June 21, 2018 • 43 mins
Nothing can escape the pull of a black hole, not even Stuff to Blow Your Mind. Join Robert Lamb and Joe McCormick for a three-part exploration of these incredible, invisible regions of the cosmos where ponderous mass warps the very fabric of space and time. In this episode, learn all about the science of black hole detection.
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Episode Transcript
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Speaker 1 (00:00):
My welcome to Stuff to Blow Your Mind from how
Stuff Works dot com. Hey you welcome to Stuff to
Blow your Mind. My name is Robert Lamb and I'm
Joe McCormick, and we're back. It's part two of our
multi part exploration of black holes. Because you know what,
(00:22):
this year Robert went to the World Science Festival in
New York and came back with black Hole Fever. Yeah.
It was a great It was a great talk that
really opened my eyes a little more to some of
the finer details of of black holes. And you mean
that Brian Green talk with the guests. Yeah, Darkness made visible,
wonderful talk. It's available online. Will include a link to
that in the landing page for this episode. Certainly inspired
(00:42):
us to to really give black holes a proper shake
on Stuff to Blow your Mind. Yeah, I mean, there's
so much interesting stuff to talk about, and the fact
that they're just one of the most interesting objects in
the entire universe. It's not that they're probably I would say,
maybe the most interesting non living thing in the universe.
What do you think about that? Yeah, yeah, I would
say that because we're pretty interesting ultimately humans are. Um.
(01:05):
I do want to remind everyone. If you did not
listen to the previous episode on black holes, you do
want to go back and listen to it, because this
is this is not one of those where you can
kind of take part one and part two in any order.
You really need to hit the first episode. I mean,
you could if you really wanted, But we're going to
be referring back to the groundwork we laid in the
previous episode. And the previous episode we talked a lot
about the development of black holes. Uh, sort of as
(01:27):
the history of an idea, something that was unlike the
stars in the sky. You know, the stars in the sky,
we first observed and we could see them, and then
by making observations about them, we were able to come
up with theories to explain them. Black holes weren't like that.
It went the other way around. Black Holes existed in
theory long before anybody accepted that they existed in reality,
(01:49):
and long after they existed in theory, many scientists ardently
opposed the idea that black holes could exist in nature. Yeah,
it's the idea that that these various individuals said, well, X, Y,
and Z are true, then this thing might exist and uh,
and and that thing is the black hole. But of course,
you know, lots of people when a thing sounds outlandish,
(02:12):
even if your best theories tell you it might be possible,
people want to find a way to say, no, that
just sounds unintuitive. It couldn't be real. It doesn't fit
my picture of how the universe works. It doesn't feel right. Yeah,
maybe that's a thought experiment, but I doubt will actually
find something like this when we start looking out into
the cosmos with better observational technology. You know, it's often
(02:34):
said that Albert Einstein did some of his worst work ever,
Like the worst science of his entire career was him
trying to write papers to prove that black holes didn't
exist in reality. It just didn't seem right to him,
even though his general relativity became the basis of our
modern theory of black holes. But so anyway, yeah, so
(02:54):
how did today? We want to explore making the darkness flesh,
making the black hole into a thing that is real
in existence in the universe and we can detect it.
So I think first we want to tell the story
of sort of like a bridging the gap between the
black holes of general relativity theory and the actual observations
of them and then talk a little bit about what's
(03:16):
it like to detect black holes and how we might
do it. And we do have to distress that in
today's world, black holes are pretty much an established reality.
You talk to experts and they say yes, without a
shadow of a doubt. Yeah. I don't know if it's
the case that every single expert would say without a
shadow of a doubt, but yeah, they're They're generally accepted
as a fact of reality. You know, we've reached the
(03:38):
point where black holes exist and they're completely non politicized.
That's the other great Yeah, oh man, I love a
scientific controversy that doesn't never have a political angle. Yeah,
it's the black holes are are. Thus far, they've remained
pretty safe. Well, maybe we can muck it up today.
Let's let's get people taking tribal sides on it. Okay,
(03:59):
So the story of how black holes went from this
theoretical anomaly to a thing known to exist in the world,
it's a long, complicated story, so we definitely can't explore
all of it, but I just want to mention a
few highlights, and one of the first ones is serious
b Now, Serious is the brightest star in the night.
Sky from Earth, often known as the Dog Star because
(04:22):
it's part of the Cannus Major constellation, the Great Dog constellation.
Side note, I didn't know this until I was reading
this the other day. Do you know the origin of
the term dog days of summer doesn't actually have anything
to do with the behavior of dogs. Really. I always
thought it came from a Don Henley song. Wait, one
of the Boys of Summer. Sorry, after the dog Days
(04:43):
of Summer have gone. Yeah, man, I grew so hard
whenever that song comes on the radios. It's a great
it's a great track. I love it. It's yacht rock
that touches my heart. Yeah. So the term dog days
of Summer actually refers to the period of Serious, the
star in the Cannus Major constellation, rising roughly in conjunction
with the Sun, which happens in July through August in
(05:06):
the Northern Hemisphere, and so this is also the hottest
time of the summer, and so it came to be
associated with Okay, so Serious is coming up with the
sun in the morning, and that means it's going to
be real hot out. But back in the eighteen hundreds,
it had been observed that the extremely bright star we
now call Serious A behaved oddly. Its motion was not
(05:29):
it was it was not smooth. It was kind of wobbly,
as if it were being destabilized and tugged on by
an invisible hand. And it turned out that Serious A
actually had a very dim companion star. It was a
binary star system, and the companion was what we now
call Serious B. But it was a very strange type
(05:50):
of companion because based on the motion of the two
bodies and the light they produced, astrophysicists could calculate that
the companion of Sirius at the same time was somewhere
around the mass of our Sun, and yet was barely
larger than the size of planet Earth and burning extremely hot,
much hotter than the Sun. So Serious Be turned out
(06:14):
to be an early example of what would later be
called a white dwarf, a tiny, hot, massive star that
proved matter could be compressed to pressures previously thought absolutely impossible.
In the words of Arthur Eddington, quote a ton, and
he's talking about the the material making up the star.
A ton of this material would be a little nugget
(06:35):
that you could put in a matchbox. So imagine something
matchbox size. But that weighs a ton, and so for many,
including Eddington, the very concept of this density was so
absurd that it should just basically cause us to dismiss
the observations out of hand, dismiss the idea of a
white dwarf. It's absurd, but reality is stranger than our imagination.
(06:56):
White dwarves came to be accepted as a feature of
the universe and a part of ller revolution, especially after
quantum mechanics eventually came along. To explain how matter could
be compressed to such an unbelievable density. Basically has to
do with packing atomic nuclei tighter and tighter, and you
can actually do this to some extent because most of
an adam is empty space. There's a good explanation of
(07:18):
this actually in a book that's one of our sources
on this episode, Black Hole, by Marcia Bartousciak, which I
thought I should mention again, which is a good good
book if you want to go in more depth than
we're going into here. But so with serious b you've
got these white dwarves, You've got these objects that are
observed to be tiny and very hot and very bright
(07:39):
and very massive, and so what would be the limits
on what a star like that could be like uh
In nineteen thirty, the young Indian astrophysicist Supermania and Chandra
Sheker calculated that there was an upper limit to the
mass of a white dwarf. White dwarves could vary in size,
but somewhere around one point four solar masses. If a
(08:02):
white dwarf is about one point four times the mass
of our Sun, something happens. This is now known as
the chander Shaker limit, and it around this mass, the
force of gravity chander Shaker calculated appears to become more
powerful than the force that's known as the electron degeneracy pressure.
(08:22):
And what that is is it just causes atoms to
push against one another and resist compression. So why can't
you keep compressing it down more and more? There's this
electron degeneracy pressure pushing back, but at a certain point, gravity,
at least on paper, appears to completely overwhelm this degeneracy
pressure and just crush everything down. So any clump of
(08:45):
white dwarf stellar matter more massive than this could not
maintain the white dwarf density at a stable pressure given
the laws of general relativity. Past this point of star's
density would just not scale up regularly, but would collapse,
and it would collapse toward infinity. But when you think
about that, like try to imagine your in Chonder Shaker's
(09:07):
position infinite density, what does it mean to collapse to
infinite density? You'd almost be tempted to think, Okay, well
I made a mistake. Yeah. It's like it's like suddenly
everything is reduced to zero and you know that the
equation must be flowed. Yeah, it's like you've you've hit
a divide by zero area or something. You you know
that you must have done something wrong. It was difficult
(09:28):
to believe that something like this could be possible in reality.
How could a real physical object collapse toward a point
of infinite density? Though this is what the math appeared
to show. But Chonder Shaker did not actually argue about
what physically happened to the white dwarf past the limit
that he had established, only that the limit of stability
at about one point four solar masses existed, and Chandra
(09:52):
Shaker spent years arguing against the grain of scholarship on
this point. There's a famous story about how when he
presented his findings at a meeting of the Royal last
Atronomical Society of London and nineteen thirty five our old
friend Arthur Eddington's uh. He supposedly exclaimed there should be
a law of nature to prevent a star from behaving
in this absurd way. That's some wicked cantankerousness, just like
(10:15):
yelling at the laws of physics. But but no, I
mean so, that kind of attitude from Eddington actually kept
this idea down for a long time, even though we
would eventually find out that chander Shaker was on the
right side of this argument, and the prolific Soviet physicist
live Landau also made a similar calculation around this point,
and he also arrived at the conclusion that a heavy
(10:37):
enough star could collapse to what appears to be a point.
But he said, that can't be quite right, so he
ignored this result and instead concluded that the core of
a star like this that at the core of a
star like this, matter sort of begins to ignore the
laws of physics and becomes quote, one gigantic nucleus. Now,
chander Shaker was eventually recognized for being in the right
(10:58):
on this question. He see the Nobel Prize in Physics
for his work on stellar evolution, and he got that
in nineteen eighty three. Now, also in the nineteen thirties,
a parallel idea to the idea of the black hole emerges,
and that is the idea of a neutron star. Now,
a neutron star is another form that stellar collapse can take,
(11:19):
in which you've got protons and electrons that form the
core of a star and they compressed together with such
force that they combine and form neutrons, which have mass
but no electric charge. And a neutron star is not
as a reality warping as a black hole, but it
is an unbelievably exotic type of object composed matter so
(11:39):
dense that it's been compared to an atomic nucleus the
size of a city. If you can picture that, Uh,
can you picture that? Of course you can't, nobody can,
but just just try. I can picture an illustration that
was presented of this. That's that's the best I can do. Well.
I mean, part of the problem is that matter already
looks solid enough to us, right, I mean, you take
(12:01):
a rock or something like that, You're like, this looks
really really solid, but most of it is empty space.
Most of it is just the space between the atomic
nuclei and the electrons orbiting them, and the other atomic
nuclei that they're bonded with. Um. I mean, the molecules
that make that very solid seeming object are mostly empty space,
(12:22):
and there's a lot of space you can press things
further and further into if you really must. You may
not be able to get blood from a stone, but
there's a lot of empty space there. If empty space
is when you're after, it's there, you can get space
from a stone. So, just to show how much things
can be compressed, it's often said that, like a square
centimeter of a neutron star, material might weigh more than
(12:44):
a billion tons. Uh So. In the late nineteen thirties, J.
Robert Oppenheimer, who's famous for working on the Manhattan Project,
among many things. Oppenheimer and some students of his published
work tending in the same direction as Chandra shako Are.
Oppenheimer and George Volkoff did work on the emerging idea
of neutron stars, which we were just talking about, and
(13:05):
found that neutron stars, like white dwarves, had an upper
limit of mass, after which something very strange seems to
happen to them. You've got this upper limit, and if
they have more mass than this limit, there's some kind
of collapse, something, something goes wrong with the physics. Oppenheimer
also published a paper on stellar evolution with Heartland Snyder
(13:27):
in which they determined that late stage stellar remnants of
stars passed a certain mass would seem to enter this
state of permanent infinite collapse. The matter within them would
exist in this perpetual free fall towards a point of
infinite density, the singularity. And that is a that is
a mind boggling concept to toy around with, falling forever.
(13:49):
The never ending pit essentially, which was it was something
like as a kid, you, or at least when I
was a kid, that's what we played instead of the
floor is lava. Always said the floor is an never
ending pit. That's more than lava. Yeah. I think it's
because we saw it on like key Man cartoons or something.
I feel like it isn't that what's underneath Castle Gray
Skull and never ending pit? I don't remember it is
in my mind. Well, then what's Castle gray Skull built on.
(14:13):
It's built over and never ending. I see it's called
a strut since yeah, yeah, I guess they had to
cap that thing, you know up, They're like, don't people
gonna fall into that, Let's put a castle on top
of it. So it's playing fast and loose with masters
of the universe. Um myth those here. By the way,
I apologize for just trying to move us along. I
think we should dwell. No, no, I'm good, I'm good. Okay,
(14:34):
don't ever let me be too square. Okay. Uh So,
starting in the nineteen fifties and sixties, both experimental and
theoretical work really seems to accelerate in the direction of
indicating the reality of neutron stars and black holes. These
these really exotic collapsed star remnant objects and theoretical models
(14:55):
are affirmed over and over and they appear increasingly sound.
While new astro comical observations really seem to make us think, wow, yeah,
there could be black holes out there. I think some
of the skepticism could be unfounded. Like in the nineteen
sixties you had scientists identifying quasars, which are these distant
high energy objects, possibly young galaxies, with black holes at
(15:17):
the center of them, emitting trillions of times the energy
of a sun. And you had pulsars, which are spinning
objects emitting a repeating pattern of radio bursts. And around
the same time, astronomers identified sources of X rays and
gamma rays from all over the celestial map. And these
signals really strongly pointed to the physical reality of collapse
(15:38):
stars like neutron stars and black holes. And now we
know that actually pretty much every mature galaxy in the
universe that we know of seems to have a supermassive
black hole at its center. It may be the black
holes are necessary for the formation of galaxies, and galaxies
are where things like us live. The black hole the
life giver. Yeah, we were rebrand rebranding the black hole today. So,
(16:03):
speaking of supermassive black holes, I I do want to
just touch in once more on the three forms of
black holes that we tend to discuss. Okay, so we've
mainly been talking about stellar black holes, right right. The
idea of a collapse star. Yeah, these would be as
massive as as twenty of our sons uh fit inside
a one mile radius sphere. Uh. These are the would
(16:24):
be the remnants of very massive stars that have run
through their innergy energy reserves. They go supernova and then
they collapse upon themselves and they're thought to be the
most common type of black holes, and there are likely
dozens within our own Milky Way galaxy. And then they're
the primordial black holes. These tho I touched on the
first episode that the size of an atom. They have
the massive a mountain, So these are hypothetical, and they
(16:47):
probably formed soon after the Big Bang. And then of
course they're the big ones, the supermassive black holes. They
likely exist at the center of most galaxies. Our own
galaxy boast Sagittarius A, and it has a mass equal
to about four million sons. And uh, these black holes
formed with their respective galaxies and are proportional in size.
(17:10):
And again these these are these are a part of
our universe. You know, as much as we we tend
to sort of fall into the trap of thinking of
black holes as you know, cosmic love crafty and evil consumers,
they're they're just a part of the life cycle of stars.
They are part of the general physical reality of the universe. Yeah,
(17:30):
they're not reapers from another dimension. They're the life givers.
Let's not go too far alright. Well, on that note,
we're gonna take a quick break and when we come back,
we will get into the science detecting black holes. Thank you,
thank you. All Right, we're back. So I want to
(17:50):
tell you a story about signas X one. Okay, let's
have it. So. Way back in the nineteen sixties and
the Swinging sixties, the astronomers out there, we're making use
of a new class of tools to study distant regions
of the sky, and these were space based X ray detectors.
They were attached to orbital rockets and artificial satellites, and
(18:12):
these instruments looked for X ray signals the astronomers and
astrophysicists thought they might find emanating from all kinds of
celestial sources, from say, the surface of the Moon. You know,
it's the moon shooting X rays. Two distant star systems
and nebulae, and one strong source of X ray radiation
detected by rockets in the nineteen sixties was a point
(18:35):
in the constellation Scorpius, and the source of the radiation
came to be known as s c O X one
or SCO X one. I don't know if you say
it like SCO that makes it sound kind of scummy,
but it was a truly remarkable fine because this radiation
source was about nine thousand light years from our solar system,
and it's X ray output was millions of times stronger
(18:57):
than that of normal sun like stars. And this massive
energy output came we discovered from a neutron star in
a binary system, and since then other similar sources have
been discovered. These X rays are generated when matter from
so you've got a binary system, you've got like a
neutron star or a black hole, and then some other
kind of object like a star. They're dancing, Yeah, they're
(19:21):
they're they're doing the polka out there in space. And
the X rays are generated when matter from the surface
of the more normal star gets sucked violently into the
gravitational field and onto the surface of the neutron star.
That's what's going on in the case of s c
O X one. And during so so this this gets
(19:42):
sucked in, the matter gets heated up a lot, and
X rays get blasted out into space. But during these
surveys of the nineteen sixties, one X ray source in
the sky was not like the others. In nineteen sixty
four we started to get a clear picture of the
radiation output of one source in the Sickness constellation, and
this source came to be known as signus X one,
(20:03):
and unlike the X ray sources that emitted like regular
pulses you know sometimes that would happen be be beep,
Signus X one seemed to be releasing unbelievably powerful, irregular
bursts of this deadly high frequency radiation, and sometimes these
irregular bursts were incredibly short, like on the scale of
millionths of a second, and so at a meeting in
(20:26):
March ninety one, the Italian astrophysicist Ricardi Giaconi speculated that
the source of the X one signal might be a
real black hole, the first black hole apparently observed in space,
and later analysis did seem to bear out this hypothesis.
The signus X one system seems to consist of a
(20:47):
blue giant star orbiting with a much smaller object that
we can't see. And by observing the size of the
companion star, the blue giant known as h d E
two to six six eight, and the rate of its
orbit it completes an orbit in less than six earth
days and the size of that orbit, astronomers began to
get a picture of this unseen orbital center. It appears
(21:11):
to be invisible, tiny and heavy. Current estimates of its
mass are at about fourteen point eight of our sons,
and the radiation coming from this source is emitted as
this apparent black hole sucks matter off of the orbiting
star like we were just talking about with the neutron star.
It sucks gas or matter off of that star, and
the matter swirls down into the gravity pit of this object,
(21:34):
heating up as it does, and eventually it heats to
the point that it gives off X rays, and of course,
once that gas falls past the event horizon, presumably nothing
more is emitted. It's stuck inside. But you've got so
you've got these observations. It's massive, it's tiny, it's invisible,
and it shoots radiation out into space as it appears
to suck matter from neighboring bodies. Really really seems like
(21:58):
a black hole. But was it proof? This was actually
famously the subject of a bet between physicist Stephen Hawking,
who did plenty of his own important work on black
holes in Kip Thorn in nineteen seventy four. Real quick
Kip Thorne, by the way, not only physicists, but executive
producer of the two thousand fourteen film Interstellar. Oh yeah,
(22:19):
that that was probably the best black hole movie I've seen. Yeah,
and that's why. Right, So he tried to get them
to like get the science right, Yeah, to say, be accurate,
make it look like a black hole would really look
Let's do some math. Yeah, and they did the math,
and that's a that's that's that's something that most people
tend to to praise Interstellar for as being the best
(22:40):
depiction of a black hole in at least cinematic science fiction. Well,
as I've said on the show before, my favorite thing
about it is how it actually deals with the time
dilation effects of relativity. Uh. Yeah, there's a lot to
like about Interstellar. But coming back to that bet. I'm
sure you've heard about this bet before. This is a
famous bet in the history of physics astrophysics. So Thorn
(23:00):
and Hawking had this bet. Hawking was the pessimist, Thorn
was the optimist. Well, I guess depending on what you
think you know regarding the nature of black holes, right,
Thorn bet that Signals X one would turn out to
be a black hole. Hawking bet that it would not
turn out to be a black hole, and Hawking was wrong.
By Hawking admitted that the evidence for X one's black
(23:21):
hole status was so strong that he had to concede
the bet. So we live in a world now where
astronomers and astrophysicists are almost totally convinced that black holes exist.
You can fly out into space in theory, and you
could fly right into them, but they nevertheless remain tricky
from an observational standpoint. So I think now for the
rest of the episode, we should try to explain some
(23:44):
of the ways that we can use to try to
detect black holes in space. Yeah, a thing that by
its very definition cannot be seen, cannot be seen directly,
of what are the ways in which we can observe
their presence? Right? Because one of the very things that
makes a black hole unique is that it neither emits
nor reflects detectable light of its own. So how would
(24:05):
we ever know if it one exists? Well, there are
lots of indirect ways of detecting them. And of course,
even though it doesn't emit light of its own, that
doesn't mean it's necessarily dark, because, as we explained in
the last episode, there's stuff going on around it. And
in fact, we just touched on one example of this.
Uh of the idea of stuff falling into the black hole,
stuff being material being sucked into it. Yeah, so black
(24:28):
holes themselves are dark, but from our perspective, the region
around the black hole can be anything. But So imagine
there's this region of space where we observe extremely hot,
high energy radiation. You've got X rays spewing out all
over the place. What's going on there? Well, a good
chances you've got a black hole with matter falling into it.
The matter gets heated up to hundreds of millions of
(24:50):
degrees and produces all these kinds of powerful radiation that
are visible from Earth until it passes that threshold, however,
and falls into the black hole, after which admits nothing.
To revisit what we uh the example I brought up
in the last episode, I think it's kind of like
you've got a haunted house and you've got like a
car that takes people around the haunted house. And the
(25:11):
car is soundproof, so you can't hear people screams from
inside the car, but as the tourists line up to
get into the car, you will probably hear them doing
all kinds of things as they're like sort of loading in.
And the fact that you can observe. Often all of
this violence and radiation around a black hole came up
in that darkness visible presentation. Right. Yeah, it was pointed
(25:31):
out that the despite they're inherent darkness, black holes are
among the brightest objects and the cosmos often, uh pinpointed
is points of extreme brightness in a relatively compact region
of space. And this is due to all of the
material and light surging in and orbiting around the objects
of the horizon, the point again at which even light
(25:51):
cannot escape. Right, this is probably a terrible, a terrible comparison.
But to come back to the Texas chainsaw mask your house,
it's like, oh again, yeah, they're all the is, all
these missing teenagers and all of these looted graveyards. Uh.
And then we have this one area here, uh clear,
look at all this activity around the house. That's how
we have some idea about what's going on inside it. Right,
(26:12):
Maybe you can't get a warrant to go inside the house,
but you can see there's a ruckus going on or
in the general vicinity, right, And that's what we're looking
at here, the black hole ruckus. But that's not the
only way that we can we can detect the presence
of a black hole. No, there are lots of other
really interesting ways. So here's another one. Imagine you are
to look at a place in the galaxy where visible
(26:33):
objects are acting weird. Planets are stars travel in these
repeating loops as if in orbit around something, but we
can't see what that thing is for them to be
an orbit around, or if we can see it, maybe
it's like they're orbiting an invisible star, or we can
see something very bright that they're orbiting, and the way
that they're orbiting it indicates that this thing they're orbiting
(26:56):
might be both very very small and very very massive.
It's essentially the invisible man scenario, you know, like you
can see the hat, but there's no person there. Well,
something must be holding up the hat. Yeah, something's hold
up the hat and the umbrella. So, uh, for example,
what do we see when we look closely at the
center of our own Milky Way galaxy? We mentioned this
(27:17):
darkness visible presentation at the World Science Festival this year.
Uh So that presentation featured, among others, the u c
l A astronomer Andrea Gays, who has spent her career
examining exactly this question. What's going on at the center
of the galaxy. Now, of course, we mentioned in the
previous episode and earlier today that researchers have come to
(27:37):
believe that there is a supermassive black hole at the
center of most are all mature galaxies, and our galaxy
is no different. At the center of our galaxy, there's
an object called Sagittary Essay, which is believed to be
a black hole about four point three million times the
mass of our Sun, though Gays actually says that this
is on the low end of supermassive black holes, which
(27:59):
can be up to a billion times the mass of
our son. Though I want, I want to be impressed
by that, but I'm running into like the scale problem
right where somebody says like, hey, Robert, I want to
give you a hundred billion dollars or I want to
give you five hundred billion dollars. Yeah, up saying with
(28:20):
the scales that they might as well be the same
number because they're just so beyond my ability to, you know,
to fit them within the confines of my own life. Yeah,
what does that mean? What does that difference even matter?
What am I supposed to do with that information? Yeah?
So even though I recognize that that is a big difference,
and that that's it should be really impressive. I can't
actually picture it, so I'm I'm kind of stuck there.
(28:41):
You often run into this with some of the most
impressive stuff, and in astronomy it's like you want to
be accurately appreciative, but you can't visualize the scale. Yeah,
because then the numbers just become meaningless to most minds
after a point. But anyway, back to so Sagittary is,
say this thing that we believe to be a super
supermassive black hole. How how would you detect if it
(29:03):
really were a supermassive black hole? And just to note,
we keep calling it Sagittarius A, but technically the object
believed to be the black hole is Sagittarius A with
little asterisks. They call that Sagittarius A star. While Sagittarius
A as a whole is this more complex source of
radio signals, including the object we're talking about. So technically
it's Sagittarius A star, but I think we will keep
(29:25):
calling it Sagittarius A because when you're also talking about stars,
saying a star over and over can be confusing. So
the main method that Gaye talks about is to demonstrate
that a mass is within its short shield radius. We
talked about the short shield sphere in the last episode,
and in simple terms, what you're looking for is big mass,
(29:45):
small volume. We know that any mass contained within the
volume of its short shield radius will inevitably collapse into
a black hole. Nothing can stop it. At this scale,
gravity always wins, and a if you can show this,
if you can show that an object is of a
mass that's within the volume of its short shield radius,
(30:07):
you've effectively demonstrated that it must be a black hole.
So to see what's happening at the center of our galaxy,
we can look toward the constellation Sagittarius, and if you
have the right kind of telescope, you can peer straight
through to the group of stars at the core of
the Milky Way, the galactic center. And these stars really
do behave in an odd way, especially like a central
(30:27):
star called s O two, which orbits the object Sagittarius
A in a pattern of one orbit every sixteen years.
There are animations of this that are worth looking up.
In fact, there's even direct imaging. I don't know, but
it might be infrared imaging. But they're there. You can
like see the stars actually moving over a long time
lapse video, and the path of s O two looks
(30:48):
almost like a I'm trying to find the right point
of comparison. It's sort of like a pendulum or something,
you know, where you see something kind of slowly go
up to one side and then zoom down along the
other side. Um. And so that's what happens with the
start cruises slowly through a lot of its elliptical path
and then whips lightning fast through one end of the
(31:10):
ellipse of its orbit. And what's going on there is
apparently when s O two travels through the closest part
of its orbit with Sagittarius AY about seventeen light hours away,
it's moving at about three percent of the speed of light,
or roughly thirty million kilometers per hour, and that even
if you just look at the animations, you can tell
(31:30):
it's super fast. So because we can image the region
of Sagittarius AY and the objects traveling around Sagittarius A,
we can do physics calculations to determine the size and
the mass of what this object is, and it turns
out that it's more than four million times the mass
of our sun and appears to be crammed into this
very very tiny region at the center of the galaxy.
(31:52):
So it looks very much like a supermassive black hole.
All Right, we're gonna take one more break and we
come back. We will jump into more ways that we
detect black holes, including gravitational lensing. Thank thank Alright, we're back, Hey, Robert,
So what would happen do you think if you were
looking at something and a black hole passed between you
(32:15):
and the thing you were looking at. Ah? Well, I
think on one hand, a lot of people are attempted
to say, oh, you wouldn't be able to see it,
because the black hole would be in the way. It'd
be opaque. It would be like taking a black piece
of paper across your field division just blotted out. But
that doesn't quite seem to be the case. Definitely, not necessarily.
(32:35):
What occurs is something called gravitational lensing, and this occurs
when a strong gravitational field bends light around it, creating
a lens like effect, warping and magnifying light coming from
the opposite direction of the view. Yeah. So the simplified
version of this, I suspect it wouldn't actually work for
objects this small. But it's that if you, you know, Robert,
(32:56):
you and I stand on opposite ends of the room
and you put a black hole directly between us, instead
of just being completely blotted out, we'll sort of see weird,
warped fun house mirror versions of each other wrapped around
this dark spot. In our field of view. We will
be essentially distorted through the lens created by the gravity
(33:18):
distortion of the black hole. Yeah. One example of this
is frequently um used is what's known as Einstein's cross
These are four images of the same distant quasar that
appear around a four ground galaxy due to strong grave
gravitational lensing. So there's kind of this blur in the center,
and then the same star is pictured four different places
(33:42):
around it. That's interesting, So you might think of it
that way. In our our our rough example, here, I'm
looking across the room. I see a basic like blur
where you should be, where the black hole is is
blocking my view. And then perhaps to either side of you,
I see distorted versions of Joe, a beautiful image. Yeah,
maybe one floating a of you as well, kind of
like an angelic visitor with like kind of crazy warped
(34:05):
arms flapping around on both sides, like one of those
inflatable dude dads you see it to use car dealership.
Another example that I came across was that in two
thousand and ten, the Keck two telescope in Hawaii and
it's in I r C two instruments observed a four
ground quasar causing gravitational lensing of a galaxy in the
(34:27):
background behind it. So I think it's actually the reverse
of the example you just gave. So the quaysar is
likely to be a giant black hole that's spewing huge
amounts of radiation into the universe around it, making it
extremely bright. And this foreground quasar is known as sd
s J zero zero thirteen plus one to three. I
(34:48):
almost stopped reading there, but you know, you got to
say all the numbers, uh. And it's about one point
six billion light years from Earth, so this is very,
very far away. I included a picture here for us
to look at, but you can see how the quays
are in the foreground because of its great gravitational distortion effects,
seems to create a lensed image. These distorted side effects
(35:10):
of a galaxy that's in the background right behind it.
But we should get to the next method because actually,
I think this is maybe the most interesting and one
of the most conclusive methods that we have come up
with so far to demonstrate not only the existence of
black holes in the universe, but some of the most
violent black hole behaviors in the known universe. And that
(35:31):
is finally getting to a world where we can observe
gravitational waves. That's right, So we already discussed the general
relativity concept that mass distorts space time. As part of this,
Einstein also predicted that we'd observed ripples in spacetime gravitational
waves caused by some of the more extreme occurrences linked
to massive accelerating objects, like like a massive star being
(35:55):
hit with God's pool cue what ripping up the fabric
or just just the shock wave, the sound, you know,
however you want to, you know, interpret it just the
violence of the act. Well, you know, one of the
funny things in the last episode we mentioned the English
you guess you might call him a poly mauth, John Michelle,
who was one of the early people to write about
(36:16):
the idea of something like a black hole and a
thing that he posited that many people might not have
been able to imagine at the time, was the idea
of ripples going through the earth. The earth the like
earthquakes could be caused by shock waves and the earth
flexing up and down due to friction events. And so
you know, it's hard for somebody to imagine, how could
(36:37):
there be ripples in the ground. The ground is just solid.
You know, I see waves in water, but surely not
in the ground. Take this the next step. Take this
to ripples and waves emanating through the geometry of spacetime itself.
So what kind of violence would we be talking about here?
So obviously God doesn't play pool, so we can't go
with the pool que example as far as you know
(36:58):
as well. Yes, so he doesn't play it in this
universe in a way that we can observe it, But
we can look to other cataclysmic events like supernova and
colliding black holes. Now, we were not able to observe
any proof of this until nineteen four and that's when
astronomers at Aricibo Radio Observatory in Puerto Rico discovered a
(37:20):
binary pulsar. And then it wasn't until astronomers using the
Ligo that's a laser interferometer gravitational wave observatory actually physically,
since gravitational waves emitted by two colliding black holes nearly
one point three billion light years away billion light years,
(37:42):
So how could we detect something that far away? Well,
the whole set up here is really fascinating because when
you when you look at pictures of it, it does
not look like a telescope. Uh. They use special detectors
in at the time to locations Washington State and Louisiana, uh,
(38:02):
separated Uh, this way across you know, of what, three
thousand kilometers in order to rule out localized distortions, right,
So you wouldn't want to rumble in one place to
give you a false positive on gravitational waves. So what
these things looked like are two blind l shaped detectors
with with the four kilometer long vacuum chambers essentially long
(38:26):
tubes with lasers shining through them, uh, calibrated to detect
like just just minute motions to measure emotion ten thousand
times smaller than an atomic nucleus, the smallest measurement ever
attempted by science. And again this is calibrated to to
observe these oscillations caused by the most violent and cataclysmic
(38:50):
events in the universe that are occurring millions or billions
of light years away. So both detectors picked up on
the black hole emitted gravitational waves at the expected intervals
dancing black holes in another galaxy, and then the waves
stop as the merger becomes absolute. Is the two black
holes stop dancing and become one. Okay, So you've got
(39:10):
this picture created by these two different laser observatories at
different parts of the country that something happened very very
far away where suddenly there was this escalating ripple as
these black holes kind of swirled into each other and
then merged and then boom nothing right, And that's exactly
what they expected to find. That the results match simulations
(39:32):
and therefore expectations the basic template for black hole merger.
And because they've got these two different stations, they could
say with really good confidence that they know this really
came from space and what it really is. It wasn't
just some kind of local fluke. Yeah, or you know,
like a car driving by with its stereo turned up right.
Uh No, Jack Burton and his rig uh. And And
(39:52):
since that time we've added there's they've added a less
sensitive Italian telescope into the mix and have observed waves
generated by a pair of neutron stars as well. Now,
when you were talking to Brian Green, the physicist at
the World Science Festival, and you asked him what the
most interesting research frontier and experimental physics was today, he
named gravitational waves because he basically said that this opens
(40:14):
up a whole new way of looking at the universe
that we did not have before, and so there are
all kinds of surprises we could discover through it. Yeah,
I mean in a in a in a weird way.
And it's almost like we're suddenly able to to listen
to the pulse of of of things in the universe
that were previously silent to us but that we suspected
(40:36):
would be present. I like that, And so that brings
us back, That brings us up to that that basically
brings us up to the present. Now, that's definitely not everything.
I mean, there's all kinds of interesting work that's been
done in the years in between on black holes, like
all the work of Stephen Hawking and everything, but um
Hawking radiation and entropy and information loss and uh and stuff.
(40:56):
And so I think we in the next episode should
explore a little bit of the weirder side and outstanding
mysteries about black holes, questions that are as yet unsolved,
or the weirdest thought experiments about black holes. Oh yes,
because that's the that's the wonderful part, right. Black holes
began as thought experiments, and thought experiments concerning black holes continue.
(41:19):
So black holes already maybe the weirdest thing in the
universe that's not alive. And in the next episode we're
going to find out what are the weirdest things about
them and the biggest mysteries yet unsolved. That's right. And
I'm also going to try and rewatch Event Horizon before
that episode as well. Prepare for leather punk Spaceship. Yeah,
and and I can truly, I can truly say where
(41:39):
we're going. You won't need eyes to see because it's
a podcast, you really don't have to to see anything.
And because it's a black hole and no light escapes exactly,
it all fits together. It's a great script that Event
Horizon alright. In the meantime, head on over to Stuff
to Blow your Mind dot com. That is the mothership.
That's where we'll find all the episodes of the podcast,
as well as links out to our us social media accounts.
(42:01):
As always, I urge you if you want to support
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(42:22):
us know a topic you might let us like us
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(42:43):
Is it how stuff works dot com proper Postschi Baba
My welcome to Stuff to Blow Your Mind from how
Stuff Works dot com. Hey you welcome to Stuff to
Blow your Mind. My name is Robert Lamb and I'm
Joe McCormick, and we're back. It's part two of our
multi part exploration of black holes. Because you know what,
(00:22):
this year Robert went to the World Science Festival in
New York and came back with black Hole Fever. Yeah.
It was a great It was a great talk that
really opened my eyes a little more to some of
the finer details of of black holes. And you mean
that Brian Green talk with the guests. Yeah, Darkness made visible,
wonderful talk. It's available online. Will include a link to
that in the landing page for this episode. Certainly inspired
(00:42):
us to to really give black holes a proper shake
on Stuff to Blow your Mind. Yeah, I mean, there's
so much interesting stuff to talk about, and the fact
that they're just one of the most interesting objects in
the entire universe. It's not that they're probably I would say,
maybe the most interesting non living thing in the universe.
What do you think about that? Yeah, yeah, I would
say that because we're pretty interesting ultimately humans are. Um.
(01:05):
I do want to remind everyone. If you did not
listen to the previous episode on black holes, you do
want to go back and listen to it, because this
is this is not one of those where you can
kind of take part one and part two in any order.
You really need to hit the first episode. I mean,
you could if you really wanted, But we're going to
be referring back to the groundwork we laid in the
previous episode. And the previous episode we talked a lot
about the development of black holes. Uh, sort of as
(01:27):
the history of an idea, something that was unlike the
stars in the sky. You know, the stars in the sky,
we first observed and we could see them, and then
by making observations about them, we were able to come
up with theories to explain them. Black holes weren't like that.
It went the other way around. Black Holes existed in
theory long before anybody accepted that they existed in reality,
(01:49):
and long after they existed in theory, many scientists ardently
opposed the idea that black holes could exist in nature. Yeah,
it's the idea that that these various individuals said, well, X, Y,
and Z are true, then this thing might exist and uh,
and and that thing is the black hole. But of course,
you know, lots of people when a thing sounds outlandish,
(02:12):
even if your best theories tell you it might be possible,
people want to find a way to say, no, that
just sounds unintuitive. It couldn't be real. It doesn't fit
my picture of how the universe works. It doesn't feel right. Yeah,
maybe that's a thought experiment, but I doubt will actually
find something like this when we start looking out into
the cosmos with better observational technology. You know, it's often
(02:34):
said that Albert Einstein did some of his worst work ever,
Like the worst science of his entire career was him
trying to write papers to prove that black holes didn't
exist in reality. It just didn't seem right to him,
even though his general relativity became the basis of our
modern theory of black holes. But so anyway, yeah, so
(02:54):
how did today? We want to explore making the darkness flesh,
making the black hole into a thing that is real
in existence in the universe and we can detect it.
So I think first we want to tell the story
of sort of like a bridging the gap between the
black holes of general relativity theory and the actual observations
of them and then talk a little bit about what's
(03:16):
it like to detect black holes and how we might
do it. And we do have to distress that in
today's world, black holes are pretty much an established reality.
You talk to experts and they say yes, without a
shadow of a doubt. Yeah. I don't know if it's
the case that every single expert would say without a
shadow of a doubt, but yeah, they're They're generally accepted
as a fact of reality. You know, we've reached the
(03:38):
point where black holes exist and they're completely non politicized.
That's the other great Yeah, oh man, I love a
scientific controversy that doesn't never have a political angle. Yeah,
it's the black holes are are. Thus far, they've remained
pretty safe. Well, maybe we can muck it up today.
Let's let's get people taking tribal sides on it. Okay,
(03:59):
So the story of how black holes went from this
theoretical anomaly to a thing known to exist in the world,
it's a long, complicated story, so we definitely can't explore
all of it, but I just want to mention a
few highlights, and one of the first ones is serious
b Now, Serious is the brightest star in the night.
Sky from Earth, often known as the Dog Star because
(04:22):
it's part of the Cannus Major constellation, the Great Dog constellation.
Side note, I didn't know this until I was reading
this the other day. Do you know the origin of
the term dog days of summer doesn't actually have anything
to do with the behavior of dogs. Really. I always
thought it came from a Don Henley song. Wait, one
of the Boys of Summer. Sorry, after the dog Days
(04:43):
of Summer have gone. Yeah, man, I grew so hard
whenever that song comes on the radios. It's a great
it's a great track. I love it. It's yacht rock
that touches my heart. Yeah. So the term dog days
of Summer actually refers to the period of Serious, the
star in the Cannus Major constellation, rising roughly in conjunction
with the Sun, which happens in July through August in
(05:06):
the Northern Hemisphere, and so this is also the hottest
time of the summer, and so it came to be
associated with Okay, so Serious is coming up with the
sun in the morning, and that means it's going to
be real hot out. But back in the eighteen hundreds,
it had been observed that the extremely bright star we
now call Serious A behaved oddly. Its motion was not
(05:29):
it was it was not smooth. It was kind of wobbly,
as if it were being destabilized and tugged on by
an invisible hand. And it turned out that Serious A
actually had a very dim companion star. It was a
binary star system, and the companion was what we now
call Serious B. But it was a very strange type
(05:50):
of companion because based on the motion of the two
bodies and the light they produced, astrophysicists could calculate that
the companion of Sirius at the same time was somewhere
around the mass of our Sun, and yet was barely
larger than the size of planet Earth and burning extremely hot,
much hotter than the Sun. So Serious Be turned out
(06:14):
to be an early example of what would later be
called a white dwarf, a tiny, hot, massive star that
proved matter could be compressed to pressures previously thought absolutely impossible.
In the words of Arthur Eddington, quote a ton, and
he's talking about the the material making up the star.
A ton of this material would be a little nugget
(06:35):
that you could put in a matchbox. So imagine something
matchbox size. But that weighs a ton, and so for many,
including Eddington, the very concept of this density was so
absurd that it should just basically cause us to dismiss
the observations out of hand, dismiss the idea of a
white dwarf. It's absurd, but reality is stranger than our imagination.
(06:56):
White dwarves came to be accepted as a feature of
the universe and a part of ller revolution, especially after
quantum mechanics eventually came along. To explain how matter could
be compressed to such an unbelievable density. Basically has to
do with packing atomic nuclei tighter and tighter, and you
can actually do this to some extent because most of
an adam is empty space. There's a good explanation of
(07:18):
this actually in a book that's one of our sources
on this episode, Black Hole, by Marcia Bartousciak, which I
thought I should mention again, which is a good good
book if you want to go in more depth than
we're going into here. But so with serious b you've
got these white dwarves, You've got these objects that are
observed to be tiny and very hot and very bright
(07:39):
and very massive, and so what would be the limits
on what a star like that could be like uh
In nineteen thirty, the young Indian astrophysicist Supermania and Chandra
Sheker calculated that there was an upper limit to the
mass of a white dwarf. White dwarves could vary in size,
but somewhere around one point four solar masses. If a
(08:02):
white dwarf is about one point four times the mass
of our Sun, something happens. This is now known as
the chander Shaker limit, and it around this mass, the
force of gravity chander Shaker calculated appears to become more
powerful than the force that's known as the electron degeneracy pressure.
(08:22):
And what that is is it just causes atoms to
push against one another and resist compression. So why can't
you keep compressing it down more and more? There's this
electron degeneracy pressure pushing back, but at a certain point, gravity,
at least on paper, appears to completely overwhelm this degeneracy
pressure and just crush everything down. So any clump of
(08:45):
white dwarf stellar matter more massive than this could not
maintain the white dwarf density at a stable pressure given
the laws of general relativity. Past this point of star's
density would just not scale up regularly, but would collapse,
and it would collapse toward infinity. But when you think
about that, like try to imagine your in Chonder Shaker's
(09:07):
position infinite density, what does it mean to collapse to
infinite density? You'd almost be tempted to think, Okay, well
I made a mistake. Yeah. It's like it's like suddenly
everything is reduced to zero and you know that the
equation must be flowed. Yeah, it's like you've you've hit
a divide by zero area or something. You you know
that you must have done something wrong. It was difficult
(09:28):
to believe that something like this could be possible in reality.
How could a real physical object collapse toward a point
of infinite density? Though this is what the math appeared
to show. But Chonder Shaker did not actually argue about
what physically happened to the white dwarf past the limit
that he had established, only that the limit of stability
at about one point four solar masses existed, and Chandra
(09:52):
Shaker spent years arguing against the grain of scholarship on
this point. There's a famous story about how when he
presented his findings at a meeting of the Royal last
Atronomical Society of London and nineteen thirty five our old
friend Arthur Eddington's uh. He supposedly exclaimed there should be
a law of nature to prevent a star from behaving
in this absurd way. That's some wicked cantankerousness, just like
(10:15):
yelling at the laws of physics. But but no, I
mean so, that kind of attitude from Eddington actually kept
this idea down for a long time, even though we
would eventually find out that chander Shaker was on the
right side of this argument, and the prolific Soviet physicist
live Landau also made a similar calculation around this point,
and he also arrived at the conclusion that a heavy
(10:37):
enough star could collapse to what appears to be a point.
But he said, that can't be quite right, so he
ignored this result and instead concluded that the core of
a star like this that at the core of a
star like this, matter sort of begins to ignore the
laws of physics and becomes quote, one gigantic nucleus. Now,
chander Shaker was eventually recognized for being in the right
(10:58):
on this question. He see the Nobel Prize in Physics
for his work on stellar evolution, and he got that
in nineteen eighty three. Now, also in the nineteen thirties,
a parallel idea to the idea of the black hole emerges,
and that is the idea of a neutron star. Now,
a neutron star is another form that stellar collapse can take,
(11:19):
in which you've got protons and electrons that form the
core of a star and they compressed together with such
force that they combine and form neutrons, which have mass
but no electric charge. And a neutron star is not
as a reality warping as a black hole, but it
is an unbelievably exotic type of object composed matter so
(11:39):
dense that it's been compared to an atomic nucleus the
size of a city. If you can picture that, Uh,
can you picture that? Of course you can't, nobody can,
but just just try. I can picture an illustration that
was presented of this. That's that's the best I can do. Well.
I mean, part of the problem is that matter already
looks solid enough to us, right, I mean, you take
(12:01):
a rock or something like that, You're like, this looks
really really solid, but most of it is empty space.
Most of it is just the space between the atomic
nuclei and the electrons orbiting them, and the other atomic
nuclei that they're bonded with. Um. I mean, the molecules
that make that very solid seeming object are mostly empty space,
(12:22):
and there's a lot of space you can press things
further and further into if you really must. You may
not be able to get blood from a stone, but
there's a lot of empty space there. If empty space
is when you're after, it's there, you can get space
from a stone. So, just to show how much things
can be compressed, it's often said that, like a square
centimeter of a neutron star, material might weigh more than
(12:44):
a billion tons. Uh So. In the late nineteen thirties, J.
Robert Oppenheimer, who's famous for working on the Manhattan Project,
among many things. Oppenheimer and some students of his published
work tending in the same direction as Chandra shako Are.
Oppenheimer and George Volkoff did work on the emerging idea
of neutron stars, which we were just talking about, and
(13:05):
found that neutron stars, like white dwarves, had an upper
limit of mass, after which something very strange seems to
happen to them. You've got this upper limit, and if
they have more mass than this limit, there's some kind
of collapse, something, something goes wrong with the physics. Oppenheimer
also published a paper on stellar evolution with Heartland Snyder
(13:27):
in which they determined that late stage stellar remnants of
stars passed a certain mass would seem to enter this
state of permanent infinite collapse. The matter within them would
exist in this perpetual free fall towards a point of
infinite density, the singularity. And that is a that is
a mind boggling concept to toy around with, falling forever.
(13:49):
The never ending pit essentially, which was it was something
like as a kid, you, or at least when I
was a kid, that's what we played instead of the
floor is lava. Always said the floor is an never
ending pit. That's more than lava. Yeah. I think it's
because we saw it on like key Man cartoons or something.
I feel like it isn't that what's underneath Castle Gray
Skull and never ending pit? I don't remember it is
in my mind. Well, then what's Castle gray Skull built on.
(14:13):
It's built over and never ending. I see it's called
a strut since yeah, yeah, I guess they had to
cap that thing, you know up, They're like, don't people
gonna fall into that, Let's put a castle on top
of it. So it's playing fast and loose with masters
of the universe. Um myth those here. By the way,
I apologize for just trying to move us along. I
think we should dwell. No, no, I'm good, I'm good. Okay,
(14:34):
don't ever let me be too square. Okay. Uh So,
starting in the nineteen fifties and sixties, both experimental and
theoretical work really seems to accelerate in the direction of
indicating the reality of neutron stars and black holes. These
these really exotic collapsed star remnant objects and theoretical models
(14:55):
are affirmed over and over and they appear increasingly sound.
While new astro comical observations really seem to make us think, wow, yeah,
there could be black holes out there. I think some
of the skepticism could be unfounded. Like in the nineteen
sixties you had scientists identifying quasars, which are these distant
high energy objects, possibly young galaxies, with black holes at
(15:17):
the center of them, emitting trillions of times the energy
of a sun. And you had pulsars, which are spinning
objects emitting a repeating pattern of radio bursts. And around
the same time, astronomers identified sources of X rays and
gamma rays from all over the celestial map. And these
signals really strongly pointed to the physical reality of collapse
(15:38):
stars like neutron stars and black holes. And now we
know that actually pretty much every mature galaxy in the
universe that we know of seems to have a supermassive
black hole at its center. It may be the black
holes are necessary for the formation of galaxies, and galaxies
are where things like us live. The black hole the
life giver. Yeah, we were rebrand rebranding the black hole today. So,
(16:03):
speaking of supermassive black holes, I I do want to
just touch in once more on the three forms of
black holes that we tend to discuss. Okay, so we've
mainly been talking about stellar black holes, right right. The
idea of a collapse star. Yeah, these would be as
massive as as twenty of our sons uh fit inside
a one mile radius sphere. Uh. These are the would
(16:24):
be the remnants of very massive stars that have run
through their innergy energy reserves. They go supernova and then
they collapse upon themselves and they're thought to be the
most common type of black holes, and there are likely
dozens within our own Milky Way galaxy. And then they're
the primordial black holes. These tho I touched on the
first episode that the size of an atom. They have
the massive a mountain, So these are hypothetical, and they
(16:47):
probably formed soon after the Big Bang. And then of
course they're the big ones, the supermassive black holes. They
likely exist at the center of most galaxies. Our own
galaxy boast Sagittarius A, and it has a mass equal
to about four million sons. And uh, these black holes
formed with their respective galaxies and are proportional in size.
(17:10):
And again these these are these are a part of
our universe. You know, as much as we we tend
to sort of fall into the trap of thinking of
black holes as you know, cosmic love crafty and evil consumers,
they're they're just a part of the life cycle of stars.
They are part of the general physical reality of the universe. Yeah,
(17:30):
they're not reapers from another dimension. They're the life givers.
Let's not go too far alright. Well, on that note,
we're gonna take a quick break and when we come back,
we will get into the science detecting black holes. Thank you,
thank you. All Right, we're back. So I want to
(17:50):
tell you a story about signas X one. Okay, let's
have it. So. Way back in the nineteen sixties and
the Swinging sixties, the astronomers out there, we're making use
of a new class of tools to study distant regions
of the sky, and these were space based X ray detectors.
They were attached to orbital rockets and artificial satellites, and
(18:12):
these instruments looked for X ray signals the astronomers and
astrophysicists thought they might find emanating from all kinds of
celestial sources, from say, the surface of the Moon. You know,
it's the moon shooting X rays. Two distant star systems
and nebulae, and one strong source of X ray radiation
detected by rockets in the nineteen sixties was a point
(18:35):
in the constellation Scorpius, and the source of the radiation
came to be known as s c O X one
or SCO X one. I don't know if you say
it like SCO that makes it sound kind of scummy,
but it was a truly remarkable fine because this radiation
source was about nine thousand light years from our solar system,
and it's X ray output was millions of times stronger
(18:57):
than that of normal sun like stars. And this massive
energy output came we discovered from a neutron star in
a binary system, and since then other similar sources have
been discovered. These X rays are generated when matter from
so you've got a binary system, you've got like a
neutron star or a black hole, and then some other
kind of object like a star. They're dancing, Yeah, they're
(19:21):
they're they're doing the polka out there in space. And
the X rays are generated when matter from the surface
of the more normal star gets sucked violently into the
gravitational field and onto the surface of the neutron star.
That's what's going on in the case of s c
O X one. And during so so this this gets
(19:42):
sucked in, the matter gets heated up a lot, and
X rays get blasted out into space. But during these
surveys of the nineteen sixties, one X ray source in
the sky was not like the others. In nineteen sixty
four we started to get a clear picture of the
radiation output of one source in the Sickness constellation, and
this source came to be known as signus X one,
(20:03):
and unlike the X ray sources that emitted like regular
pulses you know sometimes that would happen be be beep,
Signus X one seemed to be releasing unbelievably powerful, irregular
bursts of this deadly high frequency radiation, and sometimes these
irregular bursts were incredibly short, like on the scale of
millionths of a second, and so at a meeting in
(20:26):
March ninety one, the Italian astrophysicist Ricardi Giaconi speculated that
the source of the X one signal might be a
real black hole, the first black hole apparently observed in space,
and later analysis did seem to bear out this hypothesis.
The signus X one system seems to consist of a
(20:47):
blue giant star orbiting with a much smaller object that
we can't see. And by observing the size of the
companion star, the blue giant known as h d E
two to six six eight, and the rate of its
orbit it completes an orbit in less than six earth
days and the size of that orbit, astronomers began to
get a picture of this unseen orbital center. It appears
(21:11):
to be invisible, tiny and heavy. Current estimates of its
mass are at about fourteen point eight of our sons,
and the radiation coming from this source is emitted as
this apparent black hole sucks matter off of the orbiting
star like we were just talking about with the neutron star.
It sucks gas or matter off of that star, and
the matter swirls down into the gravity pit of this object,
(21:34):
heating up as it does, and eventually it heats to
the point that it gives off X rays, and of course,
once that gas falls past the event horizon, presumably nothing
more is emitted. It's stuck inside. But you've got so
you've got these observations. It's massive, it's tiny, it's invisible,
and it shoots radiation out into space as it appears
to suck matter from neighboring bodies. Really really seems like
(21:58):
a black hole. But was it proof? This was actually
famously the subject of a bet between physicist Stephen Hawking,
who did plenty of his own important work on black
holes in Kip Thorn in nineteen seventy four. Real quick
Kip Thorne, by the way, not only physicists, but executive
producer of the two thousand fourteen film Interstellar. Oh yeah,
(22:19):
that that was probably the best black hole movie I've seen. Yeah,
and that's why. Right, So he tried to get them
to like get the science right, Yeah, to say, be accurate,
make it look like a black hole would really look
Let's do some math. Yeah, and they did the math,
and that's a that's that's that's something that most people
tend to to praise Interstellar for as being the best
(22:40):
depiction of a black hole in at least cinematic science fiction. Well,
as I've said on the show before, my favorite thing
about it is how it actually deals with the time
dilation effects of relativity. Uh. Yeah, there's a lot to
like about Interstellar. But coming back to that bet. I'm
sure you've heard about this bet before. This is a
famous bet in the history of physics astrophysics. So Thorn
(23:00):
and Hawking had this bet. Hawking was the pessimist, Thorn
was the optimist. Well, I guess depending on what you
think you know regarding the nature of black holes, right,
Thorn bet that Signals X one would turn out to
be a black hole. Hawking bet that it would not
turn out to be a black hole, and Hawking was wrong.
By Hawking admitted that the evidence for X one's black
(23:21):
hole status was so strong that he had to concede
the bet. So we live in a world now where
astronomers and astrophysicists are almost totally convinced that black holes exist.
You can fly out into space in theory, and you
could fly right into them, but they nevertheless remain tricky
from an observational standpoint. So I think now for the
rest of the episode, we should try to explain some
(23:44):
of the ways that we can use to try to
detect black holes in space. Yeah, a thing that by
its very definition cannot be seen, cannot be seen directly,
of what are the ways in which we can observe
their presence? Right? Because one of the very things that
makes a black hole unique is that it neither emits
nor reflects detectable light of its own. So how would
(24:05):
we ever know if it one exists? Well, there are
lots of indirect ways of detecting them. And of course,
even though it doesn't emit light of its own, that
doesn't mean it's necessarily dark, because, as we explained in
the last episode, there's stuff going on around it. And
in fact, we just touched on one example of this.
Uh of the idea of stuff falling into the black hole,
stuff being material being sucked into it. Yeah, so black
(24:28):
holes themselves are dark, but from our perspective, the region
around the black hole can be anything. But So imagine
there's this region of space where we observe extremely hot,
high energy radiation. You've got X rays spewing out all
over the place. What's going on there? Well, a good
chances you've got a black hole with matter falling into it.
The matter gets heated up to hundreds of millions of
(24:50):
degrees and produces all these kinds of powerful radiation that
are visible from Earth until it passes that threshold, however,
and falls into the black hole, after which admits nothing.
To revisit what we uh the example I brought up
in the last episode, I think it's kind of like
you've got a haunted house and you've got like a
car that takes people around the haunted house. And the
(25:11):
car is soundproof, so you can't hear people screams from
inside the car, but as the tourists line up to
get into the car, you will probably hear them doing
all kinds of things as they're like sort of loading in.
And the fact that you can observe. Often all of
this violence and radiation around a black hole came up
in that darkness visible presentation. Right. Yeah, it was pointed
(25:31):
out that the despite they're inherent darkness, black holes are
among the brightest objects and the cosmos often, uh pinpointed
is points of extreme brightness in a relatively compact region
of space. And this is due to all of the
material and light surging in and orbiting around the objects
of the horizon, the point again at which even light
(25:51):
cannot escape. Right, this is probably a terrible, a terrible comparison.
But to come back to the Texas chainsaw mask your house,
it's like, oh again, yeah, they're all the is, all
these missing teenagers and all of these looted graveyards. Uh.
And then we have this one area here, uh clear,
look at all this activity around the house. That's how
we have some idea about what's going on inside it. Right,
(26:12):
Maybe you can't get a warrant to go inside the house,
but you can see there's a ruckus going on or
in the general vicinity, right, And that's what we're looking
at here, the black hole ruckus. But that's not the
only way that we can we can detect the presence
of a black hole. No, there are lots of other
really interesting ways. So here's another one. Imagine you are
to look at a place in the galaxy where visible
(26:33):
objects are acting weird. Planets are stars travel in these
repeating loops as if in orbit around something, but we
can't see what that thing is for them to be
an orbit around, or if we can see it, maybe
it's like they're orbiting an invisible star, or we can
see something very bright that they're orbiting, and the way
that they're orbiting it indicates that this thing they're orbiting
(26:56):
might be both very very small and very very massive.
It's essentially the invisible man scenario, you know, like you
can see the hat, but there's no person there. Well,
something must be holding up the hat. Yeah, something's hold
up the hat and the umbrella. So, uh, for example,
what do we see when we look closely at the
center of our own Milky Way galaxy? We mentioned this
(27:17):
darkness visible presentation at the World Science Festival this year.
Uh So that presentation featured, among others, the u c
l A astronomer Andrea Gays, who has spent her career
examining exactly this question. What's going on at the center
of the galaxy. Now, of course, we mentioned in the
previous episode and earlier today that researchers have come to
(27:37):
believe that there is a supermassive black hole at the
center of most are all mature galaxies, and our galaxy
is no different. At the center of our galaxy, there's
an object called Sagittary Essay, which is believed to be
a black hole about four point three million times the
mass of our Sun, though Gays actually says that this
is on the low end of supermassive black holes, which
(27:59):
can be up to a billion times the mass of
our son. Though I want, I want to be impressed
by that, but I'm running into like the scale problem
right where somebody says like, hey, Robert, I want to
give you a hundred billion dollars or I want to
give you five hundred billion dollars. Yeah, up saying with
(28:20):
the scales that they might as well be the same
number because they're just so beyond my ability to, you know,
to fit them within the confines of my own life. Yeah,
what does that mean? What does that difference even matter?
What am I supposed to do with that information? Yeah?
So even though I recognize that that is a big difference,
and that that's it should be really impressive. I can't
actually picture it, so I'm I'm kind of stuck there.
(28:41):
You often run into this with some of the most
impressive stuff, and in astronomy it's like you want to
be accurately appreciative, but you can't visualize the scale. Yeah,
because then the numbers just become meaningless to most minds
after a point. But anyway, back to so Sagittary is,
say this thing that we believe to be a super
supermassive black hole. How how would you detect if it
(29:03):
really were a supermassive black hole? And just to note,
we keep calling it Sagittarius A, but technically the object
believed to be the black hole is Sagittarius A with
little asterisks. They call that Sagittarius A star. While Sagittarius
A as a whole is this more complex source of
radio signals, including the object we're talking about. So technically
it's Sagittarius A star, but I think we will keep
(29:25):
calling it Sagittarius A because when you're also talking about stars,
saying a star over and over can be confusing. So
the main method that Gaye talks about is to demonstrate
that a mass is within its short shield radius. We
talked about the short shield sphere in the last episode,
and in simple terms, what you're looking for is big mass,
(29:45):
small volume. We know that any mass contained within the
volume of its short shield radius will inevitably collapse into
a black hole. Nothing can stop it. At this scale,
gravity always wins, and a if you can show this,
if you can show that an object is of a
mass that's within the volume of its short shield radius,
(30:07):
you've effectively demonstrated that it must be a black hole.
So to see what's happening at the center of our galaxy,
we can look toward the constellation Sagittarius, and if you
have the right kind of telescope, you can peer straight
through to the group of stars at the core of
the Milky Way, the galactic center. And these stars really
do behave in an odd way, especially like a central
(30:27):
star called s O two, which orbits the object Sagittarius
A in a pattern of one orbit every sixteen years.
There are animations of this that are worth looking up.
In fact, there's even direct imaging. I don't know, but
it might be infrared imaging. But they're there. You can
like see the stars actually moving over a long time
lapse video, and the path of s O two looks
(30:48):
almost like a I'm trying to find the right point
of comparison. It's sort of like a pendulum or something,
you know, where you see something kind of slowly go
up to one side and then zoom down along the
other side. Um. And so that's what happens with the
start cruises slowly through a lot of its elliptical path
and then whips lightning fast through one end of the
(31:10):
ellipse of its orbit. And what's going on there is
apparently when s O two travels through the closest part
of its orbit with Sagittarius AY about seventeen light hours away,
it's moving at about three percent of the speed of light,
or roughly thirty million kilometers per hour, and that even
if you just look at the animations, you can tell
(31:30):
it's super fast. So because we can image the region
of Sagittarius AY and the objects traveling around Sagittarius A,
we can do physics calculations to determine the size and
the mass of what this object is, and it turns
out that it's more than four million times the mass
of our sun and appears to be crammed into this
very very tiny region at the center of the galaxy.
(31:52):
So it looks very much like a supermassive black hole.
All Right, we're gonna take one more break and we
come back. We will jump into more ways that we
detect black holes, including gravitational lensing. Thank thank Alright, we're back, Hey, Robert,
So what would happen do you think if you were
looking at something and a black hole passed between you
(32:15):
and the thing you were looking at. Ah? Well, I
think on one hand, a lot of people are attempted
to say, oh, you wouldn't be able to see it,
because the black hole would be in the way. It'd
be opaque. It would be like taking a black piece
of paper across your field division just blotted out. But
that doesn't quite seem to be the case. Definitely, not necessarily.
(32:35):
What occurs is something called gravitational lensing, and this occurs
when a strong gravitational field bends light around it, creating
a lens like effect, warping and magnifying light coming from
the opposite direction of the view. Yeah. So the simplified
version of this, I suspect it wouldn't actually work for
objects this small. But it's that if you, you know, Robert,
(32:56):
you and I stand on opposite ends of the room
and you put a black hole directly between us, instead
of just being completely blotted out, we'll sort of see weird,
warped fun house mirror versions of each other wrapped around
this dark spot. In our field of view. We will
be essentially distorted through the lens created by the gravity
(33:18):
distortion of the black hole. Yeah. One example of this
is frequently um used is what's known as Einstein's cross
These are four images of the same distant quasar that
appear around a four ground galaxy due to strong grave
gravitational lensing. So there's kind of this blur in the center,
and then the same star is pictured four different places
(33:42):
around it. That's interesting, So you might think of it
that way. In our our our rough example, here, I'm
looking across the room. I see a basic like blur
where you should be, where the black hole is is
blocking my view. And then perhaps to either side of you,
I see distorted versions of Joe, a beautiful image. Yeah,
maybe one floating a of you as well, kind of
like an angelic visitor with like kind of crazy warped
(34:05):
arms flapping around on both sides, like one of those
inflatable dude dads you see it to use car dealership.
Another example that I came across was that in two
thousand and ten, the Keck two telescope in Hawaii and
it's in I r C two instruments observed a four
ground quasar causing gravitational lensing of a galaxy in the
(34:27):
background behind it. So I think it's actually the reverse
of the example you just gave. So the quaysar is
likely to be a giant black hole that's spewing huge
amounts of radiation into the universe around it, making it
extremely bright. And this foreground quasar is known as sd
s J zero zero thirteen plus one to three. I
(34:48):
almost stopped reading there, but you know, you got to
say all the numbers, uh. And it's about one point
six billion light years from Earth, so this is very,
very far away. I included a picture here for us
to look at, but you can see how the quays
are in the foreground because of its great gravitational distortion effects,
seems to create a lensed image. These distorted side effects
(35:10):
of a galaxy that's in the background right behind it.
But we should get to the next method because actually,
I think this is maybe the most interesting and one
of the most conclusive methods that we have come up
with so far to demonstrate not only the existence of
black holes in the universe, but some of the most
violent black hole behaviors in the known universe. And that
(35:31):
is finally getting to a world where we can observe
gravitational waves. That's right, So we already discussed the general
relativity concept that mass distorts space time. As part of this,
Einstein also predicted that we'd observed ripples in spacetime gravitational
waves caused by some of the more extreme occurrences linked
to massive accelerating objects, like like a massive star being
(35:55):
hit with God's pool cue what ripping up the fabric
or just just the shock wave, the sound, you know,
however you want to, you know, interpret it just the
violence of the act. Well, you know, one of the
funny things in the last episode we mentioned the English
you guess you might call him a poly mauth, John Michelle,
who was one of the early people to write about
(36:16):
the idea of something like a black hole and a
thing that he posited that many people might not have
been able to imagine at the time, was the idea
of ripples going through the earth. The earth the like
earthquakes could be caused by shock waves and the earth
flexing up and down due to friction events. And so
you know, it's hard for somebody to imagine, how could
(36:37):
there be ripples in the ground. The ground is just solid.
You know, I see waves in water, but surely not
in the ground. Take this the next step. Take this
to ripples and waves emanating through the geometry of spacetime itself.
So what kind of violence would we be talking about here?
So obviously God doesn't play pool, so we can't go
with the pool que example as far as you know
(36:58):
as well. Yes, so he doesn't play it in this
universe in a way that we can observe it, But
we can look to other cataclysmic events like supernova and
colliding black holes. Now, we were not able to observe
any proof of this until nineteen four and that's when
astronomers at Aricibo Radio Observatory in Puerto Rico discovered a
(37:20):
binary pulsar. And then it wasn't until astronomers using the
Ligo that's a laser interferometer gravitational wave observatory actually physically,
since gravitational waves emitted by two colliding black holes nearly
one point three billion light years away billion light years,
(37:42):
So how could we detect something that far away? Well,
the whole set up here is really fascinating because when
you when you look at pictures of it, it does
not look like a telescope. Uh. They use special detectors
in at the time to locations Washington State and Louisiana, uh,
(38:02):
separated Uh, this way across you know, of what, three
thousand kilometers in order to rule out localized distortions, right,
So you wouldn't want to rumble in one place to
give you a false positive on gravitational waves. So what
these things looked like are two blind l shaped detectors
with with the four kilometer long vacuum chambers essentially long
(38:26):
tubes with lasers shining through them, uh, calibrated to detect
like just just minute motions to measure emotion ten thousand
times smaller than an atomic nucleus, the smallest measurement ever
attempted by science. And again this is calibrated to to
observe these oscillations caused by the most violent and cataclysmic
(38:50):
events in the universe that are occurring millions or billions
of light years away. So both detectors picked up on
the black hole emitted gravitational waves at the expected intervals
dancing black holes in another galaxy, and then the waves
stop as the merger becomes absolute. Is the two black
holes stop dancing and become one. Okay, So you've got
(39:10):
this picture created by these two different laser observatories at
different parts of the country that something happened very very
far away where suddenly there was this escalating ripple as
these black holes kind of swirled into each other and
then merged and then boom nothing right, And that's exactly
what they expected to find. That the results match simulations
(39:32):
and therefore expectations the basic template for black hole merger.
And because they've got these two different stations, they could
say with really good confidence that they know this really
came from space and what it really is. It wasn't
just some kind of local fluke. Yeah, or you know,
like a car driving by with its stereo turned up right.
Uh No, Jack Burton and his rig uh. And And
(39:52):
since that time we've added there's they've added a less
sensitive Italian telescope into the mix and have observed waves
generated by a pair of neutron stars as well. Now,
when you were talking to Brian Green, the physicist at
the World Science Festival, and you asked him what the
most interesting research frontier and experimental physics was today, he
named gravitational waves because he basically said that this opens
(40:14):
up a whole new way of looking at the universe
that we did not have before, and so there are
all kinds of surprises we could discover through it. Yeah,
I mean in a in a in a weird way.
And it's almost like we're suddenly able to to listen
to the pulse of of of things in the universe
that were previously silent to us but that we suspected
(40:36):
would be present. I like that, And so that brings
us back, That brings us up to that that basically
brings us up to the present. Now, that's definitely not everything.
I mean, there's all kinds of interesting work that's been
done in the years in between on black holes, like
all the work of Stephen Hawking and everything, but um
Hawking radiation and entropy and information loss and uh and stuff.
(40:56):
And so I think we in the next episode should
explore a little bit of the weirder side and outstanding
mysteries about black holes, questions that are as yet unsolved,
or the weirdest thought experiments about black holes. Oh yes,
because that's the that's the wonderful part, right. Black holes
began as thought experiments, and thought experiments concerning black holes continue.
(41:19):
So black holes already maybe the weirdest thing in the
universe that's not alive. And in the next episode we're
going to find out what are the weirdest things about
them and the biggest mysteries yet unsolved. That's right. And
I'm also going to try and rewatch Event Horizon before
that episode as well. Prepare for leather punk Spaceship. Yeah,
and and I can truly, I can truly say where
(41:39):
we're going. You won't need eyes to see because it's
a podcast, you really don't have to to see anything.
And because it's a black hole and no light escapes exactly,
it all fits together. It's a great script that Event
Horizon alright. In the meantime, head on over to Stuff
to Blow your Mind dot com. That is the mothership.
That's where we'll find all the episodes of the podcast,
as well as links out to our us social media accounts.
(42:01):
As always, I urge you if you want to support
this podcast, A great way to do it is to
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know feedback on this episode or any other, to let
(42:22):
us know a topic you might let us like us
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(42:43):
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