June 4, 2025 • 31 mins
Sure, there's a lot of space out there, but not all of it is prime real estate. Jorge answers questions about exoplanets for popular cartoonist Randall Munroe (XKCD).
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Speaker 1 (00:00):
Hey, welcome to sign Stuff, a production of iHeartRadio. I'm
Horhea Cham and today we are asking what is the
worst place to live in the galaxy. We live in
a nice, cozy place in the Milky Way, but is
there a spot where you definitely don't want your planet
to be. We think we have the answer, and it
came up during a conversation I had with Randall Munroe.
(00:21):
Randall's the number one New York Times best selling creator
of XKCD comics and the what If books and YouTube channel.
If you are in designs, chances are you've seen his
comics and videos featuring stick figures and nerdy humor. Randall
had questions for me about exoplanets, which are planets outside
of our solar system, and he specifically wondered what it
(00:42):
would be like to live in a particular location in
our galaxy. So get ready to travel to the worst
place to live in the Milky Way galaxy. Here's my
conversation with Randall Munroe. Hey everyone, Okay, I started off
by asking my friend Randall, what if I so interesting
about exoplanets, which are planets outside of our Solar system.
Speaker 2 (01:05):
Here's what he said, I don't really know I feel
like it's as close to like intrinsically interesting as something
can be. It's like, did you know there's other worlds
out there? And we have never taken a picture of
one of them where it's more than a pixel, But
we just learned they're out there. And I think it's
the novelty of it, like the newness of it, that
is really exciting for me. Like when I was born,
(01:27):
we had not confirmed the existence of any exoplanets. It
was all entirely speculative, and then all of a sudden
in my lifetime it's like, oh, hey, we spotted one
of them, and then we spotted another one, and then more,
and now we know about like thousands and thousands of exoplanets.
So it's like, Okay, I want to see them. I
want to know what they're like.
Speaker 1 (01:45):
Would you want to go there?
Speaker 2 (01:46):
I feel like physics means that I don't really have
to make that decision. Oh right. I think any kind
of space travel such a big commitment. I could see
wanting to travel in the Solar System, but something where
it's one of those one way across the universe, I
mean that sounds cool. I don't know that I personally
would opt for it, but I figure I'll worry about
(02:09):
that once the tickets become available.
Speaker 1 (02:11):
Right right, you wouldn't be a tour as you'd be
a migrant.
Speaker 2 (02:13):
Yeah, Like getting to another star one way is already
such a big lift, because just getting there is going
to be so hard, But I think I would put
like huge amounts of work into just like seeing them,
even if we just get a telescope that gives us
a handful of pixels or some kind of detailed atmospheric
breakdown clouds, anything that gives us a sense of like
what this place is like. I love that, you know.
Speaker 1 (02:37):
Awesome, So you had some questions for me. What's the
first question?
Speaker 2 (02:40):
I know, I've heard that there are these stars that
are orbiting the Milky Way super massive black hole, and
that's part of how we know that there's a black
hole there. We see these stars orbiting really close to
something that we can't see that seems to be really heavy.
And it just occurred to me, what would it be
like if you were on a planet around those stars?
Is it possible for there to be a planet around
the star? Would you notice you were around a black hole?
Speaker 1 (03:03):
Okay, what Randall is asking here? Is what would it
be like to live in a planet near the super
massive black hole at the center of our galaxy. It
turns out that most galaxies out there, including ours, has
a super massive black hole at their center. These are
huge black holes. For example, the one at the center
of our galaxy is called Sagittarius, a star, and it
(03:24):
has a mass that is about four million times heavier
than our sun. We recently took a picture of it,
but the main reason we knew it was there was
that we could see stars in clouds of gas circling
a spot that looked empty, which was a sign that
there was something really heavy there. Okay, back to Randall's.
Speaker 2 (03:43):
Question, would you be affected in any way? Is there
like a weird radiation environment?
Speaker 1 (03:50):
Like?
Speaker 2 (03:50):
What's it like there? Is it just like anywhere else
in the galaxy. It's just you happen to be near
a black hole? Or is it a bad place to be? Yeah?
Speaker 1 (03:58):
Excellent question. Did you up with this while trying to
figure out places to move to? No?
Speaker 2 (04:04):
I mean that's like fifty thousand light years something like that,
So I feel like if you're paying for a moving
van by the mile, that's going to get pretty expensive.
But I think I'm I'm going to keep black holes
at a healthy distance until I've talked to someone about
whether or not it's a good place to be.
Speaker 1 (04:19):
Yeah. Super amazing question. And by the way, I should
mention Randall that everyone I talked to, all the experts
I've talked to, they're all huge fans of yours.
Speaker 2 (04:25):
Oh, thank you.
Speaker 1 (04:26):
So for this question, I reached out to Professor Anne
Marie Madigan. Okay, I'm always excited when I find the
right person to talk to about a question, and in
this case, I found the perfect person. Anne Marie Madigan
is a professor of astrophysics and planetary sciences at the
University of Colorado at Boulder, and she happens to study
how stars and clouds of gases move around super massive
(04:49):
black holes like the one at the center of our galaxy. Now,
the first thing she wanted to do in her answer
was to paint us a picture of what space is
like at the center of our galaxy? Is it like
the space around us? Right now? Here's what she said.
Speaker 3 (05:05):
Okay, so this is a really fun question. So I'm
going to perform this little thought experiment. We're going to
make a bubble around the Sun that has a radius
of four light years. Okay, so got this sphere around
the Sun, and we're going to think how much stuff
is in here. We've left the Sun of one solar
mass that makes sense, and the next biggest thing is
(05:27):
Jupiter and that's a thousandth the mass of the Sun,
and everything else has just changed. There's you know, Saturn, Mars.
Nothing really matters here. It's just one star.
Speaker 4 (05:39):
All right.
Speaker 1 (05:40):
Imagine a bubble around us right now. That's four light
years or twenty four trillion miles in all directions. The
only thing you'd find in that bubble is our solar system,
meaning that there's four light years of empty space all
around us. Now, what happens if you draw that same
bubble in the center of our galaxy.
Speaker 3 (06:02):
I'm going to take this bubble. We're going to put
it in the center of our galaxy, centered on the
supermassive black hole, and ask the same question, what's inside
this bubble. First of all, you've got the supermass black hole,
and it's four million times the mass of the Sun.
And then you've got about ten million stars.
Speaker 1 (06:24):
Ten million stars.
Speaker 3 (06:26):
We can see some red giant stars. They're like absolutely
huge stars. Just like pumping out a lot of radiation.
But we also think there's a lot of stellar mass
black holes, neutron stars, white dwarfs, so like the remnants
of stars that have already died, and they're all just
swimming around the black hole. And that's a big problem
(06:47):
for planets.
Speaker 1 (06:50):
Whoa, yes, it's pretty busy in the center of the galaxy.
Speaker 2 (06:53):
Wait a minute, so a four light year bubble around
the Solar System. The nearest stars are a little over
four light years from us. So yeah, in that bubble
there are no stars. And I think of that as like,
that's how normal space is. But did she say ten
million stars? That is more than I would have guessed.
Speaker 1 (07:16):
Yeah. If you take that same bubble you put it
in the center of our galaxy, you not only have
this super massive black hole, which is four million times
the mass of our Sun, but you also have ten
million stars, which is ten million times more than what
we have around us.
Speaker 2 (07:31):
I am suddenly feeling less good about the possibility of
having planets. I'm a little concerned because I've seen diagrams
of the super massive black hole and like some of
the nearby star orbits, but they only showed one or two.
They didn't show millions or billions. I'm getting very nervous
here about my plans to move to one of these.
Speaker 1 (07:55):
Yeah, the center of our galaxy is a busy place.
There's about ten million more stars there than what's around
us right now. It's like we live in the equivalent
of a farmhouse in a field in the middle of nowhere,
and the center of the galaxy is Times Square in
New York City. Now you might think, well, that's exciting.
(08:16):
I want to live in Times Square in New York City.
But when space is that busy, there are a lot
of bad things that can happen. Here's how doctor Madigan
describes it.
Speaker 3 (08:28):
So let's say you're a planet in orbit around a
star that's in orbit. It's all for end the supermassive
black hole. The problem is that average density in that
region is so much higher that your closest star is
going to be, on average, about three hundred times closer
than our closest star is to us. And so there's
(08:51):
just stars whizzing past all the time, and you can
just be ripped off your orbit, completely ripped away from
your host star.
Speaker 1 (09:02):
Okay, what can happen is if another star flies too
close to you. It's gravity can actually pull you away
from the star that you're orbiting, Like if another star
flew close to our Solar system right now, it might
pull away Neptune or Saturn or even Us.
Speaker 3 (09:20):
And this is kind of fun. So you could actually
start orbiting that star that ripped you away, so you
can incinded this like interstellar hopping of planets, which is
exciting but terrible for stability for obvious reasons. Or you
could just be ripped off your host star and you'll
be freely floating in this sea around the black hole
(09:42):
and indeed directly just orbit the black hole itself. Again,
very cool, bad for stability.
Speaker 1 (09:50):
Being bad for like whatever might be alive there.
Speaker 3 (09:53):
Yeah, it's very unpredictable. You'd have to evolve to really
deal with not just like hostile environment, but changing you're
changing circumstances, and that seems like a tall order.
Speaker 1 (10:08):
So yeah, it's pretty dangerous at the center of the galaxy.
And if you think that's bad, just wait a little
bit and you'll see it's going to get a lot worse.
And it involves deadly solar flares and explosive super novas.
Speaker 4 (10:25):
We'll dig into those stay with us. We'll be right back,
and we're back.
Speaker 2 (10:39):
Okay. That is a sort of more exciting answer than
I was expecting. Ah yeah, that's man. That is a
lot of stars in a very small space. So okay,
you get ripped free from your host star. You know,
if you say the Sun falls into this zone for
some reason, all the planets get gravitationally yanked away from
the Sun and either up orbiting this other star or
(11:01):
just kind of freely orbiting the black hole, you know,
with this many stars around, maybe and here's me being
optimistic in hey, maybe we'll just always be near enough
to one of them that it's like nice weather. We
got like enough sunlight to keep the earth warm but
not too much.
Speaker 1 (11:17):
Uh huh.
Speaker 2 (11:17):
I wonder how long we could keep that going, like
stay in the habitable zone by sheer luck of just
like going between the stars far enough away that they're
not toasting us, but close enough that it's keeping the
surface warm and the water liquid. I wonder how long
we could keep that up?
Speaker 1 (11:33):
You mean, like, how long can we keep couch surfing
hopping from star to star or flying around between stars?
Speaker 2 (11:39):
Yeah, yeah, you know, I'm just like, maybe we could
like nudge the Earth and like, look at all the
stars swarming around and be like, there's a path where
if we go plunge between those two stars. It's like
setting up a complicated pool shot, Like we can ricochet
near this one and then over to that one and
around to that one, and hopefully we can get a
trajectory that keeps the Earth habitable, you know, for the
next I don't know, let's say a hundred years, so
(12:02):
at least in all of our lifetimes, and then after that,
that's a problem for the next generation to solve.
Speaker 1 (12:07):
Well, Randald, that's just one problem. Oh okay, So you
not only have to worry about a star coming near
your solar system and maybe affecting your orbit and getting
you thrown out of your solar system or sucking you
into their solar system. You also have to worry about
the black hole itself.
Speaker 2 (12:24):
Okay, I was afraid of that.
Speaker 3 (12:28):
There's another thing that I need to bring up as well.
It's not just the stellar density, it's the black hole.
As your host star moves around, it will change the
shape of your orbit.
Speaker 1 (12:40):
Ah.
Speaker 3 (12:41):
The dynamics are actually the gorgeous, it's fascinating. Okay, we're
going to have a star, and we're going to have
a planet, an orbiter and the star, and the star
isn't orbiting the super massive black hole. So we got
those three bodies. And if there's any tilt but respect
to each other, they actually torque each other. Does that
make sense.
Speaker 1 (13:00):
They try to make each other a ligne.
Speaker 3 (13:02):
That's exactly right. They try and make each other a
line because they're just like massive gravitating rings. It's a
conservation of angular momentum iss you and in doing so,
you have to change the shape of the planetary orbit.
Speaker 1 (13:17):
What doctor Matigan is saying is that if you're orbiting
a star that's orbiting a black hole, the black hole
is going to change how you orbit around your star.
So if you were moving around in a nice circle
around your star, the gravity from that black hole nearby,
it's going to squish your orbit so it's thinner and
more stretched out, eventually making it almost like a straight line,
(13:41):
which means sometimes you're going to be super close to
your star and sometimes you're going to be super far.
Speaker 3 (13:48):
Okay, and you might be like, that's not so bad.
But if you can think about going from a near
circular orbit that the Earth has as a moves round
the Sun to going much more elongated, eccentric to almost
a straight line. You see, the problem is that your
closest approach to your star, you're going to get lots
of different levels of radiation. That could be a problem
(14:10):
for life. But if you even just thinking of stability,
you can actually go so close to your host star
that you just smash into it. There's a lot of
pathways to destruction.
Speaker 1 (14:22):
Why does the orbit change shape because of the black hole?
Speaker 3 (14:25):
Is it called Kosi leadoff oscillations? Orbit shape would be
changing as a function of time.
Speaker 1 (14:32):
Yeah, so you not only have to worry about stars
affecting your orbit, the black hole itself that your star
is orbiting will change your orbit over time. And these
are what she calls Kosei leadoff oscillations that I may
have you've heard of these before.
Speaker 2 (14:46):
I think I've heard of them, but I didn't know
that they would apply to a star orbiting a black hole.
So what you're saying is that even if we were
riding in toward the black hole on the Sun, that
we have, due to a series of bad decisions, somehow
steered toward the center of the gallicy And even if
we managed to like plot a course that avoids all
of those stars, our orbit would be getting more and
(15:07):
more eccentric, so the Earth would be frozen, you know,
on the outer part of its orbit, assuming it's not
getting toasted by nearby stars, and then we would crash
into the Sun. Which I'm pretty optimistic, but I feel
like it's hard to come up with a version of
that that's good for us. Crashing into the Sun is
definitely bad.
Speaker 1 (15:23):
Yeah, imagine here on Earth we have pretty extreme winters,
hot summers, cold winters, We've had ice ages, and it's
still our orbit. It's pretty much a circle, right, Yeah,
So imagine because you're going close to the black hole,
it's going to change the shape of that orbit. It's
going to make it more narrow and longer, and so
you're going to just get super extreme seasons.
Speaker 2 (15:44):
Well, okay, I can see this is a bad idea.
Speaker 1 (15:48):
Okay, we're talking about the worst place to live in
the galaxy, and it seems to be the center of it.
It's so busy and crowded there that it's a pretty
dangerous place. There is a way to have a stable
orbit around a star there, but as you'll hear later, on.
It might not help you very much. It is kind
(16:09):
of a bad idea, but Professor Madigan does think it's
still possible to survive in that environment.
Speaker 3 (16:16):
Okay, you need to get out to a few light
years from the black hole for the stellar density to
drop enough that this isn't going to be completely catastrophic
for your stability, and that closer you were a bit
your host star, the better.
Speaker 1 (16:32):
Okay.
Speaker 3 (16:33):
Kind of like to keep in tight within the orbit
of mercury, so passing stars don't grab you as easily.
Oh yeah, if you're a neptune or something, you're a gunner.
Speaker 1 (16:43):
M's just no hope.
Speaker 3 (16:44):
A few light years away from the black hole is
where the stellar density drops sufficiently that if you're orbiting
very close to your host star, you might be okay.
Speaker 1 (16:55):
Yeah, so there's a little bit of hope. So this
super density of stars around black holes is not even
throughout that four light year bubble that she mentioned. It's
denser in the center. So she did some math on
this for us, and she figured out that at about
two light years away you kind of stand the chance
that the density is not so high that maybe you
could survive maybe a few billion years without some star
(17:17):
passing too close to you to disrupt you.
Speaker 2 (17:19):
Okay, but you have to be orbiting really close to
the star. If you have to be orbit closer than mercury,
suddenly those little tiny stars, those aren't looking so bad.
Speaker 1 (17:30):
According to doctor Madigan, one way to protect yourself in
the center of the galaxy is to live in a
planet that orbits really close to its sun, as close
as mercury circles our Sun. But of course being that
close to a sun would roast you, so you need
to circle what are called M dwarf stars. Yeah. So
(17:53):
it turns out that about three quarters of all the
stars that we know about are these M dwarfs type
of stars, and they're smaller and they're cooler than the sun,
our sun.
Speaker 2 (18:02):
So our sun is it's really like a bigger than
average star, Like these are normal stars and we have
a really big one.
Speaker 1 (18:08):
Yeah. That is exactly what she said, is that our
only hope for living in this environment is to find
an M dwarf type of star, small, not super hot,
so that we can be really close to it so
that our orbit is really tight until we don't get
as influenced by the black hole or stars passing by.
Speaker 2 (18:25):
I like that she's brought up challenges and problems with
these ideas that are so big.
Speaker 1 (18:31):
Okay, Now, let's say that we happen to be orbiting
an M dwarf type of star. We're close to the star,
we have a tight orbit that's stable on a rocky
planet with an atmosphere. You're still not home safe.
Speaker 2 (18:44):
Okay.
Speaker 1 (18:44):
Yeah, And this kind of gets to your second question,
which is how habitable would these planets be? Like, if
such a planet was possible and you're stable for billions
of years, would it be habitable? And the answer is
probably not.
Speaker 3 (18:59):
There are problems. One problem is that these types of
stars flare intensely. So Proximus century, again, this is our
nearest star to our Sun. It is a low mass
red dwarf stars by an eighth the mass of the Sun,
so it's not producing as much radiation, it's much less luminous.
(19:21):
It actually has a planet in its habitable zone, which
is really exciting. But a few years ago, in a
monitoring campaign, astronomers saw Proximus Andury flare by a factor
of ten thousand in ultraviolet radiation. Whoa, and you can
imagine if the Sun did that, like all of a
sudden not a factor of two brighter and UV, but
(19:43):
a factor of ten thousand. Yeah.
Speaker 1 (19:45):
I don't think they make ten thousand spf sunblocks exactly.
Speaker 3 (19:48):
You'd really have to have a really good thick atmosphere
to withstand that bombardment.
Speaker 2 (19:55):
You know. I always heard if the littler stars live
longer because they're not burning through their fuel as it's like,
really big stars might burn out in a few billion,
a few million years. Even the Sun lasts maybe twelve
billion years, but those little stars can last for way longer.
And so I thought of them as being more chill
and quiet. But boy, they're really not seeming chill.
Speaker 1 (20:15):
They're small and angry. Yeah, yeah, you know, and something
flares ten thousand times brighter than normal that will fry anything. Yeah,
So the planet to orbit a small nuts a bright
star so you can have a super tight black hole
and steel proof orbit in the center of the galaxy
just went out the window. These small stars are crazy.
(20:37):
They flare up, burning everything on the surface of your planet.
And that's not the only thing you have to worry
about burning you to a crisp. There are two other
big sources of radiation. So when we come back. We'll
talk about those two sources, how they definitely make the
center of the galaxy the worst place to have your planet.
(20:57):
Will be right back, and we're back. But these solar
flares are not the only thing you would have to
worry about. So if you are around one of these
stars near the galactic center, there's other things you also
have to worry about. One of them are sort of
(21:19):
brief quasars that happen near the black hole.
Speaker 3 (21:23):
Okay, I'm going to tell you two more issues.
Speaker 1 (21:26):
Okay, so let's.
Speaker 3 (21:27):
Say you're a planet in the habit of plisode. You're
close to this en dwarf star, but you've got a
nice atmosphere, you're doing just fine. There are two very
explosive events that could be dangerous for you. One they're
called tidal disruption events. These are wonderful, it's a little destructive.
This happens when a star gets shoved down to an
(21:48):
orbit that brings it so close to a supermassive black
hole that it gets ripped apart. And in essence, what's
happening is the gravity acting on one side of the
star is so much greater than the gravity acting on
the other side of the star that actually overcomes the
gravity that binds the star together, so it just rips
it apart. It's half of the star. It gets slunk
(22:10):
shot out of the system, which is kind of fun.
But the other half forms an accretion disc. So this
is a disc of ionized plasma made up of the
star that's been ripped apart and forms like a mini quasar.
It lights up the whole region and at peak, this
title disruption event can actually produce so much energy per
(22:32):
second it can I shine the galaxy what just for
a split second, And we see this happening in external galaxies,
and our estimates are that this should happen once every
ten thousand years.
Speaker 1 (22:45):
Oh, I see, you're saying. We might be stable, but
around you these things might be popping.
Speaker 3 (22:50):
Off exactly and it's like, all of a sudden, you've
got a galaxy's worth of luminosity just blasting from the
very center at the galaxy. So if you're host to that,
that two could be really bad for your atmosphere.
Speaker 2 (23:06):
That does seem bad now, And then we see a
flash of light from across the universe. There will be
like a star that something goes very wrong and they
explode and it's so bright that we can see it
from all the way across the visible observable universe. And
I always think like, well, luckily those seem to be
rare enough that we don't have to worry about one
happening in our galaxy, because that seems like that could
(23:27):
be bad being right next to it, even when a
one or two light years away. Yeah, okay, that does
sound worrying.
Speaker 1 (23:34):
Yeah, and it's not just these quasars. You also have
to worry about supernovas. You said, that's number two, number two.
Speaker 3 (23:42):
There's a third one, and that is a supernova, which
I'm sure a lot of people have heard of. There
are a lot of very massive stars in orbit about
the super musbuckle at the center of our galaxy. We
actually think that massive stars are forming in the center
of the galaxy kind of like in a disk, just
(24:02):
like planets form a right, stars, massive stars are forming
in a disk around the black hole, exciting. But when
they run out of fuel, which they do quickly, their
cores collapse. You know, if they don't have enough fuel
to keep up thermonuclear fusion, they don't have that pressure support,
(24:23):
so gravity just like catastrophically collapses. The core. But the
outer layers of the star just go bananas. And it's
not a technical term, but they just explode. And that
too is very energetic, very exciting. But yes, you're going
to have explosions in your sky if you're in that region,
(24:44):
and that can also, i'm afraid, just really damage your atmosphere.
Speaker 1 (24:51):
In other words, if you're living on a planet near
the center of the galaxy, you're going to have front
row seeds to stars getting ripped apart and first thing
super brightly and two giant stars collapsing and going supernova
all around you every few thousand years.
Speaker 2 (25:10):
Yeah, that also seems not ideal. I heard the rule
of thumb is like, if you're trying to estimate anything
involving a supernova, whatever your intuition says, it's bigger than that.
So like, what's the safe distance from a supernova? Like
farther than you think?
Speaker 1 (25:24):
Two light years doesn't seem enough, especially because she estimates
that these quasar events and also these supernova events probably
happen in near the galactic center around every ten thousand years.
Speaker 2 (25:36):
Okay, that is about as long as the Neolithic Revolution,
as long as humans have been farming and building cities. Yeah,
we'd have one of those happened sometime in there.
Speaker 1 (25:45):
Yeah. If you're trying to evolve in this planet and
trying to be intelligent things, you'd have to contend with
every ten thousand years, basically your whole planet getting fried.
Speaker 2 (25:54):
Yeah, that seems bad. Hey, look at least now the
flaring and dwarf started and seems so bad. You know,
astronomers talking to astronomers, it's always great for a perspective.
They're like, there's this horrible thing, but don't worry. It's
actually very small compared to this other even worse thing.
Speaker 1 (26:12):
It could be worse. Yeah, but we did come up
with sort of a solution together.
Speaker 2 (26:16):
Oh okay, I'm listening.
Speaker 1 (26:17):
And the solution is that it might be possible for
life to be there and for us to live in
that place. If you're living in an icy planet. Okay, okay, but.
Speaker 3 (26:26):
But I do I do have I do have a thought. Okay,
this is this is very like Earth centric and thinking,
like you want a rocky planet with a thin atmosphere
and you want humans walking around all over it with
plants and stuff. Maybe if you're a planet near the
galactic center and your atmosphere is just getting destroyed continuously.
(26:48):
Maybe you just evolved to not really need that thing,
you know, so.
Speaker 1 (26:53):
You could still have water. Is that what you're saying.
Maybe the water is underground.
Speaker 3 (26:59):
Yeah, let's let's go with that. Maybe you're an icy planet,
so maybe not too This is good. We're like doing
science in real time. Let's say you're you're not in
the habitable zone of your M dwarf stars, so we'll
put you a little bit further away. So you're icy,
but you've got liquid water under that surface, the surface ice,
and you know, your your atmosphere can come and go
(27:22):
and that's fine. But you're just living in the ocean.
Speaker 1 (27:25):
And you have that ice to kind of shield you
maybe from all this.
Speaker 3 (27:28):
Yeah, yeah, exactly. Yeah, maybe it's a little like little
tardy grades, just like floating around these little mass piglets
in water or oct octopus people. Was the next thing
I was going to.
Speaker 1 (27:42):
Say, Yeah, meaning it wouldn't be habitable for something like us.
But you know, if we expand our definition of what
is habitable, or if we just imagine something that doesn't
need an atmosphere, it could be habitable.
Speaker 3 (27:57):
Yeah.
Speaker 1 (27:57):
Yeah, wow, Well you said there's a ton of stars there, right.
Speaker 3 (28:01):
Yeah, so you know there's about ten million stars just
the bubble of four light years in radius from the
supermass black hole. There's a lot of stars.
Speaker 1 (28:11):
There may be millions of planets potentially, right.
Speaker 3 (28:14):
Yeah, and then there's no reason planets couldn't form about
a light year out from the black hole. You know,
you see stars forming in that region, and it could
be discs around these stars out of which planets form.
So there could be a little planet formation there.
Speaker 1 (28:30):
For sure.
Speaker 3 (28:31):
There's life in the center of our galaxy and conclusion.
Speaker 1 (28:39):
So yeah, it might be possible for there to be
life in the center of the galaxy.
Speaker 2 (28:44):
Okay, so you just got to hide under an ice sheet.
It's almost like a planet sized a glue surrounding you,
just for protection against the Sun. I guess that would
at least be Yeah, what's the SPF of Europa's icy shell?
Speaker 1 (28:58):
Good question.
Speaker 2 (28:59):
Yeah, yeah, we should figure out the SPF and then
for posing as emission to land on Europa and put
the label there saying what SPF Europa is.
Speaker 1 (29:08):
So, like, if there is life out there, maybe it
would have to be sort of like octopus people or
octopus type of beings or underwater type of beans.
Speaker 2 (29:16):
They sound nice.
Speaker 1 (29:17):
Yeah, all right, Well I think that answers all of
your questions. Randall.
Speaker 2 (29:21):
Hey, thanks so much to you and all the experts
for answering these questions. That was so much more than
I could have imagined. I feel like whenever I ask
scientists things, I always think like, oh, this question is
too silly for them to want to spend time on.
And then it's always so cool to see how excited
they are to talk about the thing. Yeah, space is
too big to fit in the inside our heads. It's
really cool.
Speaker 4 (29:41):
Yeah all right.
Speaker 1 (29:44):
So to recap, the center of the galaxy is definitely
the worst place to live in the galaxy. If you
manage to avoid something crashing into your planet, another star
might steal or kick your planet off its orbit, or
maybe the gravity of the super massive black hole at
the will cause you to crash into your star, or
movie stars getting ripped apart by the black hole or
(30:06):
stars exploding near you might fry you. It would be
extremely chaotic, but there could still be life near the center,
maybe a few light years away, in underground oceans, in
icy planets, around angry red dwarf stars. So if you're
thinking of moving there, just remember to bearing a scuba
suit and some toe warmers. Or maybe we should just
(30:29):
stay where we are and be glad live in a
peaceful neighborhood in the Milky Way Galaxy. Thanks for joining us,
see you next time, and thanks to Randall Monroe and
Professor and Marie Madigan for being on the show. Check
out Randall's work at xkcd dot com. You've been listening
(30:50):
to Science Stuff production of iHeartRadio, written and produced by
me or Cham, edited by Rose Seguda, executive producer Jerry Rowland,
and audio engineer and mixer Ksey Peckrom And you can
follow me on social media. Just search for PhD Comics
and the name of your favorite platform. Be sure to
subscribe to Sign Stuff on the iHeartRadio app, Apple Podcasts,
(31:11):
or wherever you get your podcasts. Please tell your friends
we'll be back next Wednesday with another episode.
Hey, welcome to sign Stuff, a production of iHeartRadio. I'm
Horhea Cham and today we are asking what is the
worst place to live in the galaxy. We live in
a nice, cozy place in the Milky Way, but is
there a spot where you definitely don't want your planet
to be. We think we have the answer, and it
came up during a conversation I had with Randall Munroe.
(00:21):
Randall's the number one New York Times best selling creator
of XKCD comics and the what If books and YouTube channel.
If you are in designs, chances are you've seen his
comics and videos featuring stick figures and nerdy humor. Randall
had questions for me about exoplanets, which are planets outside
of our solar system, and he specifically wondered what it
(00:42):
would be like to live in a particular location in
our galaxy. So get ready to travel to the worst
place to live in the Milky Way galaxy. Here's my
conversation with Randall Munroe. Hey everyone, Okay, I started off
by asking my friend Randall, what if I so interesting
about exoplanets, which are planets outside of our Solar system.
Speaker 2 (01:05):
Here's what he said, I don't really know I feel
like it's as close to like intrinsically interesting as something
can be. It's like, did you know there's other worlds
out there? And we have never taken a picture of
one of them where it's more than a pixel, But
we just learned they're out there. And I think it's
the novelty of it, like the newness of it, that
is really exciting for me. Like when I was born,
(01:27):
we had not confirmed the existence of any exoplanets. It
was all entirely speculative, and then all of a sudden
in my lifetime it's like, oh, hey, we spotted one
of them, and then we spotted another one, and then more,
and now we know about like thousands and thousands of exoplanets.
So it's like, Okay, I want to see them. I
want to know what they're like.
Speaker 1 (01:45):
Would you want to go there?
Speaker 2 (01:46):
I feel like physics means that I don't really have
to make that decision. Oh right. I think any kind
of space travel such a big commitment. I could see
wanting to travel in the Solar System, but something where
it's one of those one way across the universe, I
mean that sounds cool. I don't know that I personally
would opt for it, but I figure I'll worry about
(02:09):
that once the tickets become available.
Speaker 1 (02:11):
Right right, you wouldn't be a tour as you'd be
a migrant.
Speaker 2 (02:13):
Yeah, Like getting to another star one way is already
such a big lift, because just getting there is going
to be so hard, But I think I would put
like huge amounts of work into just like seeing them,
even if we just get a telescope that gives us
a handful of pixels or some kind of detailed atmospheric
breakdown clouds, anything that gives us a sense of like
what this place is like. I love that, you know.
Speaker 1 (02:37):
Awesome, So you had some questions for me. What's the
first question?
Speaker 2 (02:40):
I know, I've heard that there are these stars that
are orbiting the Milky Way super massive black hole, and
that's part of how we know that there's a black
hole there. We see these stars orbiting really close to
something that we can't see that seems to be really heavy.
And it just occurred to me, what would it be
like if you were on a planet around those stars?
Is it possible for there to be a planet around
the star? Would you notice you were around a black hole?
Speaker 1 (03:03):
Okay, what Randall is asking here? Is what would it
be like to live in a planet near the super
massive black hole at the center of our galaxy. It
turns out that most galaxies out there, including ours, has
a super massive black hole at their center. These are
huge black holes. For example, the one at the center
of our galaxy is called Sagittarius, a star, and it
(03:24):
has a mass that is about four million times heavier
than our sun. We recently took a picture of it,
but the main reason we knew it was there was
that we could see stars in clouds of gas circling
a spot that looked empty, which was a sign that
there was something really heavy there. Okay, back to Randall's.
Speaker 2 (03:43):
Question, would you be affected in any way? Is there
like a weird radiation environment?
Speaker 1 (03:50):
Like?
Speaker 2 (03:50):
What's it like there? Is it just like anywhere else
in the galaxy. It's just you happen to be near
a black hole? Or is it a bad place to be? Yeah?
Speaker 1 (03:58):
Excellent question. Did you up with this while trying to
figure out places to move to? No?
Speaker 2 (04:04):
I mean that's like fifty thousand light years something like that,
So I feel like if you're paying for a moving
van by the mile, that's going to get pretty expensive.
But I think I'm I'm going to keep black holes
at a healthy distance until I've talked to someone about
whether or not it's a good place to be.
Speaker 1 (04:19):
Yeah. Super amazing question. And by the way, I should
mention Randall that everyone I talked to, all the experts
I've talked to, they're all huge fans of yours.
Speaker 2 (04:25):
Oh, thank you.
Speaker 1 (04:26):
So for this question, I reached out to Professor Anne
Marie Madigan. Okay, I'm always excited when I find the
right person to talk to about a question, and in
this case, I found the perfect person. Anne Marie Madigan
is a professor of astrophysics and planetary sciences at the
University of Colorado at Boulder, and she happens to study
how stars and clouds of gases move around super massive
(04:49):
black holes like the one at the center of our galaxy. Now,
the first thing she wanted to do in her answer
was to paint us a picture of what space is
like at the center of our galaxy? Is it like
the space around us? Right now? Here's what she said.
Speaker 3 (05:05):
Okay, so this is a really fun question. So I'm
going to perform this little thought experiment. We're going to
make a bubble around the Sun that has a radius
of four light years. Okay, so got this sphere around
the Sun, and we're going to think how much stuff
is in here. We've left the Sun of one solar
mass that makes sense, and the next biggest thing is
(05:27):
Jupiter and that's a thousandth the mass of the Sun,
and everything else has just changed. There's you know, Saturn, Mars.
Nothing really matters here. It's just one star.
Speaker 4 (05:39):
All right.
Speaker 1 (05:40):
Imagine a bubble around us right now. That's four light
years or twenty four trillion miles in all directions. The
only thing you'd find in that bubble is our solar system,
meaning that there's four light years of empty space all
around us. Now, what happens if you draw that same
bubble in the center of our galaxy.
Speaker 3 (06:02):
I'm going to take this bubble. We're going to put
it in the center of our galaxy, centered on the
supermassive black hole, and ask the same question, what's inside
this bubble. First of all, you've got the supermass black hole,
and it's four million times the mass of the Sun.
And then you've got about ten million stars.
Speaker 1 (06:24):
Ten million stars.
Speaker 3 (06:26):
We can see some red giant stars. They're like absolutely
huge stars. Just like pumping out a lot of radiation.
But we also think there's a lot of stellar mass
black holes, neutron stars, white dwarfs, so like the remnants
of stars that have already died, and they're all just
swimming around the black hole. And that's a big problem
(06:47):
for planets.
Speaker 1 (06:50):
Whoa, yes, it's pretty busy in the center of the galaxy.
Speaker 2 (06:53):
Wait a minute, so a four light year bubble around
the Solar System. The nearest stars are a little over
four light years from us. So yeah, in that bubble
there are no stars. And I think of that as like,
that's how normal space is. But did she say ten
million stars? That is more than I would have guessed.
Speaker 1 (07:16):
Yeah. If you take that same bubble you put it
in the center of our galaxy, you not only have
this super massive black hole, which is four million times
the mass of our Sun, but you also have ten
million stars, which is ten million times more than what
we have around us.
Speaker 2 (07:31):
I am suddenly feeling less good about the possibility of
having planets. I'm a little concerned because I've seen diagrams
of the super massive black hole and like some of
the nearby star orbits, but they only showed one or two.
They didn't show millions or billions. I'm getting very nervous
here about my plans to move to one of these.
Speaker 1 (07:55):
Yeah, the center of our galaxy is a busy place.
There's about ten million more stars there than what's around
us right now. It's like we live in the equivalent
of a farmhouse in a field in the middle of nowhere,
and the center of the galaxy is Times Square in
New York City. Now you might think, well, that's exciting.
(08:16):
I want to live in Times Square in New York City.
But when space is that busy, there are a lot
of bad things that can happen. Here's how doctor Madigan
describes it.
Speaker 3 (08:28):
So let's say you're a planet in orbit around a
star that's in orbit. It's all for end the supermassive
black hole. The problem is that average density in that
region is so much higher that your closest star is
going to be, on average, about three hundred times closer
than our closest star is to us. And so there's
(08:51):
just stars whizzing past all the time, and you can
just be ripped off your orbit, completely ripped away from
your host star.
Speaker 1 (09:02):
Okay, what can happen is if another star flies too
close to you. It's gravity can actually pull you away
from the star that you're orbiting, Like if another star
flew close to our Solar system right now, it might
pull away Neptune or Saturn or even Us.
Speaker 3 (09:20):
And this is kind of fun. So you could actually
start orbiting that star that ripped you away, so you
can incinded this like interstellar hopping of planets, which is
exciting but terrible for stability for obvious reasons. Or you
could just be ripped off your host star and you'll
be freely floating in this sea around the black hole
(09:42):
and indeed directly just orbit the black hole itself. Again,
very cool, bad for stability.
Speaker 1 (09:50):
Being bad for like whatever might be alive there.
Speaker 3 (09:53):
Yeah, it's very unpredictable. You'd have to evolve to really
deal with not just like hostile environment, but changing you're
changing circumstances, and that seems like a tall order.
Speaker 1 (10:08):
So yeah, it's pretty dangerous at the center of the galaxy.
And if you think that's bad, just wait a little
bit and you'll see it's going to get a lot worse.
And it involves deadly solar flares and explosive super novas.
Speaker 4 (10:25):
We'll dig into those stay with us. We'll be right back,
and we're back.
Speaker 2 (10:39):
Okay. That is a sort of more exciting answer than
I was expecting. Ah yeah, that's man. That is a
lot of stars in a very small space. So okay,
you get ripped free from your host star. You know,
if you say the Sun falls into this zone for
some reason, all the planets get gravitationally yanked away from
the Sun and either up orbiting this other star or
(11:01):
just kind of freely orbiting the black hole, you know,
with this many stars around, maybe and here's me being
optimistic in hey, maybe we'll just always be near enough
to one of them that it's like nice weather. We
got like enough sunlight to keep the earth warm but
not too much.
Speaker 1 (11:17):
Uh huh.
Speaker 2 (11:17):
I wonder how long we could keep that going, like
stay in the habitable zone by sheer luck of just
like going between the stars far enough away that they're
not toasting us, but close enough that it's keeping the
surface warm and the water liquid. I wonder how long
we could keep that up?
Speaker 1 (11:33):
You mean, like, how long can we keep couch surfing
hopping from star to star or flying around between stars?
Speaker 2 (11:39):
Yeah, yeah, you know, I'm just like, maybe we could
like nudge the Earth and like, look at all the
stars swarming around and be like, there's a path where
if we go plunge between those two stars. It's like
setting up a complicated pool shot, Like we can ricochet
near this one and then over to that one and
around to that one, and hopefully we can get a
trajectory that keeps the Earth habitable, you know, for the
next I don't know, let's say a hundred years, so
(12:02):
at least in all of our lifetimes, and then after that,
that's a problem for the next generation to solve.
Speaker 1 (12:07):
Well, Randald, that's just one problem. Oh okay, So you
not only have to worry about a star coming near
your solar system and maybe affecting your orbit and getting
you thrown out of your solar system or sucking you
into their solar system. You also have to worry about
the black hole itself.
Speaker 2 (12:24):
Okay, I was afraid of that.
Speaker 3 (12:28):
There's another thing that I need to bring up as well.
It's not just the stellar density, it's the black hole.
As your host star moves around, it will change the
shape of your orbit.
Speaker 1 (12:40):
Ah.
Speaker 3 (12:41):
The dynamics are actually the gorgeous, it's fascinating. Okay, we're
going to have a star, and we're going to have
a planet, an orbiter and the star, and the star
isn't orbiting the super massive black hole. So we got
those three bodies. And if there's any tilt but respect
to each other, they actually torque each other. Does that
make sense.
Speaker 1 (13:00):
They try to make each other a ligne.
Speaker 3 (13:02):
That's exactly right. They try and make each other a
line because they're just like massive gravitating rings. It's a
conservation of angular momentum iss you and in doing so,
you have to change the shape of the planetary orbit.
Speaker 1 (13:17):
What doctor Matigan is saying is that if you're orbiting
a star that's orbiting a black hole, the black hole
is going to change how you orbit around your star.
So if you were moving around in a nice circle
around your star, the gravity from that black hole nearby,
it's going to squish your orbit so it's thinner and
more stretched out, eventually making it almost like a straight line,
(13:41):
which means sometimes you're going to be super close to
your star and sometimes you're going to be super far.
Speaker 3 (13:48):
Okay, and you might be like, that's not so bad.
But if you can think about going from a near
circular orbit that the Earth has as a moves round
the Sun to going much more elongated, eccentric to almost
a straight line. You see, the problem is that your
closest approach to your star, you're going to get lots
of different levels of radiation. That could be a problem
(14:10):
for life. But if you even just thinking of stability,
you can actually go so close to your host star
that you just smash into it. There's a lot of
pathways to destruction.
Speaker 1 (14:22):
Why does the orbit change shape because of the black hole?
Speaker 3 (14:25):
Is it called Kosi leadoff oscillations? Orbit shape would be
changing as a function of time.
Speaker 1 (14:32):
Yeah, so you not only have to worry about stars
affecting your orbit, the black hole itself that your star
is orbiting will change your orbit over time. And these
are what she calls Kosei leadoff oscillations that I may
have you've heard of these before.
Speaker 2 (14:46):
I think I've heard of them, but I didn't know
that they would apply to a star orbiting a black hole.
So what you're saying is that even if we were
riding in toward the black hole on the Sun, that
we have, due to a series of bad decisions, somehow
steered toward the center of the gallicy And even if
we managed to like plot a course that avoids all
of those stars, our orbit would be getting more and
(15:07):
more eccentric, so the Earth would be frozen, you know,
on the outer part of its orbit, assuming it's not
getting toasted by nearby stars, and then we would crash
into the Sun. Which I'm pretty optimistic, but I feel
like it's hard to come up with a version of
that that's good for us. Crashing into the Sun is
definitely bad.
Speaker 1 (15:23):
Yeah, imagine here on Earth we have pretty extreme winters,
hot summers, cold winters, We've had ice ages, and it's
still our orbit. It's pretty much a circle, right, Yeah,
So imagine because you're going close to the black hole,
it's going to change the shape of that orbit. It's
going to make it more narrow and longer, and so
you're going to just get super extreme seasons.
Speaker 2 (15:44):
Well, okay, I can see this is a bad idea.
Speaker 1 (15:48):
Okay, we're talking about the worst place to live in
the galaxy, and it seems to be the center of it.
It's so busy and crowded there that it's a pretty
dangerous place. There is a way to have a stable
orbit around a star there, but as you'll hear later, on.
It might not help you very much. It is kind
(16:09):
of a bad idea, but Professor Madigan does think it's
still possible to survive in that environment.
Speaker 3 (16:16):
Okay, you need to get out to a few light
years from the black hole for the stellar density to
drop enough that this isn't going to be completely catastrophic
for your stability, and that closer you were a bit
your host star, the better.
Speaker 1 (16:32):
Okay.
Speaker 3 (16:33):
Kind of like to keep in tight within the orbit
of mercury, so passing stars don't grab you as easily.
Oh yeah, if you're a neptune or something, you're a gunner.
Speaker 1 (16:43):
M's just no hope.
Speaker 3 (16:44):
A few light years away from the black hole is
where the stellar density drops sufficiently that if you're orbiting
very close to your host star, you might be okay.
Speaker 1 (16:55):
Yeah, so there's a little bit of hope. So this
super density of stars around black holes is not even
throughout that four light year bubble that she mentioned. It's
denser in the center. So she did some math on
this for us, and she figured out that at about
two light years away you kind of stand the chance
that the density is not so high that maybe you
could survive maybe a few billion years without some star
(17:17):
passing too close to you to disrupt you.
Speaker 2 (17:19):
Okay, but you have to be orbiting really close to
the star. If you have to be orbit closer than mercury,
suddenly those little tiny stars, those aren't looking so bad.
Speaker 1 (17:30):
According to doctor Madigan, one way to protect yourself in
the center of the galaxy is to live in a
planet that orbits really close to its sun, as close
as mercury circles our Sun. But of course being that
close to a sun would roast you, so you need
to circle what are called M dwarf stars. Yeah. So
(17:53):
it turns out that about three quarters of all the
stars that we know about are these M dwarfs type
of stars, and they're smaller and they're cooler than the sun,
our sun.
Speaker 2 (18:02):
So our sun is it's really like a bigger than
average star, Like these are normal stars and we have
a really big one.
Speaker 1 (18:08):
Yeah. That is exactly what she said, is that our
only hope for living in this environment is to find
an M dwarf type of star, small, not super hot,
so that we can be really close to it so
that our orbit is really tight until we don't get
as influenced by the black hole or stars passing by.
Speaker 2 (18:25):
I like that she's brought up challenges and problems with
these ideas that are so big.
Speaker 1 (18:31):
Okay, Now, let's say that we happen to be orbiting
an M dwarf type of star. We're close to the star,
we have a tight orbit that's stable on a rocky
planet with an atmosphere. You're still not home safe.
Speaker 2 (18:44):
Okay.
Speaker 1 (18:44):
Yeah, And this kind of gets to your second question,
which is how habitable would these planets be? Like, if
such a planet was possible and you're stable for billions
of years, would it be habitable? And the answer is
probably not.
Speaker 3 (18:59):
There are problems. One problem is that these types of
stars flare intensely. So Proximus century, again, this is our
nearest star to our Sun. It is a low mass
red dwarf stars by an eighth the mass of the Sun,
so it's not producing as much radiation, it's much less luminous.
(19:21):
It actually has a planet in its habitable zone, which
is really exciting. But a few years ago, in a
monitoring campaign, astronomers saw Proximus Andury flare by a factor
of ten thousand in ultraviolet radiation. Whoa, and you can
imagine if the Sun did that, like all of a
sudden not a factor of two brighter and UV, but
(19:43):
a factor of ten thousand. Yeah.
Speaker 1 (19:45):
I don't think they make ten thousand spf sunblocks exactly.
Speaker 3 (19:48):
You'd really have to have a really good thick atmosphere
to withstand that bombardment.
Speaker 2 (19:55):
You know. I always heard if the littler stars live
longer because they're not burning through their fuel as it's like,
really big stars might burn out in a few billion,
a few million years. Even the Sun lasts maybe twelve
billion years, but those little stars can last for way longer.
And so I thought of them as being more chill
and quiet. But boy, they're really not seeming chill.
Speaker 1 (20:15):
They're small and angry. Yeah, yeah, you know, and something
flares ten thousand times brighter than normal that will fry anything. Yeah,
So the planet to orbit a small nuts a bright
star so you can have a super tight black hole
and steel proof orbit in the center of the galaxy
just went out the window. These small stars are crazy.
(20:37):
They flare up, burning everything on the surface of your planet.
And that's not the only thing you have to worry
about burning you to a crisp. There are two other
big sources of radiation. So when we come back. We'll
talk about those two sources, how they definitely make the
center of the galaxy the worst place to have your planet.
(20:57):
Will be right back, and we're back. But these solar
flares are not the only thing you would have to
worry about. So if you are around one of these
stars near the galactic center, there's other things you also
have to worry about. One of them are sort of
(21:19):
brief quasars that happen near the black hole.
Speaker 3 (21:23):
Okay, I'm going to tell you two more issues.
Speaker 1 (21:26):
Okay, so let's.
Speaker 3 (21:27):
Say you're a planet in the habit of plisode. You're
close to this en dwarf star, but you've got a
nice atmosphere, you're doing just fine. There are two very
explosive events that could be dangerous for you. One they're
called tidal disruption events. These are wonderful, it's a little destructive.
This happens when a star gets shoved down to an
(21:48):
orbit that brings it so close to a supermassive black
hole that it gets ripped apart. And in essence, what's
happening is the gravity acting on one side of the
star is so much greater than the gravity acting on
the other side of the star that actually overcomes the
gravity that binds the star together, so it just rips
it apart. It's half of the star. It gets slunk
(22:10):
shot out of the system, which is kind of fun.
But the other half forms an accretion disc. So this
is a disc of ionized plasma made up of the
star that's been ripped apart and forms like a mini quasar.
It lights up the whole region and at peak, this
title disruption event can actually produce so much energy per
(22:32):
second it can I shine the galaxy what just for
a split second, And we see this happening in external galaxies,
and our estimates are that this should happen once every
ten thousand years.
Speaker 1 (22:45):
Oh, I see, you're saying. We might be stable, but
around you these things might be popping.
Speaker 3 (22:50):
Off exactly and it's like, all of a sudden, you've
got a galaxy's worth of luminosity just blasting from the
very center at the galaxy. So if you're host to that,
that two could be really bad for your atmosphere.
Speaker 2 (23:06):
That does seem bad now, And then we see a
flash of light from across the universe. There will be
like a star that something goes very wrong and they
explode and it's so bright that we can see it
from all the way across the visible observable universe. And
I always think like, well, luckily those seem to be
rare enough that we don't have to worry about one
happening in our galaxy, because that seems like that could
(23:27):
be bad being right next to it, even when a
one or two light years away. Yeah, okay, that does
sound worrying.
Speaker 1 (23:34):
Yeah, and it's not just these quasars. You also have
to worry about supernovas. You said, that's number two, number two.
Speaker 3 (23:42):
There's a third one, and that is a supernova, which
I'm sure a lot of people have heard of. There
are a lot of very massive stars in orbit about
the super musbuckle at the center of our galaxy. We
actually think that massive stars are forming in the center
of the galaxy kind of like in a disk, just
(24:02):
like planets form a right, stars, massive stars are forming
in a disk around the black hole, exciting. But when
they run out of fuel, which they do quickly, their
cores collapse. You know, if they don't have enough fuel
to keep up thermonuclear fusion, they don't have that pressure support,
(24:23):
so gravity just like catastrophically collapses. The core. But the
outer layers of the star just go bananas. And it's
not a technical term, but they just explode. And that
too is very energetic, very exciting. But yes, you're going
to have explosions in your sky if you're in that region,
(24:44):
and that can also, i'm afraid, just really damage your atmosphere.
Speaker 1 (24:51):
In other words, if you're living on a planet near
the center of the galaxy, you're going to have front
row seeds to stars getting ripped apart and first thing
super brightly and two giant stars collapsing and going supernova
all around you every few thousand years.
Speaker 2 (25:10):
Yeah, that also seems not ideal. I heard the rule
of thumb is like, if you're trying to estimate anything
involving a supernova, whatever your intuition says, it's bigger than that.
So like, what's the safe distance from a supernova? Like
farther than you think?
Speaker 1 (25:24):
Two light years doesn't seem enough, especially because she estimates
that these quasar events and also these supernova events probably
happen in near the galactic center around every ten thousand years.
Speaker 2 (25:36):
Okay, that is about as long as the Neolithic Revolution,
as long as humans have been farming and building cities. Yeah,
we'd have one of those happened sometime in there.
Speaker 1 (25:45):
Yeah. If you're trying to evolve in this planet and
trying to be intelligent things, you'd have to contend with
every ten thousand years, basically your whole planet getting fried.
Speaker 2 (25:54):
Yeah, that seems bad. Hey, look at least now the
flaring and dwarf started and seems so bad. You know,
astronomers talking to astronomers, it's always great for a perspective.
They're like, there's this horrible thing, but don't worry. It's
actually very small compared to this other even worse thing.
Speaker 1 (26:12):
It could be worse. Yeah, but we did come up
with sort of a solution together.
Speaker 2 (26:16):
Oh okay, I'm listening.
Speaker 1 (26:17):
And the solution is that it might be possible for
life to be there and for us to live in
that place. If you're living in an icy planet. Okay, okay, but.
Speaker 3 (26:26):
But I do I do have I do have a thought. Okay,
this is this is very like Earth centric and thinking,
like you want a rocky planet with a thin atmosphere
and you want humans walking around all over it with
plants and stuff. Maybe if you're a planet near the
galactic center and your atmosphere is just getting destroyed continuously.
(26:48):
Maybe you just evolved to not really need that thing,
you know, so.
Speaker 1 (26:53):
You could still have water. Is that what you're saying.
Maybe the water is underground.
Speaker 3 (26:59):
Yeah, let's let's go with that. Maybe you're an icy planet,
so maybe not too This is good. We're like doing
science in real time. Let's say you're you're not in
the habitable zone of your M dwarf stars, so we'll
put you a little bit further away. So you're icy,
but you've got liquid water under that surface, the surface ice,
and you know, your your atmosphere can come and go
(27:22):
and that's fine. But you're just living in the ocean.
Speaker 1 (27:25):
And you have that ice to kind of shield you
maybe from all this.
Speaker 3 (27:28):
Yeah, yeah, exactly. Yeah, maybe it's a little like little
tardy grades, just like floating around these little mass piglets
in water or oct octopus people. Was the next thing
I was going to.
Speaker 1 (27:42):
Say, Yeah, meaning it wouldn't be habitable for something like us.
But you know, if we expand our definition of what
is habitable, or if we just imagine something that doesn't
need an atmosphere, it could be habitable.
Speaker 3 (27:57):
Yeah.
Speaker 1 (27:57):
Yeah, wow, Well you said there's a ton of stars there, right.
Speaker 3 (28:01):
Yeah, so you know there's about ten million stars just
the bubble of four light years in radius from the
supermass black hole. There's a lot of stars.
Speaker 1 (28:11):
There may be millions of planets potentially, right.
Speaker 3 (28:14):
Yeah, and then there's no reason planets couldn't form about
a light year out from the black hole. You know,
you see stars forming in that region, and it could
be discs around these stars out of which planets form.
So there could be a little planet formation there.
Speaker 1 (28:30):
For sure.
Speaker 3 (28:31):
There's life in the center of our galaxy and conclusion.
Speaker 1 (28:39):
So yeah, it might be possible for there to be
life in the center of the galaxy.
Speaker 2 (28:44):
Okay, so you just got to hide under an ice sheet.
It's almost like a planet sized a glue surrounding you,
just for protection against the Sun. I guess that would
at least be Yeah, what's the SPF of Europa's icy shell?
Speaker 1 (28:58):
Good question.
Speaker 2 (28:59):
Yeah, yeah, we should figure out the SPF and then
for posing as emission to land on Europa and put
the label there saying what SPF Europa is.
Speaker 1 (29:08):
So, like, if there is life out there, maybe it
would have to be sort of like octopus people or
octopus type of beings or underwater type of beans.
Speaker 2 (29:16):
They sound nice.
Speaker 1 (29:17):
Yeah, all right, Well I think that answers all of
your questions. Randall.
Speaker 2 (29:21):
Hey, thanks so much to you and all the experts
for answering these questions. That was so much more than
I could have imagined. I feel like whenever I ask
scientists things, I always think like, oh, this question is
too silly for them to want to spend time on.
And then it's always so cool to see how excited
they are to talk about the thing. Yeah, space is
too big to fit in the inside our heads. It's
really cool.
Speaker 4 (29:41):
Yeah all right.
Speaker 1 (29:44):
So to recap, the center of the galaxy is definitely
the worst place to live in the galaxy. If you
manage to avoid something crashing into your planet, another star
might steal or kick your planet off its orbit, or
maybe the gravity of the super massive black hole at
the will cause you to crash into your star, or
movie stars getting ripped apart by the black hole or
(30:06):
stars exploding near you might fry you. It would be
extremely chaotic, but there could still be life near the center,
maybe a few light years away, in underground oceans, in
icy planets, around angry red dwarf stars. So if you're
thinking of moving there, just remember to bearing a scuba
suit and some toe warmers. Or maybe we should just
(30:29):
stay where we are and be glad live in a
peaceful neighborhood in the Milky Way Galaxy. Thanks for joining us,
see you next time, and thanks to Randall Monroe and
Professor and Marie Madigan for being on the show. Check
out Randall's work at xkcd dot com. You've been listening
(30:50):
to Science Stuff production of iHeartRadio, written and produced by
me or Cham, edited by Rose Seguda, executive producer Jerry Rowland,
and audio engineer and mixer Ksey Peckrom And you can
follow me on social media. Just search for PhD Comics
and the name of your favorite platform. Be sure to
subscribe to Sign Stuff on the iHeartRadio app, Apple Podcasts,
(31:11):
or wherever you get your podcasts. Please tell your friends
we'll be back next Wednesday with another episode.
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