March 2, 2021 • 44 mins
Daniel and guest host Katie Goldin explore the mysteries of these weird, ancient blobs of stars.
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Episode Transcript
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Speaker 1 (00:08):
Hey, Katie, do you have science words that you especially like? Yeah,
I really like apoptosis. It makes me think of popcorn.
That does make me want to have a snack. Well,
I like the word fundamental. It sounds so important, it's
got fun in it, it does. So what science words
(00:30):
don't you like? Um, coagulate, I was afraid you're gonna
say moist coagulates pretty gross. Also, I'm not such a
fan of the word had drawn. No, the problem is
a lot of people end up with a little typo
that swaps a couple of letters and you end up
with something very not safe for work. Yeah, that gives
(00:51):
the lard hay drown collider a whole different connotation. Hi,
I'm Daniel, I'm a part of Old Physicist, and I
(01:14):
definitely am colliding hay drowns at the LHC. And I
am Katie Golden. I'm stepping in for Jorge this week,
and I am the host of Creature Feature. I'm a
science podcast interested in evolutionary biology, human psychology, and hate
also physics and Welcome to the podcast. Daniel and Jorge
(01:36):
explain the universe, in which we take you on a
mental journey to understand everything about the universe, from the
tiniest things between your toes to the things you see
in the night sky to the vast weird, crazy bonker
stuff going out in the depths of space. We take
all of it, roll it up and try to make
sure that you understand it. Like a cosmic burrito. How
(02:01):
much hot sauce you want is up to you. And
we love to talk about stuff that we see in
the night sky, but we also love to talk about
stuff you might not have even heard of. When you
look up in the sky, you see stars, and if
you have a nice telescope you can even see further
in meb see those smudges that our galaxies. But there's
a lot of other stuff out there in the universe
(02:23):
that we are not familiar with, that most people don't
even know exists. Okay, so if I'm looking at the
night sky, I see a bunch of stars. Sometimes I
see like, like you said, it looks like someone spilled
a bunch of sugar up there, and it's a galaxy.
But what can I possibly be missing? I mean other
than yeah, I guess I can't see them in detail
(02:45):
with a telescope, But but what what's up there? Like
you mean giant alien eyeballs. Well, there's a lot of
stuff out there. And basically, every time we turn on
a new telescope or a new kind of device for
we're listening to the Cosmos, we find something new. And
every time we ap peer deeper and deeper into the sky,
we see stuff that we didn't expect. On the podcast today,
(03:08):
we'll be talking about a weird thing that's in the
sky that astronomers have known about for hundreds of years,
but most people aren't aware of. All Right, well, what's
this big secret? What if astronomer has been keeping from us? Well,
unfortunately it's got a really strange and kind of an
ugly name. Oh, it's not coagulated. It stars don't coagulate.
(03:32):
I guess if a galaxy cuts itself right, a bunch
of like stars could rush in to fill in the
gap planetary platelets. No, Today on the program, we'll be
asking the question what are globular clusters? You? Doesn't sound
(03:53):
like something you want to order on the menu, does it? No?
It sounds like the worst kids cereal? Ever, like, be
sure to get globios for your globular clusters. I know,
I imagine some like scoop of some very viscous kind
of stuff. It's like jello mixed with gravy or something.
(04:13):
Oh man, I don't I have a texture thing when
it comes to food, Like I don't like cottage cheese
or other like things, little chunks suspended within goo. So
I don't know about this globular clusters thing. This does
not sound good. Well, fortunately it was not designed as
a menu item. It's an astrophysical object. It's something out
(04:34):
there in our universe that might teach us something about
how the galaxy was formed, and how old the universe is,
and weird new kinds of stars, and so it's an
opportunity to learn something. Unfortunately, we don't actually have to
taste it. That's good, that's good, all right. I'm still
with you then, But if you try to give me
a spoon on one of these globular clusters, I am check. Please.
(04:57):
So we asked what people think globular clusters are, and
this is what people have to say. I don't know
what a globular clusters. I think it might be something
found in out space, but I don't actually I'm not
(05:18):
sure entirely, but I think it's just some type of
grouping of stars, assuming it's a term from cosmology. A
cluster is a collection of stars, and globular means that
it's round like a globe, and you'll as in molecule
or module, suggests that it's small, so it's a small
(05:38):
round a bunch of stars. This one is like a
gathering of stars spherical. It's not a galaxy. It can
be within a galaxy, but it may look like a galaxy,
like a spherical galaxy. I've heard the phrase globular or cluster.
(06:01):
I'm not sure what it means. I thought that it
had something to do with a group of stars, maybe
that are clustered together in a spherical shape. This is
a gigantic group of stars sit outside and I think
maybe even all of it the galaxies. This has something
(06:23):
to do with a group of stars, maybe that they
all formed from the same nebula or um other event.
Thanks to everybody who volunteered to speculate baselessly without getting
to do any research or googling. If you'd like to
participate for a future episode, please write to me two
questions at Daniel and Jorge dot com. I think it's interesting,
(06:46):
so most of the answers more along the same lines
like this is probably a big cluster of stars or
some kind of space junk, some kind of space junk.
But then no clue in there that it's a cluster
of stars, right, it could have been a cluster of anything,
you know, jello or gravy or breakfast cereal or whatever.
(07:08):
I think when people think about space, you think of
it mostly stars. Right, you look out into space. What
do you see? You see stars. All the other stuff
that is out there is either hard to see or
isn't really perceivable. Yeah, but you hear some people speculating
like maybe it's a cluster of galaxies or a cluster
(07:29):
of galaxy clusters or something like that, because there's this
fascinating sort of hierarchy of structure out there in space. Right,
It's not like they're just stars everywhere. Things are sort
of grouped together into galaxies, and those galaxies are grouped
together into clusters of galaxies, and so there's like this
really fascinating sort of hierarchy of structure is getting bigger
and bigger and bigger. And so I guess the question
(07:51):
then is, you know, like what are globular clusters a
cluster of Yes, what kind of pyramid scheme is a
globular cluster. Who's the downstream and who's the upstream? Who's
really making money off globular clusters? Right? Who's behind big
globular taking globular clusters to the moon. So the answer
(08:13):
is that globular clusters are clusters of stars. And to me,
the fascinating thing is that there's something in between, sort
of like our Solar system and the galaxy. Do you
think about like our cosmic address. We're here on Earth,
we're zooming around our star, and then we think that
our star is just like one of many stars of
(08:33):
hundreds of billions of stars in the galaxy. But it
turns out that there's an intermediate step there. It's not
like just Solar system and then galaxy. You could have
organizations of solar systems. So when you zoom out, like
when you see these videos of here you are on
planet Earth. You're tiny and significant, flee like creature on
(08:56):
this huge planet. Then you zoom out to Solar system
and usually goes right from Solar system to galaxy. But no,
there's an extra step. You're saying, there's an extra step. Yeah,
some stars, some special stars grouped together into these big
clusters of stars called globular clusters. Now, not every star
(09:18):
is in one of these things. It's not like, you know,
another layer in this hierarchy is sort of like a
special clumping. Like most stars are just sort of like
out there on their own, sort of like out in
the middle of the countryside by themselves. But it turns
out that there are these like urban areas where stars
clump together really densely and make these things called globular clusters.
(09:39):
And they're like a fascinating relic of the ancient formation
of the galaxy and can tell us a lot about
how things work out there. So it's like you've got
a bowl of granola, and yet you have your little
oatmeal pieces in there, but then you have the big
clusters of oatmeal too. Those are the best ones. Those
are the best ones. Those are nice. Yeah. I always
(09:59):
fish those out first, and then I'm left with just
sort of a bowl of sugary oatmeal and that's not great.
But so that whole bowl is like the galaxy, but
within that bowl you have the globular clusters of the
nice crunch granola's. Yeah, exactly. The stars are not evenly
distributed through the galaxy. I mean, the overall pattern is
that there's more stars in the center of the galaxy
(10:21):
with a gravity stronger, and then it's sort of peters
out along the galactic disc. But inside there it's not smooth.
There are these clumps where you get these big collections
of stars. And we're not talking like, you know, five
ten stars. We're talking like a few hundreds of thousands
of stars. It's a big deal. Sounds like when they're
making the galaxy that just didn't stir enough. That's what
(10:43):
I learned about. Like when I'm trying to make polina,
you know, it gets clumpy. You just didn't stir enough.
Katie's globular polenda. That's not the foundation for your next
food truck, right, And so these things have like a
few hundred thousand stars in them, but they're not actually
that big, right there only like ten to sometimes like
three hundred light years wide. Okay, you say that's not
(11:04):
that big. However, how long would it take me to
drive from one end to the other of three hundred
light years? Yeah, it would take you a while. I mean,
even in your light speed polenta powered vehicle, it would
take you three hundred years to go across three hundred
light years obviously, and in a much slower, more reasonable
ship it would take much much longer. But the reason
(11:26):
I say that it's not that big is that there
are so many stars in there. So would you end
up with is stars in a very unusually dense collection
like in our part of the galaxy in our neighborhood,
there aren't that many stars, like the nearest stars more
than four light years away, right, I mean, it seems
like there would be conflict with stars being that close together, right,
(11:49):
because I know every body in the universe has some
kind of gravitational poll and stars are so big they
seem like they would be acting on each other there,
So it's it's odd that you would have them so
close together. Yeah, And that's exactly what makes them fascinating
because in these clusters we get to see stars doing
(12:09):
something they don't normally do, which is like dance around
each other and tug on each other and form new,
weird kinds of stars. And we're gonna dig into all
that crazy stuff that's happening inside the globular clusters in
a minute. But here's some numbers for you, Like the
density of stars in our neighborhood. Like around where we
live in the galaxy is like one star per three
(12:29):
hundred cubic light years, so that's pretty big area just
to get one star. But inside one of these globular
clusters there's like two stars per cubic light year, so
it's like six hundred times denser than it is in
our neighborhood. It's like going from the middle of nowhere
to Manhattan. Really packed in there, like star deans. Yeah,
(12:49):
they really are. Imagine what it would be like to
live around a star in a globular cluster. You would
have so many other like bright stars in the sky
at night. The night itself might be a lot brighter
than it is here. Yeah, it seems I would be
as bright as daylight. You just have too many suns
going on. Yeah, if you're near the center one of
(13:10):
these things, I mean, the globular cluster itself is like
twenty five thousand times brighter than the sun. These things
are really bright. Some of them are up to like
fifty times brighter than even that. You'd be in the
middle of like a lot of light bulbs all the time.
Maybe a pretty crazy experience. Well, I need to get
some more high tech sunglasses. It seems like to be
(13:30):
able to live here some of that those polarized shades.
But before I do that, why don't we take a
quick break and I will return with all new sunglasses.
(13:52):
All right, I've got my super polarized super extra anti
glare globular cluster sunglasses on. I can't see a thing indoors,
but I think it'll help me see within the globular clusters. So,
so what's going on around me? Yes, So these globular clusters.
You have this big collection of stars all packed into
one spot. And one of the amazing things is that
(14:15):
there aren't actually that many of these, Like the galaxy
has hundreds of billions of stars, but they're only about
a hundred and fifty, maybe up to two hundred of
these globular clusters. Well why are they so rare? We
don't really understand, and we can talk in a minute
about how they form, but one clue is that they're
also not always contained within the galactic disk. Like when
(14:39):
you look at the galaxy sort of from outside, which
we can't do what we can look at other galaxies.
Of course, you see that it's mostly a flat swirl,
and that's because of how the galaxy formed. Right, the
galaxy form from a huge collection of gas and dust
which collapsed into stars and then gravity took over and
try to pull all those stars together, and that's why
you have a galaxy. But it's my it's harder for
(15:00):
gravity to pull along the galactic plane because that's how
the galaxy is spinning. That's spinning keeps things from falling
in only along that plane. Perpendicular to that plane, you
can squish it flat like a pancake. Is it sort
of like when you have a bicycle wheel, You have
some torque there, so you have that kind of like
inward energy of the galaxy spinning, So it's easier for
(15:24):
it to be flat and spinning inward than it is
to spin another direction. Yeah, exactly, if you spin a
bicycle wheel, then it's harder for things to sort of
fall in towards the center. Or if you think, for example,
about like a merry go round with ping pong balls
on it, right you spin that thing, the ping pong
balls are all going to fly out, but they're gonna
fly out along that plane. So that's what we call
(15:45):
rotation supported. The rotation of the galaxy is keeping things
from falling inwards, but again only along that plane. There's
nothing that prevents the collapse perpendicular to that plane, which
is what makes it flat like a disk. Well, next
time I go on a Merry go around, I'm bringing
a bunch of ping pong balls with me. This is
probably why I'm banned for most Merry go round. Maybe
(16:05):
also because you try to eat polenta and you end
up throwing up globular chunks of polenta. Oh man, When
I was a kid, I was a throw upper kid,
and I had some moments. I had my moments, especially
on the teacups. All right, well, we don't want to
revisit that with too much to jail. But the interesting
thing about these globular clusters is that they don't tend
(16:27):
to be along this galactic disk. Like if you looked
at a diagram of where they are, there's some of
them that are in the disc, but they're also sort
of just spherically distributed around the galaxy. It's almost like
they come from a time when the galaxy was a
big puffy sphere before collapsed. Right, And I'm looking at
this image and what it looks like to me is
(16:49):
like a side view of like a fried egg, and
then above it, like scattered around it are little little
yellow dots like you just spilled a bunch of salts around. Man,
I keep coming back to food on this globular cluster episode,
don't I. We've gotta stop recording these at lunch. Whoever
thought globular clusters would make you hungry? Like, I gotta
(17:12):
bring a positive spin to it. So they're falling outside
of that disk. You're saying that maybe these had formed
back when the galaxy was sort of this big puppy cloud,
and even as it flattened down to the disk, they
didn't come with the rest of the game. Yeah, precisely.
(17:33):
And there's a bigger topic here of the galaxies halo.
Remember that galaxies are not mostly stars. Most of what's
in the galaxies actually dark matter. And if you look
at where the dark matter is in a galaxy, it
doesn't collapse the same way that normal matter does. It
tends to spin. And so this is big spherical halo
(17:54):
of dark matter around the galaxy. And that's the original
thing that's sort of like clustered together the gas of
dust that made our galaxy. And so these globular clusters
they're sort of in this larger galactic halo, but they
haven't collapsed down into this disk, and we don't know
exactly why. It could be that they didn't form with
the original galaxy but are like their own little mini
(18:17):
galaxies that were then captured later and that's why they're
orbiting around. Or it could be that they formed with
the rest of the galaxy but then didn't collapse as
well as the gas and dust because they don't collide
with each other as much as the gas clouds do,
so they avoided like losing all that angular momentum and
they can keep spinning around out there in crazy orbits.
(18:38):
Or maybe they just prefer to hang out out in
the dark matter halo. Dark Matter Halo is a really
good metal band name, I've got to say. Yeah, So
that that's interesting. We can't see dark matter, but it
is there, and so it's like this halo around the
galactic disc. And suspended in that halo are these little
(19:00):
dots and those are each a globular cluster, yeah, exactly,
and some of them happen to fall within the galactic disc,
but most of them do not. You know. The closest
one to us is about sixteen thousand light years away.
It's called the Omega cluster. But there's a bunch of
these things, and what's really interesting is how they form.
(19:21):
And as you said earlier, they might tell us something
about the age of the Milky Way, because we think
that they formed very very early on as the galaxy
was forming. You know, the way these things happened is
that you get, you know, a big clump of gas
and dust, and it may have been that you just
got sort of like an over dense pocket of gas
and dust something which was like, you know, got more
of a serbing of globs than the rest of the
(19:43):
stuff around it, and it collapsed all at once and
made a big bunch of stars. And so these globular clusters,
when we look at them, we see a bunch of
stars and no gas and dust in between, which means
like they're not forming any new stars. So there's sort
of like a little time capsule from very very early
formation of the galaxy. So when you say it happens
(20:03):
at the same time, what are we talking about, Like
it all happens within sort of one of our human
years or is it literally like within a few moments?
Oh wow, now we're talking like in within millions of years. Okay,
star times. We humans are sort of like dogs. We
live in dog years and they live in star years. Yeah,
(20:25):
they live in star years. We think that these globular
clusters are about eleven to thirteen billion years old. I remember,
the whole universe is only just under fourteen billion years old,
which makes these things some of the oldest things in
the galaxy, which is how we can sort of use
them to help understand the age of the galaxy. And
also when we see them in other galaxies like Andromeda,
(20:48):
we can use them to help understand the age of Andromeda.
And one way we can do that is because we
think that all the stars in there were formed at
the same time, which means they all sort of like
start their own clock at the same time. And you
remember that the life cycle of a star is that
it burns for a while and then ones is done
with all of its fuel. It either goes nova or
(21:09):
collapses or something. But the lifespan there depends on the
original size of the star. The more mass it has,
the faster it burns. The smaller it is, the longer
it burns. So we can tell something about the age
of these things just by looking at like the distribution
of stars, which ones have burned out already, which ones
have not. But the fact that they've all formed at
the same time makes it very easy to sort of
(21:30):
like reverse that back and understand how this thing started.
It's nice from a scientific perspective because you control for
the factor of age. You've got like these little test
tubes out there that you can look at as physicists. Yeah, exactly.
And they're also an interesting collection of stars because they're
not stars like our sun. Our universe has gone through
(21:51):
a few cycles of making stars. You know, the very
early universe, you had hydrogen helium and that fell together
to make the original first generation of ours, which weirdly
astronomers called population three stars. And those were really big
and didn't burn for very long, but they made some
like helium and some heavier stuff and things that astronomers
(22:11):
called metals. And then when they blew up and they
spread their stuff through the galaxy, there was a second
generation of stars which formed, and those are called population
two stars. Some of those burned up and collapsed and
spread their stuff through the galaxy to make population three stars,
which is like our sun is a population three stars.
But these stars in the globular clusters are only population
(22:33):
two stars. There weren't any of the population one stars,
the ones like our sun when these things formed. So
you may have explained this. It counts down. It goes
pop three pop to pop one is the newest or yeah, exactly,
which I guess makes the next generation of stars are
gonna be what pop zero and then pop negative one?
Like nobody really thought this through pop zoomers. And the
(22:56):
other fun thing about these is that that very low metallicity,
Like there's basically just helium and hydrogen because that's what
was around after the first generation of stars, the population
three stars. You know, astronomers have this weird naming system
for basically everything. Well one thing that's especially weird is
what they call them metal. Like everything that's not hydrogen
or helium is a metal to them because it's like
(23:18):
a big heavy element. See. I mean, like, you know,
there's a lot of controversy in the metal community of
what can be considered metal. There's prog metal, and some
people say, no, it's too much of a ballad to
be metal, But you know, I think it's nice to
be inclusive, and so these globular clusters that have basically
only very low metal stars. And these stars are also
(23:40):
not that big, which is why they've been burning for
so long, and they might continue to burn for billions
and billions of years more. The smaller kinds of stars,
like red dwarves, they might even last for trillions of years.
So these are very I guess gassy stars would be
fair to say these sorry gassy stars. But the interesting
thing is that they've sort of cleared out all the
ask the dust inside of them. They're not making any
(24:02):
new stars. Other parts of our galaxy still have these
big blobs of gas and dust, so there's still new
stars being made all the time, Like our son was made,
you know, fairly recently on these time scales, only five
billion years ago. But the globular clusters, they're sort of
like you know, old boys clubs. They made all their stars,
they used up all their gas and dust, and then
they're done. They're just like, we're gonna hang out. We're
(24:24):
happy with a number of stars. We have no new members. Typical. Typical.
There are some places in the universe where globular clusters
are still forming, like in the large Magellanic Cloud there's
a big positive gas and people think that it's now
forming into a new globular cluster. And by now we mean,
you know, within the last twenty million years on star time,
(24:45):
star time, not not a little human dog time. But
there's still a lot of really interesting mysteries about these things.
Most of them have sort of like a single population
of stars that we think all formed at the same time,
and you can tell based on like the star ages
and sort of how they're like popping off and dying.
But some of them have like two or three different populations.
(25:05):
It looks like there was a clump all made it once,
and then another clump all made at the same time
that was different from the first clump. So there's a
lot of interesting mysteries there. So is it more rare
for globular clusters to form in our current universe than
you think that it was like near the beginning of
the universe. Yeah, absolutely, because a lot of the gas
(25:26):
has already turned into stars or into globular clusters, and
so it's very rare for globular clusters to still be made.
Most of them were made in the early universe and
they're just sort of like hanging around. They're like, you know,
the old folks still smoking in the back of a bar,
you know, and they're just not really making them like
they used to anymore. There's just not enough gas to
go around, which I can't believe I'm saying. And so
(25:47):
we don't really understand like how these globular clusters have
multiple different populations, Like people think maybe different globular clusters
might have merged, like you had two of them formed
at different times, and they sort of came to get
there to make one that had two different populations in it.
But it's you know, it's an area of active research.
It's not something we really understand. So could I live
(26:08):
in a globular clusters? What's going on in there? Is it?
Is there anywhere for me to be? Are you looking
to move, Katie? You are happy with your current apartment.
I've got my cool shades that I currently can't say
anything through, So I've gotta gotta find a place as
bright as I am. It's a really fun question because
it's fun to imagine what would like to be on
(26:31):
a planet inside a globular cluster, And so people are wondering,
like are there planets around these stars? Do these stars
also have like planetary disks which collapse and give you
rocky stuff that you could live on. Could there be
alien life that evolved inside a globular cluster? We think
actually it's pretty unlikely for these things to have planets
(26:51):
around them, which is a bit disappointing when it comes
to like writing science fiction novel about it. But there's
really two reasons. One is that most of the material
just sort of went to making stars, Like there's mostly
gas there, so it's hard to form planets. Planets you
tend to want to have like a rocky core with
something heavy in it, But these things formed in the
early universe when there was basically just hydrogen and helium
(27:14):
and very small amounts of heavier stuff, so you didn't
have sort of the raw ingredients to make planets. And
the second is that it's pretty hard for a planet
to stay orbiting a star if there are so many
other stars nearby constantly tugging on it. Right, it seems
like even if you could have like a gas planet,
it would just get ripped apart by these quarreling stars. Yeah, exactly,
(27:39):
and it would just get tugged out of orbit. You know,
we think of our planet is mostly just orbiting the Sun,
but there are gravitational forces from other nearby stars or
things that pass nearby, and when the Sun comes nearby
other stars, those things get stronger. So in a globular cluster,
remember it's much much denser, there are many more stars,
(28:00):
your byes of these tugs are a lot stronger. So
even if you did form a planet and it did
survive being pulled apart, as you said, you woul probably
just get like passed around from star to star. Wouldn't
have like a stable orbit like a volleyball exactly like
a hot potato planet. That doesn't sound ideal for me
as a little person living on this volleyball planet. So
(28:22):
I'm gonna have to rethink my travel plans. So we'll
take a break while I look into real estate in
a different part of the universe. Alright, so we are back.
(28:45):
I am looking at man Zillo just does not really
go into like beetle juice area. There aren't very many
sales to track there, so who knows how much of
those houses cost. So we're talking about globular clusters. We
have found out that I cannot live there inside a
(29:07):
globular cluster, dream shattered but maybe there's something else we
can get out of these globular clusters. Yeah, we think
that there aren't planets around these things. And people actually
went and looked and they studied a cluster and one
of them had exactly zero planets in them. And then
they looked at another cluster and they actually did find
one planets, this huge Jupiter sized planet. But it's orbiting
(29:31):
a pulsar in a binary star system. It's like a
really rare and unusual kind of situation. And a pulsar
is not what you want for like your home sun.
So what is a pulsar? A pulsar is a star
that's already collapsed, so it's burned it through its life
and it doesn't have the energy to prevent gravitational collapse,
and so it falls down into a neutron star and
(29:52):
then it starts spinning crazily and emitting crazy radiation into
the universe, which then sweeps across the sky and pulses,
which why we call it a pulsar. We have a
whole fun podcast episode about pulsars people can dig into.
But pulsars don't emit light the same way like our
son does because there's no fusion going on inside, so
it would be a pretty chilly place to live. Well,
(30:15):
I'll pack a sweater, pack all the sweaters. But there
are some really interesting things you can do with globular clusters,
like experiments, you can do questions, you can ask things,
you can learn about the universe. To me, what's really
interesting is that you get all these stars together, like
really tightly packed, and so you get to see like
what happens when stars get really dense, when they're like
(30:37):
all tugging on each other gravitationally. Because you know, normally
stars are pretty far separated, they don't really pull on
each other that much. So it's like getting to study
what happens when they get all crammed together. It's a
starsh pit exactly. You get really interesting dynamics. Like some
of these things have had what they call core collapse,
(30:58):
where the center of the globe the cluster has a
bunch of really really big stars and all the smaller
stars are on the outside. And so they're trying to
understand like are these because of gravitational interactions where like
two stars come near each other and then sort of
like throw each other in different directions and the bigger
star always gets sort of thrown a little bit more
towards the center, so that after billions of years, you
(31:19):
end up with the smaller ones like in a little
halo around the bigger ones at the center. It's like
you have a bunch of dance partners, and you've got
a bunch of little guys and some some big guys,
and they're doing the dance from you know, the Titanic,
where you hold hands and you spin around in a
circle and then you let the other person go and
they go flying. But it's a bunch of stars, and
so maybe the little ones, like when they go flying,
(31:42):
they fly out further, keep getting slingshotted out to the outside,
whereas the bigger ones don't get tossed or heated. As
the kids say as far, Yeah, that's exactly what happens.
That makes the core of these things even crazier, because
not only is it a place where there are a
lot of stars, but now you have even bigger stars
all clustered towards the center. So the heart of these
(32:05):
globular clusters must be a really crazy place to live
or even to visit. It seems slightly deadly. Potentially, you
can also see really interesting new kinds of stars. There's
a kind of star that seems to only exist inside
a globular cluster. Yeah, and these actually I gotta give
astronomers kudos because they have a cool name. These stars
(32:25):
are called blue stragglers. Oh man, this sounds like I
can just hear sort of like a guitar toWin going
on and a country songs starting about the blue stragglers. Yeah,
they lost their dog and their truck. But the interesting
thing about these stars is that usually what happens to
(32:47):
a star is a d percent determined by how much
gas it started with and then how old it is.
So you start with a bunch of gas and it
burns for a long time, and you know, it's color
depends on its temperature, which depends on the gravitation pressure,
which depends again on just how much stuff it is.
So you get enough stuff, you're gonna have a red giant.
You get a little more, you can have a blue giant,
(33:07):
for example. And so it's a very like well known,
well understood sequence and stars should only appear like somewhere
on this curve that tells you the mass and the
age of the star. But inside these globular clusters is
a weird kind of star called a blue straggler, and
they're much bluer than you expect for a star of
that size and that age. Poor things they got the
(33:31):
blues that country music at all. It's the blues really,
all right, So why are they so down? Are you
talking about the color? Yeah, well, we don't exactly know.
It's a fascinating area of study, something people are trying
to understand. And that's what's really interesting about these globular clusters.
It's like a new experiment. You know. Astrophysicists, they don't
get to do experiments like particle physicists, where we like
(33:52):
smash stuff together to see what happens. They don't just
say I'm going to smash two stars together and see
what happens. We don't have a star canon yet, we
can't do it, yeah, exactly. We asked for funding for
the Star game seventy two trillion dollars, but we haven't
heard back yet. But what they can do is just
sort of look out into the universe and see if
these experiments are already happening. Because the universe is chalk
(34:13):
filled with weird stuff, and if you look long enough,
you'll see something that might answer your science question. And
so we think that might be what's happening inside globular clusters,
that essentially star collisions happened. That the reason these stars
are like two or three times bigger than you expect
for a blue star is that they sort of like
got captured and fell together and formed an extra big star.
(34:37):
So they just kind of like it's a collision and
instead of all spreading out, it all kind of just
starts to I hate to say it, but congealed together,
coagulated exactly. And you know, that tells us something about
star formation, because most stars we see formed outside globular clusters,
and that tells us about the distribution. You know, you
get a certain amount of helium and hydrogen, you get
(34:59):
this kind of star of that kind of star. This
tells us that under special circumstances, if you make a
bunch of big stars near each other, they can combine
together to make a super kind of star blue straggler
that doesn't appear anywhere else in the galaxy or the universe.
It's like a special star laboratory. And what's the straggler
part of the name referring to if you look at
(35:20):
the curve for where stars are, it's like color versus mass.
Then there's this population of blue stragglers that are sort
of off the curve. They're like to the left, and
so they're sort of like not hanging out with the
rest of them that are like falling behind. You know,
you don't want to judge these stars and make them
feel bad. They're just sort of different. They're differently starred. Yeah,
(35:41):
they're differently started exactly. Globular clusters also give us a
laboratory for trying to understand another mystery of the universe,
and that has to do with black holes. Black holes
form in our universe, but sort of only in two
different groups. Like we either get black holes that form
when stars collapse, and then they're about the mass of
a star. And so we see black holes from stellar
(36:02):
collapse and they're out there and they have masses of
like ten to a hundred times the mass of our Sun,
about what you would expect from the collapse of massive stars.
Then there's another whole group of black holes that are
like millions of solar masses, and these are the ones
at the centers of galaxies. So you got like stellar
black holes hanging out in the neighborhood, and then like
the really big Papa black holes in the centers of galaxies.
(36:25):
And one question in astrophysics for a long time is
like where are the intermediate ones? Like why are there
no black holes that are sort of like between a
hundred and ten thousand solar masses right the Goldilocks black holes? Yeah,
you know, why don't black holes emerge to form the
bigger ones. It's an interesting question about like where they're
made and how often it happens, and so this is
(36:46):
something people have been trying to understand. And one possibilities
that you might be able to make intermediate mass black
holes in globular clusters because here you have like an
unusual density of stars and if a bunch of them
go black hole and then formed together, you might be
able to make one of these things. So how are
we going to do this? What do we need to
make a black hole out of one of these globular clusters. Well,
(37:09):
we don't have to do much. We just sort of
sit back like astronomers and look out in the universe
that's putting on a show for us. And the idea
is sort of wait for one of these things to
turn into a black hole. And then if there are
a bunch of other black holes nearby, they could sort
of swirl into each other. And remember what happens when
you toss a black hole into a black hole is
you just get a bigger black hole. Right, black holes
(37:32):
don't like tear each other apart. Anything you tossed into
a black hole just makes a black hole bigger. This
is one of the favorite things people write in about,
like what if I threw in, you know, antimatter into
a black hole? Or what if I shot a laser
into a black hole? Right? You can't destroy a black
hole by adding more energy to it. A black hole
is just a big blob of dense energy. So the
(37:53):
more you add to it, the more black holely it gets.
This is called the Kirby principle. Is at a cartooning joke.
It's a it's a Nintendo character Kirby. He just sucks
stuff up and he gets bigger and bigger. Awesome. Well,
that's exactly what happens. And so black holes can eat
other black holes and then become super black holes. Or
(38:16):
if you start out with a bunch of smaller ones,
you might get an intermediate mass black hole, and that'd
be really interesting because maybe intermediate glass black holes do
something different from the really big ones. Are the really
little ones, you know, the really big ones are for example,
sometimes their quasars they make crazy radiation because of all
the gas and dust swirling around them. So this would
be like a cool opportunity to just see something new
(38:38):
we've never seen before. And so people are looking inside
these globular clusters trying to see if there are these
intermediate mass black holes inside of them. So when you're
looking in a globular clusters, there a trick to being
able to find a black hole inside one of these. Yeah,
that's great question because you can't obviously see them directly.
The way you can see a black hole is either
(38:59):
gravitational lensing of the stuff behind it. So for example,
of a star passes behind the black hole, than most
of the star would disappear or some of the light
from the star would bend around the black hole and
you could see that sort of distortion. And actually a
globular cluster is a great place to do that because
you have a lot of stars moving all around, so
it's easier to see this gravitational lensing effect I see.
(39:21):
So the more activity you have, like, the easier it
is to see the disruption of that activity as done
by the black hole. Yeah, because you can see the
black hole directly, you can only see its influence on
stuff around it. So you can either see it bending
the light that comes from behind it, or you could
just see its gravitational effects on the nearby stars. Like
(39:42):
the black hole that's at the center of our galaxy.
We know it's there because we've seen its pull on
the stars that are around and we see those stars
orbiting something that isn't there but obviously has a very
strong gravitational pull. And so globular clusters are a great
way to see black holes because there are so many
of these gravitation or probes. If there's a black hole somewhere,
you should be able to see its effect on the
(40:04):
nearby stars. You can calculate, like how should these stars
be moving if there wasn't the black hole, And then
you can see if there's a deviation from what you
expect and if that could be explained by putting an
invisible heavy mass in one spot, and if so, then
you think you've seen one. So have we found any
inside a globular cluster. So no confirmed sightings of intermedium
mass black holes and globular clusters. I know, stay tuned.
(40:27):
There was one where people thought maybe they saw one
with four thousand solar masses, but then follow up analysis
didn't see the same results. And actually you could explain
all of the star paths without the black hole. And
so it's a hard thing to do because these things
are not that close by, and you're looking at individual
stars in a cluster, you know, thousands of light years away.
(40:47):
But it's an exciting thing. It's a it's a cool
new object for us to look into and to ask
questions about the way stars form and new weird kinds
of stars and strange conditions for black holes. I mean,
it seems like a real, just fun happening spot in
the universe to really put your papers on. As an astronomer. Yeah,
I think it's really interesting and I love these bits
(41:09):
of the universe that are sort of left over from
an earlier time. Now, these things formed more than ten
billion years ago and they're still around, which gives us
an opportunity to learn, like what was going on back then,
because what happened back then is what determined the shape
and the nature and the content of these things. So
they really are like a little time capsule of the
early universe. And everything we're doing in physics about trying
(41:32):
to understand the universe is about trying to rewind and
trying to understand how did everything happen. So to do
that we have to find clues. We have to look
for places in the universe where stuff is left over.
You now, this is like the astrophysics analogy of a fossil,
you know, a little piece of evidence left over from
an earlier time, or like a living fossil, like a
Ceila camp. Yeah, exactly, like a living fossil. Unfortunately, there
(41:56):
probably aren't any aliens living on planets swinging arounds from
star to star inside a globular cluster. But maybe there are,
and if so, maybe they could tell us something fascinating
about what it's like to live inside such a bright environment.
I'm hoping to find a blob fish inside a globular cluster.
I think that's why globular cluster sounds gross to me,
(42:17):
because it resonates with the word blob. You know, every
time on this podcast, I wanted to say globular cluster
of almost said blobular cluster. Well, you know it's interesting
because globular clusters do not deserve that kind of nasty name. Likewise,
the blobfish actually gets a bad reputation. It does not
look like that. Have you ever seen the blobfish. It
(42:40):
looks sort of like a a sad, ziggy exploded blob
with a frown. Yes, it's not very advertising. No, no,
it looks like a slimy bloble. That's because it exploded
when you brought it up from the deep sea and
it's natural environment. I wouldn't say it's a looker. It's
not beautiful, but it it looks a lot more solid.
(43:01):
It just kind of looks like this gray, sort of solid,
bony fish. But when you bring it to the surface,
it looks like a blob. And so you know you
can't trust a glob or a blob by the name. Well,
it must be very disappointed. You know. It looked at
itself in the mirror before it leads the house, and
it's like, I'm looking good, and then it ends up
looking like a big blob when it's brought up to
the surface. And they truly do look quite pathetic because
(43:24):
it looks like they're frowning. But maybe the globular clusters
and the blobfish can come together and get some better
pr for themselves. Maybe the aliens that live in globular
clusters look like blob fish and they'll come here and
they'll recognize the blobfish as you know, really the people
they want to talk to. It seems like you'd have
(43:45):
to be sort of blobular to live in a globular
cluster because of all those stars tugging on you all
the time. Like Taffy, your planet would be a bit
of a blob as well. All right, well, thanks everyone
for sharing your curiosity with us and taking this tour
of a fascinating structure inside our galaxy, something that can
tell us all about the universe and house stars formed
(44:05):
in the age of our galaxy, and maybe about the
future of black holes. Episode. When someone says, hey, would
you like a globular cluster, don't turn your nose up
at it. It could teach you about the deepest secrets
of the universe. But please don't use that for your
next breakfast cereal. All right, everyone, thanks for tuning in,
see you next time. Thanks for listening, and remember that
(44:33):
Daniel and Jorge explained. The Universe is a production of
I heart Radio or more podcast from my heart Radio.
Visit the i heart Radio app, Apple Podcasts, or wherever
you listen to your favorite shows.
Hey, Katie, do you have science words that you especially like? Yeah,
I really like apoptosis. It makes me think of popcorn.
That does make me want to have a snack. Well,
I like the word fundamental. It sounds so important, it's
got fun in it, it does. So what science words
(00:30):
don't you like? Um, coagulate, I was afraid you're gonna
say moist coagulates pretty gross. Also, I'm not such a
fan of the word had drawn. No, the problem is
a lot of people end up with a little typo
that swaps a couple of letters and you end up
with something very not safe for work. Yeah, that gives
(00:51):
the lard hay drown collider a whole different connotation. Hi,
I'm Daniel, I'm a part of Old Physicist, and I
(01:14):
definitely am colliding hay drowns at the LHC. And I
am Katie Golden. I'm stepping in for Jorge this week,
and I am the host of Creature Feature. I'm a
science podcast interested in evolutionary biology, human psychology, and hate
also physics and Welcome to the podcast. Daniel and Jorge
(01:36):
explain the universe, in which we take you on a
mental journey to understand everything about the universe, from the
tiniest things between your toes to the things you see
in the night sky to the vast weird, crazy bonker
stuff going out in the depths of space. We take
all of it, roll it up and try to make
sure that you understand it. Like a cosmic burrito. How
(02:01):
much hot sauce you want is up to you. And
we love to talk about stuff that we see in
the night sky, but we also love to talk about
stuff you might not have even heard of. When you
look up in the sky, you see stars, and if
you have a nice telescope you can even see further
in meb see those smudges that our galaxies. But there's
a lot of other stuff out there in the universe
(02:23):
that we are not familiar with, that most people don't
even know exists. Okay, so if I'm looking at the
night sky, I see a bunch of stars. Sometimes I
see like, like you said, it looks like someone spilled
a bunch of sugar up there, and it's a galaxy.
But what can I possibly be missing? I mean other
than yeah, I guess I can't see them in detail
(02:45):
with a telescope, But but what what's up there? Like
you mean giant alien eyeballs. Well, there's a lot of
stuff out there. And basically, every time we turn on
a new telescope or a new kind of device for
we're listening to the Cosmos, we find something new. And
every time we ap peer deeper and deeper into the sky,
we see stuff that we didn't expect. On the podcast today,
(03:08):
we'll be talking about a weird thing that's in the
sky that astronomers have known about for hundreds of years,
but most people aren't aware of. All Right, well, what's
this big secret? What if astronomer has been keeping from us? Well,
unfortunately it's got a really strange and kind of an
ugly name. Oh, it's not coagulated. It stars don't coagulate.
(03:32):
I guess if a galaxy cuts itself right, a bunch
of like stars could rush in to fill in the
gap planetary platelets. No, Today on the program, we'll be
asking the question what are globular clusters? You? Doesn't sound
(03:53):
like something you want to order on the menu, does it? No?
It sounds like the worst kids cereal? Ever, like, be
sure to get globios for your globular clusters. I know,
I imagine some like scoop of some very viscous kind
of stuff. It's like jello mixed with gravy or something.
(04:13):
Oh man, I don't I have a texture thing when
it comes to food, Like I don't like cottage cheese
or other like things, little chunks suspended within goo. So
I don't know about this globular clusters thing. This does
not sound good. Well, fortunately it was not designed as
a menu item. It's an astrophysical object. It's something out
(04:34):
there in our universe that might teach us something about
how the galaxy was formed, and how old the universe is,
and weird new kinds of stars, and so it's an
opportunity to learn something. Unfortunately, we don't actually have to
taste it. That's good, that's good, all right. I'm still
with you then, But if you try to give me
a spoon on one of these globular clusters, I am check. Please.
(04:57):
So we asked what people think globular clusters are, and
this is what people have to say. I don't know
what a globular clusters. I think it might be something
found in out space, but I don't actually I'm not
(05:18):
sure entirely, but I think it's just some type of
grouping of stars, assuming it's a term from cosmology. A
cluster is a collection of stars, and globular means that
it's round like a globe, and you'll as in molecule
or module, suggests that it's small, so it's a small
(05:38):
round a bunch of stars. This one is like a
gathering of stars spherical. It's not a galaxy. It can
be within a galaxy, but it may look like a galaxy,
like a spherical galaxy. I've heard the phrase globular or cluster.
(06:01):
I'm not sure what it means. I thought that it
had something to do with a group of stars, maybe
that are clustered together in a spherical shape. This is
a gigantic group of stars sit outside and I think
maybe even all of it the galaxies. This has something
(06:23):
to do with a group of stars, maybe that they
all formed from the same nebula or um other event.
Thanks to everybody who volunteered to speculate baselessly without getting
to do any research or googling. If you'd like to
participate for a future episode, please write to me two
questions at Daniel and Jorge dot com. I think it's interesting,
(06:46):
so most of the answers more along the same lines
like this is probably a big cluster of stars or
some kind of space junk, some kind of space junk.
But then no clue in there that it's a cluster
of stars, right, it could have been a cluster of anything,
you know, jello or gravy or breakfast cereal or whatever.
(07:08):
I think when people think about space, you think of
it mostly stars. Right, you look out into space. What
do you see? You see stars. All the other stuff
that is out there is either hard to see or
isn't really perceivable. Yeah, but you hear some people speculating
like maybe it's a cluster of galaxies or a cluster
(07:29):
of galaxy clusters or something like that, because there's this
fascinating sort of hierarchy of structure out there in space. Right,
It's not like they're just stars everywhere. Things are sort
of grouped together into galaxies, and those galaxies are grouped
together into clusters of galaxies, and so there's like this
really fascinating sort of hierarchy of structure is getting bigger
and bigger and bigger. And so I guess the question
(07:51):
then is, you know, like what are globular clusters a
cluster of Yes, what kind of pyramid scheme is a
globular cluster. Who's the downstream and who's the upstream? Who's
really making money off globular clusters? Right? Who's behind big
globular taking globular clusters to the moon. So the answer
(08:13):
is that globular clusters are clusters of stars. And to me,
the fascinating thing is that there's something in between, sort
of like our Solar system and the galaxy. Do you
think about like our cosmic address. We're here on Earth,
we're zooming around our star, and then we think that
our star is just like one of many stars of
(08:33):
hundreds of billions of stars in the galaxy. But it
turns out that there's an intermediate step there. It's not
like just Solar system and then galaxy. You could have
organizations of solar systems. So when you zoom out, like
when you see these videos of here you are on
planet Earth. You're tiny and significant, flee like creature on
(08:56):
this huge planet. Then you zoom out to Solar system
and usually goes right from Solar system to galaxy. But no,
there's an extra step. You're saying, there's an extra step. Yeah,
some stars, some special stars grouped together into these big
clusters of stars called globular clusters. Now, not every star
(09:18):
is in one of these things. It's not like, you know,
another layer in this hierarchy is sort of like a
special clumping. Like most stars are just sort of like
out there on their own, sort of like out in
the middle of the countryside by themselves. But it turns
out that there are these like urban areas where stars
clump together really densely and make these things called globular clusters.
(09:39):
And they're like a fascinating relic of the ancient formation
of the galaxy and can tell us a lot about
how things work out there. So it's like you've got
a bowl of granola, and yet you have your little
oatmeal pieces in there, but then you have the big
clusters of oatmeal too. Those are the best ones. Those
are the best ones. Those are nice. Yeah. I always
(09:59):
fish those out first, and then I'm left with just
sort of a bowl of sugary oatmeal and that's not great.
But so that whole bowl is like the galaxy, but
within that bowl you have the globular clusters of the
nice crunch granola's. Yeah, exactly. The stars are not evenly
distributed through the galaxy. I mean, the overall pattern is
that there's more stars in the center of the galaxy
(10:21):
with a gravity stronger, and then it's sort of peters
out along the galactic disc. But inside there it's not smooth.
There are these clumps where you get these big collections
of stars. And we're not talking like, you know, five
ten stars. We're talking like a few hundreds of thousands
of stars. It's a big deal. Sounds like when they're
making the galaxy that just didn't stir enough. That's what
(10:43):
I learned about. Like when I'm trying to make polina,
you know, it gets clumpy. You just didn't stir enough.
Katie's globular polenda. That's not the foundation for your next
food truck, right, And so these things have like a
few hundred thousand stars in them, but they're not actually
that big, right there only like ten to sometimes like
three hundred light years wide. Okay, you say that's not
(11:04):
that big. However, how long would it take me to
drive from one end to the other of three hundred
light years? Yeah, it would take you a while. I mean,
even in your light speed polenta powered vehicle, it would
take you three hundred years to go across three hundred
light years obviously, and in a much slower, more reasonable
ship it would take much much longer. But the reason
(11:26):
I say that it's not that big is that there
are so many stars in there. So would you end
up with is stars in a very unusually dense collection
like in our part of the galaxy in our neighborhood,
there aren't that many stars, like the nearest stars more
than four light years away, right, I mean, it seems
like there would be conflict with stars being that close together, right,
(11:49):
because I know every body in the universe has some
kind of gravitational poll and stars are so big they
seem like they would be acting on each other there,
So it's it's odd that you would have them so
close together. Yeah, And that's exactly what makes them fascinating
because in these clusters we get to see stars doing
(12:09):
something they don't normally do, which is like dance around
each other and tug on each other and form new,
weird kinds of stars. And we're gonna dig into all
that crazy stuff that's happening inside the globular clusters in
a minute. But here's some numbers for you, Like the
density of stars in our neighborhood. Like around where we
live in the galaxy is like one star per three
(12:29):
hundred cubic light years, so that's pretty big area just
to get one star. But inside one of these globular
clusters there's like two stars per cubic light year, so
it's like six hundred times denser than it is in
our neighborhood. It's like going from the middle of nowhere
to Manhattan. Really packed in there, like star deans. Yeah,
(12:49):
they really are. Imagine what it would be like to
live around a star in a globular cluster. You would
have so many other like bright stars in the sky
at night. The night itself might be a lot brighter
than it is here. Yeah, it seems I would be
as bright as daylight. You just have too many suns
going on. Yeah, if you're near the center one of
(13:10):
these things, I mean, the globular cluster itself is like
twenty five thousand times brighter than the sun. These things
are really bright. Some of them are up to like
fifty times brighter than even that. You'd be in the
middle of like a lot of light bulbs all the time.
Maybe a pretty crazy experience. Well, I need to get
some more high tech sunglasses. It seems like to be
(13:30):
able to live here some of that those polarized shades.
But before I do that, why don't we take a
quick break and I will return with all new sunglasses.
(13:52):
All right, I've got my super polarized super extra anti
glare globular cluster sunglasses on. I can't see a thing indoors,
but I think it'll help me see within the globular clusters. So,
so what's going on around me? Yes, So these globular clusters.
You have this big collection of stars all packed into
one spot. And one of the amazing things is that
(14:15):
there aren't actually that many of these, Like the galaxy
has hundreds of billions of stars, but they're only about
a hundred and fifty, maybe up to two hundred of
these globular clusters. Well why are they so rare? We
don't really understand, and we can talk in a minute
about how they form, but one clue is that they're
also not always contained within the galactic disk. Like when
(14:39):
you look at the galaxy sort of from outside, which
we can't do what we can look at other galaxies.
Of course, you see that it's mostly a flat swirl,
and that's because of how the galaxy formed. Right, the
galaxy form from a huge collection of gas and dust
which collapsed into stars and then gravity took over and
try to pull all those stars together, and that's why
you have a galaxy. But it's my it's harder for
(15:00):
gravity to pull along the galactic plane because that's how
the galaxy is spinning. That's spinning keeps things from falling
in only along that plane. Perpendicular to that plane, you
can squish it flat like a pancake. Is it sort
of like when you have a bicycle wheel, You have
some torque there, so you have that kind of like
inward energy of the galaxy spinning, So it's easier for
(15:24):
it to be flat and spinning inward than it is
to spin another direction. Yeah, exactly, if you spin a
bicycle wheel, then it's harder for things to sort of
fall in towards the center. Or if you think, for example,
about like a merry go round with ping pong balls
on it, right you spin that thing, the ping pong
balls are all going to fly out, but they're gonna
fly out along that plane. So that's what we call
(15:45):
rotation supported. The rotation of the galaxy is keeping things
from falling inwards, but again only along that plane. There's
nothing that prevents the collapse perpendicular to that plane, which
is what makes it flat like a disk. Well, next
time I go on a Merry go around, I'm bringing
a bunch of ping pong balls with me. This is
probably why I'm banned for most Merry go round. Maybe
(16:05):
also because you try to eat polenta and you end
up throwing up globular chunks of polenta. Oh man, When
I was a kid, I was a throw upper kid,
and I had some moments. I had my moments, especially
on the teacups. All right, well, we don't want to
revisit that with too much to jail. But the interesting
thing about these globular clusters is that they don't tend
(16:27):
to be along this galactic disk. Like if you looked
at a diagram of where they are, there's some of
them that are in the disc, but they're also sort
of just spherically distributed around the galaxy. It's almost like
they come from a time when the galaxy was a
big puffy sphere before collapsed. Right, And I'm looking at
this image and what it looks like to me is
(16:49):
like a side view of like a fried egg, and
then above it, like scattered around it are little little
yellow dots like you just spilled a bunch of salts around. Man,
I keep coming back to food on this globular cluster episode,
don't I. We've gotta stop recording these at lunch. Whoever
thought globular clusters would make you hungry? Like, I gotta
(17:12):
bring a positive spin to it. So they're falling outside
of that disk. You're saying that maybe these had formed
back when the galaxy was sort of this big puppy cloud,
and even as it flattened down to the disk, they
didn't come with the rest of the game. Yeah, precisely.
(17:33):
And there's a bigger topic here of the galaxies halo.
Remember that galaxies are not mostly stars. Most of what's
in the galaxies actually dark matter. And if you look
at where the dark matter is in a galaxy, it
doesn't collapse the same way that normal matter does. It
tends to spin. And so this is big spherical halo
(17:54):
of dark matter around the galaxy. And that's the original
thing that's sort of like clustered together the gas of
dust that made our galaxy. And so these globular clusters
they're sort of in this larger galactic halo, but they
haven't collapsed down into this disk, and we don't know
exactly why. It could be that they didn't form with
the original galaxy but are like their own little mini
(18:17):
galaxies that were then captured later and that's why they're
orbiting around. Or it could be that they formed with
the rest of the galaxy but then didn't collapse as
well as the gas and dust because they don't collide
with each other as much as the gas clouds do,
so they avoided like losing all that angular momentum and
they can keep spinning around out there in crazy orbits.
(18:38):
Or maybe they just prefer to hang out out in
the dark matter halo. Dark Matter Halo is a really
good metal band name, I've got to say. Yeah, So
that that's interesting. We can't see dark matter, but it
is there, and so it's like this halo around the
galactic disc. And suspended in that halo are these little
(19:00):
dots and those are each a globular cluster, yeah, exactly,
and some of them happen to fall within the galactic disc,
but most of them do not. You know. The closest
one to us is about sixteen thousand light years away.
It's called the Omega cluster. But there's a bunch of
these things, and what's really interesting is how they form.
(19:21):
And as you said earlier, they might tell us something
about the age of the Milky Way, because we think
that they formed very very early on as the galaxy
was forming. You know, the way these things happened is
that you get, you know, a big clump of gas
and dust, and it may have been that you just
got sort of like an over dense pocket of gas
and dust something which was like, you know, got more
of a serbing of globs than the rest of the
(19:43):
stuff around it, and it collapsed all at once and
made a big bunch of stars. And so these globular clusters,
when we look at them, we see a bunch of
stars and no gas and dust in between, which means
like they're not forming any new stars. So there's sort
of like a little time capsule from very very early
formation of the galaxy. So when you say it happens
(20:03):
at the same time, what are we talking about, Like
it all happens within sort of one of our human
years or is it literally like within a few moments?
Oh wow, now we're talking like in within millions of years. Okay,
star times. We humans are sort of like dogs. We
live in dog years and they live in star years. Yeah,
(20:25):
they live in star years. We think that these globular
clusters are about eleven to thirteen billion years old. I remember,
the whole universe is only just under fourteen billion years old,
which makes these things some of the oldest things in
the galaxy, which is how we can sort of use
them to help understand the age of the galaxy. And
also when we see them in other galaxies like Andromeda,
(20:48):
we can use them to help understand the age of Andromeda.
And one way we can do that is because we
think that all the stars in there were formed at
the same time, which means they all sort of like
start their own clock at the same time. And you
remember that the life cycle of a star is that
it burns for a while and then ones is done
with all of its fuel. It either goes nova or
(21:09):
collapses or something. But the lifespan there depends on the
original size of the star. The more mass it has,
the faster it burns. The smaller it is, the longer
it burns. So we can tell something about the age
of these things just by looking at like the distribution
of stars, which ones have burned out already, which ones
have not. But the fact that they've all formed at
the same time makes it very easy to sort of
(21:30):
like reverse that back and understand how this thing started.
It's nice from a scientific perspective because you control for
the factor of age. You've got like these little test
tubes out there that you can look at as physicists. Yeah, exactly.
And they're also an interesting collection of stars because they're
not stars like our sun. Our universe has gone through
(21:51):
a few cycles of making stars. You know, the very
early universe, you had hydrogen helium and that fell together
to make the original first generation of ours, which weirdly
astronomers called population three stars. And those were really big
and didn't burn for very long, but they made some
like helium and some heavier stuff and things that astronomers
(22:11):
called metals. And then when they blew up and they
spread their stuff through the galaxy, there was a second
generation of stars which formed, and those are called population
two stars. Some of those burned up and collapsed and
spread their stuff through the galaxy to make population three stars,
which is like our sun is a population three stars.
But these stars in the globular clusters are only population
(22:33):
two stars. There weren't any of the population one stars,
the ones like our sun when these things formed. So
you may have explained this. It counts down. It goes
pop three pop to pop one is the newest or yeah, exactly,
which I guess makes the next generation of stars are
gonna be what pop zero and then pop negative one?
Like nobody really thought this through pop zoomers. And the
(22:56):
other fun thing about these is that that very low metallicity,
Like there's basically just helium and hydrogen because that's what
was around after the first generation of stars, the population
three stars. You know, astronomers have this weird naming system
for basically everything. Well one thing that's especially weird is
what they call them metal. Like everything that's not hydrogen
or helium is a metal to them because it's like
(23:18):
a big heavy element. See. I mean, like, you know,
there's a lot of controversy in the metal community of
what can be considered metal. There's prog metal, and some
people say, no, it's too much of a ballad to
be metal, But you know, I think it's nice to
be inclusive, and so these globular clusters that have basically
only very low metal stars. And these stars are also
(23:40):
not that big, which is why they've been burning for
so long, and they might continue to burn for billions
and billions of years more. The smaller kinds of stars,
like red dwarves, they might even last for trillions of years.
So these are very I guess gassy stars would be
fair to say these sorry gassy stars. But the interesting
thing is that they've sort of cleared out all the
ask the dust inside of them. They're not making any
(24:02):
new stars. Other parts of our galaxy still have these
big blobs of gas and dust, so there's still new
stars being made all the time, Like our son was made,
you know, fairly recently on these time scales, only five
billion years ago. But the globular clusters, they're sort of
like you know, old boys clubs. They made all their stars,
they used up all their gas and dust, and then
they're done. They're just like, we're gonna hang out. We're
(24:24):
happy with a number of stars. We have no new members. Typical. Typical.
There are some places in the universe where globular clusters
are still forming, like in the large Magellanic Cloud there's
a big positive gas and people think that it's now
forming into a new globular cluster. And by now we mean,
you know, within the last twenty million years on star time,
(24:45):
star time, not not a little human dog time. But
there's still a lot of really interesting mysteries about these things.
Most of them have sort of like a single population
of stars that we think all formed at the same time,
and you can tell based on like the star ages
and sort of how they're like popping off and dying.
But some of them have like two or three different populations.
(25:05):
It looks like there was a clump all made it once,
and then another clump all made at the same time
that was different from the first clump. So there's a
lot of interesting mysteries there. So is it more rare
for globular clusters to form in our current universe than
you think that it was like near the beginning of
the universe. Yeah, absolutely, because a lot of the gas
(25:26):
has already turned into stars or into globular clusters, and
so it's very rare for globular clusters to still be made.
Most of them were made in the early universe and
they're just sort of like hanging around. They're like, you know,
the old folks still smoking in the back of a bar,
you know, and they're just not really making them like
they used to anymore. There's just not enough gas to
go around, which I can't believe I'm saying. And so
(25:47):
we don't really understand like how these globular clusters have
multiple different populations, Like people think maybe different globular clusters
might have merged, like you had two of them formed
at different times, and they sort of came to get
there to make one that had two different populations in it.
But it's you know, it's an area of active research.
It's not something we really understand. So could I live
(26:08):
in a globular clusters? What's going on in there? Is it?
Is there anywhere for me to be? Are you looking
to move, Katie? You are happy with your current apartment.
I've got my cool shades that I currently can't say
anything through, So I've gotta gotta find a place as
bright as I am. It's a really fun question because
it's fun to imagine what would like to be on
(26:31):
a planet inside a globular cluster, And so people are wondering,
like are there planets around these stars? Do these stars
also have like planetary disks which collapse and give you
rocky stuff that you could live on. Could there be
alien life that evolved inside a globular cluster? We think
actually it's pretty unlikely for these things to have planets
(26:51):
around them, which is a bit disappointing when it comes
to like writing science fiction novel about it. But there's
really two reasons. One is that most of the material
just sort of went to making stars, Like there's mostly
gas there, so it's hard to form planets. Planets you
tend to want to have like a rocky core with
something heavy in it, But these things formed in the
early universe when there was basically just hydrogen and helium
(27:14):
and very small amounts of heavier stuff, so you didn't
have sort of the raw ingredients to make planets. And
the second is that it's pretty hard for a planet
to stay orbiting a star if there are so many
other stars nearby constantly tugging on it. Right, it seems
like even if you could have like a gas planet,
it would just get ripped apart by these quarreling stars. Yeah, exactly,
(27:39):
and it would just get tugged out of orbit. You know,
we think of our planet is mostly just orbiting the Sun,
but there are gravitational forces from other nearby stars or
things that pass nearby, and when the Sun comes nearby
other stars, those things get stronger. So in a globular cluster,
remember it's much much denser, there are many more stars,
(28:00):
your byes of these tugs are a lot stronger. So
even if you did form a planet and it did
survive being pulled apart, as you said, you woul probably
just get like passed around from star to star. Wouldn't
have like a stable orbit like a volleyball exactly like
a hot potato planet. That doesn't sound ideal for me
as a little person living on this volleyball planet. So
(28:22):
I'm gonna have to rethink my travel plans. So we'll
take a break while I look into real estate in
a different part of the universe. Alright, so we are back.
(28:45):
I am looking at man Zillo just does not really
go into like beetle juice area. There aren't very many
sales to track there, so who knows how much of
those houses cost. So we're talking about globular clusters. We
have found out that I cannot live there inside a
(29:07):
globular cluster, dream shattered but maybe there's something else we
can get out of these globular clusters. Yeah, we think
that there aren't planets around these things. And people actually
went and looked and they studied a cluster and one
of them had exactly zero planets in them. And then
they looked at another cluster and they actually did find
one planets, this huge Jupiter sized planet. But it's orbiting
(29:31):
a pulsar in a binary star system. It's like a
really rare and unusual kind of situation. And a pulsar
is not what you want for like your home sun.
So what is a pulsar? A pulsar is a star
that's already collapsed, so it's burned it through its life
and it doesn't have the energy to prevent gravitational collapse,
and so it falls down into a neutron star and
(29:52):
then it starts spinning crazily and emitting crazy radiation into
the universe, which then sweeps across the sky and pulses,
which why we call it a pulsar. We have a
whole fun podcast episode about pulsars people can dig into.
But pulsars don't emit light the same way like our
son does because there's no fusion going on inside, so
it would be a pretty chilly place to live. Well,
(30:15):
I'll pack a sweater, pack all the sweaters. But there
are some really interesting things you can do with globular clusters,
like experiments, you can do questions, you can ask things,
you can learn about the universe. To me, what's really
interesting is that you get all these stars together, like
really tightly packed, and so you get to see like
what happens when stars get really dense, when they're like
(30:37):
all tugging on each other gravitationally. Because you know, normally
stars are pretty far separated, they don't really pull on
each other that much. So it's like getting to study
what happens when they get all crammed together. It's a
starsh pit exactly. You get really interesting dynamics. Like some
of these things have had what they call core collapse,
(30:58):
where the center of the globe the cluster has a
bunch of really really big stars and all the smaller
stars are on the outside. And so they're trying to
understand like are these because of gravitational interactions where like
two stars come near each other and then sort of
like throw each other in different directions and the bigger
star always gets sort of thrown a little bit more
towards the center, so that after billions of years, you
(31:19):
end up with the smaller ones like in a little
halo around the bigger ones at the center. It's like
you have a bunch of dance partners, and you've got
a bunch of little guys and some some big guys,
and they're doing the dance from you know, the Titanic,
where you hold hands and you spin around in a
circle and then you let the other person go and
they go flying. But it's a bunch of stars, and
so maybe the little ones, like when they go flying,
(31:42):
they fly out further, keep getting slingshotted out to the outside,
whereas the bigger ones don't get tossed or heated. As
the kids say as far, Yeah, that's exactly what happens.
That makes the core of these things even crazier, because
not only is it a place where there are a
lot of stars, but now you have even bigger stars
all clustered towards the center. So the heart of these
(32:05):
globular clusters must be a really crazy place to live
or even to visit. It seems slightly deadly. Potentially, you
can also see really interesting new kinds of stars. There's
a kind of star that seems to only exist inside
a globular cluster. Yeah, and these actually I gotta give
astronomers kudos because they have a cool name. These stars
(32:25):
are called blue stragglers. Oh man, this sounds like I
can just hear sort of like a guitar toWin going
on and a country songs starting about the blue stragglers. Yeah,
they lost their dog and their truck. But the interesting
thing about these stars is that usually what happens to
(32:47):
a star is a d percent determined by how much
gas it started with and then how old it is.
So you start with a bunch of gas and it
burns for a long time, and you know, it's color
depends on its temperature, which depends on the gravitation pressure,
which depends again on just how much stuff it is.
So you get enough stuff, you're gonna have a red giant.
You get a little more, you can have a blue giant,
(33:07):
for example. And so it's a very like well known,
well understood sequence and stars should only appear like somewhere
on this curve that tells you the mass and the
age of the star. But inside these globular clusters is
a weird kind of star called a blue straggler, and
they're much bluer than you expect for a star of
that size and that age. Poor things they got the
(33:31):
blues that country music at all. It's the blues really,
all right, So why are they so down? Are you
talking about the color? Yeah, well, we don't exactly know.
It's a fascinating area of study, something people are trying
to understand. And that's what's really interesting about these globular clusters.
It's like a new experiment. You know. Astrophysicists, they don't
get to do experiments like particle physicists, where we like
(33:52):
smash stuff together to see what happens. They don't just
say I'm going to smash two stars together and see
what happens. We don't have a star canon yet, we
can't do it, yeah, exactly. We asked for funding for
the Star game seventy two trillion dollars, but we haven't
heard back yet. But what they can do is just
sort of look out into the universe and see if
these experiments are already happening. Because the universe is chalk
(34:13):
filled with weird stuff, and if you look long enough,
you'll see something that might answer your science question. And
so we think that might be what's happening inside globular clusters,
that essentially star collisions happened. That the reason these stars
are like two or three times bigger than you expect
for a blue star is that they sort of like
got captured and fell together and formed an extra big star.
(34:37):
So they just kind of like it's a collision and
instead of all spreading out, it all kind of just
starts to I hate to say it, but congealed together,
coagulated exactly. And you know, that tells us something about
star formation, because most stars we see formed outside globular clusters,
and that tells us about the distribution. You know, you
get a certain amount of helium and hydrogen, you get
(34:59):
this kind of star of that kind of star. This
tells us that under special circumstances, if you make a
bunch of big stars near each other, they can combine
together to make a super kind of star blue straggler
that doesn't appear anywhere else in the galaxy or the universe.
It's like a special star laboratory. And what's the straggler
part of the name referring to if you look at
(35:20):
the curve for where stars are, it's like color versus mass.
Then there's this population of blue stragglers that are sort
of off the curve. They're like to the left, and
so they're sort of like not hanging out with the
rest of them that are like falling behind. You know,
you don't want to judge these stars and make them
feel bad. They're just sort of different. They're differently starred. Yeah,
(35:41):
they're differently started exactly. Globular clusters also give us a
laboratory for trying to understand another mystery of the universe,
and that has to do with black holes. Black holes
form in our universe, but sort of only in two
different groups. Like we either get black holes that form
when stars collapse, and then they're about the mass of
a star. And so we see black holes from stellar
(36:02):
collapse and they're out there and they have masses of
like ten to a hundred times the mass of our Sun,
about what you would expect from the collapse of massive stars.
Then there's another whole group of black holes that are
like millions of solar masses, and these are the ones
at the centers of galaxies. So you got like stellar
black holes hanging out in the neighborhood, and then like
the really big Papa black holes in the centers of galaxies.
(36:25):
And one question in astrophysics for a long time is
like where are the intermediate ones? Like why are there
no black holes that are sort of like between a
hundred and ten thousand solar masses right the Goldilocks black holes? Yeah,
you know, why don't black holes emerge to form the
bigger ones. It's an interesting question about like where they're
made and how often it happens, and so this is
(36:46):
something people have been trying to understand. And one possibilities
that you might be able to make intermediate mass black
holes in globular clusters because here you have like an
unusual density of stars and if a bunch of them
go black hole and then formed together, you might be
able to make one of these things. So how are
we going to do this? What do we need to
make a black hole out of one of these globular clusters. Well,
(37:09):
we don't have to do much. We just sort of
sit back like astronomers and look out in the universe
that's putting on a show for us. And the idea
is sort of wait for one of these things to
turn into a black hole. And then if there are
a bunch of other black holes nearby, they could sort
of swirl into each other. And remember what happens when
you toss a black hole into a black hole is
you just get a bigger black hole. Right, black holes
(37:32):
don't like tear each other apart. Anything you tossed into
a black hole just makes a black hole bigger. This
is one of the favorite things people write in about,
like what if I threw in, you know, antimatter into
a black hole? Or what if I shot a laser
into a black hole? Right? You can't destroy a black
hole by adding more energy to it. A black hole
is just a big blob of dense energy. So the
(37:53):
more you add to it, the more black holely it gets.
This is called the Kirby principle. Is at a cartooning joke.
It's a it's a Nintendo character Kirby. He just sucks
stuff up and he gets bigger and bigger. Awesome. Well,
that's exactly what happens. And so black holes can eat
other black holes and then become super black holes. Or
(38:16):
if you start out with a bunch of smaller ones,
you might get an intermediate mass black hole, and that'd
be really interesting because maybe intermediate glass black holes do
something different from the really big ones. Are the really
little ones, you know, the really big ones are for example,
sometimes their quasars they make crazy radiation because of all
the gas and dust swirling around them. So this would
be like a cool opportunity to just see something new
(38:38):
we've never seen before. And so people are looking inside
these globular clusters trying to see if there are these
intermediate mass black holes inside of them. So when you're
looking in a globular clusters, there a trick to being
able to find a black hole inside one of these. Yeah,
that's great question because you can't obviously see them directly.
The way you can see a black hole is either
(38:59):
gravitational lensing of the stuff behind it. So for example,
of a star passes behind the black hole, than most
of the star would disappear or some of the light
from the star would bend around the black hole and
you could see that sort of distortion. And actually a
globular cluster is a great place to do that because
you have a lot of stars moving all around, so
it's easier to see this gravitational lensing effect I see.
(39:21):
So the more activity you have, like, the easier it
is to see the disruption of that activity as done
by the black hole. Yeah, because you can see the
black hole directly, you can only see its influence on
stuff around it. So you can either see it bending
the light that comes from behind it, or you could
just see its gravitational effects on the nearby stars. Like
(39:42):
the black hole that's at the center of our galaxy.
We know it's there because we've seen its pull on
the stars that are around and we see those stars
orbiting something that isn't there but obviously has a very
strong gravitational pull. And so globular clusters are a great
way to see black holes because there are so many
of these gravitation or probes. If there's a black hole somewhere,
you should be able to see its effect on the
(40:04):
nearby stars. You can calculate, like how should these stars
be moving if there wasn't the black hole, And then
you can see if there's a deviation from what you
expect and if that could be explained by putting an
invisible heavy mass in one spot, and if so, then
you think you've seen one. So have we found any
inside a globular cluster. So no confirmed sightings of intermedium
mass black holes and globular clusters. I know, stay tuned.
(40:27):
There was one where people thought maybe they saw one
with four thousand solar masses, but then follow up analysis
didn't see the same results. And actually you could explain
all of the star paths without the black hole. And
so it's a hard thing to do because these things
are not that close by, and you're looking at individual
stars in a cluster, you know, thousands of light years away.
(40:47):
But it's an exciting thing. It's a it's a cool
new object for us to look into and to ask
questions about the way stars form and new weird kinds
of stars and strange conditions for black holes. I mean,
it seems like a real, just fun happening spot in
the universe to really put your papers on. As an astronomer. Yeah,
I think it's really interesting and I love these bits
(41:09):
of the universe that are sort of left over from
an earlier time. Now, these things formed more than ten
billion years ago and they're still around, which gives us
an opportunity to learn, like what was going on back then,
because what happened back then is what determined the shape
and the nature and the content of these things. So
they really are like a little time capsule of the
early universe. And everything we're doing in physics about trying
(41:32):
to understand the universe is about trying to rewind and
trying to understand how did everything happen. So to do
that we have to find clues. We have to look
for places in the universe where stuff is left over.
You now, this is like the astrophysics analogy of a fossil,
you know, a little piece of evidence left over from
an earlier time, or like a living fossil, like a
Ceila camp. Yeah, exactly, like a living fossil. Unfortunately, there
(41:56):
probably aren't any aliens living on planets swinging arounds from
star to star inside a globular cluster. But maybe there are,
and if so, maybe they could tell us something fascinating
about what it's like to live inside such a bright environment.
I'm hoping to find a blob fish inside a globular cluster.
I think that's why globular cluster sounds gross to me,
(42:17):
because it resonates with the word blob. You know, every
time on this podcast, I wanted to say globular cluster
of almost said blobular cluster. Well, you know it's interesting
because globular clusters do not deserve that kind of nasty name. Likewise,
the blobfish actually gets a bad reputation. It does not
look like that. Have you ever seen the blobfish. It
(42:40):
looks sort of like a a sad, ziggy exploded blob
with a frown. Yes, it's not very advertising. No, no,
it looks like a slimy bloble. That's because it exploded
when you brought it up from the deep sea and
it's natural environment. I wouldn't say it's a looker. It's
not beautiful, but it it looks a lot more solid.
(43:01):
It just kind of looks like this gray, sort of solid,
bony fish. But when you bring it to the surface,
it looks like a blob. And so you know you
can't trust a glob or a blob by the name. Well,
it must be very disappointed. You know. It looked at
itself in the mirror before it leads the house, and
it's like, I'm looking good, and then it ends up
looking like a big blob when it's brought up to
the surface. And they truly do look quite pathetic because
(43:24):
it looks like they're frowning. But maybe the globular clusters
and the blobfish can come together and get some better
pr for themselves. Maybe the aliens that live in globular
clusters look like blob fish and they'll come here and
they'll recognize the blobfish as you know, really the people
they want to talk to. It seems like you'd have
(43:45):
to be sort of blobular to live in a globular
cluster because of all those stars tugging on you all
the time. Like Taffy, your planet would be a bit
of a blob as well. All right, well, thanks everyone
for sharing your curiosity with us and taking this tour
of a fascinating structure inside our galaxy, something that can
tell us all about the universe and house stars formed
(44:05):
in the age of our galaxy, and maybe about the
future of black holes. Episode. When someone says, hey, would
you like a globular cluster, don't turn your nose up
at it. It could teach you about the deepest secrets
of the universe. But please don't use that for your
next breakfast cereal. All right, everyone, thanks for tuning in,
see you next time. Thanks for listening, and remember that
(44:33):
Daniel and Jorge explained. The Universe is a production of
I heart Radio or more podcast from my heart Radio.
Visit the i heart Radio app, Apple Podcasts, or wherever
you listen to your favorite shows.
Hosts And Creators
Daniel Whiteson
Jorge Cham
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