What's happening to the Hyades Cluster?

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Speaker 1: Hey, Kelly, what's your favorite feature in the night sky? Mmmmm? You know I like spotting the Orion constellation. Oh yeah, what makes that one top your list? I like that it's easy to spot. That makes it easier to point it out to my kids. And you know, since it's so easy to find, I'd like to imagine that, like, even as the Earth has changed for thousands of years, other people have been able to find it as well, and that pulls us together. Mmm. And it's nice to think about the sweep of history. But you know that constellations aren't forever, right? Oh? What is that our fault? Did humans manage to ruin the sky and the planet? Nothing to do with us this time? But you know the sky is in motion. A t Rex looking up at this guy probably never saw the Orion constellation. Well, you know what, that's okay, because their little arms would have been too short to point it out to their t rex kids. Anyway, I can't tell what you're pointed to. Mom. Hi, I'm Daniel I'm a particle physicist and a professor at UC Irvine. And I'm Kelly Weener Smith. I'm a parasitologist and an adjunct professor with Rice University, and even though I'm technically also a professor of astronomy, I've never really been that into constellations. And you know what, neither have I Ryan Ryan and the Big Dipper are one of the two that I'm able to name. When I was really young, I like looking up at this guy and seeing the stars, of course, and who can't help but look for patterns. But I remember as a kid discovering that the constellations are sort of artificial. You only see those patterns in the sky because of where the Earth happens to be. Some of those stars are like really close to us, and some of them are really far away. It's not like an inherent part of the sky or the universe. Anybody looking at the sky from another perspective would see something totally different. And I think it wasn't until college that I realized, like, oh, constellations are not like a helpful astronomy thing. They're just a human pattern finding thing. It was kind of weirdly disappointing, I know, and it sort of encourages the false impression that the sky is two dimensional, that you're like looking at a screen. I think it's much more thrilling to look up at the night sky and see it in three D, to imagine that some of these things are much deeper and some are much closer than the others. Instead of looking at an image, it makes you feel like you're looking at a view, like the best view in the cosmos. Yes, I remember. Also when I was in college, I got to look through a giant telescope at sort of part of a constellation, and it kind of blew my mind that in all of the stories that I was able to see, they were like, you know, clusters are swirling things happening in between there, and they were sort of part of the constellation too, and like, ah, it's I don't even know what the point was, but it just sort of the closer you look, the more surprising it is. So even though I was disappointed at first to learn that constellations are sort of a pattern finding thing, the closer you look and the more you learn, the like more exciting it gets, indeed, and so welcome to the podcast. Daniel and Jorge explain the Universe, in which we try to take a closer look as possible into the very nature of this crazy universe. We zoom in on the tiniest details and try to understand how quantum particles really move, what is really going on, and we zoom out to the biggest, deepest, oldest, most dramatic questions of the universe. How old is everything, how does it all work? What's going on up there in the night sky. We take all of that and we try to explain all of it to you. And as you may have, guest Horrie isn't with us today, he's on a brake, and so we're very glad to have with us one of our favorite guest hosts, Kelly. Kelly, thanks for joining us today. Thanks. I love being here. I always love it when Jorge takes a break and I get to geek out with you. Well, today we're gonna be talking about one of the most accessible things in physics and astronomy, a place where a lot of people get attracted to the big questions of the universe, and that's just looking up at the night sky and seeing the stars. I think everybody who has questions about the universe, everybody who wonders what's out there, probably got started by just looking up and seeing those twinkling lights and wondering what it all means and So what part of the night sky are we going to focus on today? Today? I want to talk about the illusion that is the night sky. On one hand, we say that the night sky seems like it's two dimensional, but really it's three D. And it takes this sort of mental exercise to unhook yourself from the illusion that it's a screen and to remember that it's a deep, deep view that you're looking across billions of miles of empty space. But there's another illusion of the night sky, and that's that it seems to be sort of static, that it seems to be fixed. And it's true that a thousand years ago astronomers looked up at the same night sky that we see, and in a thousand year as astronomers will still be looking at basically the same night sky. But that's because the time scales for the nights guy and for the Solar system and for the universe are just much much longer than we tend to think about in human history, and that on those long time scales, the universe is actually quite chaotic. So like a thousand years ago, was it a little bit different? And that's how we know it's way different, like a billion or a million years from now, or do we know that some other way exactly? The night sky is changing very slowly, So if you have very precise measurements of where all the stars were, you could see those things in action. But mostly we understand the night sky is dynamic because we understand the processes behind it. We know that these stars are in motion. We see these crazy effects. We see snapshots of all these processes back through time, because the further we can look out into the universe, the further back in time we see. And so we can see things happening to other galaxies and other stars, galaxies, colliding stars swirling around each other, all sorts of crazy stuff is happening out there. It's sort of like we are in the middle of a white water rapids, but we're just looking at things in super slow motion, so it seems like nothing's happening, right, So can we go from like this more sort of abstract, grandiose discussion to like a more concrete example, So, like, what's happening with the Hyades Cluster. That's right, it's been in the news recently. There's a blob of stars out there called the Hyades Cluster, and astronomers have discovered that something quite dramatic is going on to this cluster. So on today's episode, let's talk about what's happening to the Hyades Cluster. And before you get too worried, you know, this is a group of stars out there. They don't have emotions or feelings, so you don't have to worry about them too much. Although I guess if there are aliens out there, you know, living on planets in this cluster, what's happening to the cluster could be disrupting their lives. So now I'm worried. So yeah, actually I changed my mind. You should totally be worried about those aliens. I'm having a bit of an existential crisis now, and so as usual, I went out there into the Internet to ask people if they knew what was happening to the Hyades Cluster, and I should have asked them how they felt about it. But if you are interested in participating for future episodes of the podcast and lending your voice to these questions and hearing your voice on the podcast, please don't be shy. Just right to me two questions, add Daniel and Jorge dot com. So before you listen to these answers, think to yourself, do you know what's going on to the high these cluster. Here's what people had to say. If it's a stock cluster, then it could be spinning itself a pot or flinging stuff out of it. Or if it's a galaxy cluster them maybe it's uh combining galaxies together or just again flinging them out of each flinging them away from each other. I have never heard of the Hyades cluster, and I'm not even sure i'm pronouncing it correctly. The Hayvis cluster, if I remember correctly, is a star cluster quite close to us, or maybe even the closest one. And if I'm correct, it's falling apart or dissipating, or at least it's the stars are not staying together in the cluster as they are, But I'm not sure what the reason for that is anymore. I'm not sure what's happening to it, but I really hope it's okay. I'm again not sure I know that much that this cluster is the closest one to us or to the Sun, but haven't actually heard what's happening to it, so I'm not sure. I assume this has to do with a constellation of stars not in our galaxy to my knowledge, but should be outside of our galaxy, and clearly it is, since you're asking a question, it is clearly an interaction or something that has not been observed by humans before. So breaking the mold pussy? Is it moving towards another cluster creating a giant explosion in space? I think that the Hades clusters all dying out. I think it's a clusters does and to go off of the name Hades, I think they're all going to the underworld. May be confusing the Hyades cluster with another one, but I think that's a youngish cluster where a lot of the dust and such from formation has already been you accumulated or blown off, and now the stars are moving apart. Their answers were a nice mix of, you know, honestly admitting that they don't know what's going on to one person who was maybe having a bit of an existential crisis, really hoping that the Hyades cluster was okay. But since nobody like seemed to have gotten it totally right, can you explain to us what what is it? Right? So, the Hyades cluster is something that astronomers call an open cluster. This is basically a group of stars that formed together. I think this is really interesting because I think it gives you a window and understanding how and when and where stars are formed. People might imagine that the stars just sort of like pop into existence in random places in the universe, but there's really actually a lot more structure and pattern to it than that. And star clusters are these groups of stars that all formed together and give us an opportunity to study exactly how and when stars are formed. And if they're still in the cluster, does that mean it's a younger group of stars. Does the clustering tell you something about age? It does, and it tells you something about mass, So you have to go back to the original blob of stuff that formed this cluster. Remember that most stars are formed from like huge clouds of gas and dust and left over remnants from other stars. You know, we're like fourteen billion years into the history of the universe that have already been generations of stars that burned for millions or billions of years and then exploded and sent their shrapnel, their dust, their compost out into the universe. To see new generations of stars. So you have this sort of like raw material floating out there, but it doesn't always just necessarily like come together into a star. There's nobody out there like scooping up huge blobs of hydrogen to form stars. Something has to happen to make those stars formed, to make this huge cloud of gas and dust actually coalesced into these burning, bright blobs. So what happens. So it's fascinating because two things have to happen. One is the blob has to get cold, like you think of stars is like obviously really really hot. But in order for them to come together, gravity has to pull those things together, and it can't do that if the particles inside it are moving really really fast. So if you have like a cloud of really really hot gas, it's never going to form a star if it can't cool down somehow. Those particles have to slow down because remember that gravity is really weak. It's the weakest force in the universe by huge number. It's much much weaker than magnetism or electricity. So for a star to form, gravity has to be able to gather together those tiny little particles, and that can only happen if the particles are really slow moving. So you have some big cloud of gas and dust, it needs a way to cool down, like radiating off its energy, sending photons out into deep space. That gives you the raw material that gravity can then use to form those stars. But usually these clouds are not just like enough cloud to make one star. There are enough cloud to make hundreds or thousands of stars all at the same time. So I'm having a little trouble wrapping my head around this. So when you say cool down, you mean like cool for a star but still ridiculously hot, or is it like actually cool, no, really cool even for you Like these are freezing, freezing cold clouds of gas and dust. They need to be moving very slowly for gravity to take over. So we say two things have to happen. One is they need to be cooled down, not like thousands of degrees Calvin, but you know, much smaller values, actually cold values. And then you need gravity to be sort of like get a foothold to like make these clouds collapse into a cluster of stars. And for that to happen, either you need like one blob that's extra dense and it starts to gather the other ones because it has stronger gravity. Than anything else around it, or you have some external event, like a supernova nearby sends a shock wave, and that can trigger the collapse because it sort of pushes a bunch of particles into another bunch of particles and then they have more density than everything else around them. So you need like a cold cloud of gas. It's like the raw ingredients, you know, like when you make a recipe and they say, like, you know, use chilled butter or whatever. It's important for the texture of your pie that you start with cold butter. Right, You're not gonna get your lamonation in your flaky crust. In the same way, you need to start with like cold gas for your stars, and then you need to trigger that lapse somehow. So it's this two step process of forming new stars and so the one once you get that you know the right pieces of the recipe so you can make your cosmic pie. What does it end up looking like? Like what kind of stars do you make? And how big is the product? It depends a lot on exactly how much metal there is in this cloud. The universe started out with only hydrogen and helium and very very tiny amounts of everything else, and astronomers called everything above helium a metal, like I know, biologists and chemists had their own definition of metals, but for astronomers, anything above helium they call the metal. And so you know, I don't know what they call heavy metal music, but you know, probably anything with a beat to it. Do astronomers listen to heavy metal? I guess some of them must. Almost everything is heavy metals for astronomers. And if your cloud has more heavy metals in it, heavier elements carbon, oxygen, nitrogen, even iron, then it's easier for it to coalesce, and so you get reasonably sized stars. If you have really really big clouds without any heavy metals, and it's harder for it to sort of cool down and to coalesce, and so you get really big stars. You get these huge clouds, and so we think like the first population of stars ever reformed in the universe were probably like enormous mega stars for that reason, whereas in later clouds of gas and dust that had these like smaller pockets of metals in them, they formed these points for the stars to form, and so you've got a larger number of sort of reasonably sized stars, you know, stars like half to ten times the mass of our sun, and do these stars are these stars that will last for a long time. There's a really close connection. They're actually the bigger the star, the greater the gravitational pressure. Once it does start to burn, the higher the temperature, and the faster it burns through its fuel. That's why that first generation of stars that had almost no metals in them, only lasted a few hundred million years, whereas the second generation of stars, some of those are still around there more than ten billion years old, and the smaller ones might even burn for trillions of years. So the smaller the star at the longer the lifetime. And the thing to realize is that these stars are not just formed one at a time. Right, you have a huge cloud of gas and dust, and so a bunch of stars are formed together. And so earlier you asked me like, well, how long do these clusters last? And so it depends on how many stars you get into that cluster. So if you get like a huge cloud of gas and dust that gives you like thousands and thousands of stars, then those stars which are formed together will hang out together for quite a long time. A smaller cloud which gives you fewer stars like you know, ten or maybe a hundred. They don't have the gravitational strength to resist the rest of the galaxy, and they mostly just end up going their own way. I have been in some social groups like that. So typically these clusters can last, you know, millions or hundreds of millions of years. Scientists are really surprised if they see a cluster that's like a billion years old, because it's hard for these clusters to resist like the tug of the rest of the galaxy, which tends to sort of pull them apart. Do they all stick around for about the same amount of time because they started at the same amount of time, or do some of them disappear at different rates? Well, the stars inside the cluster can be of varying sizes, and so because some of them are bigger, they burn brighter, they burn bluer, they tend to disappear. So as you're looking in older cluster, you tend to see fewer blue stars in them and more of the red stars and the yellow stars. So an older cluster tends to have like more yellow and red stars. One weird thing is that they have been looking at open clusters and globular clusters, which are similar and even larger, and they see something really weird, which that they see a bunch of bright blue stars even inside these clusters that are supposed to be pretty old, where all the blue stars should have already burned up. WHOA, So why do we think that they're sticking around? Scientists aren't sure, of course, but that's what makes it exciting. They call these things blue stragglers. And one idea, which I think is really fun, is that these blue stragglers might be new combinations of old stars. Like maybe you had a couple of stars that are red or yellow and are burning happily and planning to burn for billions of years, but then they merge. They smashed together, they like gravitationally bound to each other. Maybe they were in a binary system to start with, and they just sort of like fall into each other and become a big hot star. WHOA, So I wonder like the social media and that galaxy, is it like benefer when Ben Affleck and Jennifer what Lopez come together? You know, these stars have names that combine. I don't know, but instellar marriages. There are no divorces, right once you get gravitationally married to each other. I don't know how you can get separated again. You better like each other. So you've mentioned an open cluster, and I think I also heard you say globular cluster? Are there clothes clusters? How many kinds of clusters do we have? You know, if astronomical names made sense, then yes, there would be open clusters and close clusters, globular clusters, and I guess non globular clusters. But no, these things come from history of people noticing, just as you were saying earlier, they would like zoom in on a star and then discover, way a second, that's not a star, that's actually a bunch of stars and a little cluster. That's why it looked a little bit like a hazy blob instead of a bright pinpoint. And as we study these things, we discover that these categories, which is sort of historical based on who found them and what they called them, might actually just sort of sit in a spectrum. That the difference between an open cluster, you know, which tends to have tens of thousands of stars, and a globular cluster that has like a hundred thousand stars might just be the size that there might be like clusters of stars of all sizes, and we just sort of like found a few here and found a few there and gave them different names, when really it's just like a smooth spectrum and there's no like fundamental difference. But that's something astronomers are studying, like the concept of this open cluster and is it different from a globular cluster and how does it all fit together in the sort of history of the galaxy is an exciting area of research right now. It's got to be a tough thing to study, but I found it really fascinating because it gives you like a hint as to what's going on in the Ga galaxy. You know, it's not like we just got these stars and they're gonna be burning. We're making new stars, like right now, like everyday, new stars are being formed. And these clusters are especially fascinating because not only do you have stars in there, but they still have clues in the structure of the cluster about the thing that made them, this huge cloud which formed them. And so I think these clusters are super fascinating because there's sort of like little mini sub galaxies within the galaxy. They give you a clue as like the texture of the galaxy and it's particular history that is so cool. So do we have a sense for like what kind of things you most commonly find at the center of the clusters? How many of these have we've been able to study in detail? Well, you know, these things are not made that often. There's like one of these open clusters we think formed every few thousand years in the Milky Way, so like it's not like they're always popping into the night sky. But because the Milky Way is pretty old, there are a bunch of them. And we've identified more than a thousand open clusters just in our galaxy, but we think there are lots and lots more so we've they're all over the place. A thousand that's a pretty nice data set to work with. Yeah, it's something that you can you really use to study because you're going to see them at all different points in their history. Recently, foreign clusters, clusters that are just falling apart, all sorts of stuff. Of course, the one that astronomers really like to study is the one that's closest to the Earth, and is that the Hyades cluster. That is all right now that everybody's excited to learn about the Hyades Cluster. Let's wait and take a break to hear from our sponsors. All right, the moment you've all been waiting for, we're back. Let's hear about the Hyades Cluster. So you were just telling us that it is the closest of the clusters. So if I look out in the night sky, where should I be looking if I want to be looking in the right direction to find the Hyades cluster. The Hyse Cluster is actually part of a constellation. So if you know that Horace constellation, the Face of the Bull, you know, then there's this part of that constellation that's sort of like a v The High These Cluster is part of that. Another part of that constellation is sort of a famous star called Aldera Bond, which I think is famous maybe just because it sounds like the name of a planet in Star Wars, but it's also one of the brightest stars in the night sky. And so would we be able, like if we were looking at the Tourist constellation, would we see something kind of fuzzy or would it just sort of look like a point. Well, it's about a hundred and fifty three light years away, which means that it's pretty far away, right, it's not that close, and so to the naked eye it just looks like a point. But if you have a strong enough telescope, you can zoom in on it and you can tell that's not just a star, it's actually a cluster of stars. It doesn't take that powerful a telescope. So if you have a pretty good telescope in your backyard, zoom in on the high these cluster and you can see it looks like a bit of a fuzzy blob, and that's how it was discovered to be a cluster. How wide is this? So the thing is about sixty light years across, right, and so it's a hundred fifty three light years away and sixty light years across. So that gives you a sense for like how broad this thing is relative to its distance, And that means that it's large enough and close enough that we can actually measure its distance directly using parallax. Remember that the distance two stars can be hard to estimate because you can't necessarily tell the difference between a star that's really bright and far away or a star that's not so bright and closer up. They look the same in the night sky, but we have all these cool techniques for measuring how far away a star is from, like looking at type one a supernova for stars and other galaxies, just seeing if they're near one of these variable stars, these sephids, or if they're close enough, we can see how the star moves in the night sky as the Earth goes around the Sun, because as the Earth goes around the Sun, you get a slightly different view of the night sky. And for stars that are close enough, it's sort of like opening and closing one eye and looking at your finger. You've got a different view of that finger, and your brain actually automatically uses that binocular information to give you a sense for how far away something is. So Hyades is close enough that we can do that. We can use parallax to measure how far away it is. Interesting, and of course you know now that you've mentioned that I have to be blinking and looking at my finger in this room by myself. So we talked a little bit ago about how you need something in the center to pull the cloud together. Do we know what is pulling things together in the Hyades cluster? So probably all of those gravitational centers then became stars, right, So you have this like big cloud of gas and dust that forms it, and then you need these seeds, these gravitational seeds to pull stuff together. Each of those are the progenitors of a star, and so what you end up with instead of a big cloud of gas and dust, is then just a bunch of stars. And interestingly, all the gas and dust that didn't get gathered into a star gets blown out of the cluster because of the radiation from those stars. So sort of like musical chairs, like you gotta find a star to join, and if you don't, then the radiation just like blows you away and you're alone forever. You're just floating out there destined to be you know, in some next generation of stars, maybe the fourth or the fifth time around, you'll win the game of musical stars and you'll get to burn brightly in the universe. I don't know though, if gas really wants to be part of a star and get fused into something heavy, or if it's happy just the way it is. Well, some of us are loaners, and so you know, I'm glad there's lots of options out there for the dust particles, and I hope they'll get what they want. I like the introvert extrovert theory of gas. That's nice. Well, I study animal behavior. So, so about how many stars are in this particular cluster. So the high these clusters sort of like a big spherical blob, and right now it has hundreds of stars in it. And as we said earlier, probably all these stars around the similar age, and they come from the same cloud and so that the same sort of chemical makeup. And interestingly, we think, based on the light that comes from these stars, that there's more metals in those stars than there is in sort of our stellar neighborhood. So you told us that astronomers think anything more than helium is a metal, right, So that might not mean what I think it means. Does that just mean it has less helium and hydrogen? Yeah, when a star is formed, it's usually it is mostly hydrogen and helium, and that's really what the star starts to burn, because stars are factories for turning helium and hydrogen into heavier elements. But of course they often come with some left over remnants of previous stars, and at the beginning of a star's lifetime, those heavy elements just sort of hang out and get hot. If the star burns long enough so that they can fuse those heavier elements. Then eventually they can participate in the star itself. One thing we can do is we can measure the emissions from those elements. We can look at a star, we can see in what frequencies it's sending us light, and that those frequencies tell us what the star is made out of, because different elements glow with different colors. Like if you remember middle school chemistry, you probably got to put like weird chemicals and a bunsen burner and see the flame turn green or blue or whatever. Chemistry. That's part of chemistry, you know, the whiz bang factor. And so we can do the same thing with stars. You say, oh, this one is burning green, that has more copper in it. Whatever. And so this tells you, like the particular context of the neighborhood wherever the high these cluster was when it was born, happen to have more medals in it because it just happened to have like more compost from other stars that had blown up and spread those medals into the universe. Interesting, I'm trying to figure out a hippie joke or something about composting, but it's just not it's not coming together. It's a cycle of life or something, or the cycle of star life. Yes, the cycle of star life. And as you look at these clusters, you can also compare them to the other clusters nearby, and I can tell you more of like the story of what happened. I feel like this is sort of like space archaeology, you know, wondering like how did this form and what was going on here? While the high these cluster is near another cluster where there similarly difficult to pronounce a name. It might be Presepi, but it has similar metallicity and it's sort of moving in the same direction. So they might have been formed together like one big mega cluster and then gotten split up by title forces, by the gravitational forces of the Milky Way, into two separate clusters. Or they could have just come from the same neighborhood which had like the same sort of leftover bits of stars. But all these things are remnants, you know, sort of like when you see a church and it's built on top of the foundations of something else, which is built on top of the foundations of something else. It's like ten layers deep of human history. There that's sort of what we're looking at when we're looking at the stars. There's so many generations of cosmic dramatic history, and yet you have to try to disentangle it from light years away. It remains amazing to me that we know anything at all about the night sky. And you asked a really interesting question earlier about how we can know that these things are happening because we're seeing them in slow motion. I think that's a really important question, because you're right. We can't like look at one star and see its whole life cycle and say, Okay, we saw it get born, and we saw burn, and we saw it die. All we can do is look at lots of different examples. It's sort of like if you look at a town and you see there are kids, and there are teenagers, and there are grown ups, and there are people who are old and dying, and then you can sort of put together the lifespan of a human, even though you don't ever get to see a human go through the whole cycle just from one snapshot. That's sort of what we're doing in the night sky. We don't get to see a star's entire life cycle, and we definitely don't get to see an open clusters entire cycle. But we can sort of put the story together by looking at lots of them. And as you said earlier, there's like more than a thousand of them, So that gives us a pretty good picture what's going on in terms of the dynamics. And so when these clusters go away, do they go away because the stars die, or do they go get pulled aparts and sort of spread out in the night sky? What what happens to these clusters as time goes on. It depends a little on the age. Sometimes of the cluster lasts a long time. Then the stars can live their whole life in the cluster and never have to leave. But the rest of the Milky Way is tugging on these things. Remember that there's rarely strong gravitational forces from the center of the Milky Way. All of these stars, they're not just hanging out in space. They're zooming through space because they're whirling around the galaxy, which is spinning. That means that there's a very strong gravitational force towards the center of the galaxy, but their velocity keeps them from falling into it, sort of like the way the Earth doesn't fall into the Sun because it's moving so fast, and so these stars are getting pulled on by the gravity of the Milky Way, but doesn't pull on all of them equally. Some of them are closer to the center and some of them are further from the center, so they're effectively getting pulled apart, and we call it tidal forces. Anytime gravity is pulling on one part of something with a different force than it pulls on the other part of it, effectively it's pulling it apart. So we call those tidal forces. And the Milky Way is doing that to the open cluster, just like us doing it to everything else. Is trying to basically pull it apart. So if you we're living on a habitable planet and it could be anywhere in the Solar System, would you not want your habitable planet to be in a cluster because it's getting pulled on a lot, and you'd be more likely to, I don't know, get thrown out of whack. Or is it not more chaotic there than other places? These things are denser than other places, So the rest of the Milky Way sort of less dense in terms of stars, like in our neighborhood of the Milky Way, it's like one star every three or four cubic light years, so not very dense, whereas in the center of a globular cluster, for example, there's like one star every cubic light year, so they're much closer to each other. Normally, that doesn't really affect you because like that's still really far away, like a light year is a big distance. However, it really can affect you because if stars are near each other, they can perturb each other's Solar system. So, for example, if another star came close to our Sun, it might knock some things in the or cloud out. This this huge cloud of lillions of icy objects orbiting really far from the Sun. If one of them gets knocked out of orbit, you can fall into the Solar system and become a comet. And sometimes those things smack into planets, causing catastrophes. Yeah, so it's not great actually to have neighbors. You want to live out in the middle of nowhere, and this neighbors maybe getting a little bit too close. We should see if they're following all the h O rules exactly. Probably they're coming up and they're saying, hey, you'r or cloud is out of whack, and you're like, hey, that's because you came too close. Get out of here. It's your phone. You're gonna have to pay for the property damage if a comet gets too close, exactly. And so living in the center of a stellar cluster and open cluster or a globular cluster probably not great for life because you could probably get more common bombardments. Got it. It's a dangerous place out there on long time scales. So what is Hyades is history? How old is it and is it breaking up a lot right now or is it still pretty well held together so high these we think is around six hundred million years old, which is pretty old for one of these clusters. We think that usually these clusters only last for like fifty to a hundred million years before basically they get pulled apart and they just become dissolved into the background structure of the Milky Way. So this one is pretty old, which means probably it started out really big and really massive, and while we're looking at is sort of like the leftover bits. What's been able to resist those tidal forces for six hundred million years. That's incredible because that's not just a little bit longer than usual. That's longer than usual. So we've got a thousand data points. Is six hundred million years old and extreme value? Are we lucky to live next to this extreme open cluster? Or is there a lot of variability around that fifty to one hundred million years? There is a lot of variability, though they tend to peek at much smaller values, so six hundred is pretty rare that we have seen some up to like maybe a billion if they're really really massive. But this suggests the high these is definitely on the more massive end of clusters. All right, Well, so we opened by saying what's happening to Hyades? Which suggests that something interesting is happening to Hyades. So let's make everybody wait when we take a break before we get back to the big question. And we're back. So, now that we've all learned about Hyades background, we all, you know, are sort of emotionally attached to it. But you told us that something is happening to it, which we all hope is nothing bad. What is happening to Hyades? So what you usually happens to these clusters is that they get pulled apart by the galaxy, right and usually tidal forces have a very distinctive effect on something. They tend to pull it apart into long strands, and so you get like a forward tail and a trailing tail instead of just being a blob that like pulls the closer bits harder and doesn't pull on the back bits as hard. So it gets sort of like stretched out. You get these really long tails, and so that's what typically happens to these clusters. They get stretched out and eventually dispersed. And so people have been studying the high these cluster and they see these tails, but one of these tails is missing. The trailing tails seems to sort of have been like chopped off. WHOA where did it go. It's like finding a lizard in nature and be like, oh, somebody took a bite out of this one, right right, the predator got him. Yeah. And so what that means is that there's something big out there that's disrupting this thing. It's not just the normal process of the galaxy tearing this thing apart gently. Something sort of more brutal is happening. And I say more brutal as a direct quotation from one of these astronomy papers I read. And when astronomers say, you know who are used to like stars burning and exploding and supernovas. When they say something's brutal, you know, it's pretty severe. I'm scared. What is the brutal thing that's happening? Do they know? We don't know exactly because all we can do is measure the gravity, right. What we know is that these things are disrupted by grab, of course, the gravity of the galactic center. But here there's some new source of gravity. Something else is tugging on this thing, and it's like slurred up the tail of this cluster, it's like gobbled it up. And so there's some massive invisible structure out there that's tearing the high these cluster apart. So why don't the clumps get like pulled away and then form something bigger? Where where are they going? Yeah, that's a great question. It depends on the sort of the shape of this new thing that's pulling on them. It's possible that it's just sort of like yanks them out, and they get tossed out because of their high velocity, into some new direction and they can't necessarily like coalesce around this new heavy, invisible object. But in order to tear this thing apart. It needs to be some object that has like ten million times the mass of the Sun, so it's much more massive than the entire cluster, and we can't see it, and we can't see it directly. When we look, we don't see anything there, and that of course suggests that it might be something really fascinating, like you know, a supermassive black hole that somehow escaped its galaxy and it isn't surrounded by you know, glowing accretion disks and other stars. Or it could be like a huge blob of dark matter. WHOA which one do we think it is? Are those equally plausible? I think it's more likely to be dark matter, although you know, it's a bit of a catch all. Like every time we say, oh, there's gravity, and we can see the gravitational effects because we see it tugging on the stars, we don't see anything there. Then we say, okay, there's some invisible matter, and it's easy to say, well, that must be dark matter, sort of like the go to explanation for a black hole to be like ejected from its galaxy or to lose all of its stars. That could happen. Also, if you get two galaxies that merge and then one of them gobbles all these stars and the other ones sort of orbit each other for a while, but then one of them gets ejected. But it's much less likely to happen. So I think dark matter is the sort of current best explanation that we don't have any direct evidence that it is dark matter. Okay, how do we know any of this? Yeah, we can only see this stuff because of the gravitational effects, right, So what we do is we look at the path of all of these stars really, really carefully and really accurately in order to try to understand these dynamics. And we're actually entering a really exciting era in astronomy where we're getting much more precise pictures of what's going on in the Milky Way. We talked earlier about how we look at the stars is sort of like a two D screen in the sky. It takes it sort of like mental gymnastics to remember that it's three dimensions. Well, recently we've launched some telescopes that really help us build that three D map of the Milky Way. This is this thing called the Gaia satellite, whose entire job is essentially just to map the Milky Way really really precisely. Is that a NASA project or did somebody else launch it? That's from the European Space Agency, so thanks to our European colleagues, and they launched it in two thousand thirteen. Has two really powerful telescopes on it, and so what it does is it focuses on a star and it can measure the brightness of the star. But because has two telescopes, it can also do parallax. It sort of sort of like looking at the sky with binoculars. So it measures the angular precision, the distance, and the brightness really really accurately. And it also measures the velocity of those stars. Because we can look at the spectrum of the light that comes from the stars, we can say what frequency are the photons that come from those stars, and based on this frequency, we can measure the speed of the stars from the Doppler shift on those photons. Stars that are moving away from us really really fast tend to be more red shifted. Stars that are moving towards us get blue shifted. So as a result, we can build this incredible map of the Milky Way with really high precision. So having two telescopes helps us do all of that. Are these two telescopes like Hubble sized or much smaller. They're not nearly Hubble sized. Remember, anything that we launched in the space is sort of limited because you can only fit an object of a certain size into our rocket. Unfortunately, so neither of them are Hubble class telescopes. But together they can really make this very accurate map of the universe. And it's not just a three D map. It's sort of like a four D map because not only do you know where all the stars are now, but you can tell where they are going. Right, You can tell their velocity, which tells you something about their direction. And that's really exciting because it gives you this picture of the Milky Way as that dynamic entity. Right. It's like looking at all the water droplets in that white water river and knowing which direction they're going, and also gives you a sense for like the snapshot that we have of this crazy chaotic galaxy that's swirling around us. That is incredible. And so it's been out there for less than a decade, but like, you know, eight years or something, how many stars has it mapped so far? It has a map of a billion stars. It's incredible, and it's you know, it's really a new era of astronomy. And every time I talk to astronomers about what they're doing, they're always talking about this data set. You know, they can use this to measure things they could never measure before, to observe effects that they could never study before. You know, I know people here you see Irvine that are studying like how often do we get asteroids impacting on the Earth and can we tell if that's because other stars come nearby? And they can use this guy a data set to like look at the history of stars. So this one's going in that direction. It must have come by our solar system a few million years ago. It's kind of really interesting studies. And so it's it's like we've been looking at a flat screen and now we're getting like the four D picture of the galaxy. We've got our three D goggles and we're ready. And so it sounds like these data are just available to anyone and will be available a thousand years later when people want some like background data to work with. Yeah, because it's the s A, it means that it's available so and we can go and download the data and analyze it. And get in your computer a four D picture of the galaxy. And that's how we're making these really interesting discoveries, like looking at the high these cluster and be like, oh, something is chomping on this tail. Is that something where like if you knew where to look in the night sky, you could pull up the e s A data and you could see a tail sort of disappearing. That's exactly what happened. And then so these astronomers that made this discovery, that's just what they did. They looked at the guide data for the Hyades cluster and they tried to find these tails, and they noticed that this backwards tail was missing. And there's no like really big cloud of gas or other star cluster nearby that could provide this dramatic gravity. And so it's cool because you can think about these stars is sort of like tracers. You know, there's a lot more going on in the galaxy than just the things we can see, but the stars are affected by those because of the gravity of the rest of the galaxy. So you can think of the stars is like giving us a sense for the currents of mass that are flowing through the galaxy and anytime they're moving in a way that we don't understand that tells you there's something there. So is this like I guess my question was more like, is this like Google Maps where I can just sort of like plup my little guy down wherever I want in space? Or is it? Is it more of like an Excel sheet with zeros and ones and you need to know what you're looking for to see that there's a tail there. Yeah, it's more like an Excel sheet. You have to be a little bit familiar with data ealysis techniques to get a handle on it. I don't think they have yet like a Google galaxy, but that would be pretty awesome. You can zoom through the galaxy and look at all the stars. Yeah, that would be great, and then we can see, you know, what aliens are watering their law on today. That sounds great, but whatever is happening to these stars is pretty dramatic. And you know, if these stars are getting yanked out of this cluster, it's a pretty serious force. And so the dynamics of what's happening there could be very dramatic. For those solar systems. They could get like briefly very close to each other and both like induce lots of common rains on the inner planets in their solar systems, or even lose some of their planets if they get close enough each other to like steal planets from each other. So next time you're looking up at the night sky, remember that you're not looking at a flat screen. You're looking at a four dimensional view, a huge three D starscape that's evolving in time, that's crashing and smashing and flowing and doing all sorts of crazy things. And now we have a pretty good picture for what's out there and where it's going. Kid one is going to have a long lesson the next time we look at the Ryan, just be glad your arms are long enough to point it out. I am all right. Thanks for joining us, everybody, and thank you Kelly for guest hosting today. Thanks for a fun afternoon. Have a good one, Daniel, alright, tune in next time. Thanks everybody, thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of I Heart Radio. For more podcast for my Heart Radio, visit the I Heart Radio app, Apple Podcasts, or wherever you listen to your favorite shows.