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: Imagine an explosion so violent, I mean, just so incomprehensibly
Speaker 2: massive that it outshines all the stars in the observable universe.
Speaker 3: Combined, every single one.
Speaker 2: Yeah, I want you to picture an event that releases
Speaker 2: more energy in a fraction of a second than our
Speaker 2: own sun will produce in its entire what ten billion
Speaker 2: year lifespan exactly. And yet if you were, say, floating
Speaker 2: in space right next to it, you wouldn't see a
Speaker 2: blinding flash, you wouldn't hear a deafening roar.
Speaker 3: Nothing. It happens in complete pitch black.
Speaker 2: Silence, which is just to wrap your head around. The
Speaker 2: only way you would even know it occurred is that
Speaker 2: the literal fabric of space and time around you would
Speaker 2: stretch and squeeze right.
Speaker 3: You wouldn't just feel it. The actual geometry of your
Speaker 3: own body would momentarily distort.
Speaker 2: Okay, let's unpack this. Uh huh, because yesterday July first,
Speaker 2: twenty twenty six, our understanding of the universe fundamentally change.
Speaker 3: You really did.
Speaker 2: We're looking at the release of the Gravitational Wave Transient
Speaker 2: Catalog five point zero or GWTC five, and the sheer
Speaker 2: scale of what we were talking about here is almost
Speaker 2: difficult to process.
Speaker 3: It's staggering.
Speaker 2: We are talking about one hundred and sixty one newly
Speaker 2: identified black hole collisions and this was detected in just
Speaker 2: a ten month window, right between April twenty twenty four
Speaker 2: and January twenty twenty five.
Speaker 3: Yeah, and it is a monumental threshold for astrophysics. I
Speaker 3: mean to put that in perspective. Those one hundred and
Speaker 3: sixty one new events bring our total number of known
Speaker 3: confirmed black hole collisions to a staggering three ninety wow,
Speaker 3: three ninety Right. We are no longer in the era
Speaker 3: of viewing black hole mergers as these incredibly rare, you know,
Speaker 3: one off anomalies that we might catch if we're extremely lucky.
Speaker 2: Right, We're not just hoping to get lucky anymore. We're
Speaker 2: practically taking a census.
Speaker 3: Exactly, we are uncovering an entire hidden population because for
Speaker 3: the longest time, astrophysis was fundamentally constrained by the electromagnetic.
Speaker 2: Spectrum meaning light.
Speaker 3: Yeah, light, If you think about it, everything we knew
Speaker 3: about the cosmos came from catching light, radio waves, X rays,
Speaker 3: visible light. But black holes, by definition, trap light. They
Speaker 3: are the ultimate cosmic ghosts.
Speaker 2: Because the gravity is so strong, nothing escapes, right, so we.
Speaker 3: Only knew they existed because of how their gravity bullied
Speaker 3: the matter around them. You know, stars whipping around an
Speaker 3: invisible center, or accretion disks of superheated gas glowing as
Speaker 3: they fell.
Speaker 2: In, like seeing the wind blowing through trees rather than
Speaker 2: seeing the wind itself.
Speaker 3: That's a great way to put it. But when two
Speaker 3: black holes collide in a dark, empty void, there is
Speaker 3: no light to catch, total silence. Well until we learn
Speaker 3: how to listen to gravity itself.
Speaker 2: And the reason you need to know about this today
Speaker 2: is that we are crossing from a period of discovery
Speaker 2: into a period of archaeology. Oh absolutely, It is like
Speaker 2: we just mapped the ruins of a lost cosmic civilization
Speaker 2: and now we actually have enough data to understand how
Speaker 2: they lived, how they grew and how they.
Speaker 3: Died, which is the most exciting part.
Speaker 2: But before we get into the record breaking, just mind
Speaker 2: bending specifics at TWTC five, we have to talk about
Speaker 2: the how I mean a decade ago, in twenty fifteen,
Speaker 2: the very first detection of gravitational waves happens.
Speaker 3: Right, the one that proved Einstein write a century after
Speaker 3: he proposed general relativity exactly.
Speaker 2: But going from one detection a decade ago to what
Speaker 2: three or four a week today? How are we doing that?
Speaker 3: So the engine driving this revolution is the International LVK Collaboration. Okay,
Speaker 3: that is LIGO in the United States, which operates to
Speaker 3: massive detectors in Washington State and Louisiana. Then there's Virgo
Speaker 3: in Italy and KARA in Japan.
Speaker 2: And these are those massive L shaped vacuum tubes.
Speaker 3: Right, yeah, kilometers long where we fire lasers back and
Speaker 3: forth to measure the stretching of space time. But to
Speaker 3: understand why we are suddenly catching multiple events a week,
Speaker 3: you really have to look at the unsung heroes of
Speaker 3: the hardware.
Speaker 2: Who are they?
Speaker 3: Specifically the researchers at the University of Glasgow. They have
Speaker 3: been working on gravitational wave science since the nineteen seventies.
Speaker 2: Wait, the seventies, long before we had any proof these
Speaker 2: waves could actually be detected exactly long. I imagine dedicating
Speaker 2: forty years of your career to building parts for a
Speaker 2: machine to detect something that might not even be measurable.
Speaker 3: It takes a lot of faith in the math.
Speaker 2: I want to drill down into what they actually built,
Speaker 2: because I know it's not just a matter of pointing
Speaker 2: a telescope at this guy. They had to solve an
Speaker 2: absolute mechanical engineering nightmare.
Speaker 3: Oh, a total nightmare. What's fascinating here is that the
Speaker 3: core of the problem is isolation. The Earth is a
Speaker 3: remarkably noisy planet.
Speaker 2: Right.
Speaker 3: You have trucks striving on highways miles away. You have
Speaker 3: ocean wavesrushing against the continental shelf. You have continuous micro seismic.
Speaker 2: Tremors, constant vibration.
Speaker 3: Always even the wind pushing against the observatory buildings creates
Speaker 3: ground tilt. If you just bolted a highly sensitive mirror
Speaker 3: to the floor, it would shake violently.
Speaker 2: And we were trying to measure what a change in
Speaker 2: distance caused by a gravitational wave that is smaller than
Speaker 2: a fraction of an atomic.
Speaker 3: Nucleus, Right, so the background noise of the Earth is
Speaker 3: orders of magnitude louder than the signal we want.
Speaker 2: It's like trying to hear a single pin drop in
Speaker 2: the middle of a roaring hurricane using a microphone. You've
Speaker 2: suspended by a thread.
Speaker 3: That is exactly what it's like.
Speaker 2: So how do you separate the mirror from the planet
Speaker 2: it's sitting on.
Speaker 3: You suspend it. But you can't just hang it with
Speaker 3: steel wire?
Speaker 2: Why not?
Speaker 3: Because steel has internal friction. When atoms in a metal
Speaker 3: wire rub against each other, they generate thermal noise, microscopic
Speaker 3: vibrations that would travel right down to the mirror and
Speaker 3: mimic a gravitational wave. Ah okay, So the Glasgow Tea
Speaker 3: solution was to develop ultrasensitive mirror suspensions using fused silica,
Speaker 3: essentially extremely pure glass.
Speaker 2: Wait, they are hanging forty kilogram optical mirrors with glass thread.
Speaker 3: Yes, they literally pull these fused silica threads so they
Speaker 3: are incredibly thin, and then they physically weld them to
Speaker 3: the sides of the mirrors.
Speaker 2: Wow.
Speaker 3: It's called a monolithic suspension because it's glass to glass.
Speaker 3: There are no joints, no clamps, and virtually no mechanical.
Speaker 2: Friction, which means no thermal noise.
Speaker 3: Exactly when you eliminate that friction, you eliminate a massive
Speaker 3: source of the noise. The mirror essentially floats, completely decoupled
Speaker 3: from the chaotic molecular vibrations of the Earth. That's incredibly
Speaker 3: it's perfectly still waiting for the fabric of the universe
Speaker 3: itself to ripple through it.
Speaker 2: I just want to pause on that image for a second.
Speaker 2: We have a forty kilogram mirror hanging by glass threads,
Speaker 2: isolated so perfectly that it doesn't feel a truck driving
Speaker 2: by outside, but it does feel two black holes crashing
Speaker 2: into each other a billion light years away.
Speaker 3: It's beautiful engineering, and it goes even deeper than mechanical isolation.
Speaker 3: We also have to fight quantum noise, right.
Speaker 2: Because when you get down to measurements smaller than a proton,
Speaker 2: the universe just stops playing by normal rules. The Heisenberg
Speaker 2: uncertainty principle kicks in.
Speaker 3: Exactly at that scale, you can't know both the phase
Speaker 3: and the amplitude of the laser light with perfect precision.
Speaker 3: Right empty space itself is boiling with quantum vacuum fluctuations,
Speaker 3: virtual particles popping in and out of existence, randomly kicking the.
Speaker 2: Mirrors, which is just wild.
Speaker 3: It is, so the observatories use a technique called quantum squeezing.
Speaker 3: They literally manipulate the quantum state of the laser light.
Speaker 3: They choose to accept more uncertainty in a variable they
Speaker 3: don't care about, like the phase, so they can squeeze
Speaker 3: down the uncertainty in the amplitude because.
Speaker 2: The amplitude is what they actually need to measure.
Speaker 3: The wave precisely.
Speaker 2: It's like squeezing a balloon. You squeeze it in the
Speaker 2: middle to make it narrower where you need it to be,
Speaker 2: but it bulges out at the ends. We are physically
Speaker 2: pushing the quantum fuzziness out of the way of our measurement.
Speaker 3: That's a perfect analogy, and it's this relentless, obsessive upgrading
Speaker 3: that gives us catalogs like GWTC five. What's fascinating here
Speaker 3: is the way the validation cycle works.
Speaker 2: Ah.
Speaker 3: So the LVK collaboration operates in cycles. They don't just
Speaker 3: run the machines forever. They have observing runs and then
Speaker 3: they completely shut down for months of commissioning right to
Speaker 3: install the upgrades. Exactly. They install better lasers, heavier mirrors,
Speaker 3: better quantum squizzers, and more advanced glass extensions, and every
Speaker 3: time they turn the network back on, the sensitivity volume,
Speaker 3: meaning the total amount of space we can listen to,
Speaker 3: increases by a massive cube factor.
Speaker 2: Okay, but here's the question that always trips me up.
Speaker 2: We have this hyper sensitive glass pendulum and it wiggles.
Speaker 2: How did the scientist actually sitting at the computers know
Speaker 2: for sure that the wiggle was a black hole in
Speaker 2: another galaxy and not just a weird microscopic thermal burp
Speaker 2: in the glass or a rogue quantum fluctuation that slipped
Speaker 2: through the squeezing well.
Speaker 3: That is the defining challenge of data analysis in this field.
Speaker 3: Finding a gravitational wave isn't just looking for a bump
Speaker 3: on a graph.
Speaker 2: What are they looking for?
Speaker 3: You are searching for a highly specific mathematical pattern called
Speaker 3: a chirp.
Speaker 2: A chirp.
Speaker 3: Yeah. As two black holes spiral closer and closer together,
Speaker 3: they orbit faster and faster. This causes the gravitational waves
Speaker 3: they emit to increase in both frequency so the pitch
Speaker 3: goes up and amplitude so it gets louder.
Speaker 2: Yeah, I can picture that it looks like a.
Speaker 3: Very distinct sweeping curve in the data, and to quantify
Speaker 3: their confidence, researchers rely on a metric called the signal
Speaker 3: to noise ratio or SNR.
Speaker 2: So, if the background noise of the instrument is the
Speaker 2: static on an old analog TV, the signal is the
Speaker 2: actual broadcast trying to punch through exactly. For anyone familiar
Speaker 2: with signal processing, what is the usual baseline for claiming
Speaker 2: a real detection?
Speaker 3: For a typical gravitational wave detection, an SNR of around
Speaker 3: eight or ten is usually the threshold where the team
Speaker 3: feels colm that they have a real astrophysical event.
Speaker 2: Okay, eight or ten means it's real, not just a
Speaker 2: random statistical fluctuation of the noise floor. Which sets the
Speaker 2: stage perfectly for the absolute bombshell of the GWTC five catalog,
Speaker 2: because we are moving from the general how of detection
Speaker 2: to a specific event that I can only describe as
Speaker 2: the loudest whisper in the cosmos. Oh, let's talk about
Speaker 2: January fourteen, twenty twenty.
Speaker 3: Five, event GW two five zero one one two. This
Speaker 3: is an event that will be heavily cited in physics
Speaker 3: textbooks for decades. Really, oh absolutely, The black holes involved
Speaker 3: were massive, roughly thirty two and thirty four times the
Speaker 3: mass of our sun. They collided over a billion light
Speaker 3: years away. But the defining characteristic wasn't just the mass,
Speaker 3: it was the clarity.
Speaker 2: Okay, you just said an SNR of eight is a
Speaker 2: solid detection. What did GW two five zero one one
Speaker 2: fourteen come in at?
Speaker 3: It achieved a record breaking signal to noise ratio of
Speaker 3: seventy six point nine seventy.
Speaker 2: Six point nine. I mean, mathematically, that isn't just peaking
Speaker 2: above the noise floor, that is standing on a map
Speaker 2: out with a megaphone. If an SNR of eight is
Speaker 2: a blurry, grainy polaroid of a black hole, an SNR
Speaker 2: of seventy six point nine is like a four K
Speaker 2: ultra high definition uncompressed video.
Speaker 3: That's exactly what it is. It is the clearest gravitational
Speaker 3: wave signal humanity has ever recorded. And when you have
Speaker 3: a signal that pristine, the entire nature of the science shifts.
Speaker 3: Howso you transition from merely cataloging the demographics of black
Speaker 3: holes to fundamentally stress testing the laws of physics. Doctor
Speaker 3: John Vache, a researcher analyzing these signals at the University
Speaker 3: of Glasgow, noted that this unprecedented loudness allowed them to
Speaker 3: perform the most precise test of general relativity today.
Speaker 2: Wait, what are we actually testing? Though we know general
Speaker 2: relativity works. I mean, GPS satellites use it. Previous gravitational
Speaker 2: waves confirmed it true. What does a seventy six point
Speaker 2: nine SNR. Let us look at that we couldn't see
Speaker 2: before it.
Speaker 3: Lets us look at the deeply worked space time immediately
Speaker 3: before the merger and compare it with exquisite precision to
Speaker 3: the warped space time after the black pot holes become
Speaker 3: one single object, and by doing that they provided stunning
Speaker 3: confirmation of Stephen Hawking's black hole area theorem.
Speaker 2: Oh, this is where the physics gets incredibly trippy. Let's
Speaker 2: break down the area theorem because it completely defies human intuition.
Speaker 3: It really does.
Speaker 2: When we talk about the area of a black hole,
Speaker 2: we are talking about the event horizon right, the point
Speaker 2: of no return right.
Speaker 3: And it is crucial to remember that the event horizon
Speaker 3: is not a solid physical.
Speaker 2: Surface, right. It's not like the crust of the Earth.
Speaker 3: For the surface of an ocean exactly. It is a
Speaker 3: mathematical boundary in space where the escape velocity exceeds the
Speaker 3: speed of light. Decades ago, Hawking theorized that in any
Speaker 3: physical process involving black holes, the total area of their
Speaker 3: event horizons can never.
Speaker 2: Decrease, never decrease. Right.
Speaker 3: If two black holes merge, the area of the new
Speaker 3: single event horizon must be strictly greater than the sum
Speaker 3: of the areas of the two original black holes.
Speaker 2: See. I know this sounds straightforward, but about a water
Speaker 2: droplet analogy. If you take two separate water droplets on
Speaker 2: a windshield and they merge into one larger droplet, the
Speaker 2: total volume of water is conserved, but the total surface
Speaker 2: area of that new single droplet is actually less than
Speaker 2: the surface area the two separate droplets.
Speaker 3: Combined, because that is how three dimensional geometry usually works, exactly.
Speaker 2: But for a black hole, the rules are inverted. The
Speaker 2: surface area must go up. And again, this isn't physical
Speaker 2: matter expanding, It's a boundary of gravity. Right and GW
Speaker 2: two five zero one one four proved observationally that this
Speaker 2: invisible boundary physically grew exactly as Hawkings math demanded.
Speaker 3: It is a profound confirmation, but the implications go much
Speaker 3: deeper than geometry. Hawking's proposal wasn't just a quirk of relativity.
Speaker 3: It was the bridge to thermodynamics. Hawking, alongside Jacob Beekenstein,
Speaker 3: realized that the area of a black hole is a
Speaker 3: vent horizon is mathematically analogous to entropy.
Speaker 2: Okay, assuming everyone listening knows the second law of thermodynamics entropy,
Speaker 2: the measure of disorder always increases in a closed system.
Speaker 2: It's the arrow of time. It's why you can't unscramble
Speaker 2: an egg, and why a hot cup of coffee inevitably
Speaker 2: cools down. But applying the rules of a scrambled egg
Speaker 2: to a tear in space time that just feels wrong.
Speaker 3: It sounds absurd until you look at the math. The
Speaker 3: Beckenstein Hawking formula explicitly links the entropy of a black
Speaker 3: hole to the surface area of its event horizon. The
Speaker 3: area is the entropy. So when these two massive black
Speaker 3: holes in GW two five zero one to one team merged,
Speaker 3: it wasn't a clean silent fusion. The newly formed black
Speaker 3: hole was violently distorted. It literally rings like a bell,
Speaker 3: radiating away an enormous amount of energy in the form
Speaker 3: of gravitational ways as it settles down into a perfect sphere.
Speaker 2: Okay, wait, wait, if it is radiating away massive amounts
Speaker 2: of energy, shouldn't it be losing mass, Yes, and therefore shrinking.
Speaker 2: And if it shrinks, wouldn't the area and the entropy decrease,
Speaker 2: which violates the second law of thermodynamics.
Speaker 3: That is, the exact paradox. Physicists wrestled with, oh, really, yes,
Speaker 3: But analyzing the exceptionally clear waves from that ringing phase
Speaker 3: the ring down confirmed that despite throwing off several sons
Speaker 3: worth of energy during the merger, the geometry of a
Speaker 3: black hole is such that the total area still increases.
Speaker 3: That is, wild, the mass lost to gravitational waves is
Speaker 3: more than offset by the way the remaining mass configures itself.
Speaker 2: Okay.
Speaker 3: This raises an important question, though, and proves definitively that
Speaker 3: the laws of thermodynamics, the exact same equations that govern
Speaker 3: steam engines, heat flow, and the arrow of time on
Speaker 3: Earth apply to invisible gravitational boundaries a billion light years away.
Speaker 2: Here's where it gets really interesting, though. The mechanics of
Speaker 2: a nineteenth century steam engine governing the event horizon of
Speaker 2: a black hole it's poetic. It is, But if we
Speaker 2: are applying thermodynamics, I have to ask about temperature because
Speaker 2: I know there is this severe counterintuitive quirk here regarding
Speaker 2: how black holes handle heat.
Speaker 3: Ah, you are referring to negative heat capacit.
Speaker 2: Yes. If you're listening to this and wondering how on
Speaker 2: Earth a massive black hole can be cold, you aren't alone.
Speaker 2: Because on Earth, if I pump energy into a system,
Speaker 2: like if I throw a log on a campfire, the
Speaker 2: fire gets hotter naturally, but a black hole does the
Speaker 2: exact opposite.
Speaker 3: It completely upends our standard thermodynamic intuition. For a normal object,
Speaker 3: temperature is a measure of the average kinetic energy of
Speaker 3: its particles, right, But black holes emit thermal radiation Hawking
Speaker 3: radiation due to quantum effects near the event horizon, and
Speaker 3: the mathematics dictate that the temperature of this radiation is
Speaker 3: inversely proportional to the black hole's mass.
Speaker 2: So as the black hole eats matter, gets heavier and
Speaker 2: its event horizon grows, its temperature actually drops drastically.
Speaker 3: A black hole with the mass of our Sun has
Speaker 3: a temperature of about one ten millionth of a degree
Speaker 3: above absolute zero.
Speaker 2: That is, incredibly cold.
Speaker 3: It is, but the newly birthed black hole from gw
Speaker 3: two five zero one one four, which was over sixty
Speaker 3: times the mass of our Sun, it is exponentially colder.
Speaker 3: Super Massive black holes at the center of galaxies are
Speaker 3: some of the coldest objects in the known universe. As
Speaker 3: they gain energy and mass, they cool down.
Speaker 2: I just love picturing this. You had this newly birthed
Speaker 2: Leviathan born from an explosion of gravitational energy, ringing in
Speaker 2: the absolute freezing dark of space, and it is fundamentally
Speaker 2: colder than the empty space around it.
Speaker 3: It's a haunting image.
Speaker 2: And we only get to verify these incredibly exotic, almost
Speaker 2: philosophical truths because a glass thread in Washington State didn't shake.
Speaker 3: It is the ultimate triumph of fundamental physics. But you know,
Speaker 3: physics is only half the story of GWTC five right.
Speaker 2: Allowed signal is a godsend for testing Einstein and Hawking.
Speaker 2: But if we want to understand the actual architecture of
Speaker 2: the cosmos, we need to know exactly where these signals
Speaker 2: are coming from exactly. A sound in the dark is fascinating,
Speaker 2: but to map the room, you need to find the source.
Speaker 2: Let's look at the next major milestone in the catalog
Speaker 2: event GW two four zero.
Speaker 3: Six one five, detected on June fifteenth, twenty twenty four.
Speaker 3: The black holes here roughly twenty six and thirty times
Speaker 3: the mass of the Sun, but the standout metric is
Speaker 3: the distance and the localization.
Speaker 2: How far away was it?
Speaker 3: This collision happened more than three billion light years.
Speaker 2: Away, three billion, which means the ripples we felt in
Speaker 2: twenty twenty four started their journey when life on Earth
Speaker 2: was barely figuring out multicellularity exactly.
Speaker 3: But despite traveling for three billion years, this event holds
Speaker 3: the record for the most accurate sky localization ever achieved
Speaker 3: for a gravitational wave source.
Speaker 2: Wow.
Speaker 3: The researchers managed to narrow its origin down to an
Speaker 3: area covering only six square degrees on the sky.
Speaker 2: Now, anyone who follows astronomy knows that a full moon
Speaker 2: covers about half a degree of the sky, so six
Speaker 2: square degrees is still a patch of sky holding twelve
Speaker 2: full moons. To an optical astronomer with a telescope, that's
Speaker 2: a massive glory area, But in gravitational wave.
Speaker 3: Astronomy it is practically a pinpoint. Historically, gravitational wave localizations
Speaker 3: could span hundreds, sometimes thousands, of square degrees an entire
Speaker 3: hemic sphere of the sky.
Speaker 2: Basically just saying it came from up there.
Speaker 3: Right, So narrowing it down to six square degrees is
Speaker 3: a revolutionary leap in precision.
Speaker 2: How did we suddenly get that precise? Was it a
Speaker 2: hardware upgrade to the Ligo lasers or is this a
Speaker 2: software trick?
Speaker 3: It was primarily about geometry and the vital return of
Speaker 3: the Virgo detector in Italy m Okay. Virgo had been
Speaker 3: offline for upgrades during the previous run, but its return
Speaker 3: allowed the LVK collaboration to use all three major detectors simultaneously.
Speaker 3: The two Ligo facilities in the US plus Virgo in
Speaker 3: Europe form a massive intercontinental triangle.
Speaker 2: So it's essentially a cosmic GPS system. Yes, if you
Speaker 2: only have one cell tower pinging a phone, all you
Speaker 2: know is the phone is somewhere within a huge radius.
Speaker 2: Two towers give you intersecting points, but three towers let
Speaker 2: you drop a pin on the exact street corner.
Speaker 3: Exactly. Because gravitational waves travel at exactly the speed of light,
Speaker 3: they wash over the earth and hit the different detectors
Speaker 3: at slightly different.
Speaker 2: Times, like fractions of a second.
Speaker 3: We are talking about seconds of defense, the time it
Speaker 3: takes light to travel through the crust of the Earth
Speaker 3: from Louisiana to Italy. By precisely measuring those tiny time delays,
Speaker 3: scientists can calculate exactly where in the sky the wave originated.
Speaker 2: Think about that. We are using collisions that happened three
Speaker 2: billion years ago as cosmic yard sticks to measure how
Speaker 2: fast the fabric of space is stretching today. Okay, I
Speaker 2: understand the triangulation, but why is the astronomy community so
Speaker 2: obsessed with the exact zip code of a black hole?
Speaker 3: What do you mean?
Speaker 2: Well, what is the broader scientific value of knowing which
Speaker 2: specific galaxy this happened.
Speaker 3: In ah Because it is the key to solving the
Speaker 3: biggest crisis in modern cosmology, the Hubble tension.
Speaker 2: The expansion rate of the universe.
Speaker 3: Yes, the universe is expanding, and the rate at which
Speaker 3: space is stretching is defined by the Hubble constant. But
Speaker 3: we have a severe problem. It's the problem when we
Speaker 3: measure the expansion rate by looking at the early universe,
Speaker 3: meaning the leftover radiation from the Big Bang. The cosmic
Speaker 3: microwave background, we get a value of about sixty seven
Speaker 3: kilometers per second per megaparsek.
Speaker 2: Okay sixty seven. But when we measure it locally in
Speaker 2: our present day universe using standard candles like CEPIAID, variable
Speaker 2: stars and supernovas, we get a faster rate, right around
Speaker 2: seventy three kilometers per second per megaparsec.
Speaker 3: Yes, and both sets of measurements have been refined to
Speaker 3: the point where the error bars no longer overlap. Oh wow,
Speaker 3: they are both highly precise, yet they disagree. It implies
Speaker 3: there is something fundamentally broken or missing in our standard
Speaker 3: model of cosmology.
Speaker 2: Which is terrifying for physicists.
Speaker 3: It is so gravitational waves offer a completely independent third
Speaker 3: way to measure the expansion. They act as standard sirens.
Speaker 2: Standard sirens because on like light, gravity doesn't get blocked, scattered,
Speaker 2: or dimmed by interstellar dust.
Speaker 3: Exactly with light, determining true distance is notoriously difficult. A
Speaker 3: star might look dim because it's far away, or it
Speaker 3: might look dim because there's a cloud of dust in
Speaker 3: the way.
Speaker 2: Right, there's ambiguity.
Speaker 3: But with a gravitational wave, general relativity allows us to
Speaker 3: calculate the absolute luminosity distance directly from the amplitude and
Speaker 3: the frequency evolution of the wave itself. Yes, the math
Speaker 3: gives us the distance purely from the strain on the detector,
Speaker 3: no intermediate stepping stones required.
Speaker 2: But to get the expansion rate distance is only half
Speaker 2: the equation. I also need to know how fast that
Speaker 2: object is receding away from us due to the stretching
Speaker 2: of space.
Speaker 3: Right, you need the red shift, and gravitational waves alone
Speaker 3: cannot give you the red shift. To get that, you
Speaker 3: have to find the specific host galaxy where the merger
Speaker 3: occurred and analyze the light from that galaxy. If your
Speaker 3: gravitational wave localization is a huge blurry smudge covering ten
Speaker 3: thousand galaxies, you have no idea which galaxies light to measure.
Speaker 2: Ah So by pinning GW two four zero six one
Speaker 2: five down to just six square degrees, it becomes dramatically
Speaker 2: easier for optical telescopes to sweep that small patch, identify
Speaker 2: the host galaxy, and get the red shift precisely.
Speaker 3: And this new catalog didn't just rely on this one
Speaker 3: incredible event. Alex Papadoppolos, a researcher at the Institute for
Speaker 3: Gravitational research noted that GWTC five utilized two hundred thirty
Speaker 3: six signals for this Hubble constant analysis.
Speaker 2: Two hundred and thirty six. That is almost double the
Speaker 2: number of signals used in previous catalogs and in statistics
Speaker 2: sample sizes everything.
Speaker 3: It really is, each individual black hole merger contributes a
Speaker 3: small probability distribution a piece of the puzzle regarding the
Speaker 3: expansion rate. By mathematically combining two hundred and thirty six
Speaker 3: of them, the aerror bars shrink dramatically, I can imagine.
Speaker 3: But processing that volume of data isn't something you can
Speaker 3: just run on a standard desktop.
Speaker 2: Which brings us to the software, because you have two
Speaker 2: hundred and thirty six immensely complex multidimensional waveforms and you
Speaker 2: have to cross reference them with massive optical galaxy catalogs. Yeah,
Speaker 2: what was the bottleneck before and how did they fix
Speaker 2: it for this release?
Speaker 3: The computational bottleneck lies in Bayesian inference. To map the
Speaker 3: parameters of a gravitational wave, you know, mass bin distant
Speaker 3: sky location supercomputers run Markov Chain Monty Carlo algorithms. Okay,
Speaker 3: they generate millions of simulated waveforms and compare them to
Speaker 3: the actual noisy data to find the best fit. Historically,
Speaker 3: this took weeks or even months of continuing supercomputer time
Speaker 3: for a single.
Speaker 2: Event, just to process one event.
Speaker 3: Yes, but the Glasgow researchers developed and tested entirely new
Speaker 3: software architecture for this catalog. They optimize the likelihood evaluations
Speaker 3: so aggressively that the analysis runs more than a thousand
Speaker 3: times faster.
Speaker 2: A thousand times faster. That isn't just an upgrade. That
Speaker 2: is a paradigm shift in data science. Yeah, you go
Speaker 2: from waiting a month for an answer to getting it
Speaker 2: while you're at.
Speaker 3: Lunch, And that speed isn't just about impatience. When you
Speaker 3: can run a highly complex statistical model in minutes, you
Speaker 3: can vigorously test the robustness of your results. Right. You
Speaker 3: can inject artificial errors, tweak the cosmological priors, and run
Speaker 3: thousands of different scenarios to ensure that the final number
Speaker 3: you publish for the Hubble constant is bulletproof.
Speaker 2: It is computationally iterating on the architecture of the cosmos.
Speaker 2: So we've used the loudest signals to test thermodynamics. We've
Speaker 2: used the precisely located signals to map the expansion of space.
Speaker 2: But yesterday's catalog revealed something else, something about the actual
Speaker 2: identity of these black holes that completely rewrites stellar biology.
Speaker 2: You can call it that.
Speaker 3: We are talking about the family trees of the cosmos,
Speaker 3: the discovery of hierarchical mergers.
Speaker 2: For the longest time, the narrative was simple. A massive
Speaker 2: star runs out of a nuclear fuel, the core collapses
Speaker 2: under its own immense gravity, and you get a black hole.
Speaker 2: It's the final end point of a star's life. But
Speaker 2: events GW two four one is zero eleven and GW
Speaker 2: two four one one ten are screaming that this isn't
Speaker 2: the whole story.
Speaker 3: Now it's not. These two highly unusual mergers were detected
Speaker 3: a month apart in late twenty twenty four. One was
Speaker 3: about seven hundred million light years away, the other much
Speaker 3: further at two point four billion light years, And what
Speaker 3: flagged them immediately in the analysis wasn't their distance, but
Speaker 3: their intrinsic properties, which properties their masses and their spins.
Speaker 2: Let's dive deep into the spin mechanics. Yeah, because when
Speaker 2: a star collapses, conservation of angular momentum dictates that the
Speaker 2: resulting black hole should spin right like an ice skater.
Speaker 2: Pulling their arms.
Speaker 3: In Yes, the CERR parameter, which measures a black hole spin.
Speaker 3: It's crucial here. However, when we observe typical first generation
Speaker 3: black holes, meaning those born directly from collapsing stars in
Speaker 3: a binary pair, their spins tend to be relatively low. Furthermore,
Speaker 3: because those two stars likely formed together from the same
Speaker 3: swirling cloud of gas, their rotational axes are usually aligned
Speaker 3: with their mutual orbit. They spin in the same direction
Speaker 3: they orbit.
Speaker 2: But these two new events in GWTC five broke those
Speaker 2: rules completely completely.
Speaker 3: They featured highly unequal masses, meaning one black hole was
Speaker 3: significantly bulkier than its partner.
Speaker 2: Wow.
Speaker 3: But the smoking gun was the spin. They exhibited distinct,
Speaker 3: high magnitude spins that were drastically misaligned from their orbital axis.
Speaker 2: If they didn't form together from a collapsing star system,
Speaker 2: how do you get a lopsided pairing with wild misaligned spins.
Speaker 3: You get it because you are looking at a second
Speaker 3: generation black hole.
Speaker 2: The second generation, the larger black.
Speaker 3: Hole in these systems, wasn't born from a star. It
Speaker 3: was born from a previous black hole merger.
Speaker 2: It's a Frankenstein's monster.
Speaker 3: It is the product of cosmic recycling. When two first
Speaker 3: generation black holes merge, the resulting single black hole absorbs
Speaker 3: a massive amount of angular momentum from the orbital energy
Speaker 3: of the collision itself. It gets spun up exactly, it
Speaker 3: gets spin kick. The resulting second generation black hole spins
Speaker 3: incredibly fast, often reaching a Cerr parameter of point seven
Speaker 3: or point eight, which is near the theoretical maximum. That's
Speaker 3: insanely fast, and crucially, the direction of that new spin
Speaker 3: is dictated entirely by the chaotic geometry of the collision,
Speaker 3: meaning it will be randomly oriented relative to any future
Speaker 3: partner it finds.
Speaker 2: So what is this all mean? I picture this like
Speaker 2: a heavyweight demolition derby. It's not just a peaceful binary
Speaker 2: star system quietly living out its days and collapsing. It
Speaker 2: is the winner of a previous collision, finding another black hole,
Speaker 2: capturing it, and colliding again. We are looking at the
Speaker 2: heavyweight champions of the universe. That's a great analogy, but
Speaker 2: that requires a highly specific environment, doesn't it. Space is
Speaker 2: overwhelmingly empty. If two black holes merge in the quiet
Speaker 2: spiral arms of our galaxy, the resulting second generation black
Speaker 2: hole is just going to sit there alone in the
Speaker 2: dark forever.
Speaker 3: It has no one else to interact with. To get
Speaker 3: hierarchical mergers, you need a dense, highly populated environment. You
Speaker 3: need a cosmic factory floor.
Speaker 2: Where are these factory floors?
Speaker 3: We believe these environments are globular clusters, ancient tightly packed
Speaker 3: spheres containing millions of stars orbiting the outskirts of galaxies, and.
Speaker 2: The dynamics inside these clusters are wild. Because black holes
Speaker 2: are heavier than the average star. Over millions of years,
Speaker 2: they experienced dynamical frime. They essentially sink to the very
Speaker 2: center of the cluster mass segregation.
Speaker 3: You end up with a dark core, a swarm of
Speaker 3: black holes furiously buzzing around each other in a highly
Speaker 3: confined space. And in this chaotic swarm, three body interactions
Speaker 3: become common.
Speaker 2: Break down a three body interaction.
Speaker 3: For us, imagine two black holes orbiting each other. A
Speaker 3: third black hole flies close by. The gravitational interaction is
Speaker 3: incredibly chaotic, like.
Speaker 2: A gravitational mosh pit.
Speaker 3: Pretty much what usually happens is the lightest of the
Speaker 3: three black holes gets gravitationally slingshoted out of the system
Speaker 3: at high speed, but to conserve energy, the remaining two
Speaker 3: black holes are forced into a much tighter, closer orbit.
Speaker 2: Which dramatically accelerates their eventual collision.
Speaker 3: Yes, they merge, creating a massive, highly spinning second generation
Speaker 3: black hole, and because it is sitting in the middle
Speaker 3: of this dense swarm, it doesn't take long for it
Speaker 3: to gravitationally capture a new partner and start the process
Speaker 3: all over again.
Speaker 2: This change the entire paradigm of stellar revolution, and what
Speaker 2: blows my mind is that this isn't just a fringe
Speaker 2: theory based on two weird outliers anymore. The catalog proves
Speaker 2: this is happening at scale.
Speaker 3: If we connect this to the bigger picture Storm Columns
Speaker 3: a postgraduate researcher focus specifically on this. They analyze two
Speaker 3: hundred and sixty seven sources from the catalog, including over
Speaker 3: one hundred brand new observations, to measure the masses, spins,
Speaker 3: and distances. This is where the field matures into deep demographics.
Speaker 2: We aren't just finding a few interesting houses, We are
Speaker 2: running a census on the entire hidden.
Speaker 3: City, and the census data shows a clear correlation. Black
Speaker 3: holes in different mass ranges consistently exhibit different spin characteristics.
Speaker 3: The signatures of hierarchical mergers persist across the population. It
Speaker 3: proves definitively that the universe has multiple formation pathways. It
Speaker 3: is actively running assembly lines in these dense stellar clusters,
Speaker 3: forging increasingly massive black holes from the remnants of smaller ones.
Speaker 2: It is breathtaking to step back and look at the
Speaker 2: tragactory we are on. In less than ten years, we
Speaker 2: have gone from hey, we finally build a glass pendulum
Speaker 2: quiet enough to prove these invisible ripples exist to Here
Speaker 2: is a highly optimized Bayesian mapped demographic breakdown of multi
Speaker 2: generational black hole factories across billions of light years, complete
Speaker 2: with thermodynamic stress tests of their event horizon.
Speaker 3: It's moving so fast, and the statistical power is only
Speaker 3: going to grow. As the observatories upgrade for their next runs,
Speaker 3: we will transition from hundreds of events to thousands.
Speaker 2: Which brings a quote to mind from doctor Daniel Williams,
Speaker 2: the co chair of the ls's Compact Binary Science Working Group.
Speaker 2: He said that looking at this massive catalog is the
Speaker 2: astronomical equivalent of uncovering an ancient civilization.
Speaker 3: It really is.
Speaker 2: We aren't just logging individual deaths of stars. We are
Speaker 2: revealing the underlying infrastructure of a lost world. We are
Speaker 2: seeing how these dark leviathans congregate, how they grow, and
Speaker 2: how their violent interactions shape the very galaxies they inhabit.
Speaker 3: It is a found realization. We are mapping the dark
Speaker 3: skeleton of the universe.
Speaker 2: So the next time you step outside on a quiet
Speaker 2: night and look up at the dark sky, I want
Speaker 2: you to remember that it is not still, It is
Speaker 2: not silent. The empty space between the stars is actively
Speaker 2: ringing with the echoes of invisible giants colliding. We are
Speaker 2: sitting on the shore of a cosmic ocean, and finally
Speaker 2: we can hear the waves crashing.
Speaker 3: Beautifully said, but before we wrap up.
Speaker 2: I want to leave you with one final thought, something
Speaker 2: to chew want. Based on these dense globular clusters and
Speaker 2: second generation black holes, we know these environments act as
Speaker 2: factory floors, forcing black holes to merge, creating heavier, faster
Speaker 2: spinning offspring.
Speaker 3: The cosmic billiard table.
Speaker 2: Right, But if that environment is so crowded and the
Speaker 2: three body interactions keep tightening orbits, could this process theoretically
Speaker 2: continue without end If a second generation black hole eats
Speaker 2: another black hole because a third generation and that a
Speaker 2: fourth is there a physical limit to how massive a
Speaker 2: black hole can grow purely through this bumpercar style of
Speaker 2: cosmic evolution before they alter the very galaxies they live in.
Speaker 3: That is the bleeding edge of the science right now.
Speaker 3: The limiting factor is the gravitational recoil recoil. When two
Speaker 3: black holes merge, the resultant gravitational waves aren't emitted perfectly symmetrically.
Speaker 3: This gives the new black hole a massive kick, sending
Speaker 3: it hurtling through space like.
Speaker 2: A rocket effect made of pure gravity.
Speaker 3: Yes, and sometimes that kick is so violent that the
Speaker 3: recoil velocity exceeds the escape velocity of the globular cluster.
Speaker 3: The new black hole is literally shot out of the
Speaker 3: cluster into the empty intergalactic void, terminating its growth forever.
Speaker 2: But what if it's already so massive that the kick
Speaker 2: isn't enough to eject it. What if it survives the recoil,
Speaker 2: sings back to the center of the dark core, and
Speaker 2: eats again. We could be on the verge of discovering third, fourth,
Speaker 2: or fifth generation black holes. We could literally be watching
Speaker 2: the mechanical process that eventually builds the super massive black
Speaker 2: holes sitting in the centers of galaxies. And we will
Speaker 2: only know because we figured out how to measure a
Speaker 2: shift smaller than a fraction of an atomic nucleus. The
Speaker 2: universe has incredically loud, my friends. You just have to
Speaker 2: know how to listen.