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