Speaker 1: Hail. Hey, have you ever seen two stars collide? Well,
Speaker 1: I live near Hollywood, so it does happen sometimes. What
Speaker 1: do you mean, you know, like Brad Pitt and Angelina Julie,
Speaker 1: they're like binary star system. I get it. And when
Speaker 1: they collided, it sent out paparazzi waves or something. Yeah,
Speaker 1: it sends out ripples in the fabric of the entertainment
Speaker 1: space time. Well, I hope that's somewhere. Alien physicists have
Speaker 1: built a device to measure those ripples and are wondering
Speaker 1: what it is they're looking at. Probably two attractive human beings, hope,
Speaker 1: only they're not thinking how delicious they look. Ye Hi
Speaker 1: am Or Hammock cartoonists and the creator of pH D comment, Hi,
Speaker 1: I'm Daniel. I'm a particle physicist, and I live in
Speaker 1: southern California. But I've never accidentally bumped into a celebrity.
Speaker 1: How about on purpose? Have you bumped into one on purpose? No?
Speaker 1: Their bodyguards keep me away. It's so frustrating. Really, you
Speaker 1: live down here and you've never had a celebrity sighting.
Speaker 1: I've seen them from afar, but always imagine I would
Speaker 1: bump into one at the grocery store or something m
Speaker 1: I see. Well, sort of you're sort of becoming a
Speaker 1: star yourself, Daniel, And at least in the Physics Podcast
Speaker 1: universe whatever, I can walk around you see Irvine and
Speaker 1: people think I'm just some homeless person or a professor,
Speaker 1: one of those you need to confuse sometimes. How would
Speaker 1: you have you had any good celebrity sightings and all
Speaker 1: your years in Hollywood? Sure? Yeah, yeah, I've I've had severally. Yeah,
Speaker 1: sometimes you or you can't get away from them sometimes.
Speaker 1: But welcome to a podcast. Daniel and Jorge explain the
Speaker 1: university production of I Heart Radio, in which we collide
Speaker 1: your brain and the universe. We take all the incredible,
Speaker 1: all the amazing, all the bonkers, all the wild stuff
Speaker 1: that's out there, and we squish it all into your
Speaker 1: head because we think that the entire universe should be
Speaker 1: understandable and should be explainable to everyone. Yeah, because it
Speaker 1: is sort of a wild universe. It's a lot happening
Speaker 1: in it. There's obviously stars burning bright out there, and
Speaker 1: planets orbiting them and asteroids flying around. But sometimes we
Speaker 1: get some pretty interesting events happening. That's right, while you
Speaker 1: look out into the sky and it seems sort of
Speaker 1: like static. It seems like, hey, it's just sort of
Speaker 1: hanging out, it's not really doing anything. If you watch
Speaker 1: the universe in fast forward, it would seem like a crazy,
Speaker 1: chaotic place. It would seem like a drink that somebody
Speaker 1: is shaking really really fast. It would seem like the
Speaker 1: mosh pit at a crazy concert. What's the music that
Speaker 1: the universe is dancing to? Is it like punk rock
Speaker 1: but it's super slow motion? Exactly? The universe is a
Speaker 1: super slow mo punk rock concert. But it is interesting
Speaker 1: to think about all the things that could be happening
Speaker 1: out there, and all of the near misses and all
Speaker 1: of the things sort of flying by each other, and
Speaker 1: sometimes things sort of inevitably collide out there in the
Speaker 1: universe because there's a lot of space out there in space,
Speaker 1: but also a big universe, So eventually everything's going to
Speaker 1: happen at some point exactly. And we're not unfamiliar with
Speaker 1: the idea of collisions. After all, we know that sometimes
Speaker 1: asteroids hit planets, right. We see craters all over the
Speaker 1: surfaces of everything in the Solar System. We even see
Speaker 1: comets smashing the planets, like Shoemaker Levy did a few
Speaker 1: decades ago. But what about bigger collisions? Is it possible
Speaker 1: for even larger things to smash into each other? Yeah?
Speaker 1: Isn't the prevailing theory about our moon is that it
Speaker 1: came from a big collision of the Earth with an asteroid, Right,
Speaker 1: That's how the moon was born. Yeah, maybe not even
Speaker 1: an asteroid. Maybe two proto planets collided merged in the
Speaker 1: Earth on the Moon are like weird mixtures of those
Speaker 1: two planets. It's an awesome titanic collision. Yeah, but you're
Speaker 1: thinking even bigger than planets or proto planets colliding. You're
Speaker 1: thinking maybe stars colliding. That's right, Why not always think bigger? Right?
Speaker 1: These collisions are boring. Now when we go to the
Speaker 1: next level, it's like fast and furious. They gotta get
Speaker 1: even crazier. Yeah, what happens when vin diesel collides with
Speaker 1: the rock. Everyone knows about that. Exactly what happens is
Speaker 1: they each get their own movie franchise because they handworked.
Speaker 1: That's the only way that it can go on. So yeah,
Speaker 1: so that was an elastic collision because they both seem
Speaker 1: to have survived it with their careers intact. But is
Speaker 1: it always so clean? What happens when bigger things smash
Speaker 1: into each other. Does that ever happen? Has it happened
Speaker 1: to our son? These are the kind of questions that
Speaker 1: keep me up at night. Yeah, so today we'll be
Speaker 1: looking into some stellar events, and in particular, we'll be
Speaker 1: asking the question what happens when stars collide? And are
Speaker 1: their children as good looking as they are? Usually? Not? Right? Oh,
Speaker 1: are you throwing shade on the children of stars right now?
Speaker 1: Showley Jolie or whatever her name is. I thought you
Speaker 1: were still talking about stars, like real stars. Put it
Speaker 1: on me, like stellar objects. I think all stellar objects
Speaker 1: are beautiful, even the ones that might inevitably come for us.
Speaker 1: But yeah, it is pretty interesting. I guess that there
Speaker 1: are so many stars out there in the galaxy and
Speaker 1: the universe that eventually some of them might run into
Speaker 1: each other, right, they might crash into each other. It
Speaker 1: turns out to be quite interesting. In some parts of
Speaker 1: the universe, stellar collisions are quite common, and in other
Speaker 1: places they're very rare. So, as usually, we were wondering
Speaker 1: how many people out there had thought about these stellar collisions,
Speaker 1: these stars colliding, and what would happened, And so Daniel
Speaker 1: went out there to ask people on the Internet. What
Speaker 1: do you think happens when stars collide? That's right and
Speaker 1: as usual. I'm grateful to our Internet volunteers for answering
Speaker 1: random physics questions. If it sounds fun to you to
Speaker 1: get four random physics questions and your inbox that you
Speaker 1: have to answer without any preparation, please just write us
Speaker 1: an email two questions at Daniel and Jorge dot com.
Speaker 1: So think about it for a second. What do you think?
Speaker 1: What do you see in your head when you imagine
Speaker 1: two stars colliding. Here's what people have to say, Well,
Speaker 1: I don't think they usually collide because um having this
Speaker 1: um fusion inside them and all the energy coming out
Speaker 1: of the sun. I think actually it's not usually for
Speaker 1: the stars to collide. Yes, and very often, because there's
Speaker 1: so many stars out in the universe. It seems like
Speaker 1: a trick question, like everyone would say, yeah, they collide,
Speaker 1: that's how they form mergers and stuff. But it's probably
Speaker 1: really unlikely that two stars would hit each other smack
Speaker 1: on on the first pass. They would pass close to
Speaker 1: each other and lock into orbit around each other. Maybe
Speaker 1: once they're locked in orbit around each other, either that's
Speaker 1: stable or one of them is way bigger and it
Speaker 1: sucks the matter out of the other one. Well, I
Speaker 1: definitely think they do. And some terms, whole galaxies can
Speaker 1: actually collide post each other's past and just became one. Um.
Speaker 1: I could imagine that it would probably happen with a
Speaker 1: huge explosion or just I don't know, depending on their
Speaker 1: mass and like what gases are burning in them. And
Speaker 1: for example, if there's like a Jewel star star system
Speaker 1: and they just don't know, like really close to each
Speaker 1: other and orbiting each other or just being really close
Speaker 1: to each other, they can also exchange matter maybe just
Speaker 1: get closer and closer to each other by gravitational pool
Speaker 1: and at one point they can just get so close
Speaker 1: that they actually collide. They do. They circle around one
Speaker 1: another and then eventually collide into one another or fall
Speaker 1: into one another. I think yes and no. I think
Speaker 1: it is possible for things to crash into each other.
Speaker 1: Things with master fall into each other, just like how
Speaker 1: they discover gravity waves too, black holes crash into each other.
Speaker 1: But also I think space is very spacey and for
Speaker 1: things to death spiral into each other has to be
Speaker 1: special uh circumstances. Because I think when objects roach each
Speaker 1: other around each other, like say stars are rotating around
Speaker 1: each other. I think they it's possible to have stable orbits,
Speaker 1: so there has to be some special math where if
Speaker 1: they fall over a certain criteria, then then yes, objects
Speaker 1: in space like stars with mass will crash into each other.
Speaker 1: I would say, very very rarely nowadays. Maybe it was
Speaker 1: more common in the very early universe when the what
Speaker 1: is it third generation of stars was firstborn. Maybe those
Speaker 1: collided from time to time, but nowadays it's very rare.
Speaker 1: All right. I'm seeing where it's like huge explosion crashes.
Speaker 1: Some pretty exciting times here, also some very technical answers,
Speaker 1: like space is very spacey. It's a good point. It
Speaker 1: is pretty spacey. There's it's a roomy too. There's a
Speaker 1: lot of room in the space of rooms. That's right.
Speaker 1: It's very minimally appointed in the universe. It's not overcrowded. Yeah. Well,
Speaker 1: I like the person who thought it was a trick question,
Speaker 1: like maybe stars never collided, but is that possible? Maybe
Speaker 1: they just bump into each other at the supermarket by
Speaker 1: quote accident unquote. Hey, I was reaching for that box
Speaker 1: of cookies exactly, and up in a tug of war
Speaker 1: with Brad Pitt over a box of cookies. That's my
Speaker 1: Southern California dream. There you go. I'm guessing Brad Pitt
Speaker 1: will will win no offense. He's pretty strong. But yeah,
Speaker 1: it seems like some people didn't think they would actually collide,
Speaker 1: and some people thought that it happens, I mean, binary
Speaker 1: star systems. There's a wide range of answers here, and
Speaker 1: that maybe this is an interesting one. People thought that
Speaker 1: maybe it happens more often in the early universe than
Speaker 1: in the older universe. Yeah, really fascinating stuff. I like
Speaker 1: the people are using their physics brains to think about
Speaker 1: what would make this happen. Yeah, because I guess in
Speaker 1: the early universe things were more crowded, right, technically, Well,
Speaker 1: we'll get into it. It's quite interesting. You know, in
Speaker 1: the early universe the stars had just formed and so
Speaker 1: galaxies hadn't formed yet, so in some sense, things were
Speaker 1: less dense. All right, well, let's jump into it, Daniel.
Speaker 1: What happens when stars collide? How common are these star collisions?
Speaker 1: It depends on lot on where you are, because star
Speaker 1: densities vary a lot from place to place. Like in
Speaker 1: the center of the galaxy, things are much denser. The
Speaker 1: distances between stars are much smaller than they are out
Speaker 1: here where we are where like twenty thousand light years
Speaker 1: from the center of the galaxy, sort of like out
Speaker 1: in the suburbs. Out here, there's like three or four
Speaker 1: light years between stars, and so it's much less likely
Speaker 1: for stars to collide. Like the closest star to us
Speaker 1: is Proximus Centauri, just under four light years away. In
Speaker 1: terms of the width of our Sun, that's like one
Speaker 1: hundred million sun width. Like if you try to fill
Speaker 1: up the space between our Sun and the next star,
Speaker 1: you'd have to stack it with a hundred million copies
Speaker 1: of our Sun. That gives you a sense for like
Speaker 1: how far apart stars are in our neighborhood. M M,
Speaker 1: that's interesting. What about closer to the center of the
Speaker 1: galaxy or stars more crunched together, Like what are the
Speaker 1: relative distances there? So in the center of the galaxy
Speaker 1: it can get much much denser in the stars average
Speaker 1: less than a light year apart, but it grows very
Speaker 1: very quickly as you get closer to that black hole,
Speaker 1: things get very very dense. And it's not just the
Speaker 1: center of the galaxy where things are denser. Our galaxy
Speaker 1: has these things called globular clusters, which are collections of
Speaker 1: stars we think formed all at the same time or
Speaker 1: might even be like many dwarf for galaxies that got
Speaker 1: eaten by the Milky Way. But these are much much
Speaker 1: denser than the rest of the galaxy. So you're saying
Speaker 1: that even in the outer parts of the galaxy there
Speaker 1: might be sort of like dense clusters where there could
Speaker 1: be a lot of stars running into each other. Yeah,
Speaker 1: these globular clusters, they're fascinating. We did a whole podcast
Speaker 1: episode about them last year. Some of them are sort
Speaker 1: of embedded in the Milky Way, and some of them
Speaker 1: are sort of like in close orbit around the Milky Way,
Speaker 1: but people consider it all to be part of the
Speaker 1: Milky Way. So in the center of the galaxy and
Speaker 1: in globular clusters, there are better conditions for having collisions.
Speaker 1: Like out here where we are, for the Sun to
Speaker 1: get into a collision is very very unlikely. Somebody actually
Speaker 1: did a calculation and they estimate that the Sun should
Speaker 1: collide with another star every ten to the twenty eight years.
Speaker 1: Like that's a hard number to think about. Just remember
Speaker 1: that the universe is ten to the ten years old,
Speaker 1: so it would take a lot lot longer than the
Speaker 1: age of the universe, so far before we expect the
Speaker 1: Sun to collide with anything interesting, So it seems like
Speaker 1: pretty unlikely, although I wonder if it's like, you know,
Speaker 1: like in in the center of a downtown, there's a
Speaker 1: lot more traffic, but people are going slower maybe, but
Speaker 1: out in the submers where you have these empty highways
Speaker 1: that maybe people are going faster, And so wonder of
Speaker 1: that increases the likelihood of a crash. Things are actually
Speaker 1: moving really rapidly in the center of the galaxy because
Speaker 1: things are closer to the source of gravity. Right, there's
Speaker 1: a huge black hole there, and when a star, for example,
Speaker 1: swings around the back of that black hole, it picks
Speaker 1: up a lot of speed. These stars can get up
Speaker 1: to like half of the speed of light when the
Speaker 1: whizz around the back of that black hole. So things
Speaker 1: are moving pretty rapidly in the center of the galaxy.
Speaker 1: They estimate that in globular clusters there's a stellar coll
Speaker 1: vision every ten thousand years. Well it's a lot, right,
Speaker 1: I mean, in terms of the age of the universe,
Speaker 1: that's like crash every other day. That's a lot of
Speaker 1: collisions exactly. And if you estimate how many globular clusters
Speaker 1: there are in all of the galaxies out there. The
Speaker 1: current estimate is about a trillion or so, you know,
Speaker 1: give or take to a factor of ten. But if
Speaker 1: you assume that there are a trillion globular clusters in
Speaker 1: the observable universe, then that estimate tells you that there
Speaker 1: are a thousand pairs of stars colliding at every moment,
Speaker 1: Like right now, a thousand stars are colliding with a
Speaker 1: thousand other stars. Wow, that's amazing to think about, for sure. Yeah,
Speaker 1: like right now, boom or a thousand booms stars colliding
Speaker 1: a thousand booms exactly. And these are not stars that
Speaker 1: are colliding like in neighborhoods similar to our son. These
Speaker 1: are stars colliding in the center of the galaxy or
Speaker 1: again in these globular clusters that these pockets of density
Speaker 1: elsewhere in the galaxy. But we're not near any one
Speaker 1: of these globular clusters, right, I mean, we have them
Speaker 1: in the Milky Way, but are we near one. We
Speaker 1: aren't near any globular clusters, not near enough to be
Speaker 1: worried about it or like to be sucked in or anything.
Speaker 1: So these collisions are happening in other places, But globular
Speaker 1: clusters are really fascinating scientifically and help us probe really
Speaker 1: interesting questions about the formations of stars. And there's still
Speaker 1: a lot of things that we don't understand about globular clusters. Yeah,
Speaker 1: they're sort of almost sort of where people call them
Speaker 1: like the cradle of stars, right like sort of, or
Speaker 1: nursery star nurseries they call them, right, Yeah, And these
Speaker 1: things are typically really really old, like they think they
Speaker 1: might mostly be population two stars. So these things were
Speaker 1: formed billions and billions of years ago in the second
Speaker 1: generation of stars, after the first ones blew up, the
Speaker 1: second generation formed, and these sort of low metalisity. They
Speaker 1: don't have as many heavy elements in them as our
Speaker 1: stars do because the universe hadn't made as much heavy metals,
Speaker 1: but they were all born about the same time. And
Speaker 1: so when you look at the globular cluster, you're seeing
Speaker 1: a lot of really old stars, or at least we thought.
Speaker 1: And they found a bunch of stars inside these globular
Speaker 1: clusters that look sort of unusually young, like they're really
Speaker 1: really blue stars, which means that glow really really brightly
Speaker 1: and really bright glowing stars tend to not live very long,
Speaker 1: they like burn out really fast. So there are these
Speaker 1: stars in these globular clusters that look really blue, look
Speaker 1: really young when the rest of the globular cluster is
Speaker 1: really old. So they imagine that what might be happening
Speaker 1: is that you could be getting like a bunch of
Speaker 1: stars that collide. They're like on their way at the
Speaker 1: end of their life, and then they collide to form
Speaker 1: a new huge star which then burns brightly. So these
Speaker 1: are called blue stragglers. They are currently a mystery in astronomy,
Speaker 1: but that's one possible explanation for them. Interesting. So they're
Speaker 1: old and so maybe they're not as heavy metals, so
Speaker 1: maybe they're listening to music under parties. It's sort of
Speaker 1: like two stars at the end of their career decide, hey,
Speaker 1: let's have kids and they can carry on burning brightly
Speaker 1: and earning money to support us in retirement. So that's
Speaker 1: sort of our chances of running into another star or
Speaker 1: star colliining nero us doesn't seem very likely. But let's
Speaker 1: talk about maybe what would happen if our star did
Speaker 1: collide with another star, or generally what happens when stars
Speaker 1: collide with each other. Yeah, it can be pretty dramatic,
Speaker 1: But it also depends on exactly how fast the collision
Speaker 1: happens and whether there's actually a collision or just sort
Speaker 1: of a near miss. You might feel a little bit
Speaker 1: relieved to think, well, our son is not going to
Speaker 1: hit any other stars for another you know, ten to
Speaker 1: the eighteen years, so I can relax. But our Solar
Speaker 1: system might be seriously impacted. Even if just another star
Speaker 1: comes somewhere near us. You could have a real impact
Speaker 1: on our lives. Right, Like, they don't have to actually
Speaker 1: touch each other for there to be a disaster, right yeah,
Speaker 1: because those stars are huge sources of gravity and they're
Speaker 1: already sort of tugging on each other a little bit.
Speaker 1: Remember that our Solar system doesn't just have a star
Speaker 1: and a bunch of planets. It's surrounded by this vast
Speaker 1: cloud of trillions of icy objects. We call this the
Speaker 1: ort cloud, and we think that's where comments come from.
Speaker 1: And so if another star passes anywhere near our Solar system,
Speaker 1: it can perturb some of those and then they can
Speaker 1: fall into the gravitational well of our Solar system, picking
Speaker 1: up a huge amount of speed and energy as they
Speaker 1: fall in zooming down through the inner Solar System and
Speaker 1: right past the planets, and these comments, if they hit
Speaker 1: the Earth, for example, they could wipe out humanity. It's
Speaker 1: an incredible source of energy in a real danger. So
Speaker 1: if a star comes nearby, they could disturb one of those,
Speaker 1: and if they come even closer, they could even like
Speaker 1: toss a planet out of the Solar system. Wow, you
Speaker 1: could get booted off the island or the Solar system. Yeah,
Speaker 1: because our orbits are fairly fragile. We have to be
Speaker 1: going in the right direction, at the right velocity and
Speaker 1: at the right radius for everything to balance. So orbits
Speaker 1: are not that hard to perturb and they're sort of
Speaker 1: hard to recover. And so you're saying that even if
Speaker 1: our star doesn't collide with another star, just having a
Speaker 1: near miss could be potentially fatal to us. It could
Speaker 1: be fatally Earth could get tossed out of our Solar
Speaker 1: system into the galaxy itself without a star, or we
Speaker 1: could get hit by a comment that gets perturbed by
Speaker 1: a passing star. So how close do we need to
Speaker 1: come to another star for it to be sort of dangerous?
Speaker 1: In order for the Earth to get like tossed out
Speaker 1: of orbit, the star would need to come sort of
Speaker 1: within a few au of our star in order to
Speaker 1: have like the gravity to really perturb the orbit, in
Speaker 1: order to perturb the Org cloud. Well, we don't really know.
Speaker 1: And there's actually a lot of really interesting theories that
Speaker 1: suggests that there might be another star out there. It's
Speaker 1: called the Nemesis that every like thirty million years swoops
Speaker 1: around near our Sun and perturbs all those objects in
Speaker 1: the Org cloud and rains down comments on us. People
Speaker 1: look back at the history of commentary impacts on Earth
Speaker 1: and they think they might see like a pattern, like
Speaker 1: a thirty million years cycle, and that suggests there could
Speaker 1: be something out there doing this regularly every thirty million years.
Speaker 1: Maybe that's how we got our water. It was one
Speaker 1: of these commage howers, right, Yeah, it could be exactly
Speaker 1: a lot of the water on Earth came from comets,
Speaker 1: and so maybe you know, fed us, nurtured us, and
Speaker 1: then it's going to come back and kill us. Well,
Speaker 1: we just have to get umbrellas to fend off all
Speaker 1: that water rain and down giant ice block. So you're saying,
Speaker 1: if another star comes within a few a U s,
Speaker 1: and a U is sort of the distance between the
Speaker 1: Sun and the Earth, right, So if it comes within
Speaker 1: a few distances of Earth and the Sun, then it
Speaker 1: could be big trouble. But if it comes far away,
Speaker 1: it could still cause some trouble by raining comments on us. Yeah,
Speaker 1: anything less than like a light year or so, it
Speaker 1: could be serious problems. What about a direct hit? What
Speaker 1: would happen when two stars sort of directly hit each other,
Speaker 1: So this is much more exciting. If another star comes
Speaker 1: in sort of at high speed, then basically what's going
Speaker 1: to happen is the Sun would be destroyed. If you imagine,
Speaker 1: for example, like a white dwarf, which is a solar remnant,
Speaker 1: like a big hot chunk of metal, and it plows
Speaker 1: into the Sun, and people actually have done simulations about this,
Speaker 1: it would trigger the whole Sun to start burning. Currently,
Speaker 1: fusion is happening, but mostly at the heart of the Sun.
Speaker 1: If a white dwarf comes in, it would increase the
Speaker 1: pressure and the temperature of the Sun so dramatically that
Speaker 1: it would release as much energy through fusion in an
Speaker 1: hour as it would have otherwise in a hundred million years.
Speaker 1: You mean, like just from the impact. It would sort
Speaker 1: of as it's impacting or crashing into the Sun, it
Speaker 1: would actually cause fusion on its way in exactly, it
Speaker 1: would increase the temperature, and so the rate of fusion
Speaker 1: depends on the temperature. So basically the Sun would just
Speaker 1: like burn up super duper fast as this thing passes
Speaker 1: through it. But then it would also explode like that
Speaker 1: much fusion would blow the star out, and so a
Speaker 1: huge chunk of the Sun's energy would be burned up
Speaker 1: in this rapid fusion. A lot of it would get
Speaker 1: blown out because of the radiation from this fusion. And
Speaker 1: then also the Sun might lose its cohesion, like it
Speaker 1: might get sprayed out, like you know, an egg yolk
Speaker 1: or something against the wall sprayed out into the galaxy. Whoa,
Speaker 1: and there goes plans for an over easy solar system.
Speaker 1: But I guess you're saying, you know, the Sun is
Speaker 1: not solid, right, It's a sort of a giant cloud
Speaker 1: of plasma, and so when something crashes into it, it it
Speaker 1: doesn't like crack or break or you know, sort of
Speaker 1: break apart. It sort of takes in whatever it comes
Speaker 1: at it, and maybe that's a lot of energy. Then
Speaker 1: it starts to burn faster. Yeah, but if it comes
Speaker 1: in with enough energy, it could also like pop that
Speaker 1: yoke and spread it everywhere. Imagine like, you know, a
Speaker 1: big fraction of the Sun getting ejected out into the
Speaker 1: Solar system. It could just like totally vaporize a planet.
Speaker 1: What about if it comes in at low speed. If
Speaker 1: it comes in at a smaller speed, then there's a
Speaker 1: chance that it wouldn't actually impact the Sun, that the
Speaker 1: Sun could capture it, that you could end up with
Speaker 1: like a binary star system, or if it comes in
Speaker 1: at just the right angle, you could just get absorbed.
Speaker 1: It's sort of like you know, two yolks forming one
Speaker 1: mega yoke. If it comes in sort of gently and gradually,
Speaker 1: then the two stars could just sort of like merge
Speaker 1: into one bigger star. Interesting, like it can suck it
Speaker 1: in kind of, yeah, it could just suck it in
Speaker 1: because it's not that much interesting structure to the Sun.
Speaker 1: We don't actually really know that much about the convection
Speaker 1: and the currents inside the Sun because things like the
Speaker 1: solar magnetic field are still a mystery to us. But
Speaker 1: in our best model is that it's basically just a
Speaker 1: bag of hydrogen. So you add another bag of hydrogen
Speaker 1: to it, and you know it take a little while
Speaker 1: to stay able. Eyes well, get brighter and have shock
Speaker 1: waves and all sorts of stuff for a few million years,
Speaker 1: but eventually we'd settle down and just be a bigger star.
Speaker 1: So I guess what you're saying is that, you know,
Speaker 1: the collision itself is sort of rare, and you would
Speaker 1: eat sort of a high speed and just enough luck
Speaker 1: to actually have the two stars hit each other. But
Speaker 1: a lot of interesting things canna happen even if there
Speaker 1: are near missus. Yeah, even if they are near missus.
Speaker 1: So if this is star coming near at anytime soon,
Speaker 1: it's going to be dramatic no matter what happens. All right, Well,
Speaker 1: let's talk about other places in the universe where collisions
Speaker 1: between stars are actually inevitable. But first let's take a
Speaker 1: quick break. Alright, we're talking about when stars collide, the
Speaker 1: ones in space, not the ones here on earth that
Speaker 1: make movies, although those are the best crossover events, right, Yeah,
Speaker 1: it does make the best headlines Batman versus Superman, Marvel
Speaker 1: versus DC. When does that movie come? Now? I'm looking
Speaker 1: forward to. Yeah, I know, but we're talking about stars colliding,
Speaker 1: and we talked about how they're sort of rare in
Speaker 1: our neighborhood, but there they happen a lot in other
Speaker 1: places in the galaxy, in the center of the galaxy
Speaker 1: and colobular clusters, and there are sort of um other
Speaker 1: particular situations where these collisions happen a lot and almost
Speaker 1: all the time. Yeah, and our solar system is a
Speaker 1: little bit unusual because it just has one star. If
Speaker 1: you look out into the night sky, turns out that
Speaker 1: a lot of the solar systems out there are binary
Speaker 1: star systems. Stars that were born together, like near each other,
Speaker 1: from the same huge cloud of gas and dust. Doesn't
Speaker 1: always just coalesce into a single star. Sometimes you get
Speaker 1: two dense points there and you get two stars forming.
Speaker 1: It's a lot more common than we used to think.
Speaker 1: And the binary star system like that is really cool.
Speaker 1: It's fun to imagine, but also it's not stable. That
Speaker 1: kind of situation can't last forever. Eventually those two stars
Speaker 1: will collide. Interesting, Now, why are two stars sy them's
Speaker 1: unstable like it's our sources them unstable? Or are all
Speaker 1: orbits unstable? Or is it just the ones between two
Speaker 1: stars that are particularly unstable? Fundamentally, all orbits are unstable.
Speaker 1: And the reason is that when you move in a circle,
Speaker 1: that's acceleration like acceleration is anytime you change your velocity,
Speaker 1: and not just the magnitude of your velocity, not just
Speaker 1: your speed, but your direction. So when the Earth is
Speaker 1: moving around the Sun, for example, it's accelerating. Is a
Speaker 1: velocity vector goes from pointing in one way to pointing
Speaker 1: another way. And anytime there's acceleration, there is radiation. Like
Speaker 1: when an electron turns and goes left, it has to
Speaker 1: kick off a photon in the other direction it radiates.
Speaker 1: This is actually a major puzzle In early quantum mechanics,
Speaker 1: people were wondering, like, why do electrons orbit the atom
Speaker 1: in a stable way? Why don't they emit photons and
Speaker 1: just collapse into the center of the atom. Now, of
Speaker 1: course we understand the answer to that is quantum mechanics
Speaker 1: prevents it from happening. But what about planets. When planets
Speaker 1: orbit a star, or when stars orbit each other, or
Speaker 1: two black holes orbit each other, they are giving off
Speaker 1: gravitational radiation. They are emitting gravitational waves. Any acceleration of
Speaker 1: an object emits gravitational waves. So two huge objects in
Speaker 1: orbit around each other eventually will radiate away some of
Speaker 1: that energy and collapse into the center. Interesting, and that's
Speaker 1: sort of true also for even our Solar system, right like,
Speaker 1: eventually in the far far far far far future are
Speaker 1: orbit it will eventually have fall into the Sun. That
Speaker 1: is true. There's competing effects there because the Earth is
Speaker 1: not nearly as massive as another star, so it doesn't
Speaker 1: generate as much gravitational radiation. But you know, even the
Speaker 1: Earth moving through sort of the solar wind, right the
Speaker 1: Solar system is not empty. As we move through that stuff,
Speaker 1: we lose energy and so we are slowing down. So
Speaker 1: eventually the Earth will fall into the Sun. But that's
Speaker 1: going to happen in a long long time. But when
Speaker 1: two stars orbit each other, two very massive objects, there's
Speaker 1: a lot more gravitational radiation emitted. So two stars orbiting
Speaker 1: each other, that orbit will decay faster than just planets
Speaker 1: orbiting a star. Interesting, and so we we also had
Speaker 1: a whole episode about binary star systems and multi star
Speaker 1: systems and we talked about how unstable and fun they are.
Speaker 1: But you're saying that sort of if you have a
Speaker 1: binary star system, pretty soon it will become I guess
Speaker 1: a one star system. When the two stars collide, either
Speaker 1: something will come by and perturb it, like you have
Speaker 1: a planet and the planet will get thrown out, or
Speaker 1: it will perturb the orbits of the stars around each
Speaker 1: other and they'll just sort of like run off in
Speaker 1: other directions. But if they don't, if nothing comes along
Speaker 1: to perturb it, then eventually they will spiral into each
Speaker 1: other because they'll lose that relative energy and they will collide.
Speaker 1: It's inevitable. Well, it's um kind of a tragic I guess,
Speaker 1: because you know, the binary star systems are pretty cool.
Speaker 1: They're pretty beautiful, right like in Star Wars when Luke
Speaker 1: Skywalker looks out into the sunset he sees two stars. Yeah,
Speaker 1: they are beautiful, but also they're lesions are beautiful. These
Speaker 1: cataclysmic events are really important for creating the elements that
Speaker 1: helped make up you and me and the very nature
Speaker 1: of the universe. So I'm glad that these events exist.
Speaker 1: They're pretty awesome to study, as long as we know
Speaker 1: we're not living around one of those stars. Yes, my
Speaker 1: story now looked Skywalker. That's right, not in my star yard.
Speaker 1: And actually one kind of supernova out there in the
Speaker 1: universe is due to stars colliding, right, It's like, not
Speaker 1: all supernovas are just stars imploding. Some of them come
Speaker 1: from stars colliding. Yeah, one of the most important kinds
Speaker 1: of supernova type one A come exactly when that happens.
Speaker 1: You have a binary star system and one of the
Speaker 1: stars has died distinguished itself, but it wasn't big enough
Speaker 1: to go all the way down to a black hole.
Speaker 1: Like it burned and it generated a lot of light,
Speaker 1: and it came to the end of its life and
Speaker 1: it blew out its outer layers, and what's left is
Speaker 1: a hot core, this thing called a white dwarf. And
Speaker 1: this is like the future of our son. Our son
Speaker 1: doesn't have enough energy in it to go supernova or
Speaker 1: to go black hole. It's just gonna sort of like
Speaker 1: burn explode out its outer layers and then leave us
Speaker 1: with a hot, dense mass at the center, not dense
Speaker 1: enough to become a neutron star or to go supernova
Speaker 1: or become a black hole. So that's sort of the
Speaker 1: future of our star and stars like it. Like it
Speaker 1: just becomes like a white hot object floating in space, right,
Speaker 1: made out of sort of heavier elements. Yeah, it's just
Speaker 1: like white hot metal, you know, like carbon or wherever
Speaker 1: the process stopped. It's the hot heavy core of the star. Remember,
Speaker 1: these stars start burning hydrogen and then they make helium,
Speaker 1: that they make heavier elements, and they just keep burning
Speaker 1: as long as they can. But eventually they make so
Speaker 1: many heavy metals that they can no longer fuse that
Speaker 1: they could basically go out. But what you're left with
Speaker 1: is a huge white, hot chunk of those heavy metals
Speaker 1: just glowing in space. No more fusion happening. So it's
Speaker 1: sort of like a dead end for a star, and
Speaker 1: it just sits there, radiating away its energy until eventually
Speaker 1: it cools. It takes like trillions of years to become
Speaker 1: a black dwarf unless it gets a second act, unless
Speaker 1: it makes a comeback and then somebody cast him in
Speaker 1: an indie movie that gets a critical acclaim. That's right.
Speaker 1: We call this going John Travolta. And what happens is
Speaker 1: that if you have another big star nearby, then this
Speaker 1: white dwarf can steal some of its mass and so
Speaker 1: it like gobbles up the outer layers of like a
Speaker 1: red giant. And so this happens, especially when a white
Speaker 1: dwarf is part of a binary star system, it can
Speaker 1: gobble up some of the mass of the other star
Speaker 1: when it gets close enough and then it has enough
Speaker 1: stuff and it to go supernova. So the supernova that
Speaker 1: didn't happen during the first part of its life can
Speaker 1: now get triggered after the star has basically already died
Speaker 1: because it's getting this additional mass, this extra helping of stuff,
Speaker 1: and it sucks it out of the other star. It's
Speaker 1: just from gravity, right, Like they're near each other, they're
Speaker 1: circling around each other, and it's just the gravity. Sometimes
Speaker 1: the stuff from the red giant sort of hops over
Speaker 1: to the white wharf. Yeah, because the stars have to
Speaker 1: get closer and closer as time goes on, because they're
Speaker 1: radiating away energy, and because that other stars also can
Speaker 1: be expanding its radius. Stars get bigger as they get older,
Speaker 1: and so now the white dwarfs is just gonna be
Speaker 1: like siphoning off some of that mass and the outer
Speaker 1: layers of that star. And so at somebody gets enough
Speaker 1: and then it collapses, right or it doesn't start burning again.
Speaker 1: It just sort of collapses, right, It collapses into a
Speaker 1: supernova and goes boom, yeah, m m yeah, like the
Speaker 1: it turns into iron, right, Like it gets enough pressure
Speaker 1: to actually collapse. What happens to the core depends a
Speaker 1: lot on where it's stopped in its fusion process. But yeah,
Speaker 1: the key is but now gravity can overcome the structure
Speaker 1: of that material, it can compress it even further, and
Speaker 1: so you get this shock wave which causes the supernova.
Speaker 1: Mm hmm. Interesting And so that's the type one A supernovas.
Speaker 1: So it's not like a star naturally exploding. It's like
Speaker 1: it's like another star came in and like excited it,
Speaker 1: and it then it collapsed right exactly. And it's fascinating
Speaker 1: because these are really really important for measuring distances. Like
Speaker 1: when that happens, it happens in a very specific way,
Speaker 1: and the stars have this peak brightness. The whole thing
Speaker 1: lasts just a few days or weeks, depending on the star,
Speaker 1: but we can calibrate that brightness, you know, how bright
Speaker 1: these things are, which means when we see them here
Speaker 1: on Earth, we can tell how far away they are
Speaker 1: by measuring how bright they appear in our telescopes. So
Speaker 1: they've become a really really useful way to measure distances
Speaker 1: to other galaxies, which are otherwise very hard to estimate. Right, Yeah,
Speaker 1: because I think you know, we understand stars so well
Speaker 1: now at this at this point that we know that
Speaker 1: if we see a certain process, we know that it
Speaker 1: involved the star of this size and another star of
Speaker 1: that size, and it couldn't have happened any other way
Speaker 1: with a bigger or a smaller star. So sort of
Speaker 1: we can sort of standardize it, right, and we can
Speaker 1: say that little bright spot there, that's when this size
Speaker 1: star collided with that size star, and that lets us
Speaker 1: know just exactly how far away it is. Yeah, it's
Speaker 1: really pretty cool. We have a whole episode about how
Speaker 1: to know the distance two stars. You should check that out,
Speaker 1: and it requires, you know, calibrating. We using other ideas
Speaker 1: and other strategies for measuring distances and overlapping ladders, so
Speaker 1: we can cause calibrate different metrics. It's really like an
Speaker 1: amazing tour to force of modern science. And so that
Speaker 1: one interesting thing that can happen when two stars glided.
Speaker 1: What are some other interesting mergers or collisions that we
Speaker 1: see out there in the universe. So something we've discovered
Speaker 1: recently is that we can actually see this gravitational radiation
Speaker 1: when stars collide. Einstein predicted this a long long time
Speaker 1: ago that when two stars aren't orbited around each other,
Speaker 1: they will give off gravitational radiation, and that radiation increases
Speaker 1: as the stars get closer and closer and they spin
Speaker 1: around each other faster and faster and faster. And this
Speaker 1: was sort of first detected indirectly when people found a
Speaker 1: pair of pulsars that were orbiting each other and they
Speaker 1: watched them over a few years, and they were able
Speaker 1: to tell that the orbit of the pulsars around each other,
Speaker 1: it was getting faster and faster, that they were sort
Speaker 1: of like falling into each other. The distance between them
Speaker 1: was decreasing and they were speeding up how fast they
Speaker 1: were going around each other. That was sort of indirect
Speaker 1: but then decades later we developed this gravitational wave observatory
Speaker 1: that can see those actual ripples in space time itself,
Speaker 1: the radiation of that energy we were talking about when
Speaker 1: two heavy objects orbit each other, and what happens is
Speaker 1: they go faster and faster and eventually they do collide,
Speaker 1: and cataclysmic collisions like between two neutron stars actually happen
Speaker 1: out there in the universe, and we have seen it. Yeah,
Speaker 1: you can sort of picture did like it two bowling
Speaker 1: balls in a giant rubber sheet sort of circling around
Speaker 1: each other, and like, if they're going fast enough, they
Speaker 1: sort caused ripples and in this rubber sheet. And that's
Speaker 1: kind of what these gravitational waves are, right yeah, And
Speaker 1: it's incredible we can see them out here on Earth.
Speaker 1: We have these lasers underground in mile long tunnels, bouncing
Speaker 1: laser beames off of mirrors, and we can tell when
Speaker 1: a gravitational wave has passed because it makes the path
Speaker 1: of that laser a tiny bit longer or a tiny
Speaker 1: bit shorter, because again it's a ripple in space itself.
Speaker 1: We have a whole podcast episode about gravitational waves and
Speaker 1: you should check out. But today what we're talking about
Speaker 1: is the source of those gravitational waves, which can be,
Speaker 1: for example, the collision of two neutron stars. These things
Speaker 1: are crazy objects, things that are like the mass of
Speaker 1: the Sun but compare acted into something like ten kilometers wide.
Speaker 1: So it's just a really incredible dense stellar remnant, like
Speaker 1: left over from when a star burned and collapsed. This
Speaker 1: is the leftover core the neutron star. Now you get
Speaker 1: two of these things zipping around each other and eventually
Speaker 1: slamming into each other as they radiate away all of
Speaker 1: their energy. Yeah, and I think it's a density that
Speaker 1: makes them special, right, It's like they can get so
Speaker 1: close to each other that the gravity gravitational forces are huge, right,
Speaker 1: Like bigger than anything that we can see here in
Speaker 1: our solar system. Yeah, there's like this hierarchy of density
Speaker 1: like a normal star and then like a white dwarf
Speaker 1: is it is very dense, and then if you get
Speaker 1: enough stuff added to the white dwarf, it could become
Speaker 1: like a neutron star. And then of course even denser
Speaker 1: than neutron star is a black hole, which we think
Speaker 1: is the densest thing in the universe. So it just
Speaker 1: all sort of depends on how much stuff the star
Speaker 1: started with, because that determines how much gravity there is,
Speaker 1: which lets you sort of overcome these thresholds compacting something
Speaker 1: like imagine taking the Earth and trying to turn it
Speaker 1: into a neutron star or a black hole. You have
Speaker 1: to really squeeze it down hard to get to be
Speaker 1: that dense Earth mass and black hole would have to
Speaker 1: be like a centimeter wide. How can you possibly squeeze
Speaker 1: the whole Earth down to a centimeter would take incredible forces.
Speaker 1: That's why it's hard to get these things to be
Speaker 1: so dense. You need a huge mass to get the
Speaker 1: gravity to make it that dense, right, yeah. And you
Speaker 1: know when we listen out for those gravitational waves, you
Speaker 1: can sort of reconstruct what happens when these things collide, right,
Speaker 1: Like you can see them from the waves wave pattern.
Speaker 1: You can see them like circling each other slowly, and
Speaker 1: then it picks up speed and it goes faster and faster,
Speaker 1: and then they're like circling each other super fast, and
Speaker 1: then suddenly pop. You actually sort of see the pop
Speaker 1: where they collide with each other, right, yeah. Absolutely, It's
Speaker 1: like those little machines at science museums where you put
Speaker 1: a penny in it slowly rolls around the top of
Speaker 1: a funnel and by the time it spirals down to
Speaker 1: the core, it's going super duper fast. So you have
Speaker 1: two of these things, and you're right, you can see
Speaker 1: this in the gravitational waves. Like the gravitational waves, they
Speaker 1: start out slow and sort of low amplitude, and they
Speaker 1: get louder and louder and faster and faster. The period
Speaker 1: decreases a lot, and so you can see this exactly happening.
Speaker 1: It's it's really sort of incredible. And then when they collide,
Speaker 1: of course you get something very spectacular. Yeah. I was
Speaker 1: gonna use the analogy of like when you flush the toilet,
Speaker 1: and not a science museum demonstration, but like when you
Speaker 1: flush the toilet, right, you see things circling around the drain,
Speaker 1: and then as they get closer, they go faster and faster,
Speaker 1: and then they collide before they fall down the down
Speaker 1: the hall. Yeah. Also, so it depends on what's in
Speaker 1: the toilet, but yes, yeah, well it could be a
Speaker 1: brown dwarf, Yeah, brown dwarf black hole. All right, well,
Speaker 1: let's get into more interesting collisions of stars out there
Speaker 1: in the universe and what our future of our star
Speaker 1: and our galaxy might be. But first let's take another
Speaker 1: quick break. All Right, we're talking about star visions, and
Speaker 1: we're talking about interesting collisions. We've just talked about what
Speaker 1: happens when a neutron star or a black hole, or
Speaker 1: two black holes or two neutron stars collide with each other.
Speaker 1: It's pretty dramatic. What are some of the other fun
Speaker 1: things that can collide out there in the universe. Well,
Speaker 1: we've been talking about neutron stars colliding with each other,
Speaker 1: which is pretty awesome. And before we move on from that,
Speaker 1: I just want to make the point that that's really
Speaker 1: important for the whole nature of the universe. We used
Speaker 1: to think that the production of really heavy metals, things
Speaker 1: heavier than iron, for example, that can't happen inside stars.
Speaker 1: We used to think that mostly happened in supernova. But
Speaker 1: now we actually know different. We know that that mostly
Speaker 1: happens when neutron stars collide. So most of the gold
Speaker 1: and the platinum and the uranium in the universe came
Speaker 1: from events like that, two neutron stars colliding. To me,
Speaker 1: it's just sort of awesome, Like every piece of jewelry
Speaker 1: you see out on somebody's arm or on their ear
Speaker 1: or somebody's finger came from the collision of two neutron
Speaker 1: stars billions of years ago. Interesting, So it's not made
Speaker 1: out to start dust. It's made like start debris or
Speaker 1: you know, star shrapnel, star glitter, dead stars. Kids out
Speaker 1: there playing with glitter. That's all from dead stars. I
Speaker 1: don't know. But what are some other interesting collisions that
Speaker 1: can happen. Well, sometimes a neutron star collides with something
Speaker 1: that's not a neutron star, like when it's a dual
Speaker 1: neutron star collision. You have two objects really dense boom,
Speaker 1: very cataclysmic. Another time, you can get a neutron star
Speaker 1: colliding with something like a red giant. A red giant
Speaker 1: is a star near the end of its life. It's red,
Speaker 1: it's cooled down a little bit, and it's a giant,
Speaker 1: which means that it's like puffed out its outer layers
Speaker 1: because its core has become really heavy, and so now
Speaker 1: fusion is happening more in the outer layers and that's
Speaker 1: the future of our star. So these really big puffy stars, well,
Speaker 1: if a neutron star hits one of these guys, it's
Speaker 1: really interesting. It might just sort of like fall into it,
Speaker 1: and it could just sort of like hang out inside
Speaker 1: the red giant. It's so dense that it could like
Speaker 1: survive inside another star, like it's an orbit around that star,
Speaker 1: but it's actually sort of inside the limits of it. Yeah,
Speaker 1: this is called a thorn Zitoo object after two astrophysicists
Speaker 1: that predicted it, and we think it's very very rare,
Speaker 1: but there are a few objects out there in the
Speaker 1: sky that sort of have the characteristic signature of one
Speaker 1: of these things, so it might just happen, so maybe
Speaker 1: step me through it. So the super dense neutron star,
Speaker 1: which is not burning but it's super bright, it falls
Speaker 1: into a bigger star that is burning, and so it
Speaker 1: lives inside of it. It does it disrupt it does
Speaker 1: it sort of like stir things up and suck stuff
Speaker 1: out of it. And remember neutron stars not that bright.
Speaker 1: There's no fusion happening in a neutron star, so like
Speaker 1: a white dwarf, it's just sort of like a big
Speaker 1: hot chunk of metal. And we think they mostly glow
Speaker 1: in the X ray at least that's how we study them.
Speaker 1: So what happens is that it orbits in the outside
Speaker 1: part of the star, but eventually it spirals in towards
Speaker 1: the center for the same reason that the neutron star
Speaker 1: like falls into this red giant. Eventually it will fall
Speaker 1: and become like the core and it will suck up
Speaker 1: stuff from that red giant and become a black hole
Speaker 1: and just like eat the entire rest of the star. Well,
Speaker 1: it's like a bad virus kind it's like it comes in.
Speaker 1: It's like an impurity, right, Like the star is happily
Speaker 1: burning along and then this thing comes in and it
Speaker 1: totally disrupts it and takes over it. Yeah, they're like
Speaker 1: eats the star from the inside out. And we've seen
Speaker 1: a bunch of these red giants, and people think that
Speaker 1: you might be able to tell what's happening on the
Speaker 1: inside of the star by looking at what's happening on
Speaker 1: the outside of the star. Like the fraction of various
Speaker 1: kinds of nuclei that appear on the surface depend on
Speaker 1: the temperature of the inside of the star. And if
Speaker 1: you have one of these red super giants with a
Speaker 1: neutron star at its core that's turning into a black hole,
Speaker 1: that would make the star much hotter, so it burn
Speaker 1: a little differently, so it look a little bit different
Speaker 1: on the outside. But it's pretty interesting. Yeah, And you
Speaker 1: can actually see maybe one of these events happening out there, right,
Speaker 1: I mean, the space is so big you probably can
Speaker 1: find an example of it. And there's a sort of
Speaker 1: a cool one that you can see called the necklace nebula, right, Yeah,
Speaker 1: the necklace nebula is this beautiful sort of like glitter
Speaker 1: are of shiny diamonds in the sky like surrounding a
Speaker 1: central object and a stromers think that ten thousand years ago,
Speaker 1: one star expanded sort of like sucked up its neighbor
Speaker 1: companion star, which then continues to sort of orbit inside
Speaker 1: the larger star, which you know, sort of like stirred
Speaker 1: it up like a you know, a spoon in batter.
Speaker 1: If you mix up your spoon too fast, you end
Speaker 1: up like spewing batter outside of the bowl. And so
Speaker 1: this sort of happened to the bigger star. The little
Speaker 1: star inside of it sort of like ruined it and
Speaker 1: spewed bits of it out. And so now what we
Speaker 1: see is this like pattern of basically splashes in the sky. Yeah,
Speaker 1: you can look it up on the internet. The necklace
Speaker 1: nebula and it sort of looks like a necklace, right
Speaker 1: with a shiny diamonds in it. Yeah, exactly. And that's
Speaker 1: what happens when one star totally messes with another star,
Speaker 1: like it stirred it up and spread it out. It
Speaker 1: made beautiful jewelry made blink for all the Hollywood Stars
Speaker 1: universe bling. All right, Well, um, those are some pretty
Speaker 1: cool collisions we can see out there in the universe
Speaker 1: with what at our future, Like, what's going to happen
Speaker 1: to our star, our galaxy. I mean, we talked about
Speaker 1: how it's sort of rare that they probably won't happen
Speaker 1: to us anytime soon. But there's another galaxy coming our way.
Speaker 1: There is another galaxy coming our way, our neighbor, galaxy Andromeda,
Speaker 1: is going to impact the Milky Way in about four
Speaker 1: and a half a billion years. It's coming right for us.
Speaker 1: And people who look up at the sky, you know,
Speaker 1: you're familiar with the Moon, of course, and a bunch
Speaker 1: of stars and maybe even like the splash of the
Speaker 1: Milky Way, but also up there in the sky our galaxies.
Speaker 1: You can see galaxies up there in the sky. The
Speaker 1: problem is that mostly they're very, very dim, so you
Speaker 1: need a telescope to see them. But they're out there,
Speaker 1: and that's sort of like the vast cosmic sweep of
Speaker 1: your view. You can see out there billions of light
Speaker 1: years past our Milky Way. Yeah, and you can see
Speaker 1: a ton of galaxies out there. There are trillions of
Speaker 1: them out there, right, that's right. And mostly they're really
Speaker 1: really distant, and so they're super duper small and not
Speaker 1: very bright. And Dromeda, however, is our neighbor, and so
Speaker 1: it's actually quite near and quite large in the sky.
Speaker 1: You can't see it with the naked eye because it's
Speaker 1: so dim, but if it were brighter, it would appear
Speaker 1: larger in the night sky than the full moon. It's
Speaker 1: like really big and quite close. Interesting, and it's coming
Speaker 1: our way sort of like right, we're on a collision course,
Speaker 1: but we are on a collision course with it exactly.
Speaker 1: So the gravity of all those billions and billions of
Speaker 1: stars are tugging on our billions and billions of stars,
Speaker 1: and eventually we will collide. Because Andromeda in the Milky
Speaker 1: Way are part of this cluster of galaxies we call
Speaker 1: the local cluster, sort of like a loosely bound group
Speaker 1: of clusters. They're held together by each other's gravity and
Speaker 1: sort of swirling around each other. It's all very slow
Speaker 1: motion and takes billions of years for anything interesting to happen.
Speaker 1: But galaxies do collide. And if you look out there
Speaker 1: in the space, we can see so many galaxies that
Speaker 1: there are lots of examples of galaxies colliding, perturbing each other,
Speaker 1: then settling down again into spiral galaxies. And we think,
Speaker 1: for example, the Milky Way has already survived several collisions.
Speaker 1: Really you can see sort of the scars of it,
Speaker 1: or like, are you saying some of these globular clusters
Speaker 1: maybe we're collisions, maybe the globular clusters. But also if
Speaker 1: you look at the shape of the Milky Way, for example,
Speaker 1: it's not flat, like it's not a flat disc. It
Speaker 1: has a bit of a warp to it. And some
Speaker 1: people think that might be because we're still settling down
Speaker 1: from a recent collision or merger with another galaxy. So
Speaker 1: now we're we just went up a level, right when
Speaker 1: we went up from stars colliding to galaxies colliding, and
Speaker 1: so kind of what happens when two galaxies collide, because
Speaker 1: galaxies don't have sort of a structure, right, they're more
Speaker 1: mostly like sort of clouds of stuff. Yeah, there is
Speaker 1: a structure in the sense that there's like a density
Speaker 1: of the core and sometimes a supermassive black hole. Mostly
Speaker 1: they're just big, diffuse clouds of stars and gas and dust.
Speaker 1: And you might imagine that when two galaxies collide it
Speaker 1: would be really dramatic all the stars would explode, etcetera.
Speaker 1: But actually stars are really far apart, and so when
Speaker 1: two galaxies collide, you don't actually get very many collisions,
Speaker 1: maybe just like a few you know, five or ten
Speaker 1: stars actually collide. Mostly it happens sort of slowly and
Speaker 1: they just kind of merge. It's like two crowds walking
Speaker 1: into each other. Right, they just sort of like become
Speaker 1: one bigger crowd. Very few actually, like you know, accidents really,
Speaker 1: so I'm a nott of surprised only five to ten
Speaker 1: collisions of stars would happen, Like, aren't doesn't each galaxy have,
Speaker 1: you know, trillions of stars. Wouldn't that just sort of
Speaker 1: increase exponentially the likelihood of collisions happening, Like, thanks, you
Speaker 1: just got twice as crowded, right, Well, it becomes a
Speaker 1: bigger galaxy, so it's not necessarily twice as crowded, just
Speaker 1: a larger number of stars, like and Drama is already
Speaker 1: much bigger than the Milky Way, probably because it's already
Speaker 1: eaten other galaxies. And so what happens. You just become
Speaker 1: like a bigger galaxy orbiting like a common center of mass.
Speaker 1: So you don't actually get that many star collisions. You
Speaker 1: just get this sort of like new shape. It takes
Speaker 1: like sometimes a billion years or so to settle down
Speaker 1: into a steady path, but the stars are pretty far
Speaker 1: apart from each other. Wouldn't they merge though, wouldn't Like
Speaker 1: the dramatic cloud sort of merged with our cloud and
Speaker 1: suddenly things are more dense. Well, they definitely do merge,
Speaker 1: but because of the rotation speed, things don't all collapse
Speaker 1: into the center. So you get a lot of stars
Speaker 1: that are still far out from the center that are
Speaker 1: moving really really fast. Right. The reason that the galaxy
Speaker 1: doesn't collapse into like a super dense blob of stars
Speaker 1: is because all these stars are moving pretty fast around
Speaker 1: the center, the same reason the Earth doesn't fall into
Speaker 1: the Sun immediately. So when these galaxies collide, they keep
Speaker 1: that spin and they keep going around the center and
Speaker 1: sometimes even faster because now you have like the relative
Speaker 1: angular velocity of the two galaxies, and so they don't
Speaker 1: all just collapse into a dense blob. It can become
Speaker 1: like a really huge, spread out new galaxy. Right Yeah.
Speaker 1: But also like the collision would disrupt the structure of
Speaker 1: both galaxies, right, just like if you have two stars
Speaker 1: or two solar systems colliding into each other, like it
Speaker 1: would be chaos kind of, right, Like everything would be
Speaker 1: thrown out of balance, it would, But those things are
Speaker 1: typically much more separated like a solar system is a
Speaker 1: very dense object compared to a galaxy. The distances between
Speaker 1: stars as much much bigger relatively speaking than the distances
Speaker 1: between planets. But also galaxies of other stuff. And then
Speaker 1: they're not just stars, right. Galaxies also have huge clouds
Speaker 1: of gas and dust places that new stars can form.
Speaker 1: And when two galaxies collide, what does happen is that
Speaker 1: those clouds of gas and dust collide. Those are not
Speaker 1: like diffuse, those are really thick clouds relatively speaking, So
Speaker 1: that triggers a lot of activity because that triggers like
Speaker 1: new star formation. You shoot one big cloud or another
Speaker 1: big cloud, and those shock waves can trigger the gravitational
Speaker 1: runaway effect that leads to new stars being formed. Wow.
Speaker 1: So mostly we should be looking at the collision of
Speaker 1: gas and dust because then that makes new stars exactly.
Speaker 1: Mostly what happens when galaxies collide is the collision of
Speaker 1: the gas and dust that makes new stars. And so
Speaker 1: we'll have some stars from the Milky Way, some stars
Speaker 1: from and Drameda, and then some brand new stars from
Speaker 1: this new galaxy. New neighbors are moving in, hopefully not
Speaker 1: too close, but that's if we survive long enough to
Speaker 1: even see that collision. Yeah, I guess four point five
Speaker 1: billion years is a long time, right, Like by then
Speaker 1: the we might not even be on Earth. The Sun
Speaker 1: is gonna pete route ride around then, and so we
Speaker 1: got a few billion years to make a plan for,
Speaker 1: you know, get to a new home because the Sun
Speaker 1: will no longer be a happy place to orbit in
Speaker 1: five billion years. Sounds like a good time to hop
Speaker 1: over to our new galaxy jump ship. That's right, there's
Speaker 1: lots of empty apartments over there, hopefully may or maybe
Speaker 1: stored there. Maybe they're crowded too, but there's some dangerous
Speaker 1: coming well before four billion years have passed. You mean,
Speaker 1: not from Andromeda. Yeah, we talked about how it's very
Speaker 1: unlikely for our star to collide with another star, but
Speaker 1: astronomers have looked all the stars nearby and tried to
Speaker 1: calculate like when there might be a near miss. And
Speaker 1: there is another star it's called Glease, and astronomers think
Speaker 1: that in a million years it's going to pass within
Speaker 1: one fifteen of a light year of our solar system.
Speaker 1: So not a direct collision, but like pretty close to
Speaker 1: our neighborhood and thing, So what do you mean we
Speaker 1: think like we we can see all the stars in
Speaker 1: our neighborhood and we can probably track them. What where's
Speaker 1: the uncertainty? I was just trying to make people feel better. Yeah,
Speaker 1: it's pretty certain it. I see it's coming. It's coming exactly.
Speaker 1: So at one fifteenth of a idea, how much is
Speaker 1: that in kilometers or a US? So that's about four
Speaker 1: thousand a US. So it's well within our solar system
Speaker 1: if you include, for example, the Orc Cloud, which goes
Speaker 1: out like tens of thousands of a use, but it's
Speaker 1: much further out than like the most distant planets, but
Speaker 1: plenty close to disturb the Orc Cloud. It's gonna pass
Speaker 1: right through the Orc Cloud. It's going to create crazy
Speaker 1: showers of comments. So it is we are sort of
Speaker 1: technically going to collide our solar system if you include
Speaker 1: the Orc Cloud and all those things out there in
Speaker 1: the fringes, it is going to collide with this other star. Yeah,
Speaker 1: and you know, our Orc cloud is probably always getting
Speaker 1: little gravitational tugs from close by stars and that might
Speaker 1: be what's driving comments. But yeah, this star is going
Speaker 1: to come smash right into our Orc Cloud, and it's
Speaker 1: going to be a crazy meteor shower. I hope that
Speaker 1: we survive it. Wow, well again, we just we need
Speaker 1: a pretty big umbrella. And it's probably coming with its
Speaker 1: own or cloud, right like, every solar system probably has
Speaker 1: a collection of these icy objects. So when our I
Speaker 1: objects glide with its icy objects, who knows what's going
Speaker 1: to happen? Right like, our solar systems might mix. So
Speaker 1: do scientists know what's gonna happen? Are we're gonna emerge
Speaker 1: with it? It is just going to be a drive by.
Speaker 1: It's gonna start orbiting our solar system. What's gonna happen, Well,
Speaker 1: it's going to pass through fast enough that it's not
Speaker 1: going to form a binary star system, but it's very
Speaker 1: likely to perturb the orbits of the planets and to
Speaker 1: cause a lot of commentary showers. Exactly what happens depends
Speaker 1: on exactly where the planets are when it comes by,
Speaker 1: and we don't have enough certainty to make that prediction.
Speaker 1: But we will probably see it in the night sky though,
Speaker 1: right like we'll see the star swinging by. Yeah, it's
Speaker 1: gonna be brighter than the planet Venus, and you'll be
Speaker 1: able to see it during the day, So you know,
Speaker 1: put a notification in your calendar, Siri, set a reminder
Speaker 1: for one million years from today, look for this star,
Speaker 1: look outside and bring an umbrella. All right, well, that
Speaker 1: might be maybe the closest to a star collision our
Speaker 1: sun will ever get right, I mean, that's that's about it, right,
Speaker 1: let's hope. What do you mean, could something unexpected happen?
Speaker 1: I don't want a collision even closer than that. Anything
Speaker 1: close to that is guaranteed to be a cataclysm for humanity.
Speaker 1: But you're saying that's the closest we can expect, at
Speaker 1: least in the next you know, a few billion years,
Speaker 1: a few million years. Yes, all right, Well, I guess
Speaker 1: it's a pretty wild and crazy universe. You know. Collisions
Speaker 1: do happen. Stars do collide. Even though there's a lot
Speaker 1: of space out there, and there are there's a lot
Speaker 1: of space between stars. It does happen because it's a
Speaker 1: it's a big universe. Yeah. We are in a tiny
Speaker 1: little cosmic road floating on a huge, crazy chaotic ocean,
Speaker 1: and it seems stable only because it's moving so slowly. Yeah,
Speaker 1: so make sure you bring an umbrella, were a helmet
Speaker 1: when you jump into the stellar mosh pit of the
Speaker 1: universe and hope for the best and keep an eye out.
Speaker 1: I guess well, maybe we'll bump into the stellar version
Speaker 1: of Brad Pitt at the grocery store and just don't
Speaker 1: steal his cookies. That might anger Angelina Julian and then
Speaker 1: you'll have two stars, you know, colliding with you. Well,
Speaker 1: we hope you enjoyed that. Thanks for joining us, see
Speaker 1: you next time. Thanks for listening, and remember that Daniel
Speaker 1: and Jorge Explain the Universe is a production of I
Speaker 1: Heart Radio or more podcast from my heart Radio. Visit
Speaker 1: the I heart Radio app, Apple Podcasts, or wherever you
Speaker 1: listen to your favorite shows.