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