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cc >> Welcome to UW Space Place. Tonight is our monthly guest speaker, and our speaker this month is Dr. Karen Lewis. Karen is a UW Madison alum. Got her bachelor's here at UW Madison in physics and astronomy before getting a PhD at the University of Pennsylvania, then worked for NASA, she tells me, at Goddard Space Flight Center for a few years before moving to the College of Wooster where she now teaches physics and astronomy there in Ohio. So we're very lucky to have Karen here tonight. She works on searching for active galactic nuclei, that's the AGN there, and she's going to tell us how they pick those out of the sky there. So the title is Black Hole Sleuth. So, Karen, thanks very much. >> Okay, well, thanks for having me. I'm really delighted to be here. I'm going to share with you sort of my own little personal seven-year detective story. I sort of feel like I can describe to you it's kind of like being in the trenches of astronomy, trying to solve all sorts of mysteries. So I'm going to take a detective theme this evening. And so what I want to show you, just an overview of my talk. First, there's the mystery. What are active galactic nuclei? Why am I even looking for them, and why do I want to look for the ones that are in our backyard, so to speak, cosmically speaking? And then I have to introduce the suspects. So, who do I think might be an active galaxy? And I'm using an X-ray survey. So I need to think about all the different types of objects that might emit X-rays. And how do I figure out ahead of time which ones I feel like interrogating by going to the observatory and taking further data because observatory time is very expensive so I can't just show up and say, oh, well, maybe it's this guy, maybe it's that guy. I need to go in with a plan. So the first thing I actually want to talk to you about is just what a normal galaxy is. So a galaxy like our Milky Way or the Andromeda galaxy, they're very exciting. There's a lot of things interesting things happening in normal galaxies, but pretty much they have cooler stars, they have hotter stars which emit more bluish light, and then there's some dead stars. These are stars that have gone through the life cycle and they're no longer emitting all that much light that we can see with our eyes. But when we look at a galaxy in the light that we can detect with our eyes, although in this case we're letting a telescope gather the light for us, what we're seeing is light emitted by stars, mostly. We also see some pesky things. I've pointed out some dust. Those are regions where it's darker, and it's not that there's not any light there to be seen, it's that there's dust. So it's like being in LA where it's very smoggy. We can't really see the light that's there. So it's blocking the light that we would normally want to see. So normal galaxy, when you look at them, as far as we can see with our eyes, they're just stars. Okay? Well, it turns our that there's a lot more out there in the universe than we can see with our eyes. Our eyes have evolved to receive the sunlight that can make it through our atmosphere, and that's a very, very small region. So I want to introduce this idea of what's called the electromagnetic spectrum. Basically, that's just a fancy term for lots of different light. So what we see here, there's a couple things. There's the wavelength of the light, and it sort of gives you an idea of what type of object might have that wavelength. So, for example, we look here, there's light that's traveling like a wave, just like an ocean wave, and between crest to crest there's a wavelength, and it's about the size of a baseball. But if we go to the visible part, this tiny little portion, when you think about it, what we're able to see with our eyes is such a tiny portion of what is out there. Here those wavelengths are incredibly small. They're the small of viruses. So we can categorize light by its wavelength. And so here we have visible light. So, for example, a light bulb emits visible light, an incandescent light bulb. It also emits a lot of heat when you put your hand by the light bulb. So if we go to slightly longer wavelengths, we get into this big region called infrared. Infrared, there's a couple ways that we can see infrared light. One is by things that are warm. So the human body emits a lot of infrared light. Light bulbs. So things that are kind of room temperature or body temperature emit infrared light. But as we go even further, longer wavelengths, where now we can start to maybe visualize that wavelength. It's about the size of a cell. There's a slightly different reason why objects emit infrared light there. And it's usually because you have dust. So really not too much different than the dust you'd have on your coffee table. That dust is able to absorb light and then it reemits it in the infrared. As we keep going, we get into microwaves, which of course we have in our kitchens. And as we keep going, we get into radio waves. And that's exactly what you'd be picking up with your radio. We usually associate radio with sound waves because we're listening to the radio, but really what we're doing is we're using a light wave with very long wavelength as sort of the carrier for that sound information. So radio waves are actually also a form of light. All these are forms of light. And by the time we get to radio waves, these waves have wavelengths as big as a soccer field. So going to the other extreme, starting back at visible, we can also go to things that have shorter wavelengths and also have a little bit more oomph, a little bit more energy. So the first one we come to is ultraviolet, which thankfully our atmosphere blocks out most of, but we all know it's very dangerous to get too much UV exposure because that UV light has enough energy they can actually damage the cells in your body, knock around some electrons, create free radicals. So that's light that we can't, thankfully, see from Earth too easily. As we keep going, we get into the regime of X-rays. It's a very big region of the electromagnetic spectrum. We have what are called soft X-rays. Just basically means lower energy. They're all pretty high. They all have a lot of energy, but there's sort of lower energy and higher energy. Now, when you go to a doctor's or a dentist and they take an X-ray, those are very high energy X-rays, and we know that they can penetrate through your skin and tissue and reveal your bones. So X-rays have this ability to penetrate through matter when they have very high energy. And these X-rays are created by radioactive elements and things like that. So they try not to X-ray you too often and you wear the lead protection. But objects out in space also emit X-rays for slightly different reasons. But what I'm going to be focusing on a lot of today is trying to find these objects out in space that emit these X-rays. So I'm not really X-raying the objects, but they're creating the X-rays which thankfully can penetrate through lots of gas and dust in the way so I can detect them here. Now, most of these things have to be observed from space. And each type of radiation tells a very different story. And so we want to gather as much information as possible, which is why we have all these observatories in space observing infrared light and X-rays and ultraviolet. So just to give you a few visuals, humans, we all emit infrared radiation. So, for example, if you're wearing night vision goggles, here you would see these humans in the middle of the night. But it also, infrared light or heat also has this amazing ability to penetrate through dust. So here is an example of if you were a firefighter, sometimes they wear infrared night vision glasses, basically, because here is what you would see if you looked with the light our eyes could see. You see this smoky doorway. If you could then switch off and put in glasses that can see infrared light, can detect infrared light and create an image for you, you suddenly see that there's a person there. So infrared light has this amazing ability to penetrate through dust. And that's going to be important in a little bit. So let's look at our nearest neighbor, Andromeda. I showed you that picture. It's this beautiful spiral galaxy. We presume that's what we would look like if we could get out of our galaxy and look back on ourselves. So this is this beautiful image. It's very pretty, but it's not the whole picture. So, for example, if I look in the infrared, you notice it has the same kind of shape. It's also flat like a pancake. It's got some structure. But what's interesting is when you compare them, they're almost completely misaligned. Where you don't see visible light, you do see infrared light and vice versa. So they're actually telling us a little bit different story. And then when we look in X-rays, we don't really see a galaxy. We don't see a disc. Maybe if you really squint, you can see. But mostly what we have are a collection of small fairly faint sources right around the center. So these are all types of sources. I'll talk about it in a little bit. There are certain types of stars that emit X-rays. So when we look at a normal galaxy, like the Andromeda galaxy or our own, most of the source of X-rays are just stars. They're very interesting stars. But they're just normal processes that happen in galaxies. So we have, there's sort of a cheat sheet for how we can think about, as an astronomer, when I see certain light, what is it telling me. So, for example, when I see a lot of radio emission, that usually means that there's really cold, dense gas. And when I say cold, I mean not very much below the coldest temperature you can get. So minus 250 degrees Celsius. Very cold. When I look in the infrared, I'm going to often be seeing stars that are a little bit cooler. They're not as warm as our sun. They're maybe just getting started. I might also be seeing some emission from dust. And it tends to be those longer wavelengths I'm seeing more emission from dust. Nearby I'm seeing stars. Visible, I just see stars. That's what our eyes can provide us. Ultraviolet, I'm seeing sort of the tail end. I'm seeing the very hot stars. And when I look in the X-rays, I just see this little cluster. This is Andromeda again. I'm just seeing some stars that have died and are doing some kind of interesting things postmortem. So the idea is that normal galaxies, they do emit many, many types of light. We just saw that, but almost all their light is coming out in a fairly narrow region where it's the visible and a little bit in the ultraviolet and then in some of that infrared radiation that's really just next to visible. So this is what a normal galaxy does. Now, I'm going to show you a picture of an active galaxy. And this is color coded. So it's an active galactic nucleus, so that's where the AGN comes from. This is an image they've combined three different types of data. So in this green, that's visible light from the Hubble Space Telescope. You can kind of see, it just kind of looks like a disc. But when we look in X-ray, which is in blue, or in infrared, which is in red, we see these big plumes coming out of this galaxy. That is not something you see in Andromeda. There's something really strange and extra special going on in this galaxy. And this is evidence of unusual activity in the center. So one way that we can sort of think about this, oh, yeah? >>

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>> Well, actually, no, there really isn't much visible light being created here. All the visible light is coming from the stars, and they're confined in the pancake disc. But there's this other emission in the X-ray and the infrared that's sort of escaping from the galaxy. >>

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>> Mm-hmm. Yes. >>

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>> Mm-hmm. Exactly. So this is an interesting way. Maybe just ignore these numbers on the bottom. This is frequency. It's an alternative to wavelength. But I want you to just think about the amount of light that's being emitted by the object. So I'm going from long wavelengths at radio all the way up through X-ray. So what this is kind of saying is taking a census of all the data. Now, if you were to look at a normal galaxy, it's very confined. It emits in the visible, in the ultraviolet, and this is the normal galaxy right here, and in the near infrared. Now, if I take one of those active galaxies and plot up all of its data, I see something completely different, which is telling us there's something different going on here than just stars. I see that there's all this radiation here in the far infrared where normal stars don't make radiation. I see that there's a lot of UV. Stars don't make that amount of ultraviolet radiation nor do they make this many X-rays. So there's something definitely strange going on in these objects, and it's not just they're not bright just because they have more stars. There has to be something fundamentally different taking place. So another clue that we can get is through something called spectroscopy. So this is just looking, I just look in the X-rays, I'm not doing any really detailed study, but another powerful tool we have is spectroscopy. So we know that a prism will take white sunlight and split it up into a rainbow. It splits it into it's component colors. We can take light, whether it's the visible light that we can see with our eye or X-rays or infrared, all those types of light can be split apart into finer categories. So it's not just X-ray. We can say it's X-rays with that wavelength or visible light with that wavelength. And so what we want to do is do the same thing for our stars. Astronomers have gotten very good at figuring out ways to get information from light because it's all we have. Unless we're studying the solar system, we will never touch or collect a physical sample from anything we're studying. So we have to be clever and use light to do anything we might want to do. And so, for example, this diagram here is showing what would happen if you took tubes that were filled with a gas and then run an electrical current through them. This is exactly how your compact fluorescent light bulb works. If you've ever looked at a compact fluorescent light bulb with a little plastic grating or prism, you'll see that it's not continuous light. It's not a rainbow. There's sharp, there's places where there's a lot of light emitted and then places where there isn't. So we get this type of spectrum. And so each atom has its own characteristic fingerprint. I can look at this set of lines that I'm seeing in a galaxy and say I know exactly what gases are in that galaxy. Furthermore, I can tell how fast the matter is moving because these lines are very narrow, which is a powerful tool because just like you hear a fire engine as it comes towards you, you hear the pitch increase and then it decreases, or a race car you hear that -- sound, light does the same thing. When an object is moving towards you, the wavelengths get shorter, and when it's moving away from you, they get longer. So I can actually see these lines becoming broader just because the gas that's emitting it is moving, swirling in a circle. Part of it's coming towards me, part of it's moving, and combined, what that does is it's broadens the line up. And I could go on. I teach a whole class on how many cool things you can get from a spectrum, but I don't have all night. But there's a lot of things that I can get by breaking apart the light that's coming from these galaxies. So when I do that, this didn't come out as well as I hoped, we see another clue that there's something different about these guys. They're not just a galaxy emitting more stars than usual. This is what a normal galaxy looks like. There's not a whole lot going on. There's actually what we call absorption light. So there's absence of light. Basically, a normal galaxy, when you take a spectrum in the visible wavelengths, you're just seeing a collection of stars. So I could add together stars of this temperature plus some stars of that temperature. It's really kind of boring. I'm biased. When I look at one of these active galaxies, you see immediately that there's something different. We see these very strong emission lines, and sometimes they're broad and sometimes they're narrow. The way that we see emission lines, we don't have an electrical current running through a galaxy. What's happening in your compact fluorescent light bulb is there's atoms and their electrons are getting excited and ripped completely off the atom, and then they recombine with the atom, and as they kind of work their way back down to lower energy, they emit light. And what's happening in these active galaxies is there's no electrical current. What we have is UV light. That UV light is so powerful that it can actually rip the electrons right off the atoms, and then it's a free for all. You have electrons flying around, and they reattach themselves to a new atom and sort of cascade their way to their lowest energy. And so each one of these lines I can pinpoint exactly where that electron is moving, from where in the atom to some other location in the atom. So these are really powerful diagnostics. So these things here that are broad, that has to be coming from gases moving around very rapidly. These things that are narrow must be coming from gases not moving too rapidly. When I say rapidly, I mean 10% of the speed of light. So this gas is really clipping along. So among these active galaxies we can kind of break them into two categories. We call them, we're very creative in astronomy, type one and type two. Yes. And actually I just said this. I got ahead of myself. Because suffice it to say, there's something that's creating a lot of UV radiation. And there's something that makes the gas move around really fast. So, what could it be? What is lurking at the center of these galaxies? This is an artist rendition. So what we're seeing is something like a galaxy. It's disc shaped. It's flattened. But this is happening on scales that are very small. If you could go to the center of our galaxy and look in a region that's maybe about the extended size of our solar system, so going out to where the comets are and the Oort cloud, this is the scale that we're talking about here. So we have sort of a miniature pancake here in the center of this galaxy, and there's something going on. We can sort of see ominous bursts of energy coming out. Some of these objects do have jets of particles that are going almost the speed of light, spewing out from both ends. That's a whole other talk in and of itself because these are really interesting guys. So what do we think is going on in there? Well, we think it's a supermassive black hole. So now for the most text heavy slide for the evening. What we think is that there's a black hole and has a mass anywhere from one to a hundred million times the mass of our own sun. So our own Milky Way has a black hole. It's about three million times the mass of our sun, but it's not doing a whole lot, which is probably good for us. So what makes these guys different is not that they have a supermassive black hole. We think almost every galaxy has one. We think it's just part of being a galaxy. What's different is that something has triggered a lot of gas to fall into that black hole. So we're basically hearing the primal scream of the gas as it falls into the black hole because it has a very strong gravitational pull. But usually the gas in our galaxy is not in any danger of falling into our black hole. We're safe out here. But if something were to happen, for example a collision with another galaxy or some kind of event that destabilized the gas and made it drift out of its orbit a little bit, it could funnel in towards the center. So something has happened probably to trigger this activity, but all we know now is that there is matter that's falling in. And this matter, like most things that are spinning, they kind of flatten. If you imagine tossing a pizza and the dough flattens and spreads out as you spin it. It's a very common thing to happen. And as we saw in this picture, it gets very dusty on the outskirts. We have all this matter kind of funneling into the black hole, but out here it becomes quite dusty because there's not as much of that harsh UV radiation anymore. Those dust grains are very fragile. Very close to the black hole there's so much radiation they can't hold together. They keep getting broken apart. But as we get further out, those dust grains naturally start to reform, and we almost have this whole thing is just shrouded with this big doughnut of dust. So, again, close to the black hole is very hot. So maybe a hundred thousand degrees. And the matter is moving at about 10% the speed of light. Again, because it's so close to that black hole. There's a lot of gravity pulling that matter in. but it turns out black holes are really messy eaters. And this is something that we're trying to really study. It's an unsolved mystery. It seems like about half of what is trying to fall into the black hole actually never makes it. It gets spit out. So it's like trying to feed a baby that doesn't want to eat, and you put the food in and half of it comes out. So this is one of the big mysteries that we don't quite understand. How exactly do these things feed? You think, what could be easier? Just throw some matter in a black hole. But it turns out it's not as easy as you might think. Someone once made the analogy that it's like trying to fill a dog dish, like a bowl for the dog's water with a fire hose Most of it's not going to go in. so it turns out they're not always so efficient at eating. >>

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>> Mm-hmm. Yeah, they're usually in the middle. >>

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>> Mm-hmm. Yeah, they just kind of hang out in the center. >>

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>> Yeah, it's usually circular. As far as we can tell. We don't know exactly. So what's the anatomy of one of these active galaxies? Well, they basically have three main structures. They have this inner part where all the excitement is happening. There's a black hole. There's matter flowing in. There's matter flowing out. There's ultraviolet radiation. There's X-rays. All the cool stuff is happening right here. Probably within the, if we're looking at our scale, within the orbit of Mercury. That's where a lot of the action is happening, or maybe Earth. So the inner solar system. And then it's shrouded by this dust. And it has kind of a doughnut shape to it. It gets a little bit thicker. And then we have this thing, it's called the narrow optical emission line region. It's a very creative name. Basically, this is gas that it can feel, it can absorb the UV light from the center here. So it's getting that harsh radiation so we see those emission lines, but this gas is very far away from the black hole so it's not moving very fast. So that's why we say, okay, well, we must have some gas up here. And this is the one structure of an active galaxy that actually has been observed by the Hubble Space Telescope. Remember, you're taking something about the size of our solar system and putting it in another galaxy. We don't really have a chance of actually seeing what's happening. We have to piece it together. But this structure here, this narrow line region is big enough that at the nearest active galaxies to Earth, when we look with the Hubble Space Telescope and we put in a special filter that says I'm only going to see the light coming from these gases that have their electrons ripped off, the ionized gas, we can actually see these cones of ionized radiation coming out of these objects. So this we actually know that's there. >>

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>> Mm-hmm, yeah. So what we want to do is somehow we have to be clever to figure out how do all these things work together even though we actually can't see it and we'll never see it. So we have to figure out how do we use all the tools at our disposal to figure out what's going on in here. So one thing that's really key is it depends on where you are. So here I'm the smiley face observer. If I happen to be looking at this object this way, kind of looking through the doughnut, I'm out of luck because that doughnut blocks a lot of things. Because it's dusty, I can't see any visible light, I can't see any UV light, I won't see any of those beautiful broad emission lines from that fast-moving gas. I will see some of the X-rays, but the ones that are kind of wimpy can't make it through. The really powerful ones can make it through, but I'm missing a lot of the goody bag here when I see it this way. Now, if I look from here, then I can see everything. Right? So this is what adds an interesting conundrum to how we study these objects is that part of it is just dumb luck. It just depends on how I'm looking at it. So if I'm looking at it in the right way, then I'll get to see all this stuff, and if I don't, well, I kind of have to work with what I have. But it turns out that that's very interesting. The ability to study it from two different points of view, it gives us a little bit more information. For example, looking through this way I probably have a much better way to study this dusty doughnut than I would looking this way. So it gives us two complimentary views. It might seem like, oh, not another one, I don't want to look through the dust, but it actually ends up being a very powerful tool. So we have this whole idea of sheer dumb luck that we have no control over. So what we do is we tend to have some stereotypes about active galaxies based on this idea of which way I happen to be looking. So we assume, our first model is that every single active galaxy looks pretty much like this. They have the same structures, and the reason they look different is because I just see it from a different angle. So, for example, type one are the ones that have everything. So I can see broad emission lines, narrow, and I can see all the X-rays that that object is emitting. Type two is when I'm looking through the dust. I lose my lower energy X-rays, and I lose those broad emission lines, but I still have these. And so for a long time if I were an X-ray astronomer and I went out and studied all these active galaxies and I said, okay, I'm missing my low energy X-rays. I would say I know which way I'm looking at this object. Right? Things should either fall into one of these two categories, and it should satisfy across the board all those criteria. Well, that's not actually what happens. We're finding an increasing number of cases where there's a discrepancy The X-ray astronomer would say, oh, I'm definitely looking through the doughnut, and the optical astronomer would say, what are you talking about, I see all these broad emission lines, I see UV light. Well, it can't be at two different angles. It's one or the other. And so we have a little bit of a conundrum. This is the big mystery that I'm kind of curious about at the moment is, is this model correct or are we missing something really big? It only happens maybe about 10% or 15% of the time, but it's enough that it should make you scratch you head and say this model is maybe not complete. It's not off the table; it just needs some work. So this is the big question that I have. Is there something actually wrong with this model? There's some other clues that there might some things that need to be improved. But it could be something wrong with our observations because it turns out most of the observations that led us to this conclusion had really poor quality X-ray data. And I'll describe in a moment why it was not so good. So I'm not completely sure there's a problem yet. So my big thing that I would like to do is look for these objects really close by where I can study them to death and know exactly what's going on. Is there a problem with the observations, or is there something really that we don't understand about these objects? So I can say that I have some more immediate questions. Those are kind of big questions. So what I want to do is almost take a census. I want to interrogate all these active galaxies and say how frequently do their X-ray and optical data disagree with each other. And if there is a disagreement, is it just a mild disagreement or are they completely flat out contradictory? And I also want to see, maybe they don't agree but maybe it's not something that's going on in that central region. Maybe there's something else going on in the larger galaxy that's creating this discrepancy. And these are questions that I can only answer if I can see something really close by. I need to study our neighbors, not the quasar that you hear about in the news that's towards the edge of the observable universe. That's really exciting but it's not going to answer these questions. So, what I'm using to go on my hunt, my sleuthing, are X-rays. And that's because very few normal galaxies make X-rays. So automatically I'm eliminating most of the objects in the universe. They won't appear in this study. So I don't have to get rid of them. Again, according to our best theories, every single active galaxy will make X-rays. You might have trouble detecting them if they're too far away, but every one of them should make them, and if we're looking at those higher energy X-rays like I will be, you can see through the doughnut. So it doesn't matter. You don't have to say, well, I'm going to miss all the ones where I'm looking through the doughnut, in principle. So I want to use X-rays. That's the viewpoint I'm taking, and it's perfectly valid. Lots of people look for active galaxies, trying to find objects that are unusually bright in the infrared or the visible or ultraviolet. We all work together, and hopefully we should get a clearer picture. That's great but collecting, X-ray data is very challenging. First and foremost because we need a telescope in space, so we have to money to send a telescope into orbit and then maintain it. So that's a challenge. And if we want to have really good statistics, I don't want to just interrogate 10 of these guys or even 50. I want to interrogate hundreds of these galaxies and say, do you agree? Your X-ray and optical data, do you agree or don't you? So we need to find lots of sources. Now, the way you usually do this in X-ray is by taking your telescope and pointing it at one space in the sky for about two weeks. Maybe even three. I think the longest survey ended up being a month's worth of time. Just staring at the same patch of sky. And that's what they did with the Hubble Space Telescope with the Hubble Deep Field which was revolutionary. We had no idea that you could see so much pointing your telescope at a purposely blank piece of sky. And there's galaxies galore. But that gives you one kind of information. It will help you find all those little nuggets. It's like going on a safari and someone says, okay, you are going to find every grasshopper and bug and snake within 50 square yards of where you're standing. Well, there's a danger to that. If you collect in a small region, what are you going to miss? The chances of a lion crossing you path are fairly small. Hopefully, actually. If you're doing this census. But ironically, what happens is that almost all your sources are far away. So what I have, again my smiley face observer. So this cone represents what I see in the sky. So if you think about it, if you go out on the street and you sort of hold your thumbs like this, or your thumb and finger, close up that maybe fits someone's head, but far away it fits someone's whole body and suddenly it's fitting a whole building. So we have this skewed perspective. As something gets farther away, it appears smaller. But that also means that our collecting area is bigger. If I had really, really, really great glasses and I took a toilet paper tube, I could count all the people that I see within that toilet paper tube, or even a straw. But if I'm sitting here in my tunnel vision with my toilet paper tube, you could be sitting right next to me and I won't even know you're there. So that's a problem. If I want to find things that are close by so I can really interrogate them and study them, this is not the kind of survey I want to do because almost everything that is coming in my path is far away. So I want to open this up. I want to see all these things. And there's going to be a compromise. I can't look at every patch in the sky for 10 days. I get about 10 seconds in this survey, but it's getting the whole sky. So there's always a tradeoff. You can do your survey of the savanna from a helicopter and kind of fly by and get big things. That has a place too. So why am I so desperate to find these things close by? Well, I can just get more information, and it's not as hard to get. Anything that's closer is brighter. So I don't need the biggest, fanciest telescope. I just need a good, solid telescope to give me my data. And what's even more important is this active galaxy is not just sitting out there in isolation. It's sitting inside a galaxy just like our Milky Way or Andromeda. And for me, that very interesting galaxy is a source of contamination. What I measure in my telescope is not just from the active galaxy or the active galactic nucleus; it's also the galaxy that it resides in. So there's a lot of contamination. The closer I am, the more easily I can get rid of that noise. Someone else's treasure is my noise. And I can also get images. I can say, well, how is this galaxy oriented relative to Earth? Is there something else going on that's really not having anything to do with the central activity that might explain discrepancies? So it's really important to be close. So this brings me to my survey. So it's XMM-Newton. So they named it after it made it safely into orbit. They then attended the Newton in honor of Sir Isaac Newton. And XMM is just a regular X-ray telescope that's been a powerhouse. It tends to take slightly shorter observations because it's a bigger mirror. It can collect more X-rays at a go. Well, it's providing a completely new kind of survey. It's completely free. All they do is leave the shutter open. So it would be like you purposely not closing you shutter if you had that capability and whizzing through the room. So it's kind of an odd thing to do. And what you end up with is something that looks like this. You get these trails very much like star trail photography that some of you might do where you just set up your telescope on a tripod, or your camera on a tripod, and just let it go. It's exactly the same idea. Now, I would say it's a free lunch because I'm just getting this data. These data are free. They just appear on the internet, and then I use them. It's not really a free lunch. It's definitely a lot of hard work by other people. There's many challenges. One is that, effectively, you're looking at any individual object in the sky for about 10 seconds. So you don't collect a whole lot of data. You just have an idea that there's something there and its rough characteristics and that's it. So this has not been a very thorough interrogation in the X-ray. Imagine trying to take these trails and work out exactly where the star is that created that trail. That's very challenging. It's a very difficult process, and most of the time it works really well, but when it doesn't it's catastrophically wrong. So we'll say we think this X-ray source is here, and it turns out it's over here. And sometimes you get a source that isn't even actually related to anything actually in the universe. It's just a glitch of the detector. So trying to figure out, weed these objects out, gets kind of interesting. And it turns out there's a lot of objects in our own Milky Way galaxy that create X-rays, and they're very interesting. There's a lot of people who are excited about them. For me, again, I have to get rid of them. So you think, this is great, there's all these free data, but there's a lot of work to do something. Because the ultimate litmus test, the way that I really know this guy is an active galaxy is to go take one of those optical spectra and see those emission lines. I need to see those emission lines. That's expensive, not just in the use of those telescopes. There's only so many nights. I've been very lucky to get a lot of time, but it's also expensive to actually go to the telescope, travel to Arizona and Chile. I'm not complaining. I love the travel, but it gets very expensive. So you want to make the most of that time, the most of that resource as you can. So I have to figure out who the viable suspects are. My very first trip that I went on for this project, I was so sad because I came home and realized that about 50% of the objects I looked at were just some kind of star and I wasn't even sure that they were emitting X-rays. So I really, really botched it. But, over time, I've become a better detective, and on my most recent one, 95% of the objects that I interrogated were actually active galaxies. So here's my little journey of how I became the -- sleuth. So, some pictures of the telescopes that I go to. So far I've had 19 observing nights, and three more over the Fourth of July weekend. I guess that's not three, that's fourth through sixth. And what's exciting about that is that I actually get to control the telescope from my office on the UW campus. So that's very exciting. I will be Skyping with the observatory. So I go to observatories in Chile. And this is Kitt Peak in Arizona. This is not showing up too well, but basically these old fashioned ones have these gigantic mirrors. They're very, very heavy, and they're very large. These buildings are both probably about 12 stories high. They're behemoths. In contrast, this telescope is another one I use, also in Chile. It's the same size mirror, four meters in diameter or about 20, I can't even think. >>

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>> Yeah. >>

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>> Three feet, yeah. So 12 feet in diameter. So very large. And what we can see is when there's two noticeable differences, this takes up almost that entire dome. This dome is very compact. This telescope takes up almost all the space. And I don't know how well you can see, but there's little actuators here. And they actually deform this mirror to get the best image quality that they can. And it's funny when you're watching them go to a new target, if it's kind of low to the horizon, all the sudden it goes completely out of focus and then they run their routine and these little pivots, it's like pushing on the mirror with your fingernail. These mirrors are very thin now, and you push on them with these little pivots, these actuators back there. About the equivalent of pushing with just you finger, and it reshapes the mirror so you get perfect image quality. They're really, really spectacular. So before I go to those great telescopes, I have to weed some guys out. And so to do that, I have to have a really good understanding of what are all the different types of things that might be emitting X-rays and showing up in my survey, and then use any information that I have ahead of time to eliminate suspects before I go to the telescope. And that includes looking to see if there were any previous observations with X-rays. Any observations in other wavelengths, such as infrared or ultraviolet. And then images, look at the shape of it. Does it look like a galaxy or does it look like a star. But also where it is in the sky, and does its position seem to be changing. So, obviously the ones I want are the active galaxies. So that's the easy one. First of all, on the time scale of human observation, active galaxies don't really turn on and off. We've maybe caught a few of them, but for the most part when they're on, they're on for millions of years. So they're not going to stop emitting X-rays. So I should expect that they're persistent. They're going to be fairly bright at all wavelengths. Remember, I said that a hallmark feature of these guys is they emit infrared, they emit all different wavelengths of light. So if I see something that suddenly just drops off the map as soon as I leave visible and infrared light, it's probably not an active galaxy. If it's close enough, it should be fuzzy. Okay? Now, it's far enough away that it doesn't change position on the sky. So, what do I mean by that? Well, when you see a plane, when it's very high up in the atmosphere, it barely seems to move. Or if you look at a satellite, even though it's whipping by at a tremendous speed, it kind of moves slowly across the sky. When it's kind of low to the horizon, it seems to pass very quickly. We have the same effect that objects that are close to Earth tend to change their position on the sky noticeably so that you can tell even in a couple decades that it had clearly moved position. So the one problem that I have to watch out for, this is a cluster of galaxies, and some of them are, this one here is an active galaxy, and I believe maybe this one is. But this blue radiation here is X-rays that are coming from hot gas within that cluster of galaxies. It's actually not due to an active galaxy. So I have to watch out for those. Unfortunately, I don't usually have enough X-ray data to tell if it's spread out or if it's all coming from a point. But I have to watch out for that. So what about some of the stuff I want to get rid of? Well, the main thing I want to get rid of are low mass stars. So this is an image of our sun in X-ray when it's going through an active period, when there's solar flares that sometimes threaten to shut down communication satellites. So we see these big loops and different activity. This is an X-ray image. It looks completely different than the sun that we should never look at. It just looks like a disc of light. So low mass stars have particularly intense flares. It's due to the structure of the star and its outer atmosphere. But this X-ray emission is very intermittent, just like our solar flares. It comes and then it goes. It comes and goes. So I can expect that these things will flicker. So if I have a couple different observations, I can say, well, I looked in X-rays in this part of the sky and I should have been able to see it and it's not there. That's my first big clue that this is not an active galaxy because they don't disappear. >> Excuse me. >> Mm-hmm. >>

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>> Well, not an X-ray machine. You're collecting the X-rays from the sun. >> Yeah.

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>> Well, these are X-rays coming from our sun, and they're picked up by a detector. >>

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>> Mm-hmm. >>

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>> Yes, these are X-rays that are created by the sun that we pick up with an X-ray telescope. Though, also because it's a star, it's going to emit a lot of visible light. So I should expect something like this to be very fairly bright when I look invisible, but as soon as I go into the infrared or ultraviolet, it should just drop off the map. It will appear to be insignificant. And these guys are not very luminous. Even in X-rays. They're probably pretty close by which means, like that nearby helicopter, it actually will change position on the sky pretty noticeably. So I have lots of ways to get rid of these guys. They're pretty obvious. What's a little bit less obvious are another group of stars in our galaxy that will emit X-rays, and these are almost like mini active galaxies except instead of a supermassive black hole, you have what we would call some variety of dead star. Sometimes we call them compact objects. It could be a white dwarf or a neutron star or a small black hole. A black hole that's maybe only a couple times the mass of our sun, and you have a regular star orbiting it. So here's our regular star. And here, again, you have matter that's falling onto this object that has a strong gravitational pull, but here the source of that matter is another star. So it's basically cannibalizing its neighbor. It's very unpleasant for both involved. But you again form this kind of disc. It really is just a little mini active galaxy which is really interesting, and, fortunately, it behaves very much like an active galaxy. So it tends to be fairly bright in many different wavelengths except the very far infrared. So that's one way I can try and weed these guys out. And the X-ray emission usually is persistent but sometimes I have flares. So really, in these cases, the only way I can rule them out is if they appear to be moving on the sky. And if they happen to be moving towards me or away from me, I'm not going to see that motion when I look at an image separated by 10 years. So these are my main source of contamination, but that's okay because these guys are really interesting so I just pass them along to other people. And the trickiest scenarios is when I have no idea what to do. So here is one example. This is the field. This is what, these are all the stars that were in this neighborhood. This yellow circle is where the survey told me I should look. Well, this guy is there, but he's zipping across the sky. He's definitely not it. So what do I do? I have some friends that have access to an X-ray telescope who can look for just short amounts of time. Maybe like 10-15 minutes when they have some spare time. So I said, hey, can you take a look at this object? And sure enough, that's that green one. They said no, there's something there. Whether it's the same thing that my survey saw, who knows. But there is something there, and it had been previously picked up by another X-ray emission. There's definitely something there. And it was so exciting, I went to the telescope and I said I'm going to get a better image than this one here. And sure enough, when I looked at it for about five minutes, got a good exposure, there's a little blob right there. Sadly, my telescope wasn't powerful enough to then take that small amount of light and split it up, but now I know there's definitely something there. So sometimes I luck out. Sometimes, though, I say can you pretty please look at this with your X-ray telescope, and there's nothing there. And I don't know, maybe there was never anything there. Maybe it was one of those low mass stars. Who knows. So after I do all that, what do I get? Well, I get these beautiful spectra. So again I have the wavelength. So this is all in visible light. And then just fluxes the amount of light coming out. I have these big, beautiful broad lines and these narrow lines. Most of the objects are like this. They're exactly what I expect. They have these broad lines. They have the full compliment of everything. All the X-rays, everything. So this is matching our basic theory. Then I have ones like this. And the red and blue just mean that they were taken at different times and I had to combine them. This one, it looks like one of those things that has the broad lines, but when I look in the X-ray, it has absolutely no low energy X-rays. So something is there that's effecting the X-rays, not letting them through, but it's allowing us, from the visible point of view, I'd say I'm looking not through the doughnut. From the X-ray point of view, I'd say I'm looking through the doughnut. So this is one of those cases of a very clear mismatch. Then there's some, I don't know what's going on. It doesn't even have emission lines, but it's a very strong X-ray source. So this is one that I need to look at again and get an even better spectrum. It's very strange, very strange. So what have I found so far? Well, I've found 75 new active galaxies that had been missed in every other survey. Most of them are local. And again, as an astronomer, local has a different meaning, but less than a million light years. And they're excellent candidates for studying further with a whole variety of telescopes. They're so close that even with just 30 minutes of data I can get some really nice results. So far only about 10% show this mismatch. But I am seeing them, and I have to figure out if there's other reasons. What's puzzling is that almost all of them have these broad lines, whereas other surveys have found about equal mix with having broad lines and 50% not having them. So I have to make sure that I'm not missing some objects. I don't think it's because of my detective work, but it might be the whole way the survey is designed. Maybe I'm biased. I'm not getting everything that I want to. So I need to think really carefully about that. So what do I have to do to continue my detective efforts? I have to continue making observations and getting to go to all those telescopes. I have to better understand whether I'm missing something. Whether there's a whole population that I'm missing just by the way I'm doing my survey. Just like if I were going to do a survey for presidential, who are you going to vote for, I have to be very careful what group of people I decide to call because if I don't think about that, I might have a completely wrong result. So I need to think about that. And then I have to really go and interrogate those guys that have a conflict, and say, why do you have a conflict? Is there something wrong with our model for what's going on in the inside? In the very center? Or is there some other confounding factor? And in general, all these nearby active galaxies are a great resource for doing lots of other studies. So, concluding thoughts. Studying nearby active galaxies is important. As exciting as it is to see those headlines of the most distant quasar ever found, there's a lot of important science that we can only do with objects that are close by. We need to have X-ray surveys that cover the whole sky. That comes at a cost because there's a lot of ground to cover. And they come with their unique challenges, but I have to say, there is this wealth of publicly available data that never would have been here even 10 years ago. Really, astronomy is moving towards having everything available for everybody, including yourselves, and it's amazing how much work you can get done without ever having to ask for new data. A great way to make sure we use our public resources to the best of our abilities is to share our data and make it in a form that we can all be astronomical detectives with other people's data. It's great. So I would just like to thank Vanessa Logan. She was the undergraduate who worked primarily with me on this project. She was a great student. I'm always so pleased to see what a great undergraduate student can do. And of course, all the scientists and staff. Nineteen nights of observing, they've really seen me through a lot. And just financial support that I've received from NASA, American Astronomical Society, and the College of Wooster so I can do this research. Thanks.

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