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