What is a black hole eclipse?

Daniel and Jorge talk about whether black holes can be blocked or can block other objects.

See omnystudio.com/listener for privacy information.

Episode Transcript

Speaker 1 (00:08):
Hey or hey, are you a fan of Pokemon cards? Yeah,
a little bit. My son used to play them. My
son also, though I think he mostly collected and traded them.
I don't think he ever actually played with them. M Yeah,
I think that happens a lot, although I did play
with him for a few times. It's a pretty interesting game.
And do you have any of those cards with like
super awesome powers? Yeah? They have pretty good names, like

(00:29):
flame body. My personal favorite is the card that can
do a black hole eclipse. Although that sounds kind of
like a random combination of words from physics that they
just kind of put together. I think that's the same
way that physicist name things though. Ah, so you admitted
it's all random. We just type the words into an

(00:49):
online random number generator and that's where we go with.
They have a bunch of physicists working for Pokemon, just
in case that the whole physics scurity doesn't work out.
Do you have a promising career working for That's always
been my backup plane. Hi am Poor Hamming, cartoonist and

(01:18):
the co author of Frequently Asked Questions about the Universe. Hi.
I'm Daniel. I'm a particle physicist and a professor at
UC Irvine, and I probably have hundreds of dollars worth
of Pokemon cards somewhere in the closets of my home.
Are they wrapped an individual plastic though, to keep him
in mint condition? Otherwise I'm not sure they're worth that much.

(01:38):
They have definitely been prepared as an investment in the future.
That's how you plan to pay for your son's college education.
I think that's how my son plans to pay for
his retirement. Yeah. Wow, if it's worth that much, maybe
they should conveniently disappear from your closet. Only if I
could find them in my son's closet. I think that's
part of his security plan. Yes, it's such a mess,
it's like a black hole in itself, but anyway is

(02:00):
Welcome to our podcast Daniel and Jorge Explain the Universe,
a production of I Heart Radio in which we try
to clean up a mess that is this universe and
all of its crazy, confusing glory. We dig right into
everything that doesn't make sense, everything that should make sense,
and things that might never make sense. We talked about
the biggest questions at the heart of philosophical inquiries about

(02:21):
the nature of our universe, and we talk about practical
stuff like how things around you actually work. We dive
into all of these questions and try to explain to
you what scientists do and do not know about them
because it is a pretty fun universe full of interesting
and amazing characters, not all of them with superpowers like
Pokemon characters, but there are a lot of interesting objects

(02:42):
out there in the universe with the seemingly superpowerful powers.
And it is our belief, or at least our hope,
that the universe does make sense, that it's following some
set of rules, and that if we dig into it
hard enough, if we use our brains, if we come
up with a clever set of experiments, we can figure
out what those rules are. That in the end, there
isn't magic in the universe, but that everything can be

(03:04):
explained with science. I'm not sure the same can be
said about Pokemon powers. What are you saying that Pokemon
aren't physically accurate there? How do you know, Daniel, I'm
not sure we have to suspend disbelief. But I did
do a bit of research into what the black hole
eclipse move is for the Pokemon character, and here's the
official description. The user gathers dark energy with its Z

(03:28):
power and forms a black hole that sucks the opponent up. Interesting.
That seems like a bit of a dangerous weapon there,
because once you start the black hole, I guess, can
you turn it off? Or is there a Z switch
for it? It depends on what your Z power can do.
If you can tap into dark energy and expand or
contract space, then hey, you have got a lot of options. Well,

(03:50):
there is the idea that maybe there are unknown forces
in the universe we haven't discovered. Maybe the Z force
is one of them. And if I discovered an unknown
force and called it the Z force, would you be
impress with my naming? I guess I mean to try
out any of the other letters in the alphabet first.
The Z force makes me think it's related to the
Z boson, which we know is a very feeble boson.

(04:10):
It carries the weak force, probably not capable of making
black holes. So there is technically a Z force in
the universe right now, like the force made by a
Z boson is technically a Z force. Yeah, that's right,
though I'm not sure you can use it to gather
any dark energy and throw your opponent into a black hole.
But hey, best to luck to you. How do you know, Daniel,

(04:32):
have you tried? I haven't tried, but I'm going to
write a grand proposal to the Pokemon Science Foundation to
see if I can get some funds to try it out. Yeah,
the PSF, they fund a lot of work out here.
But technically, in a multiverse, isn't it possible that there
are Pokemon characters out there? I mean, if you say
in a multiverse, isn't it possible that I suppose almost
anything is possible because in some theories of the multiverse

(04:54):
there are universes with other laws of physics, which basically
allows almost anything to happen. Oh, there you go, It's official.
Here in the podcast, Daniel thinks Pokemon are real. They
are a really good investment in my son's feature and
a real possibility. But it is interesting. How did you
end up googling Pokemon powers online? What's going on there? Daniel? No,

(05:17):
I was googling black hole eclipse, of course, in preparation
for today's episode. And the top hit was not black
holes or eclipses or anything scientific. The top like ten
hits were all about Pokemon. I think that tells you
a little bit about the priority of the Internet. But
it is interesting. What do you think is going on
inside the head of those Pokemon creators, artists and writers

(05:37):
when they come up with these things, Right, because they
used to work dark energy, they must know a little
bit of something about physics. Well, you know, I think
as they make more and more Pokemon characters, that have
to be more and more powerful or as my son
would say, totally opie, and so they want to come
up with something really dramatics and they're really crazy. And
I guess black holes are on the top of the
list of like aspirational powers to whether you can make

(06:00):
a black hole using dark energy. You know, we don't
really know what dark energy is at all. We just
know that it's accelerating the expansion of space and separating
the black holes from each other. So if anything, it's
keeping black holes from getting bigger. Well, I guess my
question is what kind of energy car does that attack us?
Dark energy cars? Is there such a thing? If there

(06:21):
isn't such a thing, then there should be Pokemon Science Foundation,
please fund that. There should be a science type Pokemon.
You know, there's like a water type, fire type. There
should be like a physics type. We have exhausted my
knowledge of Pokemon. Now I have nothing else to contribute
to this conversation. I went a little opie on you
all overpowered you. But it is an interesting name to

(06:42):
give a power to a fictional character. But it kind
of makes you think, is it actually possible for something
like that to happen? And we know that crazy things
happen out there in the universe. We are constantly surprised
by what's going on in the hearts of other galaxies
and even in between galaxies, and so you should never
say never, and so do they. On the podcast, we'll
be asking the question can a black hole be eclipsed?

(07:11):
And can you use it to suck up your enemies?
Is the question that a lot of kids are probably asking,
and maybe some physicists. Please, if you do have the
z power to manipulate dark energy to create black holes,
don't do it. You might win the battle and then
destroy the planet. Although they'll give you a Nobel prize, though,
wouldn't they in the five minutes between the creation of

(07:31):
your black hole and the destruction of the Earth. I'm
not sure the Swedish Academy acts that fast. I don't know.
I've seen you talk, Daniel, you will sacrifice anything for science.
If you have such a Z power, create a black
hole out in the depths of space where we can
study it. Please. I guess if you have that kind
of power, you can afford to go out into space. Right.
Maybe you also have the ex power and the why power?
Right right? Although I thought the why power was physicist

(07:53):
superpower or is that the philosophers? It's the four year
olds power? Why? Why? Why? Why? Yes, it's an interminable
source of energy. But it is an interesting question, and
as usual, we were wondering how many people out there
had thought about this question whether a black hole can
be eclipsed. So thanks very much to everybody who volunteers
to answer these questions in advance. Were very grateful to you,

(08:15):
and we hope that you enjoy hearing your voice on
the podcast. If any of you out there would like
to participate, please don't be shy. Right to me two
questions at Daniel and Jorne dot com. So think about
it for a second. Do you think a black hole
can be eclipsed? Here's what people had to say. Assuming
the definition of eclipse is for one body to obscure

(08:37):
another body from a given a vantage point. Um sure,
I don't see why a black hole could not be
eclipsed by another celestial body. I thought that might be
how we discovered them or something. I guess a black
hole can be eclipsed. I mean normally in eclipse is
when the light from something is blocked by something else

(08:58):
in space. So as a black hole doesn't have any
light emitting from it, I wouldn't have thought it could
be eclipsed as such. But I guess if you get
something massive enough in front of it, in between us
and it, then it would be eclipsed. I don't see
why not. As long as something subjectively larger than them
is between them and the observer, it would eclipse. The

(09:22):
black hole might have to be subjectively larger than the
disc around it to really have a shot at it. Well,
the concept of eclipse, the way I understand it, is
that light from a star as blocked from Earth's view
by an intervening body. Certain's black holes do not emit light.

(09:44):
I don't think they can be eclipsed. I don't think
so because I believe when black holes mass passes before
a gravity you see lensing effects. And I don't know
I've ever heard of one being eclipsed before. Yes, I
think they can do if they're is a planet or
star closer to us in the right alignment with the

(10:06):
black hole. Yes, I think they can be eclipsed. Yes,
I think it can in the sense that is coming
in front of something else. Um. But like instead of
blocking the light like the moon we block the Sun's light,
I think it would just absorb the light of whatever
is behind it. But um, it could also have this
gravitational lensing effect where the light of the objects that

(10:27):
aren't directly behind it kind of get curved um due
to the black hole, and we perceive it um in
that way. So that's kind of the black hole version
of an eclipse. Yes, they can be eclips Let's say
instead of our son, it will be a black hole
like we heard at a podcast Danielle and Horhan. We

(10:49):
would need to be at a safe distance from it,
and we can safely go around it. And if we
have the moon that would be between us and the
that hole. I don't see why not the more collectives
the site of the black hole. All right, A wide
range of answers here. Somebody said, why not always a

(11:10):
good answer? Am I talking about physics of the universe.
Why not, there's the multiverse, Doctor Strange says, anything can
happen in the multiverse. Or do you think they were
taking it as a proposal, like, hey, should we make
a black hole eclipse? Why not? Let's go right now.
I'm up for it. I guess it made me think,
what do you mean by eclipse, like in terms of
attention or in terms of blocking its light? But it's

(11:34):
a black hole. Yeah, it's a good question. And I
noticed that there was like two different interpretations of eclipse there,
one the black hole being eclipsed like something blocking light
from a black hole, and the other the black hole
doing the eclipsing, like passing in front of something else
that makes light. So there's sort of two possibilities there. Interesting,

(11:54):
and I guess we're going to argue about which one
is more correct. For the next hour, we're going to
talk about both possibility. At least. Of course, we're gonna
do the quantum superposition. We're gonna do the forwards and
the backwards. All right, Well, let's start with the basics here, Daniel,
What is a black hole? First of all, so we
don't really know what a black hole is in the
actual universe, and we don't actually even really know if

(12:15):
black holes exist. As described by the theory, we have
this concept in general relativity that if you get enough
stuff together, it's gravity will overcome any sort of internal strength,
any power of the material to resist being compressed. The
gravity will eventually get so strong that it will just
squeeze it down further and further and further, and as

(12:36):
it gets denser and denser, and the gravity gets stronger
and stronger, and you get this crazy runaway effect, and
where gravity essentially becomes infinitely strong in a tiny little dot,
this singularity at the point in space where you have
not infinite mass but infinite density, because gravity is compressed
some blob of stuff down to a very very small distance,

(12:57):
and because it's compressed it so far and means that
you can get pretty close to a lot of mass,
which means the gravity even nearby it would be very strong,
so strong that we think that it curves space so
much that light cannot even escape it. So if these
things are real, if they're out there in the universe,
then whatever falls into this black hole you will never
see again because light from it cannot escape. Would you

(13:20):
say it's an actual hole in space, Daniel. And you know,
if you define a hole is something that you can
fall into, then it's technically it is. That's why it's
called a whole. Right, if you accept the general relativity
view of it, it's kind of a hole because it
makes a portion of space that's cut off from the
rest of the universe. It's like a little sub universe,
and once you enter that sub universe, you really are

(13:41):
cut off from the rest of it. I mean inside
the black hole, you can still see the rest of
the universe. Light from the rest of the universe can
still reach you, so you can see out from it,
but nobody can see into it, right, So in that sense,
it's a hole in space, right, Although that's assuming your
eyeball is still in one piece when you're inside of
a black hole, right, Yeah, precisely, assuming that you survive

(14:02):
long enough to look out into the black hole. And
black holes can come in all sorts of sizes. You
can make a black hole in theory out of a
pretty small amount of mass as long as you squeeze
it down to a small enough radius. You can also
make black holes out of enormous masses. Some of the
things out there that we think are black holes probably
have millions or billion times the mass of our sun.

(14:24):
Those black holes are really really big, and if you
fall into one of those, the gravity at the outskirts
of the black hole is not actually that strong. I mean,
it's strong enough to suck up light, but it's not
so strong to like tear you apart to spaghettify you.
So you might be able to survive the very first
few moments of falling into a really really big black hole,

(14:44):
and then you can take it selfie, although you can
never send that selfie to anyone. Hey, selfies are just
for yourself, right, that's why they're called selfie. Ironically, that
is the opposite purpose of a selfie. They should be
called that everyone else's. But it is interesting what you
said about the black holes having a size, because it's
it's kind of into it's like a hole in space,
but it does have volume, right, Like, it does occupy

(15:07):
three dimensional space. In fact, it's a sphere in space, right,
I mean, it's just kind of distort space, but it
does sort of occupy a certain you know, length, width
and in height. Yeah, if you say black hole, you're
probably imagining like a circle on the ground a two
dimensional object that things can fall into and disappear, like
in cartoon shows. But as you say, they are three

(15:27):
dimensional objects. So the simplest black hole, one that isn't spinning,
would be a perfect sphere, and you can fall into
it from any direction. If you're looking at a perfect
sphere that's perfectly black, it's always just gonna look like
a circle to you because there's no texture to it,
so you can't sort of like tell how much curvature
it has. But actually, if you look at a black hole,
you don't even really just see a black sphere. It

(15:51):
looks even bigger than it actually is because the paths
of light around the black hole are really really weird.
Like if somebody was very close to the edge of
the black hole on the back side of it and
turned on a flashlight, you could see it from the
other side of the black hole because the light from
that flashlight would curve around the black hole, bent by
its incredible gravity to your eyeballs. So if you're near

(16:11):
a black hole, if you're just looking at it, you
can actually see the entire surface of the black hole
right in front of you. You can see the front
and the back right though it just looks black, right, Yeah,
it just looks like a bigger black circle than it
actually is. It's like puffed up, yeah, like puffed up
because in the vicinity of a black hole, space is curved,
and when space is curved, you can't trust your eyes

(16:33):
to be just showing you what he's there. You're seeing
now an image of what is there, and then image
can be distorted, just like if you're in a fun
house mirror and it's not flat and what you're seeing
isn't reality the same as true. Near a black hole,
light doesn't travel in straight lines anymore, and so what
you see is an image is generated by the physical
stuff that's there, but it's not a fully faithful image

(16:55):
of what's actually out there. It's a little bit mind
bending because a black hole is sort of like a sphere.
It sort of has the surface, but it's not really
a surface because it's not solid. It's just kind of
like the edge of the hole. So it's like a
three dimensional edge of a hole is the surface of
a black hole. Yeah, And what you call the edge
of a black hole is a little bit arbitrary. We
usually use the location of the event horizon, the point

(17:16):
past which light and particles and nothing can escape, and
to mark the edge of the black hole. But there's
nothing there at the edge. It's sort of like a
calculation we do to say where it is, and you
can't actually even tell where the event horizon is until
the end of the universe. The definition of the event
horizon is any particle past this point never escapes. But

(17:38):
it's not always easy to tell exactly what can escape
and what can't, and so you can't actually know in
any moment where the event horizon is. You have to
sort of like wait to the end of time and
then say, particles that got closer than this, none of
them escaped. So here was the event horizon, right, because
we actually like fall into the hole that sort of
almost sort of never happens, right, because time gets distorted

(18:00):
around the black hole that it basically as you said,
happens never. Yeah. And also there's just like nothing there
at the event horizon. It's not like a surface you
land on. It's just a point of no return. It's
like if you got into your car and you drove
too far away from a gas station so that you
didn't have enough gas to get to the next gas station.
Nothing would happen at that moment when you had gone
too far. You would only realize it later, like, oops,

(18:21):
we forgot to get gas and now we're stranded. The
moment when you crossed that threshold where you now too
far away from the nearest gas station you don't have
enough fuel to get one, no warning light necessarily goes off.
And the same is true for the event horizon. It
just feels like the rest of space. You pass through it,
and unbeknownst to you, you are now wrapped inside the
black hole. Right, Although you know, if you're flying that

(18:43):
close to a black hole, you can't claim not to
have seen it because it's going to look pretty big
to flying close to a black hole. Right. Oh yeah,
it's definitely irresponsible space flight in the same way like
you should know if you're about to run out of gas,
and somebody should be paying attention to it, or at
least there should be a warning alarm on your space ship.
Black hole ahead, turn right, use your Z powers now.

(19:05):
But as you said, it doesn't occupy space because it
is an object. It doesn't have less solid surface, and
it's also like moving around in space, right, black holes
can move around in space. Even though their holes in space,
they can move around in space. It's like a moving hole. Yeah,
well they are a thing, right, They are made out
of mass, and so like everything else, they have a location,
and then they can have a velocity. But you know,

(19:27):
the velocity of the black hole is relative, just like
everything else. If you are moving towards a black hole,
you could also say the black hole is moving towards you.
There is no difference in the physics of the universe
in those two pictures, and so black holes, like everything else,
can have location and velocity. Yeah, there could be one
moving towards us right now, right almost definitely, because we

(19:47):
know that there's a supermassive black hole at the heart
of the Andromeda Galaxy which is coming for us. Right
The Andromeda Galaxy is going to collide with the Milky
Way in a few billion years, and so the black
holes at the heart of each galaxy are moving towards
the other galaxy. So, yeah, black holes are headed our way.
Better get working on that Z force, Daniel. We're counting
on you. I only have the P force, the physics force.

(20:09):
Other people have to work on the Z force, or
it could be the W force. For whites and there
you go. I guess the the Andromeda black hole. That's
something we don't want to catch alther if you find
a good container for it. I guess, yeah, maybe you do.
All right, well, let's talk about whether or not a
black hole can be involved in an eclipse, whether it
can eclipse other things, or whether you can eclipse a
black hole. But first let's take a quick break. All right,

(20:45):
we're talking about the physics of Pokemon, right, that's the
title of the episode. That's right, Pokemon characters use physics
on each other. I feel like that would be a
pretty viral title to put on this episode. What do
you think, physics of Pokemon? It might be viral. It
would also be totally misleading, but I guess that's how
everything goes viral. But we could do a whole episode
on this, right, just pick a bunch of Pokemon cars

(21:06):
and we'll break down the physics of their superpowers. Yeah,
le's good like this. Yeah that's totally made up. Yeah
that doesn't where Yeah that's ridiculous, But could it happened?
Aren't there books about the physics of Star Trek and
Star Wars in a multiverse where Pokemon is real, But
we are talking about the powers of one specific Pokemon.
Which Pokemon has this power? Daniel did, did you look
up the name? Well, according to my research, it says

(21:28):
any non mega evolved non primal Pokemon can use black
hole eclipse if it knows a damaging dark type move
and holds darkinium z and if it's trainer where's a
z ring? So if that made sense to you, please
explain it to me. Well, that's a lot of preconditions there,
so any Pokemon that checks those boxes can use it. Yeah,

(21:51):
apparently any non mega evolved non primal Pokemon. I don't
know if there's a lot of them or just one.
We we should you should have interviewed an expert. But anyways,
we're asking the question of whether or not you can
actually eclipse a black hole or I guess involved a
black hole in an eclipse. And you said, Daniels, there's
two possibilities here. You can either eclipse a black hole

(22:12):
or have the black hole eclipse something else. And so
I guess, first of all, Daniel, what's the legal definition
of an eclipse? So an eclipse is a fun astronomical
situation where two things fall along the same line, your
line of sight. So you're looking out into the universe
and you can imagine a line between your eyeball and
some object. If something else passes along that line, then

(22:34):
it has eclipsed whatever you were looking at. So if
you're looking at the Sun not recommended, and the Moon
passes in front of it, then that's a solar eclipse. Right.
The moon is eclipsing the Sun because it's passing along
the line between your eyeball and the Sun. Interesting, so
if a technically, if I put my thumb in front
of me and block out the Sun, I'm creating a

(22:55):
solar eclipse. That's what you're saying. Yeah, I mean your
thumb is not an astronomical object. Have you seen my sun?
It's pretty stiller. It's been a while, So assuming you've
upgraded it with your Z powers, than maybe or his
them can perform in eclipse. One of my favorite things
though about solar eclipses is that they're possible. Right, Like,
the moon can block the Sun in the sky, which

(23:19):
requires not just that the Moon goes in front of
the Sun, but that the Moon is the same size
or bigger than the Sun in the sky. The amazing
thing is that the Moon and the Sun are just
about the same size in our sky, like they can
eclipse each other just about, which is a total cosmic coincidence.
The Moon could have been bigger, or it could have
been further, or it could have been closer. They don't

(23:41):
have to be the same apparent size in the sky,
and yet they are. Yeah, that's a pretty wild coincidence.
Although it is also a function of where we are
right now, right, because eventually the Moon is going to
move further away from Earth and so it will look
smaller than the Sun. Yeah, exactly, it gets smaller and
smaller every year, and before like it maybe increased or
times or millions of years ago, the moon looked bigger

(24:02):
than the Sun during a solar eclipse. Yeah, And the
Sun is also growing in size as it gets older, right,
and pushing out more of its layers further and further.
So the Sun is getting bigger and the Moon is
getting smaller. And it's a really valuable lesson about coincidences.
You know, sometimes we see coincidences out there in the
universe and we go, oh, there must be an explanation
for that, and can't be by chance, But sometimes it is, right.

(24:25):
We don't think there's a reason that the Moon and
the Sun happened to appear to be the same size
in our sky, but it seems like a huge coincidence.
But sometimes they just happen. Yeah, And I guess the
coincidence is that they're almost the same size and from
our point of view and the sky. But it's sort
of not a coincidence that it just happens to fly
in front of the Sun, right, because the Moon is,

(24:46):
you know, spinning around Earth all the time, and we're
spinning around the Sun all the time, and so technically
the Moon kind of sits everywhere at any point in
the sky at some point eventually, right, So it's not
a coincidence that it just happens to line front of
the Sun, that's right. And most of the things in
the Solar System are in the same plane, and so
it's possible for them to line up. If the Moon,

(25:07):
for example, was orbiting the Earth outside the plane of
the Earth's orbit, it would be much harder for it
to eclipse the Sun. But because it moves around in
the same plane than it gets itself between the Earth
and the Sun, and of course it doesn't eclipse the
entire Earth. The Moon casts a shadow on the Earth,
and that shadow moves across the surface of the Earth.
When you're in that shadow, then you can see the eclipse.

(25:29):
And at the same time, there are people who are
not in that shadow who can still see the Sun
sort of around the side of the moon because they
have a different angle. I saw the total eclips back
in two thousand eighteen. Was it? It was pretty awesome event. Yeah,
And there's another one coming up in a in a
year or two. Right. There are a bunch of eclipses
all around the world the next few years, and if
you have the opportunity to see them, I totally encourage you.

(25:50):
Even though it has no deep astronomical significance, is just
sort of like a cool event. It makes you feel
connected to people who have seen these things since prehistoric
times and looked up and wondered, like, WHOA, something is
different about the sky today. I wonder what that means. Yeah,
just like I feel connected to my thumb whenever I
put it in front of the sun. Are there times
you don't feel connected to your thumb. That's what we

(26:12):
should worry about. Sometimes I feel like the thumb is
like we're not connecting into a deep level. You know,
you and your thumb needs to go to therapy. It
sounds like work out these issues. Yeah, yeah, do you
know anyone Maybe there's a good podcast for that. Maybe
I can point you to one I could point off
with my index finger isn't talking to me either, so

(26:33):
there's always a surprise in the podcast. This is the
direction I never would have guessed. Yeah, but it's interesting.
So what do you call a solar eclipse? Is when
something blocks your view of it? Right, Like, you can
also have a moon eclipse, right, the lunar eclipse, Yeah,
that's right. That's when the Earth gets between the Sun
and the Moon, and so the Moon is then blocked

(26:54):
from the Sun by the Earth, and so you can
still see the Moon, but it's sort of like shaded.
It turns a funny color because it's no longer getting
as much direct sunlight because it's in the Earth's shadow.
So basically, eclipses are like when somebody gets into somebody
else's shadow, right, or I guess technically a lunar eclipse
is like an earth eclipse if you were standing on
the moon. Yeah, although if you were in the moon

(27:14):
you would probably call that is solar eclipse, right, because
the Sun would be getting eclipsed. Are you saying it's
all relative, Daniel, It's all relative and the names are
not consistent. That's exactly the lesson of the podcast, all right.
And so it's interesting that you can you can block
out the light from the Sun, but that applies also
to any star, right, Like, you can have eclipses out

(27:35):
there in space with any star, not just our sun.
That's right. Stars out there have their own planets, and
those planets have moons, and so on those planets there
are eclipses happening. Those planets. Moons are blocking that Sun's
light and creating shadows which crawl along the surface of
those planets around other stars, and maybe aliens are looking
up at those and being impressed by the astronomical display.

(27:58):
But we can actually see those eclipses as well, because
sometimes those planets pass in front of their star, blocking
a little bit of the light from that star. So
instead of making a line from your eyeball to our sun, now,
imagine a line from your eyeball to some star far
far away, millions or billions of miles away, and a
planet can pass along that line. Now, because you're so

(28:21):
far away. The planet can't hope to block the entire star,
but what it can do is dim it a tiny
little bit. And that's actually one way that we discover
planets around other stars. We see them making these sort
of many or partial eclipses of their star. Yeah, it's
one way we can detect a planet and other stars.

(28:42):
And in fact, you sort of look for its stars
that twinkle a little bit periodically, right with a constant beat,
and that kind of tells you, hey, maybe it has
a planet swinging around it. Yeah. You study the brightness
of the star and you notice a dimming and it
dims periodically. So it dims for like a few days,
and then it gets bright again for a fixed amount
of days, and then dims again, and it happens periodically,

(29:02):
and that's how you can tell that something is going
in front of it and blocking it, because otherwise stars
can just twinkle and dust clouds can interfere with your observation.
But if it's something regular, then you know that it's
probably something orbiting near the star that's moving around it.
And so it's a really powerful way to discover these
other planets and also to measure their size because the

(29:23):
more dimming you get the bigger the planet is, and
these are always tiny little eclipses. You need really sensitive
telescopes to even notice that these things are dimming. You
could never see this with a naked eye, right, And
so if you see a star out there dimming and
being eclipse regularly, it might be a planet in its orbit.
But it's kind of interesting also to think about that.
You know, there are probably eclips is happening all the

(29:45):
time with all the stars out there, right, Like maybe
even asteroid flies near us, or it gets in our
way between us and another star. Technically that's an eclipse too. Yeah,
that's probably true, And there are eclips is happening that
we can't see, right this technique of seeing these planets
and we're lo eyes on the planet lining up with
our line of sight to that star. There are plenty
of planets out there around stars that are just not

(30:06):
aligned with us. Like we talked about how in our
Solar system, the Moon and the Earth and the Sun
of mostly aligned in the disc of the Solar system.
But the disc of our Solar system is not the
same as the disc of other solar systems. Those are
mostly random. I mean every solar system has its own
disc and the planets mostly follow that disc, but the
arrangement of our disc relative to other Solar System discs

(30:28):
is kind of random, which means that most stars, when
their planets passes in front of them, don't cause an
eclipse that we can see. All right, Well, we're talking
about whether or not you can involve a black hole
in an eclipse, and so Daniel, can can you eclipse
a black hole? Or can a black hole eclipse something else? Yeah,
it's a really fun question. Let's first talk about whether
you can eclipse a black hole. And the very question

(30:49):
is like, well, could you see a black hole anyway? Right? Like, technically,
what does it mean to see a black hole? Like,
even if there was nothing between you and the black hole,
are you actually seeing a hole? Like the whole it
was the absence of something, right, Exactly. A shadow can't
cast a shadow, right in the case of an eclipse
on the Earth, the moon is casting a shadow on
the Earth. But a black hole doesn't give off anything

(31:11):
to create a shadow. And so technically a pure classical
general relativity black hole is completely black. You saw it
out in the middle of space, you would not see
it doesn't give off any light. The only way you
could see it is if it was in front of
something else that was bright. It was like passing in
front of a star and eclipsing it. So a classical
black hole doesn't give off any light. Something could technically

(31:34):
block your view of the black hole, right, Like if
a planet happened to fly between you and the black hole,
you wouldn't see the black hole anymore? Would you call
that an eclipse? That sounds like a legal decision? Mean
the black hole not giving off any light than is
it being eclipsed? Right, And let's say behind the black
hole isn't like a galaxy or something bright or a

(31:55):
cloud of a bright cloud of gas or something, so
you can actually without the planet blocking, you would see
the black hole. But now there's a planet between you
and the black hole, so you don't see the black hole.
And technically it would sort of look like an eclipse, right,
It would be like a black circle getting blocked by
something maybe brighter. Yeah, that's technically possible. But we do
think that black holes do give off a little bit

(32:17):
of radiation in some cases, and the black holes create
an environment that gives off a lot of radiation, a
lot of light. So if you move away from just
like the classical general relativity pure black sphere and talk
about like the quantum version of it, or if you
talk about the stuff around the black hole, in the
environment created by the black hole, then that could be eclipsed, right,

(32:38):
because what stuff falls into the black hole, it tends
to get sped up so fast that it actually burns up.
And then that's right right. So things when they come
near the black hole, they don't always fall right in.
I mean, if your head is straight for the black hole,
you're going into the black hole. But if you sort
of go near the black hole, then you get bent
towards it and you sort of spin around it for
a long time before falling in. And so that's all

(33:00):
the accretion disc. It's like stuff that's on deck to
be sucked into the black hole. And while you're in
the accretion disk, the black hole is still working you.
It's got these tidal forces. It's pulling on the part
that's closer to you harder than the part that's further
from you, because gravity is stronger for closer things, and
so big clouds of gas and dust that are about
to fall into the black hole have a lot of

(33:20):
internal friction because of the black holes tidal forces, so
they get heated up incredibly hot and admit a lot
of radiation, and some stuff almost falls into the black hole,
but the strong magnetic fields like guided around the black
hole and it gets spun out at the top of
the black hole, making these enormous jets of radiation. So
black holes, even though themselves past the event horizon are black,

(33:43):
the stuff around them could actually be very, very bright.
These things quasars are some of the brightest things in
the universe. Yeah, we've had episodes about that. Now. It's
kind of ironic, right that some of the brightest things
in the universe actually come from black holes. Yeah, because
they are the source of a lot of gravitational energy,
so they can speed stuff up, they can focus stuff,
they can shoot stuff in another direction, even though you know,

(34:05):
if they actually ate that stuff up, you would never
see it. But when they're not actually eating stuff, they're
also powering the acceleration of other stuff nearby, which creates
fantastical light shows. And those light shows can be eclipsed
right right, although, as you said earlier, not every black
hole has these light shows, right, Like, there's a whole
range of black holes. There are maybe black holes who

(34:25):
are sitting all by themselves somewhere with nothing around it
to feed it to make it bright. And there are
black holes with huge clouds of stuff that is constantly
falling into the black holes. Yeah, there's a broad diversity
of black holes. The ones with big accretion disks are
the ones that are easier for us to see because
you can see the accretion disk right. Otherwise, it's very
difficult to spot a black hole. You have to see

(34:46):
it passing in front of something else. You have to
see it eclipsing something in order to spot it. Mostly
the way that we've identified black holes is from their
accretion disk or from like the motion of stuff near them,
indicating that there must be something very very heavy but
not right there. Well, I think I see what you're saying. Like,
if you define an eclipse as when you're blocking the
light that's coming from something else, then you sort of

(35:08):
need the situation where the black hole is giving off
light from its incretion disk to have a black hole eclipse. Yeah,
Otherwise you're just having a shadow of a shadow. And
I don't even know what that is, but probably exists
in the Pokemon universe. A shadow of a shadow is
a it's a double shadow, it's a shadow squared. But
I guess you could thankically block the shadow of a shadow, right,
like you could blog looking at the shadow. Yeah, I suppose.

(35:31):
I mean, if you stand in a shadow, do you
still have your own shadow? I don't know. That's a
philosophical question. That's like the sound of one hand clapping. Well,
I guess you need like a third source of light
or something, right, right, Yeah, and then you can also
it's a complicated shadows, but you're saying there's a situation
in which a black hole could have an increation disk
around it, which would make it bright, in which case
something could float between you and it and block your

(35:52):
view of this light source exactly, And that would be
a really powerful way to see interesting things really really
far away. Because black holes are very very bright when
we see them. We can see them in very very distant,
very ancient galaxies. So the very powerful probe of what's
out there in the universe. There's sort of like these
pencil rays of light that shine out into the universe.

(36:13):
We can use them to measure like the density of
stuff along that ray. We once talked about the cosmic
web and how we use these pencil rays of light
from quasars to like illuminate the universe and tell like
where the dark matter is and where these filaments of
gas between the galaxies are super interesting. And when something
else happens to pass in front of that pencil ray

(36:34):
of light in a way that we can see it,
then we can use that to identify something. We can
use that to see something that otherwise would have been
invisible to us. So we can use these eclipses as
ways to find stuff really really far away. Wait wait
you mean, what what does this stuff do well? For example,
the technique we talked about for finding planets around other
stars that mostly only works in our galaxy because the

(36:56):
stars have to be close enough for us to like
resolve a single star and measure its brightness very effectively.
So it's very difficult to see exoplanets in other galaxies
because remember, our galaxies like a hundred thousand light years across.
Other galaxies are like millions of light years away, So
we can't really use that technique to find planets around
stars in other galaxies. But scientists have recently used this

(37:20):
to find planets passing in front of black holes in
other galaxies because black holes are such intense sources of
this kind of radiation whoa, because they act like a
beacon within that other galaxy. But is this a planet
that is part of the black hole system or is
this like a random planet floating around another star that

(37:40):
just happens to ones fly in front of the black hole.
We don't know, and in the case of a recent observation,
the theories that it might be a planet orbiting black
hole with a period of about seventy years, which means
that we wouldn't know for another seventy years because we'd
have to wait that long to see the next eclipse.
If it is in fact orbiting that black hole, it's

(38:02):
just like a random transit, some blob passing in front
of the black hole. Then it won't happen again. But
they actually did see this. They looked out with the
Chandra X ray telescope at a galaxy called the Whirlpool
galaxy and they saw this kind of eclipse, meaning that
we're looking at this galaxy that's far away, and we
think that the light coming from it is a black hole.

(38:23):
That's right. We can zoom in on one part of
that galaxy, and they think that there's a binary system there.
They have like a normal like star and around it
is orbiting a black hole, and the black holes probably
from some other star which collapsed and left a black hole.
So the origin is probably some binary star system. Two
stars orbiting each other, and that's a little bit surprisingly

(38:44):
not uncommon, because stars tend to form near each other.
One of them becomes a black hole. They have this
binary system where the black hole is now like sucking
material from the other star and it generates a very
bright accretion disk. And so from that black hole you
now have this invariant hence source of radiation, and the
telescope consume in on that and see the radiation from

(39:04):
the accretion disc of this black hole as it eats
its sibling. Wait, the black hole is orbiting the Sun.
I guess it. It's it's a smaller mass than the Sun. Well,
the sort of orbiting each other, right, the two both
came from stars, and the black hole doesn't have all
the mass of the original star came from Probably these
two stars started out similar mass, and so more accurately

(39:27):
you would say they orbit each other m And then
on top of that they think that maybe there's a
planet orbiting around the black hole that's orbiting around the
Sun exactly, because the black hole is actually quite small,
it's very compact, and so when this planet passes in
front of the black hole, it actually eclipses a good
fraction of it. We would think about a planet transitting

(39:47):
in front of a star in our galaxy, it's a
tiny little dip in front of that star. But here,
because the accretion disc in the black hole are very compact,
every compressed by gravity, this planet actually blocked most of
the light from the secretion disc as it passed forward.
So you can look at like the brightness of this
black hole over time, and they see this huge dip

(40:08):
as something apparently eclipsed it. It clips the black hole,
lips the black hole. Yeah, but they only saw this once,
or have they seen this periodically. They've only seen it
once and now have a model for this system and
how far aware this plant would have to be and
how big it is, and in that model it takes
about seventy years to orbit this system. But of course
they're not making the grad student wait seventy years to graduate,

(40:29):
although it could have also been like an asteroid passing
in front of the Chindra telescope or something that could
have caused this dip. Right, Yeah, there's a lot of possibilities.
We don't see this thing very directly. We only just
see a dip in this black hole, which we otherwise
can't explain, which means something probably passed in front of
it to block our view. And one hypothesis is a planet,
but we can't tell very precisely. Right, it could have

(40:51):
been somebody's thumb. Maybe did you put your thumb on
Chindre that day? Is that what happened? I don't know.
My son doesn't tell me everything it does. That's the
whole problem. But if it's true, then it's really interesting
because it's the first time we've discovered a planet in
a far away galaxy using this transit technique. Interesting. That's amazing,

(41:14):
and it would be amazing to be on that planet.
Can you imagine living on that planet and having like
not just a sun but a black hole also kind
of like sunrising and sunsetting every day and seeing the
black hole eat your sun. Right, That sun gets dimmer
and dimmer every year as the black hole pulls the
material out of it. Wow, that'd be a pretty amazing
view when you look up from that planet. I wonder

(41:36):
if that's where Pokemon out from, that's where they get
their Z power from the view. It's so amazing. Alright, Well,
we've seen a black hole get eclipse, and there are
other examples of that, and there's also the reverse situation
of whether or not a black hole can eclip something else.
So let's get into those. But first let's take another
quick break. All right, we're talking about black hole eclipses,

(42:11):
whether or not you can eclipse a black hole or
whether a black hole can eclip something else. And it
turns out that yes, you can eclipse a black hole.
We've seen it. We have data from a black hole
being eclipse out there in another galaxy. That's right. Even
though black holes are super powerful in the real world
and in Pokemon, you can just stand in front of
them and block their light. Yeah, it's pretty amazing. We

(42:31):
have data from that. And you said there's another example
of a black hole eclipse that we've seen. That's right.
There's a really cool galaxy about sixty million light years away.
It goes by the exciting name of n GC, and
it's exciting because it has a very active galactic nucleus.
This is what astronomers say when they mean that there's
a big black hole at the heart of it, and

(42:53):
it's very powerful and it's shooting a lot of stuff out.
So if you imagine a galaxy is like a big
flat disc of stuff, maybe with arms trailing behind it.
Now add to that huge jets of stuff shooting up
and down sort of from the middle of that disk.
So the galaxy is no longer just like flat. It
now has like an axle around which it's spinning. And

(43:13):
so we've seen this galaxy and and has something eclipses. Yeah,
astronomers were really curious about what was going on in
the heart of that galaxy, and they wanted to know
how big was the black hole and how big was
the active part of it, this sort of like really
intense part of the center of the galaxy. How big
is that accretion disk. Problem is that the galaxy is
so far away that it's really hard to measure that.

(43:34):
Like we've taken pictures of black holes and their acreation disks,
but it's very very difficult, and for this galaxy, it's
too far away for us to even use the event
horizon telescope. So they were trying to figure out how
big this thing was. And then they got lucky. They
got lucky because a big cloud of gas, when they
already knew and they had studied before, passed in front
of the black hole and eclipsed it. Because they knew

(43:56):
how big this cloud was and how fast it was going,
they were able to use that to measure the size
of the black hole accretion disc itself. Wait, what so
there was a black hole in another galaxy far waing
and a gas cloud within that galaxy pass in front
of it, or between us and that other galaxy. The
gas cloud is part of that other galaxy. You know, Oh,

(44:18):
I see? And how do we know how big that
gas cloud was? Because it's so far away. It's so
far away, but it's really big. And so they were
able to measure the size of this gas cloud. It's
much bigger than the black hole, but it's big enough
to see with the telescopes. It's big enough to see. You.
We can see other galaxies and we can see individual
components of it. We can't always resolve things as small
as stars, but big gas clouds we can resolve. And

(44:41):
so the cloud eclipse the black hole in the middle
or the quasar in in the middle, like it blocked
it completely or it just made it kind of fuzzy
for a while. It blocked it almost completely. I mean,
some light can get through it at some wavelengths. But
you can see definitely the dramatic dimming of this black
hole because this cloud passes in front of the accretion disk,

(45:01):
and so as it passes in front of one side
of the acreation disc, it starts to dim. And then
if it's totally blocking the disk, then you get the
minimum brightness. And then as it starts to reveal the
accretion disc again, the light comes back up. And so
from the size of the gas cloud and the speed
and with the gas cloud was moving, you can figure
out the size of the accretion disk, which is what
the astronomers are really curious to know. Interesting, So these

(45:24):
are recorded instances of black hole eclipses, Like you could
be the astronomer that saw a black hole eclip. Yeah, exactly.
And these are lucky coincidences, right, just like the Sun
and the moon lining up. In the case that these
things line up in the sky, we can use that
to learn something about these systems. We're always taking an
advantage of what's going on in the universe. Astronomers never

(45:45):
get to like build experiments and say what happens if
I crash these two things together, or if I pass
this in front of the other thing. They have to
just be clever in other ways of saying, well, I
didn't get to design this situation, but what can I
do to learn about the universe? Frum it anyway, And
so I love seeing astronomers be clever this way and
figure out, like how to use the lucky lining up

(46:06):
of these two objects to learn something about them. And
in this case, I used the gas cloud to learn
about the size of this black hole. What did they
learn about it? So they learned the size not just
to the black hole, but also the disc around it, right,
because it's the disc around it, the accretion disc that
really is generating that radiation. So they learned that this
disc is about seven a U wide, where a us
the distance from the Earth to the Sun. And so

(46:28):
if you put this thing in our solar system and
you extend out past the Earth's orbit and out past Mars,
so this thing is really pretty big. Wait, we can
measure the size of the cloud before, but we couldn't
measure the size of the black hole. Yeah, and the
cloud is bigger than the black hole, so we were
able to resolve it all right. Well, the final question
is whether a black hole could eclipse something else. Like

(46:49):
if there's a star or a sun out there and
a black hole pass in between it and us, would
it create an eclipse? That would be pretty dramatic, wouldn't it.
That would be pretty dramatic, But it's almost impossible. If
somebody standing on the other side of a black hole
and like turning on and off a flashlight, then a
lot of those photons would get to you anyway. Remember

(47:09):
that space around the black hole is really really curved,
so light doesn't always travel in straight lines. So light
that comes out from their flashlight that wouldn't otherwise get
to your eye gets bent by the black hole towards
your eye. So the black hole would eat some of
the photons from the flashlight, but other photons that were
going in other directions would get bent towards your eyeball,

(47:29):
so you would still see it. Right, Like if a
black hole just happened to fly into our solar system
and get between us and the Sun, it wouldn't totally
block the Sun. It would only block some of it. Yeah, Like,
if somebody stood on the other side of a black
hole with a laser of single photons, they could shoot
them at the black hole and you would eat them
and you wouldn't see it. But if their source has
any sort of width to it, if the photons come

(47:51):
out at any sort of angle, then some of those
are going to get bent around the black hole and
towards your eye. We see the same thing happening actually
already with the moon the Desiginstein's famous proof of general
relativity that space is curved by mass, because he showed
that photons from the Sun don't always get blocked by
the Moon. The Moon bends them around itself a tiny

(48:12):
little bit. The Moon is lensing the light from the
Sun a little bit, and a black hole would be
a very very powerful gravitational lens. So it's almost impossible
to hide behind a black hole, right, you're saying, like,
because the Moon is almost the same size as the
Sun and the sky, it doesn't totally block the Sun
because some of the light kind of flows around the
Moon and gets to us anyway. But if the Moon

(48:34):
was bigger, right, and the sky might like ten times
bigger than the Sun. It would almost totally blocked the Sun, right, Yeah, exactly.
Although the Moon was more massive than it would be
more effective at bending some of the Sun's light towards us.
And so there's two different effects going on there. And
so something is very small, like a black hole and
very very dense, it's going to be excellent at gathering

(48:55):
light that otherwise wouldn't have gone to you and sending
it your direction. So what would we see if a
black hole stood between us and our son. We would
see like a black circle with a bright ring around it, right,
and then that ring would sort of merge with the
Sun and kind of distort the light around it, and
then they would block the Sun, and then it would

(49:16):
keep going. Yeah exactly. It would look really weird and awesome.
It reminds me actually of a great science fiction book
I read, Paraheli In by Greg Egan. He talks about
what happens when a black hole enters our solar system,
and it's not something you should look forward to because
it would disrupt everything in the solar system even before
it made an impressive distortion of the Sun's light. Would
be bad news, but let's say it was a really

(49:38):
big black hole. It would totally eclipse our sun, right,
or we we still see all of the light from
the sun. We wouldn't, right, We would only see some
of the light from the sun get bent around the
black hole, but mostly it would be blocked. We wouldn't
see all of the light from the sun because photons
shot directly towards the center of the black hole would
still fall into the black hole, but photons shot in

(49:58):
other directions would get bent around it. To us, well,
there would be a range, right, wouldn't there be a range? Like,
It's not just the ones directly to the center of
the black hole and the ones a little bit off
to the side also get sucked into the black hole. Yeah,
the bigger the black hole, or the closer you are
to it, the sort of the wider range of photons
that do fall into the black hole. But also the
more powerful the black hole, the more it's able to

(50:20):
bend other photons around it so that you can see it.
And have we seen an example of this, I guess
we kind of have, right, I mean, we've taken pictures
of black holes, right, we have pictures of black holes,
and presumably there are stars behind the black hole that
we're not seeing because they're getting blocked by this black hole.
I don't know that we've seen that directly. We've discovered

(50:42):
smaller black holes because of their gravitational effects on the
nearby stars. Like if you see a star and it's
moving in such a way that you can tell it's
orbiting something, but you don't see the thing there, then
you deduce that there's probably a black hole there, even
if you don't see it. I don't know if we've
seen direct lensing of background stuff from a tellar mass
black hole. Well, I guess if we have a picture

(51:02):
of a black hole, technically it was blocking something behind it, right,
assuming there was something behind it, then yeah, it's getting blocked. Yeah, well,
technically there that has to be something behind it, doesn't there.
I mean, it's not like they're it's totally empty space
behind it, right, Yeah, there's always background galaxies no matter
how far you look. All right, Well, I think your
point is that it's complicated, right, because black holes bend
space so much that it and they act like lenses

(51:25):
out there in space that it's it's kind of a
complicated situation to have a black hole block something else. Yeah,
black holes are great at bending light and eating photons,
but they're also great at showing you what's behind them. Yeah,
but definitely, for sure, we've seen things block black holes
from our view. It's just that the situation is more
complicated for a black hole blocking our view of something else. Yeah, exactly.

(51:46):
All right, Well, I think the main lesson is Pokemon
is right. I think that's what you're seeing, right, that's right.
You don't need a physics degree. You just invest your
college savings in Pokemon. That's right. Just catch them all
and you can't retired to that tropical island or at
least pay for your son's college. It kind of caused
the same these days, does cause the same. Maybe you'll

(52:06):
get a PhD in Pokemon. I think there are pro
hard people getting their PhDs on the cultural impact of Pokemon.
I'm sure you can get a PhD on anything, exactly.
Everybody can get a PhD. Al right, Well, I guess
the next time you look out into the night sky
or even the daytime sky, imagine that there are black
holes out there being eclipse and also eclipsing our view

(52:27):
of the universe. Because the universe is full of all
these amazing objects and be impressed by how astronomers are
taking an advantage of coincidences and happenstands out there in
the universe to teach us lessons, to reveal the nature
of the mysteries of our cosmos. That's right. The main
lesson here is don't put your thumb down on physics.
Give it those thumbs up. Yeah, two thumbs up to astronomy.

(52:47):
All right. We hope you enjoyed that. Thanks for joining us,
See you next time. Thanks for listening, and remember that
Daniel and Jorge explained. The Universe is a production of
I Heart Radio. For more podcast from my Heart Radio,
visit the I Heart Radio app, Apple Podcasts, or wherever

(53:10):
you listen to your favorite shows. Ye