January 3, 2019 • 35 mins
Will our lives be affected when the Milky Way collides with Andromeda?
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Episode Transcript
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Speaker 1 (00:07):
Hey, Daniel, what keeps you up at night? Oh? I
worry about a lot of things. Financial crises, my kids
growing up to be just like me, all sorts of stuff.
I worry about that too for them. You worry about
my kids growing up to be just like me. We
can't have more of him in the world, Okay, But
like on a galactic scale, on a universe scale, what's
(00:29):
something we should be concerned about. Well, we do have
a lot of things look forward to in terms of
our galaxy. If we survived the Sun exploding and the
waters the Earth boiling off, then we have something pretty
dramatic to look forward to, which is that our galaxy,
the Milky Way, is going to collide with their nearest
neighbor and Dromeda. Meaning right now, there's an entire galaxy
Drameda heading towards us at this very moment. That's right.
(00:51):
It's like somebody shot it at us with a slingshot
and it's zooming right towards us, and it's going to
hit us smack on him. And I'm Daniel, and this
(01:17):
is our podcast. Daniel and Jorge explained the universe on
the episode. Today, we're going to talk about what will
happen when galaxies collide. Is this something we should all
be worrying about our packing our bags, about building our
underground shelters or are we all screwed? Or is it
just going to be like a big nothing? How much
(01:39):
should I pack? You should definitely be stalking lentils no
matter what. Lentils are a good investment for any of
these end of the world. Not just beans, no, no, lentils.
I mean lentils are kind of lego for a galactic emergency.
That's the that's the one to go with. Yeah, absolutely,
I would. I would invest in lentils heavily. And it's
not just because I happened to purchase lentils just before
(02:00):
we recorded this podcast and I'm trying to drum up
the lentil futures, you know. I'm I'm sincerely worried about
our listeners, and I encourage you all to go out
there in stockpi lentils. Well that's a whole hill of
beans worth of advice right there, that's right. And so
this is the question and today's podcast, what will happen
when our galaxy, the Milky Way, collides with the neighboring galaxy?
(02:21):
And this question I love not just because it's huge
and dramatic and galactic and all this sort of stuff,
but because it was suggested by one of our listeners.
That's right. It's Blake from Australia who listens to this
podcast on her commute to work every day. That's right.
And she didn't tell us what she uses to commute.
Maybe she rides in a beautiful pickup truck, maybe she's
in the back of a limo, maybe rides kangaroo who knows,
(02:45):
that's right, with a really nice sound system. Yeah, but
she has some interesting feedback for us about our podcast. Right,
what did she say? Yeah, she said that she likes
listening to me explain things, but she also likes when
you interrupted me. She said that often you interrupt me
just the same moment when she has a question and
you pose the same question that was bouncing around in
(03:05):
her head that she was shouting at her limo sound
system or kangaroo speakers or whatever it is she us
going to listen to. And so I was glad for that,
because you know, I like when you interrupt me. Also
it breaks the flow and it keeps me from just
droning on and on and on. So Thank you Blake
for suggesting this topic, and thank you Orge for occasionally interrupting. Yeah, no,
I'm happy to be rude. It seems to come naturally. Yeah, yeah,
(03:31):
And so that's the topic of today's podcast, And we
thought first before we dove into it, we would walk
around like we usually do and ask people, are you
worried about a galactic collision? What do you think will
happen when our galaxy collides with a neighboring galaxy? So
put that image in your mind to giant galaxies, full
stars running into each other. What do you think is
(03:52):
going to happen? Here's what people had to say, big explosion.
We'd probably all die. It is going to be mostly
nothing because of all the empty space around the world,
although there will be some crushes and so on in
the way. Okay, probably somewhere between a glacial, slow event
that we won't even notice and nothing at all. Maybe
(04:13):
leaning towards nothing at all. I think it would probably
be a big explosion with something pretty crazy happening. All right,
That was a little anti climatic. People seem to have
very low expectations of this event. What do you mean
It seems like half of the people are like it's
gonna be nothing, and the other half of like big explosions,
we're all gonna die. Well, why do you why do
(04:36):
you think Blake asked this question? Do you think there's
something she's concerned about or is something she's curious about?
You know? I think Blake is probably deciding whether or
not to stock up on lentils. You know, Um, she's
probably right now, story she asked. I think it's part
of just trying to be a sort of a citizen
of the larger universe, you know, wondering where we stand
(04:56):
and trying to think bigger than just our planet, you know,
because there's so much going on out there, it's so
easy to just walk around on the surfaces planet never
really look up and remember that there is an enormous
amount of stuff happening out there, And then you wonder like, well,
how is that relevant to me? And is he going
to ruin my life? Or can I go on ignoring it? Um? So,
I think maybe she was just sort of thinking into
(05:16):
the deep future and wondering like, how long can this
whole ridiculous, beautiful thing we call life on Earth go on? Right?
Is it going to change from how it is now, right, Yeah,
exactly do I need to change the way I live?
Does it affect any decision making? On the other hand,
it could be that Blake, like many people, is just
a thinker and likes to think about these scenarios, and
she probably heard that the Milky Way will collide with
(05:38):
Andromeda and wonder like, what's that going to be? Like?
You know this this this is the other side of
me that likes to smash stuff together. I mean, I'm
a particle physicist, but then we have the whole universe
to play with, right, and so you might wonder, like
what happens when planets collide, what happens when solarcisms? Like
oh my gosh, what if we could build a galaxy
collider and shoot them against each other and smash them
into each other? Right, So it just comes out of
(05:59):
like a curiosity to see stuff break by smashing it together. Yeah, well,
let's let's take it step back and just kind of
think about why even galaxies would collect, Like is this
a relevant question that is something that happens a lot
galaxies colliding, or is it something that's incredibly rare. It
turns out galaxies colliding happens all the time. It's like
a totally natural thing. And our galaxy. Yeah, not only
(06:22):
will our galaxy collide with and John Day in a
few billion years, it's currently colliding with other smaller galaxies.
That what Yeah, we're in a collision right now. Yeah,
that's right. And remember that the galactic time scales are
very different. You know, the galaxy takes about two hundred
million years just to rotate once, to go around once. Yeah,
(06:44):
so one galactic year is two hundred million earth years.
But it looks so swirly. It looks you know, you
know what I mean, Like it looks like it's in motion,
but it's actually it is. It is in motion, it's
just very slow, right, And so all these things are
dancing around each other and sometimes they bump into each other.
And the thing I think is amazing is that, you know,
(07:05):
until like a hundred years ago, we didn't even know
there were other galaxies. Like we looked up at the
night sky and we saw stars, and we thought, oh,
there's just stars that go on forever. At the universe
is just filled with stars. The universe is just like
a giant MESSI pinpoints, right, just stars. Yeah, yeah, like
somebody had scattered stars across the cosmos, right, And it
(07:26):
was Hubble, the guy for whom the telescope and the
constant are named. He's the guy who figured out, oh,
some of those things that are really far out there
are not stars. There are other galaxies. Right, So there's
the universe is filled with other galaxies. And of course
there are more galaxies than stars, and and then each galaxy,
of course, contains hundreds of billions of stars, and so
the numbers pretty quickly blow your head up before you
(07:48):
can understand them. But the point I wanted to make
was that we didn't realize there were galaxies until recently,
and now we're realizing that galaxies are in motion relative
to each other, and they're moving. Like the these galaxies
that we see out there in the sky, they're not
just like hanging there in space never to change, right,
They are moving their dynamic things, and they're constantly in motion,
(08:09):
and they have huge gravitational attraction. Well, let's break it down.
What exactly is a galaxy? I mean, I know it's
like kind of like a collection of stars, but you
know what, why do stars clump together like that? First
of all? And what makes a galaxy special? Like, why
is it more than just a clump of stars. Well,
what makes our galaxy special is that you're in it. Horse.
(08:29):
There's no other galaxy that features such a good looking,
funny cartoonists, meet me and lentils. We make it, make
it habitable, right, Okay, so what's the recipe for a galaxy? Right? Well,
the thing that the galaxies have the most of, remember,
is dark matter. In general, there's about five times as
much dark matter as there is any other kind of matter,
(08:52):
you know, the stuff that makes up gas and dustin
stars and people and cartoonists and and and ice cream.
So it's mostly dark matter. So that's the stuff we
can't see your touch. I mean, we did a whole
podcast episode on dark matter, but it just in case
somebody didn't listen to it. Um, it's like this weird
invisible dark gravity thing that's hanging out every galaxy has,
(09:15):
that's right. Yeah, we call it dark and matter because
we can't see it. So it's dark and we know
it gives gravity, so therefore it's matter and the crazy
things that until you know, a few decades ago, we
didn't even know it existed. And now we know that
galaxies are mostly made up of this stuff. Right. So
number one ingredient when you want to make a galaxy
is you have to have dark matter. It's like five
(09:35):
times more than the stars, right, yeah, exactly, Like a
galaxy is basically a clump of dark matter with a
few sprinkles of stars in it. That's right. Yeah. If
a galaxy was a cupcake, right, the dark matter would
be the chocolate cake, and you know there everything else
would be the frosting and the sprinkles. The gas and
the dust would be the frosting. The stars would be
the sprinkles on top. Oh I see, Okay, that's kind
(09:55):
of the right proportions. Yeah, something like that. Um, So
you start with big blob of dark matter and that's
most of it, and then after that you have huge
amounts of gas and dust, right, And that's the stuff
that's left over from the Big Bang or left over
from stars exploding, and those the ingredients you need to
make planets and stars and all sorts of stuff that
you're familiar with, right. And so you have dark matter,
(10:18):
you have gas, you have dust, you have planets and
stars and black holes right, Like there's just a little
black hole sprinkled throughout throughout probably, But there's a huge
giant black hole at the center of every galaxy. That's right.
I can't believe I forgot the black hole. The black
hole at the center of almost every galaxy is huge.
It's like, you know, millions of solar masses and it's
(10:40):
sitting there at the center of the black hole, and
it's it's got a lot of stuff to it also, right,
it carries a lot of mass and so it contributes.
So that's what a galaxy is. And you know, a
galaxy couldn't really form without all those elements, Like you
couldn't really have a galaxy without dark matter because dark
matter provides the gravitational attraction to suck all this stuff together.
You know, they do these simulations of the universe. They say,
what would the universe look like if you never had
(11:02):
dark matter in it? And it would take a lot
longer for galaxies to form because dark matter has pulled
all this stuff together. It's like it's made a you know,
like a well in the rubber sheet of the universe,
so everything rolls together more closely. Okay, so that's a
that's a galaxy. It's a black hole surrounded by dark
(11:23):
matter and sprinkles of stars and gas and dust and
lintels and lintels exactly yes, And so they're not just
hanging out in space. They're moving around. That's right there.
Each one is spinning, right, which is why you see
a lot of them having these these spiral features. Each
one is spinning, and then they're also moving around each other.
They have gravity and they're moving around each other, and
(11:45):
they have these Each galaxy is a member of a
cluster of galaxies, and so these guys are orbiting the
center of the cluster. And then the clusters are members
of superclusters. So these things have a lot of gravitational
interactions everywhere. It's like a system of galaxy. They all
interact with each other, and they all spin around their
common center of mass exactly right, And they're all spinning
(12:07):
around that center. So it's sort of like a big
slow motion tornado. Right you looked at it. If you
looked at it really really slow, you're like, oh, nothing's
really moving. I mean, I guess a little bit, but
you you you watch it at natural speed of tornado,
and obviously it's going really fast, and so a galaxy
is that's sort of that same way. The gather system
of galaxies is sort of that same way, but they're
all moving around each other and then occasionally, you know,
(12:28):
they bump into each other. Wow, that's so weird to
think that gravity works the way like we are, you know,
moving around the center of the Earth. The Earth is
moving around our solar system, around the center of gravity,
which is mostly the Sun, but the Sun is also
we were moving around the center of gravity of the galaxy,
and the galaxy is also moving around the center of
gravity of its cluster of galaxies. That's right, Yeah, and
(12:50):
on and on and on like a bunch of nested
Russian dolls, you know, until you get to the biggest
structures in the universe, you know, which are the superclusters,
and then the filaments of superclusters, and beyond that, we
don't know anything about whether there are bigger and bigger structures.
That's as far as we've seen. So we're moving around
and sometimes these two two galaxies can just run into
each other. In the giant, vastness of space, all these
(13:12):
moving galaxies can sometimes cross pass right. Yeah. And there's
another thing I want to say about that before we
talk about what actually happens, which is that it's incredible
to me that gravity is the force that's dominant on
these scales, right, Like, that's the thing that's controlling how
galaxies form and how they dance around each other, and
that's pulling them all the way through the universe and
forming these crazy structures. It's all gravity, right. But gravity
(13:35):
is the weakest force of nature. It's weaker than electromagnetism,
it's weaker than any of the nuclear forces. It's pathetically weak,
but it's the only one that operates on these huge scales,
and it can't be balanced out. And so because it's
only an attractive force, there's no repulsive version of it.
And so that's why, like on these huge scales, gravity
is the thing that dominates. Gravity determines the structure the
(13:57):
Solar system, the structure the galaxy, the structure of the clusters.
Gravity sort of winds in the end. It's like, you know,
revenge of the nerd forces, Right, It's the weakest force
in the end controls the universe. It's like slow and
steady wins the race. It's the turtle of forces. Yeah, Anyway,
we need to do a whole other podcast on why
gravity is so weird and weak and whatever, and we're
(14:18):
into that. Okay, so we have a cult clusters and
galaxies are moving around space and sometimes they collide. So yeah,
let's talk about what actually happens when two of these
things collide. But first let's take a quick break. All right.
(14:42):
So we're sitting in a galaxy and we are moving
inside of this galaxy, and this galaxy is moving in space.
But there's another galaxy nearby called the Andromeda galaxy, and
it's kind of an interset course with us, right, like
we're going to run into it in about four and
a half billion years. Yeah, not kind of. They've measured it.
They can measure the velocity of Andromeda relative to us,
(15:04):
and they can see that it's getting closer and closer
every year, and they can also measure the lateral velocity,
like is it going to shoot by us or just
or come right at us? And after for a while
they weren't sure. They were like, oh, it's heading our way,
but it could miss, you know, like every time they
say there's an asteroid coming within, you know, a certain
thousands of miles of the Earth, and usually it misses.
(15:24):
For a while, they weren't sure, but now they're pretty
certain they've taken enough measurements, they've seen it move, and
they can project confidently that these two things are going
to collide. Also, Andromeda and Milky, we have a lot
of gravity, and so you don't have to aim perfectly
to get a collision, right, They're gonna um pull each
other closer and closer. They want to collide, you know,
(15:44):
you know what I mean, Like, it's not like a
random asteroid. It's like we're we're pulling towards each other. Yeah, well,
I don't know if you can really say they want Like,
do you understand the psychology of the galaxy? Do you you
know what galaxy wants in life? You know, Hey, galaxy
have feelings, right, I think I read that science fiction
novel right where every galaxy is actually a living thing
and we're just like the tiny moats on the on
(16:06):
an island of red blood cells instead of galaxy. Anyway, Yeah,
so you don't have to shoot perfectly, and they're gonna collide.
So to think about what happens in the collision, you
probably think about each individual piece separately, Like we're a
cluster of things. Like a galaxy is not a solid object.
It's like a word almost like a cloud of things,
right is that kind of way? Mean? Yeah, yeah, exactly.
And you know, imagine two crowds right passing into each other,
(16:28):
and like one gets off the train and one's coming
down the stairs and they pass each other in the platform.
What's going to happen, Well, it depends on how they interact, right,
and how dense they are. So we can start with
something and the obvious parts, like the stars. Okay, so
you might think, oh my gosh, there's a hundred billion
stars coming right at us. That's going to be a
big deal. Is that the right size? Like it isn't
(16:48):
drama about the same size as the Milky Way. Actually
I think it's bigger than the Milky Way. But you know,
factors of ten here are not important. Um, so it's
hundreds of billions of stars, and each star, of course
is really big. And you might think, while they're heading
right at us, you know, this is gonna be a
big deal, But remember that the stars are really far apart. Also, like,
galaxies are huge, not just in terms of the number
(17:08):
of stars, in terms of the amount of space they
take up. And you know, you look around you in
our galaxy, there aren't that many stars nearby, right, and
the closest stars are light years away. I like this
crowd analogy that's pretty interesting. Like we're a crowd of
people getting off the subway. There's a crowd of people
coming down the stairs to get on the subway. It's
(17:29):
going to be a disaster potentially. Potentially, But if it's
not rush hour and the crowds are pretty light, you know,
there's like enough space the two crowds can just pass
right through each other. Like if the stairways and the
hallways are huge and people are pretty spread out, it
may not be like a riot, you know, it may
just be like a busy intersection. Right, It's like two
people leaving Yankee Stadium at the same time as as
(17:50):
somebody else's trying to come in. Like there's plenty of exits,
nobody's gonna bump into each other, right, And that's sort
of the case with stars. I read this one comparison
where if you imagine the stars the size of a
ping pong ball on average, the nearest stars three kilometers away, right,
So like if you were going to throw a ping
pong ball into a cloud of ping pong balls, where
(18:11):
the spaces between them were three kilometers away. You'd be
lucky if you hit anything, right, even if you were trying.
Oh I see, Okay, So our galaxy is actually pretty sparse,
meaning the stars are pretty far apart from each other.
We're not sort of clumped together. Yeah, exactly, and astronomically speaking,
astronomically speaking, and so there's gonna be very few or
probably zero direct collisions. You know, where one star like
(18:34):
actually slams into another one, you get stellar explosions. I mean,
that would be pretty awesome. I would pay for front
road seat, but I think it's pretty unlikely that's going
to happen. But you know, there's a hundred billion stars
running into a hundred billion other stars. Surely some of
them are going to hit head on, isn't it. Aren't they?
I mean, there's always a non zero probability, and you
could get lucky you're unlucky, depending on which which outcome
(18:57):
you're rooting for. But if they're diffuse enough, right, they're
they're far enough apart, then then all of them could
pass through without hitting. I mean, I think probably the
most likely scenarios that maybe you get one. The stars
also don't have to hit directly to affect each other. Right.
Each one is a big blob of mass, which means
it has gravity, and so they can jostle each other.
I mean, if another star came by and near our
(19:18):
Solar System and pass nearby, it could affect the orbits
of all the planets, like nudge a planet out of orbit.
Didn't have to hit the star directly head on or
to affect our lives. It could maybe pull us out
of orbit or sunk us into that other star. That's right, Um,
it could it could steal planets right exactly. Or um,
one of our planets could get ejected out of the
(19:39):
Solar System right, or it could even kick our star
out of the galaxy. Our star is in orbit around
the center of the galaxy, right, and if it comes,
if another star comes near enough, it could get pulled
and so that it gets you out of that orbit, right.
And orbit is sort of a delicate thing. You have
to be the right radius and the right velocity for
it all to work and start going to fast and
(20:00):
you each escape velocity. And our star could even get
kicked out of the galaxy. So we could be you know,
sort of evicted from the Milky Way, floating in intergalactic space,
just our star with the planets and everything. Oh, I see.
So when two galaxies collided, it's not it's not we
don't have to worry about things running into each other.
But it is going to be pretty chaotic, right, Like,
(20:21):
suddenly there's going to be you know, twice the number
of stars, and that's just going to change everything, right, yeah, exactly,
So things that definitely get mixed up. The stars won't
necessarily smash into each other, but it definitely mix each
other up and disturb each other. So are they are
these two messages going to kind of go towards each other,
makes a little bit and then keep going, or are
(20:41):
they you know, slamming to each other and then become
this giant mega galaxy. It depends a little bit on
their relative velocity. If they're going fast enough relative to
each other, then they'll pass through each other, right, But
if if they're not, and it doesn't seem like they are,
the most like scenario is that they merge, that they
come together and there's a little bit of slashing or whatever,
but eventually becomes one big galaxy. But wait, what does
(21:04):
that mean? It's like the other stars and from the
other galaxy. They're gonna come, but then they're going to
kind of go pass us a little bit, and then
they're gonna get pulled back in kind of thing like
it's gonna like a giant jelly out in space, like
it's going to go move, you know what I mean,
but in slow motion, yeah, or sort of like things
getting flushed down the toilet. You know, they come closer
and closer and closer and circle each other faster and faster.
(21:26):
You know, where we might circle each other, the two galaxies, Yeah,
and sort of a wall being on top of each other,
you know, so coming together pass a little the centers
of mass might pass a little bit and then turn
and come the other direction and spin it faster and
faster until the center is a massive line. So being
flushed down the toilet. That doesn't doesn't sound pleasant. Like
that doesn't sound like it's going to be easy, do
(21:46):
you know what I mean? Like, it doesn't sound like
it's going to uh leave us unscathed. It might, though,
you know, our sun could be totally fine, and it
could be that the planets are not distorted, their orbits
are not distorted, and we could just have a front
row seat to a pretty amazing event. And the other
thing is that we see this happening all the time.
Like you look out into space with the hubble zoom
in on other galaxies. There's lots of galaxies out there,
(22:08):
and lots of them are in state various stages of emerging.
And you can see galaxies that are just starting to merge.
You can see galaxies that have been merging for a
billion years. You can see galaxy that obviously merged a
long time ago. And there's sort of like an uncomfortable
blob of two galaxies, like one spiral arms sort of
knocked off over here and there's another one over there.
And so we have a lot of catalogs of examples
(22:30):
of galaxies that have mergy. That's how we know so
much about it. Yeah, if you look at there's a
bunch of crashes that you can study. Yeah, exactly. So
you want to know what galaxy collisions look like, you
don't have to build a galaxy collider. This is one
thing I love about astronomy. You have to google. You
can just that's right, cosmic googling, otherwise known as telescopes. Um.
You just look out into space and eventually you will
(22:51):
see that thing happening, like you want to imagine some
crazy scenario, or this kind of galaxy hits that kind
of galaxy, and then from behind comes a third one
that's happening somewhere out there there and you just need
to find it and watch it. And so that's the
amazing thing about astronomy is that all these cosmic experiments
are happening. We just need to look for them. Okay,
well we process that. Let's say, let's take a quick break,
(23:24):
all right, So that's what might happen to the stars
in the galaxy. What's going to happen to all these
other parts of the galaxy when these two galaxies collide, right?
And I like that we started with the stars because
that's like the most important thing to us, because we're
sort of staro centric, right, because we think stars are
most the most important element of the galaxy. But the
biggest element of the galaxy, remember, is dark matter. And
(23:45):
so you might ask, well, what's going to happen to
all our dark matter? And just like with the stars,
what what happens there depends on how much it interacts. Currently,
we don't really know anything about how much dark matter interacts.
We know that it doesn't interact with normal matter. We
think it doesn't interact with itself, or if it does,
it doesn't interact very strongly and so, but it does
have gravitational attraction. So if the galaxies are are going
(24:07):
to hit each other and they're not moving too fast
that they just basically pass right through each other, then
the gravity from dark matter is going to affect the
gravity from the other galaxies dark matter just the same
way the stars are, and the two will sort of
merge eventually become one big dark matter halo. And it's
the kind of thing I would love to watch, but
you can't really see the dark matter. It could be
(24:27):
just another version of the cluster of stars. You know.
It's like one blob goes into the other blob and
then they kind of slash around and then just becomes
a bigger blob. Yeah, you can think of the stars.
It's sort of like a collisionless liquid, right, It's like
a you have a liquid of stars that don't interact
with each other the same way the dark matter does.
So dark matter in stars are basically operating this under
(24:49):
the same principles. The only relevant interaction that we know
about is gravity, So everything we said about stars is
also going to affect the big blobs of dark matter.
The dark matter is much more continuous. We think it's smooth.
It's not like there's just dots of it here and there.
But because it hardly interacts with each other, it doesn't
matter if it rams smack into itself. Right, It mainly
affect is gravitational. It may not interact with itself. It
(25:12):
could just pass by itself and not really kind of
explode or collide or do anything besides pull itself gravitationally. Yeah, exactly.
And we don't even know what dark matter is made out,
so we can't say things like dark runner particles can
do this. Dark matter as far as we know, it's
just smooth, collisionless blob of something. And we know it
has gravitational interactions, and that's really about all we know
(25:33):
about it. So we think that that that's what's going
to happen. And you know, we've seen dark matter in
these gravitational collisions and we see that it basically sticks
with the galaxies, right, it sticks with the stars. Okay,
so then the last part is the black hole at
the center of each galaxy. What no, no, don't forget
the dust, right, this gas dust, which a lot of
people overlook, and this is actually the most exciting part
(25:55):
because the dust is the most the coolest part. That's
how you know you're listening to a nerdy podcast and
they get excited about dust. Oh my god. You know
if if for those people who are like expecting dramatic
events and explosions, this is where you get them. Okay,
because dust is not diffuse, right's spread everywhere, Like you
(26:16):
have a big blob of dust. It's not like little
clusters of mass the way stars are. It's a huge
extended blob of dust. And when it smashes into another
blob of dust, you're going to get fireworks. Like those
clouds of dust interact with each other the way dark
matter doesn't. And they're um spread everywhere the way stars aren't,
and so you get huge collisions. And what happens when
(26:39):
you compress gas and dust. What happens when you collide
huge blobs of gas and dust is you get more
dense and then you get stars. And so you could
see like new stars being born where these two huge
clouds of gas and dust being into each literally like fireworks.
Like that's right, cosmic fireworks. I mean, what's more are
(27:00):
dramatic and what's a better cosmic firework than seeing stars
be born? Yeah, so this one is going to be
like to you know, you know, two liquids kind of
running into each other. It is going to be kind
of dramatic, you know, like it is going to be
like with the sound effects and everything in space. No, yeah, exactly,
It's just like two water balloons hitting each other. Right,
(27:21):
You're gonna get an initial shop wave. And you know,
you don't get stars born when you fire water balloons
at each other because the density isn't great enough obviously,
But yeah, you're gonna get a shock wave. You're gonna
get friction between the fluids, and you're going to get
stars being born. It's gonna be pretty dramatic. So you
don't want to be there. You don't want to want
to But we are, aren't We surrounded by gas clouds
and stuff? Oh? I think you need denser stuff. I mean,
(27:43):
the milky wave definitely has big clouds of gas and dust.
Oh I see, But when those clouds running to the
other clouds, then that's where this stuff happens. But we're
not necessarily sitting in one of those clouds. That's right, yeah, okay,
the last element is the black hole, right, and so
our galaxy is a huge black hole the center, and
(28:03):
the other guy, almost every other galaxy is a huge
black hole of the center. And there it's gonna be
mostly dominated by gravity, right, because they're gonna pull each
on each other really hard, and they're gonna pass by
each other a little bit, perhaps because they're probably not
gonna hit dead on and then they're gonna swing around.
They're gonna pull on each other, so they'll probably be
you know, some sort of a near miss, and then
(28:24):
they'll turn around and come back. And then they'll just
circle each other faster and faster and faster. And if
you remember the episode we did on gravitational waves, or
if you've heard about the discovery of gravitational waves, you
know that what happens when black holes get close to
each other as they start to circle each other faster
and faster, until eventually they spend really really fast and
the distance get closer and closer and closer, and then
(28:46):
they merge and they become one enormous black hole. They
like eat each other, right, But and it's not a
peaceful event it's like a pretty violent thing, right, Like
they've been super super fast, there's energy spewed out everywhere,
and then suddenly have these huge cataclysmic gravitational waves. Oh yeah,
when black holes fight, it's a big mess. Absolutely. You
don't want to be anywhere near that because huge amounts
(29:09):
of radiation, not just gravitational waves. Right, yeah, you make
gravitational waves, which are pretty awesome from a physics point
of view, but you know, these things tear up into
each other and amid huge amounts of radiation, and so
you don't want to be anywhere near that. Yeah, I
mean that that's gonna like sterilize life on any nearby
star system for sure. But anyway, there probably isn't any
life in the center of art galaxy for that same
reason that the galactic black hole is already emitting huge
(29:31):
amounts of life killing radiation, so you don't want to
get too close anyway. It's like the eye of a storm.
There's nothing living in the middle of it, that's right.
I don't know if it's calm inside the black hole.
That we did a whole episode actually on what it's
like to be inside a black hole. So you guys
should go listen to that. But yeah, it's a it's
everything is swirling around that central black hole. And so
probably what will happen is they'll merge and the new milk,
(29:51):
the new galaxy. I wonder what that galaxy would be called. Actually,
how would you combine and Rameda in the Milky Way,
like Drama Dinky Way, milk milk Drameda, I don't know,
and ramedaway the Andromeda Away. There you go, the Andromeda Way. Yeah,
the new galaxy would have a huge, super duper massive
(30:14):
black hole at its center. Yeah, and so I think
that basically sums it up. You'd have the black holes
will probably emerge huge violent eruption of radiation there gas
and the dust would have a lot of friction caused
caused star formation, big explosion, bigion work, Yeah, exactly. Friction, Yeah,
just all the kind of stuff you expect to see
in the next Transformers movie. And then stuff. He'll be there,
(30:38):
He'll be there everything. If there's money to be made,
he'll be there. Um. And then the stars and the
dark matter will just have a gravitational effect, but they'll
know eventually settle down and in a few more billion years,
the new galaxy will have its own shape. It will
sort of settle into its own new shape. But it
kind of sounds like every part will do something. Friend,
(31:00):
do you know what I mean? Yeah, they will because
they follow different rules, right, they interact differently and so
but so, then kind of the nice structure we have
now is going to be pretty much obliterated right when
it we're just with the other one. Yeah, exactly. You
shouldn't count on your real estate being the same value.
After the galaxy collision, Everything's going to be shook up, right, Absolutely,
it's going to be disrupt the entire Both galaxies gonna
(31:21):
be totally disrupted. Fireworks collisions. But you're saying it's possible
we may survive it, right, that it's possible nothing will
actually happen to our solar system. I think that's the
most likely outcome. Yeah, is it will just be sort
of interesting likely, Yeah, most likely most likely thing. I mean,
we're a star. We were basically part of our star,
right you think of the Solar system is just one
(31:41):
big blob, And the most likely thing is that nothing
gets close enough to disrupt our orbit around the star.
And you know what, even if our star gets like
ejected from the galaxy. So what we don't need the galaxy.
We could live just fine, just a star with a
bunch of planets in the middle of intergalactic space. We
don't need anything else. We just never start to provide
energy for life. So so we don't mean just in
(32:03):
the same way we're talking about the beginning of the episode,
like you don't really notice what's going out in space
because you don't usually have to. And if all those
if all those stars disappeared and all we and we
were in the middle of intergalactic space, it wouldn't change
your life at all. You would still still need to
stock up on lentils for the coming Apoco lips. You know,
it wouldn't save you or change your plans at all.
You wouldn't mind getting kicked out of town like that.
(32:24):
That's kind of what it would feel like, like the
whole town, our whole town. We just get kicked out,
you know, and we just go on living the way
what we did before. But things will definitely change for
us even if we survived it's galactic collision, the night
sky will look very different. I mean, as Andromeda approaches
in the next few billion years, it will grow in
the sky and eventually look really big. And then after
(32:47):
the collision, right when things have settled down, the night
sky would look totally different because all the stars will
have been rearranged and we won't see that band in
the milky Way anymore. Well, that makes me feel better.
I was sweating. I was sweating what was gonna happen
for and I have been years from now. But now
now I feel better and I and I hope Blake
you also feel a little bit better. Yeah, that's right, Bake,
chill out, don't worry about it. Um, you have nothing
(33:08):
to worry about. I think it's fun to think about
things happening deep into the future, and also even further
into the future. You know, the universe has been around
fourteen billion years, right, and that's just sort of like
the initial bits, not before we get to the interesting part.
But it could be they were not even at the
(33:30):
interesting part. You know. Thinking about galaxies in this way
reminds you that they're spinning their dynamic, they're swirling around
each other. What's going to happen? We don't know, right,
they could continue to swirl and form crazy new structures
that know, the universe has never seen before. Because there
hasn't been time to make them. And so this is
the kind of thing makes me think about the universe,
like on the trillion or two trillion life year cycle,
(33:53):
Like if life is still around ten trillion years into
the history of the universe, they'll think about these first
few moments of lactic formation as you know, almost irrelevant,
just like just warming up. The best maybe yet to come. Now,
that's right. I'm an optimistic person, so I'm always hoping
that the best thing is yet to come. Exactly well, great, um,
(34:14):
thank you so much Bla for sending us this question.
We really enjoyed answering it. That's right. And check out
our book called We Have No Idea. It's a guide
to the unknown questions of the universe, all the things
that physics wants to know the answer to but really
hasn't got a clue about. And thanks for listening. Yeah,
and if you're hungry or want to stuck up, just
don't forget to get Daniel's Spicy lentils, now available at
(34:39):
your local grocery store. If you still have a question
after listening to all these explanations, please drop us a line.
We'd love to hear from you. You can find us
at Facebook, Twitter, and Instagram at Daniel and Jorge That's
one Word, or smail us at Feedback at Daniel and
(35:02):
Orge dot com. H m hm
Hey, Daniel, what keeps you up at night? Oh? I
worry about a lot of things. Financial crises, my kids
growing up to be just like me, all sorts of stuff.
I worry about that too for them. You worry about
my kids growing up to be just like me. We
can't have more of him in the world, Okay, But
like on a galactic scale, on a universe scale, what's
(00:29):
something we should be concerned about. Well, we do have
a lot of things look forward to in terms of
our galaxy. If we survived the Sun exploding and the
waters the Earth boiling off, then we have something pretty
dramatic to look forward to, which is that our galaxy,
the Milky Way, is going to collide with their nearest
neighbor and Dromeda. Meaning right now, there's an entire galaxy
Drameda heading towards us at this very moment. That's right.
(00:51):
It's like somebody shot it at us with a slingshot
and it's zooming right towards us, and it's going to
hit us smack on him. And I'm Daniel, and this
(01:17):
is our podcast. Daniel and Jorge explained the universe on
the episode. Today, we're going to talk about what will
happen when galaxies collide. Is this something we should all
be worrying about our packing our bags, about building our
underground shelters or are we all screwed? Or is it
just going to be like a big nothing? How much
(01:39):
should I pack? You should definitely be stalking lentils no
matter what. Lentils are a good investment for any of
these end of the world. Not just beans, no, no, lentils.
I mean lentils are kind of lego for a galactic emergency.
That's the that's the one to go with. Yeah, absolutely,
I would. I would invest in lentils heavily. And it's
not just because I happened to purchase lentils just before
(02:00):
we recorded this podcast and I'm trying to drum up
the lentil futures, you know. I'm I'm sincerely worried about
our listeners, and I encourage you all to go out
there in stockpi lentils. Well that's a whole hill of
beans worth of advice right there, that's right. And so
this is the question and today's podcast, what will happen
when our galaxy, the Milky Way, collides with the neighboring galaxy?
(02:21):
And this question I love not just because it's huge
and dramatic and galactic and all this sort of stuff,
but because it was suggested by one of our listeners.
That's right. It's Blake from Australia who listens to this
podcast on her commute to work every day. That's right.
And she didn't tell us what she uses to commute.
Maybe she rides in a beautiful pickup truck, maybe she's
in the back of a limo, maybe rides kangaroo who knows,
(02:45):
that's right, with a really nice sound system. Yeah, but
she has some interesting feedback for us about our podcast. Right,
what did she say? Yeah, she said that she likes
listening to me explain things, but she also likes when
you interrupted me. She said that often you interrupt me
just the same moment when she has a question and
you pose the same question that was bouncing around in
(03:05):
her head that she was shouting at her limo sound
system or kangaroo speakers or whatever it is she us
going to listen to. And so I was glad for that,
because you know, I like when you interrupt me. Also
it breaks the flow and it keeps me from just
droning on and on and on. So Thank you Blake
for suggesting this topic, and thank you Orge for occasionally interrupting. Yeah, no,
I'm happy to be rude. It seems to come naturally. Yeah, yeah,
(03:31):
And so that's the topic of today's podcast, And we
thought first before we dove into it, we would walk
around like we usually do and ask people, are you
worried about a galactic collision? What do you think will
happen when our galaxy collides with a neighboring galaxy? So
put that image in your mind to giant galaxies, full
stars running into each other. What do you think is
(03:52):
going to happen? Here's what people had to say, big explosion.
We'd probably all die. It is going to be mostly
nothing because of all the empty space around the world,
although there will be some crushes and so on in
the way. Okay, probably somewhere between a glacial, slow event
that we won't even notice and nothing at all. Maybe
(04:13):
leaning towards nothing at all. I think it would probably
be a big explosion with something pretty crazy happening. All right,
That was a little anti climatic. People seem to have
very low expectations of this event. What do you mean
It seems like half of the people are like it's
gonna be nothing, and the other half of like big explosions,
we're all gonna die. Well, why do you why do
(04:36):
you think Blake asked this question? Do you think there's
something she's concerned about or is something she's curious about?
You know? I think Blake is probably deciding whether or
not to stock up on lentils. You know, Um, she's
probably right now, story she asked. I think it's part
of just trying to be a sort of a citizen
of the larger universe, you know, wondering where we stand
(04:56):
and trying to think bigger than just our planet, you know,
because there's so much going on out there, it's so
easy to just walk around on the surfaces planet never
really look up and remember that there is an enormous
amount of stuff happening out there, And then you wonder like, well,
how is that relevant to me? And is he going
to ruin my life? Or can I go on ignoring it? Um? So,
I think maybe she was just sort of thinking into
(05:16):
the deep future and wondering like, how long can this
whole ridiculous, beautiful thing we call life on Earth go on? Right?
Is it going to change from how it is now, right, Yeah,
exactly do I need to change the way I live?
Does it affect any decision making? On the other hand,
it could be that Blake, like many people, is just
a thinker and likes to think about these scenarios, and
she probably heard that the Milky Way will collide with
(05:38):
Andromeda and wonder like, what's that going to be? Like?
You know this this this is the other side of
me that likes to smash stuff together. I mean, I'm
a particle physicist, but then we have the whole universe
to play with, right, and so you might wonder, like
what happens when planets collide, what happens when solarcisms? Like
oh my gosh, what if we could build a galaxy
collider and shoot them against each other and smash them
into each other? Right, So it just comes out of
(05:59):
like a curiosity to see stuff break by smashing it together. Yeah, well,
let's let's take it step back and just kind of
think about why even galaxies would collect, Like is this
a relevant question that is something that happens a lot
galaxies colliding, or is it something that's incredibly rare. It
turns out galaxies colliding happens all the time. It's like
a totally natural thing. And our galaxy. Yeah, not only
(06:22):
will our galaxy collide with and John Day in a
few billion years, it's currently colliding with other smaller galaxies.
That what Yeah, we're in a collision right now. Yeah,
that's right. And remember that the galactic time scales are
very different. You know, the galaxy takes about two hundred
million years just to rotate once, to go around once. Yeah,
(06:44):
so one galactic year is two hundred million earth years.
But it looks so swirly. It looks you know, you
know what I mean, Like it looks like it's in motion,
but it's actually it is. It is in motion, it's
just very slow, right, And so all these things are
dancing around each other and sometimes they bump into each other.
And the thing I think is amazing is that, you know,
(07:05):
until like a hundred years ago, we didn't even know
there were other galaxies. Like we looked up at the
night sky and we saw stars, and we thought, oh,
there's just stars that go on forever. At the universe
is just filled with stars. The universe is just like
a giant MESSI pinpoints, right, just stars. Yeah, yeah, like
somebody had scattered stars across the cosmos, right, And it
(07:26):
was Hubble, the guy for whom the telescope and the
constant are named. He's the guy who figured out, oh,
some of those things that are really far out there
are not stars. There are other galaxies. Right, So there's
the universe is filled with other galaxies. And of course
there are more galaxies than stars, and and then each galaxy,
of course, contains hundreds of billions of stars, and so
the numbers pretty quickly blow your head up before you
(07:48):
can understand them. But the point I wanted to make
was that we didn't realize there were galaxies until recently,
and now we're realizing that galaxies are in motion relative
to each other, and they're moving. Like the these galaxies
that we see out there in the sky, they're not
just like hanging there in space never to change, right,
They are moving their dynamic things, and they're constantly in motion,
(08:09):
and they have huge gravitational attraction. Well, let's break it down.
What exactly is a galaxy? I mean, I know it's
like kind of like a collection of stars, but you
know what, why do stars clump together like that? First
of all? And what makes a galaxy special? Like, why
is it more than just a clump of stars. Well,
what makes our galaxy special is that you're in it. Horse.
(08:29):
There's no other galaxy that features such a good looking,
funny cartoonists, meet me and lentils. We make it, make
it habitable, right, Okay, so what's the recipe for a galaxy? Right? Well,
the thing that the galaxies have the most of, remember,
is dark matter. In general, there's about five times as
much dark matter as there is any other kind of matter,
(08:52):
you know, the stuff that makes up gas and dustin
stars and people and cartoonists and and and ice cream.
So it's mostly dark matter. So that's the stuff we
can't see your touch. I mean, we did a whole
podcast episode on dark matter, but it just in case
somebody didn't listen to it. Um, it's like this weird
invisible dark gravity thing that's hanging out every galaxy has,
(09:15):
that's right. Yeah, we call it dark and matter because
we can't see it. So it's dark and we know
it gives gravity, so therefore it's matter and the crazy
things that until you know, a few decades ago, we
didn't even know it existed. And now we know that
galaxies are mostly made up of this stuff. Right. So
number one ingredient when you want to make a galaxy
is you have to have dark matter. It's like five
(09:35):
times more than the stars, right, yeah, exactly, Like a
galaxy is basically a clump of dark matter with a
few sprinkles of stars in it. That's right. Yeah. If
a galaxy was a cupcake, right, the dark matter would
be the chocolate cake, and you know there everything else
would be the frosting and the sprinkles. The gas and
the dust would be the frosting. The stars would be
the sprinkles on top. Oh I see, Okay, that's kind
(09:55):
of the right proportions. Yeah, something like that. Um, So
you start with big blob of dark matter and that's
most of it, and then after that you have huge
amounts of gas and dust, right, And that's the stuff
that's left over from the Big Bang or left over
from stars exploding, and those the ingredients you need to
make planets and stars and all sorts of stuff that
you're familiar with, right. And so you have dark matter,
(10:18):
you have gas, you have dust, you have planets and
stars and black holes right, Like there's just a little
black hole sprinkled throughout throughout probably, But there's a huge
giant black hole at the center of every galaxy. That's right.
I can't believe I forgot the black hole. The black
hole at the center of almost every galaxy is huge.
It's like, you know, millions of solar masses and it's
(10:40):
sitting there at the center of the black hole, and
it's it's got a lot of stuff to it also, right,
it carries a lot of mass and so it contributes.
So that's what a galaxy is. And you know, a
galaxy couldn't really form without all those elements, Like you
couldn't really have a galaxy without dark matter because dark
matter provides the gravitational attraction to suck all this stuff together.
You know, they do these simulations of the universe. They say,
what would the universe look like if you never had
(11:02):
dark matter in it? And it would take a lot
longer for galaxies to form because dark matter has pulled
all this stuff together. It's like it's made a you know,
like a well in the rubber sheet of the universe,
so everything rolls together more closely. Okay, so that's a
that's a galaxy. It's a black hole surrounded by dark
(11:23):
matter and sprinkles of stars and gas and dust and
lintels and lintels exactly yes, And so they're not just
hanging out in space. They're moving around. That's right there.
Each one is spinning, right, which is why you see
a lot of them having these these spiral features. Each
one is spinning, and then they're also moving around each other.
They have gravity and they're moving around each other, and
(11:45):
they have these Each galaxy is a member of a
cluster of galaxies, and so these guys are orbiting the
center of the cluster. And then the clusters are members
of superclusters. So these things have a lot of gravitational
interactions everywhere. It's like a system of galaxy. They all
interact with each other, and they all spin around their
common center of mass exactly right, And they're all spinning
(12:07):
around that center. So it's sort of like a big
slow motion tornado. Right you looked at it. If you
looked at it really really slow, you're like, oh, nothing's
really moving. I mean, I guess a little bit, but
you you you watch it at natural speed of tornado,
and obviously it's going really fast, and so a galaxy
is that's sort of that same way. The gather system
of galaxies is sort of that same way, but they're
all moving around each other and then occasionally, you know,
(12:28):
they bump into each other. Wow, that's so weird to
think that gravity works the way like we are, you know,
moving around the center of the Earth. The Earth is
moving around our solar system, around the center of gravity,
which is mostly the Sun, but the Sun is also
we were moving around the center of gravity of the galaxy,
and the galaxy is also moving around the center of
gravity of its cluster of galaxies. That's right, Yeah, and
(12:50):
on and on and on like a bunch of nested
Russian dolls, you know, until you get to the biggest
structures in the universe, you know, which are the superclusters,
and then the filaments of superclusters, and beyond that, we
don't know anything about whether there are bigger and bigger structures.
That's as far as we've seen. So we're moving around
and sometimes these two two galaxies can just run into
each other. In the giant, vastness of space, all these
(13:12):
moving galaxies can sometimes cross pass right. Yeah. And there's
another thing I want to say about that before we
talk about what actually happens, which is that it's incredible
to me that gravity is the force that's dominant on
these scales, right, Like, that's the thing that's controlling how
galaxies form and how they dance around each other, and
that's pulling them all the way through the universe and
forming these crazy structures. It's all gravity, right. But gravity
(13:35):
is the weakest force of nature. It's weaker than electromagnetism,
it's weaker than any of the nuclear forces. It's pathetically weak,
but it's the only one that operates on these huge scales,
and it can't be balanced out. And so because it's
only an attractive force, there's no repulsive version of it.
And so that's why, like on these huge scales, gravity
is the thing that dominates. Gravity determines the structure the
(13:57):
Solar system, the structure the galaxy, the structure of the clusters.
Gravity sort of winds in the end. It's like, you know,
revenge of the nerd forces, Right, It's the weakest force
in the end controls the universe. It's like slow and
steady wins the race. It's the turtle of forces. Yeah, Anyway,
we need to do a whole other podcast on why
gravity is so weird and weak and whatever, and we're
(14:18):
into that. Okay, so we have a cult clusters and
galaxies are moving around space and sometimes they collide. So yeah,
let's talk about what actually happens when two of these
things collide. But first let's take a quick break. All right.
(14:42):
So we're sitting in a galaxy and we are moving
inside of this galaxy, and this galaxy is moving in space.
But there's another galaxy nearby called the Andromeda galaxy, and
it's kind of an interset course with us, right, like
we're going to run into it in about four and
a half billion years. Yeah, not kind of. They've measured it.
They can measure the velocity of Andromeda relative to us,
(15:04):
and they can see that it's getting closer and closer
every year, and they can also measure the lateral velocity,
like is it going to shoot by us or just
or come right at us? And after for a while
they weren't sure. They were like, oh, it's heading our way,
but it could miss, you know, like every time they
say there's an asteroid coming within, you know, a certain
thousands of miles of the Earth, and usually it misses.
(15:24):
For a while, they weren't sure, but now they're pretty
certain they've taken enough measurements, they've seen it move, and
they can project confidently that these two things are going
to collide. Also, Andromeda and Milky, we have a lot
of gravity, and so you don't have to aim perfectly
to get a collision, right, They're gonna um pull each
other closer and closer. They want to collide, you know,
(15:44):
you know what I mean, Like, it's not like a
random asteroid. It's like we're we're pulling towards each other. Yeah, well,
I don't know if you can really say they want Like,
do you understand the psychology of the galaxy? Do you you
know what galaxy wants in life? You know, Hey, galaxy
have feelings, right, I think I read that science fiction
novel right where every galaxy is actually a living thing
and we're just like the tiny moats on the on
(16:06):
an island of red blood cells instead of galaxy. Anyway, Yeah,
so you don't have to shoot perfectly, and they're gonna collide.
So to think about what happens in the collision, you
probably think about each individual piece separately, Like we're a
cluster of things. Like a galaxy is not a solid object.
It's like a word almost like a cloud of things,
right is that kind of way? Mean? Yeah, yeah, exactly.
And you know, imagine two crowds right passing into each other,
(16:28):
and like one gets off the train and one's coming
down the stairs and they pass each other in the platform.
What's going to happen, Well, it depends on how they interact, right,
and how dense they are. So we can start with
something and the obvious parts, like the stars. Okay, so
you might think, oh my gosh, there's a hundred billion
stars coming right at us. That's going to be a
big deal. Is that the right size? Like it isn't
(16:48):
drama about the same size as the Milky Way. Actually
I think it's bigger than the Milky Way. But you know,
factors of ten here are not important. Um, so it's
hundreds of billions of stars, and each star, of course
is really big. And you might think, while they're heading
right at us, you know, this is gonna be a
big deal, But remember that the stars are really far apart. Also, like,
galaxies are huge, not just in terms of the number
(17:08):
of stars, in terms of the amount of space they
take up. And you know, you look around you in
our galaxy, there aren't that many stars nearby, right, and
the closest stars are light years away. I like this
crowd analogy that's pretty interesting. Like we're a crowd of
people getting off the subway. There's a crowd of people
coming down the stairs to get on the subway. It's
(17:29):
going to be a disaster potentially. Potentially, But if it's
not rush hour and the crowds are pretty light, you know,
there's like enough space the two crowds can just pass
right through each other. Like if the stairways and the
hallways are huge and people are pretty spread out, it
may not be like a riot, you know, it may
just be like a busy intersection. Right, It's like two
people leaving Yankee Stadium at the same time as as
(17:50):
somebody else's trying to come in. Like there's plenty of exits,
nobody's gonna bump into each other, right, And that's sort
of the case with stars. I read this one comparison
where if you imagine the stars the size of a
ping pong ball on average, the nearest stars three kilometers away, right,
So like if you were going to throw a ping
pong ball into a cloud of ping pong balls, where
(18:11):
the spaces between them were three kilometers away. You'd be
lucky if you hit anything, right, even if you were trying.
Oh I see, Okay, So our galaxy is actually pretty sparse,
meaning the stars are pretty far apart from each other.
We're not sort of clumped together. Yeah, exactly, and astronomically speaking,
astronomically speaking, and so there's gonna be very few or
probably zero direct collisions. You know, where one star like
(18:34):
actually slams into another one, you get stellar explosions. I mean,
that would be pretty awesome. I would pay for front
road seat, but I think it's pretty unlikely that's going
to happen. But you know, there's a hundred billion stars
running into a hundred billion other stars. Surely some of
them are going to hit head on, isn't it. Aren't they?
I mean, there's always a non zero probability, and you
could get lucky you're unlucky, depending on which which outcome
(18:57):
you're rooting for. But if they're diffuse enough, right, they're
they're far enough apart, then then all of them could
pass through without hitting. I mean, I think probably the
most likely scenarios that maybe you get one. The stars
also don't have to hit directly to affect each other. Right.
Each one is a big blob of mass, which means
it has gravity, and so they can jostle each other.
I mean, if another star came by and near our
(19:18):
Solar System and pass nearby, it could affect the orbits
of all the planets, like nudge a planet out of orbit.
Didn't have to hit the star directly head on or
to affect our lives. It could maybe pull us out
of orbit or sunk us into that other star. That's right, Um,
it could it could steal planets right exactly. Or um,
one of our planets could get ejected out of the
(19:39):
Solar System right, or it could even kick our star
out of the galaxy. Our star is in orbit around
the center of the galaxy, right, and if it comes,
if another star comes near enough, it could get pulled
and so that it gets you out of that orbit, right.
And orbit is sort of a delicate thing. You have
to be the right radius and the right velocity for
it all to work and start going to fast and
(20:00):
you each escape velocity. And our star could even get
kicked out of the galaxy. So we could be you know,
sort of evicted from the Milky Way, floating in intergalactic space,
just our star with the planets and everything. Oh, I see.
So when two galaxies collided, it's not it's not we
don't have to worry about things running into each other.
But it is going to be pretty chaotic, right, Like,
(20:21):
suddenly there's going to be you know, twice the number
of stars, and that's just going to change everything, right, yeah, exactly,
So things that definitely get mixed up. The stars won't
necessarily smash into each other, but it definitely mix each
other up and disturb each other. So are they are
these two messages going to kind of go towards each other,
makes a little bit and then keep going, or are
(20:41):
they you know, slamming to each other and then become
this giant mega galaxy. It depends a little bit on
their relative velocity. If they're going fast enough relative to
each other, then they'll pass through each other, right, But
if if they're not, and it doesn't seem like they are,
the most like scenario is that they merge, that they
come together and there's a little bit of slashing or whatever,
but eventually becomes one big galaxy. But wait, what does
(21:04):
that mean? It's like the other stars and from the
other galaxy. They're gonna come, but then they're going to
kind of go pass us a little bit, and then
they're gonna get pulled back in kind of thing like
it's gonna like a giant jelly out in space, like
it's going to go move, you know what I mean,
but in slow motion, yeah, or sort of like things
getting flushed down the toilet. You know, they come closer
and closer and closer and circle each other faster and faster.
(21:26):
You know, where we might circle each other, the two galaxies, Yeah,
and sort of a wall being on top of each other,
you know, so coming together pass a little the centers
of mass might pass a little bit and then turn
and come the other direction and spin it faster and
faster until the center is a massive line. So being
flushed down the toilet. That doesn't doesn't sound pleasant. Like
that doesn't sound like it's going to be easy, do
(21:46):
you know what I mean? Like, it doesn't sound like
it's going to uh leave us unscathed. It might, though,
you know, our sun could be totally fine, and it
could be that the planets are not distorted, their orbits
are not distorted, and we could just have a front
row seat to a pretty amazing event. And the other
thing is that we see this happening all the time.
Like you look out into space with the hubble zoom
in on other galaxies. There's lots of galaxies out there,
(22:08):
and lots of them are in state various stages of emerging.
And you can see galaxies that are just starting to merge.
You can see galaxies that have been merging for a
billion years. You can see galaxy that obviously merged a
long time ago. And there's sort of like an uncomfortable
blob of two galaxies, like one spiral arms sort of
knocked off over here and there's another one over there.
And so we have a lot of catalogs of examples
(22:30):
of galaxies that have mergy. That's how we know so
much about it. Yeah, if you look at there's a
bunch of crashes that you can study. Yeah, exactly. So
you want to know what galaxy collisions look like, you
don't have to build a galaxy collider. This is one
thing I love about astronomy. You have to google. You
can just that's right, cosmic googling, otherwise known as telescopes. Um.
You just look out into space and eventually you will
(22:51):
see that thing happening, like you want to imagine some
crazy scenario, or this kind of galaxy hits that kind
of galaxy, and then from behind comes a third one
that's happening somewhere out there there and you just need
to find it and watch it. And so that's the
amazing thing about astronomy is that all these cosmic experiments
are happening. We just need to look for them. Okay,
well we process that. Let's say, let's take a quick break,
(23:24):
all right, So that's what might happen to the stars
in the galaxy. What's going to happen to all these
other parts of the galaxy when these two galaxies collide, right?
And I like that we started with the stars because
that's like the most important thing to us, because we're
sort of staro centric, right, because we think stars are
most the most important element of the galaxy. But the
biggest element of the galaxy, remember, is dark matter. And
(23:45):
so you might ask, well, what's going to happen to
all our dark matter? And just like with the stars,
what what happens there depends on how much it interacts. Currently,
we don't really know anything about how much dark matter interacts.
We know that it doesn't interact with normal matter. We
think it doesn't interact with itself, or if it does,
it doesn't interact very strongly and so, but it does
have gravitational attraction. So if the galaxies are are going
(24:07):
to hit each other and they're not moving too fast
that they just basically pass right through each other, then
the gravity from dark matter is going to affect the
gravity from the other galaxies dark matter just the same
way the stars are, and the two will sort of
merge eventually become one big dark matter halo. And it's
the kind of thing I would love to watch, but
you can't really see the dark matter. It could be
(24:27):
just another version of the cluster of stars. You know.
It's like one blob goes into the other blob and
then they kind of slash around and then just becomes
a bigger blob. Yeah, you can think of the stars.
It's sort of like a collisionless liquid, right, It's like
a you have a liquid of stars that don't interact
with each other the same way the dark matter does.
So dark matter in stars are basically operating this under
(24:49):
the same principles. The only relevant interaction that we know
about is gravity, So everything we said about stars is
also going to affect the big blobs of dark matter.
The dark matter is much more continuous. We think it's smooth.
It's not like there's just dots of it here and there.
But because it hardly interacts with each other, it doesn't
matter if it rams smack into itself. Right, It mainly
affect is gravitational. It may not interact with itself. It
(25:12):
could just pass by itself and not really kind of
explode or collide or do anything besides pull itself gravitationally. Yeah, exactly.
And we don't even know what dark matter is made out,
so we can't say things like dark runner particles can
do this. Dark matter as far as we know, it's
just smooth, collisionless blob of something. And we know it
has gravitational interactions, and that's really about all we know
(25:33):
about it. So we think that that that's what's going
to happen. And you know, we've seen dark matter in
these gravitational collisions and we see that it basically sticks
with the galaxies, right, it sticks with the stars. Okay,
so then the last part is the black hole at
the center of each galaxy. What no, no, don't forget
the dust, right, this gas dust, which a lot of
people overlook, and this is actually the most exciting part
(25:55):
because the dust is the most the coolest part. That's
how you know you're listening to a nerdy podcast and
they get excited about dust. Oh my god. You know
if if for those people who are like expecting dramatic
events and explosions, this is where you get them. Okay,
because dust is not diffuse, right's spread everywhere, Like you
(26:16):
have a big blob of dust. It's not like little
clusters of mass the way stars are. It's a huge
extended blob of dust. And when it smashes into another
blob of dust, you're going to get fireworks. Like those
clouds of dust interact with each other the way dark
matter doesn't. And they're um spread everywhere the way stars aren't,
and so you get huge collisions. And what happens when
(26:39):
you compress gas and dust. What happens when you collide
huge blobs of gas and dust is you get more
dense and then you get stars. And so you could
see like new stars being born where these two huge
clouds of gas and dust being into each literally like fireworks.
Like that's right, cosmic fireworks. I mean, what's more are
(27:00):
dramatic and what's a better cosmic firework than seeing stars
be born? Yeah, so this one is going to be
like to you know, you know, two liquids kind of
running into each other. It is going to be kind
of dramatic, you know, like it is going to be
like with the sound effects and everything in space. No, yeah, exactly,
It's just like two water balloons hitting each other. Right,
(27:21):
You're gonna get an initial shop wave. And you know,
you don't get stars born when you fire water balloons
at each other because the density isn't great enough obviously,
But yeah, you're gonna get a shock wave. You're gonna
get friction between the fluids, and you're going to get
stars being born. It's gonna be pretty dramatic. So you
don't want to be there. You don't want to want
to But we are, aren't We surrounded by gas clouds
and stuff? Oh? I think you need denser stuff. I mean,
(27:43):
the milky wave definitely has big clouds of gas and dust.
Oh I see, But when those clouds running to the
other clouds, then that's where this stuff happens. But we're
not necessarily sitting in one of those clouds. That's right, yeah, okay,
the last element is the black hole, right, and so
our galaxy is a huge black hole the center, and
(28:03):
the other guy, almost every other galaxy is a huge
black hole of the center. And there it's gonna be
mostly dominated by gravity, right, because they're gonna pull each
on each other really hard, and they're gonna pass by
each other a little bit, perhaps because they're probably not
gonna hit dead on and then they're gonna swing around.
They're gonna pull on each other, so they'll probably be
you know, some sort of a near miss, and then
(28:24):
they'll turn around and come back. And then they'll just
circle each other faster and faster and faster. And if
you remember the episode we did on gravitational waves, or
if you've heard about the discovery of gravitational waves, you
know that what happens when black holes get close to
each other as they start to circle each other faster
and faster, until eventually they spend really really fast and
the distance get closer and closer and closer, and then
(28:46):
they merge and they become one enormous black hole. They
like eat each other, right, But and it's not a
peaceful event it's like a pretty violent thing, right, Like
they've been super super fast, there's energy spewed out everywhere,
and then suddenly have these huge cataclysmic gravitational waves. Oh yeah,
when black holes fight, it's a big mess. Absolutely. You
don't want to be anywhere near that because huge amounts
(29:09):
of radiation, not just gravitational waves. Right, yeah, you make
gravitational waves, which are pretty awesome from a physics point
of view, but you know, these things tear up into
each other and amid huge amounts of radiation, and so
you don't want to be anywhere near that. Yeah, I
mean that that's gonna like sterilize life on any nearby
star system for sure. But anyway, there probably isn't any
life in the center of art galaxy for that same
reason that the galactic black hole is already emitting huge
(29:31):
amounts of life killing radiation, so you don't want to
get too close anyway. It's like the eye of a storm.
There's nothing living in the middle of it, that's right.
I don't know if it's calm inside the black hole.
That we did a whole episode actually on what it's
like to be inside a black hole. So you guys
should go listen to that. But yeah, it's a it's
everything is swirling around that central black hole. And so
probably what will happen is they'll merge and the new milk,
(29:51):
the new galaxy. I wonder what that galaxy would be called. Actually,
how would you combine and Rameda in the Milky Way,
like Drama Dinky Way, milk milk Drameda, I don't know,
and ramedaway the Andromeda Away. There you go, the Andromeda Way. Yeah,
the new galaxy would have a huge, super duper massive
(30:14):
black hole at its center. Yeah, and so I think
that basically sums it up. You'd have the black holes
will probably emerge huge violent eruption of radiation there gas
and the dust would have a lot of friction caused
caused star formation, big explosion, bigion work, Yeah, exactly. Friction, Yeah,
just all the kind of stuff you expect to see
in the next Transformers movie. And then stuff. He'll be there,
(30:38):
He'll be there everything. If there's money to be made,
he'll be there. Um. And then the stars and the
dark matter will just have a gravitational effect, but they'll
know eventually settle down and in a few more billion years,
the new galaxy will have its own shape. It will
sort of settle into its own new shape. But it
kind of sounds like every part will do something. Friend,
(31:00):
do you know what I mean? Yeah, they will because
they follow different rules, right, they interact differently and so
but so, then kind of the nice structure we have
now is going to be pretty much obliterated right when
it we're just with the other one. Yeah, exactly. You
shouldn't count on your real estate being the same value.
After the galaxy collision, Everything's going to be shook up, right, Absolutely,
it's going to be disrupt the entire Both galaxies gonna
(31:21):
be totally disrupted. Fireworks collisions. But you're saying it's possible
we may survive it, right, that it's possible nothing will
actually happen to our solar system. I think that's the
most likely outcome. Yeah, is it will just be sort
of interesting likely, Yeah, most likely most likely thing. I mean,
we're a star. We were basically part of our star,
right you think of the Solar system is just one
(31:41):
big blob, And the most likely thing is that nothing
gets close enough to disrupt our orbit around the star.
And you know what, even if our star gets like
ejected from the galaxy. So what we don't need the galaxy.
We could live just fine, just a star with a
bunch of planets in the middle of intergalactic space. We
don't need anything else. We just never start to provide
energy for life. So so we don't mean just in
(32:03):
the same way we're talking about the beginning of the episode,
like you don't really notice what's going out in space
because you don't usually have to. And if all those
if all those stars disappeared and all we and we
were in the middle of intergalactic space, it wouldn't change
your life at all. You would still still need to
stock up on lentils for the coming Apoco lips. You know,
it wouldn't save you or change your plans at all.
You wouldn't mind getting kicked out of town like that.
(32:24):
That's kind of what it would feel like, like the
whole town, our whole town. We just get kicked out,
you know, and we just go on living the way
what we did before. But things will definitely change for
us even if we survived it's galactic collision, the night
sky will look very different. I mean, as Andromeda approaches
in the next few billion years, it will grow in
the sky and eventually look really big. And then after
(32:47):
the collision, right when things have settled down, the night
sky would look totally different because all the stars will
have been rearranged and we won't see that band in
the milky Way anymore. Well, that makes me feel better.
I was sweating. I was sweating what was gonna happen
for and I have been years from now. But now
now I feel better and I and I hope Blake
you also feel a little bit better. Yeah, that's right, Bake,
chill out, don't worry about it. Um, you have nothing
(33:08):
to worry about. I think it's fun to think about
things happening deep into the future, and also even further
into the future. You know, the universe has been around
fourteen billion years, right, and that's just sort of like
the initial bits, not before we get to the interesting part.
But it could be they were not even at the
(33:30):
interesting part. You know. Thinking about galaxies in this way
reminds you that they're spinning their dynamic, they're swirling around
each other. What's going to happen? We don't know, right,
they could continue to swirl and form crazy new structures
that know, the universe has never seen before. Because there
hasn't been time to make them. And so this is
the kind of thing makes me think about the universe,
like on the trillion or two trillion life year cycle,
(33:53):
Like if life is still around ten trillion years into
the history of the universe, they'll think about these first
few moments of lactic formation as you know, almost irrelevant,
just like just warming up. The best maybe yet to come. Now,
that's right. I'm an optimistic person, so I'm always hoping
that the best thing is yet to come. Exactly well, great, um,
(34:14):
thank you so much Bla for sending us this question.
We really enjoyed answering it. That's right. And check out
our book called We Have No Idea. It's a guide
to the unknown questions of the universe, all the things
that physics wants to know the answer to but really
hasn't got a clue about. And thanks for listening. Yeah,
and if you're hungry or want to stuck up, just
don't forget to get Daniel's Spicy lentils, now available at
(34:39):
your local grocery store. If you still have a question
after listening to all these explanations, please drop us a line.
We'd love to hear from you. You can find us
at Facebook, Twitter, and Instagram at Daniel and Jorge That's
one Word, or smail us at Feedback at Daniel and
(35:02):
Orge dot com. H m hm
Hosts And Creators
Daniel Whiteson
Kelly Weinersmith
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