Black Holes, Part 2: Detection

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 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. 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 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, 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, 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 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

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 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 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, 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 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 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 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 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 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

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 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. 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 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 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 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. 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 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 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 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 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

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 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 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, 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 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 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, 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 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 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 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.

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.

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,

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 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 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 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, 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 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 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. 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, 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 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 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 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 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 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 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, 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 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 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

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, 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 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, 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 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 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 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 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

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 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 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 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 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 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, 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

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 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 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 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 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 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. 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 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 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,

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, 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 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 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

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

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. 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 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. 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, 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

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 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 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 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 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 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 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 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 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 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

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

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, 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, 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 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 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 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 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 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 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 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. 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. 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 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.

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