Why black holes are actually bright.

Daniel and Jorge talk about the incredible, ironic brightness of black holes.

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Episode Transcript

Speaker 1 (00:08):
Hey, Jorgey, I have a pop quiz for you. Was
this in the syllabus? Did you read the syllabus? And
then another was one? Then yes, it was on the syllabus.
All right, that sounds fair. All right, hit me up.
What is the object that astronomers call a blondet? Interesting?
It sounds like a block internet, maybe like the less

(00:31):
exciting version of the Internet. Close. All right, well it's
it's it's astronomy. So I'm guessing maybe it sounds like planet,
but maybe it's like a black planet or or i know,
like a black hole planet ding ding ding. You it's
a planet that orbits a black hole. Oh? Interesting? So

(00:51):
sometimes astronomy does come up with sort of names that
makes sense. Sometimes it's being generous. Just be glad I
didn't ask you what a plun it is. I'm glad
you didn't ask me that what what a plunent is? Weight?
Is a pluted a real thing? Absolutely? Is it a
more pluish version of the Internet. Hi am or Handmae

(01:25):
cartoonists and the creator of PhD commics. Hi, I'm Daniel.
I am a particle physicist and a professor UC Irvine,
and I would never joke about plunets. Does that make
you a plute? Pessor I always try to tell the plute, well,
that's a real plus. But plunets are a real thing. Really,
what are they? What's a plutt? A plunt is a

(01:47):
moon turned planet. It used to be a moon orbiting
a planet, but then it was set free and is
now wandering the Solar System and counts as a planet. Oh. Interesting,
so you started the word moon inside of the planet.
Interesting You didn't like combine it or you like literally
merged it. Yeah, exactly. You know, take the old job

(02:08):
and in certain inside the new jobs. So for example,
you know your job would be car engineer, tunist engineers.
I like that a little bit better engineer engineers. There
you go, anything that involves ingenuity, and you're no longer
orbiting anything but Welcome to our podcast Daniel and Jorge

(02:28):
Explain the Universe, a production of I Heart Radio in
which we mash up all of the crazy ideas that
are out there in the universe. The planets, the moons,
the pluets, the blondet's, the black holes, the new drown stars,
the quasars, the tiny little particles, and even the hypothetical
stuff that might not exist all in a desperate attempt
to understand this glorious and incredible universe that we find

(02:51):
ourselves in that provides us with so many satisfying, deep, rich,
and cosmically contextual questions about the nature and meaning of
our lives. Cosmically contextual questions. That's a great alliteration there,
it's positivitivitally fluish. I am inspiring a literationist, but it
is at an incredible and wonderful universe out there, full

(03:12):
of interesting things that we've named, that we haven't named,
things that we understand, and things that we don't understand
and we have yet to understand and that will hopefully
learn more about in the future. That's right, it's a
never ending journey to answer the questions about the universe.
Or he asked me earlier, if somebody is wants a physicist,
if they're always a physicist, and I think that the

(03:32):
answer is that everybody out there is a physicist because
we all want to know answers to the deepest questions
about the universe. Yeah, we all have questions, we all
wonder about the world around us. And I guess that
makes you a physicist, right, I mean technically, anyone who
wonders about the universe and how it works is sort
of a scientist, right. Yeah, physics is just trying to
tell mathematical stories to answer our questions about the universe,

(03:56):
and we all have those questions and trying to build
in our heads models about how the universe works. Professional
physicists who do it for their day job take it
one step further and devote their lives to it. But
I think it's something that everybody and some level is doing. Interesting.
Does that mean you go around saying, Hi, I'm a
pro physicist. Stand back, I'm a professional. That's right. Like

(04:19):
professional wrestlers. You need to take professional physicists much more seriously. Yeah,
I'm sure you get paid as much as professional athletes
as well. You should see me in costume. Yeah, and
I'm sure there's an n p A also a National
Physics Association, Right. You have a world championship too, Oh yeah,
we call it a SmackDown. Also, you technically kind of
have teams, right like you and the people in your department.

(04:41):
You're sort of a team, and you're sort of competing
against other teams in a way, right to uncover the
secrets of the universe. That's true. We do have a
group here at Irvine that all sort of works together
probing the universe in different ways, plasma physics, condensed matter physics,
all the way to astronomy um also a member of
other teams like I'm a member of the Atlas Collaboration,
which is a group of thousands of scientists all working

(05:02):
together to try to understand the basic constituents of matter.
And we have competition. The CMS Collaboration is like five
thousand other scientists trying to beat us to the punch. Interesting.
How many teams are you a part of that? Do? It?
Sounds like you're very promising businesses. I'm a prolific collaborator,
that's true. Yes, you're a professional, prolific promisk business That
sounds very positive. Well, I'm pro you anyways. But yeah,

(05:26):
it's an interesting universe full of mysterious things, and nothing
is more mysterious, it seems, than an interesting object that
we thought was theoretical for a long time, but that
we now have pictures of out there in the cosmos.
Maybe the most challenging thing to wrap our minds around
to understand that it might really be out there in
our universe. Not just a product of mathematical calculations, but

(05:49):
a reality, something one could actually fall into and experience,
something one could actually see with their own eyes. Are
these weird mysterious corners of space black holes? Were gravity
and space time are so intense that nothing, not even
light can escape. Yeah, and they are frustrating to think
about and to wonder about because they are They are
literally sort of hidden from the universe. They are not

(06:11):
just black holes and names. They are actual sort of
holes in the fabric of spacetime and reality itself. Yeah,
they're almost like a separate universe. They are detached from
our universe. Once you fall into a black hole, it's
not that you can't escape because you can't go fast
enough because the limit of the speed of light. It's
because the shape of space is so crazy, so distorted,

(06:32):
so curved, that they are one directional, that every path
leads you towards the center. So in some sense, everything
inside the event horizon is like its own little universe.
It's detached from normal space time. Yeah, whatever happens in
a black hole stays in a black hole. You can
do whatever you want. You can relive your wild days
inside of a black hole. That's right, the original Las

(06:53):
Vegas and did that Vegas instead of a black hole?
If you think about it, at least for people's money
and prudence, that's right, it leaves a black hole in
their hearts. Yeah, black holes are super mysterious and they
seem to sort of occupy a big hole and and
people's curiosity. It's one of the things we get asked
about the most on our social media and through email.

(07:13):
That's right. And it's not just you folks out there
who are super curious about black holes and what's inside
of them. Professional physicist experts in relativity and quantum mechanics
are also desperately curious to know what's inside a black
hole because, at their hearts, they might contain the answer
to one of the biggest open questions in physics, which

(07:34):
is how gravity and quantum mechanics work together, or if
they do. Gravity and quantum mechanics are our two pillars
of understanding the universe, but they have very very different
pictures about how the universe works. But most of the
time we only need to use one of them, gravity
or quantum mechanics. It's inside a black hole that both
of them are needed. But unfortunately we don't really know

(07:57):
what they are doing together inside the black hole, because
of course it's hidden from us. Yeah, those secrets are
locked inside a black holes and we may never get
to him because nothing, not even light, escapes a black hole.
And yet, somehow ironically or interestingly, black holes are some
of the brightest things in the universe. Black holes are
not completely dark, that's right, And we hope that by

(08:19):
studying what happens outside a black hole, in the neighborhood
of a black hole, the things the black hole does
to the space and objects around it, perhaps we can
start to get a glimmer of what's going on inside.
So to be on the program, we'll be asking the
question what makes black holes glow interesting? You mean like

(08:42):
glow from light or just they just have a positive
disposition about their career. Arc is just incredible. They just
get bigger and bigger and bigger second and more attention
as they go along. That's right. They go from de
list to C list, the list and then finally a
list as in astronomical st ours. Yeah, not be less
like black hole. But yeah, black holes are super interesting

(09:04):
because they are mysterious and they trapped even light itself.
But also they glow, right, They sort of glow out
there in the universe. Sometimes they are even some of
the brightest things in the night's time. Yea. And we
have been looking at black holes for almost a hundred
years without knowing it. Some of the things that we've
been studying for decades and decades and decades we only
recently discovered are actually black holes. Yeah, so they're not

(09:26):
just sort of sitting out there in space sucking stuff
up and looking dark and mysterious. They also sort of
shine brightly, and at least some of them give off
a crazy amount of radiation. That's how we sort of
know where they are. So, as usually, we were wondering
how many people out there had thought about the glow
of black holes, or whether they even knew black holes
glowed brightly. So Daniel went out there into the internet

(09:47):
to ask people why the black holes glow so brightly.
And we are very interested in hearing you speculate without
preparation on topics for future episodes. So if you'd like
to participate, please send us your name to questions at
Daniel and Jorge dot com. We'll send you the questions
back over email. You can record the answers in your
very own home. It's easy, it's fun. Don't be shy.

(10:09):
So pop quiz. Why do you think black holes glow?
That's what people had to say. They closer brightly because
they're sucking all the surrounding light and everything around it,
so you have spires of light basically coming in at
one point, and that's why it's so bright. I don't

(10:29):
think that the black holes are glowing like itself, definitely
not at the center, since there's a gravitation of bood
there is so great that not even light can escape it. However,
you can potentially detect material around them, and like gas
and dust spinning around it, throwing off hot material, and
when emitting radiation like X rays and as a matter

(10:53):
of falls into the hole, it can be detected and
it can actually brightly or glow bright. I think there's
so much energy imparted into the material that's swarming around
them that um, somehow that energy turns into light excited
electrons and stuff like that. And I also know that

(11:15):
they can focus material and jetted out, and that material
goes out and interacts with the dust and stuff around
the black holes and bumps them up into a light
emitting excited state like an emission nebula. Okay, so black
holes they're not glowing. I think that the light is

(11:37):
getting refracted around them, it's getting bounced off, and so
it's not the black hole that's glowing. But it's an
illusion almost because they're I believe they're called acretion disks,
give off just a ton of heat because they're swirling
around at almost light speed something like that. I think,

(12:02):
not the black hole itself glows. Uh, what it glows
would be the creation disks where the older gases a
Dutch speed amid energy, and also might be the curs
some black holes type qus. That would be also a

(12:24):
reason why a black hole looks so brightly. I think
this has to deal with black holes that are feeding,
that actively feeding off of other stars or other objects.
I think when they're feeding, it brings in everything on
that creation disk, and everything heats up and creates like
plasmas where like they're stripping, you know, stripping everything down
to its elemental form. And I think it causes a

(12:46):
lot of activity like the electromagnetic field. So like I know,
X black holes give off X rays and they give
off gamma rays, and they give off these strong energies
that we can measure here on Earth. So it has
to be because their feet. The black holes give off
energy because they're feeding off of surrounding objects and causing
a lot of activity in ways that we can measure
here on Earth. All Right, some pretty good answers. A

(13:06):
lot of people seem to be confident and familiar about
this topic, almost like we've been talking about black holes
for quite a while, Yeah, for three hundred episodes. It
is a popular topic, and a lot of people hit
on a really important point, which is that a lot
of the radiation from black holes doesn't come from the
actual black hole within the event horizon itself, but from

(13:27):
the stuff that's around the black hole, the impact of
the black hole on the neighboring objects, right, Yeah, or
maybe they read both of our books and our two
books we have no idea and frequently asked questions about
the universe, we do talk about black holes, and and
one when we get really into black holes, like literally, Yeah,
we talked about what it would be like to fall
into a black hole, whether you could survive, and what

(13:50):
you should pack along the way and what you experience.
So please check out our books, our second book now
out frequently asked questions about the universe, but in this
case we're talking about why they glow. And a lot
of people seem to associated with not the black hole itself,
but sort of the things around it, or at least
what's happening around it in terms of the space distortion. Yeah,

(14:10):
and there's several effects here that are important to pull apart.
One is weather black holes actually do glow themselves, and
the second are how they make things around them glow.
But there's more than just the accretion disc there, which
we'll get into later. But first let's talk about the
black holes themselves. Most people said black holes don't glow
because they're black. That's mostly true, but not actually a

(14:33):
hundred percent true. A black hole, even if it had
nothing around it, just sitting in empty space, wouldn't be
a hundred percent black. They do give off a very
small amount of radiation. Yeah, super interesting, and so let's
dive into this topic and make it glow. So, Daniel,
I guess to refresh everyone out there, what is exactly

(14:53):
a black hole. A black hole is a region of
space where it is curved so much that not even
light can escape. So this portion of space is then
encircled by something we call an event horizon. Any object
or photon or particle which falls within this event horizon
is trapped forever it moves towards the center of the
black hole. And this event horizon is not like a

(15:15):
physical barrier. There's nothing, there's nobody to greet you or
to say hello and welcome to the black hole. It's
just sort of a region of space which if you pass,
you will never escape. So these black holes are these
curved regions of space time, as we said earlier, sort
of detached from the rest of the universe, and they
form when stars collapse, or sometimes they form at the

(15:35):
center of galaxies. And they can be extraordinarily massive. Yeah,
and we've talked about how you can have them of
any size. You can have tiny, little mini black holes,
or you can have giant black holes that are billions
of times more massive than our sun. And like you said,
there's sort of regions of space where suddenly, like everywhere
you can go can only go take you inside of
the black hole, right, instead of a weird thing to

(15:57):
think about that space can bend that way. Yeah, and
space says something you might think of. It's just sort
of like the backdrop of the universe, like the stage
on which events happen. But we now know that it's
much more interesting and it can do fascinating things like
bend and twist. Most of the time you don't notice
that gravity, turns out is an effect of space is curvature,
so you feel that every day when you walk around

(16:17):
on the planet. But mostly things seem to move in
a way that makes sense to you. But a black
holes like the extreme version of that, like crank it
up to eleven, where things get really distorted and the
shape of space like dominates. You know, it's the thing
that determines everything that happens. Right, and I guess specifically
you mean like the shape of space time, right, Like
maybe it's not so much space but space time, meaning

(16:39):
like where you will be in the future in in
that space. Yeah, we bundle space and time together into
a sort of a four dimensional object. One thing that's
really fascinating is that inside the black hole, space becomes
one directional. You can only move towards the center of it.
That seems a little counter intuitive until you remember that
outside the black hole, time is already one direction the

(17:00):
way you can only move forwards in time in that
same way. Inside the black hole, every path leads towards
the center. The future of every particle trajectory inside a
black hole hits the singularity. So that's what we mean
when we say that space is one directional, and that's
directly because space is curved so much so once you're

(17:20):
inside of the event of horizon of a black hole,
you can't get out, and not even you can't even
shoot a laser out of it because the light from
the laser, which just should back around and come back
to the center of the black hole. And so it's
sort of surprising that a black hole can glow then,
So like, how do they glow? How can they give
off or emit anything? Yeah, black holes can glow, and
the way they do that is by Hawking radiation. Hawking

(17:42):
radiation is the recognition that black holes have a temperature,
like everything else in the universe almost has a temperature.
I have a temperature, You have a temperature, the Sun
as a temperature, and everything that has a temperature and
has electromagnetic interactions glows just sort of like gives off heat.
The for example, a pie sitting on your counter cools

(18:02):
off it does that by radiating away some of its energy.
So this is called black body radiation, and we talked
about this on the podcast recently. How everything with a
temperature glows. So Stephen Hawking realized that black holes also
have a temperature. They're not at absolute zero, which means
that they must glow, and so he speculated that they
must give off very faint radiation, meaning little particles created

(18:25):
just outside the black hole that somehow steals some of
its energy. And there are various sort of pop side
descriptions of how Hawking radiation happens at the end of
a black hole, but it's important to understand that none
of those are really very accurate. We have no accurate
microscopic picture of how Hawking radiation really happens because it
requires the theory of how gravity affects particles, and we

(18:47):
just don't have that theory. We don't know what quantum
gravity is. We can't describe the effect of gravity on
tiny particles. There are some sort of hand wavy explanations
to give you a sense of how it works, but
it's important to understand that mostly it's a statistical argument
about the temperature of black holes, right, Yeah, it's pretty
cool to think about hot black holes or cool black holes.

(19:08):
But I guess, you know, most people are sort of
familiar with a pie in your desk is kind of
emanating heat through the air. But I think what's interesting
is that even if you put that pot pie out
in space where it's not touching any air, it would
still radiate heat in the form of infrared light, right, yeah,
or visible light depending on the temperature. Like the Sun.
There's a huge vacuum between us and the Sun, but

(19:29):
it's still able to warm you up on a nice
toasty southern California morning, and it does that by radiating
away its energy via photons, and the frequency of those
photons depends on the temperature of the object. So the
Sun glows in the visible spectrum the Earth and you
glow in the infrared, as does that pie. Black holes
are very very cold, so they glow in very very

(19:51):
long wavelengths. Yeah, but it's kind of interesting because you
know that hot pie in space is probably you know,
the way that it's emanating light is that you know,
the electrons and the surface of the pie are excited
and they dropped down an energy level maybe and they
admit a photon in the infrared, so you can sort
of imagine that mechanism for giving off energy. But a

(20:11):
black hole is kind of weird, right, because the surface
of a black hole is not actually like a surface,
and it's not actually like stuff, right. It's weird to
think that it can just emanate heat or light out
of basically, you know, a hole own space exactly. It
is very weird, And as you said, we have a
pretty good understanding for how that happens for pies, like
the physics of pies, we have a pretty solid understanding,

(20:33):
Like quantum pie dynamics pretty well understood, but that's because
we understand that kind of matter and the forces of
gravity there are pretty weak. But in the case of
a black hole, we don't really understand what happens to
electrons very very close to the event horizon, or virtual
particles created near the event horizon. We just don't have
an understanding of it. Neither does Stephen Hawking. He doesn't

(20:56):
have a theory of quantum gravity. What he did was
make us sort of like semi classical theory of gravity,
like a sort of patch together concept of you know,
using bits and pieces to sort of approximate what some
elements of quantum gravity might look like, and using that
you can make a sort of hand wavy picture. You know.
The picture is that you have virtual particles created outside

(21:17):
the event horizon, not within the black hole, but outside,
and those particles can pick up some extra energy because
of the incredible gravity of the black hole. Remember that
black holes, even though they have this event horizon, they
can affect things outside the event horizon. Right, Just like
the Sun pulls on you with its gravity from very
very far away, a black hole can also do that,
pulling on you with its gravity and giving you extra energy.

(21:40):
When it does so, it loses that energy. It gives
that energy to one of those particles. So if a
particles created near a black hole and then boosted by
the energy of that black hole, when it leaves, it's
taking away some of the energy of that black hole.
So again, this is a hand wavy, probably not accurate
description of how hawking really is generated because we don't

(22:01):
have a solid understanding of quantum mechanics and gravity and
how they play well together. All right, well, let's dig
into this hawking radiation a little bit more, and then
also what are some of the other ways that black
holes glow. Some of them are pretty dramatic and maybe
even the brightest objects in the universe. So let's get
into all that, but first let's take a quick break.

(22:32):
All right, we're talking about glowing black holes, which is
sort of sounds like an oxymoron, sort of like a
bright dark object. I think it's sort of cool that
we think about black holes is like hidden and hard
to find, and it took us decades to discover them.
When it turns out, they're sort of like screaming about
their existence all the way through the universe, Like they
are not being shot. They're being very very obvious. They're

(22:52):
kind of matches. Actually, it's like, can you quiet down, please,
we're trying to study black holes. Settle down, settle down.
We know you're cool, but you know, you don't need
to prove yourself. And that's what makes it ironic is
that they are so bright and so intense and so
crazy that people sort of overlooked them as candidates for
black holes for a long time. Interesting, well, we were

(23:13):
talking about hawking radiation, which is sort of the glow
or a small glow that black holes have that happens
to about the boundary of the black hole due to
a quantum particles appearing and things like that. But I
guess the question is of all of this is theoretical,
we don't actually know how it emits hawking radiation, and
I'm guessing we've never seen this hawking radiation being admitted

(23:34):
because we barely have pictures of black holes, Like, how
do we know hawking radiation is a real thing? How
do we know hawking radiation is a real thing? Simple answer,
we don't. It's theoretical, it's predicted. It makes more sense
than black holes and not giving off hawking radiation because
that would require them to be an absolute zero, and
it would be in contradiction with lots of things we
know about, like entropy. Black holes have to have a

(23:56):
temperature because I have to have micro states inside, because
they have to receive eve information when something falls into
a black hole, they're gathering quantum information, and in order
to have that information, they have to have some entropy,
and entropy means temperature. So again it's sort of an
argument from statistical mechanics. But you're right, we haven't observed
it directly, but it's opened up a really rich vein

(24:19):
of area for people to explore it's like given us
a crack in the facade of black holes where people
can jump in and then explore more properties of black holes.
But it's not something that we have confirmed experimentally. It's
very very faint, really really large black holes emit very
very very faint Hawking radiation. It's actually the smaller black
holes that emit more Hawking radiation, and they would glow

(24:42):
very brightly, and just before a black hole like evaporates
into nothingness, it would be quite bright, and we've looked
for that, but we haven't seen any evaporating black holes
in the universe. I see interesting. So it's sort of
theoretical and we think it's sort of glows by this
Hawking radiation, but it's sort of what you're saying. It
makes ends based on our current theories. But our current
theories sort of don't necessarily work inside of a black

(25:05):
hole or with a black hole, right, So there might
still be surprises about this whole thing. Oh absolutely, our
current theories almost certainly wrong. And later somebody smarter, maybe
one of our podcast listeners who's going to go into
this field, will come along with a full fledged theory
of quantum gravity, and it might be that that theory
agrees with Hawkings theories and you know this concept of

(25:26):
Hawking radiation and black hole temperatures. But it might be
that it doesn't and that there are surprises. And that's
exactly why we go out and we look at these
black holes and we studied them and we take pictures
because the universe is filled with surprises and is always
confronting us with different stories than the ones we were
telling ourselves in our head. Yeah, so it's a hypothetical
guest theory based on a theory we think. We know

(25:48):
it's wrong. It's what you're saying, also known as doing
our best well. Stephen Hawking is usually pretty right about stuff.
So these black holes glowing and emanating sort of a
slow of heat or radiation is one way that black
holes can glow. But they can also glow more dramatically,
right like a big time. Yes, they can glow very

(26:08):
dramatically because they have very strong effects on the gas
around them. The way the black holes grows that they
gobble gas and stars in their vicinity and before the
things fall into them, they swirl around for a while
because they have angular momentum, just the way the Earth
is going around the Sun doesn't just fall straight in.
Things around a black hole swirl around for a while

(26:29):
before they bump into each other and eventually fall in.
And that bumping into each other is very intense because
the gravity is very intense. So if you have a
huge cloud of gas around a black hole, there's a
lot of gravitational friction and that heats it up and
that glows and they can create incredible sources of light. Yeah,
I guess that's kind of maybe hard for people to grasp, right, Like,

(26:51):
you know, the Earth is orbiting around the Sun, but
we're not sort of glowing or we're not we're not
getting sort of shredded and rub into bright bright So
maybe is it because black holes are so intense and
the gravity around the black holes is like super extra
intense that things just get shredded even if they're just
going around them. Absolutely, But the Earth does have that

(27:12):
effect a little bit, Like the effect of the Moon
is to sort of squeeze the Earth a little bit
and it like massages the Earth's oceans. Or if you
were a moon going around Jupiter for example, Io, why
are those moons so hot on the inside because of
the gravitational squeezing from Jupiter, and so the Sun is
doing that also to the Earth. So if the Sun

(27:34):
was larger and more massive and the Earth was closer
to it than those tidal forces would really heat up
the center of the Earth. And so black holes are
much much more intense gravitationally, and these accretion discs are
much much closer to them, and so this gravitational sort
of squeezing and tugging heats them up. It's more of
a gravitational pulling, right, Like the Moon is not so

(27:55):
much squeezing the water on Earth, but it's sort of
like pulling on it more in one side and the other,
and that's what's causing the tidal forces, right. Yeah, Gravity
depends very strongly on the distance, and so the bits
of the Earth that are closer to the Moon get
pulled on harder than the bits of the Earth that
are further from the Moon. And so the result is
the Moon is basically trying to pull the Earth apart

(28:16):
because it's pulling on one side harder than the other side.
The same with Jupiter and its moons. You can think
of it like taking a piece of chewing gum and
pulling on one end only it stretches it out. But
then if that chewing gum is spinning, then you're like
constantly stretching out different parts of it, so you're keeping
it warm. You're you're like massaging it like a dough,
like if you need a dough. It it sort of

(28:36):
heats up a little bit, right, and now it's spinning
like a pizza dough where we're a little hungry here.
I don't know if you can tell. So that's what's
kind of what's happening to things around a black hole.
They're getting kind of like stretched a lot by this
the intense gravitational forces, but they're also it also sort
of happens not just because of the tidal forces, but
just because it's going so fast around the black hole, right,

(28:57):
because things get sucked in pretty fast, pending on how
fast the black hole is spinning and this stuff around
it is spinning, absolutely, it can get going pretty fast,
just like a figure skater speeds up and spins faster
if she pulls in her arms because of conservation of
angle momentum, or just the way like comets as they
approach the Sun from the outer Solar System get going
really really fast as you fall in towards the center

(29:21):
of the black hole. Then you go faster and faster
both in spin and in velocity. So you get a
lot of particles moving really really fast, bumping into each other.
And that's what temperature is. Temperature is basically like spedometer
of particles, right, right, So thanks are crazy spinning around
a black hole, and so somehow that gives us energy,
right like things are getting pulled apart, rubbing, exploding, crashing,

(29:43):
and that just gives us a lot of light and radiation. Yeah,
like we said before, things that are hot, they glow,
and so this gas is super duper hot, and so
it glows in the X ray gives us these very
very powerful X ray radiation, which is just another kind
of photon, just much higher fe quency. Yeah, pretty close.
And so for a long time we thought that these
glowing black holes were actually stars. Right. In fact, we

(30:06):
call them quasi stars. Yeah, they've been seen since the
early parts of last century. In the nineteen fifties, they
started to study them more intensely, but they didn't really
understand what they were because they were very very bright,
but their spectrum was very very weird, Like if you
look at the frequency of the light that they emitted,
it didn't match what typical stars emitted. They looked like

(30:28):
they were a red shifted super duper far like the
photons were shifted really far down in wavelength compared to
most stars. And usually when that happens, it means that
the thing you're looking at is really really far away,
so it's moving away from you quickly. That's how we
measured the distance to things sometimes so that we measured
this red shift. But in this case, these red shifts

(30:48):
were super dramatic, and yet the objects were really bright,
and so at first glance it seems like something which
is really bright and also crazy far away, which means
it must be like riduculously bright. So first atronomers were
really scratching their heads wondering what these things were interesting
like to the naked eye, and when when you look
up at the night sky, it just looks like a
little pin bright pin point, But when you look at

(31:09):
the like the frequency of the light, it actually tells
you that it's crazy bright and crazy far. Yeah, they
can be like a hundred times brighter than the other
galaxies near them. So people like, what's going on? How
are these things so bright? Because they're already really really
far away, these things, like just to get a scale,
you know, these things like at their source would have
to be like four trillion times brighter than the sun,

(31:32):
like at the same distance. And so then it turned
out that those are actually black holes, that the ones
that we saw in this guy that were so bright
and so far so people saw these before black holes
were really taken seriously as an astronomical object, and so
it took a few decades for people to sort of
put those two puzzles together. You know, what are these
quasars and also our black holes? Real people put that together, like, wow,

(31:54):
black holes. Maybe that's what these things are. Maybe they
are powering these quasars. And they came all together when
people started studying like the size of these quasars. One
thing that's really interesting about them is that quasars are
highly variable. They don't just like burn brightly all the time.
That's because the gas around the black hole is really volatile.
But if the brightness is varying, like over a few days,

(32:16):
that actually tells you something about the size of the object,
because it means it can only be like a few
light days across. It can't be really really large and
also like coherently varying in time very quickly, and so
that tells you that it's really small and also really intense.
It takes a lot of mass to power all that brightness,
So that's when people start to realize maybe these things

(32:38):
are powered by black holes. You're saying that if something
is that bright and if it's large, it wouldn't be
you know, changing in terms of the light it gives up.
You can't have two things that are like a light
year apart, coherently varying in time, like having the same
pattern over in just a few days, because they have
to be somehow communicating with each other. But they are
light year apart, so they can't. So if two things

(33:00):
are in sync over a period of like a day
or an hour, then they have to be within a
light day or a light hour of each other if
the same process is driving them. So it's like a
cool indirect way to get a sense of the size
of an object by seeing how quickly it's light varies. Interesting,
I guess the speed of light limits even like how
fast you can coordinate different parts of a bright object.

(33:22):
It's kind of what you're saying, you know, if they're
driven by the same fundamental mechanism. They have the same
underlying cause, like two sides of an object grow brighter
or darker because of the same underlying physics that's happening
inside of it. Then they can't be that far apart.
So you concluded, well, this must be something super bright,
super far and also super small, or at least, you know,
at least the size of like the our solar system

(33:44):
or a sun exactly. And another interesting piece of the
puzzle is that we mostly see them really far away. Right,
we said earlier that we see them really high red shifts,
which means they're mostly far away. And you might wonder, like, well,
if these things are really bright, shouldn't we see a
bunch of them close are up that are like obviously
really really bright. But the thing is that these things
were made mostly in the early part of the universe's history,

(34:07):
like around three billion years was the peak time to
make these quasars, and since then we haven't really been
making them very much anymore. So most of the quasars
in the universe are far away from us because the
ones close by have already died out. They don't last
that long. They only last like ten or twenty million years.
I guess what you're saying is that, you know, not
all black holes have an accretion disc or like stuff

(34:30):
blowing brightly around them. And so the ones that we
that do seem to have that we can see are
probably old because it's probably the black holes are closer
to us. I've already burrowed out their accretion disk. Yes,
And it's not something that we understand very well because
we'll talk about a bit more later, like what's going
on very close to the black hole, how they gather
gas and how they blow that gas away due to

(34:52):
the intense radiation is not something that's currently very well understood.
We think that about five to ten of galaxies with
black holes at their core have quaisars. So a lot
of the galaxies around us that have black holes don't
have a quasar. Its requires like sort of special conditions.
Not every single one does it right, or maybe they did,
but they it's no longer kind of burning bright. Yeah,

(35:14):
if they grew to a certain size and they've blown
away a lot of the gas that they would otherwise feed.
Remember we had another episode about how you could quickly
make a black hole, and it's not actually that easy
to just like dump a lot of stuff into a
black hole, because as they grow, their gravity gets stronger
and they create this intense radiation which actually works against
them because it blows away a lot of the stuff nearby. Interesting,

(35:38):
it's like it it gets indigestion, you get you get
a feed it slowly. You gotta burp your black hole
just right, yea, otherwise still burp other things out. So
then that's kind of so we don't see quasars near us,
meaning black holes that blow brightly, but they are out there,
and they do it through this kind of mechanism of
the acreation, this burning stuff up, crashing it around itself.

(36:00):
And also sometimes that radiation can be very focused, right,
in which case we get super extra bright quasars. Yeah,
if quasars happen to be pointed right at us or
they're moving towards us, that we call them blaze ours
because their radiation gets boosted by being pointed right at us. Right.
But I guess this is a kind of a subtle
point is that sometimes in a black hole, the ecreation

(36:21):
disc is glowing. It's bright, we can see it from
far away. And sometimes but sometimes it's sort of aligned
in the right way where it's super extra bright. Right, Yeah,
if it's lined up directly to Earth, like the most
intense part of the quasar mission is pointing right at
the Earth, then they get super extra bright. Does that
mean that all quasars are all glowing? Accretion discs are directional,

(36:42):
like they all sort of point in a particular way
like a flashlight. They do, but not that intensely. They're
not like extremely focused the way like a pulsar is
a pulsar, you just won't even see that radiation if
it's not pointed at the Earth. These are not as directional.
But if the intense part of it is pointed at
the Earth, then yeah, there's an enhancement factor there. But
black holes do have another way that they glow, which

(37:04):
is very pointed. Oh yeah, what is that? Well, on
top of the accretion disc, they also sometimes create these
incredible jets of matter which fly out from the poles
of the black hole, both sort of north and south,
and these things are really extraordinary. So some black holes
don't have an increation disc, some of them do. It's glowing,
it's glowing in a sort of general direction, and some

(37:26):
of them are even more focused what you're saying, like,
somehow this accretion disk gathers things and shoots it in
one way, sort of like a like a tornado. Sort
of like a tornado. Some of these black holes have
these incredible things we call jets, which shoot out photons
and other kinds of matter, really really long jets, like
much larger than the black hole itself. For example, some

(37:48):
of these jets are like five thousand to a hundred
thousand light years long. Whoa, and so what do they
look like? They sort of look like a spotlight shining
out into the night skuy kind of, yeah, you can
you like a little dot from the quas are at
the core, and then you see these incredibly long rays
which shoot out into the interstellar medium. And because that

(38:08):
then hit stuff like gas and dust, they can create
these big shock waves. And so you can google a
picture of like astrophysical jets. But they look like these
incredible fireballs shooting out both sides of the black hole,
and they're much much bigger than the actual extent of
the black hole. One astronomer described as like seeing the
statue of Liberty popping out of a marble. Decide to

(38:32):
see but you're saying, we don't really understand how these
jets are formed, right, Like I imagine they're creating. This
is stuff kind of orbiting around the black hole, waiting
to fall into the black hole. So how does stuff
actually kind of pop out. It's all connected into this
question of how stuff falls into the black hole and
what happens. But we think that a lot of black
holes are not just curved regions of space time. They're

(38:53):
also spinning, and also they probably have electric charge, and
those are the three things that black holes can have
ass spin, and charge. And if a black hole has
electric charge and it's spinning, then it also has a
very very powerful magnetic field, and that magnetic field will
direct the path of particles just the same way that
the Earth's magnetic field changes how the solar wind hits

(39:15):
the Earth. Most of those particles don't end up coming
down and hitting us. They spiral around magnetic field lines
and go to the north pole or the south pole,
and that's what the northern lights are. In the same way,
this incredibly intense magnetic field of a black hole, some
of these particles, which otherwise might have fallen into the
black hole gets sort of like funneled up and shot
out the top or the bottom of the black hole. Interesting,

(39:39):
it's sort of channeled by this magnetic field. But I
guess the question is how does a black hole get
a charge? Like, does it because it absorbs more electrons
than than positive charges? Or how does it get a charge? Yeah,
we think that charge is conserved in the universe. And
so if you have a black hole that's neutral and
you toss an electron into it, that black hole now
has a charge, and you can't like tell where the

(40:00):
electron is inside the event horizon. All you can tell
is that the black hole itself is now charged. And
so any black hole which eats more positive than negative
particles will have a positive charge. And the same is
true for the opposite scenario. So somehow the black hole
ate more electrons then and then then post trons, And
we do have an asymmetry in our universe right. There

(40:20):
are a lot more electrons out there than positrons, and
stars and other matter have more electrons in them than positrons,
while they are also protons in there to balance things out.
The matter antimatter asymmetry the universe means that there are
lots of these charge particles sloating around for black holes
to gobble up. Interesting, that's true for the whole universe.
You're saying the whole universe has a negative charge. Well,

(40:41):
that's a really fun question. What is the charge of
the whole Is it positive, is it negative? Is it
an optimist, is it a pessimist. That's a really cool question.
I think that if charge has always been conserved, then
the universe must have the same charge it had early on,
And so if it came from like an in phloton
field or something that we've discussed recently, it probably has

(41:01):
an overall zero charge. But in the end those charges
break up into electrons and protons and other kinds of particles,
some of which might be more likely to be eaten
and by black holes. But they're also just there are
patches throughout the universe is not completely smooth, and so
in the same way that like black holes spin because
there's angular momentum. Even if the total spin of the

(41:22):
universe is zero, there are patches of it that's spin
left or spin right. In the same way there are
patches of the universe that have more matter or less matter.
There probably are patches of the universe that have like
more positive charge and more negative charge, and so black
holes end up accumulating some charge. Like the chances of
getting exactly zero charge if you have you know, ten
to the fifty particles is like the chances of flipping

(41:44):
a coin tend to the fifty times and getting exactly heads.
It's very unlikely. Yeah, it seems like it. So you're
if you're a black hole, you could be team positive
or team negative. There's two teams exactly probably very few
black holes like exactly on that knife's edge, and as
a result, they get very strong magnetic fields, right, and

(42:04):
so that's kind of the most intense way that a
black hole can glow, although it's technically not glowing. It's
just kind of redirecting and swirling and igniting the stuff
around it and then shooting it in one particular direction. Yeah,
and so these astrophysical jets are super fascinating and really
a source of research right now. People trying to use
them to understand what happens to a particle as it

(42:27):
falls into a spinning, electrically charged black hole, whether it
gets repelled by the magnetic field of the black hole,
or whether it gets sucked in all this kind of
stuff that must be pretty cool to think about and model.
All right, well, let's get into what happens if you
focus one of these jets on Earth. Is it good
news or bad news? And let's talk about our most
recent pictures of black holes. But first let's take another

(42:49):
quick break. All right, we're talking about glowing black holes,
and this is, I guess a pretty glowing reveal of
black holes. Would you say that we can black holes
five stars absolutely, or a million stars sometimes the trillion stars,

(43:13):
who knows. So sometimes they admit these intense jets, and
that's when they really shine in the sky, but they
can be sort of dangerous, right, like if black hole
suddenly focus its jet on us, we it might fry
us kind of right. Yes, these are very intense sources
of radiation. Fortunately none of them are shined at Earth
right now because they go really, really far. And the
black hole is the center of our galaxy, which is

(43:35):
like one that might be capable of creating very intense radiation.
We don't think that it has any of these jets.
It might have very small ones, but we're not sure.
We're going to try to take a picture of it soon. Well,
it's sort of sad that black holes are getting their
jet packs before humans are. But we we do have
sort of photos of black holes glowing like it's not
just something that we're posting or wondering about. We do

(43:57):
have a more recent pictures black holes, right, and you
can see them going. Yeah. Several years ago, they tied
together a bunch of radio telescopes around the world into
sort of like a huge meta telescope, and by taking
data together for about ten days, different parts of the Earth,
all working together, all pointed at the same black hole,

(44:17):
they were able to sort of tie those together into
a radio telescope effectively the size of the Earth. This
is called the event Horizon telescope. And they took data
for about ten days and then crunched it with their
computers for like two years. And in April two thousand nineteen,
they put out what was called the first direct image
of a black hole. And you might remember it. It It
looks sort of like a glowing donut. Yeah, So you

(44:40):
can google this and and image and do an image
starch where I guess what would you start for black
hole photo? Yeah, black hole photo. Absolutely, that pops right
up and so you can see you can see sort
of the dark circle in the middle of the glowing disk,
and it's sort of skewed though, right, It's it's not
like a perfectly round donut. It's sort of skewed one
in one direction. Yeah, it's like a crispy cream you're
of angling in at as you're about to take your

(45:02):
first bite, got kind of squished on one side. And
once you're looking at their the glow, of course, is
not from the actual black hole. You're not seeing hawking radiation.
You're seeing the glow of the accretion disk. And that
black hole is M eight seven. It's at the center
of a galaxy that's about fifty five million light years away,
but they chose it because it's incredibly powerful black hole.

(45:25):
There's like six point five billion solar masses inside of it. Wow,
six point five billion times the mass of our Sun.
And it's a fairly close enough for us to sort
of look at it. And so we have a picture
of its accretion disk, and there's sort of different theories
about what's going on there, that's right, And so the
first picture just sort of like give us the first glance,

(45:46):
and we saw the accretion disk, we saw the glow.
We confirmed what we thought you see the hole in
the center of it, which is the event horizon, and
that's about as big as we expected it to be.
It's really incredibly huge though, Like that event horizon is
larger than the radius of Pluto. Like that black hole
is a monster wow, meaning like you could sit in
inside of our solar system and it would basically take

(46:07):
take over the whole solar system. It would take over
the whole solar system exactly. And recently what they've done
is they've studied that data in more detail. They went
back and they reanalyze the data trying to get more
information about what's swirling around inside that acretion disk. Because
what they did at first, we just sort of like
look at the photons and gather them and say where
is it bright, where is it not that bright? And

(46:29):
that's the picture that you see is like an intensity
map essentially shows you where it's glowing hot and where
it's not glowing as much. What they did now is
they went back and they analyzed it to see how
those photons are polarized. Like photons when they move through
space can do so in various ways, like we sometimes
talk about how electrons have spin, spin up or spin down.
Photons also have spin, so they don't just fly through

(46:51):
space with energy. They can also spin in various ways
you might be familiar with, like sunglasses that filter out
polarized light, for example, and so like comes in sort
of different spins. And what they did is they looked
at the photons and counted how many spin in different ways,
because this tells you something really interesting about the magnetic
field inside that accretion disk, which affects how photons spin.

(47:14):
It's like you're you're looking at for extra information in
the light that they might tell you what's going on,
because we we don't understand it right exactly. It's like
you first had a black and white picture, and now
you're looking at the different colors, right, You're looking for
extra information, new dimensions to this. So they crunched the
same picture, the same data through their computers for another
two years, and now they have an updated photograph. And

(47:36):
this one looks quite different because it's still the acreation disc.
But you can see these stripes. You can see these
like twists, this spiral pattern that tells you sort of
where the magnetic field is in the accretion disk and
sort of what its intensity. Is interesting, like the whole
disc has a magnetic field or there's like variations in
the field all around their variations in the field, and

(47:58):
from the pattern of where the hootons are and how
they are polarized, you can get a sense for the
strength of the magnetic field and like how those magnetic
field lines look, which tells you a lot about how
things must be moving inside the accretion disk, because those
very intensive magnetic fields are sort of like funneling particles.
They're telling particles where they can and can't go. Interesting,

(48:18):
like you're looking at the texture of the accretion disk. Yeah,
and so there are two theories about what's going on there,
and they have pretty fun acronyms matt and sane. It's
either crazy black hole or or a reasonable black hole.
Reasonable black Yeah. People were wondering how this works, and
they developed these different models for how things in the
acretion disk gets sort of slurped up by the magnetic

(48:40):
fields and then shot into this helix which pushes them
out into this astrophysical jet. Like how do particles when
they fall in through the accretion disk, how do they
sort of miss falling into the black hole and end
up pumped out into this incredibly long death ray through space.
So first people thought like, mostly it's just sort of
crazy and turbulent that you don't have really intense magnetic fields,

(49:02):
but that stuff just sort of like falls into the
center and the accretion disc sort of controls the helix.
That it's an angular momentum is sort of what's driving
the spinning of everything, and that the helix sort of
forms eventually from that spin. That was the model they
call sane stable and normal evolution s a n E.
And then there was a competing model they call MAD

(49:23):
for magnetically arrested disk. This is a model for what
happens if you like really crank up the magnetic fields,
like really strong, powerful magnetic fields, so that they're sort
of in control. And what happens there is that you
expect like coherent channels of particles. You expect like tubes
of particles being funneled by this magnetic field really quickly

(49:45):
wrapping up into a very powerful helix. And it also
predicts more polarized light because of these strong magnetic fields. Interesting,
it's like we know that there's an acreation disk, but
we don't know what's kind of dominating the way it works.
It's gravity, is it magnetic fields? And it sounds like
it's mostly magnetic fields or or at least they play
a huge part that we didn't think about before. Yeah,

(50:06):
and so this updated picture that shows us the polarization
of the photons, it helps us determine which of these
two models is accurate. And so the data supports that
black holes are mad rather than sane, that they have
really intense magnetic fields, and that that's what's creating this helix,
and that's what pulling the particles out of the increation
disk and then into this jet that reaches out through space.

(50:27):
But what do you think make the mad of not
getting enough attention? It's because they got overcharged. Nice, they
stop being positive. Exactly. You eat too many electrons and
you end up feeling kind of negative. Yeah, they had
a negative experience, for sure. Now they're mad. They lost
their sanity. There you go, exactly. And so it's it's

(50:50):
cool because it's the first time we've really seen something
about the dynamics of the increation disk. Before we saw
sort of like a static image like Okay, it's there,
it's a blob, we know the shape. That's cool. Now
we're seeing sort of like how it's moving with the
energy flow is inside of it, which really helps us
build a picture for how the matter is flowing in
and how it's getting ejected. Yeah, pretty cool. And I
guess what's interesting is that we are getting these sort

(51:12):
of you know, more accurate, more interesting pictures about what's
going on outside of a black hole, Like we're getting
closer and closer to the actual black hole itself and
kind of maybe looking at what's going on in it. Yeah,
we'll be pushing up harder and harder against that envelope
of the event horizon. The more information we can gather
about what happens very close to the black hole, the
more it helps us refine our models for what's going

(51:33):
on inside the black hole. People talk a lot about
science being testable and falsifiable, right, but even if we
can't ever see what's inside a black hole, we might
be able to develop a pretty strong theory for what's
going on based on its impacts on the outside. If
we can build a theory which very accurately predicts what's
going on outside black holes, or predicts what happens in

(51:54):
areas we haven't seen yet, we could still test it
outside the black hole. And draw conclusions about what might
be going on inside. Wow, pretty cool. And what's amazing
is that we can do that from all the way
out here, right, Like we are along distance away from
this black hole. It's not like you can see it
in the night sky. It's like it's hidden inside of
a whole galaxy even right exactly, And each galaxy itself

(52:16):
is quite faint, right, this one is really really far away.
It's much further away than Andromeda. So it's in the
nice guy. It's just like a fuzzy little dot. But
these radio telescopes are very powerful, and so using a
huge telescope sort of like get pictures with slightly different angles,
and then we can figure out something about the dynamics
of what's going on the heart of that galaxy. And

(52:36):
we can study that galaxy better than we can study
the center of our own galaxy, right because I guess
there there aren't that many stars kind of block into view.
Is that where is that? What's going on? Two things
are happening there. One is that the galaxy is sort
of oriented in such a way that we can see
it's heart, whereas in the milky Way, we're like right
in the middle of it, and there's a lot of
gas and dust between us and the center of our

(52:57):
galaxy and other stars. As you say, the other thing
is that this thing is a monster compared to our
black hole, so it's much bigger and it's glowing very
very brightly, whereas our black hole in the center of
the Milky Way. Sagittarius a star is not as big.
I mean, it's quite impressive, but if we don't think
it's a quaisar, and they might or might not have
sort of faint astrophysical jets for us to study, but

(53:19):
we'll know soon. Because the same group is hoping to
point their ritual event horizon telescope at the center of
our galaxy and try to take a picture of Sagittarius
a Star. Well, they've been pointing at it all this time,
and it's it's just that the images from this larger
black hole were sort of easier or radio sooner, right, Yeah, Well,
they need dedicated time on these radio telescopes, which are
of course, you know, of interest for lots of other

(53:40):
things like searching for intelligent life and looking for exoplanets
and whatever. So you need dedicated, coordinated time on all
of these telescopes. In order to gather this data. So
if you've ever wonder what a black hole looks like
or want to see what it looks like just looking
up on the internet black hole photo. Although we think
it's a black hole, right, we talked last time about
how it could just be maybe a really a dark
star or a neutron star. Right, Yeah, we don't actually know.

(54:03):
All of this information is indirect. Most of the evidence
is it's something, it's very massive, it's very small, and
black hole is the only thing we think that fit
the bill. Though there are some folks out there coming
up with other crazy ideas, like dark stars which are
powered by quantum mechanics and not actually having event horizon.
So maybe one day we'll just have to get closer

(54:24):
so we can see one of these things with our
own eyes. Yeah, it could be like a gray hole.
We talked about that last time. Yeah, So another awesome
reminder of how mysterious the universe is, but also how
discoverable it is if we can eventually get pictures of
it and maybe even figure out what's going on inside
of the texture of the black hole itself, and how
physics and math can really guide is to an understanding

(54:46):
of the craziest corners of the universe, so that even
things like black holes and astrophysical jets can start to
make sense to you and to me. Physics and math,
how would you combine those two words? And fast fath
fast math mimsis mrs me, that's the one. I'm a methodist, yours?
Are you a mystic? Is that what you're saying. I'm

(55:08):
a mythical feature, I'm a mythical figure, you're mathematical mystical
most on his cosmic quest for understanding the contextual clues
of the cosmos. Yeah. Well, we hope they gave you
a lot to think about and we hope you enjoyed that.
Thanks for joining us, See you next time. Thanks for listening,

(55:32):
and remember that Daniel and Jorge explained the universe is
a production of I Heart Radio. For more podcast for
my heart Radio, visit the I heart Radio app, Apple Podcasts,
or wherever you listen to your favorite shows. Ye