Could stars have black holes at their cores?

Daniel and Kelly dive deep into the event horizon and discuss an outlandish theory of stars with black hole cores.

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Episode Transcript

Speaker 1 (00:08):
What mysteries lie inside the Earth, inside stars, or at
the hearts of black holes? We always seem drawn to
cracking things open and looking for the surprises inside. We've
been walking around on this planet for hundreds of thousands
of years until recently had no idea what was hidden within?
Was it all just dirt? Is it hollow? Was Godzilla

(00:30):
sleeping in his lair down there? What about in the
hearts of stars? Science tells us that at their core
matter is incredibly dense, the fusion furnaces that illuminate the
universe and forge the heavy metals needed for life and podcasts.
But what if there was something else, even more exotic
in the hearts of stars? What if instead of iron

(00:52):
or nickel or even nuclear pasta, stars hearts might contain
the most mysterious objects in the universe holes? And what
if that could solve another longstanding cosmic mystery. Today on
the pod, we'll ask whether stars could have black holes
at their cores. Welcome to Daniel and Kelly's extraordinarily dense

(01:15):
but brilliant Universe.

Speaker 2 (01:30):
Hello, I'm Kelly Wadersmith. I study parasites and space and
I love pizza. HM.

Speaker 1 (01:36):
My name is Daniel I'm a particle physicist, and I'm
particularly particular about my pizza.

Speaker 2 (01:41):
I remember you and I had a discussion once about
what we were like level twenty experts on, and you
said that you were like a level twenty expert on pizza.
And I'm embarrassed to say I couldn't figure out anything
to say that I was a level twenty expert on.
But anyway, you just visited Chicago, and so I have
to ask you a very important question, which city makes

(02:01):
the best pizza.

Speaker 1 (02:04):
It's easy. New York obviously near pizza, hands down.

Speaker 2 (02:10):
I'm so glad we can stay friends. I wasn't sure
if there's gonna be like a white chocolate dark chocolate
divide where I admit that I actually don't dislike white
chocolate that much and then you get upset and then
I pretend that I hate it. Moving forward, but yeah,
New York does have the best pizza.

Speaker 1 (02:23):
It's similar to that, actually, because some people defend Chicago
pizza and it's a tasty thing, but it's not pizza. Yeah,
you know, it's like Mari Andara bathtub or something. I mean,
it's delicious and greasy and it's good, but it's not pizza. Yeah,
and when I gotta choose and I gotta make it myself,
I'm definitely making thin crust pizza, though with a little

(02:43):
bit more of a Neapolitan puffy crust around the edge.

Speaker 2 (02:47):
Yeah. I love that all. I mean, I love all
kinds of pizza. But yeah, whenever I go to New York,
I've got to get some pizza.

Speaker 1 (02:53):
And I don't know why they got to call it pizza,
you know, like they don't call the Chicago hot dog
like a taco, you know, like just call it its
own thing. Why we use this word pizza for something
which is to totally different from pizza.

Speaker 2 (03:04):
I mean, it's got the same ingredients, but just in
different like depth. No you disagree, I don't know.

Speaker 1 (03:14):
I recently tried Detroit Pizza, also quite tasty, very weird, delicious,
but still in my opinion, not pizza. But you know
that's semantic. It's all delicious combination of excellent ingredients. My
personal preference is the thin stuff. But you know, I
get why people like Chicago pizza.

Speaker 2 (03:31):
We won't talk about pizza for that much longer because
we have important sites to get to you. But I
heard that Detroit Pizza is like in an like an
automotive pan of some sort, or like what is the
defining feature of Detroit pizza? Presumably you clean the pan first.

Speaker 1 (03:48):
Detroit is also a deep dish kind of pizza. But
you have like sauce on the top in these rows
on top of the cheese, and you get this crispy
edge of cooks up if you do it right. Anyway,
it's quite good.

Speaker 2 (03:58):
Okay, I should have eaten before we started recording this
because now I'm hungry.

Speaker 1 (04:02):
But all right, but you know, if you eat too
much Chicago pizza or too much Detroit pizza, you risk
collapsing into a black hole.

Speaker 2 (04:08):
Ah, that's where it was going. You got there first.
I was actually gonna like contribute a transition. But okay,
so today we're talking about black holes, all right, and
we are specifically talking about whether or not stars could
have black holes at their core. And I will be honest.
When you first sent this question to me, my thought was, well,
could a star exist if it had a black hole

(04:29):
in its core? It seems like the answer should be no.
And so let's see if our audience's guts had the
same response.

Speaker 1 (04:36):
No matter what pizza they happen to be digesting.

Speaker 2 (04:38):
We hope it's delicious no matter what it is.

Speaker 3 (04:40):
I guess stuff in the core of a star could
get dance enough that it would turn into a black hole,
but maybe that will eventually end up extinguishing the star,
because I can see how the star could keep on
burning only with its alter or shell. So I guess
if that happens, it will be short lived and the

(05:01):
star will die and turn into a black hole.

Speaker 4 (05:03):
I suspect a star can have a black hole for
a core as long as the star is both big
enough to survive then usual black hole formation and big
enough that the black hole's gravity doesn't affect the outermost
layers of the star.

Speaker 2 (05:15):
I suspect not it would collapse the whole star material,
I think, into itself that's no longer being a star.

Speaker 5 (05:22):
I think it's possible to have a black hole inside
the star in the core, because a black hole can
be small enough even for you to have it in
your hand, isn't it, And it would not.

Speaker 3 (05:35):
Affect the surrounded Because it's more.

Speaker 6 (05:38):
I don't believe a star could have a black hole core,
mainly because for want to fall in the first place,
a star would have to collapse, and if there was
such a condition where it did have a black hole
as its core, the gravitational force would pull in the
surrounding matter that makes up the star anyway, so it
could never be stable enough.

Speaker 7 (05:53):
It seems possible, but then you'd have to ask how
did it get there and how does it stay there?
And I don't know how it would form, but for
it to stay there, the star around it would have
to be spinning very very fast so it doesn't get
pulled in, and I don't really know how that would
ever start happening.

Speaker 2 (06:12):
Okay, so I'm feeling pretty good because a handful of
our audience members had the same feeling as I did.
And you know, I haven't gotten to the end of
the outline yet, so I don't know if I'm right
or if I'm wrong. It'll be an exciting journey that
we'll take together.

Speaker 1 (06:25):
And these are great ideas. I like the way they're thinking.
But you know, it strikes me that a lot of
people think of black holes as like this infinitely powerful
thing that will suck in anything. But you know, we've
seen pictures of black holes, and we know what black
holes should look like out there in nature and they're
not totally by themselves. You can have stuff around the
black hole, Like the famous picture of a black hole

(06:45):
has a hot disk of gas right around it, because
the environment around a black hole is quite complex and
there's pressure out and gravitational attraction in, and so we're
going to learn it's not quite so simple. Yeah.

Speaker 2 (06:57):
I was talking to Sarah Gallagher at Western University the
other day and she studies the gases that like emit
out of black holes, and I just kind of stared
at her for a second because I was like, I
didn't think anything could escape from black holes, and so
we had a fascinating conversation about how I was wrong.

Speaker 1 (07:12):
Yeah, well, you're right that nothing can escape from a
black hole, but things can escape from the vicinity of
a black hole, right, And so it depends what you
count as the black hole. If it's a black hole,
plus it's accretion disk and all that stuff, then yeah,
it can emit, and they certainly do. We see quasars
from across the universe these incredibly bright emitters.

Speaker 2 (07:31):
Okay, but I think we can all agree that nothing
escapes from the center of a black hole. So if
you are a star that has a black hole, in
your belly. It feels like that shouldn't work out. So
where do we start. What do we think stars have
at their center?

Speaker 1 (07:46):
Yeah? Stars already super fascinating objects even without the black hole. Right,
It's incredible that these things exist. There are this delicate
balance between gravity and fusion. But they're also stable. They
can last for millions or billions, or we think sometimes
trillions of years. It's really incredible, and understanding what's going
on at their heart has taught us a lot about
the nature of physics and even chemistry.

Speaker 6 (08:09):
Yeah.

Speaker 2 (08:09):
I also had the urge to sort of spit and costs,
so I understand I'm.

Speaker 1 (08:15):
Going to wipe my face before we go on. Yeah,
and also the distribution of stars that are out there,
the sizes, the colors, the ages tell us a lot
about the history of the universe. I love this about
science that you can piece together a whole history from
what you see around you. It's not just like does
this work, but it's like, how did we end up here?
Why do we have this arrangement of stuff? And that's
some other arrangement. There's so much information just encoded in

(08:38):
what's out there, So I love that we can dig
into it, and from that we've put together a pretty
good model for house stars form and what should be
at their center before we get into exotic black hole stars.

Speaker 2 (08:50):
Yeah, I also love that kind of detective work into
the past, using science to understand things we couldn't have seen.
But okay, let's jump into stars. What should be in
the center of those stars.

Speaker 1 (09:00):
So stars are basically just a scoop of universe, you know,
go all the way back to Big Bang, hot, dense
soup of stuff. It expands and therefore it cools, and
you get particles that form. You get electrons and quarks,
and then the quarks bind into protons, and then you
have protons and electrons in the universe. It keeps cooling,
and those electrons then get captured by the protons, and

(09:22):
so now you have hydrogen. And most of the universe
at the very beginning is hydrogen. It's like overwhelmingly hydrogen.
Tiny little bit of helium that forms because you can
actually have hydrogen fusion during the first few moments of
the universe to make a little bit of helium trace
anything else. So the universe is hydrogen, but it's not
perfectly smooth. The original quantum fluctuations in the early universe

(09:46):
lead to over densities in some places and under densities
in others, which gives gravity a handle to pull that
stuff together to make stars. And so you have these
big clouds of hydrogen. Some spots are little. They have
more gravity, they pull on more hydrogen, gives them more gravity,
gives them more hydrogen. You get this runaway effect, and
then you get a collapse. So the first stars we

(10:08):
think were mostly hydrogen and a little bit of helium.

Speaker 2 (10:12):
And if you were explaining how black holes are formed,
would you have used all the same words or is
that a totally different process?

Speaker 1 (10:21):
No, basically the same. But you need to get to
a critical density to form a black hole. And what
happens when a star is collapsing is that gravity isn't
the only game in town. You get to a certain
density at the core of the star and it ignites fusion.
So it's hot enough and it's dense enough that the protons,
which don't usually like to talk to each other because
they're both positively charged, are squeezed together close enough that

(10:42):
eventually they will fuse and they'll give you helium and
release some energy. So this is fusion. You get protons
fusing into helium and energy comes out, and that energy
pushes back out on the star. It's effectively a pressure outwards,
so you have gravity squeezing in and radiation pressure pushing out.
That's what keeps the star from collapsing into a black hole.

(11:05):
So you're right, black hole collapse very very similar, but
you don't get there in a star because of fusion.
Fusion keeps the universe from collapsing into black holes and
keeps it bright. Right without fusion, we wouldn't have light,
and the whole universe would be dark.

Speaker 2 (11:18):
Thank you fusion. If only we could use it to
power our toasters, we'll get there one day.

Speaker 1 (11:23):
And this is not the primary topic of today's episode,
but there is a theory that in the very very
early universe, there might have been enough over density, maybe
even before you formed all those protons to create primordial
black holes, which exist like before there are quirks and
protons and all sorts of stuff, so it's possible to
form black holes in the very very early universe. A

(11:45):
lot of people ask, like, if the universe was super dense,
why didn't the whole thing collapse into a black hole?
And the reason is that for a black hole to form,
you need density in one place relative to the density
around it. If everything is super dense, then nothing is
getting pulled. But if you happen to have once which
is super overdense, potentially you can have direct collapse into
a black hole in the early universe. But we're not

(12:06):
talking about that today. We're imagining what happens to normal stars.
So you get this collapse, you get fusion, and then
you have a balance. Gravity and radiation are doing this
delic balance and it can keep going for millions and
millions of years. And at the core you're manufacturing new elements.
So we're talking about what's at the core of stars. Well,
it starts out with just hydrogen, and then you get helium,

(12:27):
and if the star is big enough and massive enough,
it could also fuse that helium into heavier stuff. You
get carbon, you get neon, you get oxygen, and if
it's big enough and massive enough, you can get silicon.
You can get all the way up to nickel and
then to iron. So that's how we manufacture these elements.
They're made at the hearts of stars.

Speaker 2 (12:45):
All right, Let's see if I can pass the qualifying exam
for my pod. If I remember correctly, the bigger the
elements that you're getting, the more like heat you're losing,
and over time that cools the star. Is that right?

Speaker 1 (12:58):
Almost? No, Definitely, the spirit of it is right. You know,
up to a certain point, you are generating heat. So
before iron fusion creates heat, like when you go from
lighter elements to heavier elements, you release heat above iron
fusion costs heat, right, it takes energy, So it can

(13:19):
happen because there is energy there, but effectively cools the
star when you fuse iron nuclei together to make something
even heavier. And so that doesn't mean it doesn't happen,
but it means it effectively kills the star because now
the star is cooling down, and if it's cooling down,
it can't push back against gravity. And what do you
have is you start to have a gravitational collapse again,
and then you can form like a normal vanilla black hole,

(13:42):
like the kind that we have seen in our universe
where the whole star becomes a black hole. And we
talk about that a little bit more detail in a minute.
But there's another thing that we need to understand first
about normal stars, which is the limit on their size,
and the connection between the size and the age of
the star. You have the whole early universe, big cloud
of hydrogen, some clumps of which collapse to make stars.

(14:03):
And you might wonder, like, is there a limit to
the size of the star, Like can you just get
huge clouds that form together to make enormous mega stars?
And the answer is that there is kind of a
limit because the bigger the star, the higher the pressure
and the density and the temperature of the core, and
the faster fusion happens. Because fusion is very sensitive to

(14:24):
the temperature and the pressure. Like you increase the pressure
by a little bit, the rate of fusion increases very
very quickly. And so what happens if you have a
star that's too big is that the radiation pressure from
the fusion is so intense that actually blows the star apart.
It'll like rip apart the star and blow away its
outer layers so effectively, you can't get a star that's

(14:44):
like more than three hundred times the mass of our Sun.
It'll tear itself apart.

Speaker 2 (14:49):
That would be a pretty epic way to go. I
think my new goal is to become super massive towards
the end of my life.

Speaker 1 (14:57):
Blow yourself apart from the fusion that you're That's what
happens if you eat too much Chicago pizza.

Speaker 2 (15:03):
Yeah, yeah, you gotta be careful. You gotta be careful.

Speaker 1 (15:05):
And there's something else happening at the core of the star,
which is really crucial. You've made those elements, right, you've
made helium or iron or nickel or whatever. They're at
the core of the star. But when the star dies,
it goes supernova and it blows that material out into
the universe, and then those heavy metals become the seeds
of the next generation of stars. So when we start out,
we have a universe mostly filled with gas that makes

(15:27):
these really big stars, huge stars that don't last very long,
maybe a few million years because they're so big. But
the next generation it's different because now you have these
heavy seeds to start stars. You don't just have to
have a big hydrogen clump to start a big hydrogen star.
You have like a blob of iron over here and
some nickel over there, and those are excellent. It's seeding

(15:48):
new stars. So then the next generation of stars are
smaller because there's like more places to start, So the
big clouds of hydrogen breakup into more chunks, and because
they're smaller, they don't burn its hot and they ask longer.
So the second generation of stars that have more metals
in them last a lot longer than the first generation
and are also smaller.

Speaker 2 (16:08):
That is beautiful, But my brain has gotten totally off
on a tangent imagining Kelly at the bend of her
life exploding into lots of little Kelly's, and that really
would be a great way to go.

Speaker 1 (16:20):
Next generation of Kelly's will all be mini Kelly's. Yeah exactly,
that's right, that's right.

Speaker 2 (16:24):
But at least there'll be more of them anyway. That
is beautiful that a giant star produces more stars.

Speaker 1 (16:29):
Yeah, exactly. And in our universe we still have some
big stars, Like if you look at the star mass distribution,
mostly the stars in the universe are smaller, like our
star is on the heavier, larger side compared to the
average star. We may have yellow star, but most of
the stars out there are red dwarfs. They're smaller and colder,
and therefore they burn cooler than our star. So the

(16:51):
smaller the star, the cooler, the redder it is. The
bigger the star, the hotter and bluer.

Speaker 6 (16:56):
It is.

Speaker 1 (16:56):
So if you look out into the universe, you can
actually tell the age distribute of stars because the blue
stars disappear more quickly. So if you're like looking at
a part of the universe and there's a bunch of
blue stars, you know that stars have been formed there recently,
Whereas if you look at some corner of the universe
you're like, oh, it's all red stars, then you know
there have been no stars born recently. It's like a
retirement home versus a new subdivision or something.

Speaker 2 (17:18):
But like, could you make a reasonable guess at star siblings,
Like this star exploded and produced these thirty stars in response.

Speaker 1 (17:26):
You can understand stars siblings in the sense of like
you can estimate the age of a star from its neighbors, right, Like,
if there are no blue stars around, you can guess
that it's probably older, and if there's lots of blue
stars around, you can guess that it's probably younger. It's
really hard to trace back an individual star and say
this one was formed from the explosion of that earlier
star which no longer exists, and the other ones that

(17:48):
came from that star that's really tricky. And also it's
complicated because like our sun was formed from the remnants
of other stars, but not just one. Right, It's not
like one chunk of some other star landed in a
gas of high It's like a huge conglomeration of probably many,
many stars that all came together. So yeah, the family
tree gets pretty messy there. Yeah, it's like a big

(18:08):
orgy that happened to make our star.

Speaker 2 (18:10):
Good. Good way to make this a non kid appropriate episode.

Speaker 1 (18:13):
You can have totally family friendly orgies. You can have
like an orgy of pizza for example, right, sampling lots
of different pizzas.

Speaker 2 (18:20):
Yeah, I'm not sure that you know what people usually
mean when they use that word, Daniel.

Speaker 1 (18:25):
I know what people usually mean. I'm saying for folks
that they're listening with your kids, there's an explanation for you.

Speaker 7 (18:31):
Yeah.

Speaker 2 (18:31):
I hope they don't repeat it at school. All right, So,
should we talk about any other stars on our tour
of local Stars?

Speaker 1 (18:39):
Yeah? So there are some really big stars in our universe,
and they're really fun to think about because the sizes
are just really incredible. A famous big star is Beetlejuice.

Speaker 2 (18:50):
Beetlejuice is Oh, that's two, don't say it a third time.

Speaker 1 (18:56):
That star is famous because it's in Orion and it
has a radius a thousand times that of our Sun. Wow,
Like the Sun is already enormous compared to Jupiter, which
is gigantic compared to the Earth. And now Beetle Juice,
it's showtime. It's a thousand times the radius, which means

(19:16):
a billion times the volume.

Speaker 2 (19:18):
Holy cos it's just.

Speaker 1 (19:20):
Hard to really wrap your mind around. If you put
it in our solar system, its edge would be at
the orbit of Jupiter, right, we would be inside Beetlejuice. Also,
it's a weird star because recently it's been seen to
be dimming, so it's like quite variable in ways people
don't understand, which some people think might mean it's about
to go supernova and there's interesting stuff happening at its core.
But again, we don't really understand the core of stars

(19:42):
in detail. It's so chaotic and difficult to describe with
simple equations and expensive to model with supercomputers. So it's
really an active area of research. But that's a really cool,
really big star.

Speaker 2 (19:53):
So my interest in a topic is directly proportional to
how much it impacts me. So if beetlejuice explodes, is
that going to be bad for me?

Speaker 1 (20:01):
If beetlejuice explodes, it'll be dramatic and exciting, but probably
not super dangerous. It's six hundred and fifty light years away.
It's not the time of travel that keeps us safe.
It's not like, oh, it explodes, we have six hundred
and fifty years to do something about it. We won't
know it explodes until six hundred and fifty years after
it explodes, because that's when the signal is going to
arrive here on Earth. But because it's so far away,

(20:22):
the radiation it produces will be quite diluted. That radiation
is going to spread out in a huge sphere and
cover the inside of that sphere, and the Earth is
a tiny, tiny slice of that. So we're only in
danger to supernovas that are much closer than that.

Speaker 2 (20:36):
Okay, that's good. I feel great. Now that I feel great,
Let's take a break, have some pizza, and when we
come back, we'll talk some more about some big stars
in our galaxy. All right, so I hope you had

(21:06):
some delicious New York style pizza. Let's go and talk
about yet another star in our galaxy? Which one are
we talking about next, Daniel?

Speaker 1 (21:14):
So the biggest star that we know about is a
star called Stephenson to eighteen. This one has twice the
radius of Beetlejuice. Right, Beetle Juice already a thousand times
the radius of the Sun. This one's twenty one hundred.
And it's so big that it's so hot. It's five
hundred thousand times brighter than the sun. Wow, Like, imagine

(21:35):
five hundred thousand suns in the sky. That's Stevenson two eighteen.
It's not kidding around.

Speaker 2 (21:41):
So how is it that I have heard of Beetlejuice before,
but I haven't heard of Stevenson to eighteen.

Speaker 1 (21:45):
Beetlejuice is a star in the sky, it's a constellation.
Stevenson to eighteen is much much further away. It's like
nineteen thousand light years away, so it's still in our galaxy,
but it's like a completely different arm so you can't
really see it with the naked eye. It's something we've discovered,
and there's still a lot of uncertainty about what we
know about it because it's so far away. But yeah,

(22:06):
it's a pretty dramatic star. And this is one of
the things I love about astrophysics and astronomy is like
the more you look out into the universe, the more
weird stuff you see that you can't explain, you know.
It's just like always a surprise when you build something new,
which is why I think we should have like ten
times as many space telescopes as we do and ground
telescopes and satellites, and like, wow, think about the things

(22:28):
we're missing in the universe just because we're not looking.

Speaker 2 (22:31):
That's right, And we in more money for fish research too.
We're missing things we could be looking all over the place, guys,
and we're not looking. Enough more money for science.

Speaker 1 (22:40):
Let's build a space telescope that's excellent at finding alien
fish on exoplanets. How about that? Is that a good compromise, Daniel?

Speaker 2 (22:46):
I am so glad we found something we can agree on. Yes, amazing.
As long as those alien fish have alien parasites, I'm
one hundred percent in and I bet they.

Speaker 1 (22:55):
Will, all right, excellent. I look forward to building that
telescope with you. Okay, it's slam dunk funding case for sure.

Speaker 2 (23:02):
They can't turn us down, all right, So let's focus
away from fish unfortunately onto black holes. All right, so
let's go you. You told us that some of the
process for starting a star is similar to the process
for starting a black hole. Remind me where those processes diverge, please.

Speaker 1 (23:18):
Yeah, So a lot of stars end up as black
holes because fusion can't last forever. Right, it's eating the
stars using the star as fuel. It's converting the light
stuff into heavy stuff, and eventually converts it into heavy
stuff that it can no longer burn. Like our sun
is hot enough to burn hydrogen, and near the end
of its life, it's going to be hot enough to

(23:38):
burn helium very very briefly. But anything heavier than that.
Our sun doesn't create the temperatures and the pressures and
the densities to fuse, and so anything else that it
makes is inert. It interferes with the process of the star.
And so that's why our sun, for example, is going
to get a core that's basically dead. It's not participating
in fusion anymore, and then fusions are going to move

(24:00):
to outer layers of the star, and that's why the
star puffs up near the end of its life. You hear,
like the sun is getting hotter and bigger and in
billion years it's going to be really big. And that's
true because the fusion is moving to the outer layers
where there still is hydrogen. But eventually the star accumulates
so much heavy inert stuff, stuff that can't participate in fusion,
that the star collapses. Gravity winds right, Eventually fusion just

(24:24):
peters out, and this collapse is really spectacular. You get
this pressure wave that goes into the star and then
it bounces back and comes out and explodes the star.
And that's where you get a supernova. Right, It's like
this shock wave that goes in and then out that
travels are like incredible velocities, really violent stuff, really amazing.

Speaker 2 (24:43):
You sound like my daughter. She's really into violent stuff
right now. She also sounds very excited when she's fucking
about explosions and stuff.

Speaker 1 (24:50):
Well, it's not that I want anybody start to blow up,
it's just the energy is just incredible. The numbers here
are just mind boggling. And then what happens at the
core of the star depends on the amount of mass,
So you get this really hot dense thing left over.
If it's not quite dense enough, it can form a
neutron star, which doesn't collapse into a black hole because

(25:10):
there's something else pushing back. Now, it's not fusion pressure.
Neutron star is a star, but there's no fusion happening.
It's just electron degeneracy pressure. Like the particles that are
in there, they're all fermions, which means they don't like
to be on top of each other the way electrons don't,
and that effectively creates a pressure. Like they can't squeeze
down and cool down into the lowest energy levels because

(25:32):
they can't be in the same energy levels, and so
they have to be in higher energy levels, which means
they keep some energy, they move around, they basically push back.
That's what degeneracy pressure is. People write in sometimes and
ask like what force is degeneracy pressure, or like why
does the universe keep particles from entering the same state?
You know, And there's no special force there. It's just
that the particles cannot be in the same state, and

(25:54):
so they stay in higher energy levels to avoid each other,
and that creates pressure. Effectively. Start doesn't collapse because of
quantum mechanics. But you know, eventually, if you have enough mass,
it can overcome that. It can push these things together,
so they're no longer really neutrons. Like they get smushed
together and their neutron this sort of goes away as
the quarks form this soup, and then the proto black

(26:17):
hole can collapse. So if you have enough pressure to
squeeze those neutrons out of their fermion states and form
a soup, you can form a black hole. And that's
when you get above this critical threshold.

Speaker 2 (26:27):
Okay, So when we first started talking about fermions and
you said that they don't like to be near each
other the same way that electrons don't, I have been
thinking about fermions as something that was kind of electron adjacent,
and I forgot that fermions are more like neutrons.

Speaker 1 (26:41):
Well, fermions are category particle. All matter are fermions, electrons, quarks, neutrons, protons,
they're all fermions. And fermions have this particular property that
you can't have two of them in the same quantum state,
which is why electrons, for example, are not all in
the lowest energy level around hydrogen. When the lowest energy
levels filled, the next one can't be there. It's got
to be in the next level, and then the next

(27:02):
level and then the next level. That's why electrons spread
out on the ladder of energy levels, one per level.
You know, there's like different spins you can have or whatever,
but they all have to be in a unique state,
which keeps the electrons effectively hotter. Right, If the electrons
could all collapse into the lowest energy level, they would
be cooler, but they're not, which keeps some electrons at
high energy. And that's the same thing that's happening in

(27:23):
the neutron star. The neutrons have to stay at higher
energy because they can't collapse all into the lowest energy state,
and that keeps the star hot, and that keeps pressure going.

Speaker 2 (27:32):
Okay, and so when a big star collapses, presumably there's
still fermions around. But what you said was that the
black hole is so immense that it just squishes them
down anyway and overcomes their desire to remain in happy
states and push back out.

Speaker 1 (27:48):
Yeah, exactly, because neutrons are fermions because they're combinations of quarks,
and so the rule still applies because you have fermions there.
But if you squeeze those quarks together, you can get
other states that are not fermions, and then it can
collapse them exactly. And the crucial thing to know for
our later discussion is that when this collapse happens, you
get a black hole. You get an enormous shockwave that

(28:09):
comes out right. This gravitational collapse produces an enormous shock wave,
and a black hole heats up everything around it. The
gravity the black hole is really intense. The accretion disc
the stuff around the black hole gets heated up by
the gravity of the black hole, and it radiates. This
is why black holes are so hot, because they heat
up everything around them, which then blows that stuff out.

(28:30):
So like, black holes is a limit to how fast
they can grow in the universe because they emit so
much radiation. They're pushing their food away from them. Yeah,
the more massive they get, the more they heat up
the stuff near them, which then blows the food away
from them. There's no theoretical limit to the size of
a black hole, but there's an effective limit to how
quickly they can grow because they push away their food.

Speaker 2 (28:51):
Baffling. This blows my mind. I can't understand that behavior.

Speaker 1 (28:54):
Yeah, and so these are normal stellar black holes, right,
These are black holes that form the end of the
life of a star. And so we call these small
black holes, even though they can be up to like
fifty or one hundred times the mass of the sun.
But there's another category of black holes that we need
to understand for today's episode, which are called super massive
black holes.

Speaker 2 (29:15):
It's a great song.

Speaker 1 (29:18):
And if I opened to Chicago Pizza doing, I would
call it super massive pizza because these are definitely like
a lot bigger. These are a few million to a
few billion times the mass of the sun. Wow, right,
like normal black holes, just one hundred times fifty times
the mass of the sun. This is millions or billions
of suns into a black hole. It's really incredible.

Speaker 2 (29:38):
So how do you go from an exploding star to
something that's so much more massive than the star was initially?

Speaker 1 (29:45):
Yeah, it's a good question, and people have been wondering
about this in particular for a long time, and they
asked exactly your question, and they did a bunch of simulations.
They thought, well, maybe you have early galaxies with early
stars and some of them formed black holes, and then
those black hole clump together and they just gather together
at the center, which makes sort of sense. And they
ran simulations, but those simulations do not describe what we

(30:08):
see like in those simulations, you do not get super
massive black holes. You get much smaller ones. But when
we look out into the universe, we can look really
far back in time at the formation of super massive
black holes and ask how long did it take in
the universe to form these black holes, And it didn't
take very long. We see super massive black holes at
the hearts of very very young galaxies much earlier than

(30:31):
we expect. So they're like super massive black holes that
are like thirteen billion years old, which is like about
a billion years after the universe began. You already have
black holes with like two billion solar masses. Nobody knows
how they got so big so fast.

Speaker 2 (30:49):
So is that the answer, Like, we just we don't
know full step.

Speaker 1 (30:54):
We don't know how super massive black holes have formed.
That is definitely a huge open question in astrophysics. There
are lots of crazy ideas out there. One of them
is the one I mentioned earlier, primordial black holes. People
thought maybe black holes formed in another special way, like
in the early universe there were already black holes formed
before even hydrogen, and so these guys were around to

(31:17):
see the formation of super massive black holes in the
universe perhaps, but nobody's ever seen a primordial black hole,
and we should have seen one if they existed, so
it's pretty hard to support that theory anymore. Although for
a while they were an exciting candidate for dark matter
because like, they're big, they're massive, they're dark. Maybe they
explain the missing matter, but again, we haven't seen them

(31:38):
and we should have. Another fun explanation for super massive
black holes came recently when people noticed that the rate
of super massive black hole formation, the rate of their growth,
seemed to link weirdly with the dark energy in the universe.
That like, the amount of dark energy in the universe
is increasing because the universe expands, and as it expands
makes more space than that space comes with more dark energy,

(32:00):
so the dark energy fraction is increasing as time goes on,
just like the super massive black hole mass is increasing.
They noticed a very tight correlation and they came up
with this theory, which went everywhere on social media when
it came out like last year or so, that maybe
super massive black holes are the source of dark energy.
That like, weirdly they're creating dark energy or they are

(32:21):
expanding the universe somehow. It's not a theory that's really
become mainstream. There's some questions and uncertainties about it. There's
a whole podcast episode about it. You should check it out.
But the point is that this is an open mystery.
How do you get black holes that are this big,
this massive in the early universe?

Speaker 2 (32:38):
So how we how do? Real quick? Maybe you can
just tell me? So how does it get bigger and
more massive while also creating more dark energy?

Speaker 1 (32:46):
Like?

Speaker 2 (32:47):
Where is the energy for that coming from? You know what?
I'll listen to the episode. You didn't do that episode
with me? Right, and I've forgotten the answer? That was
one with Orgey.

Speaker 1 (32:54):
Yeah, it's an episode I did with Jorgey quite a
while ago. It's a really fun idea, And there's two
things to understand that. One is that we do have
a theoretical model for black holes, like we can solve
the equations of general relativity for a black hole. But
there's a detail that's often left out when people say that,
which is that we only know how to solve these
equations for a black hole in an empty universe, Like

(33:16):
we can solve the equations for a super dense object
and nothing else. All right, but that's not our universe,
and more importantly, our universe is expanding, so we don't
know how to solve the equations for a black hole
in an expanding universe or a universe filled with stuff,
and so theoretically there is a question mark there, like
how do black holes form an expanding universe? What are

(33:38):
those rules? We don't really know because we don't understand
the solutions of general relativity. We basically only solved it
for a very few simple cases, like a black hole
in an empty universe or a universe filled with uniform dust.
We can't even solve it for like the Earth going
around the Sun. That's too hard.

Speaker 2 (33:54):
Wow, what is it? All models are wrong? But some
models are useful? Are they are?

Speaker 1 (33:59):
These?

Speaker 2 (33:59):
These are still models, right?

Speaker 1 (34:02):
Gr is still usable and we can do in americal
approximations a lot of times. But basically we don't understand
how black holes form in an expanding universe in theory.
And so these guys have an idea for what's inside
the black hole that inside the black hole is not
a singularity, but some weird vacuum energy that contributes to
the expansion of the universe, and like, hey, that's possible.

(34:25):
You know, it's a violation of general relativity, but we
know general relativity has to be wrong at some point,
and we don't understand how the expansion can be everywhere
if it's sourced from the black holes, So there's a
lot of open questions about that. You know, black holes
also are really big and massive, but there are a
tiny fraction of the mass of the universe, whereas dark
energy is like seventy percent of the energy in the universe,

(34:46):
So this doesn't really answer that. But the point is
that we still don't understand how super massive black holes form,
but they are out there in the universe. So there's
another really crazy and exciting theory that we'll talk about
after the break that might tell us what was inside
even bigger stars than we can imagine.

Speaker 2 (35:26):
All Right, we're back and it's time for the big payoff.
Could black holes be inside of a star? Daniel?

Speaker 1 (35:33):
So we talked about how stars form, and the crucial
things to remember there is that stars can't get too
big because they blow out their stuff, and if a
black hole forms, it blows stuff away from it also,
And then we talked about how we don't understand how
super massive black holes formed in the universe. So The
idea is bring these two things together and say, what
if there was a special kind of star in the

(35:54):
early universe that was so big, so massive that it
formed a black hole at its core, which ended up
being the seed for a super massive black hole, and
so big that it was protected against that shock wave
of blowing stuff out, so.

Speaker 2 (36:11):
It would just be a star until the black hole
took over.

Speaker 1 (36:14):
So let's walk through the life cycle of it, because
it's kind of crazy and kind of a fun theory.
So you start in the very early universe. Just like
we talked about before, everything is very dense, everything is
very hot, and you know, we have areas of over
density that are pulling stuff in. Something I should have
mentioned before, which I think is super cool, is that
it's not just over densities in the normal matter, not
just like, oh, here's a little bit more hydrogen. It's

(36:36):
actually over densities in the dark matter that are really important.
Because remember, dark matter is the dominant source of matter
in the universe. That's most of the matter. So if
you happen to have a clump of dark matter, then
the normal matter is going to get pulled towards that.
So dark matter actually controls where normal matter forms structure,
or you can think of it that way or the
other way, which is like normal matter tells us where

(36:59):
the dark matter is. It's like tracers. So if you
look at in the night sky and see a bunch
of stars, you know, oh, there's probably a big blob
of dark matter there. That's why stars formed there. Anyway,
that's super cool, But in the very early universe, we
didn't have metals to form these stars, right, So you
have either an over density of hydrogen or an overdensity
of dark matter. Pulls this stuff together. You get super massive,

(37:19):
short lived stars. And in the standard theory, remember that
if it gets too big, it gets too hot and
it blows that stuff away. But if the star is
big enough, like really enormous, not three hundred times the
mass of the sun, not a thousand times the mass
of the sun, We're talking millions of times of the
mass of the sun. If you happen to get a
blob of stuff together from a dark matter over density

(37:42):
and then try to collapse that gravitationally, the idea is
maybe something special happens at the core of the star,
and the star's mass protects it against the radiation. That's
coming out because gravity is just so overwhelming.

Speaker 2 (37:54):
And it becomes black hole.

Speaker 1 (37:56):
Yes, And so what happens is you have this huge
blob of stuff. We're talking about like a million times
the radius of the Sun, right, so like blow your
mind trying to hold this thing in your head. The
core gets hotter and gets denser, just like we talked
about before. But now there's enough gravitational pressure to turn
the core into a black hole. So you have this
enormous star and at the heart is this tiny but

(38:18):
very very dense black hole, like a few tens of
a kilometers across. How cute, How cute, but terrifying that's right. Now. Normally,
when you form a black hole or you have this
gravitational collapse of the core, you would get a shockwave
that would like tear the star apart, right, That's what
supernovas are in general. But this one is so massive
that the shockwave just like it just gets absorbed, right,

(38:41):
It doesn't get all the way to the outside. The
outside layers are squeezing back in. It's like you know,
a violent crowd or an English football game or something,
you know, squeezing back in. And so something else happens.
The outer layers of the star that are squeezing the
gas are forcing it into the black hole. Usually black
holes can grow only slowly because they're pushing their food away. Right, Well,

(39:03):
what if there's like a huge blob of gas on
the outside forcing it back. So now it's being force
fed gas even though the radiation pressure is pushing it away.
So now your black hole is growing pretty quickly as
it's like being force fed gas at the heart of
this star. So, yes, it is a star and there's
a black hole at its core, and the thing that
keeps it from blowing apart is its sheer mass. It's

(39:26):
too big to collapse.

Speaker 2 (39:28):
Holy cow, I'm impressed. Okay, so it seems to me
that this process should pretty quickly result in the star
becoming a giant black hole. Is that the point you
can get black holes forming in the center of stars
before they're at their end of their life, and it
hastens the end of the life of the star.

Speaker 1 (39:46):
Yeah, so eventually this thing will collapse. It can't last forever.
It's got a pretty good run though for the few
moments in the universe's history that it glows like it's
super duper bright. You know, we talked about fusion happening
more rapidly at high temperatures and pressures. So this one
single massive star with the black hole core would have
been about as bright as the entire galaxy. Wow, so

(40:07):
like really incredible. Essentially as bright as a supernova. A
supernova is also as bright as a galaxy. And so
the black hole is growing, the star is expanding, right,
Eventually the whole thing becomes thirty times the width of
our solar system.

Speaker 4 (40:20):
Wow.

Speaker 1 (40:21):
So we were talking beetle juice is like orbit and jube,
but wow, that's big. Yeah, this thing is monster as
compared to that, right, and then you get magnetic fields
which create radiation and quasar. It's just like we talk about.
But eventually the black hole grows so much that it
will tear the star apart because their radiation pressure from
the black hole is pushing out and that will eventually

(40:41):
take over because there's only so much star to eat.
And the thing that was keeping this stable was the
outer layers of the star. The more you eat the star,
the less protection you have. It's like you're eating your
own spaceship. Right, So it only lasts like ten million
years or so in the early universe. But what's left
over is a very massive black hole, much more massive

(41:02):
than you would expect from the death of a normal star.
And if you have a very massive black hole around
and other stars are forming nearby, you could imagine that
they would start orbiting that really massive black hole and
it could end up being the center of a galaxy.

Speaker 2 (41:16):
Okay, so we've seen super massive black holes. Yeah, but
we have not seen this in the process of happening
because this would have happened so long ago. Exactly could
we still see this happening super far away, or this
happened so long ago that that light would have already
passed us or something.

Speaker 1 (41:34):
Great question, we're going to.

Speaker 2 (41:35):
Take away my pod in physics.

Speaker 1 (41:36):
No, PD and physics come from asking sincere and curious
questions about the universe, not about being right. Okay, so
I never want to discourage somebody from thinking. And that's physics, right.
What you're doing right there is physics. You're like, this
is what I understand, this is what you're telling me.
How do I fit it together into a model in
my head? That's the essential step of doing science. And
so yeah, absolutely, you earn your PhD twice over ya.

(41:58):
The answer is if it happen in the early universe,
we should be able to see it because we could
just look further and further away. Because if it happened
a long time ago, we just need to look at
light that's been traveling since then, which means it's been
a really long distance and we can see pretty far back.
We can't see all the way back to that far
in the universe. The James Web space telescope can see

(42:19):
like formation of young galaxies, and that's helping us understand
the super massive black hole question. But we can't with
the James Web see that far back yet. But in
principle we could be able to write these things would
have been very bright even though they're super far away.
We might be able to make them out. The other
comment is like with the light from them have passed us,
that's true for some of them. Like if there was

(42:41):
one of these things at the heart of our galaxy
and it admitted a bunch of light, its light would
not be too far away for us to see. But
the universe just goes on and on and on, and
so there's always some more universe to send us light
that's just arriving now. So that's why we can see
the whole history of the universe from here if we
look further and further.

Speaker 2 (42:58):
Away of today is fund more telescopes.

Speaker 1 (43:02):
Yes, exactly, it's fun more telescopes because there are deep
mysteries here about how stars form and how matter works.
And you know, this is a fun theory because it
makes you think about huge stars and stars with exotic
cores in them and maybe something else is happening at
the hearts of stars or whatever, and because it solves
a mystery, but probably the answer is something else, something

(43:23):
even weirder than we have imagined. And so you know,
it's a useful exercise in physics to be like, what
about this? What about that? Could this even work? Very valuable,
but it's also just a useful exercise to go out
and look, you know, to ask the universe tell us,
show us what's going on out there. And then we
got to piece that together into our puzzle how the
universe works and maybe have one of those moments of

(43:45):
insight where we're like, oh, I get it, and it
clicks into place and you're like, yeah, Universe, you make
sense to me.

Speaker 2 (43:51):
Oh. It's so nice to have those moments with your partner.
It's nice to have those moments with your universe as well.

Speaker 1 (43:57):
Do you have a similar relationship with the universe as
you do with Zach.

Speaker 2 (44:00):
Both of them surprise me from time to time. You know,
life should keep you on your toes.

Speaker 1 (44:07):
I hope you keep building a husband telescope so you
can keep observing new surprises in your relationships.

Speaker 2 (44:13):
Well, my training was an animal behavior, so I'm always
collecting data. I mess with him every once in a while.
I'll do things like see how close I have to
put the laundry bin to, like where he always throws
the clothes on the floor before they'll actually end up
in the bin? Like will he throw it if it's
just an inch out of where he usually throw it? Anyway,
I digress.

Speaker 1 (44:32):
Do you need an IRB to do experiments on your husband?

Speaker 2 (44:34):
Like, well, you know, I'm not really in academia right now,
and so don't tell Rice.

Speaker 1 (44:39):
Okay, So was I gonna ask we were talking about
the black hole of Zack's laundry.

Speaker 2 (44:46):
Oh God, that's actually a different topic. But okay, so.

Speaker 1 (44:51):
We're supposed to keep this family friendly, all.

Speaker 2 (44:53):
Right, all right, I'm back on track. I'm back on track. Okay,
so you hear this theory that you've just presented to us.
Do all the steps in this theory sound good to you?
Does this sound plausible? You said that it's probably something
else just because the universe is hard to figure out.
But is there any step in this process that makes
you feel like, I don't know, maybe not.

Speaker 1 (45:12):
There's nothing about this that's obviously wrong, there's no red flags,
but there is a lot of speculation here, you know,
there's like, well, maybe this can survive that, and maybe
this happens and it gets force fed. But it's complicated,
Like what you would really need to do is to
model this, yeah, and not just be like more my
intuition says it's probably correct. You need to see what
it actually happened and put this thing into a computer.

(45:34):
But that's hard. You know, we have trouble modeling individual
stars turning into black holes and going supernova because you
need to keep track of so many particles and they're
very sensitive to the details we don't really understand, like
why does this star go supernova and that one doesn't.
It's not just a function of the mass, like it
requires some special circumstance to happen or to not happen,

(45:54):
and so there's probably just a lot of that, a
lot of details that need to be filled in, and
it's a lot of work. We should not only build
new telescopes, we should hire more scientists and give them
lots of computers.

Speaker 2 (46:05):
Yes, amen, because you got to start somewhere, and ideas
like this help you identify the assumptions that you need
to be testing in order to move forward. So yeah,
very cool idea.

Speaker 1 (46:13):
And if you discover, oh, this doesn't work, it's going
to give you another idea. And that's how we make progress. Yep. Right,
start out with terrible ideas that inspire less terrible ideas. Yeah,
dot dot dot science.

Speaker 2 (46:23):
Yeah, I think the answer to my PhD work was no,
Kelly was wrong. But here's some other interesting stuff you
could ask exactly.

Speaker 1 (46:31):
It's always fun follow up questions, that's right. And on
that note, if you have follow up questions from today's
episode or anything else you've heard about in physics, please
write to us. We would love to answer your questions physics, biology,
maybe even chemistry once in a while.

Speaker 2 (46:47):
Pizza related questions.

Speaker 1 (46:48):
Definitely, absolutely pizza related, especially the physics of pizza. No,
I guess pizza's mostly chemistry, isn't it anyway? Write to
us Questions at danieland Kelly dot org. We love hearing
from you, really do, and we really will write you back.

Speaker 2 (47:02):
Enjoy your pizza. Daniel and Kelly's Extraordinary Universe is produced
by iHeartRadio. We would love to hear from you.

Speaker 1 (47:17):
We really would. We want to know what questions you
have about this Extraordinary Universe.

Speaker 2 (47:22):
We want to know your thoughts on recent shows, suggestions
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Speaker 1 (47:29):
We really mean it. We answer every message. Email us
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Speaker 2 (47:35):
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