 we have protected in our galaxy. This star is so old. For extra trust your life last month, very serious public service announcement that there are too many stars. So with that, Jim. I'll also stop coming after this. There's, I, there's too many stars. I think that's my message. Uh, in Seattle, you can see, well. One plus or minus one. Plus you. Plus me. But in general, there are too many stars. And I don't mean to say that, like, we need to get rid of them. Like some kind of cartoon super villain. But I'm just saying if we did, my job would be easier. This is my favorite map or image of the night sky. This is a picture taken by the guy at Space Telescope of something like 1.8 billion stars in our galaxy. Every little dot, every little bright spot here is a star in our galaxy. Well, that's a lie too. These are different galaxies, but they're, they're part of our galaxy. This is too many stars. We can't count all these. We can't, we can't study them all. We can't understand them all. This is too many. Here's a plot that I made in preparation for this talk. Something that I've wanted to see for a long time. There was a little trivia question, so I'll ask it again to you. How many stars can you see, what would you say with your naked eye, with your visible eye? Again, presuming we weren't in Seattle, presuming it was actually dark outside and not cloudy. How many stars could we see? And so, that's your turn. Less than 10,000. Only dimmed out before. You could only see me, I would outshine them all. That's right. You'd see less than 10,000. Depending on where you are, something like five to 8,000 is the answer that you get usually. It's not that many, right? In antiquity, we would look up, humans would look up, and depending on the quality of your eyesight, you'd see something like thousands of stars. And there were probably, I'm not a scientist of people, there were more than 1,000 people, more than 10,000 people on the planet. Somewhere around 1800, we started doing a better job of counting. These are names of catalogs of stars. These are like, in the olden days, like literal books, just full of tables of stars, like their location on the sky, and roughly how bright somebody thought it was with their eyeball. The brightest few hundred stars have names, like Vega or Sirius or Beetlejuice, right? The very bright stars have names. And then at some point, we start naming them with Greek letters like Alpha Centauri. That's the brightest star in the Centauri, in the Centauri's constellation. And then we start getting down to numbers, and then we start getting down to just like phone numbers, big catalog numbers. But back here, back in the good old days, I'm not that old, but back in the good old days, we have like the Landa catalog. This is a French catalog that had something like 40,000 stars. This was a major achievement. 40,000 stars in like 1801, before they could take photographic plates of the sky. They had telescopes. They could look at the sky, but they didn't have like a photographic archive. And yet they recorded the positions and brightnesses of like 40,000 stars. What an amazing triumph. It's good enough. That's enough, we don't need any more, that's enough. But a couple of Germans came along, something like 50 years later. This is the Bonner-Durchmuntström, I apologize, maybe you actually speak German catalog, we just call it BD. They raised it by about a factor of 10. This is the Henry Draper catalog, right about the same number. They had a lot more information, another 50 years later they included spectroscopy, regular velocities, anything else they could learn about the star. So here around, you know, like 1920, a century ago, we were at like 100,000 stars. This is plenty. This is plenty of stars. The Smithsonian Astronomical Observatory, just notched that number up just a little bit. They moved up a little bit. I'm leaving a lot of catalogs out of course. But there was this transformation. It started in the mid-90s with the Hipparchus mission, studying about 100,000 stars precisely and an accompanying mission called TIKO or TIKO. And so the TIKO II catalog, something like tens of millions of stars. We're already getting suspicious here. It's a lot of stars. We can't know much about all of them, right? Tens of millions of stars. And right around the year 2000, you see this like incredible ramp up. Now I'm an astronomer, so I love logarithms, right? I love seeing things in log space because the universe is incomprehensibly big. I only understand things in log size. So you were all of order 10 to the one feet away from me. That's good enough for an astronomer. My car is like 10 to the two feet away and my house is like 10 to the three feet away. And that's close enough. So these are orders of magnitude in size. And so somewhere around 2000, we make this catastrophic leap upwards from tens of millions, 10 to the six to like 10 to the eight. This is like a huge problem. My job becomes a lot harder now. Now we have 300 million stars in the two micron all-sky survey and in the US Naval Observatory catalog B, one billion stars, one billion objects. There's some galaxies hiding in there. We'll give them a pass tonight. Something like a billion objects. Right around 2001, we hit a billion. Thank God this stopped. We've been right at a billion now for something like 20 years. This is a lot of stars. What happened in the year 2000? Computers. Oh, yeah. I mean like computers were, for the young people in the room, computers were invented before the year 2000. But computers started to get really powerful and really cheap and we all started to have the internet. And so we started having a great need to send each other catalogs of data. Now I will say USNOB, this catalog here, was only available either through if you knew a friend who had it or if you sent away for a box of CDs. But it was a very important catalog. We still use it today more than 20 years later. So this image that I showed here, this beautiful image, pristine, incredible map of our slice of the galaxy by the Dias Space Telescope. That came out just a few, just a couple of years ago. I actually came here to Strom and Tach to tell you all about it. So I'm sure you all remember, this is the Gaia day release three. This is 1.8 billion stars. That's plenty. We don't need to be greedy, guys. That's plenty. We need to stop here. The astronomers are never satisfied. Because the more we keep studying stars, the more we learn about the stars, let's be honest, the less we think we actually understand. And so we're about to take this huge leap forward again. Well, I mean, it's not 10,000 to 100 million, but we're about to take a really, really important leap forward. I'm super worried about it, guys. That's true. Starting in about one year, the Rube Observatory, which you have already heard about, located in the mountains in Chile, beautiful desert above Chile, is gonna observe something like 17 billion stars in this galaxy alone. The Milky Way has something like 400 billion stars in it. We're gonna observe a large fraction of it. It's called a digital. 17 billion. And about that many galaxies as well, we're gonna have catalogs of 40 to 50 billion things we gotta deal with. This is a lot. For comparison, the population of this planet, while it is increasing, and that's a good thing, it's going up. We hit around a billion people right around the turn of the 1800s. We hit about the first billion, the second billion almost a century later, and then we've been on a steady march upwards. 10 billion will happen somewhere in the next, I don't know, 30 years. Again, I'm not a people scientist. I'm a star scientist. The Rubin Observatory, this catalog of stars will for the first time observe and catalog and record the brightnesses and positions for more stars than there are people on this planet. And to me that seems like a fundamental change in how we think about the universe, how we think about the stars in our galaxy. We have to start thinking differently about how we do astronomy. So a new era in astronomy is here and it's transformed every other science and it's transformed this city and it's transformed I think a lot of our lives and you all have supercomputers in your pockets now, but this era of computational data-driven astronomy is here. We're already here, we've already let this genie out of the bottle unfortunately. We don't have the luxury of getting to know our stars by name anymore. We have to look them up by telephone number or like 12 digit ID number now and hope that we get the right star and we have to look them up on the internet through this machine. And again, this beautiful, incredible 8.4 meter telescope that will go online in about a year, year and a half, more stars than people in the galaxy. I don't know, that kind of blows my mind for somebody. So the job for us now has to change. So I started doing astronomy 20 years ago. Back when we hit that ramp up, right? The two micron all-sky survey, two masses just come out, other digital sky surveys, USNOB had just come out. So we had just entered this exciting new era and we had to learn what to do with these big catalogs. We didn't have any tools. We were astronomers. We spent all of our time studying visits, learning a little bit of math, trying to understand how creation and gas and orbits work. And then you dropped this catalog that wouldn't fit on our ancient laptops. They wouldn't fit on there anymore. We had to change how we did astronomy and we're having to keep changing it. Here's another good example of how the field is changing right under our feet. Here is the mentions just in the abstract of papers. For the word algorithm, you can see it's steady rise up over the last 30 years. And of course the word machine learning, like the hype beast of machine learning is exploding since like 2017. It's just completely exploding. Now, I mean, okay, these are not all papers. These are also posters and conference presentations. But this is anything that professional astronomers are doing and publishing and saving in the literature mentioning word machine learning. It's skyrocketing, right? The only way we have, the only tools we have to deal with this catastrophic amount of data is let the computer do it. And this is exciting. And I'll show you some examples of why I think this is really exciting and why we could do some cool science. But a little piece of me, I'm just old enough to remember, a little piece of me is a little sad about this, right? I'm a little sad that the next generation of astronomers may not have a favorite star. I mean, other than the sun. All right, so the field is changing. We're teaching differently. We're trying to integrate computer science into our classrooms. We have all these like astro statistics, astroinformatics as a whole field. And even here at the University of Washington in lovely Seattle where the cherry blossoms are out and you should come see it before they're gone. The Dirac Institute, the Data Intensive Research and Astrophysics and Cosmology Institute. Not that Davenport is making, Davenport is making asteroids more expensive than this. Increasing asteroid costs, that's what it looks like. I hope I'm not increasing costs. We have a whole institute now which is a large fraction of our astronomy department that is just focused on how do we ask questions of large data sets, particularly this new room of observatory. There are now fellowship programs for graduate students, summer schools to learn advanced statistics, data science schools, you can actually go to Chile. This is a really cool program in Chile to learn statistics about stuff that will be done with telescopes in Chile. I love this program. We're having to change how we teach our students. Okay, so this provides an interesting opportunity. What do you do with 17 billion stars? Like if you are here because you thought the sun is neat or because eclipsing binaries are cool or pick anything you think you've heard of in astronomy and now when you have 17 billion things, we've got like 50 or 100 or 10,000 of them now. It's all boring. Like nobody cares. Like, oh, you've got eclipsing binaries, we have 50 million of them. Okay, so what? Do you like supernova? 10,000 a night. We're like asteroids if we're gonna double the population in the first three months that we know about it. Well, I mean, which is good. These guys are gonna like it. This is good. It's good job superior for them. But like, you know, this changes our relationship with the field. So we have to change how we're asking questions. One way to do this is accept that the stars as a whole the population, the demographics, if you will, of the stars that we see are telling us a story about our galaxy, a history of our galaxy, if you will. One example that's come out from the guy I dated that I'm very excited about. Which makes me sad because I thought I had this idea of what the Milky Way was. And now it's shadowed. Now I have to relearn it. We thought the Milky Way was like this big pancake or a pizza with like a grapefruit in the middle. We had the little ball of stars, big plane. We live out here fine. Good, it's good enough. But no, but no. Astronomers had to keep asking questions. We had to go take the guy telescope and map stars out 50,000 light years to the edges of the galaxy. And then we realized that the galaxy is not flat. It's worse, like a pringled chip. And we don't know why. I mean, we have some ideas. Something like 50% of the other galaxies that look Milky Way-ish, they show this kind of work. Like look at this. This is so weird looking. Something like 50% of the galaxies we see have this kind of shape. And now we know the Milky Way looks like this too. It's terrible. Okay, we don't quite know why it's this way. There's a couple of theories. One is that there's a bar of stars. We call it the bar. There's this large structure in the middle of the galaxy. There's craziness about orbital mechanics that can cause the galaxy to work. But probably the answer, probably, like we're all having fears here. I don't have to go on this record here. Probably the answer is that the Milky Way ate another galaxy. It collided with another galaxy and that has caused this ripple, like a ripple in a pond. Something like that. It's a gravitational ripple. It's not just the Milky Way's works like some weird cosmic pringled chip. The whole outside of the Milky Way is a complete mess. It's a complete mess. It's not a nice, beautiful distribution of stars that fades off and that's our galaxy, our beautiful, perfect galaxy. No, no, no, no. Now there's these big streams of destroyed other galaxies floating around in the outskirts of our galaxy. We call these tidal streams. You can see an example of this passing through the middle of our galaxy. Here's this line of stars that when you search for a particular kind of star, you can see there's this big clump, a little cluster and then these giant tails stretching 50 degrees across the sky at least. Huge chunk of the sky, this band of stars. And this is not the only one. They're all over the night sky. The Milky Way is a complete cosmic mess. What a disaster. So you've got something like 100 of these streams. Every single one of them is an entire galaxy that the Milky Way ate or collided with and destroyed. I mean, okay, it's kind of cool. It's a little sad for those galaxies. And it's not done. The Milky Way is gonna keep on killing you. If you look at the very first image, the large and the small Magellanic cloud are the sort of satellite galaxies that we're used to seeing orbiting around the Milky Way. And we think they're just out there and they're pretty and they make a nice picture. For a long time, they were the only other galaxies that we knew were in orbit around the Milky Way. You could see other galaxies, but these two, they're clearly close. They're clearly like hangers on. They're not the only ones. This is just a map of the old ones, the nearest, brightest, biggest ones. Here's a picture of Fornax, one of the oldest known so-called dwarf galaxies, tiny little galaxies, just minding their own business with the misfortune of having walked by the Milky Way and then the Milky Way traps them and then it destroys them. The poor galaxies. This is Fornax, if it looks to you in the back like just a fuzzy faint blob, that's all it is. Some of these things, some of these little galaxies, the tenuous ones, we only see them as maybe 100 stars in a little ball moving together through the sky. But when we take spectroscopy, we measure the masses and all the other dynamics, we can tell that it's actually thousands and thousands and thousands of solar masses of stuff and it's actually a galaxy and there's dark matter and it has this whole amazing rich history and the Milky Way is this like monster that's going around eating little galaxies, eating these four stars. The other way we can study this topic, it's okay, okay, so the first part here is that when you have 17 billion things, you can start to understand the structure of the forest. You can start to see that the forest has structure around you, that the disc of the galaxy is bent, it has funny shapes, there are little clumps, there are other galaxies. We can actually see, not on this map, but right over here you can see that Andromeda, our nearest neighbor, big galaxy, it's so close, it's the outskirts of its halo of stuff is almost touching our halo of stuff, we're almost touching, it's really amazing. And you can tell that because we have so many stars, so many little clumps and patches of moving stars, we can map the structure of the galactic forest that we live in. That's what you do with 17 billion stars. But what about the individual stars? I did my PhD thesis on like one star, one particular star that we got lucky, we had a lot of data on and I knew its name and at one point I knew its coordinates and its telephone number in every catalog and it was my favorite star. And my thesis advisor, she had her favorite star that she had spent six years sitting at a telescope staring at, waiting for it to do something. She had a favorite star as well. Every star is interesting and this is where this analogy of we have more stars than people comes up. Every person is interesting, right? We are all leading amazing, complicated, tragic, interesting lives. Some of us are maybe more interesting than others. There are certainly popularity contests, there are celebrities and so too in stars. Right now there are stars, there are celebrities, there's the Trappist system or the Proxima system or the systems, everybody cares about them right now but they'll get old and no one will care about them again. But matters and every star matters and has a story to tell and with 17 billion you can't tell all these stories. So we need to learn statistics so we can pull out the weird, fine structure of the Milky Way, the very faint structures in the outskirts but we also need to become reporters. We need to become journalists and learn how to tell the good stories because we can't tell 17 billion stories. This picture is one degree of a sky survey, a new sky survey, one by one, it's like one degree this way, one and a half degrees this way, right? You need something like 40,000 pictures like this to put that mosaic of the night sky together. We won't be able to tell all these stories, y'all. There's too many stories to tell but every one of them has a story to tell and let me tell you a few of them now. The first, I will just say briefly, HD, this is again a hundred degree catalog, still using that telephone number, it's a relatively bright star, HD 140283, it's an old catalog, it's only got a six digit number, so-called the Methuselah Star. This we think is the oldest star that we have detected in our galaxy. This star is so old. How old? The star is so old that at one point, the model for its age was older than the universe, right? It was like, oh, the star is 14 billion years old, plus or minus a billion, and the universe is 13.7. It was at one point, this was a controversy, that this star was so old that it kind of pushed the limits. Now, two years ago, somebody published a paper that looks a little better, they think it's 12, 12 and a half billion years old. That still means this star was born in the first half billion years in the universe. That's phenomenal, right? This thing is super old. This thing has been in this galaxy since before this galaxy was a big beast in this any other galaxies. It probably came from one of these little dwarf galaxies we're floating around in the first millions of years of the universe in the very first clumps of stuff that made our galaxy, this Methuselah Star showed up. That's pretty cool. That's a story worth telling, right? That star, the chemistry, the age, how fast does it rotate? Where is it moving? All this dynamics, everything about this star is particularly interesting. This star is a minor celebrity. We care about this star in particular. It's telling us something very interesting about the history of our galaxy. Here's another Henry Jaiper object, HD-166-620. Also a bright star. A so-called Monder Minimum Candidate. All right, that's jargon, what the hell is that? Here's the data. Here's the data for this star. Now astronomers get very excited about squiggly curves and last talk we showed some of the squiggly curves that were like rotation periods. These are not rotation periods. This is decades of data measuring the brightness of this star, waving our hands a bit, the brightness of the star. You can see it's modulating. It's doing this like up and down thing. It is a period of something like, I don't know, 10, 15 years. Okay, fine. And then it flatlined. Like the star is still there, it's not dead, don't worry. But it's not modulating anymore. Like our data keeps getting better. The air bars aren't able to get better and this star is not changing anymore. It was going up and down quite a bit. This was something like a few percent. For a context, the sun does not change by a few percent. That would be bad. The sun is very constant. It's going up and down over a decade by a few percent and then it flatlines what's going on. So the sun does this kind of behavior. The sun has this kind of modulation. Now it's so-called activity cycle from its bright phase to its calm phase. The amplitude is smaller than the star, but it's doing this in an 11 year pattern. And we have traced this 11 year pattern back to the very beginning of the telescope era, back to the 1600s. There were 400 years of data that traced this 11 year period back to the time of Galileo. This is some very complicated process about how the sun generates magnetic fields and we can get a whole dissertation on why this phase arises. But we see this in other stars. It's hard to measure, but we know about it. Neat. I think it's neat. So it gets discovered in the 16, you know, 20s. They measure a couple of periods and then the sun goes quiet and they think they broke it. And then for 50 years, the sun basically had no spots, no sunspots. This is how they measure it, usually on the sun. We go out and look and check the number of sunspots. Here the sunspots look bright, the ultraviolet. For 50 years, the sun has no spots. And then it comes back on and we don't know why. This happened in the 1700s and we don't know why. We have some theories. Some models can recreate it. Nobody can agree why this happens. It's awesome. It's awesome, we don't understand it. And what's so cool about HD 166620, it's in the middle of that monitor minimum, this minimum of activity we think. This is one of the only candidates who've ever seen this. This surely is a story worth telling. And a couple more that I just pulled off of the web randomly yesterday. Here's an example. It's got a shorter phone number, guy at 24ALL. Started using letters again. It's this guy. Here's a star that's mining its own business. This is 2014, I recognize the plot is a little small. 2014, and here we are, it's 2024, just for reference, if you didn't know. So 10 years of data, the star is mining its own business and like a month and a half ago, the star, boom, 20% increase in brightness. I don't know why, but I'm super interested I can't wait to find out why. This is a mystery right now. This star, nobody has cared about before. Here's another example, guy at 19CUW, this little fake blue guy right here. Again, 10 years of data, this thing can't sit still. This like me, Fidgets, has like ADHD for stars. It's like rising and wiggling around and going up. And then like in 2022, it said that's enough and it's going back down. You don't know, like maybe this is another activity cycle. Maybe it's another 10 year timescale. If we watch it another decade, we'll go through another of these modulations. We don't know. I'm excited about these stories. With 17 billion stars, we can start pulling out these stories. These very specific stories. The stars themselves are really interesting. The last example, Assassin 21QJ. Okay, so Guy was the mission to discover the previous ones, Assassin, all-sky astronomical survey for supernova, I think. Some very clever acronym. Here's a star that just trimmed off the edge. Again, years and years of nice, mind-y its own business data. And then all of a sudden, the star starts to wobble a little bit. 20% to 20% modulations in its brightness. This is brightness on the y-axis and some of two's unit. And then the star loses 90% of its light. Now there's a gap here. If you observe on the Earth, the sun comes up. It's summertime. This is like a winter star. The summertime came up. You couldn't observe the star for a few months. So they have a gap here. They come back, somebody broke the star. It's like 90% fainter than it was the year before. And then it jumps around like crazy. They come back a few days later. It's almost back to its main brightness. They come back a night later. It's back down again. It's all over the place. It's super strange. This picture came from a tweet that an astronomer posted saying, what happened to this poor star? And we think now, that was two years ago. We think now, we know the answer. So here is its original modulation. Here is that catastrophic dip. And then it just went wild for months and months and months and finally settled down and came back up. And it now has returned even up here off the baseline. This is optical, it's a visible light. The assassin is basically a fancy camera, like a consumer camera strapped to a telescope. And now it goes back up. In the infrared, we have infrared telescopes, which is sweet. In the infrared, before this, we went back into an archive, a very sparse archive. It takes a picture of this star every six months or so. A wise survey. The infrared data here, it jumps up before this. This is totally wild. The thing doubles in brightness in the infrared. The infrared, by the way, is the wavelength of light that you glow in. If I had infrared eyes, you would all be glowing. So it doubles in its heat and its warmth. And then six months, no, sorry, a year and a half later, the brightness in the visible light plants. This is a really, really wonderful mystery. What we think happened, the prevailing theory, Matt Kent where they published a nice paper last year on this, we think what happened, somewhere here, this is like 20, let's see, six months, one, two, three, four, it's like six years ago. Right here, right before this wise observation right there. Two planets in this system smashed into each other. Two planets, mind-knowing business, collided. Now this is what Chad GPT thinks this looks like, I asked it. This is not the official artistic rendition, but this is what I asked it to publish for this. I said, please give me two planets, smashing into each other for a public outreach talk that is going to happen. And it said, feel free to use it. So I did. So what we think happened, two planets smashed into each other. Probably early in this star's life, the disk is forming, there are planetesimals, there's lots of asteroids, lots of things are running around and two big rocks ran into each other and a huge cloud of debris and rocks and hot gas erupted and caused a huge infrared glow. The whole star seemed to like double in its brightness in the infrared. In the optical, not really, maybe this is it, maybe this teeny little bump here, maybe that's it. Like no real science happened in the optical, but in the infrared, you can see that dust glowing, almost like soot glowing. This stuff was on orbit, circling around the star and it just so happened, it probably smashed over here and then a couple of years later on its orbit, wandered through this debris cloud, wandered through and blocked out 90% of the starlight. Wow, so cool, so cool. This is not so exotic in the sense that probably this is how our moon formed or something related to this is how our moon formed, that the moon was a Mars-sized thing, a rock floating around, mining its own business and had a really, really bad day with the proto-Earth caused a cosmic explosion. Some other alien astronomer was like, wow, that's strange. They went to astronomy on tap and said there was something weird in this. This is surely a story worth telling, right? This is probably related to why we are here, why this planet has the right magical ingredients for life and something to do with that crazy moon, it may be over there, I don't know. I'll say it's over here. That crazy moon that's up there causing tides, stabilizing our orbit, protecting us from too many comets hitting us, but just enough to get rid of the dinosaurs. Probably this happens a lot. We just got lucky that we saw it because this survey was monitoring millions of stars. We just got lucky, we saw if it had happened here, we probably wouldn't have noticed. Nobody was checking the wise data for this, but this 90% drop in the optical, people noticed really easily. These are the stories we need to tell. So in conclusion, there's too many stars. Like there's too many, I can't keep track of them all, but every single one of them has a story to tell. And I think that's what's exciting to me about the next decade of astronomy. We can tell stories about the structure of our galaxy, why is it shaped the way it is, what's all this junk out here in the outskirts? And then if we zoom in with these precision surveys and these high performance computers, we can have this personal relationship with our data with the stars, which I think is still why we're doing this. I think every star still has a story to tell. Thank you. Thank you. The question is how do we know the age of the star? We asked it.