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: So I want you to just picture looking back to
Speaker 2: a time when the universe was well essentially an infant,
Speaker 2: like less than a billion years old.
Speaker 3: Right right, A very different place than it.
Speaker 2: Is today, completely different. The cosmic web is just unbelievably
Speaker 2: dense and volatile, and at that incredible distance, specifically at
Speaker 2: a redshift of five point seven, we are witnessing this
Speaker 2: literal cosmic dance between two of the brightest, most violent
Speaker 2: objects and existence.
Speaker 3: It really is staggering. We are talking about the system
Speaker 3: J twenty three seven four five three seven, which is
Speaker 3: a confirmed spatially resolved dual quasar.
Speaker 2: Yeah, and that's the whole mission today to unpack what
Speaker 2: these colossal engines actually are and how astronomers even prove
Speaker 2: they weren't just some cosmic optical illusion, which is a
Speaker 2: huge part of this story.
Speaker 3: Oh, absolutely, Proving what is actually real in the universe
Speaker 3: that is just full of mirages is half the battle.
Speaker 2: Exactly because when we talk about peering that far back,
Speaker 2: it's not just distant trivia. It's a full on detective
Speaker 2: story for you, the listener, about the invisible fabric of
Speaker 2: the universe itself. But I just keep getting stuck on
Speaker 2: the awe of the sheer distance.
Speaker 3: I mean, you have to the improbability hears off the charts.
Speaker 3: When we look at quasars at a red shift greater
Speaker 3: than five, we are already looking at the rarest most
Speaker 3: extreme objects in the early universe.
Speaker 2: Just finding one is a big deal exactly.
Speaker 3: So finding two of them, separated by just a few
Speaker 3: kiloparsex locked in this violent gravitational spiral, it's basically absurd,
Speaker 3: it really is. I mean, this is literally one of
Speaker 3: only two confirmed quasar pairs we have ever found at
Speaker 3: a red shift that high. It forces us to completely
Speaker 3: reevaluate our models of how fast these super massive black
Speaker 3: holes were growing during the cosmic dawn.
Speaker 2: But there's a paradox here, right, because the whole hierarchical
Speaker 2: model of cosmology, the idea of how structures assemble. It
Speaker 2: basically says galaxy should be slamming together all the time
Speaker 2: in the early universe.
Speaker 3: That's right. The early universe was crowded, mergers were common.
Speaker 2: Right, So if galaxy mergers are happening all the time,
Speaker 2: why is finding two blazing quasars in a single system
Speaker 2: so extraordinarily rare? I mean, shouldn't the sky be lit
Speaker 2: up with these things?
Speaker 3: Well, it comes down to a really brutal timing problem.
Speaker 3: A galaxy merger is a slow, agonizing process. We're talking
Speaker 3: hundreds of millions, sometimes over a billion years to actually complete.
Speaker 2: Which is a massive amount of time, even on a
Speaker 2: cosmic scale exactly.
Speaker 3: But the active quasar phase, the part where the black
Speaker 3: hole is actually eating and glowing, that is highly transient.
Speaker 2: It doesn't last long at all.
Speaker 3: No, the supermassive black hole only it creates matter fast
Speaker 3: enough to outshine the whole galaxy for a tiny fraction
Speaker 3: of that merger timescale. The duty cycle might only be
Speaker 3: a few million, maybe tens of millions of years.
Speaker 2: So it's kind of like having a spectacularly lazy, picky
Speaker 2: eater of a black hole, right. It just sits there,
Speaker 2: dormant until a galactic collision forcefully shoves this cosmic buffet
Speaker 2: right into its mouth.
Speaker 3: That is a very visceral way to put it, but yeah,
Speaker 3: it's accurate. In a normal stable disc galaxy, the gas
Speaker 3: is just orbiting smoothly. It's supported by its own rotation.
Speaker 2: You're not just falling in right.
Speaker 3: It will stay in orbit practically forever unless something violently
Speaker 3: extracts that rotational energy. And that's what the major merger does.
Speaker 3: It provides these extreme gravitational torques. It disrupts everything exactly.
Speaker 3: It creates these massive shocks, funnels unimaginable amounts of gas
Speaker 3: straight down into the nucleus. But the accretion isn't smooth.
Speaker 3: The gas piles up, the quasar ignites, and then the
Speaker 3: radiation pressure from the quasar itself creates these massive outflows.
Speaker 2: Oh right, the feedback. It basically blows its own food
Speaker 2: source away.
Speaker 3: Precisely, it chokes off its own shiel. It suffocates itself.
Speaker 3: So to catch j two to three seven four or
Speaker 3: five three seven with both super massive black holes actively
Speaker 3: lit up at the exact same moment from our perspective
Speaker 3: twelve point eight billion light years away, it's wise. It's
Speaker 3: like catching two separate lightning strikes in the exact same photograph.
Speaker 2: And because it's that incredibly rare, the initial reaction from
Speaker 2: the scientific community wasn't just you know, popping champagne. It
Speaker 2: was profound skepticism. People thought it was a trick.
Speaker 3: Oh. The scrutiny was intense because when this was first
Speaker 3: reported as a candidate back in twenty twenty one, observers
Speaker 3: just saw two identical, incredibly bright dots separated by a
Speaker 3: tiny fraction of an arcsecond. And when you see that
Speaker 3: at redshift five point seven, the default assumption in astronomy
Speaker 3: is absolutely not a binary quasar. The default assumption is
Speaker 3: an optical illusion caused by strong gravitational.
Speaker 2: Lensing, which we really have to unpack because gravitational lensing
Speaker 2: is such a common imposter in deep space observations. It
Speaker 2: forces astronomers to second guess their own eyes constantly.
Speaker 3: It really does. General relativity tells us that massive four
Speaker 3: ground objects like a galaxy cluster literally warp the space
Speaker 3: time around them.
Speaker 2: Right. It acts quite literally like a massive invisible glass
Speaker 2: LEDs exactly.
Speaker 3: So if you have a single solitary quasar way in
Speaker 3: the background, its light passes through that warped space, time
Speaker 3: gets bent, and that geometry can easily produce two or
Speaker 3: even four separate images of the exact same quasar.
Speaker 2: I always think of it like looking through a distorted
Speaker 2: funhouse mirror, or like the curved bottom of a wineglass.
Speaker 2: You hold up one candle, but through the glass it
Speaker 2: looks like two distinct flames.
Speaker 3: That's a perfect analogy. And because it's just a mirage
Speaker 3: of the same object, the light from those two dots
Speaker 3: will look identical.
Speaker 1: Right.
Speaker 2: Their spectrum match perfectly.
Speaker 3: Exactly, their red shifts, their colors, everything matches, and the
Speaker 3: degeneracy there the difficulty in telling them apart is just
Speaker 3: notoriously hard to break.
Speaker 2: But wait, I want to push back on that a bit.
Speaker 2: If you're looking at two identical dots of light from
Speaker 2: billions of light years away, and a literal cosmic funhouse
Speaker 2: mirror can perfectly fake that image, how can you possibly
Speaker 2: prove what you're looking at is real?
Speaker 3: Well, in traditional optical astronomy, it's incredibly difficult because the
Speaker 3: deflector galaxy, the lens itself might be completely hidden by
Speaker 3: the blinding glare of the quasars.
Speaker 2: It's buried in the light.
Speaker 3: Right, So you look at the optical data. You see
Speaker 3: two bright dots. You extract the spectra and their twins photometrically,
Speaker 3: a lens system and a real binary look exactly the same.
Speaker 2: So if you can't see the lens, you can't map
Speaker 2: the distortion. It sounds like a total dead end.
Speaker 3: It is a dead end if you only look at
Speaker 3: the point sources. The rigorous burden of proof here requires
Speaker 3: you to look away from the bright lights. You have
Speaker 3: to look at the dark space between the quasars for
Speaker 3: physical interactions that a mirage couldn't possibly fake.
Speaker 2: You have to find the physical wreckage of the collision precisely.
Speaker 3: A gravitational lens will distort the background host galaxy into
Speaker 3: smooth arcs or a ring, but it will never create localized,
Speaker 3: chaotic asymmetric wreckage between two independent gravity wells.
Speaker 2: Because a mirage doesn't leave muddy footprints connecting two houses exactly.
Speaker 3: But to see those footprints you have to completely bypass
Speaker 3: the brilliant optical light of the quasars. You have to
Speaker 3: move to the far infrared and submillimeter wavelengths to see
Speaker 3: the cold.
Speaker 2: Gas, which brings us right to the smoking gun. This
Speaker 2: is where the team led by minghow YU brings in ALELMA.
Speaker 2: The Atacoma Large Millimeter Submillimeter Array.
Speaker 3: Right, ALMA is the perfect tool for this. It's spatial
Speaker 3: resolution at submillimeter wavelengths is just unpreced in it. They
Speaker 3: weren't looking at the black holes at all. They were
Speaker 3: mapping the cold, neutral gas of the host galaxies.
Speaker 2: And specifically, they were mapping the emission lines of ionized carbon,
Speaker 2: which is noted as C two. I really want to
Speaker 2: dig into this because why map ionized carbon specifically? What
Speaker 2: makes this exact element the perfect cosmic fingerprint here?
Speaker 3: It really is a phenomenal diagnostic tool. It's tied directly
Speaker 3: to how galaxies form stars. See in a galaxy, gas
Speaker 3: has to cool down before it can collapse under gravity
Speaker 3: to form a star.
Speaker 2: Right if it's too hot, it just expands.
Speaker 3: Exactly And when young massive stars are born, they blast
Speaker 3: the surrounding area with ultraviolet radiation. That UV light hits
Speaker 3: dust grains, ejects electrons, and those electrons bounce around and
Speaker 3: heat up the gas.
Speaker 2: So the star formation is heating the gas, which should
Speaker 2: stop more stars from forming. It needs a release valve.
Speaker 3: It absolutely needs a release valve to radiate that energy away,
Speaker 3: and carbon is perfect for this because it has a
Speaker 3: very low ionization potential. Even in cold clouds, carbon gets
Speaker 3: ionized easily by starlight, So those bouncing electrons hit the
Speaker 3: ionized carbon atoms, exciting them. When the carbon atom drops
Speaker 3: back down to its normal state, it releases a photon
Speaker 3: at a very specific wavelength one hundred and fifty eight
Speaker 3: micrometers ah.
Speaker 2: So that specific flash of light is the cooling process happening.
Speaker 3: Right By mapping that one hundred and fifty eight my
Speaker 3: chrometer emission, you are literally mapping the cold gas reservoir
Speaker 3: that fuels the whole galaxy. And the best part is
Speaker 3: at that wavelength, the light punches right through the dust
Speaker 3: that blocks our optical telescopes.
Speaker 2: It cuts right through the glare. So they point Alma
Speaker 2: at the system, they look for that specific carbon signal,
Speaker 2: and they find an absolute mess.
Speaker 3: They found a massive tidle bridge. It wasn't just two
Speaker 3: neat pools of gas around the black holes. There was
Speaker 3: a physical, contiguous stream of cold interstellar gas stretched across
Speaker 3: the space between.
Speaker 2: Them, ripped out by sheer gravitational violence. But let me
Speaker 2: play devil's advocate for a second. Couldn't a skeptic to say, well,
Speaker 2: maybe the lens is incredibly complex, maybe a weird four
Speaker 2: ground cluster is magnifying a background spiral arm to just
Speaker 2: look like a bridge.
Speaker 3: That is exactly the kind of rigor of the community demands.
Speaker 3: But LMA didn't just give us a static picture. It
Speaker 3: gave us kinematics. It showed us exactly how fast the
Speaker 3: gas in that bridge was moving.
Speaker 2: Because of the Doppler shift.
Speaker 3: Exactly. They mapped the velocity field and they found co plex, chaotic,
Speaker 3: non circular motions. A lensed spiral arm would still look
Speaker 3: like a spinning disc, just distorted.
Speaker 2: We'd have a neat orderly rotation.
Speaker 3: Right, But this was total kinematic chaos. Yeah, definitively the
Speaker 3: signature of two massive gravity wells tearing each other apart.
Speaker 3: The optical illusion theory was officially dead.
Speaker 2: Wow. So we are genuinely looking at two immense galaxies
Speaker 2: and a death spiral and finding this bridge of star
Speaker 2: forming gas just naturally leads us to the realization that
Speaker 2: these black holes aren't just destroying things. Far from it, right,
Speaker 2: They are residing in galaxies that are frantically creating new stars.
Speaker 2: These are literal star forming factories. The ALMA data showed
Speaker 2: that these host galaxies are incredibly massive.
Speaker 3: Oh, they're behemoths. The dynamical mass calculations show that each
Speaker 3: of these merging components is at least ten billion solar masses.
Speaker 2: Ten billion at redshift five point seven. That is highly evolved.
Speaker 2: We aren't talking about tiny dwarf galaxies bumping into each other.
Speaker 3: No, these are assive systems. But the number that really
Speaker 3: jumps out is the star formation rate. The data suggests
Speaker 3: they are churning out over five hundred solar masses of
Speaker 3: new stars every single year.
Speaker 2: Five hundred a year. I mean, just to ground that
Speaker 2: our own Milky Way produces what maybe one or two
Speaker 2: solar masses a year.
Speaker 3: Yeah, about one to two. So J twenty thirty seven
Speaker 3: four five three seven is operating in an overdrive that
Speaker 3: is hundreds of times more intense than our own galaxy.
Speaker 2: It's like an assembly line running at a dangerous frantic pace.
Speaker 2: If you were floating in the halo of one of
Speaker 2: these galaxies, the sky would just be a chaotic mess
Speaker 2: of ultraviolet light from massive young stars blowing up in supernovae.
Speaker 3: It'd be an incredibly violent engine of creation.
Speaker 2: Yeah, But I do want to push back on that
Speaker 2: five hundred number for a second, because the researchers explicitly
Speaker 2: mention systematic uncertainties regarding dust temperatures. If our calculations rely
Speaker 2: on assuming the temperature of invisible dust billions of light
Speaker 2: years away, how wildly could these numbers swing.
Speaker 3: That is a fantastic question, and it's a critical caveat
Speaker 3: When we measure starform rates with alma in this way,
Speaker 3: we are actually measuring the thermal glow of the dust, right.
Speaker 2: The dust absorbs the starlight and glows in the infrared exactly.
Speaker 3: And to calculate the total mass of that dust and
Speaker 3: therefore the star formation, we have to assume a dust
Speaker 3: temperature usually around forty five kelvin for these early galaxies.
Speaker 2: But it's an underdetermined system, right. We don't have enough
Speaker 2: data points to know for sure.
Speaker 3: Right, we only have a few data points on the spectrum.
Speaker 3: So what if the incredible radiation from the quasars and
Speaker 3: the sheer violence of the starburst has heated that dust
Speaker 3: up to say sixty five kelvin instead?
Speaker 2: Oh, because of the stuff and Boltzman law, hotter things
Speaker 2: radiate way more energy exactly.
Speaker 3: It scales to the fourth power of the temperature. So
Speaker 3: if the dust is hotter, you need significantly less dust
Speaker 3: mass to produce the bright glow we see.
Speaker 2: And if there's less dust, there's less gas, and your
Speaker 2: five hundred solar mass figure might be a massive overestimate.
Speaker 3: It could be off by a factor of two or
Speaker 3: three easily. On the flip side, if the dust has
Speaker 3: a different mmical composition, maybe more silicates in the early universe,
Speaker 3: the real rate could be even higher.
Speaker 2: Are we looking at a conservative baseline or could we
Speaker 2: be drastically overestimating the chaos.
Speaker 3: We won't know the exact number without follow up observations,
Speaker 3: maybe using the James Web Space telescope combined with deeper
Speaker 3: Ala maps. But honestly, even if the rate is three
Speaker 3: hundred instead of five hundred, the physical reality is the same.
Speaker 2: It's still an extreme starburst system exactly.
Speaker 3: The merger is violently compressing the gas, fueling the quasars,
Speaker 3: and sparking a massive, rapid assembly of stars all at
Speaker 3: the same time.
Speaker 2: It's just spectacular. So we've established the massive scale the
Speaker 2: violent waltz they're locked in. But this dance has a
Speaker 2: grand finale, right, a finale that won't happen for a.
Speaker 3: Very very long time, a very long time right now,
Speaker 3: at the moment we observe them at rench of five
Speaker 3: point seven, these supermassive black holes are still separated by
Speaker 3: thousands of late years. They aren't a true binary system.
Speaker 2: Yet they still have to navigate this incredibly chaotic, turbulent
Speaker 2: soup of gas and star just to get to each other.
Speaker 2: How do they actually close that gap?
Speaker 3: The main driver at these large scales is something called
Speaker 3: dynamical friction. As the black hole plows through the dense
Speaker 3: background of the galaxy, it's gravity pulls on the stars
Speaker 3: and gas around it.
Speaker 2: It deflects their orbits.
Speaker 3: Right, and as the black hole moves forward, it leads
Speaker 3: to behind a localized cluster a wake of all that
Speaker 3: material is just pulled on.
Speaker 2: Oh so it's literally dragging a heavy tail of stars
Speaker 2: behind it.
Speaker 3: Exactly, and the gravitational pull of that trailing wake acts
Speaker 3: as a constant break. It SAPs the black hole's kinetic energy,
Speaker 3: forcing it to slowly, relentlessly spiral inward.
Speaker 2: And the models say this dynamical friction process is going
Speaker 2: to take a staggering amount of time. For j twenty
Speaker 2: three h thirty seven four five thirty seven, something like
Speaker 2: two point one billion years.
Speaker 3: Right, It will take over two billion years for them
Speaker 3: to finally become a gravitationally bound binary, which would happen
Speaker 3: around redshift two.
Speaker 2: But just getting to the center isn't the end of
Speaker 2: the story. Once they get really close, like within a
Speaker 2: parsec of each other, that friction stops working, doesn't it.
Speaker 3: It does. It's called the final parsec problem. The volume
Speaker 3: of space gets too small to hold enough background stars
Speaker 3: to create that drag.
Speaker 2: So how do they keep falling inward? Do they just
Speaker 2: stall out?
Speaker 3: If it were a dry merger without gas, they might stall,
Speaker 3: But here they enter the hardening phase. The binary acts
Speaker 3: like a giant gravitational baseball bat. Any star that wanders
Speaker 3: too close gets violently ejected from the galactic center.
Speaker 2: Oh wow, it just slingshots stars away.
Speaker 3: Exactly, and the energy to kick that star out comes
Speaker 3: from the black hole's orbit. So they step slightly closer together,
Speaker 3: but eventually they kick away all the stars in the center.
Speaker 3: They run out amo.
Speaker 2: Right, they clear out the whole core. So what bridge
Speaker 2: is that final gap?
Speaker 3: The gas? Because this is a very wet, gas rich merger.
Speaker 3: The black holes are swimming in a massive circumbinary accretion disc.
Speaker 3: The sheer viscous friction of that gas provides the drag
Speaker 3: needed to push them down to milliparsec scales.
Speaker 2: And once they get that close, separated by mirror light
Speaker 2: months and moving at a huge fraction of the speed
Speaker 2: of light, physics fundamentally shifts. General relativity totally takes over.
Speaker 3: Absolutely at that point. The dominant way they lose energy
Speaker 3: is by radiating gravitational waves.
Speaker 2: Ripples in the literal fabric of space time, and this
Speaker 2: connects our ancient red shift five point seven quasars directly
Speaker 2: to the most cutting edge physics happening right now on Earth.
Speaker 2: Because these aren't the quick, high frequency chirps we hear
Speaker 2: from small black holes with ligo right.
Speaker 3: No, not at all. A supermassive black hole binary takes
Speaker 3: millions of years to inspiral. The gravitational waves they produce
Speaker 3: have incredibly long wavelengths. We're talking nanohurtz frequencies.
Speaker 2: So the wave takes years just to complete a single oscillation.
Speaker 2: You can't catch that in a laboratory.
Speaker 3: No, you need a detector the size of a galaxy.
Speaker 2: Which is exactly what pulsar timing arrays are it's brilliant.
Speaker 2: We use millisecond pulsars, these rapidly spinning dead stars that
Speaker 2: shoot radio beams at Earth with perfect precision, like cosmic clocks.
Speaker 3: They are staggeringly precise.
Speaker 2: And if a massive of nanohertz gravitational wave rolls through
Speaker 2: the Milky Way, it actually stretches and squeezes the space
Speaker 2: between Earth and those pulsars.
Speaker 3: Right the distance the radio pulse has to travel physically changes, which.
Speaker 2: Means the pulse arrives just a tiny fraction of a
Speaker 2: microsecond early or late. And by monitoring dozens of these pulsars,
Speaker 2: scientists act like a giant cosmic seismograph, listening for that
Speaker 2: rumble exactly.
Speaker 3: Groups like Nanograph have actually found compelling evidence for this recently,
Speaker 3: a stochastic gravitational wave background. It's a constant, low frequency
Speaker 3: hum vibrating through the universe.
Speaker 2: It's the combine noise of millions of supermassive black holes
Speaker 2: slowly spiraling together across all of cosmic time, like the
Speaker 2: low rumble of distant traffic in a busy city.
Speaker 3: That's exactly what it is. But here is the kicker.
Speaker 3: The background hum they detected is actually stronger than our
Speaker 3: baseline models predicted.
Speaker 2: Wait, really, so if it's louder than expected, does that
Speaker 2: mean our fundamental ideas about how crowded and violent the
Speaker 2: early universe was have just been too conservative.
Speaker 3: That is the leading thing right now. A louder hum
Speaker 3: means there are either more supermassive binaries out there, or
Speaker 3: they're much more massive than we thought.
Speaker 2: And that brings us right back to j twenty three
Speaker 2: seven four five three seven exactly.
Speaker 3: If massive chaotic dust and shrouded early mergers like this
Speaker 3: are more common than we realized, which optal surveys missed
Speaker 3: because of the dust, then they could be the exact
Speaker 3: source of that extra gravitational noise.
Speaker 2: Wow, it's a perfect loop. We use the submillimeter ALMA
Speaker 2: data to prove the quasar pair exists and cut through
Speaker 2: the optical illusion, and that proves these massive early mergers happen,
Speaker 2: which perfectly explains the invisible gravitational hum vibrating through our detectors.
Speaker 3: Right now, it links the entire history of the cosmos
Speaker 3: into one mechanical framework.
Speaker 2: It really does. I mean, we started with a suspicious,
Speaker 2: tiny dot at the edge of the observable universe. We
Speaker 2: unpack the invisible ionized carbon, mapped the tidal wreckage of
Speaker 2: galaxies churning out five hundred stars a year, and tracked
Speaker 2: their brutal two point one billion year or decay.
Speaker 3: And the timeline of that decay is just it's fundamentally
Speaker 3: hard to wrap your head around.
Speaker 2: It is because we are observing them at redshift five
Speaker 2: point seven. The light we just analyzed has been traveling
Speaker 2: through expanding space for nearly thirteen billion years. But the
Speaker 2: actual physics we just talked about, the friction, the scattering,
Speaker 2: the final merger only takes two point one billion years, right,
Speaker 2: which means from an objective standpoint, the future of these
Speaker 2: black holes is already ancient history. They merged over ten
Speaker 2: billion years ago.
Speaker 3: That grand finale happened before our Solar system even existed exactly.
Speaker 2: The immense burst of gravitational waves from their final collision
Speaker 2: was injected into space time billions of years before the
Speaker 2: Earth formed. Yet, because those ripples travel at the speed
Speaker 2: of light just like the photons, those exact shockwaves are
Speaker 2: still racing toward us right now.
Speaker 3: They're still in transit.
Speaker 2: It's mind bending. When you look up at the night sky,
Speaker 2: you aren't just looking at stars. You are literally wading
Speaker 2: through a sea of invisible shockwaves from colossal collisions in
Speaker 2: a universe that doesn't even exist anymore. The echoes of
Speaker 2: j twenty zero three seven four five three seven haven't
Speaker 2: even washed over us yet. We are literally just waiting
Speaker 2: for the ripples to arrive. What other invisible ghosts of
Speaker 2: the ancient cosmos are watching over us right now?