Folks, good evening and welcome to the first of our speaker series for the spring semester. Tonight we have Dr. Bill DiRienzo, who is our new professor of physics here on campus, starting his second semester. I'll finish his PhD in astronomy at the University of Virginia after an undergrad at UW-Madison and is here tonight to talk about star formation in the Milky Way. Without further ado, Bill DiRienzo. All right, great, thanks. Thank you all for coming. Just for my own curiosity, how many of you are students in astronomy 106 right now that are required to be here because it's class? All right, only about half of you. All right, good. Sorry it's going to be dark in here, but in astronomy, one of the most important things that we like to do is look at really pretty pictures and they're going to be completely washed out unless we make it real dark. So if anybody needs to take a nap, that's fine. Just please don't snore. So I'm an astronomer. You can also call me an astrophysicist. We kind of use those terms pretty interchangeably these days. If you want to split hairs about it, astronomy is really about looking at the sky. So anybody can be an astronomer.  Astrophysicists, we're trying to understand what we're looking at. We're trying to do the physics of astronomy. So we're doing really extreme physics, very large energetic things, very cold things, very dense things, very low density things. So that's really what I try to do. And in my own personal research, I study star formation. So that's what I'm going to talk to you about today, is how we actually form new stars, what that process is like, and a little bit of what these sort of outstanding questions are and a little bit about what I do specifically. Since I just finished my dissertation in summer, when we get to sort of the end of the talk, we'll be getting into the things that I presented in my dissertation defense. But we're going to start with a little bit of an overview of some basic concepts first and sort of work our way up. In trying to title this talk, I gave it about 30 seconds of thought and kind of threw out a couple words that I thought would be interesting. Snakes, bubbles, and stellar nurseries. When we talk about star formation and new stars being born, we sometimes talk about the environments in which they're born as being stellar nurseries, and we call the new stars baby stars. So that's my baby star here, isn't that cute? I don't care about the older stars or even toddler stars, those are kind of boring. New baby stars are very interesting. And when I talk about snakes or bubbles, what I'm really talking about is sort of the morphology of the environments that I look at, the shapes of the nebulae in which stars form at different stages in their development. So for example, bubbles are down here. All these little roundish things that are kind of red with green rims on them, those are our bubbles. That's what's telling us that there are new stars forming there. Not just any new stars, but actually really massive energetic ones. And on the top is an example of a snake, or what we call an infrared dark cloud. That dark thing you see going across there. That's actually not a hole in the sky. It's not a lack of anything in that place. It's actually where there's something very cold and dark in front of something brighter in the background. There are a lot of infrared dark clouds, but this one is actually specifically called the snake. It's kind of a famous one. So these are sort of the two projects I looked at in my dissertation. So we'll get to those towards the end of the talk. Now we'll start with a couple basic things about modern astronomy. When we talk about science and scientific research today, a lot of it gets broken down into experimental and theoretical. Experimental, you're coming up with hypotheses based on existing models, trying to come up with ways to test these models to maybe disprove them, maybe differentiate between different models, things like that. And theorists do a lot of math, a lot of simulation, a lot of trying to extrapolate known physical principles to new situations. And those two things work together. In astronomy, we can't really be experimental and theoretical most of the time. Theory still works fine. But most of the things that we're studying are so far away, so big, so energetic. We can't tune the variables like you would in a lab. We can't mix things together like you would in a chemistry lab. We can't shoot particles together like you would in a particle accelerator, which what particle physicists do. So we have to observe what nature gives us. And we have to look at it the way that we're able to see it from Earth. This doesn't mean that we can't progress scientifically, it just means we have to be very clever in how we design our observational projects. Another thing to keep in mind is that when we're looking out into space, the universe is obviously a three-dimensional thing. Maybe more than that if you're into string theory or general relativity, but let's keep it simple right now. Three-dimensional universe. When you look out at the sky, the plane of the sky is basically a two-dimensional thing. It exists in three dimensions, it's all around you, but when you look at things that are this far away, that are really far away as they are in space, you just see something as it is on the sky, and there's no really going to the left or the right above or below it to get a different angle. You have what you have, that's the view you're stuck with. We would like to know what's going on in this third dimension sort of towards an array from us, but we usually don't get to see that when we look at pictures. We actually can tell pretty easily how things are moving in this direction, we just can't tell how they're extended, and I'll talk more about that in a minute. It's also important to keep in mind that a lot of things change slowly compared to human timescales. So when I talk about star formation, the time that it takes to form a star is something like three to five million years. So I'm going to talk about the evolutionary steps in forming a star. We have never watched a star go from a protonebula to form star in the end. It's just not possible. We're not patient enough to wait around and watch that happen. What we can do is look at a whole bunch of different objects that are at different stages of formation and try to stick them together to come up with some kind of sequence to understand what we're looking at. The other important thing to sort of keep in mind, just because I want to plug this a little bit, modern telescopes operate a lot like digital cameras. In fact, the reason, or at least a primary reason why you guys all have cameras on your phones today is because astronomers really pushed for digital detectors to replace classical photography because it's much more efficient for doing astronomical observing. It used to be very difficult and expensive to manufacture those kinds of digital detectors and because we wanted them so badly, they got a lot easier and cheaper to make and now everybody can have one. So you're welcome. Now before we go into star formation specifically, let's do a couple sort of introductory things just to sort of get a sense of where we are in the universe. So the first thing that we should really talk about are the size scales and distance scales that we're concerned with when we're looking out into space. So here's a picture of the Sun, the eight major planets and two dwarf planets, Pluto and Eris, all on the same size scale. This is not the correct distance scale up on top. I will say that. So as you might notice, Earth looks pretty tiny. This is one thing that I always try to instill in my students. In the grand scheme of the universe, you are nothing. Even within the scheme of the solar system, which itself is nothing in the scheme of the galaxy, which itself is nothing in the scheme of the universe, you're nothing. So if anybody has an ego, we should be bringing that down pretty quickly. Now, so that's for size comparison. Now, if you want to think about distance comparison, how big the orbits of the planets around the Sun are. Well, we have a very nice model we can look at. We're going to take a 1 to 10 billion scale. So we're going to shrink down the solar system by a factor of 10 billion. That's how much we need to shrink it down so it becomes attractable, something you can actually think about. So there are places like the National Mall outside the Smithsonian there in Space Museum in Washington, D.C., where they actually have models on this scale. This little yellow dot here represents the Sun. I know it's getting a little hard to read what's actually going on. And then all these other little dots kind of represent where the planets would be, given their orbital sizes, if they were all on the line. So in reality, everything starts to spread out over a region about that big, a big. So on this scale, our Sun here becomes about the size of a grapefruit. Our big planets like Jupiter and Saturn are close to about the size of a marble. Our planets like Earth are closer to the ballpoint and a ballpoint pen in terms of their size. And it's spread out over about a block and a half. All right? Does anybody want to guess on this size scale how far west of Washington, D.C., you'd have to go to get to the next grapefruit? The next near star to Earth. Let's hear some guesses. Did you guys learn that already in class? No. All right. Great, that is an excellent guess. If you put a grapefruit in Washington, D.C., the next closest star is a grapefruit in California. That is how big and empty space is. And that is our next closest star. All right, again, you're nothing. Now, in space, because we're looking at such big distance scales, there's actually a really neat consequence from this that can be maybe a little tricky to wrap your mind around, but it's actually incredibly useful. Now, light doesn't travel instantaneously. It has a finite fixed speed. So whenever you look at something, you're not seeing it as it is exactly right now. You're seeing it as it was when the light left that object that you're looking at. I'm seeing you guys almost instantaneously because light goes very fast and it's covering almost no distance here. But even when we look at the moon, you can do an experiment. Apollo astronauts left little reflectors on the moon. You can shoot laser beams off of them. A one-way travel time for light from the moon to Earth is a full second. So when you look up at the moon at night, you're seeing it as it was a full second ago. The sun is further away, so you're actually seeing it as it was about eight minutes ago. As you look further and further out, you see things further and further back in time. Sirius is a relatively close by star. You're seeing it as it was about eight years ago. It's eight light years away. Light year is a unit of distance, not time. And if you look at the Andromeda galaxy, the other major galaxy in our local group, you're seeing it as it was over two million years ago. So astronomy has this really neat feature that is unlike almost any other field of study. We can actually see things in the past. You look at more and more distant objects. You see things closer and closer to the beginning of the universe. It gets harder and harder to study them because they look really tiny and dim, but in principle you can study them. So that's just a really neat thing that we can do. Now when I talk about light, we've got to broaden our eyes in here. I'm not just talking about light that your eyes can see. That would be called visible or optical light in the middle here. There's actually this whole big spectrum of different kinds of light that we can use as astronomers. Our eyes can't see it, but we have instruments sensitive to these different forms of light. You may know some of these terms already. They fit into a nice sequence. Radio, microwave, infrared, visible, ultraviolet, X-ray, gamma ray. These are all fundamentally the same thing. They are all just like light. Going from left to right on this image, what we're doing is we're going from very low energy light to very high energy light. Light travels like a wave, so what that actually corresponds to is also what we would call the wavelength, the distance peak to peak, or the frequency. How often does the wave oscillate as it goes past you? On the far left, that's our low energy side. That's the nice long wavelengths, very low frequency. The frequency and the energy increase as we go to the right here. The wavelength gets smaller. This graph here actually over-represents how big the visible light range is. It's very, very, very narrow. There's a whole lot of light that you just don't see, but it's really useful to us because different physical processes emit different kinds of light. The reason that these regimes have different names is because they came up at different points in history before people realized there was all the same thing. They didn't realize immediately that radio waves and visible light were the same thing because they were experienced differently. There were different instruments and physical phenomena that they were sensitive to. The telescopes that we built to look at these different kinds of light will look differently. They'll use different technology, but it's all fundamentally the same thing. What's important to keep in mind is that no one wavelength of light can tell you the whole story. In astronomy, we try to look at objects in space in a bunch of different wavelengths and frequencies to understand what's really going on in that object. Here's an example of what happens if you look at the Milky Way in different forms of light. You might be most familiar with the optical one down here. This is most like what you would see if you went out into a really dark location, low light pollution on a clear night, and you looked up. You might see this nice band that almost kind of looks like serious clouds going across the sky. You're definitely not going to see it tonight because of the clouds, unfortunately.  Your eyes are just not that sensitive, but that's the closest image up here. And then all of these other images are that same part of the sky, but taken in, say, gamma ray or x-ray down here. Different wavelengths of infrared radiation and some different wavelengths of radio up here. You probably notice a lot of similarities about these different pictures. You'll probably also see some key differences here. There's something here that's very bright in x-ray and gamma ray. Also some wavelengths of radio. It's almost no optical or infrared. If you looked at just the optical, you completely missed that. You have no idea that there's anything there at all. It's clearly something very interesting because it's very bright in the other wavelengths. It's a continuous spectrum, so there's a whole range. In principle, you can go as low and as high as you can imagine. Those boundaries are largely human-defined and actually kind of fuzzy. The best-defined boundary is the visible light spectrum on either side because human eyes don't vary a whole lot in what that means. There actually isn't some variability. There are some people that are actually born with four kinds of cones instead of three and they can actually see a little bit into the ultraviolet, I think it is, just a little bit. To them, it doesn't seem all that different. Even that one's not a hard limit.  It gradually fades away. Beyond that, those are just sort of names historical conventions. I guess we could come up with a new one if we wanted to invent a new one. In fact, a lot of times textbooks don't even label microwave as a separate regime. It's partly radio, partly infrared to them. So it's all subjective. In principle, you can go as low and as high of energy as you can imagine. What really limits us is our ability to come up with technology that's sensitive at either end. Does anybody know what this is a picture of? Hubble Space Telescope. Can anybody name another orbiting space telescope? What's that? Which one are you going to name? That's not up yet. The next one. The next one? Do you remember its name? So JWSD, the James Webb Space Telescope. That's more or less going to replace Hubble. So I guess nobody knows what telescope that is. This is my favorite space telescope. This is the Spitzer Space Telescope. Hubble's the really famous space telescope because it's been very successful. It takes a lot of very, very pretty optical images. It had that whole optics problem that had to be corrected and was very expensive and potentially going to be a huge failure but turned out to be a huge success. But there have been dozens of orbiting telescopes by different countries and different wavelength ranges at different points in time. Going back over a few decades now. Spitzer is now more or less defunct, still kind of operates a little bit. It's an infrared telescope. The key reason why Spitzer had a limited lifetime and is no longer operating, even though it's much younger than Hubble, does anybody know, does anybody know how night vision goggles tend to work on Earth? It's related to the infrared emission. Almost like a negative? Not quite. Why is the sun bright? Anybody know that one? It is very intense. The key reason why the sun is bright is because it's very hot. Oh, you got it. Right, okay, there we go. Things emit light when they have a temperature. There's nothing we know of that's that absolute zero, so everything emits light. You know this, if you turn on an electrical stove, it starts to glow red. It's getting hotter, it's glowing red. The sun is hotter than that. It actually glows yellow. You actually start moving up along that spectrum I was talking about, to higher and higher energy. You guys in here are not hot enough to emit optical light.  You are however hot enough to be emitting infrared light and lots of it. A lot of times night vision goggles actually are just infrared detectors that translate that into an optical image for your eye. False color. If it's not optical, you can make it whatever color you want when you project it as optical. Any image I show you that's not optical will be false color. We're just going to pick colors to represent different wavelengths. We'll probably still keep the same convention, red is low energy to blue at high energy, but I pick whatever I want. Spitzer itself is warm enough to emit much more infrared light than it's collecting from anything out in space. It's orbiting the earth. You think it's cold, right? Still receiving about as much sunlight as anything on earth because it's orbiting the earth. It's the same distance from the sun. So you need to put coolant on these telescopes that operate in the infrared. Eventually the coolant runs out. The really sophisticated coolant systems are very efficient, but they only last a few years, and then you really can't use the telescope anymore. While it was still operating, though, it was incredibly useful at taking pictures of the Milky Way to help us out and understand star formation. In particular, there is a survey with a very long name, the Galactic Legacy Infrared Midplane Survey Extraordinaire, or GLIMPS. Acronym-making is a key part of being an astronomer. It's got a very large data set. It basically mapped out the entire disc of the Milky Way in several different wavelengths of infrared light. Here's a composite, a nice false-color image, three different wavelengths of infrared light. It actually wraps around this way, because it's very long and skinny. And so this is more or less what I used for the first half of my dissertation, this data set. What do you guys notice when you look at this? How does the Milky Way look? What do you see in it? There are a lot of bubbles, a lot of little sort of red-dotty things. That's what I really care about. You might also notice it's brightest in the middle. If you look directly through the plane on the Milky Way, it's brightest. Brighter towards the center than if you look more or less away from the center. You're looking through more material in that direction. So we use infrared light to study star formation, because star-forming environments are usually very dense and dusty. High densities of dust tend to block out optical light, so you can't actually see in the optical what's happening inside a star-forming nebula. You basically just see the outside of the nebula. Infrared, however, is much better at traveling through dust, so you can actually get some idea of what's going on the inside. So think about X-ray glasses, except it's infrared glasses. In particular, what we call YSOs are young stellar objects. These baby stars I like so much. What they do is really heat up the dust around them, and we see the dust glowing. That's what we're seeing directly in the infrared. So here's an example. This is Orion, probably one of the most famous constellations. Now is actually a really good time of year to see Orion early in the night. Not tonight because it's cloudy, but it's relatively easy to find. Pretty big, unique shape, lots of bright stars in it, so it's easy to find. If you look in the optical, you see a couple of the bright stars that make the constellation. You see that guy down here. This is what we call the Orion nebula.  I really like the Orion nebula. If you look in the infrared, what you see is that there's this whole big cloud of gas and dust, and a lot of it is forming stars, and you had no idea in the optical. So let's just break down what are some of the components of space that we can look at. Well, stars is the obvious one. The astro and astronomy mean star, so we're studying stars. I only care about the young ones. In caring about the young ones, and in caring about how they form, I also got to look at the gas and dust, because that's what these stars form out of, and that's what's enshrouding these young stars.  I don't care. So if we look at Orion again, a little bit closer in view, the colors brought out a little bit more. Now, you can see that the stars have different colors. Some are redder, some are bluer. Let's see if you guys were paying attention. Why are they different colors? They're different temperatures. They're different temperatures. The bluer ones are burning hotter than the redder ones. Now, there's a whole field concerned with stellar interiors and stellar evolution that I'm not going to talk about, but suffice it to say that the most important characteristic of a star is its mass, how much material you put into a single star. Our sun is relatively sort of median-ish, but there are stars that have a lot less mass, a lot less material, and stars with a lot more. Once you determine the mass of a star, that pretty much sets what its life is going to be like. Between the mass and the age of a star, you can determine pretty reliably what it's going to look like. How many times should they form? How many generations of material it's been gone through? That actually affects the composition a little bit, and that does play a part in the evolution, but it's not nearly as strong as the effect of the mass and the age. It is discernible, but it's not huge. It has a lot more to do with planets, that's for sure. We owe our existence here on Earth to their being previous generations of stars making heavier elements. The key thing here is that the mass sets the properties of the star because the most massive ones have the strongest gravity, which means the fusion in their cores that's powering these stars is progressing at the fastest rate. More massive stars have more material to fuse, but they burn so much faster that they actually go through it in a much shorter time. They live shorter.  But in their short lifetime, they've had a profound effect on their environment because they've been shining brightly in really energetic light, X-rays, and ultraviolet, so there's a supernova. So the massive stars, even though they're actually relatively rare compared to all the stars in the galaxy, are some of the most interesting ones and most important ones for understanding the evolution of our galaxy. And here's just a zoom in on the Orion neighbor because it's really pretty. So this is again something that's way better than probably what you can ever see with your own eye, but this is still one of the best possible things that you can ever see with your telescope or binoculars. So like the gels being different colors, are those colors attributed to it by any of those false colors too? Yeah, probably. Even a lot of optical images, their contrast is sort of turned up. You actually, in astronomy, you never do what your camera does, which is take a color photo at once, all in color. What your camera actually does is takes a red, green, and blue photo very, very quickly and adds them together in astronomy, we take those separately and then put it together so you can pretty much everything's false color in some sense. Now when we actually talk about dust, what I don't mean is the dust under your bed. Dust is a lot more like these tiny little things, very, very, very, very small rocks, sand, something that's made out of a lot of carbon and silicon. But not really at all like dust on Earth. We just sort of co-opted that term because that seemed the most appropriate. And we should probably talk a little bit about the different elements. Here's the periodic table. If you've ever taken a chem class, or even a general science class, you've probably seen it. Do you guys know where the metals are on the periodic table? What's that? Under the title. Somewhere around here. I mean, we do this. When the Big Bang went off, about 75% of the universe was hydrogen, about 25% was helium and there was basically nothing else. Even today, if you look at most of the interstellar gas or in stars, there's very little by percentage of anything that's down here. So we just throw that all into one bin and call that the metals. Being a little bit more precise, here's a periodic table with the most common elements in the universe and the size of the white boxes represents their relative abundance. The reason for this has a lot to do with how stars evolve and how they actually operate with fusion, but we're not going to get into that. So I'll just point that out real quick. So when we're talking about the gas in these nebulae, we're mostly talking about hydrogen and some helium and then the little bit of extra stuff down here, you're going to get a lot of that. Some of that in the gas and a lot of that in the dust grains. So an important thing to keep in mind about star formation because sometimes here doesn't the Big Bang just throw out everything fully formed? Don't we just get galaxies and solar systems and stars right away? We don't. The Big Bang throws out a bunch of hydrogen and helium and gas. Somehow that turns into stars with planets that are arranged in galaxies and all this other stuff. So what I'm trying to understand is that process of how you actually get the stars out of gas in the first place. And as I mentioned, it's really important to understand this because stars, as they live and die, they go through this cycle where they recycle material, they turn lighter elements into heavier elements, which is why we're here today. So this is all important stuff that we want to understand. It's also interesting to talk about the chemistry. Astrochemistry is sort of a relatively new thing. We in astronomy have been doing for quite a while now using studies of molecules and atoms in space to try and understand the physical environment. The temperatures, the densities, ages of things, stuff like that. An inherent difficulty in that is extrapolating what you can do in a chemistry laboratory on Earth to the conditions that you see in space that are much hotter and much colder, much lower density, things like that. More recently, in modern times, there's been more of a push to actually try and understand that better, to actually try and do experiments in chem labs that are more extreme that try to replicate environments that we see in space so we can understand it a little better. The reason why you guys might care about this, if you care about where you come from or the origin of life. We know by looking out at these star-forming environments that they have really rich chemistry. They have organic compounds. Complex molecules with carbonate. They may have amino acids. We don't actually know how amino acids would behave in space all that well, so we can't actually identify them yet, but it's possible they're there.  Some people have speculated that. It's possible that life on Earth actually originated in the proto-solar nebula before the planet was even here, or at least the amino acids that formed life on Earth already existed at the beginning of the planet. So that's one reason that we're interested in this. And the massive star-forming environments in particular have the really richest chemistry. So now let's actually start talking about how a star is formed. Basic picture goes like this. This is highly simplified in cartoony, but it'll get the point across. We're going to start with some kind of nebula, a big cloud of mostly hydrogen gas, helium gas, and dust grain, some other bits of other stuff. There are places in that bigger cloud where it's denser than other places, where there is more material compacted in. Whenever you have matter, you have gravity, mutual attraction between all matter. So when you have a setup like this, your dense cores are going to pull in matter from the less dense parts of the cloud under gravity, and you'll start to collapse and form something that's even denser at the center. If it gets denser enough in the middle, you start to build yourself a star, or what we'd call at this stage a proto-star, or a young stellar object. This is where I get really interested. For reasons we'll discuss in a minute, at the center, it doesn't just all collapse symmetrically into a nice spherical body. You actually start to form what we call a disk, or an accretion disk, rotating around this thing, by which material funnels on to the star, or sometimes material actually gets thrown out in jets along the poles of the axis of rotation here. As time goes on, and this thing starts to heat up, it clears away a lot of the material around itself, and so you're left with the disk and the jet. Eventually the jet turns off, and somewhere in this phase you actually start forming planets with the same material in the accretion disk. This is why all the planets in our solar system go around in the same direction, nearly circular orbits in the same plane. Eventually all the material either falls onto the star, onto the planet, or it gets blown out of the solar system by the stellar wind. Once the star starts to get hot, basically material boils off of it. Our sun has a solar wind right now, very low density, and it gets blown off of it in all directions. And then you're left with a solar system. That's the general picture. We're done. We've solved star formation. Let's go home. I think I'm going to skip over these next two slides just in the interest of time. You can ask me about them later. It has to do with why we get a disk in the first place. I'm just going to play this little movie for you. As I keep the stages up here and a couple images that I'm going to talk about in a second, actually observational evidence of this process. This is also a highly cartoony model, this video of how this actually takes place. I had my dense core collapse form to disk, start forming protostar in the center. In a second here it's going to start clearing away material and some planets will pop out of the disk here. There we go. We've got a nice solar system. That's all well and good to have a nice working model that obeys physics and seems to make sense. But you also need to have observational evidence to support that. We see a lot of objects that corroborate this method. You can see if we block out sort of the bright central star you can see the disk either edge on so you're looking at it sort of from this angle or more face on here you're looking at it more like this. If we look at Orion again we find a whole bunch of objects like this where you see the bright sort of central star and then the disk all around it. And we also see nice examples of edge on disks that have jets as well. Something at the center and material shooting off on either side. So this seems to all fit together pretty nicely and actually a relatively new image, this one was actually really exciting just a couple months ago. There is a relatively new observatory in Chile. It's an international observatory the U.S. is one of the partners in it. It's called ALMA. It's the Atacama Large Millimeter and Submillimeter Array. It's a configuration of a whole bunch of different radio dishes sort of microwave range actually. In Chile in the Atacama Desert that's where the Nazca lines are in the Atacama Desert. And in the microwave what you can see is dust very effectively. So this is an image of a known protostar and what we're actually starting to see is in the disk these places where the dust is getting cleared out. What do you guys think is happening in there? In those rings? Yeah, presumably you have planets forming and they're eating up material all around the protostar. So you'd surmise from this we haven't gotten to the point of taking an image that actually shows us the forming planet yet although I would bet that will happen within at least a few years. This is still like a relatively new instrument. They're actually still learning how to best use it. It's that new. But presumably there's a planet here, there's a planet here a couple planets here. We're actually starting to see planet formation. Is that the same planet? Because they form out of the accretion disk which is a planar. So that's kind of what I skipped over the reason why it actually flattens. We can talk about that at the end if we want to talk about the flattening. So it's actually a really interesting time to be alive. We're actually getting to the point of finding planets around other stars and actually finding information. So a couple of the key things that we have to keep in mind when we're forming planets is that we don't just have gravity to worry about.  In fact there are so many of them that it's almost a wonder that we form stars at all. Two of the big things to keep in mind are angular momentum and pressure. Now the way that we usually teach angular momentum in intro physics is an ice skater. So the ice skater is spinning around arms out. You guys know how he or she spins faster? What do they do? What's that? Don't get lower. Fling their arms in? So angular momentum is what we call a conserved quantity meaning it can't be created or destroyed. And angular momentum depends on the size of an object and how fast it's rotating. And it's mass. There's the other one. So basically the statement of conservation of angular momentum means that if something's rotating it tends to keep rotating. Ice skater brings arms in. Ice skater's mass hasn't changed but you've effectively decreased the size of the ice skater so the rate of rotation goes up because angular momentum has to be conserved. In forming a star we're taking a very large cloud of gas and compressing it down a whole lot. If my nebula was starting out the size of this room I guarantee you the protostar is going to fit into my hand. Compressing down a whole lot. So I'm going to get something that wasn't really rotating in the first place but it had random motions in the gas and the dust and by the time you contract it it's rotating real fast so you have to sort of overcome that when you're forming a star. There's also the issue of pressure. As you keep compressing the gas and it gets denser and denser it also gets hotter and hotter it pushes back. If you imagine trying to take a balloon and compress it down make it smaller it's difficult. The balloon pushes back when you push in. So that's what you have to overcome. So we have gravity opposing also magnetic fields and the fact that the star eventually starts to turn on with the solar wind and blow material away. And somehow you have to get enough material in a small space in a fast enough amount of time that you form a star. And this process is harder to explain for the more massive stars the ones that are really interesting and that really affect galaxy evolution. So that's where my research starts to come in. We want to understand star formation if we want to understand galaxy formation and astrochemistry but it's hard to explain how massive stars actually form using just this simple picture that I presented. So we need to make some changes to that little six stage model that I presented. And two of the proposed methods that you might add on to this model are what's called triggered star formation or by looking at the evolutionary phase known as infrared dark clouds which is where my own research comes in. So here's where we're going to start getting into the more technical stuff but I'm still going to try and keep it sort of simple. Now the idea of triggered star formation is that if you can form a massive star we won't ask where the first massive star comes from. It'll actually induce more star formation around it and in particular massive stars. So remember we're forming a star out of a large nebula and it's just one particular part of the nebula that has collapsed to form a single star. What happens with these massive stars because they're so energetic they have strong winds, they emit a lot of light a lot of its X-ray and ultraviolet is a very high energy light has a very profound effect on the rest of the nebula that it formed out of right away from very early in its lifetime. The primary effect is what we call ionization. This really high energy light the X-rays and the ultraviolet rays kick electrons off of the hydrogen and helium atoms in the gas and they heat them up quite a bit. This input of energy from the massive star into the environment makes it get very highly pressured so it wants to expand out like a balloon. Because it does that it pushes out the material that's in the rest of the nebula and often times this expansion is very fast what we call supersonic. So this is essentially a sonic boom going through the nebula because this massive star has turned on. This is not a supernova that happens when they die but this is still a very energetic sort of event. Now because the current is expanding out faster than the speed of sound in the cloud, what that means is the material that's getting swept up can't get away. It's just getting accumulated. Now as this shell grows bigger and bigger this bubble gets bigger and bigger it accumulates more and more material as it pushes outward. And the thought that triggered star formation is that eventually you get so much material in this shell that's so dense that you have a whole bunch of new dense cores all of a sudden and they'll start to contract quickly under their own gravity. And the theorists tell us that this more or less works. Theoretical astronomers do a lot of simulations where they basically set up computer model. I'm going to start with sort of a spherical thing of gas I'm going to let it fall under its own gravity I'm going to put in thermal pressure things like that physics and I'm going to see what pops out of it. Here's an example of one such model a couple of different simulations if you start forming a couple of stars in the beginning and you start forming these bubbles eventually you get things that have really dense spots in them or presumably new stars would form. We also see places in space where it sort of looks like this happens. Does anybody recognize what Nebula this is or maybe that picture in particular? This is called the Pillars of Creation very famous picture in what's called the Eagle Nebula this is the whole Eagle Nebula here the pillars are right about there those things Here's another example of looking at something in multiple different wavelengths and seeing different things This is more or less a bubble in the Eagle Nebula This denser stuff around the outside here this is where that front of the bubble has pushed out there's a bunch of massive stars in the center here that have pushed out this bubble and there are a couple of places where it hasn't pushed out the material it forms a really dense core at a couple of these places really dense cores that are starting to form stars actually if you're just getting pushed out again So if you look at the Pillars of Creation they're called the Pillars of Creation because they're actively forming stars If you look in the tips what you see is a lot of infrared radiation here this is where the protostars are heating up the dust in those Pillars So this is just one example of where we think this might actually be happening The stars that formed in the center here first are actually triggering more star formation in the rest of the Nebula Now I'll note that that round spherical bubble picture I put up is basically never going to happen exactly like that in space Most of these sort of bubble-ish features are not all that round in fact some of them are very asymmetric So in trying to identify catalog and study these things we have a whole bunch of data we have that glimpse catalog of basically the whole Milky Way that we want to study has a lot of bubbles in it we want to analyze it in some sort of systematic way so it's not you don't just have one person investing hours and hours and hours and looking at it and then ever after you're subject to what their opinion was for what constitutes a bubble and what not So this is a picture taken from a project called the Milky Way project it's one of several citizen science projects basically crowdsourcing science and using the human ability to identify things that are really hard to code up for a computer to do but when you have a lot of people do them that reduces the effort any one individual has to do and it also starts to take out some of the individual biases that were crop up if you just had one person doing all the analysis So in this particular example I think anyone of you could go do this you could go look up the Milky Way project or Galaxy Zoo is another example of a citizen science project they're always looking for people to do this stuff you open it up it gives you an image and it says go pick out all the bubbles draw circles rotate them around maybe stretch them out make them the right size and a bunch of different people do it they average all the results together and they end up with a catalog of where all the bubbles are we know about how big they are they're more elliptical or circular they're sort of closed all the way around or they're open it's actually really really useful to do stuff like this and the averaging is kind of sophisticated it waits by how many times you've done this so more advanced people get weighted and more stuff like that but really a great idea so this more or less came out as I was finishing my project on triggered star formation so I did not get to use their results and use a very large catalog I used six bubbles which I looked at by hand myself and this is the array of bubbles that I have they're also sometimes called H2 regions we won't get into what the terminology means so what you see is there's a combination of things that are kind of roundish and some things that are maybe not so round things that are definitely not round so these things are these massive stars are forming in clouds that are not spherical that aren't homogeneous all the way across they might actually be closer to the edge of a nebula instead of in the middle so you get all this range of morphologies so when you look at this the green parts here are more or less that rim that edge that we're concerned with where the stars would be forming if there really is triggered star formation going on so they're presumably massive stars at the centers of all these things ok so now what I wanted to do after identifying a couple candidates six out of the hundreds or thousands that you could look at because it's very time intensive to do this I have to actually go and find all the baby stars that are forming in these things any idea how I would do that look at the color so I told you that stars tend to form in really dense dusty environments where optical light does not get out but infrared light does because the baby star is heating up the dust so in fact the baby stars will be the reddest looking thing because you will probably only be able to see them in the infrared and not the optical at all so we can even do better than that we can actually kind of classify how far they are along in the formation process because the earlier ones will still be more heavily embedded in dust and so they'll be really red you'll only see them towards the longest infrared wavelengths and as they get older they start to peek out more and more at shorter wavelengths so this also raises the question how do you get the color or the brightness of a star from an image if you look at this you can probably see what you think are brighter and dimmer stars good we need to quantify that so we can be scientific about this we have to put a number to how bright a star is at every wavelength so this is just an example of one way to do it here is one particular point source what turns out to be a protostar this is a zoom in on that source in how many is this nine different wavelengths in the infrared shortest wavelength up here and then increasing in wavelength as we go out here a regular star it's not a baby star would be brightest somewhere up in the optical to maybe short the near infrared up here and then get dimmer as we go along that's not what this guy does he kind of does the opposite you don't even see it at the shortest wavelength and then it starts getting brighter and brighter as you go to longer wavelengths so this is a good indication that this thing in the center here all along is actually a protostar and it's actually a fairly embedded one it's fairly early on in that formation process so what you do is you plop down some circles around these things, count up all the emission in the circle and then you throw a donut around the outside count up all the emission from the gas that's just ambient, that's around it subtract that contribution off so you're left with just what's in the star and then at each of these wavelengths you have how bright it is and so we make plots like this where you start plotting down how bright it is at the different wavelengths and you put error bars on if you know it and sometimes you can't get a good measurement because you can't actually see anything so you throw an upper limit on that's what these little arrows are now to be really sophisticated and precise about is it a protostar is it not, where is it in its evolution how massive is it, things like that what we actually do is generate a whole bunch of models of these curves brightness is a function of wavelength for a couple hundred thousand different examples of models of young stellar objects and then run a computer code that spends several hours trying to fit those couple hundred thousand simulated models to the data that we have and see what the best fit is and if that's a protostar or not and what the properties are for that model in general what happens is that there are several things that fit really well but they tend to be very similar in properties so you do that, you find out where all the protostars are and you find out all the regular stars and I think we had something like ten thousand bright star like things that we looked at and about five or ten percent of all those turned out to be baby stars for which we had to do this process a lot of it highly automated otherwise I'd still be doing it and just to show the key result in here is that we actually found well in about half of the bubbles I looked at there wasn't any clear indication that there were more baby stars on that bright rim and then about half of them there was indication that there were more baby stars in that bright rim so triggering star formation might actually be important but maybe doesn't happen all the time that's sort of the key point of my very long paper on it so just an example here's one of these bubbles so this is probably the best example of what we found I'll draw your attention to this one this is where I marked all the baby stars the red ones are younger alright you see there's a whole bunch of baby stars right on that rim okay so this is the part where we go from being very quantitative to being kind of qualitative there is a whole bunch of baby stars on that rim it's probably triggered end of paper we'll do more studies do more examples and see if this result holds up so that's more or less triggered star formation as deep as I'm going to go today and just in the last couple of minutes I'll talk about the other research that I do which is where most of my focus is today which is about looking at infrared dark clouds okay so this is another image from the glimpse survey alright you see a whole bunch of green emission this is just from the ambient dust that's all throughout the Milky Way emitting infrared light you see a couple bubbles in here and maybe some proto bubbles some young bubbles and then what you see is there are some places where there's not as much just emission okay but you still see a lot of stars through there there's just natural variations in how much dust there is throughout the Milky Way but I'll draw your attention to this guy right here it's very very very dark it's not actually a lack of dust and lack of stars in that area it's that in the foreground there is a lot of dust and it's very cold let's skip over that for time so we've known about dark clouds for a long time now so even in the optical if you look out in the sky you see patches of things that look like this where all of a sudden the density of stars goes to almost zero even though there's a whole bunch of stars all around this thing people actually debated for a while whether or not there was something dark in the way or whether there was actually a lack of stars in that direction on the sky once people started doing infrared astronomy you start seeing all the things that are in and behind that cloud because the infrared goes through the dust much better now infrared dark clouds are so cold and dense that infrared light doesn't even go through them so it's just this idea but a little bit more extreme and so here's one of my favorite infrared dark clouds you see this one has a couple of very red things these are going to be our proto stars again this is all the dense cold dust and this snakey looking thing actually you see there's a bubble down here this whole thing is part of a much larger kind of space this whole thing is part of a much larger molecular cloud a much larger nebula that's forming stars and it's just that the star formation will progress a little bit further down here than it has up here on the right hand side this is an image of the dust emission from the Orion molecular cloud so that really pretty nebula I showed you before the Orion nebula that's down in Orion's sword that would fall more or less right about here so when I'm looking at infrared dark clouds I'm basically looking at things that are a lot like Orion except that having a sample of one is never any good so you need to look at more things that are like this that are forming massive stars you have to look at other things that's where these guys come in primary way that I study them is by looking at the molecular emission in these things most of the material in the cloud is hydrogen gas hydrogen gas is actually really hard to detect but there are other molecules that are easier to detect and in particular I like using ammonia that's this guy right here it's a nitrogen with the hydrogens hanging off of it after hydrogen carbon monoxide CO is the next most abundant molecule in this nebula and then ammonia is not that far behind ammonia is actually relatively abundant in star forming regions so what I identify these molecules and these different molecules in different atoms in space is that they each emit very specific frequencies of light that we call spectral lines ammonia like a lot of molecules happens to have lines in the radio range it's actually got a whole bunch of lines that it emits in the radio so if we look at a particular wavelength of radio and we see these lines pop up we say ha ha there is ammonia there because ammonia is the only thing that emits this and actually by looking at the shape of this thing in detail you can figure out a whole bunch about the temperature and density of the environment you're looking at because that affects the shape I'll skip over the right hand side of the slide right now just because I think it looks really impressive this is a relatively simple molecule in terms of astrochemistry but this is what I coded up for part of my thesis to model the spectra I say it's simple it actually fits all in one slide you don't need to know any of that just for people to know how much work I had to do for this so to do the observing I used the green bank telescope in West Virginia and the very large array in New Mexico these are both radio observer toys the light from space the radio light bounces off the dish goes up to the detector and that's how we do our measurement this thing right here is a football field it is one of the either one of the or the largest fully steerable land objects in the world so if you take out the AeroCable radio observatory which doesn't steer and you take out all the aircraft carriers which are not on the land this is among the biggest if not the biggest and I've steered it so that was really fun the control room is about a mile away but of course it's big enough that you can see it out the window so you push buttons and it turns around it's really awesome so these are the nine clouds that I looked at for this study so there's a whole bunch of dark clouds you see some of them have proto stars in them some don't, some are very sneaky, some are kind of blobby kind of a different range of properties here here's what they look like in a couple different ranges of wavelengths so moving from shortest wavelength to longest in these three panels see if you go up to long enough wavelength that actually goes from being dark to bright, actually see the dust emission in the far infrared here and over on the right hand side I just picked three of these colors that kind of look nice together in these contours are where all the ammonia lives in the cloud so it matches very nicely to the dust lanes and actually peaks up a lot where the proto stars are and actually if you look at this in detail what's really neat is you find places that are completely dark in the infrared but there are ammonia peaks and these are the very, very, very earliest forming stars that you can't even see in the infrared which is awesome and so primarily what I looked at is sort of what's the structure in here how is this stuff moving what are the different components and suffice it to say it's a big mess you have a whole bunch of gas colliding with other gas all the time so I don't know if you hear me but sort of the idea that I and a couple other people are pushing is that you tend to form really massive stars in these environments because they're already really dense and now you're just colliding really dense clouds together and sort of a crash you make something super dense and so you can form a really massive star because you've thrown a lot of material into a relatively small space in a quick amount of time it's also kind of interesting to think about how these things larger complexes so these are two of the really dense clouds that I'm looking at but you can kind of also see these other little dark features running off of it this is what's called a hub filament structure the idea is that maybe material actually falls down along some channels in towards the central hub where it all collides and we actually start to form stars but that's very early stages not a whole lot of people actually looked at that yet but we do see examples of really, really long filaments including one that's called Nessie alright this is the original Nessie in here and you see some other dark clouds here that may or may not have been connected to it when you actually look at the molecular gas like ammonia and things like that you actually see there's one long continuous thing all the way through and then the final thing I'll say is that I've also used another radio array called Karma which is in California lifetime canceled government funding, RIP but there are a whole bunch of other molecules that we look at in these things as well to understand the chemistry, to get a better handle of the characteristics of the environment and so here's just a sample of nine that I looked at with Karma and I modeled those spectra too so the very last thing I'll say because I know some of you would be disappointed if I didn't talk about this interesting astronomical things that we've got this year I follow a slate author named Phil Plate he goes by the moniker Bad Astronomer he actually went to the same grad school I did and after his postdoc and working on instruments that went up on Hubble he found out that he could have more fun and make not a lot of money but make money talking about astronomy to the public kind of like a small version of Neil deGrasse Tyson though I think he's just as entertaining anyway he writes for Slate Bad Astronomy he had up an article from the beginning of the year called 101 reasons to go look outside and look up in 2015 so I picked out the highlights from his list that are still coming up so I cut out the things we missed already so a couple of things like a total solar eclipse in a couple of days Jupiter is going to be at opposition meaning it's the brightest it's going to be never ever until it's at opposition again couple meteor showers in here so if you want to look for things to look for this year go look this guy up he's also really interesting to follow he's got a couple of pieces every day usually mostly astronomical stuff but he also comments on general sort of science things as well so alright thanks for coming I'll take any of your questions I hope you enjoyed the talk