 Hello, everyone. Welcome to our love physics webinar. Remember that this is a webinar cycle created to join physicists all around the world working on astro particles, high-energy physics, and astrophysics. The whole transmission will last 60 minutes, and this will include questions from our participants. And please don't forget to follow us on Twitter, Facebook, and subscribe to our YouTube channel. Our next speaker is Annie Anne Luffing. I'll say this for all the everything wrong. She's originally from Germany. She graduated as a physicist from the Friedrich Alexander Universitat Erligard-Nurwe in Germany, and then she moved to the U.S. and did her master's and PhD at the University of Maryland College Park under the supervision of Dr. Chris Reynolds. Then she moved to England as a postdoctoral research at the Institute of Astronomy at Cambridge University, and then last year she came back to the U.S. as an assistant professor at the Extreme Gravity Institute at Montana State University. She works like in a nutshell trying to explain understanding fundamental physics around compact objects using many X-ray missions such as Chandra, Susaku, and Newton. She also studies the long-term behavior of black hole binaries to see and disentangle physics. So please join us in a warmly welcome to our low physics speaker today, Dr. Luffing. Thank you, Alejandro. Trying the screen share. Thank you very much for having me, and welcome to today's low physics from Montana State. And today I'll be talking about black holes. But first, before I even start off with that, I wanted to mention my main collaborators in all this work that I'll be presenting to you. There are many of them, because all those satellite emissions that I use and I'll be talking about, they obviously involve lots of people. So it's always a joint worldwide effort, really. Okay. So black holes, I think you all have like a very good idea of what a black hole is. It's a result of a prediction of Einstein's GR. It's an object from which no particle can escape, or even light cannot escape. And the way it's shown here, this is obviously not the way black holes look like at all. If it looked like this, I wouldn't be studying it. And so by the end of this talk, you'll hopefully understand that this is a terrible representation of a black hole. Okay. So what kind of black holes do I study? There are two types of black holes. There are small black holes and big black holes. What I study are big black holes. They're a million to a billion times the mass of our sun, and they can be found in the centers of galaxies, including in the center of our own Milky Way galaxy. And the black holes, usually they will just sit there and they're very difficult to observe, but I like to observe them. So in order to be observable, they need to be accreting matter, or matter needs to be falling onto them. And if they are actively accreting matter, they will shine very brightly in lots of different wavelengths. And I'll go into that in a little bit more detail. And then you call them active galactic nuclei or AGM. And these are the kind of black holes I study. So they are supermassive black holes, which are actively accreting matter, not just a little bit, but quite substantially. And their radiation can be so strong that it out shines the whole galaxy. Okay. So why would you even care to study supermassive black holes? Well, first of all, black holes are a lot of fun. The surrounding of black holes is a great way to probe GR and all sorts of other fundamental physics. Black holes are, for example, the only objects in the universe that don't have a surface like neutron stars are very extreme objects, but they do have a surface white walls have a surface, pretty much anything else you can imagine has a surface, but black holes, they don't, they don't really have a surface. So when I had to decide what to study, I decided for black holes, because essentially, it's the craziest, weirdest physics you can possibly imagine. But supermassive black holes, they have also a wider range of like studying them can give you a wider range of knowledge. Turns out that they're really important for the evolution of galaxies or shaping the galaxies into what we see them today. Without black holes, galaxies would look very different. And it is impossible to simulate the universe like we see it today without black holes. So understanding the radiation from black holes is really important because it can also shape shapes the galaxies around them. And they're pretty much although they're tiny at the center, they interact with their whole surroundings. So for example, they regulate star formation in the central region around the galaxy. Okay, so which part am I really interested? So in my case, I've shown you here an example of a galaxy. Say it's about 85,000 light years across. But what I'm interested in is really the central and most region around the black hole, like say four light days in this case, depends on the mass of the object. But for this particular example would only be four days large. So really tiny region of this whole galaxy and this tiny region, the emission coming out of this tiny region determines what happens to the galaxy as a whole, which is pretty cool. And how that exactly goes down, we don't understand yet. Okay, so what about the black hole? Obviously for this central region, the thing that is shaping everything there is the black hole itself. And the black hole itself can be described by three distinct parameters essentially. Mass, the spin or the angular momentum of the black hole and its charge, but in astrophysical settings, they essentially assume to have no charge. It's assumed that they will just discharge. Okay, so really, we're just worrying about the mass and the spin. Okay, so because everything, the spin is kind of a smaller correction, mass is really the biggest factor that determines all the size of the region and everything that happens around the black hole, it makes sense to kind of define kind of spatial unit that is dependent on the mass and that's called the gravitational radius and it's just GM over C squared. So that means all everything that happens around the black hole, all the scales, just scale with its mass. And then there's a small correction for the spin, and we'll talk about what the spin does in a second. Okay, so now we're now like basics about black holes. I want to talk to you about a few open questions in AGM astrophysics that I look into. One is what is the black hole spin and what can we learn from knowing it and how do we even measure it. And then the second is you've probably heard that AGM can have strong relativistic jets or like streams of matter outflowing from them and we don't very well understand how these are created or powered and the spin can maybe help us with that. And but most and overall the question of my research is how exactly is matter created and converted into radiation around the black hole and what is the therefore the layout of the central engine around the black hole. So obviously we can't look inside the black hole unfortunately, but it doesn't really matter what is inside the black hole anyway. Really, we just want to understand the outside where all this radiation is coming from. And then if we can understand how this radiation is being generated, we can understand how much black holes have emitted over time, say at ratio of three or four, and therefore how they've been shaping the galaxies that we see today. Okay, so let's talk a little bit about what we do know and now we'll go into what we don't know or what we try to understand. So if we have matter and it's close to a black hole and the gravitational pull will pull it towards the black hole, but because the material has angular momentum, it will not just jump in. In fact, it will form a disk around it and we call this disk an accretion disk. So here we have our black hole in the center and around it we have our accretion disk and like a typical kind of spatial scale for that, it's maybe about 1000 RG. So really most of the things I study are within this 1000 RG, which I've given you before as four light days. For this one example of I think a 10 to this 6 solar mass black hole. Okay, now we have an accretion disk around it. So the material doesn't just fall in, but how does the material fall in? So what happens as the material is in this disk, it will have magnetic friction between the particles. In this way, first of all, the disk heats up and it emits thermally in the optical and then in the UV as the temperature increases it inwards. But what it also does, this is the way that the material sheds angular momentum. So essentially it's just, you can imagine it's like rings of particles that are just rubbing against each other. It is via magnetic friction, but even if you think about normal viscous friction, that is not wrong. And the angular momentum moves outward and the material moves inward. And the other most particles have so much angular momentum that they'll eventually get kicked off and they are not actually accreted. Okay, so we now have this temperature structure where we locally at each given point of the disk emit like a black body. So as some accretion, the spectrum will be kind of like a sum of black bodies shown here above in the energy versus flux range. Because I'm an X-ray astronomer, we like to do everything in energy rather than in wavelength. So I think later on there will be some wavelengths, but most of the time it will be about energy. Okay, so now we know that just from the accretion disk itself, just from the accretion process, we expect emission and this emission is observed. Okay, but it turns out that this isn't the only emission that you can get from the surrounding of a black hole. The other thing that must be near a black hole is the so-called corona, which is a set of very hot, very energetic relativistic electrons just shown here and its size is very small. We'll talk about this a little bit later. Okay, so these are also there, generated somehow, we don't exactly understand yet. But what then happens is, so we had our accretion disk emission and some of those photons from this accretion disk would be scattered of those hot electrons via inverse Compton scattering. So you're probably familiar with normal Compton scattering, where it's just like an electron interacts with a photon and usually the photon loses energy. For the inverse Compton scattering, it's the opposite. The photons gain energy. Every scattering, they gain energy of this really hot electrons. And what that does is, you had your original accretion disk spectrum shown here in like the dotted line, it will then gain energy essentially and it will be upscattered to higher energy until the temperature kT, which is pretty much the characteristic temperature of the electrons. Obviously above this energy, you cannot gain any more energy of them. So the photons will actually lose energy again, reverting back to the normal Comptonization process, the normal Compton scattering and you'll just alter the spectra will roll over. Okay, this process is called Comptonization. And this is how we make x-rays. So so far we've just had optical emission and UV emission, but now we have just made x-rays. Okay, but things that even further were complicated. Now we've made x-rays. And some of these x-rays come straight to us and that's that's how we know this is happening. But some of these x-rays will be directed back towards the accretion disk. And they will be backscattered off the accretion disk. And this process is called reflection, confusingly, although it is a backscattering process really and not proper reflection. And depending on where they're scattered off, the material that they're scattered off might be ironized. And if it is ironized, you get a whole set of lines. But either way, you get a very characteristic spectrum. So essentially you get the imprint of what you just scattered off. And if the scattering is taking place from really close to the black hole, then relativistic effects become important, especially like like bending, gravitational redshift. And those nice lines that you had will be blurred out into a kind of pseudo continuum shown here as the solid line. So if we can measure the reflection spectrum with hyacuracy, we can measure the effects of the black hole itself. Okay, so we talked a little bit about what kind of radiation is being produced around the black hole, but how do we like go about observing it? So these black holes are very far away. So although we have this picture that I have just told you about, this picture is created from studying essentially the emission, distribution of the emission with wavelength. We don't understand. We cannot like take a picture of it yet, unfortunately. So it's all just coming from one single point source. But which wavelength can we even observe from the ground? We can only observe in the visible, essentially, and then somewhat in the radio. But in other way things, our atmosphere prevents us from observing. So we need to go to space. But in order to get really close to the black hole, right, the emission we would like to study is mostly the x-ray emission because it's the from the very closest part around the black hole. So we can get the most information about what's going on. So what I use in my research mostly is a variety of x-ray satellites that are capable of detecting the x-ray emission between about 0.1 KV and 100 to 200 KV. So that's already into the soft gamma ray. And I also use HST and another satellite called Swift, which I'll talk about a little bit later to study the UV and the optical emission. So most of my observations are done from space. That also resolves some of those issues with the atmosphere. Okay, now that we know how to measure it, let's just try to make use of all this knowledge and go out measuring something. So how about that black hole spin? How do we get the black hole spin? How does that work? And why would we even care about it? I mean, yeah, it's fancy. It's one of the three parameters that defines a black hole. Cool. But why? So first of all, if we could measure the spin and the changes to our measurements due to the spin very accurately, we could test GR. The second thing is a bit more hands-on. The black hole spin or the angular momentum of the black hole obviously tells you what kind of matter fell into the black hole because it's just the sum of all the angular momentum of the stuff that fell into it. So as we're trying to understand how galaxies evolve over time, we like to understand how they grow. Do they grow by just gradually creating some kind of matter? Slowly stuff is falling onto it, one cloud after the other cloud, or is it a bit more dramatic and galaxies, big galaxies merge together and then their central black holes merge together? And depending on which scenario is taking place, the distribution of spins that we expect will be different. It's very difficult to predict anything for one single galaxy, but we can make statistical arguments. But for that, we need to measure the black hole spin for lots of sources. And finally, it is conceivable that a black hole spin or the angular momentum could power these relativistic jets that we have. We have rotational energy for the black hole. And I've just shown you here again how big these jets are. This can be thousands of light years across, really big. Okay, so how do we get the black hole spin? So I've already told you we talked about x-ray reflection or the backscattering of the x-ray emission of the inner disk. So this is cool because this gives us a tool to probe where the inner disk is. And it turns out that depending on the black hole spin, the accretion disk can get closer or further from the black hole. And what that means, so essentially for a high spin or prograd rotation, the accretion disk can reach much closer to the black hole than for retrograd rotation or no rotation at all. And if you can fall deeper into the potential well, your maximum gravitational redshift is going to be larger. So we can measure this maximum gravitational redshift by looking at the reflection spectrum. We have characteristic lines in that spectrum and we can measure how redshifted they are and how gravitational, how distorted they are to this gravitational redshift. So this is shown here kind of at the bottom. So in the middle one, you have like some kind of average scenario. You have this one line here, characteristic iron k alpha line, which is very spiky here. And it's even more spiky if the accretion disk is further out. But then as you move the accretion disk further in, you get gravitational redshifting. So some of these, some part of this line, this line has been emitted at most radii, but a larger fraction that will come from radii, which are very close to the black hole, which will have a very strong gravitational redshift. So you get this kind of red wing to the line. And if you can measure this accurately by comparing to template spectrum, we can measure the black hole spin. So what do we find? So here I've shown you like a measured reflection spectrum. And if we model this properly, we can find some things. So I've split it up here into jetted A.J.N. and non-jetted A.J.N. So for example, for jetted A.J.N., we find like for the swan source 3C120, we find a high spin. And the same thing seems to materialize for other sources as well. It seems to be that jetted A.J.N. in general have very high spins. So does that mean that we can use the rotational energy of the black hole to power relativistic jets? Well, it's not so clear to me because the problem is if you look at the spins of non-jetted A.J.N.s, you can also find high spins. In general, we find lots of high spins. So why is that? Well, here you have shown you the distribution of spins and you can see clearly again one, which is the number of maximum procreate rotation with this zero, no rotation. It's much more frequently observed. Okay, why is that? Well, the problem is that we have a strong bias towards observing higher spins because you know already that high spin means that the accretion just can extend further towards the black hole. This means the matter can fall further down the gravitational potential. This means they can also release more energy. What this means in other words is that objects where the black hole is highly spinning are going to emit more radiation, but we need radiation in order to see them. They're very far away. So we only look at the really bright ones. So we're essentially biasing ourselves towards looking at really bright ones. However, I think we can still say that there's no clear difference between jetted and non-jetted A.J.N.s. So the angular momentum by itself cannot be the deciding factor between whether a black hole shows strong relativistic jets or it does not. In fact, it is probably some combination of the magnetic field strength that determines how jetted they are. But this is still not very well understood because simulations are very difficult. Okay, so now we looked at the first two questions. How can we find out a little bit more about how is this whole picture being built up that I've been telling you about at the beginning? Like, oh, there's this accretion disc and then there's a temperature structure in it. How can we learn more about this? Where is all this information coming from? So if you think a little bit more about what I told you is that I told you, yes, there's this x-ray emission being made in this corona, which is somewhere around above the black hole or somewhere around close to the black hole, and it emits x-rays. And I told you that you get backscattered emission, which is our reflection spectrum. But this is not the only thing that happens. Some of this emission is being backscattered, but some of it is actually heating the disc. And we know that our disc emits in the UV or in the optical. So essentially, we're heating the disc and we're making, because it emits like a black body, we are shifting the temperature a little bit and we're making more radiation because this is how black body emission essentially works. But we're not just making this instantaneously, we need to account for the light travel time that it takes our x-ray emission to hit this certain part of the disc where the emission and the certain wavelengths is coming from that we're interested in. And this is like kind of shown here with the simulated light curves, you have your x-ray emission, which is kind of your driving light curve, shown in blue. You can see I made it variable. And then sometime later, your UV emission would respond to this with a time delay delta t. And if you could measure this, you can map out at what distances from the black hole, assuming that, you know, the corona is at the black hole, emission from a certain wavelength is coming from, because you don't change the wavelength that much by heating it a little bit. So that's kind of cool. This is a way we can measure out the temperature structure of the disc. So in order to do this, we use this Swift satellite, which is one of NASA satellites, that is pretty cool because it can move very quickly across the sky. Most satellites are very slow at moving across the sky. So there's a lot of overhead time from moving from one target to another target. But Swift is designed to detect gamma reverse, which are violent explosions in space. So it's really fast at moving about. So it's really easy to re-observe the same target over and over and over again. So this is what we've done here. We've observed this one agent here. And you can see the real data over here, the x-ray at the top. You can see the x-ray emission varies. It's kind of more noisy, of course, than the simulated light curve. And at the bottom, you can see the 2246 angstrom emission. And that's also variable. So what you then can do is you can do a calculated cross-correlation function or discrete cross-correlation function, which essentially just tells you how correlated your light curves are for a certain amount of delay. And so here over here, you can see, first of all, that they are correlated quite strongly. At least 50% of the emission or something is correlated. And if you look closely and you do some fitting, you can also find there's a time delay. And positive time delay here means that the UV is lacking the x-rays. So this here would be that the x-ray would be lacking. So here we observe a lack of 1.66 days, which is very small, but still very measurable. And kind of what do you expect? So what do you expect for this kind of distribution? So what do we expect? So we do expect that the time delay with wavelength is going to go like the red curve. And what we did is we looked at the sample of 21 AG and actually my PhD student did. And we tried to figure out what this delay is on average for all of them. So we averaged it all out. And if you compare it to the expected red curve, you can see that a longer wavelength disagrees really, really well, but towards shoulder wavelength, it clearly seems to deviate. So what does that mean for our temperature profile? Well, a shorter wavelength, of course, means higher temperature. So it means either our temperature profile is not as we expected it would be. Or alternatively, it means that our accretion is larger than we had previously thought. So our delay is longer, which means essentially it's coming from further out than we had expected it to come from. That's strange. So clearly we don't 100% understand how this works yet. But this method has a very high potential of, you know, reeling to us in the future. What exactly is this temperature structure? And then to compare it to simulations of accretion disks and just confront them directly and be like, no, this cannot be right. You cannot make this assumption for the temperature profile, because this is not what we observe at all. But so this seems like a kind of cool method. But more recently, we found that unfortunately, it doesn't always work. So you might think, well, we did this for 21 AGN, why not do it for like 100 AGN and get like, even better measurements, like try to like understand exactly how this goes down. They'd be all great. But sometimes we just, we just don't see it. And why is that? So for example, in this source, you can see the top is the x-ray emission again, and it's strongly variable. It's really very variable. And then if you look at the UV emission which is shown at the bottom here, at around, again, 2000 angstrom, first of all, it's not very variable. And secondly, you can already see by this does not seem to be very correlated with each other. Delay or no delay is just the second one, especially here, all these peaks, they're just not really there. And this is what's essentially shown on the right side. It's again at 95% confidence and 99% confidence. And you can see the measurement for the light key and black. There's essentially nothing that is really significant. And there's definitely no significant time delay. But the data is much better than the data I just shown you for this other object. So really, if there was any light, we really should have detected it. So what does that mean? What's going on in this source? And it's even more weird because if we look at the x-ray spectrum, we see strong reflection. So we know that the emission is being backscattered off the accretion disk. So how can it not heat the disk? Well, what we think might be going on is that the emission in this case is so focused towards the central region that essentially it is only heating the innermost regions. The x-rays are only heating the innermost regions of the accretion disk. And these are not the regions that we can detect with our time lags. Our time lags of those regions are further out. So we might not be able to see it. But it could also mean that our understanding is wrong. So while it seems like a good method, there's still quite a bit of work to do to figure out what's going on. So for the rest of the talk, I want to talk about something that I've been working on more recently and that's trying to find out more about the x-ray corona. So I've kind of glossed over this a bit so far. I've said there are those electrons and they're relativistic and they have really high energy and they're there and then the disk photons, they kind of scatter off them and they gain energy and then they make x-rays. But I haven't told you where this corona comes from. I haven't told you how it's heated. I haven't told you how it looks like. I've told you nothing about it or the problem is that we don't know very much about it. So we've been trying to figure out more recently. So the heating, we think the heating is probably being heated by magnetic reconnection or some kind of magnetic fields. But this is very difficult given that we cannot actually resolve anything or observe the magnetic fields directly. I'll talk about the temperature now and why we think the temperature is being said. I'll talk about how we can get the size and then we are trying to get to the geometry. You've seen I've just drawn it as like a perfect cloud because essentially we have no clue whether it's spherical, a square or a triangle or whatever. We don't know because we don't, it's very difficult to get information about that. It's right below our resolution. Okay so what do we know? Well the first thing we do now are the x-ray coronal sizes. So I've talked to you about how you can use the time delay to map out the equation disk in the UV. But you can also detect the delay between the continuum emission, the emission that you send from the corona to the backscatter emission. And this is what's shown here. This is just the time delay with black hole mass because remember everything scares with black hole mass. And it kind of tells you that the corona must be very small because the time delay is very short. And this agrees also with what you can measure from x-ray reflection which also gives you an idea of what the exact structure is of the central region. And further on we can also use microlensing. So some other rotation body go in front and then we can magnify this region that we can usually not resolve. Although we still can't take very good pictures of it. And you can also try to use other methods like scd fitting to figure out the coronal size. So essentially what we find is the corona, it's tiny, it's less than 10 RG and remember the equation this was 1000 RG. So we're looking at the innermost part now. This must be really really close to the black hole. So that's exciting because maybe we can learn more about what's going on with the really crazy processes close to the black hole. So the other thing we can now do is they recently had the new satellite launch which goes towards higher energy and I told you already that because the corona has a finite, those electrons have a finite temperature, all spectrum must roll over at higher energies. And this will give us the temperature right. So here you can see like what the just general example of a Aegean spectrum that you measure it has like the power law has already so the main continuum emission has already been removed the first order. What you left with is you can see here is a clearly a reflection spectrum. It's got this iron line and it also has a scattering hump which is also from a fracture. So you can model this and then this goes away but then you can see it still rolls over at higher energy and this is due to the temperature. So you can then model that and you get the temperature quite straightforward. So what do we find? So on the right here I show on some distributions. So on the bottom panel is just what we measure from new star satellites alone and then in the top two panels is from other satellite missions. Essentially what there are some things we can immediately notice about the distribution of coronal temperatures. One is that they are not flat. We're not equally likely to observe coronary of the same of like random temperatures and they're also not all the same temperature. However, there seems to be kind of a peak around say 50 kV for the temperature of the corona. So where's the peak coming from and what essentially sets the temperature? And it's actually all really weird because the cooling timescale in the corona is much smaller than its light crossing timescale. So a single temperature already makes no sense but from what we can tell from the modeling a single temperature is what is observed. So what sets this single temperature? How do we get there if our cooling happens much faster than our light crossing timescale? That's just funky. That's weird. I mean things can't talk that fast to each other. Like how do the different regions know what's going on? Okay, so instead of thinking about what makes the temperature, it might be most clever to think about how are we controlling our heating? So can we just, essentially if you were to heat it magnetically, could you just crank up the heat indefinitely and would it get hotter and hotter and hotter? I mean if we don't seem to observe these really high temperatures, why are we not observing them? So is there any way we can fine tune the heating so that we'll get kind of a characteristic temperature for the corona? So in order to understand this, it's clever to look at the quantity called the radiative compactness, which is just the luminosity of the corona over its radius, essentially. And another way to think about it is kind of the opacity to pair-pair productions. So it's just how much luminosity can you jump into a certain radius? And if you jump in enough radiation into this radius, you will start forming pairs. And if you start forming pairs, you start cooling the corona. And pair production is not a very linear process. So if you just go into this plot shown here where you have l on the top, on the y-axis, and you have the temperature on the bottom axis, say we stay at l equals 10. So we have a fixed ratio between the luminosity and the radius. But now we crank up the temperature. At some point our temperature will be so high that we'll start forming pairs. But pair production is not a very linear process. So there will be this moment in time when we start suddenly forming lots of pairs. And lots of pair creation essentially means that we start cooling our corona again. Because we'll be making pairs instead of heating our corona further. So we'll take away energy again out of the system. So one idea is that this could essentially create a boundary above which corona cannot be heated further. So how about that? Like does that agree with observations? So I've shown you the distribution of our coronal temperatures already. But now I'm showing you the distribution of our coronal temperatures with the l parameter or the compactness. And you can see that all of our sources are observed to be on the left-hand side of this line. And to the right-hand side of this line we observe runaway pair production. Okay, that's kind of cool. But what about over here? Like why don't we see any sources over here? I mean this region here is not forbidden at all. But it seems like we don't observe any sources there. Well we think that it is possible that essentially corona just heats up to its maximum temperature. So it just maxes out and is regulated by pair production. Then all the sources even if they were over here temporarily they would just heat up further until they get over here closer to the line. And on the right-hand side it's just showing another example of this which so far we have just observed, assumed that our electron distribution is a thermal distribution. But you can also assume that it has a non-thermal contribution that will give you a different prediction of when pairs are formed. And if you really try to compare things directly that might be something you need to consider. And it's still even if you do that you can get some fraction of non-thermal and you're still fine. It would still work. They're clearly not in the forbidden region no matter what. Actually this can possibly explain some of those low temperatures much better. Okay so now we have like an idea or at least that we can chuck around to understand what the temperature is but what else would we like to do? Well it would be really great if we could limit the corneal geometry further. This could be done by modeling the full colonization spectrum. And it would be even better if you could figure out what the magnetic fields are doing or measure the magnetic field strength. And I have some ideas on how to do that. But it's going to be very difficult because I said we can't resolve anything and it's not like you can see magnetic field lines painted onto the sky. Okay so this brings me kind of towards the end of my talk. I hope you've understood that radiation allows us to view really close to the black hole and that it can tell us things like the angular momentum of the black hole and that at the moment we think most black holes they're actually spinning quite rapidly but that this can be a selection effect. And it might be that we're just not seeing that many of them not so rapidly spinning once. And then I've also talked about the corona and that its temperature might be regulated or even stabilized by pale production. And this is just amazing how we can learn about such an extreme environment by just looking at the spectrum. Thank you. Okay thank you and oh for your nice presentation let's see we have some questions from the public. Okay we have one first from Soudov-Sialis. So he says hello Anne can the lack be somehow be credited to random walk of foreign through the concentrated dust covering the AGM on the line of observation? Right can I see this again? Yeah let me just I think you can we can just put it on the chat. Here we are. Do you see it? Can the lack be somehow be credited to random walk of photons through the concentrated dust covering the AGM on the line of observation? Okay yeah so dust dust dust sorry about my hair. In close so we just talked about the X-ray emission from black holes and turns out that if you have lots of X-ray emission dust cannot exist like dust will get destroyed by X-ray emission. So really close to the black hole we don't have a lot of dust it will get pushed out by the radiation pressure and it will also get destroyed so that's unlikely. Okay do we have some more questions from here our coordinators? I have a question yes can you guys hear me? Yeah okay first thank you Anne for the super nice talk. So I have a question about the the accretion disk so at the very beginning of your talk you showed this sketch of the accretion disk and the the temperature anything you say that very close to the black hole the temperature is higher compared to the yes but is that obvious that that has to be the the the trend I mean hotter closer to the black hole because I was thinking I was expecting the accretion disk to rotate faster far away from the center from the black hole so I was thinking that maybe outside it could be just warmer than close by? I think intuitively it's maybe clear if you think about material dropping and the potential but it's not that triple of course like this is not what really sets your temperature right you need to account for this magnetic friction that you have that you keep heating it it's just things are more extreme as you get closer to the black hole okay okay I mean so you're dropping right you're releasing energy already as you're dropping I guess in the potential and then you're also causing more magnetic friction as you're getting closer to the black hole. Okay thanks. Do we have any other question from our coordinators? Yeah I have a question for Anne. Yeah first of all it was very interesting your talk in fact for me that is completely kind of out of my topic but it was very very intuitive and yeah I have some kind of simple question let's say when you have the equation disk you expect to have these jets coming from the kind of the axle from the from the back from the back from the axle rotation of the back hole right for the all the equation there are these jets that are coming from the black hole to outside. Yeah so is it expected to this jet to be symmetrical or not I mean can can be resolved some this with observation in x-ray asymmetry so some stuff that make you think that this black hole is a little bit weird with respect with the the vanilla conception of a black hole let's say. So the problem is with the jets okay yes you can observe jets no no question you can observe them especially in the radio you can because they emit lots of synchrotron emission you can observe them in radio really well and they don't look the same but the problem is you see the jet like it will ram into the ism around it and then it will like twist and bend around just from the interaction with the ism so it's very difficult to say how this relates to the initial jet formation if you so well does that make sense you're mostly seeing a lot of the interaction of the jet with its surroundings of the black hole right it clears out this cavity around the black hole just rams like into the material and then we see those hot spots at the end okay and then this can yeah who knows whether they were this yeah who knows what happened in the first yeah how is the material distributed outside the black hole could be not symmetric and then yeah there is no clear I mean like a priori supposition of of that stuff so yeah and another question I have it was related to this rotation of the black hole because you were one of the kind of your conclusion was also that could we happen it could be I don't know kind of a bias or a loss of it that you cannot observe this various fast spinning black holes because of the what you only observe the fact you're more likely to observe them more than the yeah but because you have more radiation yeah in x-ray but what about the other wavelength I've been there because I would expect that slower the black hole rotate maybe the the spectral shift a little bit to to wave like lower than x-ray or or the opposite maybe is it possible also to serve with gamma ray telescope at some point or has to be extremely a super massive black hole that is I mean kind of galactic center or something like so the release has to be so high that could be observing gamma raisins I don't know and they are definitely also observed in the gamma rays usually they also make gamma rays so as you remember so they wanted a okay I also want to say the one in the galactic center is not recruiting a lot of matter so that one's boring yeah but lately there was some news about some flares and stuff yeah but those flares are tiny I mean then we're not talking about the same strong radiation environment that I was talking about now yeah some at much lower creation right but still if it were to become active it will be of course the same right they all the same but it's not there's something intrinsically different about it it's just right now it's not eating anything so it's it's being tame just good probably because they will make a lot of x-ray radiation we're bad for us even if it wouldn't come into our atmosphere but it will probably wreck the atmosphere so good good so yes you're right I guess if the if the spin was lower the the spectrum will change a little bit but fundamentally it doesn't change too much like it will still emit x-rays like yeah they all do even if they are lower temperature and you should know that the disk emission right how what wavelength it emits also depends on the black hole mass actually it mostly depends on a black hole mass so smaller black holes have a steeper potential and emit higher and higher energy emission from the disk so in black hole binaries which are the baby black holes right the 10 solar mass black holes from binary stuff they will emit their creation this will be the x-ray band and just for the hgn for the big black holes that's when it will be emitting in the uvn in the optical mostly then yeah the bigger the black hole gets the lower the temperature and then the spin is like a kind of small small perturbation on top of that oh good if you look at the like dependence it will not remember that in the beginning of your talk you were talking about these spikes that is forming if it is if the black hole rotated with the same yeah absolutely reaction and stuff like this but this I mean I just just I have a question just for when we start with the rotation this uh if the what what you observe is more or less the the the difference between the rotation of the black hole with the surrounding material or when you're you were talking about retrograde or prograde I mean oh it's just in an absolute measurement let's say I would I was just thinking in the sense if the black hole is spinning much faster than the aggression disk you look at like a prograde the spinning black hole but if it is just at the same speed that the aggression disk you serve it like no speed at all or something like that right so you you don't measure the you don't measure the spin of the black hole from the from the rotation right you measure it from how close from the maximum gravitational redshift which is the which is the property of the spacetime okay oh yeah yeah okay so you're changing spacetime as you're changing the spin of the black hole so it's kind of clever it's clever and yes you are of course in the rotation of the aggression disk and I have closed closed over this right this is something that the model does include right that there will be double effect and so on and all of this is taking place and that's all taken care of in the templates but yeah this is not what this is not where you get spin from okay okay okay thanks okay do we have any other question because I do have okay okay Diego is there is there any expected correlating measurement with the gravitation gravitational waves experiments for the same sources yes for example something that can be learned once you can't figure out exactly what is a new black hole of this kind or after the formation of a black hole from the collision on the neutron stars of this yeah so I guess if we knew where so the problem is with the neutrons and neutron star collision right you will make a small black hole from that you don't have a lot of mass right yes so it will be one of the tiny ones and then if it was nearby we could possibly see if it was a creating matter the question is would matter be accreted like would matter be associated with the gravitational wave event I think so it must be because we're seeing all this emission coming from it so so something must be there but this isn't like 100% of the study right um if it was nearby then you should be able to see it accreting afterwards and you should be able to measure the spin I agree but it will be difficult because it will be a tiny black hole so it's gonna have to be nearby and never be so cool okay thank you uh I do have a question is just out of curiosity have we ever do like a simulation or a study where the geometry of the corona changes in time and then like because most of the time you assume a type of corona and then you make your observation is there a way to combine many models and see if we can make like a time-dependent corona model and see how will that affect it I think I think people have looked at it a little bit but it's very difficult to make that I think okay and we've looked at our flowing corona and we know that this changes the temperature we observe which is pretty clear you have relativistic beaming and so on um but there hasn't been like a super consistent study to do that because we don't know what's assumed in the first place and we don't know the heating so all the models are kind of they have fake heating in them because we don't understand how they're being heated if that makes sense yeah thank you so do we have another question yeah okay I have one very sure I mean it's just related a little bit with the what is the the future is there a expected new x-ray telescope so another another way like to to serve this this this phenomenon that you're studying your research yeah yeah absolutely um so there there has been multiple new x-ray telescopes approved and the the next one is going to be an x-ray polarimetry mission and they will be able to measure the polarized the polarization of the x-ray emission in uh black hole binaries so like x-ray binaries which will be cool so that can tell us more about the magnetic field strength and whether it's synchrotron emission or comptonization right the the main property will be whether they're polarized and how they're polarized and in theory the the backscatter the emission should also be polarized but who knows like what they'll get off again so this is all open questions so that will happen I think next year and then there's also a high resolution x-ray spectroscopy mission being approved it's called charm because we had a mission that failed last year or the year before so that got re-approved and then there's in the future there will be Athena which is going to be a big european mission and that will be able to measure the black hole spin out to reach if two of like a large sample of sources so that will be we forgot to like the kind of statistics that will really build up the statistics a lot so that will be exciting but that's further out that's like in the 2020s have to wait around a little bit okay thanks okay thank you Ann for this nice webinar and for all the people down for it to subscribe to our youtube channel and follow us on social media and thank you very much