Please welcome Chris Linton. Thank you. Thanks. Thank you. Thank you and and welcome back. It's uh good to see so many of you here and of course online as well. Um this is a talk that I think I've been waiting about 17 years to give. And it's also not the talk that I planned. Some of you will know this is a uh a talk that was moved from April for reasons that we'll get to, and it's changed again. Um, but the subject hasn't altered. What I want to talk to you tonight is about the initial results and the amazing promise of this thing, this marvelous machine on a hilltop high in the Chilean desert in the north of Chile. This is the Vera C. Rubin Observatory, our new window on the universe, a telescope and an instrument like no other that we've had before, which is going to completely revolutionize what we know about the cosmos. We got a taste of what it could do when the first images taken during testing were released last summer. Um this is a fairly innocuous bit of the sky. It's part of our nearby Virgo cluster, the nearest city of galaxies to our own local group that includes the Milky Way. And this is an image from the previous generation of surveys, from the Sloan Digital Sky Survey. And you can see a few stars, you can see a myriad little elliptical galaxies, these yellow things, and a couple of nice spirals at the end. Let me show you what the Rubin Observatory's cameras are capable of doing. In just a few nights observing, this view transforms into this. It's astonishing. We've almost reached the point where there's no black left in the background. Almost every pixel here has light. And you can see both that there are more galaxies. So if you look at an empty part of the sky, we see many, many more sources, because this is a large telescope with an eight-meter mirror. But you can also see that many of the galaxies are now enshrouded in a halo of faint light from stars that have been thrown out of the galaxies, perhaps by previous interactions or mergers. And we get access to what we call this low surface brightness universe, this faint glow around many of the galaxies for the first time. This is an image from one night of observation. It's in fact from the 23rd of June 2025. And just this image is enough to keep us busy for a very long time. One could, for example, do a census of galaxies in the image. You could work out how many of those faint things exist at what distance and sort of work out the total mass of the universe that way. One could pick a favorite galaxy, like this spiral down in the center right here, and study its star formation, these little blue dots that you can see in the spiral arms. Those are places where dramatic bursts of star formation, perhaps creating as many as a few thousand suns worth of stars, are happening right now, and we can see them with exquisite clarity. Or you might pick that image at the merging set of four galaxies at the top, linked by these bridges of light, and perhaps using a computer simulation, try to disentangle what they're telling us about the history of this these systems. How have they come together? How has their gravity forced them to dance around each other? What has resulted in stars being thrown out to form these shells and halos and streams? There are people in this country who are doing whole PhDs on each of these topics with this one image. But the other thing that's special about Rubin is the sheer scale on which it looks at the sky. A single image covers a few square degrees, about three and a half square degrees. So that's about 40 times the size of the full moon in the sky. And so, yes, we've got this section of the sky, but you can also zoom out. And in one image, we get enormous chunks of the cosmos delivered to us. And then you can zoom back in and you can ask different questions about different galaxies. This is actually the largest galaxy in this particular field of view. And then here we see a center of a particularly rich cluster. And I can keep going on and on and showing you these things. I like this one. This is a particular galaxy which we thought was isolated. But as you can see, it has this long stream of stars going from top left to bottom right that seems to connect it with a kind of light bridge to those two smaller galaxies down towards the bottom right. So perhaps this has passed through and is dragging them behind, or perhaps they're falling into it. You can see in the top left, there's this sharp break, a sudden stop to what appears to be a jet coming from the center of the galaxy. And if that's real, and this is an early image from an early survey, so we're still fiddling a little with the image processing. If that's real, that's probably something like a jet from a black hole crashing into a cloud of denser material. The questions from these images keep going. It's a testament to the power still of astronomy powered by looking. You know, this is still the same game that Galileo was doing. Get a telescope, look at the sky. We've just improved the tech a bit, and the camera's much better than the Mark I eyeball. We can also take images for fun. So I've talked about galaxies, but of course, Rubin is a survey of the whole sky. So this is a region in the southern Milky Way with the Lagoon Nebula and the Trifid Nebula. These are parts of the sky that will be very familiar to amateur astronomers. These are favorite targets for amateur telescopes. You can see there the moon for scale. But if we zoom in now on the heart of the Milky Way, so we're now looking at our galaxy, you can see that we see individual stars. The blue ones are newly formed young stars whose light is heating up and lighting up these swirls of gas within which thousands of stars are still forming. So we're getting a really close look at the nurseries of systems like our own sun. And we get this sort of by accident. Uh, this is just a part of the sky that happened to be in the test image. And again, this is from one night's data. And the Vera Rubin Observatory will carry out a survey called the Legacy Survey of Space and Time, or LSST, for 10 years, producing deeper and deeper images. And so we're really excited to be at the start of this adventure. And it's important to realize, I think, and I want to talk about right at the start, that this is sort of the culmination of a new way of doing astronomy. This idea that you build an instrument that surveys the sky, Rubin will roughly, the the um fiducial cadence was that it would cover the whole sky every three nights. We've since had an argument about whether, about a 10-year-long argument about whether to actually do that. If you want to find asteroids, you want to look at the same patch of sky every hour. If you want to take images of galaxies, you want the best conditions and stare at the same patch of sky for a long while. But roughly, we do the whole sky every three nights. That data's processed centrally, and it's distributed to astronomers all around the world, and eventually to anyone who wants to use it. So this survey astronomy is very different from the kind of astronomy that I was doing when I started my career a little more than 20 years ago. When I was a PhD student down the road at UCL, we spent our time writing observing proposals, suggesting what we would use the great telescopes of the world to do. So I, for example, spent a lot of time trying to use this thing. This is the James Clark Maxwell telescope on the summit of Mauna Kia on the big island of Hawaii. And we'd spend a couple of months writing a proposal to use this telescope. If you got lucky, you got a letter in the post. Um, for the younger members of the audience, that's like an email, but slower. Um we got a letter. And I remember vividly that it would say, you've been awarded, I don't know, four nights of time on JCMT. And then at the bottom it would say, This time is worth, I think four nights was about £75,000 if you take the cost of the telescope and divide it by 365. And I remember thinking, I'm a PhD student. Why are you giving me £75,000 worth of telescope? And then they said, well, you have to fly to Hawaii to use it. And I thought, this is great. I will I will do my best. Um visiting Mauna Kea was a privilege. It was amazing to be at the telescope. Uh, I learned a huge amount. Um, they don't let you operate it. There's no joystick. There's uh usually a role called a telescope operator who's actually in charge of looking after the telescope. In Hawaii, uh, they were mostly ex-submariners because being in a dark box on top of the mountain was as close as they could get to submarineering in a civilian life. Um, but you'd go and as the data rolled in, you could adjust what you were doing, choose different targets, uh, fiddle with how the instrument was working, and we got great results. Well, this is uh the galaxy M82, which will come up later, the Cigar Galaxy. It's a place where stars are being born, uh, where supernovae are going off and driving what you can see in red here is a wind from the center of the galaxy. Um that's the Hubble Space Telescope view. We did the thing on the right. This is with Estelle Bay, who was working with me at the time. Um, these are detections of the um CS molecule, carbon and sulfur, in this galaxy, which we were using to understand something about how the stars were forming. The really cool thing about going to JCMT was getting to be up on this mountain on Mauna Kea. I remember the first time I was there, we set the telescope up, we set it observing, pointing at a nearby star-forming region, and I thought, I'm gonna go out and I'm gonna look at this glorious night sky. Mauna Kia has some of the clearest and most beautiful skies in the world. So I went and stood in the garage, as you can see on the left there, thinking I would allow my eyes to get used to the dark for 20 minutes. So I was properly dark adapted. And I thought I was gonna step out of the garage and look up and see a beautiful sky. And instead, what happened was I went out, I looked up, and it was alright. There were stars, it was clear, but it wasn't anything more impressive than I'd seen from Dartmoor. And I realized that on Monica you're high enough up that there's not enough oxygen going to your brain, and one of the things your brain shuts down is the ability to see faint things. And so if you hyperventilate, which you shouldn't do, if you take lots of deep breaths, then suddenly all the stars come out. It's a sort of um very psychedelic experience. So I did that a bit and then I went back to my work. Um, and the point is the fact that there's lack of oxygen up there makes it a difficult place to work. You're not allowed to make decisions without calling somebody at sea level if they're going to involve anything technical, because otherwise you do very strange things. We were shipping astronomers around the world, um, which isn't very efficient. There were nights when I was there doing my PhD student research, but they had the best ever clearest night that had been recorded in the history of the telescope. And there were projects in the queue from other people that needed that clear weather, but I did my science instead because I was there. And so you can see that there's an inefficiency here. And of course, people just get unlucky. And as the poster child for this sort of bad luck as an astronomer, I want to introduce you to this chap. This is Tobias Garon, who was my PhD student along with Dr. Becky Smethurst in Oxford. But he completed his thesis. His thesis is fabulous on the impact of strong and weak bars on galaxy evolution, which he submitted and passed the exam in flying colours in 2023. But the reason I'm telling you about it is that this is a mostly theoretical study, including observations from the archives. So it had very little new observational work. Tobias didn't get to go to Hawaii every few months for his PhD. Um, but he did want to study these 21, actually, how many of those here? Yeah, 21 galaxies. In particular, we wanted to know how the gas was flowing from the disk of the galaxy down towards the black holes at the center of these things. And we knew what the perfect instrument was. It's called the Isaac Newton telescope on the island of La Palma. Here it is. There's Tobias, uh that's David O'Rion, who now works for the European Space Agency and myself, intrepidly on the Canary Islands with our telescope ready to go. The only problem is that Tobias first was awarded five nights of time on this telescope in 2020. So travel wasn't possible. So he reapplied. He went to La Palma. There was a storm, there was so much snow that the dome froze shut. No data for Tobias. He reapplied. A volcano went off on the island, and the dome was covered in ash. He reapplied again. He got his five nights once more, and he went. And tropical storm uh Hermene, which is the most easterly tropical storm ever to form in the Atlantic, sat on top of the island for all but half an hour of our observing time. So Tobias's thesis finished with this figure showing snowstorm, volcano, and weather map of tropical storm to explain why he hadn't managed to make any observations. And it's almost to the last thing he wrote in his thesis was I would advise extreme caution to anyone considering including me in future telescope proposals. The point is, there's a lot of romance in this. There's a lot of fun. And if you want to hear more of these sorts of stories, there's a wonderful book by Emily Levesque called The Last Stargazers about the culture and traditions of astronomers going to observatories. But it was realized in the 90s that we probably needed to get a bit more professional. And people started building surveys, surveys like this one. This is the Sloan Digital Sky Survey. This provided a lot of data that I used actually just after my PhD. It's a two-meter telescope, it's in New Mexico, it's run by a professional team of observers, and most astronomers who use its data don't go anywhere near it. All it does, all it did for eight years, was to allow the sky to turn over it and to take and just take pictures of whatever drifted through its field of view. And then on the clearest nights, it went back and it recorded the distance to about a million nearby galaxies. And from that survey, what we produced was this. This is, what they produced was this. This is a three-dimensional map of our local universe. And this single data set has taught astronomers more about how galaxies form and evolve, about how the structure of our universe, which has these big clusters and filaments and these empty areas we call voids, how this structure came to be and how it shapes everything that we see around us. But it came from sort of this experiment, not an observatory. This happens in other fields as well. This is, as a random example, this set of camera lenses belongs to a uh a project called SuperWASP, originally in the Canaries, now in South Africa. SuperWASP is the wide-angle search for planets, and I guess it's super, so super WASP. And it's a bit like Rubin in that it has a wide field of view, and it kept an eye out for blinking stars. Stars that blink when planets get in front of them and cause their brightness to dip. And as an example, here's an artist's impression of a fabulous planet called Wasp 19B, one of about 30 that they found. This is one of the fastest moving planets we know of. It goes around its star every 19 hours. Uh it's about the size of Jupiter, but the temperature in the atmosphere of Wasp 19B appears to be about 2,000 degrees Kelvin, which is hot enough that it rains quartz on this kind of world. Um, discovered by this survey, data distributed. And astronomers who like looking at changing things have got into this game as well. This is a telescope in uh California, Samuel Oshin telescope. The blue box on the bottom, there used to be an eyepiece there. I've been there and observed through this telescope, and people used to take images. Now there's a blue box which says ZTF, sorry, ZTF if you're American. Uh it's the Zwicky Transient Factory, which is there to look for changing things in the sky. So between taking images of the sky over and over again and some clever machine learning, this one instrument has discovered something like 12,000 supernovae and all sorts of other transients as well. It's a very efficient way of doing astronomy. So at the cost of not going to Hawaii anymore, we get to do much more science. And I will, on most days, take that trade-off. So this is the background to Rubin. So all of these projects were sort of happening in the 90s, a bit later for ZTF. And in the early 2000s, a group of astronomers led by a man called Tony Tyson set out to make the case for essentially doing this properly. They were mostly US-based, though with international collaboration from the start, and they put forward a proposal for what that was then called the Large Synoptic Survey Telescope, LSST. So Large speaks for itself. Survey, I've explained. Synoptic means does a bit of everything. So this is one telescope that's capable of doing many different sorts of science from asteroids to cosmology. And in 2009, that was put forward to a process called the Decadal Survey. So in the US, every 10 years, a very senior group of astronomers write a list of priorities for government funding for astronomy. And that for the last 50 years has pretty much been followed. So things like Hubble and the JWST have all come from recommendations from the Decadal survey. I was at the meeting in 2010 in August, we had a week-long meeting of people interested in the survey, and on the Friday morning, the 2010 Decadal survey was published, and as reported here in Nature, we were the top recommended project. So LSST was recommended for funding, and it's essentially a billion-dollar project. To give you an idea of the scale of this thing, just to get the data from the telescope back to the US and then to distribute it around the world, they laid a new undersea cable from Chile to the US. So at that point, you sort of that for me, that sort of gives me the sense of the scale of the construction project. Also had a strange experience. Once the money started flowing in 2012, I went back to the annual team meeting of people who were building this project, and suddenly, instead of the 200 or so scientists who'd been happily designing the thing, there were all these people who knew about cameras and mirrors and engineering and so on. And it was a very different community of people who were going to make this thing happen. Because all we had at the time was this sort of engineering diagram which showed a squat mobile telescope. But this thing now exists. Took much longer than we hoped, but it exists. And there are a few special things about it. One of the special things about it is the way its mirrors are set up. So large telescopes these days have mirrors. And like many of the best telescopes in the world, this one, the Charles Simone telescope, technically, in the Vera Rubin Observatory, has an 8.4-meter mirror, which was cast in the foundations of the University of Arizona's football stadium. Because that's where the world's best mirrors are made. The story, which I can't vouch for, but I'm going to tell you anyway, because it sounds true, is that they couldn't get any donors to the university to pay for a new mirror lab, but they could get them to pay for a new football stadium. So all you do is you design the basement of the football stadium as a place where you can make your nice stable mirrors. But it's the other optics that make this special. So light comes in from the universe at the top, it hits the primary mirror at the bottom, you'll see this in a sec, and then it bounces back up to a secondary mirror, which is just like any other telescope, but then it's bent back down to the middle of the primary mirror, which is actually a third, slightly different shaped mirror, and then up to the camera. And what this means is you can have a large field of view and get good images right across it. So we can take an image of a large part of the sky all at once. The next thing you want to do if you've got a survey telescope is you need to survey the sky. We need to move smoothly and rapidly around the sky in whatever pattern that we want to do. So there's obviously exquisite computer control, but this is obviously also an engineering problem. And the point where I realized that this was going to work was a few years ago. We got this video. This is from the early days of construction on site. So this is the telescope before the mirrors are put in. But what you can see is that we can move it, this is real time, this isn't sped up. So we can move from one side of the sky to the other with a precision of a fraction of a degree, a tiny fraction of a degree, within a minute or two. And so that means we can dance around the sky in whatever pattern makes sense to carry out our survey. So now we've got good mirrors and good optics. We've got a telescope mount that works and can move us around the sky. The dome is constructed and ready, but of course, the heart of any observatory is the camera. And the camera for Rubin is spectacular. Designed by a huge team of people, including my old boss Ian Shipsy, and involving Chips that were built here in the UK. It was constructed in Stanford, and this is the construction of the camera. So you can see here each block here is an array, like the chip on your phone, being installed into the camera. And taken together, this is a 3,200 megapixel camera. It's the largest camera ever built for astronomy. It's possibly the largest camera that exists everywhere. Once you've installed the chips, then you have to give it essentially life support. So this is all the electronics, and we cool it down using liquid nitrogen so that it has very little noise in the background. Once you've got all of that done, you need to put the optics in. So they put the camera together, mount it onto its permanent home. You can see everyone's in clean room gear at this point because the optics are exposed. And then it's installed into the baffle and made ready for a long trip to Chile. And what I love about this thing, other than the fact it's a 3,200 megapixel camera that we can use for astronomy, and it produces those images that I showed you, is that it looks like something you should put on a telescope. If any of you are amateur astronomers who have an expensive eyepiece, this is basically what it looks like. You've got a barrel that you plug in and optics on the end. Anyway, they took it off to Chile in 2024, drove up the dusty road, admittedly, to the mountain, straight into the observatory which was waiting for it. Further testing was carried out. There it is, getting ready to be lifted up into the telescope and into position. And this is a huge thing, right? This is the size of a minibus, but it's being positioned with pinpoint accuracy to everyone's great relief. And at this point, we realized we were gonna actually have a telescope and camera. So we've got our telescope, we've got our optics, we've got our camera. And we're in Chile, so we have amazingly clear skies. Um, you could see some little lights down in the distance there. That's a mine that's about 60 miles away, and that's the only source of light that isn't from the heavens on the surface here. Um I remember when I've been in Chile before talking to some of the local astronomers about the quality of the sky, and one of them said to me that good skies are grey in Chile. If you could see a gap between the stars, then it's no good. And I've actually been just down the road from here and been able to read a newspaper by Starlight, which is an eccentric activity, but it gives you some idea of the brightness of what's going on. So we've got a great site and everything's ready. So the point of this lecture was that I was going to tell you what Ruben observed yesterday. Because this is an ongoing survey, but it's going to send alerts about what's happening in the sky. And so, what I wanted to do, what I've been waiting since I got involved in the project in 2009, what other people have been working on for 25 years, is to be able to tell you with one of the largest telescopes in the world and the largest camera ever built what happened yesterday in the sky. We had a few teething problems. So we moved the lecture from April to now. And then in July, this happened. This is base camp, essentially. It was known as base camp before it snowed. But this was a once-in-a-generation, once in a hundred year snowstorm, uh, which hit the site on the 23rd of July. Um, it actually was a serious event in this rural part of Chile because once the snow melted, there were the floods that caused devastation to lots of communities. It was bad enough that for about three weeks, no one could even get to the telescope. Um, so it was only on the 20th of August, after a storm on the 23rd of July, that this intrepid bunch of essentially mountain rescue volunteers and observatory staff made it to the door of the observatory and were able to start restoring. It's incredibly bad luck that we just started the survey that we've been working towards, and then we get this unprecedented weather event. I mean, I I say it's bad luck. Tobias now works for the Rubin Observatory. So it's sort of our fault, is what I'm saying. So there is now some planned engineering work that should have been done in the summer. We're hoping to be back on Sky soon. Um and I'll tell you at the end how you can follow along. But let me tell you about some of the things we have discovered already in the data that Ruben has provided. Um, let's go back to our nice galaxy images. And these are a couple of spirals again on the edge of the Virgo cluster. But what I didn't tell you when I was putting these images up is they're slightly processed. This isn't the raw image straight off the telescope. For starters, we've combined several different exposures here because Rubin can look through different filters to get different colors. So it can take an image of red light or green light or blue light or infrared light, or even slightly in the ultraviolet, so that we get more information. This is obviously a colour composite, so it combines several of those. I think it combines three of those filters. But also, if I show you an unclean composite, you can maybe see there are now traffic lights, uh little strings of dots covering the image. And these are asteroids, rocky members of our solar system, that are moving during the course of the night that these images were taken. And so they end up as traffic lights because in different filters they're in slightly different places. And the thing is, when you've got an eight-meter telescope and a sensitive camera, these things are everywhere. In fact, in that first week data that I showed you, you get stars, we've got galaxies, but there are also these asteroids, and we can watch them move. And the thing is that with Rubin, there are lots of these. There are, in fact, an incredible number of these. So many that I'm tempted to go back to the original descriptions of asteroids in the 19th century when they found loads of these, where they were the vermin of the skies. And it's not quite that, but over the course of seven nights, not only did we detect many of these, but Rubin in the first seven nights found about 2,000 new asteroids. And in the first year, we think we'll find five million new asteroids in the solar system. It will be the first census of the solar system. It's going to be transformative. At the minute, as you can see, if we zoom out, we can see where they are. So they're mostly in the main asteroid belt that lives between Mars and Jupiter. But there are a few much further away, and Rubin will also play a crucial role in spotting near-Earth asteroids, completing the census of asteroids that might hit us one day. So there's a planetary defense part to this. In fact, I looked up the scoreboard this morning. This is from a live website where you can go and see how we're doing. So just in testing, Rubin, as of this morning, has observed 8,96,956 observations of nearly 300,000 asteroids, and about 35,000 of those are probably new. We're just waiting for them to be categorized. So that's 35,000 asteroids, by the way, that we need names for. And so if you know people who work on Rubin and you fancy having an asteroid named after you, be nice to them. Now, I promised the Gresham team I wasn't going to read a list of all 35,000 new ones. But I did want to talk about two solar system objects that Rubin had observed. And I think it's appropriate to do that because the solar system science from Rubin will come first. Because once you turn this telescope on and we've got a sufficient template of the sky and we can scan it, we'll get all five million objects almost immediately. The first thing I want to talk about was an object that was discovered not with Rubin, but with another sky survey called Atlas last July. Here it is. So this these are images taken over the course of about an hour and a half. And what you can see is that the thing in the middle is moving. The orange crosshairs were added afterwards. Otherwise, this would be easier. Just by looking at this thing, which was originally mistaken for an ordinary asteroid or comet, we could work out its orbit. And it became very clear that this was a visitor from beyond the solar system. So this is an interstellar object called 3i Atlas. And I've talked about interstellar objects on this stage before. You can go back and look at the discussion of those from a previous Gresham lecture, but at that point we'd only ever found two of these things. And 3i Atlas was our third. What was particularly exciting about it, and this is work that was led by my then PhD student Matthew Hopkins, who's sort of the luckiest PhD student I've had, 3I Atlas arrived about a week before he was due to hand in the final version of his thesis. He used models he'd worked on to calculate that this thing was the oldest thing that we've ever seen close up. So there's a more than two-thirds chance that it's more than 9 billion years old. And when Matthew came into my, oops, when Matthew came into my office to tell me that, I went, all right, yeah, 9 billion, interesting, and went back to work. And then about three hours later, the back of my brain caught up with me and said, hang on, that's older than the solar system. And this is something that formed in a time in our galaxy before the sun had even formed, and we get to see it up close, just briefly as it passes through the solar system. It's more or less escaped now. But by coincidence, this was in the early Rubin testing data that we'd been taking. So this is Rubin's image of it. You can see it's a comet, you can see it's a fuzzy ball. There's a tail actually leading off down further down that developed later on. And the first science from Rubin was characterizing the orbit and how this thing moved through the solar system. And we hope that Rubin will find somewhere between 50 and 100 of these interstellar objects. And so for the first time, we'll really be able to study sort of the flotsum and jetsum of the galaxy. And each one will bring with it a story about a time and a place in the galaxy's history when it formed. And we'll be able to piece that together. So, for example, we're learning that 3i Atlas, this ancient piece of ice that has come to visit, formed very early in the Milky Way's history in a place that was already enriched in heavy metals. So it's a place where stars had already formed. We now know that our Milky Way had a very early burst of star formation that produced the star, that produced this comet that was then ejected and which traveled through the galaxy. Rumens also found at least one other comet. This is the discovery image. I know it doesn't look like much. This is a faint comet, now known, we think, though I'll come back to that, as comet 2026 N2P LSST. So it's the first discovery. It's on a five and a half year orbit that takes it out sort of a little way beyond the asteroid belt and in towards the inner bit of the astro belt. It doesn't get anywhere close to Earth, which is why it's faint. It was discovered by a PhD student, Madeline McLaud, in Edinburgh, who had worked out along with her supervisor Colin Snodgrass, that you could look at the data that Rubin was passing to astronomers, and they found a way to look for fuzzy things, essentially. And they discovered that reliably this finds comets. So here we are, here's the first comet. There is an argument going on about whether it gets named after the telescope, so this is comet LSST, or whether it gets named after the discoverer, in which case it's comet McLeod. I'm not going to weigh in on that argument, but one of them is clearly better than the other. They followed this up. Here's an image from the NTT, the new technology telescope. You can see it's got the tiny tail. It's not much of a thing, it's a damp squib of a comet. But that's what's interesting about it. Because it lives in this region of the solar system, which we thought was populated with asteroids, with rocky bodies. And yet comets, particularly comets that grow a tail like this one, are indisputably icy. And so it may be an example of a growing class of object called an active asteroid, a rock that where the dust or rock on the surface is hidden ice, which when exposed develops into a comet, either permanently like this one or just occasionally. And if you want to help with this stuff, Christine was generous enough to mention in her introduction to me that I used to run and still work with the Zooniverse Citizen Science Platform. We have a set of projects, which you can get to at zuniverse.org slash Rubin, where we're asking people to help us sort through Rubin data to find interesting things. And the most successful of those projects so far is a project called Rubin Comet Catchers, which is looking at asteroids, which should be rocky and should appear like stars, that's what the name means, and hoping to catch them if they occasionally develop a tail or a coma, an atmosphere. And the idea is that many of the things we've assumed were rocky are actually icy bodies that when they collide with something or a meteor hits them or something like that, they briefly become comety. And so if you want to help us sort through this data, as soon as Rubin gets back on sky, we'll be feeding more data to comet catchers. You can help us find these pseudo-comets. Maybe, probably not, but maybe have them named after you, depending on which way that argument goes. Now, I've talked about moving things in the solar system, but a big part of the attraction for Rubin is that it can keep an eye on how things change brightness as well. And so even in these first data sets, over the few nights that they were taken, we got changes in brightness. So software is able to go through and look for individual stars in this case where the brightness is changing over time. There's one, quite another one. And obviously, you don't really pan around like this, but it looks good for the movie. And you can see that this star changes in a regular pattern. These are all uh happen to be variables called RR Lyrie variables that change with a uh a pattern because the star is pulsing. Uh Rubin found a few thousand of them. But really, it was built to find dramatic explosions. This is a pre-Rubin example. This is M82 again, the cigar galaxy. This is a supernova, the death of a star. In particular, this is supernova 2004 J, January 31st, 2014, and which was discovered by a guy called Steve Fossey and some undergraduate students from UCL and an observatory at Mill Hill just up the road. So this must be the most recent spectacular astronomical discovery made with observations from the centre of London. Um it's really, really fun story. And it's a supernova, it's a star that came to the end of its life and it exploded. Uh, it's been watched since. Um, these are echoes of light around the thing from about a year later as the shock wave has spread out uh into the surrounding gas, as seen by Hubble. But what RSST can do is A, help us find more of these things. Once the survey gets going, we'll find more supernovae in a month than we have in all of human history put together. It's going to be a remarkable bonanza for understanding stellar astrophysics and evolution. We can also see things in new ways. And there's a really nice recent example where we've got a glimpse of the physics of a supernova. So this is a cartoon, an illustration of how a supernova works. So what happens here is that the star, a large star, in this case a red giant, runs out of fuel at its center. And a star is a delicate balance between gravity, which wants to pull things together, and the energy that's produced by nuclear reactions at the center, which, as it releases light, pushes the star up. So you have this thermostatic balance between the two. When you cut off the fusion at the center, the star collapses and then rebounds in an explosion. That's what a supernova is. But it takes 20 minutes, and time is running in the bottom right here. It takes about 20 minutes to an hour for that rebound to reach the surface of the star. And so what happens is you get this expansion, then about 20 minutes in, you get this shock wave that hits the surface, and then you get this blinding flash. It's called a shock breakout. And then you get to the supernova proper. So at this point, material is thrown into space, nuclear fusion in the debris produces unstable nucleotides, unstable elements, which then decay. And most of the light we see from most supernovae comes from the decay of those elements that are produced in the supernova. Whereas Rubin, because it's scanning the whole sky very often, can catch the early breakout. And that happened with a recent supernova just a couple of months ago called SN2026 GZF. We've gone up giving these sensible names, they just get labels. It was detected actually first by a German, sorry, a Chinese European German satellite called the Einstein probe, which scans the skies in X-ray. But it was caught early by Rubin, and so we saw this breakout, the shock wave hitting the surface of the star, and it triggered automatic follow-up, so we have spectra of that as well. And it's the faintest such object ever seen, but observed automatically. No human got involved in making this decision. The system worked, the telescope detected the thing, the algorithms identified it, and then we managed to follow it up all automatically. And this is going to happen more and more and more as the Rubin survey goes on. It's a really exciting sign that this is working. So that's two of the pillars of Rubin science. We've got solar system and we've got transients. I'm particularly interested in looking for unusual explosions in space, but I'll tell you about those another time. But mostly what people want to find are supernovae like the one in M82 that I showed you. This is a type 1a supernova. So it's a particular type of explosion caused by the interaction we think between two stars, a giant star and a white dwarf, and which has a particular property, actually, two properties that are useful. One is that these things are extremely luminous, so you can see them from the distant universe. The M82 example is actually a relatively recent uh nearby example. So they're luminous, so you see them from a long way away, but also they always go bang with the same power. They're always the same luminosity. Or rather, we can work out what the luminosity is. They're what's called in the trade a standard candle or a standardizable candle. So when you see one of these things, you know how bright it would appear if you were standing next to it, and you know how bright it is in the sky. And from these two numbers, you can work out the distance. So these are cosmic yardsticks or meter rules. They allow us to measure the expansion of the universe. And since people looked at these systematically in the 90s, it's these things that have driven us to an understanding that the expansion of the universe isn't just continuing, it's speeding up thanks to the influence of, well, we did we don't know why it's speeding up. We call it dark energy, because that sounds like a good name for it. And we think that dark energy accounts for about 70% of the energy density in the universe today. So some mysterious force is causing the expansion of the universe to speed up. Rubin, by finding all of these supernovae, will help us test whether that's true. But more importantly, what it's going to do is we're hoping it will tell us whether that expansion, that acceleration is itself speeding up or slowing down. So is there a change to the power of dark energy over time? Because if there is, that would be a really valuable clue to what the unknown physics that's driving it is. There are predictions as to whether that must be the case or not. And it's the great hope of cosmology that there's a clue there that we're missing and that we can help understand what this dark energy is. Now, on this graph, which is shows the energy distribution, energy density distribution in the local universe, you can see the ordinary matter, everything that we're used to talking about, hydrogen, helium, oxygen, carbon, all of that stuff, protons, neutrons, neutrinos, all of that stuff, is only about 5% of the universe. Much of the rest is dark matter. Because we also have this problem in cosmology that most of the stuff in the universe, even if you ignore dark energy, is in a form that we don't understand. Rubin will help here too. The game at the minute is to try and understand the distribution of dark matter, to understand how it relates to the distribution of the visible matter that we can see, and to compare what we know about those things to large computer simulations that tell us about the physics in the hope of understanding maybe whether what type of particle this dark matter could be. There are numerous ways that Rubin's going to be able to do that. My favorite is through gravitational lensing. And so the idea here is that you have a distant source of light. This is a Hubble example, because this is a previous one, but you have a distant source of light, and this says a quasar. Think of it as a distant galaxy. And then you have a nearby galaxy, and this nearby galaxy is embedded in a halo of dark matter. The point is it has gravity. And so as light from this distant galaxy passes through the nearby galaxy, it's bent by the gravity. This is an effect that Einstein predicted that we've tested and we know happens. And so you end up with a displaced image of. The quasar. And in fact, in this case, if everything lines up perfectly, what you end up with is several images of the same distant quasar superimposed on the nearby galaxy. And if that sounds far-fetched, here it is. There's the foreground galaxy, and the four dots are all images of the same distant quasar. And we know that because we see them brighten and fade in turn, depending on the path length the light has traveled for each one. And Rubin will, depending on who you believe, we've got a few thousand of these types of objects in the catalogs. Rubin will produce in ten years somewhere between 70,000 and 120,000 of them. And so we'll have an atlas of galaxies that can help us understand how dark matter behaves. And we can also play this game on a larger scale. I'm very grateful to Jesse Muir for these uh cartoon versions, but I think they're really clear. So the game here is not everything lines up perfectly. So you don't always get your quasar and galaxy in a line, but you can just look at distant galaxies in general. Oops. That's Mars, that's nothing to do with Rubin. Um we can look at, and my phone's ringing. Interesting. Uh maybe I've said something I shouldn't. Um anyway. Um what you can see here is this is that's Rubin, obviously, and then there's a set of distant galaxies. And they have light shown systematically here in blue, schism uh in blue, symbolically, that's the word, uh, heading towards Rubin. But there's matter between us and those galaxies. And the light from those distant galaxies will be bent just slightly by its passage through the mass that sits between us and them. And so the image of the galaxy you would get without any interfering matter is actually slightly different from what you see. And it shows up in the shapes of the galaxies, which are all slightly disturbed. So this is a phenomenon called weak gravitational lensing. You don't detect it by looking at a single galaxy, you detect it by looking at loads of galaxies at once. And if you can do that carefully enough across a large enough bit sky, with sharp enough images, you can pull out the signal and it tells you about where dark matter exists in the universe. And Rubin will do this assisted by two space telescopes, both Euclid, which is uh a European mission, and then um the NASA's Rome, Nancy Roman Space Telescope, which launched at the end of August, is on its way to station in L2 by the end of the year. And these two will do a sort of space-based equivalent of the survey, and we'll put them together. We've even managed to do this locally as well. So the fourth pillar for Rubin Science is looking at the galaxy. And here we don't have many results yet, but we do have a discovery. On the left is probably the least impressive Rubin image you will ever see. This is an image of a small patch of sky in the constellation of Aquarius, where within that circle, which is uh about half a degree across, so it's about the size of the full moon, researchers announced a couple of weeks ago that there are slightly more stars than you would expect. And the graphs on the right tell you that those stars all seem to have formed at about the same time. And their interpretation of this is that this is a distant dwarf galaxy on the outskirts of the Milky Way. It's about 300, yeah, it's about 100,000 kiloparsecs away. So it's it's way on the outskirts of the Milky Way in the outer galactic kalo. It's bigger than a cluster of galaxies, but it seems to be what's called an ultra-compact dwarf, so a small galaxy that's in the process of colliding with our own. And these are interesting because they tell us about the history of our own galaxy, which as I've discussed before, is a cannibalistic one. We consume these small galaxies and hence grow. But also, these galaxies are rich, we think, in dark matter. And studying them might tell us more about what this mysterious dark matter is. And so we're beginning to get science, we're beginning to get routine science from the solar system, from transients, and even from staring at the sky and picking out objects like Aquarius 4, we're beginning to get science from Rubin. But I keep coming back to images like these. Even though I can't tell you what the sky above Chile did last night, um, because we're still recovering from the storm, we can still look at these images and we can realize that in the next 10 years, I've got a year left as Gresham Professor. I'm willing to bet that every one of my successors from here on in, in almost every one of their lectures, will show you Rubin images. Because with this marvelous telescope, thanks to the work of thousands of people over decades, the universe now looks like this. And it's pretty awesome. Thank you very much.