic dark matter? How many would you, I mean, would you just be overloaded with these and couldn't even get Hubble time because it's like looking at, you know, staring directly at the sun or something? Yeah, so it's a great question. So is dark matter just made up 100% of primordial black holes? And so you were mentioning the Macho Project earlier said, no, that can't be the case, but that was for a very specific, if all primordial black holes are a specific mass. Let's say the universe conspires and that dark matter is all primordial black holes, but they run a huge range of masses. Stars don't all have one mass, so why should primordial black holes have all one mass? Yeah. So maybe they run from moon masses up to 100 solar masses. So if that were

the case, I don't think we yet have the observations to totally rule out that scenario. So that's something where I think people are still actively working on is do primordial black holes exist? Do they make up all or some of dark matter and what is their mass range? Right. So yeah, so I think that's a really super exciting question. Could dark matter just be these primordial black holes? Now, even if it is, they're still pretty exotic. These are not black holes born from dying stars. They're black holes that were born at the beginning of the universe during the Big Bang. And how does that happen? Who knows? Right. So I think there's still a lot of exciting things to do with primordial black holes and and still a lot of exciting experiments to conduct to prove that they exist or not.

Excellent. Next question comes from Erin Lampa. She says, other than being really interesting and cool, what's the main goal of studying black holes? What kind of science or technology could this eventually lead to? I'll let you answer them. Yeah. So in terms of science, understanding the universe,

I want to know when our star dies, what's going to happen? Well, we think it's going to turn into a white dwarf. But a lot of our neighbor stars are way bigger than the sun. They're 10 times as massive. What's going to happen when they die? Are they going to supernova? And will that impact us? Or are they just going to direct collapse into a black hole?

Are they going to turn into a neutron star? You know, we don't know. This is what we're trying to answer. So that's a fun one we're trying to understand. And then if we want to understand the whole history of the universe, how our galaxy came to be, these stellar mass black holes play a role. They provide a lot of feedback that when they are accreting

in their early young days, they can have jets and influence their surroundings out to huge distances. They can heat up the whole galaxy. Lots of and lots of fun astrophysical questions. In terms of sort of fundamental physics, I think it'll be a combination of gravitational waves, event horizon telescope, that are where they're probing this interface between gravity and quantum mechanics, and then a lot of theoretical work and experimental work in labs. So I would say these stellar mass black holes are more about the, astrophysics we want to learn about the understanding what the universe is doing around us.

Interesting. Great. Yes. I often say, you know, the problem with basic science research like you and I do is that sometimes it does produce technology and then everybody expects it to keep making, you know, a faster internet speed or something like that. So the last couple of questions before we wrap up, you and I both have telecons. We spend more time on telecons and telescopes. At least I do. I wish I could spend more time on telescopes. George Anderson's asking, what kinds of things we'll be able to learn once we have data on thousands of such black holes

or some large number, when can we start, you know, go from n equals 1 to n equals, you know, 10 to the 3rd or something? Yep, I want to know how many black holes are in our galaxy. Is it 100 million? Is it 10 million? Is it a billion?

That's the level of uncertainty we have. We don't know. And that tells me how close is the nearest black holes. hole. You know, how big of a spaceship do I have to build if I really wanted to go probe and event horizon, for instance? You want to be Matthew McConaughey in real life. Yeah, right. Exactly. Yeah, what's the biggest black hole? What's the smallest black hole? What's the difference between a black hole and a neutron star? Do they overlap in mass space or not? Yeah, so those are some of the fun questions I hope we can answer in the not too distant future.

Amazing. And let's see. The last question, I think, have time for today. We'll have to get you back on the show. It comes from again, Ernesto. He gets most frequently asked question of the day. So he's asking, is it possible that relativistic particles coming from black holes fall into gravitational or interact with gravitational waves and you could get some kind of amplification perhaps or compression from the, from somehow gravitational waves interacting or the particles interacting with. gravitational waves produced by black hole. This is an isolated one, right? So this one has no gravitational radiation, Jessica. Am I wrong? That's right. This one is completely dark. Black

or neutron star, it has no electromagnetic radiation that we know of at the moment. It might, it's probably a small amount if it's a neutron star. But yeah, these are these are dark enough that we don't see any big EM-6 star. Right, okay. Abbas, Safari, I think I asked, would you please answer my important question? Would you not first know what a black hole is, how is it created or how it looks like before you look at it. So I think this person's asking, you know, how can you really tell it's a black hole? And I think what Jessica said, and if I don't misinterpret you, is that you as a scientist, you want to be cautious, you want to say, here are different possibilities. She's not saying it's 100% guaranteed to be a black hole

or your money back, which is nothing. But, well, actually, these people, many of them pay our tax, our salary in the state of California. So we can't be too cavalier about it. So I think if I'm not mistaken, Jessica, that's the answer. You say what the likely, you know, possibilities are, and then nature will tell us the right answer once we have an update. Yep. And I think at the center of the galaxy, the Milky Way, the supermassive black hole, that's where we've got the best results. We've looked, we have such good data that there's nothing left. People have tried to, at least that we know, people have tried to invent exotic quark stars and all kinds of fun things that could reside and instead not be a black hole.

and all of them have been disproven by our ability to smash so much matter into such a tiny, tiny little volume. The only thing we know right now that fits that picture is a black hole. It's a black hole. Well, Jessica, it's been a delight. I know my audience just keeps growing and growing over a couple hundred people watching us right now. Chat about rogue black holes on the rampage. Thanks to the discovery of you and your massive, amazing team at UC Berkeley. Any exciting other things that you're interested in sharing with the audience before we break for the next telecom?

Sure. I think there's lots more black holes to come. And I think there was a question about the technology. I'm really excited to also help work on the technology that will make this possible to measure, you know, not just one every once in a while, but to throw this into tens or hundreds of black holes that we know about in our own Milky Way backyard. Would that be a new telescope or like a dedicated survey like Zwicki or something? So it's a all of the above. Ruben and Roman are telescopes that are being built now and will be launched and available soon.

And then we're upgrading the Keck Adaptive Optic Systems to make our biggest telescopes capable of taking the sharpest images. And, you know, JWST. So, yeah, I think this will all be with things we're working on actively today. So it won't be too long in our lifetimes for sure. And hopefully in my next round of graduate students. So in the next 10, two decades. Jessica, if you guys like these kinds of episodes, let me know, leave a comment. If you ask me more office hours with my brilliant colleagues and friends from around the world of astrophysics,

we've got some exciting episodes coming up, Bill Phillips, who won the Nobel Prize in 1997, recorded an episode with him recently about technology that's been used to standardize our measurement of time and space over the millennia. So that's an exciting episode. I have Govert Schilling, who wrote a new book about Dark Matter. That's a coming out called the Elephant in the Universe. I'm interviewing him. A man by the name of Bernardo Castro is coming on the show of the podcast this summer.

So let me know. Do you want to see more episodes like this with my brilliant, luminous colleagues like Jessica? Or more solo deep dives. How would you like to see the direction of the Into the Impossible podcast going in the future? But for now, I want to thank Jessica so much. I love your work. You have an awesome, as I said. You have this killer brand.

It's like Louis Vuitton of a lot. astronomy. It's been such a delight talking to you. I really appreciate it, Jessica. Thank you so much. And thank you everybody for tuning in. And we'll tune in next time for the Into the Impossible Podcasts. Thanks so much, Brian. Back to you later. Bye. Take care. Bye, guys. Any sufficiently advanced technology is indistinguishable from magic. Ambition comes in all shapes and sizes. At First Citizens Bank, we roll with your goals because we're built for what you're building. fit for your ambition for citizens back.