Speaker 1: Hey, Daniel, what keeps you up at night? Oh? I
Speaker 1: worry about a lot of things. Financial crises, my kids
Speaker 1: growing up to be just like me, all sorts of stuff.
Speaker 1: I worry about that too for them. You worry about
Speaker 1: my kids growing up to be just like me. We
Speaker 1: can't have more of him in the world, Okay, But
Speaker 1: like on a galactic scale, on a universe scale, what's
Speaker 1: something we should be concerned about. Well, we do have
Speaker 1: a lot of things look forward to in terms of
Speaker 1: our galaxy. If we survived the Sun exploding and the
Speaker 1: waters the Earth boiling off, then we have something pretty
Speaker 1: dramatic to look forward to, which is that our galaxy,
Speaker 1: the Milky Way, is going to collide with their nearest
Speaker 1: neighbor and Dromeda. Meaning right now, there's an entire galaxy
Speaker 1: Drameda heading towards us at this very moment. That's right.
Speaker 1: It's like somebody shot it at us with a slingshot
Speaker 1: and it's zooming right towards us, and it's going to
Speaker 1: hit us smack on him. And I'm Daniel, and this
Speaker 1: is our podcast. Daniel and Jorge explained the universe on
Speaker 1: the episode. Today, we're going to talk about what will
Speaker 1: happen when galaxies collide. Is this something we should all
Speaker 1: be worrying about our packing our bags, about building our
Speaker 1: underground shelters or are we all screwed? Or is it
Speaker 1: just going to be like a big nothing? How much
Speaker 1: should I pack? You should definitely be stalking lentils no
Speaker 1: matter what. Lentils are a good investment for any of
Speaker 1: these end of the world. Not just beans, no, no, lentils.
Speaker 1: I mean lentils are kind of lego for a galactic emergency.
Speaker 1: That's the that's the one to go with. Yeah, absolutely,
Speaker 1: I would. I would invest in lentils heavily. And it's
Speaker 1: not just because I happened to purchase lentils just before
Speaker 1: we recorded this podcast and I'm trying to drum up
Speaker 1: the lentil futures, you know. I'm I'm sincerely worried about
Speaker 1: our listeners, and I encourage you all to go out
Speaker 1: there in stockpi lentils. Well that's a whole hill of
Speaker 1: beans worth of advice right there, that's right. And so
Speaker 1: this is the question and today's podcast, what will happen
Speaker 1: when our galaxy, the Milky Way, collides with the neighboring galaxy?
Speaker 1: And this question I love not just because it's huge
Speaker 1: and dramatic and galactic and all this sort of stuff,
Speaker 1: but because it was suggested by one of our listeners.
Speaker 1: That's right. It's Blake from Australia who listens to this
Speaker 1: podcast on her commute to work every day. That's right.
Speaker 1: And she didn't tell us what she uses to commute.
Speaker 1: Maybe she rides in a beautiful pickup truck, maybe she's
Speaker 1: in the back of a limo, maybe rides kangaroo who knows,
Speaker 1: that's right, with a really nice sound system. Yeah, but
Speaker 1: she has some interesting feedback for us about our podcast. Right,
Speaker 1: what did she say? Yeah, she said that she likes
Speaker 1: listening to me explain things, but she also likes when
Speaker 1: you interrupted me. She said that often you interrupt me
Speaker 1: just the same moment when she has a question and
Speaker 1: you pose the same question that was bouncing around in
Speaker 1: her head that she was shouting at her limo sound
Speaker 1: system or kangaroo speakers or whatever it is she us
Speaker 1: going to listen to. And so I was glad for that,
Speaker 1: because you know, I like when you interrupt me. Also
Speaker 1: it breaks the flow and it keeps me from just
Speaker 1: droning on and on and on. So Thank you Blake
Speaker 1: for suggesting this topic, and thank you Orge for occasionally interrupting. Yeah, no,
Speaker 1: I'm happy to be rude. It seems to come naturally. Yeah, yeah,
Speaker 1: And so that's the topic of today's podcast, And we
Speaker 1: thought first before we dove into it, we would walk
Speaker 1: around like we usually do and ask people, are you
Speaker 1: worried about a galactic collision? What do you think will
Speaker 1: happen when our galaxy collides with a neighboring galaxy? So
Speaker 1: put that image in your mind to giant galaxies, full
Speaker 1: stars running into each other. What do you think is
Speaker 1: going to happen? Here's what people had to say, big explosion.
Speaker 1: We'd probably all die. It is going to be mostly
Speaker 1: nothing because of all the empty space around the world,
Speaker 1: although there will be some crushes and so on in
Speaker 1: the way. Okay, probably somewhere between a glacial, slow event
Speaker 1: that we won't even notice and nothing at all. Maybe
Speaker 1: leaning towards nothing at all. I think it would probably
Speaker 1: be a big explosion with something pretty crazy happening. All right,
Speaker 1: That was a little anti climatic. People seem to have
Speaker 1: very low expectations of this event. What do you mean
Speaker 1: It seems like half of the people are like it's
Speaker 1: gonna be nothing, and the other half of like big explosions,
Speaker 1: we're all gonna die. Well, why do you why do
Speaker 1: you think Blake asked this question? Do you think there's
Speaker 1: something she's concerned about or is something she's curious about?
Speaker 1: You know? I think Blake is probably deciding whether or
Speaker 1: not to stock up on lentils. You know, Um, she's
Speaker 1: probably right now, story she asked. I think it's part
Speaker 1: of just trying to be a sort of a citizen
Speaker 1: of the larger universe, you know, wondering where we stand
Speaker 1: and trying to think bigger than just our planet, you know,
Speaker 1: because there's so much going on out there, it's so
Speaker 1: easy to just walk around on the surfaces planet never
Speaker 1: really look up and remember that there is an enormous
Speaker 1: amount of stuff happening out there, And then you wonder like, well,
Speaker 1: how is that relevant to me? And is he going
Speaker 1: to ruin my life? Or can I go on ignoring it? Um? So,
Speaker 1: I think maybe she was just sort of thinking into
Speaker 1: the deep future and wondering like, how long can this
Speaker 1: whole ridiculous, beautiful thing we call life on Earth go on? Right?
Speaker 1: Is it going to change from how it is now, right, Yeah,
Speaker 1: exactly do I need to change the way I live?
Speaker 1: Does it affect any decision making? On the other hand,
Speaker 1: it could be that Blake, like many people, is just
Speaker 1: a thinker and likes to think about these scenarios, and
Speaker 1: she probably heard that the Milky Way will collide with
Speaker 1: Andromeda and wonder like, what's that going to be? Like?
Speaker 1: You know this this this is the other side of
Speaker 1: me that likes to smash stuff together. I mean, I'm
Speaker 1: a particle physicist, but then we have the whole universe
Speaker 1: to play with, right, and so you might wonder, like
Speaker 1: what happens when planets collide, what happens when solarcisms? Like
Speaker 1: oh my gosh, what if we could build a galaxy
Speaker 1: collider and shoot them against each other and smash them
Speaker 1: into each other? Right, So it just comes out of
Speaker 1: like a curiosity to see stuff break by smashing it together. Yeah, well,
Speaker 1: let's let's take it step back and just kind of
Speaker 1: think about why even galaxies would collect, Like is this
Speaker 1: a relevant question that is something that happens a lot
Speaker 1: galaxies colliding, or is it something that's incredibly rare. It
Speaker 1: turns out galaxies colliding happens all the time. It's like
Speaker 1: a totally natural thing. And our galaxy. Yeah, not only
Speaker 1: will our galaxy collide with and John Day in a
Speaker 1: few billion years, it's currently colliding with other smaller galaxies.
Speaker 1: That what Yeah, we're in a collision right now. Yeah,
Speaker 1: that's right. And remember that the galactic time scales are
Speaker 1: very different. You know, the galaxy takes about two hundred
Speaker 1: million years just to rotate once, to go around once. Yeah,
Speaker 1: so one galactic year is two hundred million earth years.
Speaker 1: But it looks so swirly. It looks you know, you
Speaker 1: know what I mean, Like it looks like it's in motion,
Speaker 1: but it's actually it is. It is in motion, it's
Speaker 1: just very slow, right, And so all these things are
Speaker 1: dancing around each other and sometimes they bump into each other.
Speaker 1: And the thing I think is amazing is that, you know,
Speaker 1: until like a hundred years ago, we didn't even know
Speaker 1: there were other galaxies. Like we looked up at the
Speaker 1: night sky and we saw stars, and we thought, oh,
Speaker 1: there's just stars that go on forever. At the universe
Speaker 1: is just filled with stars. The universe is just like
Speaker 1: a giant MESSI pinpoints, right, just stars. Yeah, yeah, like
Speaker 1: somebody had scattered stars across the cosmos, right, And it
Speaker 1: was Hubble, the guy for whom the telescope and the
Speaker 1: constant are named. He's the guy who figured out, oh,
Speaker 1: some of those things that are really far out there
Speaker 1: are not stars. There are other galaxies. Right, So there's
Speaker 1: the universe is filled with other galaxies. And of course
Speaker 1: there are more galaxies than stars, and and then each galaxy,
Speaker 1: of course, contains hundreds of billions of stars, and so
Speaker 1: the numbers pretty quickly blow your head up before you
Speaker 1: can understand them. But the point I wanted to make
Speaker 1: was that we didn't realize there were galaxies until recently,
Speaker 1: and now we're realizing that galaxies are in motion relative
Speaker 1: to each other, and they're moving. Like the these galaxies
Speaker 1: that we see out there in the sky, they're not
Speaker 1: just like hanging there in space never to change, right,
Speaker 1: They are moving their dynamic things, and they're constantly in motion,
Speaker 1: and they have huge gravitational attraction. Well, let's break it down.
Speaker 1: What exactly is a galaxy? I mean, I know it's
Speaker 1: like kind of like a collection of stars, but you
Speaker 1: know what, why do stars clump together like that? First
Speaker 1: of all? And what makes a galaxy special? Like, why
Speaker 1: is it more than just a clump of stars. Well,
Speaker 1: what makes our galaxy special is that you're in it. Horse.
Speaker 1: There's no other galaxy that features such a good looking,
Speaker 1: funny cartoonists, meet me and lentils. We make it, make
Speaker 1: it habitable, right, Okay, so what's the recipe for a galaxy? Right? Well,
Speaker 1: the thing that the galaxies have the most of, remember,
Speaker 1: is dark matter. In general, there's about five times as
Speaker 1: much dark matter as there is any other kind of matter,
Speaker 1: you know, the stuff that makes up gas and dustin
Speaker 1: stars and people and cartoonists and and and ice cream.
Speaker 1: So it's mostly dark matter. So that's the stuff we
Speaker 1: can't see your touch. I mean, we did a whole
Speaker 1: podcast episode on dark matter, but it just in case
Speaker 1: somebody didn't listen to it. Um, it's like this weird
Speaker 1: invisible dark gravity thing that's hanging out every galaxy has,
Speaker 1: that's right. Yeah, we call it dark and matter because
Speaker 1: we can't see it. So it's dark and we know
Speaker 1: it gives gravity, so therefore it's matter and the crazy
Speaker 1: things that until you know, a few decades ago, we
Speaker 1: didn't even know it existed. And now we know that
Speaker 1: galaxies are mostly made up of this stuff. Right. So
Speaker 1: number one ingredient when you want to make a galaxy
Speaker 1: is you have to have dark matter. It's like five
Speaker 1: times more than the stars, right, yeah, exactly, Like a
Speaker 1: galaxy is basically a clump of dark matter with a
Speaker 1: few sprinkles of stars in it. That's right. Yeah. If
Speaker 1: a galaxy was a cupcake, right, the dark matter would
Speaker 1: be the chocolate cake, and you know there everything else
Speaker 1: would be the frosting and the sprinkles. The gas and
Speaker 1: the dust would be the frosting. The stars would be
Speaker 1: the sprinkles on top. Oh I see, Okay, that's kind
Speaker 1: of the right proportions. Yeah, something like that. Um, So
Speaker 1: you start with big blob of dark matter and that's
Speaker 1: most of it, and then after that you have huge
Speaker 1: amounts of gas and dust, right, And that's the stuff
Speaker 1: that's left over from the Big Bang or left over
Speaker 1: from stars exploding, and those the ingredients you need to
Speaker 1: make planets and stars and all sorts of stuff that
Speaker 1: you're familiar with, right. And so you have dark matter,
Speaker 1: you have gas, you have dust, you have planets and
Speaker 1: stars and black holes right, Like there's just a little
Speaker 1: black hole sprinkled throughout throughout probably, But there's a huge
Speaker 1: giant black hole at the center of every galaxy. That's right.
Speaker 1: I can't believe I forgot the black hole. The black
Speaker 1: hole at the center of almost every galaxy is huge.
Speaker 1: It's like, you know, millions of solar masses and it's
Speaker 1: sitting there at the center of the black hole, and
Speaker 1: it's it's got a lot of stuff to it also, right,
Speaker 1: it carries a lot of mass and so it contributes.
Speaker 1: So that's what a galaxy is. And you know, a
Speaker 1: galaxy couldn't really form without all those elements, Like you
Speaker 1: couldn't really have a galaxy without dark matter because dark
Speaker 1: matter provides the gravitational attraction to suck all this stuff together.
Speaker 1: You know, they do these simulations of the universe. They say,
Speaker 1: what would the universe look like if you never had
Speaker 1: dark matter in it? And it would take a lot
Speaker 1: longer for galaxies to form because dark matter has pulled
Speaker 1: all this stuff together. It's like it's made a you know,
Speaker 1: like a well in the rubber sheet of the universe,
Speaker 1: so everything rolls together more closely. Okay, so that's a
Speaker 1: that's a galaxy. It's a black hole surrounded by dark
Speaker 1: matter and sprinkles of stars and gas and dust and
Speaker 1: lintels and lintels exactly yes, And so they're not just
Speaker 1: hanging out in space. They're moving around. That's right there.
Speaker 1: Each one is spinning, right, which is why you see
Speaker 1: a lot of them having these these spiral features. Each
Speaker 1: one is spinning, and then they're also moving around each other.
Speaker 1: They have gravity and they're moving around each other, and
Speaker 1: they have these Each galaxy is a member of a
Speaker 1: cluster of galaxies, and so these guys are orbiting the
Speaker 1: center of the cluster. And then the clusters are members
Speaker 1: of superclusters. So these things have a lot of gravitational
Speaker 1: interactions everywhere. It's like a system of galaxy. They all
Speaker 1: interact with each other, and they all spin around their
Speaker 1: common center of mass exactly right, And they're all spinning
Speaker 1: around that center. So it's sort of like a big
Speaker 1: slow motion tornado. Right you looked at it. If you
Speaker 1: looked at it really really slow, you're like, oh, nothing's
Speaker 1: really moving. I mean, I guess a little bit, but
Speaker 1: you you you watch it at natural speed of tornado,
Speaker 1: and obviously it's going really fast, and so a galaxy
Speaker 1: is that's sort of that same way. The gather system
Speaker 1: of galaxies is sort of that same way, but they're
Speaker 1: all moving around each other and then occasionally, you know,
Speaker 1: they bump into each other. Wow, that's so weird to
Speaker 1: think that gravity works the way like we are, you know,
Speaker 1: moving around the center of the Earth. The Earth is
Speaker 1: moving around our solar system, around the center of gravity,
Speaker 1: which is mostly the Sun, but the Sun is also
Speaker 1: we were moving around the center of gravity of the galaxy,
Speaker 1: and the galaxy is also moving around the center of
Speaker 1: gravity of its cluster of galaxies. That's right, Yeah, and
Speaker 1: on and on and on like a bunch of nested
Speaker 1: Russian dolls, you know, until you get to the biggest
Speaker 1: structures in the universe, you know, which are the superclusters,
Speaker 1: and then the filaments of superclusters, and beyond that, we
Speaker 1: don't know anything about whether there are bigger and bigger structures.
Speaker 1: That's as far as we've seen. So we're moving around
Speaker 1: and sometimes these two two galaxies can just run into
Speaker 1: each other. In the giant, vastness of space, all these
Speaker 1: moving galaxies can sometimes cross pass right. Yeah. And there's
Speaker 1: another thing I want to say about that before we
Speaker 1: talk about what actually happens, which is that it's incredible
Speaker 1: to me that gravity is the force that's dominant on
Speaker 1: these scales, right, Like, that's the thing that's controlling how
Speaker 1: galaxies form and how they dance around each other, and
Speaker 1: that's pulling them all the way through the universe and
Speaker 1: forming these crazy structures. It's all gravity, right. But gravity
Speaker 1: is the weakest force of nature. It's weaker than electromagnetism,
Speaker 1: it's weaker than any of the nuclear forces. It's pathetically weak,
Speaker 1: but it's the only one that operates on these huge scales,
Speaker 1: and it can't be balanced out. And so because it's
Speaker 1: only an attractive force, there's no repulsive version of it.
Speaker 1: And so that's why, like on these huge scales, gravity
Speaker 1: is the thing that dominates. Gravity determines the structure the
Speaker 1: Solar system, the structure the galaxy, the structure of the clusters.
Speaker 1: Gravity sort of winds in the end. It's like, you know,
Speaker 1: revenge of the nerd forces, Right, It's the weakest force
Speaker 1: in the end controls the universe. It's like slow and
Speaker 1: steady wins the race. It's the turtle of forces. Yeah, Anyway,
Speaker 1: we need to do a whole other podcast on why
Speaker 1: gravity is so weird and weak and whatever, and we're
Speaker 1: into that. Okay, so we have a cult clusters and
Speaker 1: galaxies are moving around space and sometimes they collide. So yeah,
Speaker 1: let's talk about what actually happens when two of these
Speaker 1: things collide. But first let's take a quick break. All right.
Speaker 1: So we're sitting in a galaxy and we are moving
Speaker 1: inside of this galaxy, and this galaxy is moving in space.
Speaker 1: But there's another galaxy nearby called the Andromeda galaxy, and
Speaker 1: it's kind of an interset course with us, right, like
Speaker 1: we're going to run into it in about four and
Speaker 1: a half billion years. Yeah, not kind of. They've measured it.
Speaker 1: They can measure the velocity of Andromeda relative to us,
Speaker 1: and they can see that it's getting closer and closer
Speaker 1: every year, and they can also measure the lateral velocity,
Speaker 1: like is it going to shoot by us or just
Speaker 1: or come right at us? And after for a while
Speaker 1: they weren't sure. They were like, oh, it's heading our way,
Speaker 1: but it could miss, you know, like every time they
Speaker 1: say there's an asteroid coming within, you know, a certain
Speaker 1: thousands of miles of the Earth, and usually it misses.
Speaker 1: For a while, they weren't sure, but now they're pretty
Speaker 1: certain they've taken enough measurements, they've seen it move, and
Speaker 1: they can project confidently that these two things are going
Speaker 1: to collide. Also, Andromeda and Milky, we have a lot
Speaker 1: of gravity, and so you don't have to aim perfectly
Speaker 1: to get a collision, right, They're gonna um pull each
Speaker 1: other closer and closer. They want to collide, you know,
Speaker 1: you know what I mean, Like, it's not like a
Speaker 1: random asteroid. It's like we're we're pulling towards each other. Yeah, well,
Speaker 1: I don't know if you can really say they want Like,
Speaker 1: do you understand the psychology of the galaxy? Do you you
Speaker 1: know what galaxy wants in life? You know, Hey, galaxy
Speaker 1: have feelings, right, I think I read that science fiction
Speaker 1: novel right where every galaxy is actually a living thing
Speaker 1: and we're just like the tiny moats on the on
Speaker 1: an island of red blood cells instead of galaxy. Anyway, Yeah,
Speaker 1: so you don't have to shoot perfectly, and they're gonna collide.
Speaker 1: So to think about what happens in the collision, you
Speaker 1: probably think about each individual piece separately, Like we're a
Speaker 1: cluster of things. Like a galaxy is not a solid object.
Speaker 1: It's like a word almost like a cloud of things,
Speaker 1: right is that kind of way? Mean? Yeah, yeah, exactly.
Speaker 1: And you know, imagine two crowds right passing into each other,
Speaker 1: and like one gets off the train and one's coming
Speaker 1: down the stairs and they pass each other in the platform.
Speaker 1: What's going to happen, Well, it depends on how they interact, right,
Speaker 1: and how dense they are. So we can start with
Speaker 1: something and the obvious parts, like the stars. Okay, so
Speaker 1: you might think, oh my gosh, there's a hundred billion
Speaker 1: stars coming right at us. That's going to be a
Speaker 1: big deal. Is that the right size? Like it isn't
Speaker 1: drama about the same size as the Milky Way. Actually
Speaker 1: I think it's bigger than the Milky Way. But you know,
Speaker 1: factors of ten here are not important. Um, so it's
Speaker 1: hundreds of billions of stars, and each star, of course
Speaker 1: is really big. And you might think, while they're heading
Speaker 1: right at us, you know, this is gonna be a
Speaker 1: big deal, But remember that the stars are really far apart. Also, like,
Speaker 1: galaxies are huge, not just in terms of the number
Speaker 1: of stars, in terms of the amount of space they
Speaker 1: take up. And you know, you look around you in
Speaker 1: our galaxy, there aren't that many stars nearby, right, and
Speaker 1: the closest stars are light years away. I like this
Speaker 1: crowd analogy that's pretty interesting. Like we're a crowd of
Speaker 1: people getting off the subway. There's a crowd of people
Speaker 1: coming down the stairs to get on the subway. It's
Speaker 1: going to be a disaster potentially. Potentially, But if it's
Speaker 1: not rush hour and the crowds are pretty light, you know,
Speaker 1: there's like enough space the two crowds can just pass
Speaker 1: right through each other. Like if the stairways and the
Speaker 1: hallways are huge and people are pretty spread out, it
Speaker 1: may not be like a riot, you know, it may
Speaker 1: just be like a busy intersection. Right, It's like two
Speaker 1: people leaving Yankee Stadium at the same time as as
Speaker 1: somebody else's trying to come in. Like there's plenty of exits,
Speaker 1: nobody's gonna bump into each other, right, And that's sort
Speaker 1: of the case with stars. I read this one comparison
Speaker 1: where if you imagine the stars the size of a
Speaker 1: ping pong ball on average, the nearest stars three kilometers away, right,
Speaker 1: So like if you were going to throw a ping
Speaker 1: pong ball into a cloud of ping pong balls, where
Speaker 1: the spaces between them were three kilometers away. You'd be
Speaker 1: lucky if you hit anything, right, even if you were trying.
Speaker 1: Oh I see, Okay, So our galaxy is actually pretty sparse,
Speaker 1: meaning the stars are pretty far apart from each other.
Speaker 1: We're not sort of clumped together. Yeah, exactly, and astronomically speaking,
Speaker 1: astronomically speaking, and so there's gonna be very few or
Speaker 1: probably zero direct collisions. You know, where one star like
Speaker 1: actually slams into another one, you get stellar explosions. I mean,
Speaker 1: that would be pretty awesome. I would pay for front
Speaker 1: road seat, but I think it's pretty unlikely that's going
Speaker 1: to happen. But you know, there's a hundred billion stars
Speaker 1: running into a hundred billion other stars. Surely some of
Speaker 1: them are going to hit head on, isn't it. Aren't they?
Speaker 1: I mean, there's always a non zero probability, and you
Speaker 1: could get lucky you're unlucky, depending on which which outcome
Speaker 1: you're rooting for. But if they're diffuse enough, right, they're
Speaker 1: they're far enough apart, then then all of them could
Speaker 1: pass through without hitting. I mean, I think probably the
Speaker 1: most likely scenarios that maybe you get one. The stars
Speaker 1: also don't have to hit directly to affect each other. Right.
Speaker 1: Each one is a big blob of mass, which means
Speaker 1: it has gravity, and so they can jostle each other.
Speaker 1: I mean, if another star came by and near our
Speaker 1: Solar System and pass nearby, it could affect the orbits
Speaker 1: of all the planets, like nudge a planet out of orbit.
Speaker 1: Didn't have to hit the star directly head on or
Speaker 1: to affect our lives. It could maybe pull us out
Speaker 1: of orbit or sunk us into that other star. That's right, Um,
Speaker 1: it could it could steal planets right exactly. Or um,
Speaker 1: one of our planets could get ejected out of the
Speaker 1: Solar System right, or it could even kick our star
Speaker 1: out of the galaxy. Our star is in orbit around
Speaker 1: the center of the galaxy, right, and if it comes,
Speaker 1: if another star comes near enough, it could get pulled
Speaker 1: and so that it gets you out of that orbit, right.
Speaker 1: And orbit is sort of a delicate thing. You have
Speaker 1: to be the right radius and the right velocity for
Speaker 1: it all to work and start going to fast and
Speaker 1: you each escape velocity. And our star could even get
Speaker 1: kicked out of the galaxy. So we could be you know,
Speaker 1: sort of evicted from the Milky Way, floating in intergalactic space,
Speaker 1: just our star with the planets and everything. Oh, I see.
Speaker 1: So when two galaxies collided, it's not it's not we
Speaker 1: don't have to worry about things running into each other.
Speaker 1: But it is going to be pretty chaotic, right, Like,
Speaker 1: suddenly there's going to be you know, twice the number
Speaker 1: of stars, and that's just going to change everything, right, yeah, exactly,
Speaker 1: So things that definitely get mixed up. The stars won't
Speaker 1: necessarily smash into each other, but it definitely mix each
Speaker 1: other up and disturb each other. So are they are
Speaker 1: these two messages going to kind of go towards each other,
Speaker 1: makes a little bit and then keep going, or are
Speaker 1: they you know, slamming to each other and then become
Speaker 1: this giant mega galaxy. It depends a little bit on
Speaker 1: their relative velocity. If they're going fast enough relative to
Speaker 1: each other, then they'll pass through each other, right, But
Speaker 1: if if they're not, and it doesn't seem like they are,
Speaker 1: the most like scenario is that they merge, that they
Speaker 1: come together and there's a little bit of slashing or whatever,
Speaker 1: but eventually becomes one big galaxy. But wait, what does
Speaker 1: that mean? It's like the other stars and from the
Speaker 1: other galaxy. They're gonna come, but then they're going to
Speaker 1: kind of go pass us a little bit, and then
Speaker 1: they're gonna get pulled back in kind of thing like
Speaker 1: it's gonna like a giant jelly out in space, like
Speaker 1: it's going to go move, you know what I mean,
Speaker 1: but in slow motion, yeah, or sort of like things
Speaker 1: getting flushed down the toilet. You know, they come closer
Speaker 1: and closer and closer and circle each other faster and faster.
Speaker 1: You know, where we might circle each other, the two galaxies, Yeah,
Speaker 1: and sort of a wall being on top of each other,
Speaker 1: you know, so coming together pass a little the centers
Speaker 1: of mass might pass a little bit and then turn
Speaker 1: and come the other direction and spin it faster and
Speaker 1: faster until the center is a massive line. So being
Speaker 1: flushed down the toilet. That doesn't doesn't sound pleasant. Like
Speaker 1: that doesn't sound like it's going to be easy, do
Speaker 1: you know what I mean? Like, it doesn't sound like
Speaker 1: it's going to uh leave us unscathed. It might, though,
Speaker 1: you know, our sun could be totally fine, and it
Speaker 1: could be that the planets are not distorted, their orbits
Speaker 1: are not distorted, and we could just have a front
Speaker 1: row seat to a pretty amazing event. And the other
Speaker 1: thing is that we see this happening all the time.
Speaker 1: Like you look out into space with the hubble zoom
Speaker 1: in on other galaxies. There's lots of galaxies out there,
Speaker 1: and lots of them are in state various stages of emerging.
Speaker 1: And you can see galaxies that are just starting to merge.
Speaker 1: You can see galaxies that have been merging for a
Speaker 1: billion years. You can see galaxy that obviously merged a
Speaker 1: long time ago. And there's sort of like an uncomfortable
Speaker 1: blob of two galaxies, like one spiral arms sort of
Speaker 1: knocked off over here and there's another one over there.
Speaker 1: And so we have a lot of catalogs of examples
Speaker 1: of galaxies that have mergy. That's how we know so
Speaker 1: much about it. Yeah, if you look at there's a
Speaker 1: bunch of crashes that you can study. Yeah, exactly. So
Speaker 1: you want to know what galaxy collisions look like, you
Speaker 1: don't have to build a galaxy collider. This is one
Speaker 1: thing I love about astronomy. You have to google. You
Speaker 1: can just that's right, cosmic googling, otherwise known as telescopes. Um.
Speaker 1: You just look out into space and eventually you will
Speaker 1: see that thing happening, like you want to imagine some
Speaker 1: crazy scenario, or this kind of galaxy hits that kind
Speaker 1: of galaxy, and then from behind comes a third one
Speaker 1: that's happening somewhere out there there and you just need
Speaker 1: to find it and watch it. And so that's the
Speaker 1: amazing thing about astronomy is that all these cosmic experiments
Speaker 1: are happening. We just need to look for them. Okay,
Speaker 1: well we process that. Let's say, let's take a quick break,
Speaker 1: all right, So that's what might happen to the stars
Speaker 1: in the galaxy. What's going to happen to all these
Speaker 1: other parts of the galaxy when these two galaxies collide, right?
Speaker 1: And I like that we started with the stars because
Speaker 1: that's like the most important thing to us, because we're
Speaker 1: sort of staro centric, right, because we think stars are
Speaker 1: most the most important element of the galaxy. But the
Speaker 1: biggest element of the galaxy, remember, is dark matter. And
Speaker 1: so you might ask, well, what's going to happen to
Speaker 1: all our dark matter? And just like with the stars,
Speaker 1: what what happens there depends on how much it interacts. Currently,
Speaker 1: we don't really know anything about how much dark matter interacts.
Speaker 1: We know that it doesn't interact with normal matter. We
Speaker 1: think it doesn't interact with itself, or if it does,
Speaker 1: it doesn't interact very strongly and so, but it does
Speaker 1: have gravitational attraction. So if the galaxies are are going
Speaker 1: to hit each other and they're not moving too fast
Speaker 1: that they just basically pass right through each other, then
Speaker 1: the gravity from dark matter is going to affect the
Speaker 1: gravity from the other galaxies dark matter just the same
Speaker 1: way the stars are, and the two will sort of
Speaker 1: merge eventually become one big dark matter halo. And it's
Speaker 1: the kind of thing I would love to watch, but
Speaker 1: you can't really see the dark matter. It could be
Speaker 1: just another version of the cluster of stars. You know.
Speaker 1: It's like one blob goes into the other blob and
Speaker 1: then they kind of slash around and then just becomes
Speaker 1: a bigger blob. Yeah, you can think of the stars.
Speaker 1: It's sort of like a collisionless liquid, right, It's like
Speaker 1: a you have a liquid of stars that don't interact
Speaker 1: with each other the same way the dark matter does.
Speaker 1: So dark matter in stars are basically operating this under
Speaker 1: the same principles. The only relevant interaction that we know
Speaker 1: about is gravity, So everything we said about stars is
Speaker 1: also going to affect the big blobs of dark matter.
Speaker 1: The dark matter is much more continuous. We think it's smooth.
Speaker 1: It's not like there's just dots of it here and there.
Speaker 1: But because it hardly interacts with each other, it doesn't
Speaker 1: matter if it rams smack into itself. Right, It mainly
Speaker 1: affect is gravitational. It may not interact with itself. It
Speaker 1: could just pass by itself and not really kind of
Speaker 1: explode or collide or do anything besides pull itself gravitationally. Yeah, exactly.
Speaker 1: And we don't even know what dark matter is made out,
Speaker 1: so we can't say things like dark runner particles can
Speaker 1: do this. Dark matter as far as we know, it's
Speaker 1: just smooth, collisionless blob of something. And we know it
Speaker 1: has gravitational interactions, and that's really about all we know
Speaker 1: about it. So we think that that that's what's going
Speaker 1: to happen. And you know, we've seen dark matter in
Speaker 1: these gravitational collisions and we see that it basically sticks
Speaker 1: with the galaxies, right, it sticks with the stars. Okay,
Speaker 1: so then the last part is the black hole at
Speaker 1: the center of each galaxy. What no, no, don't forget
Speaker 1: the dust, right, this gas dust, which a lot of
Speaker 1: people overlook, and this is actually the most exciting part
Speaker 1: because the dust is the most the coolest part. That's
Speaker 1: how you know you're listening to a nerdy podcast and
Speaker 1: they get excited about dust. Oh my god. You know
Speaker 1: if if for those people who are like expecting dramatic
Speaker 1: events and explosions, this is where you get them. Okay,
Speaker 1: because dust is not diffuse, right's spread everywhere, Like you
Speaker 1: have a big blob of dust. It's not like little
Speaker 1: clusters of mass the way stars are. It's a huge
Speaker 1: extended blob of dust. And when it smashes into another
Speaker 1: blob of dust, you're going to get fireworks. Like those
Speaker 1: clouds of dust interact with each other the way dark
Speaker 1: matter doesn't. And they're um spread everywhere the way stars aren't,
Speaker 1: and so you get huge collisions. And what happens when
Speaker 1: you compress gas and dust. What happens when you collide
Speaker 1: huge blobs of gas and dust is you get more
Speaker 1: dense and then you get stars. And so you could
Speaker 1: see like new stars being born where these two huge
Speaker 1: clouds of gas and dust being into each literally like fireworks.
Speaker 1: Like that's right, cosmic fireworks. I mean, what's more are
Speaker 1: dramatic and what's a better cosmic firework than seeing stars
Speaker 1: be born? Yeah, so this one is going to be
Speaker 1: like to you know, you know, two liquids kind of
Speaker 1: running into each other. It is going to be kind
Speaker 1: of dramatic, you know, like it is going to be
Speaker 1: like with the sound effects and everything in space. No, yeah, exactly,
Speaker 1: It's just like two water balloons hitting each other. Right,
Speaker 1: You're gonna get an initial shop wave. And you know,
Speaker 1: you don't get stars born when you fire water balloons
Speaker 1: at each other because the density isn't great enough obviously,
Speaker 1: But yeah, you're gonna get a shock wave. You're gonna
Speaker 1: get friction between the fluids, and you're going to get
Speaker 1: stars being born. It's gonna be pretty dramatic. So you
Speaker 1: don't want to be there. You don't want to want
Speaker 1: to But we are, aren't We surrounded by gas clouds
Speaker 1: and stuff? Oh? I think you need denser stuff. I mean,
Speaker 1: the milky wave definitely has big clouds of gas and dust.
Speaker 1: Oh I see, But when those clouds running to the
Speaker 1: other clouds, then that's where this stuff happens. But we're
Speaker 1: not necessarily sitting in one of those clouds. That's right, yeah, okay,
Speaker 1: the last element is the black hole, right, and so
Speaker 1: our galaxy is a huge black hole the center, and
Speaker 1: the other guy, almost every other galaxy is a huge
Speaker 1: black hole of the center. And there it's gonna be
Speaker 1: mostly dominated by gravity, right, because they're gonna pull each
Speaker 1: on each other really hard, and they're gonna pass by
Speaker 1: each other a little bit, perhaps because they're probably not
Speaker 1: gonna hit dead on and then they're gonna swing around.
Speaker 1: They're gonna pull on each other, so they'll probably be
Speaker 1: you know, some sort of a near miss, and then
Speaker 1: they'll turn around and come back. And then they'll just
Speaker 1: circle each other faster and faster and faster. And if
Speaker 1: you remember the episode we did on gravitational waves, or
Speaker 1: if you've heard about the discovery of gravitational waves, you
Speaker 1: know that what happens when black holes get close to
Speaker 1: each other as they start to circle each other faster
Speaker 1: and faster, until eventually they spend really really fast and
Speaker 1: the distance get closer and closer and closer, and then
Speaker 1: they merge and they become one enormous black hole. They
Speaker 1: like eat each other, right, But and it's not a
Speaker 1: peaceful event it's like a pretty violent thing, right, Like
Speaker 1: they've been super super fast, there's energy spewed out everywhere,
Speaker 1: and then suddenly have these huge cataclysmic gravitational waves. Oh yeah,
Speaker 1: when black holes fight, it's a big mess. Absolutely. You
Speaker 1: don't want to be anywhere near that because huge amounts
Speaker 1: of radiation, not just gravitational waves. Right, yeah, you make
Speaker 1: gravitational waves, which are pretty awesome from a physics point
Speaker 1: of view, but you know, these things tear up into
Speaker 1: each other and amid huge amounts of radiation, and so
Speaker 1: you don't want to be anywhere near that. Yeah, I
Speaker 1: mean that that's gonna like sterilize life on any nearby
Speaker 1: star system for sure. But anyway, there probably isn't any
Speaker 1: life in the center of art galaxy for that same
Speaker 1: reason that the galactic black hole is already emitting huge
Speaker 1: amounts of life killing radiation, so you don't want to
Speaker 1: get too close anyway. It's like the eye of a storm.
Speaker 1: There's nothing living in the middle of it, that's right.
Speaker 1: I don't know if it's calm inside the black hole.
Speaker 1: That we did a whole episode actually on what it's
Speaker 1: like to be inside a black hole. So you guys
Speaker 1: should go listen to that. But yeah, it's a it's
Speaker 1: everything is swirling around that central black hole. And so
Speaker 1: probably what will happen is they'll merge and the new milk,
Speaker 1: the new galaxy. I wonder what that galaxy would be called. Actually,
Speaker 1: how would you combine and Rameda in the Milky Way,
Speaker 1: like Drama Dinky Way, milk milk Drameda, I don't know,
Speaker 1: and ramedaway the Andromeda Away. There you go, the Andromeda Way. Yeah,
Speaker 1: the new galaxy would have a huge, super duper massive
Speaker 1: black hole at its center. Yeah, and so I think
Speaker 1: that basically sums it up. You'd have the black holes
Speaker 1: will probably emerge huge violent eruption of radiation there gas
Speaker 1: and the dust would have a lot of friction caused
Speaker 1: caused star formation, big explosion, bigion work, Yeah, exactly. Friction, Yeah,
Speaker 1: just all the kind of stuff you expect to see
Speaker 1: in the next Transformers movie. And then stuff. He'll be there,
Speaker 1: He'll be there everything. If there's money to be made,
Speaker 1: he'll be there. Um. And then the stars and the
Speaker 1: dark matter will just have a gravitational effect, but they'll
Speaker 1: know eventually settle down and in a few more billion years,
Speaker 1: the new galaxy will have its own shape. It will
Speaker 1: sort of settle into its own new shape. But it
Speaker 1: kind of sounds like every part will do something. Friend,
Speaker 1: do you know what I mean? Yeah, they will because
Speaker 1: they follow different rules, right, they interact differently and so
Speaker 1: but so, then kind of the nice structure we have
Speaker 1: now is going to be pretty much obliterated right when
Speaker 1: it we're just with the other one. Yeah, exactly. You
Speaker 1: shouldn't count on your real estate being the same value.
Speaker 1: After the galaxy collision, Everything's going to be shook up, right, Absolutely,
Speaker 1: it's going to be disrupt the entire Both galaxies gonna
Speaker 1: be totally disrupted. Fireworks collisions. But you're saying it's possible
Speaker 1: we may survive it, right, that it's possible nothing will
Speaker 1: actually happen to our solar system. I think that's the
Speaker 1: most likely outcome. Yeah, is it will just be sort
Speaker 1: of interesting likely, Yeah, most likely most likely thing. I mean,
Speaker 1: we're a star. We were basically part of our star,
Speaker 1: right you think of the Solar system is just one
Speaker 1: big blob, And the most likely thing is that nothing
Speaker 1: gets close enough to disrupt our orbit around the star.
Speaker 1: And you know what, even if our star gets like
Speaker 1: ejected from the galaxy. So what we don't need the galaxy.
Speaker 1: We could live just fine, just a star with a
Speaker 1: bunch of planets in the middle of intergalactic space. We
Speaker 1: don't need anything else. We just never start to provide
Speaker 1: energy for life. So so we don't mean just in
Speaker 1: the same way we're talking about the beginning of the episode,
Speaker 1: like you don't really notice what's going out in space
Speaker 1: because you don't usually have to. And if all those
Speaker 1: if all those stars disappeared and all we and we
Speaker 1: were in the middle of intergalactic space, it wouldn't change
Speaker 1: your life at all. You would still still need to
Speaker 1: stock up on lentils for the coming Apoco lips. You know,
Speaker 1: it wouldn't save you or change your plans at all.
Speaker 1: You wouldn't mind getting kicked out of town like that.
Speaker 1: That's kind of what it would feel like, like the
Speaker 1: whole town, our whole town. We just get kicked out,
Speaker 1: you know, and we just go on living the way
Speaker 1: what we did before. But things will definitely change for
Speaker 1: us even if we survived it's galactic collision, the night
Speaker 1: sky will look very different. I mean, as Andromeda approaches
Speaker 1: in the next few billion years, it will grow in
Speaker 1: the sky and eventually look really big. And then after
Speaker 1: the collision, right when things have settled down, the night
Speaker 1: sky would look totally different because all the stars will
Speaker 1: have been rearranged and we won't see that band in
Speaker 1: the milky Way anymore. Well, that makes me feel better.
Speaker 1: I was sweating. I was sweating what was gonna happen
Speaker 1: for and I have been years from now. But now
Speaker 1: now I feel better and I and I hope Blake
Speaker 1: you also feel a little bit better. Yeah, that's right, Bake,
Speaker 1: chill out, don't worry about it. Um, you have nothing
Speaker 1: to worry about. I think it's fun to think about
Speaker 1: things happening deep into the future, and also even further
Speaker 1: into the future. You know, the universe has been around
Speaker 1: fourteen billion years, right, and that's just sort of like
Speaker 1: the initial bits, not before we get to the interesting part.
Speaker 1: But it could be they were not even at the
Speaker 1: interesting part. You know. Thinking about galaxies in this way
Speaker 1: reminds you that they're spinning their dynamic, they're swirling around
Speaker 1: each other. What's going to happen? We don't know, right,
Speaker 1: they could continue to swirl and form crazy new structures
Speaker 1: that know, the universe has never seen before. Because there
Speaker 1: hasn't been time to make them. And so this is
Speaker 1: the kind of thing makes me think about the universe,
Speaker 1: like on the trillion or two trillion life year cycle,
Speaker 1: Like if life is still around ten trillion years into
Speaker 1: the history of the universe, they'll think about these first
Speaker 1: few moments of lactic formation as you know, almost irrelevant,
Speaker 1: just like just warming up. The best maybe yet to come. Now,
Speaker 1: that's right. I'm an optimistic person, so I'm always hoping
Speaker 1: that the best thing is yet to come. Exactly well, great, um,
Speaker 1: thank you so much Bla for sending us this question.
Speaker 1: We really enjoyed answering it. That's right. And check out
Speaker 1: our book called We Have No Idea. It's a guide
Speaker 1: to the unknown questions of the universe, all the things
Speaker 1: that physics wants to know the answer to but really
Speaker 1: hasn't got a clue about. And thanks for listening. Yeah,
Speaker 1: and if you're hungry or want to stuck up, just
Speaker 1: don't forget to get Daniel's Spicy lentils, now available at
Speaker 1: your local grocery store. If you still have a question
Speaker 1: after listening to all these explanations, please drop us a line.
Speaker 1: We'd love to hear from you. You can find us
Speaker 1: at Facebook, Twitter, and Instagram at Daniel and Jorge That's
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Speaker 1: Orge dot com. H m hm