Speaker 1: Welcome to Bedtime Astronomy. Explore the wonders of the cosmos
Speaker 1: with our soothing Bedtime Astronomie podcast. Each episode offers a
Speaker 1: gentle journey through the stars, planets, and beyond, perfect for
Speaker 1: unwinding after a long day. Let's travel through the mysteries
Speaker 1: of the universe as you drift off into a peaceful
Speaker 1: slumber under the night sky.
Speaker 2: Hello everyone, and welcome back to the show. We have
Speaker 2: a truly massive topic on the table today. And I
Speaker 2: don't mean massive in the you know, the casual sense.
Speaker 2: I mean we are literally talking about the heaviest, densest
Speaker 2: objects in the entire universe.
Speaker 3: We really are.
Speaker 2: We're looking at a paper that just dropped yesterday February twelve,
Speaker 2: twenty twenty six, in Physical Review Letters.
Speaker 3: Yeah, it's about as hot off the press as it
Speaker 3: gets in this field.
Speaker 2: It really is. And I have to say, reading through
Speaker 2: it this morning, it just felt like one of those
Speaker 2: moments where you realize we might have been looking at
Speaker 2: the sky in well in the wrong way for the
Speaker 2: last fifty years.
Speaker 3: That's honestly not much of an exaggeration. This paper. It's
Speaker 3: by Henksy Wang and a team from the Max Planck
Speaker 3: Institute in Oxford. It takes a problem that has frustrated
Speaker 3: astrophysicists for decades and just completely flips it on its head.
Speaker 2: It really does. It turns a limitation into a tool.
Speaker 3: Exactly.
Speaker 2: We are talking about the universe as hidden strobes. More specifically,
Speaker 2: we're talking about supermassive black hole binaries, two absolute monsters
Speaker 2: locked in a death spiral, hiding in the dark.
Speaker 3: And until yesterday, hiding was definitely the right word.
Speaker 2: Right, So let's set the stage here for everyone, because
Speaker 2: I think most people have this image of a black
Speaker 2: hole as this lonely cosmic vacuum cleaner floating out there by.
Speaker 3: Itself, a solitary monster.
Speaker 2: Yeah, but that's not really the whole story.
Speaker 3: Is it not at all? I mean, sure, solitary black
Speaker 3: holes exist, of course, But if you look at the
Speaker 3: grand structure of the cosmos, the whole thing is hierarchical.
Speaker 3: Galaxies grow by eating other galaxies.
Speaker 2: It's galactic cannibalism.
Speaker 3: It is. It's a violent, messy history. Our own Milky
Speaker 3: Way has eaten smaller dwarf galaxies in the past, and
Speaker 3: we're famously on a collision course with Andromeda.
Speaker 2: Which is by the way still terrifying, but that's a
Speaker 2: problem for a few billion years from now, I guess, right.
Speaker 3: But just think about the architecture for a second. We
Speaker 3: know that pretty much every massive galaxy, including our own,
Speaker 3: has a superassive black hole in SMBH at its heart.
Speaker 3: Ours is SAGITTARIUSA, SAGITTARIUSA exactly, Andromeda has one that's much bigger.
Speaker 3: So when Galaxy A smashes into Galaxy B, the.
Speaker 2: Two big black holes have to go somewhere.
Speaker 3: They have to. They don't just vanish. As the two
Speaker 3: galaxies merge and all the stars and gas settle down
Speaker 3: into a new larger structure. Those two central black holes
Speaker 3: they have to interact. They sink.
Speaker 2: They sink towards the middle of the new galaxy.
Speaker 3: Right through a process we call dynamical friction. They sink
Speaker 3: toward the new center of gravity, and so logic dictates
Speaker 3: they must eventually find each.
Speaker 2: Other and form a pair a binary.
Speaker 3: A binary two super massive black holes orbiting each other.
Speaker 2: And this is the invisible dance we're talking about. The
Speaker 2: physics says they have to be there. All our models
Speaker 2: of how galaxies evolve say the universe should be well
Speaker 2: teeming with these.
Speaker 3: Things, it should be a common phenomenon.
Speaker 2: But when we point our best telescopes at those centers
Speaker 2: of these big merged galaxies, we see nothing.
Speaker 3: Well, not quite nothing. We see the galaxy the bright core.
Speaker 3: But trying to resolve two distinct black holes that are
Speaker 3: orbiting closely. It's arguably one of the single hardest observational
Speaker 3: challenges in all of astronomy.
Speaker 2: Okay, but why I mean we have the event horizon telescope.
Speaker 2: We literally took a picture of a black hole shadow
Speaker 2: a few years back. Why can't we just zoom in
Speaker 2: and see two of them?
Speaker 3: It's all about scale and resolution. The event Horizon telescope
Speaker 3: was an incredible feat, but it essentially turned the entire
Speaker 3: planet Earth into one giant radio dish to look at
Speaker 3: two very specific tars targets our own Sagittarius A and
Speaker 3: the one in M eighty seven.
Speaker 2: So it's not something we can just point anywhere.
Speaker 3: No, not at all. And for these binarias, we're talking
Speaker 3: about objects that could be millions or even billions of
Speaker 3: light years away. Now, when they're still very far apart
Speaker 3: from each other, say a few thousand light years, we
Speaker 3: can sometimes see them. We have confirmed cases of dual
Speaker 3: active galactic nuclei.
Speaker 2: So two bright spots and a messy colliding galaxy exactly.
Speaker 3: You can resolve them as two distinct points of light.
Speaker 2: Okay, so we can see the ones that have just
Speaker 2: started dating.
Speaker 3: You could put it that way. They're just waving at
Speaker 3: each other from across the room. But the ones we
Speaker 3: really care about, the ones that are gravitationally bound and
Speaker 3: are spiraling in towards an inevitable cataclysmic merger, those are
Speaker 3: effectively invisible.
Speaker 2: Why because they're too close, way too close.
Speaker 3: At that distance, they're separated by less than a light year,
Speaker 3: maybe much less. To our telescopes, they just blur together
Speaker 3: into a single blob of light.
Speaker 2: So they're either hiding in the glare of the galaxy's core.
Speaker 3: Or hiding in complete darkness if there isn't a lot
Speaker 3: of gas around them for them to eat and light up.
Speaker 3: And this has created this huge frustrating gap in our understanding.
Speaker 2: A cosmic blind spot.
Speaker 3: It is. We see them when they're far apart, and
Speaker 3: thanks to detectors like Lego, we can hear them in
Speaker 3: the final fraction of a second when they actually crash
Speaker 3: together and merge.
Speaker 2: But the whole middle part, the millions of years they
Speaker 2: spend spiraling closer and closer.
Speaker 3: It's a complete black box. We have almost no confirmed
Speaker 3: observations of that inspiral phase for supermassive black hole.
Speaker 2: Which is where this new paper comes in because the
Speaker 2: team from Max Plank in Oxford is basically saying, Okay,
Speaker 2: stop looking for the black holes.
Speaker 3: Exactly. They're saying, stop trying to resolve the dark objects themselves. Instead,
Speaker 3: look at the background, look at the wallpaper, look at
Speaker 3: the stars sitting behind them. They are proposing we use
Speaker 3: these binary black holes not as targets, but as lenses,
Speaker 3: as natural telescopes.
Speaker 2: Okay, this is where we need to go into the details.
Speaker 2: Because gravitational lensing is a term that gets tossed around
Speaker 2: a lot. You always hear the same analogy, you know,
Speaker 2: a bowling ball on a trampoline.
Speaker 3: The trampoline analogy.
Speaker 2: Yeah, that's not going to cut it today. We need
Speaker 2: to go deeper, we really do.
Speaker 3: The trampoline analogy is well, it's fine for getting the
Speaker 3: basic idea across, but it completely fails to explain why
Speaker 3: what this paper's proposing is so groundbreaking.
Speaker 2: So walk us through the actual mechanism. Let's start with
Speaker 2: lensing one oh one, a single black hole, okay.
Speaker 3: Einstein's general relativity mass warps the fabric of space time,
Speaker 3: and light, which we normally think of as traveling in
Speaker 3: a straight line, has to follow the curves in space time.
Speaker 2: So it's not that gravity is pulling on the light,
Speaker 2: it's that the path itself is bent precisely.
Speaker 3: Light is just taking the straightest possible path through a
Speaker 3: curved space. So if you have a massive object, the lens,
Speaker 3: and a light source directly behind it, the light from
Speaker 3: that source has to travel around the lens to get.
Speaker 2: To us, flowing around a rock in a stream.
Speaker 3: That's a decent analogy. Now, if you have a single
Speaker 3: perfectly spherical mass, like a single non spinning black hole,
Speaker 3: that lensing effect is very, very symmetric, okay. And if
Speaker 3: the alignment is perfect, the background, star, the black hole,
Speaker 3: and you, the observer are all in a perfect line.
Speaker 3: That symmetry focuses the light into what we call an
Speaker 3: Einstein ring.
Speaker 2: A perfect circle of light, a perfect circle.
Speaker 3: We've seen these. We use them to weigh distant galaxies
Speaker 3: and find exoplanets. It's a standard tool in the astronomical toolkit.
Speaker 2: But what's the catch.
Speaker 3: The catch is that word perfect. For a single spherical
Speaker 3: lens that has a single focal point, you have to
Speaker 3: be exactly on that line of sight to get that
Speaker 3: extreme magnification to see the ring. It's like a laser beam.
Speaker 2: So if a background star is just a tiny bit
Speaker 2: off to the side of the black hole, we don't
Speaker 2: see the ring.
Speaker 3: You'll see some distortion. The star might appear as two separate,
Speaker 3: slightly brighter images, but you don't get that massive, massive
Speaker 3: spike and brightness unless the alignment is just so. It's rare,
Speaker 3: very rare.
Speaker 2: Okay, that's lensing one oh one. Now enter the second
Speaker 2: black hole lensing two to two.
Speaker 3: This is where everything changes. You aren't just adding a
Speaker 3: second lens next to the first one. You are creating
Speaker 3: a complex interference pattern between two deep gravitational wells.
Speaker 2: The paper uses this term costic curves, and I know
Speaker 2: costic usually means something that burns.
Speaker 3: It does, but in optics and in gravitational lensing, it
Speaker 3: means something else. Left you back to that swimming pool
Speaker 3: analogy I mentioned earlier.
Speaker 2: The squiggly lines on the bottom.
Speaker 3: Exactly Think about why those lines are there. The surface
Speaker 3: of the water isn't flat. It's covered in little waves
Speaker 3: and ripples. Right, each ripple acts like a tiny, imperfect lens.
Speaker 2: Okay, I'm with you.
Speaker 3: So these ripples aren't focusing the sunlight into lots of
Speaker 3: little single points. They're focusing the light into lines, into curves.
Speaker 3: And those bright, dancing webs of light on the bottom
Speaker 3: of the pool, those are the caustics. It's where the
Speaker 3: light rays pile up, where the intensity is highest.
Speaker 2: Got it. So the water ripples are the imperfect lens,
Speaker 2: and the bright lines are the You've got it.
Speaker 3: Now take that concept and scale it up to the cosmos.
Speaker 3: Instead of ripples on water, you have two supermassive black
Speaker 3: holes orbiting each other. Their combined gravity creates a very
Speaker 3: complex surface in space time. It's not a smooth bowl anymore.
Speaker 2: It has ridges and valleys exactly.
Speaker 3: And those gravitational ridges focus the light from background stars,
Speaker 3: not into a point, but into a network of high
Speaker 3: magnification lines. Those are the caustic curves.
Speaker 2: And what do they look like?
Speaker 3: For a binary system? This network creates a very specific shape.
Speaker 3: The paper describes it as a diamond shaped structure. In mathematics,
Speaker 3: it's called an.
Speaker 2: Astroid, an asteroid like video game.
Speaker 3: Spelled differently, but yeah, it looks a bit like that.
Speaker 3: It's a star shape, a diamond with four points, but
Speaker 3: the sides are curved inwards. They're concave.
Speaker 2: So let me picture this floating in empty space behind
Speaker 2: these two invisible black holes. Is this other invisible thing,
Speaker 2: this geometric diamond of pure magnification?
Speaker 3: That is exactly what it is. And here is the
Speaker 3: absolute critical difference between a single black hole and a binary.
Speaker 3: For a single black hole, the region of very high
Speaker 3: magnification is a tiny point. For a binary, the region
Speaker 3: of very high magnification is this entire much larger diamond
Speaker 3: shaped perimeter.
Speaker 2: So the target is just bigger.
Speaker 3: Massively bigger. Ben's Coxus, one of the authors, makes this
Speaker 3: exact point in the press release. The chances of a
Speaker 3: background star's light being hugely amplified increase enormously for a
Speaker 3: binary compared to a single black hole.
Speaker 2: It's the difference between trying to hit the bull's eye
Speaker 2: with a single dart and just trying to hit any
Speaker 2: part of the dark.
Speaker 3: Board, a much much bigger darkboard. You've gone from trying
Speaker 3: to thread a needle to trying to hit a barn door,
Speaker 3: the probability just skyrockets.
Speaker 2: Okay, so the net is bigger. We have a much
Speaker 2: better chance of a background star lining up with this
Speaker 2: diamond shape. But the black holes aren't just sitting there.
Speaker 3: No, they're not. And this is where the strobe concept
Speaker 3: finally clicks into place. If the two black holes were
Speaker 3: just frozen in space, the diamond caustic would be frozen too.
Speaker 3: A star that falls on it would just look like
Speaker 3: a permanently distorted, brightened image.
Speaker 2: But they're not frozen. They're orbiting each other.
Speaker 3: They're orbiting. They're in a constant dance.
Speaker 2: So the diamond spins.
Speaker 3: The diamond spins, it rotates right along with the binary.
Speaker 3: Imagine a lighthouse and the beam is rotating. But in
Speaker 3: this case, the beam isn't a simple ray of light.
Speaker 3: It's this entire complex caustic structure. It's a diamond shaped
Speaker 3: beam of magnification.
Speaker 2: And that beam is sweeping across the background sky.
Speaker 3: Constantly sweeping. And the background sky, even in a seemingly
Speaker 3: empty patch, is just filled with faint, distant stars.
Speaker 2: So it's only a matter of time before that sweeping
Speaker 2: line of magnification runs over one of those stars.
Speaker 3: It's inevitable, purely by chance, the caustic curve will cross
Speaker 3: a background star.
Speaker 2: And when it hits, yeah, what do we see?
Speaker 3: We see a flash. The mathematics of the caustic means
Speaker 3: the magnification just shoots up. Hanksy Wang, the lead author,
Speaker 3: describes it as an extraor ordinarily bright flash for a
Speaker 3: brief period of time. It could be hours, could be days.
Speaker 3: It depends on the geometry and the speed. That background
Speaker 3: star will suddenly become hundreds or even thousands of times
Speaker 3: brighter than it normally.
Speaker 2: Is like someone switched on a cosmic light.
Speaker 3: Bulb, a very powerful one. And then as the caustic
Speaker 3: line passes over the star and moves on.
Speaker 2: The star goes back to normal.
Speaker 3: It fades back to its regular faint baseline brightness, as
Speaker 3: if nothing happened.
Speaker 2: But the binary is still orbiting.
Speaker 3: The binary keeps spinning, so the diamond cost it comes
Speaker 3: around again.
Speaker 2: On the next orbit, and if that star is still
Speaker 2: in the path, it hits.
Speaker 3: The star again.
Speaker 2: Flash flash. So we get a repeating signal a.
Speaker 3: Blank Hey, you get a strobe light, a repeating predictable
Speaker 3: burst of starlight, all caused by two invisible objects dancing
Speaker 3: in front of it.
Speaker 2: Okay, okay, I have to play Devil's advocate here. You know,
Speaker 2: I love this idea. But the universe is a really
Speaker 2: noisy place. It's full of things that blink and flash.
Speaker 2: We have variable stars, sefeed's, flarre stars, cataclysmic variables, super no.
Speaker 2: I mean, the list goes on. How can we possibly
Speaker 2: be sure that a blink we see is from this
Speaker 2: weird lensing effect and not just you know, a star
Speaker 2: having a hiccup.
Speaker 3: That is probably the most important question in this entire
Speaker 3: field of time domain astronomy. Is this transient, this flash unique?
Speaker 3: And the authors of this paper argue that, yes, this
Speaker 3: signal is remarkably distinct. It has a fingerprint distinction. What way,
Speaker 3: the timing, the shape, It all comes down to the
Speaker 3: light curve. That's what astronomers call a plot of an
Speaker 3: object's brightness over time. Okay, so if you look at
Speaker 3: the light curve of a typical variable star like a sephid,
Speaker 3: it often looks like a smooth wave. The brightness swells
Speaker 3: up and then it shrinks back down. It's often quite symmetric.
Speaker 3: That's because the physics is internal to the star. It's
Speaker 3: literally breathing, expanding and contracting.
Speaker 2: And a costic crossing. What does that look like on
Speaker 2: the graph?
Speaker 3: It looks nothing like that. Acostic crossing is purely geometric.
Speaker 3: It's not about stellar physics. It's about the geometry of
Speaker 3: crossing a fold in space time. The light curve is sharp,
Speaker 3: it's asymmetric. Asymmetric, you get a very very sharp rise
Speaker 3: in brightness and then a slightly slower fall. The peak
Speaker 3: is less of a gentle curve and more of a well,
Speaker 3: a spike. The math predicts a very specific U shaped
Speaker 3: profile right at the peak. It's a fingerprint that just
Speaker 3: doesn't look like anything a star does on its own.
Speaker 2: So if we see that specific, jagged spike shape, we
Speaker 2: know we're looking at gravity, not chemistry or fusion.
Speaker 3: That's the idea, and there's another layer to it. It's
Speaker 3: not just periodic. The paper calls it quasi period.
Speaker 2: Quasi periodic, so almost repeating.
Speaker 3: It repeats, but not perfectly. And the reason it's not
Speaker 3: perfect is the most exciting part. It's the very thing
Speaker 3: we've been trying to measure for.
Speaker 2: Decades, the inspiral.
Speaker 3: The inspiral. We should probably pause here and really dig
Speaker 3: into why these black holes are merging in the first place.
Speaker 3: We mentioned dynamical fresh earlier how they sink to the center,
Speaker 3: but that process isn't perfect. It leads to a famous problem.
Speaker 2: The final parsec problem. I remember this one. It's the
Speaker 2: idea that they get really close and then they just
Speaker 2: get stuck exactly.
Speaker 3: Dynamical friction works great when the black holes are far apart,
Speaker 3: moving through a dense sea of stars. They transfer their
Speaker 3: orbital energy to the stars and sink. But once they
Speaker 3: get close enough to form a tight binary, they well,
Speaker 3: they clear out their neighborhood.
Speaker 2: They kick all the nearby stars away with gravitational slingshots, right.
Speaker 3: And once they've kicked all the nearby stars away, there's
Speaker 3: nothing left to create that friction. There's nothing left for
Speaker 3: them to transfer their energy to. So in theory, they
Speaker 3: should just stall. They should orbit each other forever at
Speaker 3: a distance of about a parsec or a few light years.
Speaker 3: They should never get close enough to merge.
Speaker 2: But we know they do merge. We hear the gravitational
Speaker 2: waves from stellar mass black holes merging with lego all the.
Speaker 3: Time, exactly, so something has to bridge that final parsec gap.
Speaker 3: For a long time, we weren't sure what it was.
Speaker 3: Maybe friction from a big gas disc, maybe interactions with
Speaker 3: a third black hole. But for these really massive binaries,
Speaker 3: the dominant four that brings them together in the end
Speaker 3: is the emission of gravitational waves.
Speaker 2: And this is the key to decoding the strobes.
Speaker 3: This is the Rosetta stone. As these two huge masses
Speaker 3: whip around each other, they are constantly churning space time,
Speaker 3: radiating enormous amounts of energy away in the form of
Speaker 3: these gravitational waves.
Speaker 2: And if they're losing energy.
Speaker 3: Their orbit has to shrink. As the orbit shrinks, conservation
Speaker 3: of angular momentum means they have to speed up.
Speaker 2: And if they orbit faster, the strobe light blinks faster.
Speaker 3: Precisely, this is the decoding part of the whole thing.
Speaker 3: If we can find one of these systems and watch
Speaker 3: the flashes over time, we aren't just seeing a blink.
Speaker 3: We are seeing a cosmic clock that is ticking faster
Speaker 3: and faster and faster.
Speaker 2: So we can literally measure the rate of orbital decay
Speaker 2: just by timing the flashes from a background star.
Speaker 3: Yes, we can watch general relativity happen in real time.
Speaker 3: But the paper points out something even more profound, even
Speaker 3: more subtle. What's that The emission of gravitational waves doesn't
Speaker 3: just change the orbital period, it actually changes the shape
Speaker 3: of the caustic diamond itself.
Speaker 2: Wait, what how the waves themselves are distorting the lens
Speaker 2: in a way.
Speaker 3: Yes, the loss of energy and the shrinking separation between
Speaker 3: the two black holes alters the overall gravitational potential of
Speaker 3: the system. This, in turn subtly alters the geometrre of
Speaker 3: the caustic curve. The paper states that it imprints a
Speaker 3: characteristic modulation on.
Speaker 2: The flashes, So the lens itself is warping as the
Speaker 2: orbit decays.
Speaker 3: In cosmic real time. Yes, so maybe the peak brightness
Speaker 3: of the flash gets a tiny bit higher with each pass,
Speaker 3: or the U shape of the light curve gets a
Speaker 3: little bit wider. The timing between the flashes will shift
Speaker 3: in a very specific, predictable way. That is a direct
Speaker 3: signature of gravitational wave emission.
Speaker 2: Let me see if we get this straight. We find
Speaker 2: a star that's flashing, We check the light curve and
Speaker 2: confirm it has that jagged asymmetric shape of a costa crossing.
Speaker 2: We watch it repeat from the time between the flashes,
Speaker 2: we get the orbital period. From the brightness and shape
Speaker 2: of the flash, we can work out the total mass
Speaker 2: of the binary.
Speaker 3: In their mass ratio.
Speaker 2: Yes, and then from the tiny change in the timing
Speaker 2: and the shape of the flashes over years, we can
Speaker 2: measure how fast they're spiraling.
Speaker 1: It.
Speaker 3: You've got it. It's a complete telemetry package for an
Speaker 3: invisible system. We can extract the masses of the black holes,
Speaker 3: their distance from each other, their orbital speed, and the
Speaker 3: exact rate at which they are falling towards too.
Speaker 2: That's just that's mind blowing. It's like finding the black
Speaker 2: box of a plane crash months before the plane actually crashes.
Speaker 3: That's a grim but surprisingly accurate analogy. We are watching
Speaker 3: the slow motion collision.
Speaker 2: But we have to talk about time scales here because
Speaker 2: in astronomy, slow motion usually means check back in a
Speaker 2: million years. If a big binary has an orbited period
Speaker 2: of say five years, do we have to wait a
Speaker 2: whole career to see the orbit change?
Speaker 3: That is the practical challenge.
Speaker 2: Yes.
Speaker 3: For the most massive, super massive black holes, we're talking
Speaker 3: billions of solar masses. The orbital period in this phase
Speaker 3: could be a few years. So you see a flash
Speaker 3: and you set a reminder on your calendar for twenty
Speaker 3: thirty one and.
Speaker 2: Five years later flash hopefully. Yeah.
Speaker 3: So for any single system, yes, it's a very slow
Speaker 3: accumulation of data, But the real power of this method
Speaker 3: isn't in staring at one system forever, it's in watching
Speaker 3: all of them.
Speaker 2: A population study exactly.
Speaker 3: The paper really emphasizes this point. They say, what is
Speaker 3: possible our snapshots. Think of it like walking into a forest.
Speaker 3: You can't just sit there and watch a single acorn
Speaker 3: grow into a mighty oak tree. That takes a century.
Speaker 2: But you can look around and see an acorn on
Speaker 2: the ground, a little sapling over there, a young tree,
Speaker 2: and a huge old.
Speaker 3: One, and a rotting log. Exactly. By piecing together all
Speaker 3: those different snapshots, you can understand the entire life cycle
Speaker 3: of the tree.
Speaker 2: So we apply that to the sky. We look for
Speaker 2: these flashes everywhere, everywhere.
Speaker 3: And if we scan the whole sky, we will find
Speaker 3: binary black holes at every single stage of this inspiral process.
Speaker 3: We'll find some that are widely separated, flashing every decade
Speaker 3: or so. We'll find some that are tighter and faster,
Speaker 3: flashing every few months, and we'll find some that are
Speaker 3: right on the brink of merging.
Speaker 2: And by putting all those data points together, we can
Speaker 2: build the movie of how these things evolve.
Speaker 3: We can finally fill in that massive gap in our
Speaker 3: knowledge of galaxy evolution.
Speaker 2: Which brings us to the tools. Because to scan the
Speaker 2: whole sky and catch a random flash that might only
Speaker 2: be visible for a few days, that just sounds incredibly expensive,
Speaker 2: like we'd need a new, dedicated.
Speaker 3: Telescope, and it would be if we weren't already building
Speaker 3: the perfect machines to do it. For other reasons.
Speaker 2: This is the part I love. We don't need a
Speaker 2: new line item in the federal budget for this.
Speaker 3: No, we can just piggyback on the next generation of
Speaker 3: survey telescopes that are about to come online. The paper
Speaker 3: specifically calls out two of them, the Vera ce Reuben
Speaker 3: Observatory and the Nancy Grace Roman Space Telescope.
Speaker 2: Let's talk about Ruben first. That's the one down in Chile, right,
Speaker 2: the one that used to be called the LSST.
Speaker 3: That's the one the Legacy Survey of Space and Time.
Speaker 3: Ruben is an absolute beast of a telescope. It's not
Speaker 3: like Hubble or the James web Hubble is like a
Speaker 3: sniper rifle. It stares at one tiny, tiny patch of
Speaker 3: sky with incredible detail. Reuben is a wide angle lens.
Speaker 3: It's a shotgun.
Speaker 2: It takes a picture of the whole sky.
Speaker 3: It will photograph the entire visible southern sky every three
Speaker 3: or four nights, over and over and over again, for
Speaker 3: ten years straight.
Speaker 2: That's I can't even comprehend that amount of data.
Speaker 3: It's something like twenty terabytes of data every single night.
Speaker 3: It is literally creating a high definition movie of the
Speaker 3: night sky.
Speaker 2: So if a background star behind a binary black hole
Speaker 2: flashes on a Tuesday night and then goes back to
Speaker 2: normal by Friday.
Speaker 3: Ruben will see it. It is designed from the ground
Speaker 3: up to find transience, things that change, things that flash,
Speaker 3: things that move, supernovae, asteroids, variable.
Speaker 2: Stars, and now, thanks to this paper, binary black hole strobe.
Speaker 3: So on the list of targets. Now the data will
Speaker 3: just be sitting there in the archive.
Speaker 2: So it's not an observational problem, it's a data science problem.
Speaker 3: Exactly. The photons will hit the detector. The challenge is
Speaker 3: writing the sophisticated soft where the algorithms that can sift
Speaker 3: through those petabytes of data and automatically flag it. To
Speaker 3: have a program that says, hey, wait a minute, that
Speaker 3: little blink in sector seven G that has the asymmetric
Speaker 3: caustic light curve flag it for a human to look at.
Speaker 2: And what about the Roman Space Telescope.
Speaker 3: That's NASA's next great observatory. It's space based, so no
Speaker 3: atmosphere to worry about, and its key feature is its
Speaker 3: field of view. It can see a patch of sky
Speaker 3: one hundred times larger than Hubble can in a single
Speaker 3: pointing so.
Speaker 2: It's like a Hubble quality shotgun.
Speaker 3: That's a great way to put it. It's doing what
Speaker 3: Reuben does, but from space and in the infrared, So
Speaker 3: between the two of them, we're going to have eyes
Speaker 3: on almost the entire sky almost all the time.
Speaker 2: We're really entering a new era of astronomy.
Speaker 3: It's the golden age of time domain astronomy. For most
Speaker 3: of human history, the sky was static. We took a photograph.
Speaker 3: Now we're watching the video.
Speaker 2: I want to pivot for a minute to what you
Speaker 2: might call the competition, or maybe the partnership. We mentioned
Speaker 2: Igo before, but there's a future mission that's specifically designed
Speaker 2: for these super massive systems.
Speaker 3: Lisa LISA, the Laser Interferometer space antenna.
Speaker 2: It's still just the coolest acronym in science.
Speaker 3: It really is. LISA IS. It's essentially a gravitational wave
Speaker 3: observatory in space. Imagine three separate spacecraft flying in a
Speaker 3: perfect triangle formation, millions of kilometers apart from each.
Speaker 2: Other, and they just shoot lasers at each other.
Speaker 3: They constantly shoot lasers at each other to measure the
Speaker 3: distance between them with unbelievable precision. When a gravitational wave
Speaker 3: from a supermassive black hole merger passes through the Solar System,
Speaker 3: it will stretch and squeeze the distance between those spacecraft
Speaker 3: by less than the width.
Speaker 2: Of an atom, and LISA can detect that.
Speaker 3: LISA will be able to detect that. It's designed specifically
Speaker 3: to hear the low frequency hum of these supermassive black
Speaker 3: hole binaries as they spiral together.
Speaker 2: So Lisa, here's the gravitational waves, and this new method
Speaker 2: sees the light from the strobes. Right.
Speaker 3: But here's the timeline issue. LISA is not scheduled to
Speaker 3: launch until the mid twenty thirties, maybe twenty thirty five,
Speaker 3: twenty thirty seven, somewhere in there.
Speaker 2: So we have a decade long gap.
Speaker 3: We have a gap. And this is where the new
Speaker 3: lensing method claims a huge, huge victory in the paper
Speaker 3: Cox has caused an extremely exciting prospect. Using Reuben and
Speaker 3: other telescopes, we can detect these inspiraling binaries with the
Speaker 3: strobe method years before Lisa ever gets off the ground.
Speaker 2: We can build the catalog of targets.
Speaker 3: Now we can find them, we can map them, We
Speaker 3: can say okay, at these coordinates in the sky, we
Speaker 3: have a binary with a mass of a billion suns
Speaker 3: and a two year orbital period. We can build a
Speaker 3: watch list.
Speaker 2: And then in the twenty thirties, when LESA launches.
Speaker 3: We turn it on and we already know where to listen.
Speaker 3: And this opens the door to the holy grail of
Speaker 3: modern astrophysics. Multi messenger astronomy.
Speaker 2: That's a buzzword I hear constantly. Can you break that
Speaker 2: down for us?
Speaker 3: It just means observing the same cosmic event with more
Speaker 3: than one messenger or more than one sense, seeing it
Speaker 3: with light, and hearing it with gravitational waves. Think about
Speaker 3: watching a thunderstorm, see the flash of lightning. That's your
Speaker 3: light signal, that's the strobe. A few seconds later, you
Speaker 3: hear the boom of the thunder, that's your second signal.
Speaker 2: And from the delay between the two, you know how
Speaker 2: far away the storm is exactly.
Speaker 3: If you only have one, you have incomplete information. But
Speaker 3: if you have both you can learn so much more.
Speaker 3: Now apply that to black holes. If we can see
Speaker 3: the flash from the caustic and hear the gravitational hum
Speaker 3: from the inspiral coming from the same object at the
Speaker 3: same time, we can test fundamental physics in ways that
Speaker 3: are currently just science fiction.
Speaker 2: Like what, what's the first thing you'd test?
Speaker 3: The speed of gravity? Einstein's theory says gravitational waves travel
Speaker 3: at the speed of light, but do they do they
Speaker 3: really to the fifteenth decimal place. If the flash and
Speaker 3: the wave arrive at our detectors at slightly different times
Speaker 3: after traveling for a billion years, that could mean Einstein was.
Speaker 2: Wrong, which would be a Nobel prize.
Speaker 3: Instantly, we break physics as we know it.
Speaker 2: Wow. And it would also tell us about the environment
Speaker 2: around the black holes, wouldn't it, Because light gets affected
Speaker 2: by gas and dust, but gravity.
Speaker 3: Gravity just plows right through everything. It doesn't care. So
Speaker 3: if the light signal is a little bit delayed or
Speaker 3: scattered compared to the pristine gravity signal. It tells us
Speaker 3: exactly how much messy stuff gas, dust, accretion disks is
Speaker 3: sitting around the binary. It gives us a complete picture.
Speaker 2: It really feels like we're moving from just guessing about
Speaker 2: these systems to being able to put them on a
Speaker 2: lab bench and measure them.
Speaker 3: That's the transition the whole field is making. We are
Speaker 3: moving from purely theoretical models of binary evolution to direct
Speaker 3: observational telemetry.
Speaker 2: I want to circle back to something you mentioned earlier
Speaker 2: about the background the stars. Okay, for my whole life,
Speaker 2: I've thought of the background stars as well as just noise.
Speaker 2: They're just the wallpaper. They are the things you have
Speaker 2: to subtract from your image to see the galaxy you're
Speaker 2: actually interested in.
Speaker 3: Astronomers have a term for it, the confusion limit. When
Speaker 3: there are so many faint stars you can't distinguish your
Speaker 3: target from the background, just stuff in the way.
Speaker 2: But this paper just completely inverts that idea. It says
Speaker 2: the background stars aren't the noise, they're the tool.
Speaker 3: They are the screen. That's the best way to think
Speaker 3: about it. The binary black hole is like an invisible
Speaker 3: film projector it's projecting its gravitational shape, this spinning diamond
Speaker 3: out into the universe. We can't see the projector itself,
Speaker 3: but we.
Speaker 2: Can see the image it's casting on the screen at
Speaker 2: background stars exactly.
Speaker 3: We see the flash as the beam sweeps past. The
Speaker 3: universe is a cinema and we're finally figuring out where
Speaker 3: to look to see the show.
Speaker 2: I want to end on a thought that really struck
Speaker 2: me when I was reading the discussion section of the paper,
Speaker 2: and it's about old data, archival data.
Speaker 3: Ah, yes, the potential for data archaeology.
Speaker 2: We've been taking digital pictures of the sky for a
Speaker 2: long time now, the Sloan Digital Sky Survey, pan Stars
Speaker 2: a dozen other projects. We literally have petabytes of images
Speaker 2: sored on hard drives and server farms going back decades.
Speaker 3: We do a treasure trap of information.
Speaker 2: And if these invisible costic curves are constantly sweeping across
Speaker 2: the sky all the time, everywhere.
Speaker 3: Then they have, without a doubt, triggered flashes that we
Speaker 3: have already photographed.
Speaker 2: We've already seen them, we just didn't know what we
Speaker 2: were looking at.
Speaker 3: Statistically, it's almost a certainty we have very likely recorded
Speaker 3: these exact events.
Speaker 2: So why didn't anyone notice?
Speaker 3: Because if you're looking at an image from nineteen ninety
Speaker 3: eight and you see a faint star that for one
Speaker 3: night was one hundred times brighter, and then in the
Speaker 3: next image it's gone again, what do you do.
Speaker 2: I assume it was an error.
Speaker 3: You'd shrug, You'd call it a cosmic ray hitting the detector,
Speaker 3: a glitch in the CCD chip, an anomaly. You discard
Speaker 3: it because it doesn't fit any pattern. You know, it's
Speaker 3: a one off weirdo.
Speaker 2: We didn't have the dictionary to translate what we were seeing.
Speaker 3: We didn't know the language. We didn't know that a
Speaker 3: jagged asymmetric spike was the signature of a binary supermassive
Speaker 3: black hole caustic. We just filed it under noise. Now
Speaker 3: now we have the template. Now we can write new
Speaker 3: algorithms to go back into all that old data from
Speaker 3: Sloan from pan stars and specifically hunt for that unique
Speaker 3: light curve shape.
Speaker 2: So the very first discovery of one of these binary
Speaker 2: black hole stripes might not happen with the Rubin telescope
Speaker 2: in twenty twenty seven. It could happen on a supercomputer
Speaker 2: next week, sifting through data from twenty fifteen.
Speaker 3: That is entirely possible. The evidence could very well be
Speaker 3: sitting there gathering digital dust on a server rack somewhere.
Speaker 3: We just need to blow off the dust and look
Speaker 3: at it with these new eyes.
Speaker 2: That to me is the most exciting kind of science,
Speaker 2: the treasure hunt, where you realize the map leads back
Speaker 2: to your own basement.
Speaker 3: It's a fantastic reminder that data is never truly dead.
Speaker 3: It just waits for a new theory, a new idea
Speaker 3: to bring it back to life.
Speaker 2: Well, I think that is a perfect and very hopeful
Speaker 2: place to wrap things up. We've gone from invisible monsters,
Speaker 2: to diamond shape lenses, to cosmic strobes, and finally to
Speaker 2: divving for treasure in old hard drives. It's been quite
Speaker 2: a journey, it really has. And for everyone listening. The
Speaker 2: next time you look up at a star and you
Speaker 2: see a twinkle, well, okay, it's probably just the Earth's atmosphere,
Speaker 2: but somewhere out there a star is blinking for a much,
Speaker 2: much grander reason because two giants are dancing in front
Speaker 2: of it.
Speaker 3: Keep watching the data.
Speaker 2: Thanks for listening, everyone, We'll catch you on the next one.
Speaker 3: Sai