What are primordial black holes?

Could mysterious black holes have been formed in the first second of the Universe?

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Episode Transcript

Speaker 1 (00:08):
Hey, Daniel, you believe in the power of words, right,
I hope words have power. I mean this podcast is
literally just words. It's our superpower. Yeah. But also, don't
you think individual words have a certain energy to them?
You know? I think some words are just like inherently funny,
you know, words like booger or weasel or podcast. Yeah,
those are goofy words. But some words have drama to them,

(00:31):
you know, like dragon or chaos. And the combination there
makes me think of things like dragon boogers or chaos
weasels a soul. I was thinking more like dragon weasels.
That's a scary word. I don't know if that's scary
or silly. But what about some science words? You think
some science words have power to them? I don't know.
I feel like this is a trap. You're always making
fun of our science names, you know, charm, cork, big bang,

(00:54):
those are charming words, indeed, But I mean, can you
blame me? Do you guys ever come up with dramatic
names wol names? I got something up my sleeve. We've
got something out of the dawn of time. All right,
this better be good? Oh? Yes, it is positively primordial.

(01:24):
I am Morehammad cartoonists and the creator of PhD Comics. Hi,
I'm Daniel. I'm a particle physicist, and I believe in
the power of words to entertain and educate. Welcome to
our podcast, Dragon Boogers, brought to you by two podcasting
Chaos Weasels. I'm just kidding. Welcome to our podcast Daniel
and Jorge Explain the Universe, a production of I Heart

(01:47):
Radio in which we use words to take you on
a mental tour of the universe. We take you all
the way back to the beginning of time, we take
you to the edge of time. We take you down
to the tiny particles and out to the largest things
in the universe, and we share with you our wonder,
our joy, our curiosity for how everything works and what
science is doing to try to figure it out today. Yeah,

(02:10):
it goes straight from our brains and our hearts through
the Internet into your ears, and straight into your brains
and hopefully your hearts as well. That's right through that
weird system of tubes that is the Internet. We should
we should talk about that one day, Daniel Jorge explained
the tubes. But there are a lot of amazing things
out there in the universe. To see and to discover
and to learn about. And some of those things have

(02:31):
been around for a very long time. I mean, the
universe is it's pretty old or maybe pretty young, depending
on how you look at it, that's right, And there
are a lot of amazing things out there to understand. Stars,
exploding stars, collapsing, black holes forming. Some of these things
that you're already amazed by might have a very different
history from the one that your anticipated, Yeah, because I
think sometimes knowing the history or something gives you a

(02:53):
better perspective about it, you know, like if you know
where it came from or or what it was like before,
it kind of tells a lot about something. Yeah. Well,
that's basically the whole game of astrophysics, right. We are
looking at the universe, which is nothing but a series
of clues as to how the universe was made, and
from that set of clues, we try to unravel the
mystery of what came first and what came second, and

(03:14):
what does that mean about what's coming next? Right, So
the history of like how things were put together is
really central to all of science and all certainly all
of astrophysics, and I think one of the things that
fascinated most people about the universe is this idea of
black holes. I mean, black holes are just kind of amazing,
aren't Then there's so it's so weird and so kind

(03:34):
of a mysterious I know, and in so many ways.
You know, you have the fact that they first started
as a theoretical idea, like just a solution to equations
and pencil and paper. The idea that just this concept
is scratching of graphite on paper could predict crazy things
happening out there in the universe. That's mind blowing. And
then you know the drama in which they are formed,

(03:56):
the end of the life of a star, this cataclysmic laps,
the supernova, the precede to them. I mean, you couldn't
write anything better than that if you were fiction right now. Yeah,
there's there was drama in how they were discovered and
how they were thought of. I mean, Einstein came up
with these right in his equations and it literally just
came out in like math first. Yeah, it just came
out of the math. You know, you look at the universe,

(04:18):
you try to understand how it works. You write down
some equations that describe what you see, and then you
explore the weird edges of those equations, you say, well,
what else could these equations predict what happens in these
other weird scenarios? And then you go out and if
you believe those equations are real, that they're describing something
real about the universe, you go out and check those
predictions and see, well, is this just a weird, you know,

(04:41):
figure of math, or is this something that actually happens?
And so it's incredible when you've achieved that, when you
really described the universe, You've pulled back a layer of
reality and said, here are the fundamental underlying mechanisms, and
I can prove it by showing that I can predict
what they do. Do you think Einstein called them black holes?
Bread away or what do we call him when he
saw him on the on the math page. You know,

(05:03):
he saw these sort of singularities and they he predicted
that light cann't come out of them. Did he have
a name for them? Where you're right that the modern
idea of black holes certainly came out of Einstein's equations,
but the concept of a black hole actually predates Einstein.
The idea that you could have an object that had
so much gravity that light could not leave it. The
concept of that predated Einstein, so that the phrase black

(05:25):
hole was already sort of existing. Interesting, all right, And
we've also now have seen black holes, right, we have
pictures of a black hole, that's right. We've known for
a while that there are black holes at the centers
of galaxies, and we've seen that because we look at
the way the things swirl around and the gas and
the dust that emit from those galaxies. So you can't

(05:46):
see the black hole directly, but you can see the
sort of swirling chaos around it, you know, the chaos
weasel if you will, of the universe. And we've also
seen smaller black holes, black holes that are formed when
stars collapse, and we can see those sometimes vie lensing
when they pass in front of other stars. So black
holes are amazing and interesting and mysterious, and there are

(06:09):
a lot there's a lot about them when we that
we don't know that we don't know what's inside of them.
We don't know how big they can get, and how
the ones in the center of galaxies come together. We
also sort of don't know how old they are, right,
It's hard to tell because they keep so well, that's right,
they fit, they are pretty stable, they last a very
very long time, and you're right that we don't know

(06:32):
so much about when they were made. I mean, one
mode of making black holes is you have a star
and it collapses and then you have a black hole
about the mass of a star or several stars, etcetera.
Another is these black holes the very center of galaxies
that are millions of suns. But there's the possibility that
black holes might even be older than that. They could

(06:52):
even be older than the first stars. Really, oh man,
I thought black holes only four and from stars. But
you're saying it could be older than the ideal starts.
That's right. It could be that there were black holes
formed before there were even particles. Black holes formed in
the very first few moments of the universe predate matter,
pre date matter, yes exactly. And so what what what

(07:15):
what how could it have anything inside matter didn't exist?
I know, we'll dig into it. But these things go
by the awesome name of primordial black holes. That is
a cool name, all right. So then that's the question
for the episode today. Today on the podcast, we'll be
tackling the question what are primordial black holes? That it's

(07:41):
kind of a hard word to say, but it sounds
cool when you say it. Primordial, I know, primordial. It
sounds like primeval or something. You know, it sounds like
something is crawling out of a swamp somewhere. Yeah, it
feels like raw and like unformed and like, oh, my goodness,
predates things. Yeah, it's like from the age of giants. Know,
It's like if Thor had a black hole, it would

(08:02):
be a primordial one where the wild things come from.
Kind of exactly. I don't think it's a children's book
primordial black holes, but it's a really cool word. And
it also it touches on that mystery, right we right,
we don't know what happened in the first few moments
of the universe. We don't know how things worked, and
so it would be amazing if there were things left
over from those very first few moments. That would be fascinating.

(08:25):
So it's kind of a cool concept, and it's it's
kind of also kind of a recent concept. I feel like,
you know, like Iceland wasn't talking about primordial black holes, right, No,
definitely not. This is definitely a more recent concept. So
as usually, we were wondering how many people out there
had heard of these primorial black holes and or had
an idea of what they were. So Daniel went out
there into the wilds of the Internet to ask people

(08:47):
what are primorial black holes? That's right, I went out
into the primordial Internet, which consists of emailing our listeners
and asking them to volunteer to answer spontaneous questions. So
thank you to our listeners who participated. If you would
like to answer spontaneous questions and here your uninformed speculation
on the podcast, please write to questions at Daniel and

(09:09):
Jorge dot com. Before you hear these answers, think about
it for a second. Have you heard of primordial black holes?
Or would you know what to answer if asked this question.
Here's what people had to say. I've got nothing on that.
I would guess that it's from really early in time,
really large black holes. I would guess that it's probably
the ones that are at the center of the galaxies,

(09:30):
but I'm not sure. Well, like in are the oldest
black hole or the first one that was pretty yeah,
maybe one of the biggest black holes in the universe,
or yeah, the first ones. Primorial black holes are black
holes that were created by the original plasma of the

(09:55):
early universe, before expansion began to occur. As the matter
can collapsed and condensed, it became black holes that have
persisted since the dawn of time. Basically, I think the
black hole at the center of our galaxy is a
primordial black hole. Black holes in the center of galaxy

(10:18):
the biggest ones. A primordial black hole is a gravitational
well created at or just after the initiation of expansion.
My understanding is that they consist of mass magnitudes of
order larger than supermassive black holes. Perhaps gravitational waves from
these primordial black holes leaked through the multiverse and are
perceived by us as dark matter primordial black holes. This

(10:40):
is really kind of difficult, like, is it the original
black hole? Is it what started the big Thing? I
have no idea about that. Excited to find out, though
primordial black holes are black holes have formed way back
at the start of the universe, just after the Big Bang,
once inflation had happened and everything else severer pockets of

(11:00):
densities left that caused these black holes too to be created,
nigrew the hawk and radiation. It's unlikely that any of
them still exists. However, they could have caused the start
of all the other black holes within the universe. I
think black holes that were made during the Big Big Bang.
Maybe there they are still older. My guess is that

(11:24):
it's a cooler black hole that's like more special than
your average ones, so it got its own name. So
I think promoting your black holes are black holes have
formed shortly after the Big Bang, so that they're really
old black holes. But I don't know much more than that.
All right, these are pretty good answers. It seems like

(11:45):
the word definitely evokes feelings and people, you know, there
are like a lot of people say it's before the
dawn of time or before the beginning of time. Yeah,
the ooze that we walked out of. That was a
great answer, And I think that means that this is
well named, right, wouldn't you give this high mark? It's
like if people could guess what it means. Well, I
don't know what they are yet, Daniel, so anything that
the judgment is still out, maybe this is a better

(12:08):
word for him. I'm feeling a little bit of hesitancy
to say anything positive about physics naming, but I'm gonna
come back to this at the end of the episode.
I see this is the one you would submit to
the naming words. This one's high on my list. Yeah
you know, I see, we came up with one good name.
We're not looking for awards, We're just looking for, you know,
to no longer be criticized getting a lot of flak here.

(12:30):
He's looking for approval physicity. Want to prove all right,
well let's get let's jumb right into it, Daniel. What
is the primordial black hole and how is it different
than brand new black hole? Yeah, so brand new black
holes sort of garden variety black holes that you're familiar with,
are the ones formed when stars collapse. You have a
big blob of normal matter, you know, quirks and electrons

(12:54):
and all sorts of stuff gas and dust, and after
it's done fusing, gravity pulls it together. You get this
dense spot in space where light cannot escape. So that's
your your normal black hole. And the critical thing to
making a black hole again is having a very dense
blob of matter, so much matter that it's bent space.

(13:14):
It's bent space in this way that like the inside
of the black hole is cut off from the rest
of the universe. It's stretched space in such a way
that every path in the black hole goes deeper inside
none of them come out, And so you can visualize
it as light cannot even escape because the force of
gravity is too strong. But the more modern way to

(13:35):
think about black holes and gravity is about bending of space.
So these things create these weird structures in space that
there's no path out of even if you're traveling at
the speed of right, it's sort of bend space so
much that they kind of form a hole, almost like
a hole in space. Yeah, they sort of form a
hole in space. You can think of it like the
universe has become separated, and there's now this little piece

(13:57):
of the universe that there's only a one way door
into and once you go in there, you can't come
out to the rest of the universe. It's just impossible, right,
And like, like you said, it takes a lot to
form a black hole. I mean they're so extreme then
you know you can't just like it's hard to pack
that much mass into such a small space that you know,
you need something like a supernova or a star collapsing

(14:18):
for that to happen. Yeah, the key thing really is density.
You can make small black holes, but you need some
very strong force to squeeze the mass into a very
small space. The smaller the mass, the smaller the space,
and the denser it has to be. And black holes
can vary from fairly small masses to enormous masses like

(14:38):
millions and millions times the mass of the Sun. Yeah,
those are super duper black holes. Yeah, I think that's
the official extra califragilistic black holes. Yea, with the spoonful
of sugar. And this is the kind of thing we've
seen in the universe. We predicted it. We understand the
stellar mechanics, we understand the force of gravity, we understand
what goes into it. Our numerical similiar makes sense. We've

(15:01):
observed them. Everything sort of fits together, right, we can
you can see them like floating around in the center
of the galaxy. These are like well known. These are
well known, the well established. Nobody doubts that these black
holes exist. And we've counted them, and they exist at
roughly the rate you would expect. And you know, it's
a it's an awesome field of study, but one that
doesn't have that many surprises in it. But those are

(15:23):
stellar black holes. Those are black holes formed from matter
that was created after the Big Bang. Right, there's this
whole other category of black holes, these primordial black holes
that could have been made in the very first few
moments of the universe, right, because thanks were pretty crazy
at the beginning of the universe. Right, it was like
a loud and wild birth for the universe. That's right.

(15:46):
It was hot and nasty and wet, and you know,
you might think, well, what do you need for making
a black hole? You need a dense blob of matter.
And you know, early in the universe there was a
lot of matter and it was very dense, and so
you might expect there to be black holes made in
the early universe. It's not that surprising to think that
there will be blobs of matter capable of forming black holes. Right.

(16:08):
And in fact, this was a listener question we got
a while ago about as somebody asked, why doing the
universe just collapse into a black hole at the beginning
of time? How are we here? Amazing question? It's like,
we're here, how come? Right? Because things were so dense
at the beginning of time, why didn't it just all
collapse into a black hole? That's right. It's a great
question because things were really dense and One of the

(16:30):
ways we answer that question is that black holes and
need to be localized. You can't have the entire universe
collapse into a black hole if everything is perfectly smooth.
To form black holes, you need hot spots of density.
You need to black hole to form somewhere to pick
where the black hole forms, You need some spot to
be denser than another spot. If everything is equally homogeneous,

(16:51):
then the force of gravity just cancels out. It's almost
like if you're in a hole. You can't have holes.
You can't have a hole in a hole. It kind
of is that kind of kind of the idea, like
either everything's a hole or you only have little holes.
You can't have everything to be a whole because you
need extra gravity in one spot. And if everything is smooth,
then all the gravity cancels out. I mean, imagine a
perfectly smooth universe, even if it's filled with infinite matter.

(17:14):
There's no gravitational force on you because in every direction
the gravitational force is balanced by matter in the other direction.
So to create a black hole, you need a very
strong force of gravity, and that can only be created
by additional density, by extra density by hot spots. If
it's totally smooth. It doesn't matter how dense it is.
You can't form black holes, right, And so the idea

(17:35):
is that during the Big Bang, the whole thing can
turn into a black hole. But maybe there are things
were so intense that there that there maybe there were
hot spots during the Big Bang, the beginning of the
Big Bang, and maybe black holes did form, and that
in those early moments. Absolutely, and there had to have
been hot spots. If there weren't hot spots early on
in the universe, we wouldn't be here either, because the

(17:56):
universe is no longer perfectly smooth, right. A perfect smooth
universe stays perfectly smooth wherever there's no way to disrupt it.
So there had to have been hot spots, and those
hot spots seeded the formation of the universe and the
structure of the universe as we see it. The reason
we have matter here in not a billion light years
to the left is because of some hot spot in

(18:18):
the early universe which very slowly gathered together matter and
formed all this structure or billions of unions. But those
same fluctuations, which came from quantum randomness at the tiny scale,
could also have generated black holes. Right, that's exactly what
you need for a black holes, like an extra little
spot of density. And so it's natural the things that
you could have also gotten black holes formed in those

(18:40):
early moments when you have those hot spots of density
and and we're talking like the first few like you know,
bazillions of a second after the Big Bang. Yeah, exactly,
this is before you had a chance to even make matter. Right,
It's not like a question of is the matter made
out of corks or electrons? There's just hot stuff, right,
There is no matter at all. There's just like energy,

(19:01):
crazy energy density. We don't even really know what was there.
But yeah, this is very very early on in the
beginning of the universe, before even matter, what was cool,
before matter even existed. And so then you can ask
the fun question like, well of a black hole formed
before or matter, like what's in it? Right? What's it
made out of? What kind of stuff is there? Right?

(19:23):
How can it have anything inside of it? Well, we
don't know what it's made out of. It's made out
of whatever was in the early universe, which is unfortunately
still a huge mystery, like what was creating the inflation
of the universe. This grand expansion that stretched out these
tiny quantum mechanical fluctuations into larger fluctuations that gravity could
begin to see. We don't know, and so we don't

(19:47):
know if these black holes were made and what masses
they were made at, and what's in them. But it's
a huge mystery. You know, we don't even know what's
inside current black holes. Like if you take a star
and you squish all this stuff together to make a
black hole, are their corks in there still? Are they
turned into something else? Weird? Like what's going on inside there?

(20:07):
It's one of the deepest mysteries of the universe. So
if you take a spoonful of like weird early universe
stuff and make a black hole versus a spoonful of like,
you know, normal, boring, five billion year old star stuff,
do you get a different kind of black holes? Not
a question we know the answer to. All right, let's
get into these primordial black holes. How big they are,

(20:27):
what do they look like? And um, what do they
smell like? That's what I'm curious about. First, Let's take
a quick break, all right, Dannel, we're talking about primorial
black holes, and it sounds like the primorial suit kind

(20:48):
of well, I don't know what black holes smell like,
but these primordial ones are they're probably pretty swampy, you know,
in the suit. But you know, that reminds me if
you heard of the black hole no hair theorem, what
black holes essentially can't have hair, and so if this
thing is primoritial and swampy, it's also shaved clean. I'm

(21:08):
not making that up. Is a reference to dinosaurs, I'm
not making that up. There's a theory that says the
only thing that you can know about black holes is
their mass, whether they're spinning and they're total electric charge.
That's like the only properties they can have. You can
know nothing else about what's going on inside of it,
what matter is made to use it, whether it shaves
daily or you know, lets it self go hairy. And

(21:30):
I think that's why they call it the no hair theorem. Oh,
I see, It's like we we only know the bare
minimum and things like hair, we can't know those details
that that's right, we know the bare minimum, and that's
all the information that exists. You know. One question is
like is there information inside the black hole about what
was made? Or is that all the information that exists?
And somehow the black holes who just like remove that

(21:50):
information from the universe. But that's a topic of another party.
And they're just born bald who knows, right, But all right,
so they're at the very beginning of the universe, in
the very early micro Brazilian seconds of the Big Bang,
there could have been black holes. And so this is
this is making me ask so many questions, like, you know,
how were they form, what were they made out of?

(22:12):
How can you have a Can you have a black
hole without any matter being around? Do they just have
pure energy inside of them? Yeah? Because you know, gravity
is linked to energy density. We think of gravity is
connected to mass, but really it's connected to energy density,
and mass is just one example of how you can
store energy. So you can make a black hole just
out of super intense radiation, right, as long as you

(22:35):
have enough energy density. It's energy density that bends space,
that creates what we call gravity. And so it doesn't
matter what kind of mass or energy it is, it's
just energy density, and it has it has to be
more dense than the things around it, right, Yes, exactly,
can just be like um, like having enough energy, it's
like yet to have more energy than what's around you.
So that you can bend space enough to make these pockets. Yeah, exactly,

(22:57):
because if there's also energy around you de bens based
the opposite way, then you don't get the curvature you need.
And one thing that's really amazing about primordial black holes
is that because they don't have to come from stars,
you can make them in other ways, which means you
can make them in a whole variety of different sizes
and flavors. Probably, no, there's the no flavor theor it's equivalent.

(23:22):
There's an equivalency there, all right, that's right, they only
come in dark chocolate budge. No. Because you don't have
to start from the star, you can make black holes
that are very very small, like mermordial black holes might
be as small as like one billion of Oh wow, alright,
so the big Bang is banging and there's fluctuations in

(23:42):
the energy there, but it's so intense that suddenly you
you can floor you can pop these black holes into existence.
And you're saying that they could be really small or
they can also be really big. Yeah, it just depends
on the mechanism that gives you the energy density. And
that's something that's just like wild speculation about one theory
had some idea for how the energy density profile looked,

(24:03):
and that gives you a bunch of small black holes.
Another one thinks the energy density profile look different and
that gives you a bunch of big black holes. Another one.
Most of them actually think that you get a whole distribution,
that if you make small black holes, you should also
make big black holes and intermediate black holes down from
like one billionth of a kilogram up to like thousands
of times the mass of our sun. All right, so

(24:24):
these primordial black holes there, they sort of make sense,
right because there was a big bang and why not.
But we can't just sort of go with there was
a big bang and whynot? That sounds like you could
used to explain anything. Hey, how came you ate all
the cookies? Hey well there was a big bang and
dot dot dot the cookie I mean, it just seems

(24:46):
so crazy. What was happening then? And you know, why
why not form black holes? So we can't just kind
of go by what what may do? A cartoon is?
Or hey, cham why did you climb out Everest? Well?
You know the big bang dot dot dot? Why? All right?
I need a T shirt that says that anyway, do
you want to hold that podcast? You know, a big Bang?

(25:08):
Why not? Sure? If it's about the Big Bang? Were
still in the Big Bang? The Biggest still banging? Well, well,
what do we think they exist? I guess that is
there is there more than just kind of the speculation
about what could have been happening back there. Yeah, I mean,
it's it's a fun idea. It makes sense that they
would exist. But if they do exist, they also might

(25:28):
solve a bunch of other problems. And this is a
cool way to discover something is to see, you, like
I have an idea for what might be out there,
and then think about what else it might explain. And
if you can sort of wrap up a bunch of
other things that we didn't quite understand then and tell
a nice story that all clicked together, then that's the
best kind of discovery. Oh, I see. We we have

(25:48):
these other mysteries in the universe, and so now if
we can link them to something like primorial black holes,
and it would all make sense. They would all make sense.
And one of the biggest mysteries out there the mystery
of dark matter. Right, we know that most of the
universe is not made out of the stuff that I
made out of you're made out of Most of the
stuff is not made out of quarks and electrons. If

(26:11):
you take the budget of the universe, the energy budget
of the universe, only about thirty percent of it is
actually matter, most of its dark energy, which is pulling
the universe apart. But of that slice that's matter, right,
about eight percent of that slice of the whole universe
is dark matter, this mysterious form of matter that's holding

(26:32):
galaxies together and changing the shape of the universe. But
we don't know what it is, right, It's totally different
than our kind of matter. That's right. Our matter is
made out of atoms, which are made out of quarks
and electrons. So we call that baryonic matter because it's
made out of these particles that are familiar to us.
And what we know is that dark matter is not
made out of baryonic matter. It's not made out of

(26:53):
quarks in some weird configuration that just makes it invisible
and transparent, and so we think maybe it's related to
prem audeal black holes. So one candidate for dark matter
is primordial black holes, because what dark matter needs to
be dark, and black holes are dark. Dark matter needs
to be pretty stable because it's stuck around the whole

(27:13):
lifetime of the universe. And black holes are pretty stable, right.
They last for a very very long time, if not forever,
and they're hard to spot, and so they're a good
candidate for dark matter all this time, dark matter could
just be black holes. It could just be black holes. Yeah,
I thought we like ruled that out. Well, people have
looked for it, you know, we'll talk about that. But
it's a pretty compelling possibility. It was never the number

(27:36):
one possibility. People were looking for a weird kind of
particle that we call a WHIMP, the weekly interacting massive particle.
But you know, that particle sort of had it to
day and that's come and gone. We thought it was
probably a WHIMP, and we looked for it, we didn't
see it. And now we're like hunting around in the
attic for other ideas of dark matter that might also
explain it that we didn't look at so carefully the

(27:57):
first time around. And now that the wind ideas sort
of lost, it shine a little bit more like digging
through the attic to find these other ideas and buff
the al Right, So maybe like dark matter is just
a bunch of black holes floating around in space, that's right,
And they would have to be primordial black holes, not
stellar black hole, because we know they've been around for
a long time. Yeah, because we know they've been around

(28:18):
for a long time. And also we know a lot
about how many quarks there were in the very early universe. Right,
We know that dark matter is not made out of
quarks because we know a lot about how many quarks
there were, because we do these really careful calculations, and
we see that if you had more quarks or less quirks,
you get a different mixture of stuff in the universe,
like more helium or more lithium or more hydrogen. And

(28:41):
that's the kind of thing we can measure really really well.
And then we can backpropagate and we say, all right,
given that we know how much helium and lithium and
nitrogen and neon there is in the universe, that means
there was a certain density of quarks in the early universe.
So for dark matter to have been around then, it
can't have been made out of quarks. It had to
be like taken out of the equation before quarks, right,

(29:03):
And that's why I would have to be primordial black holes,
So sort of like scoop all that energy in that
matter out of the pie before you got around to
make it, put it into these primordial black holes, and
then wait until humans are confused about the whole thing.
Interesting exactly, And so nobody's seen these things, right, primordial

(29:25):
black holes still theoretical, nobody has seen them. We'll talk
in a minute about how you could look for them.
All right, so then what what else do they do
they explain? Possibly, well, the other thing they might explain
are these incredible black holes at the center of galaxies,
you know, the milky Way. It's very core is really
hot and dense in the stellar environment there is choked
with gas and dust and activity. But at the very

(29:47):
very core is a huge black hole. And that black
hole is called Sagittarius A, and it has you know,
the mass of millions of suns. It's enormous. It's like
an incredible object. And they're a big mystery because they're
so big. There's sort of like no way for them
to have come from stars almost right, Like it's like

(30:08):
to cramp together a billion stars that turn into black
holes is kind of hard, and it's a lot harder
than you might imagine you might think, well, doesn't the
big black hole get really powerful and just suck stuff in?
Isn't it sort of like a runaway process. Remember that
we are not falling into the center of the galaxy
for the same reason that the Earth is not plunging
into the Sun and the Moon is not crashing under

(30:29):
the Earth, and that's rotation, and you have angular momentum
which keeps you from falling in. Even a really strong
force of gravity cannot overcome angular momentum and suck stuff in.
So a really strong black hole, it's not that easy
for it to actually grow. It's mostly pull stuff in
into a decreation disk to spin around it really fast,

(30:49):
but to actually grow it doesn't happen very quickly. So
they do these studies where they say, can I make
a milky way with this black hole in it? Let
me see it with a couple of little black holes
and let it grow. And when they do those calculations,
they don't get a big enough black hole like the
black hole we get in our simulations are much smaller
than the black holes we see in real life. So

(31:10):
is the idea then that maybe that black hole center
of our galaxy was there at the beginning, like maybe
it was there before even matter formed around it. Maybe
it was one of these huge primorial black holes, and
that's how it started. It started off big, exactly. You
gotta seat it with a big black hole, like maybe
galaxies were formed around huge primordial black holes, which then

(31:32):
gathered together dark matter and all sorts of normal matter
around it, seating that sort of structure. And if you
start from the big enough black hole, then it's much
easier to get to the kind of big supermassive black
holes that we see at the centers of galaxies. And
the other critical thing to understand is that these supermassive
black holes are not new. It's not like they've just formed.

(31:55):
We see them because they're very easy to spot because
they create intense radiation the form of quasars that we've
talked about, some of the brightest things in the universe.
We can see them from very far away, which means
we see very far back in time, so we know
that they were super massive black holes making quasars in
the early universe. So not only are they huge, but

(32:16):
they've been around a long time. So you know, that's
sort of smells like there's something else going on out
there in terms of making black holes. That's a wild
idea because that would mean that galaxies almost formed because
of primordial black holes. You know, like like galaxies form
where they were because that's where the primordial black holes were,
you know, like they were the pioneers for galaxy. And

(32:39):
it makes a lot of sense, right, the seeds of
structure of the whole universe come from what happened in
those first few moments, and if those first few moments
triggered the formation of primordial black holes, then that sort
of you know, made the decision, like once you create
a primordial black hole is sort of a foregone conclusion
that everything else is going to like gather around, and
you're not gonna start a whole new party when you

(32:59):
already have a big one pumping away. So they almost
like where they form determined the shape and the look
of the universe. And the thing that I'll never stop
being amazed by is that those formations come from random fluctuations,
like quantum mechanical randomness in the very early universe, which
means that like this randomness determined the structure of our universe.

(33:20):
You run the same rules of the physics over and
over again, you get a very different universe. I mean,
you might still have black holes and galaxies, but you
get galaxies in different places. Right, somebody's rolling a die
out there and making different universes every time. It's sort
of amazing every time, every time. Yeah, you know, there's
not that many places in the world where you can

(33:41):
see the effects of quantum randomness. Mostly it's just averaged out,
you know, the quantum mechanics everywhere, but mostly just sort
of balances itself out. It's like almost like we're the
evidence of quantum fluctuation. Yes, exactly. If there were quantum fluctuations,
there would be no structure at all. So we are
all the products of quantum fluctuation. So thank you to
quantum fluctuations for having made us, said the quantum physicists

(34:05):
made of quantum particles. All right, well, let's get into
how why else we think they're there, and and whether
or not they're real and whether we can maybe actually
see or smell and touch a primordial black hole. But first,
let's take another quick break. Right then, we're talking about

(34:29):
primordial black holes, and you know, they it sounds like
maybe they could explain a lot of mysteries like how
the universe formed the way it did and where dark
matter comes from them. And so we think they're there
because not just because of these series and because they
could explain these things, but we're also kind of seeing
them kind of in a way, or we're seeing clues
that they might exist. Yeah, we see lots of things

(34:49):
that are easier to explain if primordial black holes exist,
which is sort of very indirect argument, but you know,
the kind of thing you want to see if these
things are real. And another piece of evidence is that
we sort of see more black hole collisions than we expected. Remember,
we turned on this incredible device a few years ago

(35:10):
called Ligo, which looks for gravitational waves, so kind of
shaking of space and time that only happens when incredibly
massive objects orbit each other and then collide like black holes.
And the thing to understand is when they turned this
thing on and they made it powerful, they made it
sensitive enough to see this kind of shaking of the universe,
they didn't know how often the universe got shook. Like

(35:32):
they built this device that could see these waves, but
they didn't know if the waves were everywhere or just
like once in a million years, right, it was sort
of built to listening for black holes crashing into each other,
but we had no idea how often that happened. Yeah,
And there were calculations all over the place. And the
amazing thing is that, you know, they turned this thing
on and they found one basically right away, like they

(35:52):
were still doing a lot of their calibrations and test
run when they saw a golden golden collision come in
and like the first weekend, like the best case scenario
for science, you know, and so it's like it's it's
happening more often than they expected, like like you know,
there's black holes crashing all over the place kind of yeah,
And what that means is that there are more black

(36:12):
holes than they thought in the particular sort of mass
range that they can see them. Like they're good at
seeing collisions of black holes that are like ten to
a hundred times the mass of the sun, and there
are more of those than they think. Like you can
get black holes about the mass of the sun or
five times the mass of the sun, but they get
black holes like fifty or a hundred times the mass

(36:33):
of the sun. Is not that easy, as we were
saying before, because there aren't stars that big and black
holes have to merge to make them, and so we're
seeing more of those than we would expect, which again suggests, hey,
maybe these are primordial black Maybe the universe is littered
with them. Yeah, maybe even in our own backyard. There
could there could be one here in our Solar system.

(36:54):
There could be one in our Solar system. And this
is very speculative, but super fun. We did a podcast
episode last year or about planet nine, like when you
look at the orbit of the outer planets, there's some
weird things that we don't understand that are sort of
suggestive of another gravitational body out there, something out there
that's tugging on these things that's making their orbits a
little weird. And it's not conclusive at all, but it

(37:17):
sort of makes more sense if you add one more planet. Right,
problem is we haven't seen that planet, like where is it?
You know, even Pluto we can see. And so one
super fun idea is that maybe it's like it's invisible.
Maybe it's invisible, like we can feel it, it's affecting
the orbit of the other planets in US, but you
can't see it. So maybe maybe it's a black hole. Yeah,

(37:39):
And maybe it's a small black hole. In this case,
to have the right mass, it would have to be
really small. I mean, it's still be pretty massive. But
we're not talking mass to the Sun. We're talking about
an object about the size of a tennis ball, and
like that's orbiting our Sun. It's like a black like
our Solar system. You're saying could have a tennis ball
black hole orbiting around it, like it has planets orbiting

(38:01):
around it, exactly, And a black hole that's small would
still have enough gravitational power to change the orbits of
the planet's enough to tweak them to make that visible
from Earth. So if there were such a black hole,
this is exactly what it would look like. That doesn't
mean it's there, but it's tanted right. And so the
idea I guess is that this black hole in our

(38:22):
Solar system didn't form like after the Solar system. It
almost predates the Solar System and predates you know, matter itself.
Like it's maybe the universe is literal with these tennis
balls black holes, and we just happened to catch one
in our Solar system. Yeah, maybe we should have called
them like indigenous black holes because they were here before

(38:42):
we got here right there, like, hey, this is my
solar system. What are you guys doing setting up camps?
This colonizing my part of space. Predates the atoms in
the Sun. Yeah, it predates the atoms in the STU exactly.
And so it could have been here and just fell
into orbit around the Sun. It could have been captured,
you know, it could be wandering the universe and then
been captured. The zillion possibilities. But it's got stories to tell.

(39:04):
And yeah, it's seen the birth of our sources. Yeah,
it was, It exists. It has embarrassing baby pictures about
our son. It knows you when you were small. All right, Um,
so then let's cover really quickly here whether or not
these primorial holes are real. I mean, how we seen them?
How could we see them? What? What are we doing

(39:25):
to confirm their existence? Well, we have not seen any
evidence for their existence yet, which is disappointing, except maybe
this planet nine, right or you know, indirectly as a
reason for the ones at the center of galaxies. Yeah,
we we see things that would make more sense if
primorial black holes existed, but there could also be other explanations.
It's very indirect, but we'd like to do is see
them sort of much more directly, see something which has

(39:48):
to be a primorial black hole. And this one of
the origins of this whole idea was Stephen Hawking thinking
about black holes evaporating, and he realized that, you know,
black holes might not live forever or they give off
this radiation. But the key thing about talking radiation is
that the bigger the black hole, the less it radiates.
So a super huge black hole, anything bigger than like

(40:11):
ten to the twelve ms, will take longer than the
age of the universe to evaporate, so they basically live
forever because they have so much stuff in them. If
so much stuff in them, but as a black hole
gets smaller it has much less mass, then it actually
radiates more. And so if you're less mass, you radiate more,
which means you lose mass, which means you're really even more,

(40:32):
which means you lose even more mass. And so black
holes around like ten to the ten or ten to
the eleven kilograms, they can radiate away and actually disappear
on the time scale about a billion years, which helps
us because well, wouldn't you like to see a black hole?
Dye did not? If I have to wait a billion years. Well,

(40:53):
but we're fourteen billion years in, which means if black
holes are living about a billion years, then they should
be dying all the time. We should be looking around
and seeing this happen. So you're saying, we could we
could see a black hole dye or what will we see?
We would see the like the sputtering, the last few
gasps or what. Well, it will not go out with
a whimper. Remember, it evaporates more rapidly as it gets

(41:14):
to lower mass, so the last few moments are very spectacular.
That's when it's radiating even more than it has before.
So they would go out in this big flash of
light essentially like starts off very gradually, and then it
would blow all of its energy in the last moments,
you know, in this runaway evaporation. It would be very spectacular.
Oh wow, like um, the last gasp of a black hole. Yeah,

(41:36):
and it would be very characteristic sort of radiation. And
so we've looked for this, and we've sent our satellites
out to look in space to see if we can
see these kind of flashes. And you might expect to
see them sort of like in the edge of the
galaxy where it's otherwise dark, but we haven't seen any
of them, Like, we know what kind of radiation they
would give off, because black holes give off a very
particular kind of radiation, this hawking radiation of a certain spectrum,

(41:58):
so we would expect to see it in the case
of temperature of the black hole at the moment, so
it would look like nothing else I see. So is
the idea then that, you know, if the universe is
littered with primoritial black holes, we should see a whole
bunch of them dying all the time. Yeah, that's exactly right.
They were all born big bang. But if the last
you know, billions of years, we've been around billions of years,
and so we should see some of them fuzzing out

(42:20):
of existence. But so far we haven't seen. We haven't
been seen there. We have not and we've looked pretty
carefully and we haven't seen those. So that tells us
that if there are primordial black holes sort of a
very low mass, you know, less than a billion kilograms,
then there aren't very many. We can still have one
the size of a tennis ball in our solar system,
but maybe it's not common. Yeah, and that have small

(42:42):
that's right, and the small ones therefore cannot explain the
dark matter in the universe. There's just not enough of them.
If they do exist, there's not enough of the small
mass ones to explain the dark matter. But you know,
maybe there are heavier black holes. Maybe there's really big
ones out there, so we have other ways to look
for those, or maybe all they of ones already died
or something precisely, and so we could look around to

(43:03):
see if they're heavier mass black holes, and we have
other ways to do that. Like if these black holes exist,
then we should see lensing effects. We should see them
like passing in front of stars and galaxies and and
blocking the light from the more, distorting the light from
the right, just like dark matter. Wouldn't that account for
how dark matter does that? Just like dark matter exactly,

(43:24):
except dark matters so far we thought it is more diffused.
We've only detected dark matter and like really big effects
gravitational effects and big clumps of dark matter lensing background galaxies,
for example. What we're looking for here is like micro lensing,
like a really tiny spot of something passing in front
of an object and distorting it, not a big diffused cloud.

(43:47):
If dark matter really is made of primordial black holes.
It should be made of these tiny little spots that
we can see these micro lensing effects, because I guess
you're talking about the black holes now that are about
the size of a planet or like giant asteroid. Yeah,
giant asteroids or larger, anything larger than that, we should
see these lensing effects. And if they're even larger, if
they're like really super crazy massive, then they would have

(44:10):
big effects on the structure of the galaxy itself and
the relationship between galaxies. Like if they were just like ginormous,
like mind blowing me, like billions of suns, then they
would distort the whole shape of the universe and we
would see that for sure. So we know they're not
like ridunculously big, and we're pretty sure that there aren't
really massive primordial black holes out there because we would

(44:32):
see these micro lensing effects. So we've ruled out the
very very light ones and the very very very heavy ones.
He's this interesting regions sort of in the middle. Well,
the very very big ones might be like galaxies, right, like,
that's where they might be, right, but we know the
size of the black holes in the center of galaxies
and that certainly doesn't account for the dark matter. All right,

(44:52):
so we're we're looking for them, and um, how are
we looking for them? I guess with telescopes, with radio telescopes. Well,
another a way to look for them is to see
them destroying other stars. Like if you have this sort
of intermediate class black holes something like you know, ten
of the fourteen ten of the seventeen kilograms, then they
would occasionally like pass through a white dwarf or a

(45:14):
neutron star and essentially destroy it. What, Yeah, because you
know they Yeah, I guess if you have a whole
bunch of black holes floating around everywhere, it would be
a little bit of you would expect there to be
a little bit of a chaos, right, Yeah, it would
be disruptive. And so they would pass through and they
would shat ot these things. They might ignite fusion and
a white dwarf like kick it up into actually burning again,

(45:35):
and they could totally disrupt neutron stars. And we just
don't see that happening. Like the population of white dwarfs
and neutron stars, it looks as we expect, and so
we don't see a big effectocy. You know, something assassinating
neutron stars out there. We don't see a whole bunch
of chaos. Weasels running around the guards balacy. That's right.
But this part is very is hard, Like this is

(45:56):
a hard measurement to do to find these things, to
calculate how often you would see them. So there's sort
of a lot of controversy in this middle region here.
People are still really not sure how strong those limits.
I mean that we had to be these black holes
and they would have to run into other stuff, which
in space is kind of heart Yeah. And another thing
we can do is we can just look at our
own son, Like our sun is big enough that it

(46:18):
would survive having a small black hole just like go
into it. And they've done these awesome studies where they
show that you could see it happen by looking at
ripples on the surface of the sun, like sun quakes
could be evidence of micro black holes entering the Sun
like little like would that would be incredible? Wow? Woulduld
get into that? Like what happens if a black hole

(46:39):
goes into our sun? So it sounds a little disconcerting. Well,
if it's really big, then we're in trouble. But if
it's small enough, it just sort of like causes literal
waves on the surface of the sun. The sun will
settle back down and be okay, But you can definitely
see that. So that's the kind of thing we're planning
to do in the future to see if we can
spot these things. All right, Well, it sounds like it

(47:01):
sounds like an idea that makes a lot of sense.
It's definitely a cool idea. Um, But maybe the jury
is still out whether or not they're like actually there,
the jury is definitely out. We don't we're looking, Yeah,
we're looking. We don't know if these things are real.
If they are real, they would explain a lot. But
so far, you know that it's not looking good. Like,
the best models suggest that if you made primordial black holes,

(47:24):
you should make them sort of at all masses, the
really small ones, the really big ones, And we haven't
seen them at the small masses or the really big ones,
so that makes it a little more awkward. So now
you have to play some clever game and come up
with some reason why you would only make primordial black
holes at a certain mass region. So it makes it
less fun and sort of less pretty of an idea,

(47:44):
But Hey, it's still possible. Yeah, well, yeah, I was
getting kind of excited about this idea. It's a preme
eval idea. It's primordial. Should I should check my primordial
or just all right? Well, I think once again, at
this point, I think to all the things we don't
know about universe. We don't know what happened at the
Big Bang, and we don't know whether or not maybe

(48:05):
there are still the remnants of before the Big Bang
just hanging out with us. Absolutely, And it's tantalizing to
think that those remnants could be here and they could
hold clues as to what happened in those first few moments.
They could give us insights into how the universe was made.
And if we measured the sort of spectrum of these
black holes and discovered their masses and only these were made,

(48:27):
not those were made, they would really be like a
window back in the first few moments of the universe.
So I really do hope they do exist, because primordial
is a cool word, and the idea is cool, and
I hope that they have secrets in them that they
will yeah, because you know, why not? Why not? Exactly?
The Big Bang was so much fun? Let's do it again,

(48:48):
But why not yet? Yeah, let's hold off on that.
We'll put a pin on that, all right. Well, we
hope you enjoyed that discussion. Thanks for joining us, See
you next time. Ye. Thanks for listening and remember that

(49:08):
Daniel and Jorge Explain the Universe is a production of
I Heart Radio. For more podcast from my Heart Radio,
visit the I Heart Radio Apple Apple Podcasts, or wherever
you listen to your favorite shows.