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: I want you to start by just taking a moment
Speaker 2: to imagine something that completely defies our standard, everyday understanding
Speaker 2: of the cosmos, right because you know, when you look
Speaker 2: up at the night sky, it feels timeless, it feels static, eternal. Really,
Speaker 2: the constellations you see tonight are whether the exact same
Speaker 2: ones the ancient Greeks look at and.
Speaker 3: One's the Egyptians mapped out.
Speaker 2: Yeah, exactly. But right now, I want you to picture
Speaker 2: a super massive black hole, and it is sitting in
Speaker 2: the dark one point three billion light years away from
Speaker 2: where you were sitting right now.
Speaker 3: Which is a distance that's almost impossible for the human
Speaker 3: brain to process.
Speaker 2: It really is, just to put that distance into perspective.
Speaker 2: One point three billion years ago, the only life on
Speaker 2: Earth was microscopic, single celled organisms, floating in the ocean. Yep,
Speaker 2: the light from what we are about to discuss today
Speaker 2: has been traveling through the absolute void of space for
Speaker 2: all that time just to reach our telescopes.
Speaker 3: It's staggering.
Speaker 2: So this black hole is a cosmic engine of unimaginable power.
Speaker 2: Now imagine that engine seemingly reaching out and just pulling
Speaker 2: the plug on its own immense power.
Speaker 3: Supply, plunging into relative darkness right.
Speaker 2: Only to rapidly flip the switch back on and just
Speaker 2: roar back to life.
Speaker 3: I mean, it sounds like science fiction. You expect stars
Speaker 3: to twinkle, Sure, you might even expect a supernova to
Speaker 3: flare up and fade away over the course of say
Speaker 3: a few months.
Speaker 4: Sure, things we've observed before, right, But a super massive
Speaker 4: black hole, the gravitational anchor of an entire galaxy, suddenly
Speaker 4: throttling down and then powering back up.
Speaker 3: That completely rewrites our expectations of how these behemoths operate.
Speaker 3: We are talking about objects that dictate the evolution of
Speaker 3: billions of stars suddenly changing their fundamental.
Speaker 2: State, and we are just speaking in hypotheticals. Today we
Speaker 2: are looking at a very specific, very real celestial object,
Speaker 2: the galaxy catalog by astronomers is J tw one two
Speaker 2: four two three oh nine, though you will also hear
Speaker 2: it referred to by another astronomical survey designation, which is
Speaker 2: H one two three seven two three five two. Yes,
Speaker 2: catchy name, I know, right rolls right off the tongue.
Speaker 2: But the mission for our conversation today is to truly
Speaker 2: try and grasp the sheer scale of what it means
Speaker 2: when an active galactic nucleus or an AGN suddenly changes
Speaker 2: its behavior.
Speaker 3: It's a huge paradigm shift.
Speaker 2: We are taking those beautiful, but you know, static pictures
Speaker 2: of space that we all have as our computer backgrounds,
Speaker 2: and we are stepping into a dynamic, real time cosmic mystery.
Speaker 3: Because for a long time, astrophysics was essentially an observational
Speaker 3: history sign right, We looked at things that took millions
Speaker 3: of years to change. So from a human perspective, they
Speaker 3: look frozen like a snapshot exactly. But HG one two
Speaker 3: three seven twenty two five to two forces us to
Speaker 3: look at the universe as a violently active, breathing environment.
Speaker 3: What we are examining here is a phenomenon known in
Speaker 3: astrophysics as a changing look AGN or a clay in
Speaker 3: lazy right, it is a classification that represents some of
Speaker 3: the most extreme rapid transformations we have ever witnessed in
Speaker 3: the centers of galaxies.
Speaker 2: So, okay, let's unpack this because before we can truly
Speaker 2: understand why this supermassive black hole eventually turned off and
Speaker 2: shocked the astronomical community, we need to understand what it
Speaker 2: actually looks like when it is fully on.
Speaker 3: Yes, baseline is important here.
Speaker 2: We need to understand the anatomy of this cosmic engine.
Speaker 2: If a black hole by definition lets no light escape,
Speaker 2: how can an active galactic nucleus be the brightest thing
Speaker 2: in the universe.
Speaker 3: Well, to understand a changing look agn we have to
Speaker 3: establish what an active galactic nucleus is at its core.
Speaker 3: At the heart of most, if not all, large galaxies,
Speaker 3: including our own Milky Way, by the way, lies a
Speaker 3: super massive black.
Speaker 4: Hole right Sagittarius a star for us exactly, And these
Speaker 4: can be millions or even billions of times the mass
Speaker 4: of our Sun, all crushed into a singularity.
Speaker 2: Mind bending it is.
Speaker 3: But as you point it out, a black hole by
Speaker 3: itself is just a massive gravitational sinkhole. It is invisible,
Speaker 3: it doesn't emit light. What makes an aging an active
Speaker 3: and incredibly luminous is the material surrounding it and the
Speaker 3: brutal physics of how that material falls in We.
Speaker 2: Are talking about gas, dust, maybe stars that wandered a
Speaker 2: bit too close and got shredded. Definitely shredded stars. Yes,
Speaker 2: but this material doesn't just fall straight down like an
Speaker 2: apple falling from a tree.
Speaker 3: Right, it can't, and that is due to a fundamental
Speaker 3: law of physics called the conservation of angular momentum.
Speaker 2: Okay, for anyone whose high school physics is a bit rusty,
Speaker 2: this is the classic ice skater effect.
Speaker 3: Right, that is the perfect way to visualize it. Yeah,
Speaker 3: when a figure skater is spinning on the ice with
Speaker 3: their arms outstretched, they rot tate at a certain speed,
Speaker 3: but when they pull their arms in tight to their body,
Speaker 3: they spin dramatically faster. The angular momentum has to be conserved,
Speaker 3: so a smaller radius means a higher velocity.
Speaker 2: So how does that apply to the black hole?
Speaker 3: Well, in space you have massive clouds of gas and
Speaker 3: stellar debris caught in the black hole's gravitational pull. Because
Speaker 3: that material always has some slight initial rotation, nothing is
Speaker 3: ever perfectly still as it gets pulled closer and closer
Speaker 3: to the black hole, it spins faster and faster, pulling
Speaker 3: the arms in exactly, and the centrifugal force causes this
Speaker 3: spherical cloud to flatten out into a disk. We call
Speaker 3: this an accretion disc acretion disc right. It is a
Speaker 3: rapidly swirling whirlpool of matter moving at significant fractions of
Speaker 3: the speed of light.
Speaker 2: Wow. And because the material in the inner part of
Speaker 2: the disc is closer to the black hole, it has
Speaker 2: to orbit much faster than the material in the outer
Speaker 2: edge just to keep from falling in.
Speaker 3: Yes, Kepler's laws in action at speed.
Speaker 2: Difference layers moving at different speeds that must create an
Speaker 2: unimaginable amount of friction.
Speaker 3: The friction is the engine. You have adjacent layers of
Speaker 3: gas scraping against each other at relativistic speeds so close
Speaker 3: to the speed alight exactly. But it is not just
Speaker 3: physical friction like you know, rubbing your hands together. We
Speaker 3: are dealing with plasma here.
Speaker 2: Okay, so gas where the electrons have been stripped from
Speaker 2: their atoms. Right.
Speaker 3: And because it's plasma, that means it is highly magnetized.
Speaker 3: The magnetic fields within the spinning plasma get twisted, stretched,
Speaker 3: and then they violently snap back in a process called
Speaker 3: magnetic reconnection. Oh wow, yeah, this acts as an incredibly
Speaker 3: powerful source of viscosity. The sheer mechanical and magnetic stress
Speaker 3: heats the material in the accretion disc to millions of degrees.
Speaker 3: It transforms from cold cosmic gas into a blindingly bright,
Speaker 3: superheated plasma.
Speaker 2: So the accretion disc itself is actually glowing.
Speaker 3: Radiantly glowing, and there is a halo of even hotter,
Speaker 3: thinner plasma hovering just above and below the inner disc,
Speaker 3: called the.
Speaker 2: Corona, like the Sun's corona, but way hotter, way hotter.
Speaker 3: The Agan corona reaches temperatures in the billions of degrees billions.
Speaker 2: That's just wow. Yeah.
Speaker 3: Together, the accretion disc and the corona radiate an astonishing
Speaker 3: amount of energy across the entire electromagnetic spectrum, from radio
Speaker 3: waves all the way up to high energy X rays.
Speaker 3: That brilliant radiating structure is the active galactic nucleus, so.
Speaker 2: It's basically a giant power plant.
Speaker 3: It is. The engine is so efficient at converting mass
Speaker 3: into energy that a single agn can easily outshine the
Speaker 3: combined light of every single star in its entire host galaxy.
Speaker 2: It really want you to hold onto that image. If
Speaker 2: you're listening a structure around a black hole that is
Speaker 2: brighter than billions of stars combined, which brings us to
Speaker 2: the timescale anomaly.
Speaker 3: Yes, the anomaly.
Speaker 2: This is the core fact that makes HG one two
Speaker 2: three seven twenty two fifty two seven so absolutely mind bending. Usually,
Speaker 2: when we talk about a super massive black hole going
Speaker 2: through feeding episodes, periods where it consumes more matter and
Speaker 2: gets brighter or consumes less and dims, astronomers expect those
Speaker 2: changes in luminosity to take tens of thousand or even
Speaker 2: millions of years.
Speaker 3: Right, The physics simply demands time because of the sheer
Speaker 3: physical size of the objects involved.
Speaker 2: They're just too big to change quickly exactly.
Speaker 3: And accretion disk around a supermassive black hole isn't measured
Speaker 3: in miles or kilometers. It is measured in late days
Speaker 3: or light months.
Speaker 2: Wait light months.
Speaker 3: Yes, it might take light traveling one hundred and eighty
Speaker 3: six thousand miles per second several months just across from
Speaker 3: one side of the disc to the other. So if
Speaker 3: a process is going to change the overall structure and
Speaker 3: energy output of something that vast it is limited by
Speaker 3: the speed of light and the suit of sound within
Speaker 3: the plasma. So a human lifetime is a blink of
Speaker 3: an eye compared to the feeding cycle of an agn
Speaker 3: At least, that was the standard assumption across astrophysics.
Speaker 2: Wait, so if this disc is measured in light months across,
Speaker 2: how could it possibly change fast enough for us to notice?
Speaker 2: I mean, the data for H one two, three, seven
Speaker 2: fifty two completely shattered that assumption.
Speaker 3: Completely shattered it.
Speaker 2: Observers didn't watch it dim over a millennium. They watched
Speaker 2: its X ray brightness completely collapse, dropping by a staggering
Speaker 2: factor of seventeen in just eighteen months.
Speaker 3: The factor of seventeen drop in eighteen months for an
Speaker 3: object of this magnitude is well, it's practically a free fall.
Speaker 3: It is structural failure on a galactic scale, happening in
Speaker 3: real time.
Speaker 2: To put that into perspective for you, it is like
Speaker 2: going out to your favorite national park to look at
Speaker 2: a massive, towering mountain range like the Rockies or the Alps,
Speaker 2: and watching the largest peak erode into flat dust over
Speaker 2: a single weekend.
Speaker 3: That's a really good way to think about it.
Speaker 2: It's a timescale that makes perfect sense for human events,
Speaker 2: you know, building a house, completing a work project, but
Speaker 2: it is shockingly, almost impossibly fast for astrophysics.
Speaker 3: It really highlights a crucial point about how limited our
Speaker 3: observational window of the universe really is. What do you mean, Well,
Speaker 3: we have only had X ray telescopes in orbit for
Speaker 3: a few decades. Even within that narrow window, this galaxy
Speaker 3: proved that catastrophic structural changes can happen in a.
Speaker 2: Flash, which is terrifying and exciting all at once.
Speaker 3: Exactly now. To picture this properly, we should also clarify
Speaker 3: the specific type of galaxy we are looking at. H
Speaker 3: E one two three seven twenty two five to two
Speaker 3: is not a quasar. It is a seafert.
Speaker 2: Galaxy, right, and that distinction changes how we actually view
Speaker 2: it through our telescope.
Speaker 3: It does. Both quasars and seafert galaxies possess extremely bright
Speaker 3: active nuclei powered by supermassive black holes. However, a quasar
Speaker 3: represents the most extreme end of the.
Speaker 2: Spectrum the gas guzzlers of the universe.
Speaker 3: Yes, it is so unfathomably bright that its light completely
Speaker 3: washes out the host galaxy surrounding it. When you look
Speaker 3: at a quasar. Through a telescope, you essentially just see
Speaker 3: a blinding star like point of light.
Speaker 2: You can't see the actual galaxy.
Speaker 3: No, you can't see the spiral arms or the galaxy
Speaker 3: itself without highly specialized equipment blocking that central glare. But
Speaker 3: a seafert galaxy is slightly luminous relatively speaking. It is
Speaker 3: hosted in a spiral galaxy, much like our own Milky Way,
Speaker 3: but with an agn operating at a let's say, a
Speaker 3: lower gear.
Speaker 2: So with the seafert the host galaxy doesn't get completely
Speaker 2: blown out by the central glare exactly.
Speaker 3: With a seafert galaxy, the beautiful swirling galactic structure, the
Speaker 3: spiral arms, the dark dust lanes, the regions of active
Speaker 3: star formation, it all remains clearly visible to our telescopes
Speaker 3: alongside the intensely bright core.
Speaker 2: So it's not just a floating flashlight, right.
Speaker 3: It gives astronomers a much clearer context of the environment
Speaker 3: surrounding the black hole. We can see the neighborhood, not
Speaker 3: just the floodlight.
Speaker 2: I love that. So imagine you are looking through a
Speaker 2: powerful telescope. You see this glowing, magnificent spiral galaxy, a
Speaker 2: pinwheel of billions of stars floating in the dark. The
Speaker 2: very center is a blindingly bright core the accretion disk
Speaker 2: of the supermassive black hole actively feeding. And then, over
Speaker 2: the course of just a year and a half, which
Speaker 2: is barely any time at all, you watch that blinding
Speaker 2: center suddenly dim to a tiny fraction of its original strength,
Speaker 2: while the rest of the galaxy around it keeps turning
Speaker 2: completely undisturbed.
Speaker 3: It's a haunting visual, it really is.
Speaker 2: But a visual can only tell you so much. A
Speaker 2: picture might tell you a galaxy got dimmer, but it
Speaker 2: won't tell you the physics of why or how the
Speaker 2: structure around the black hole changed. For that, astronomers have
Speaker 2: to decode the light itself using spectral fingerprints, right.
Speaker 3: Because we don't just look at photographs to understand what's happening.
Speaker 3: We rely on spectroscopy, which is arguably the most powerful
Speaker 3: tool in all of astronomy period absolutely to understand the
Speaker 3: changing look aspect of this galaxy, we have to break
Speaker 3: down how we classify active galactic nuclei into type one
Speaker 3: and type two.
Speaker 2: Okay, for those of us who haven't played with a
Speaker 2: prism since elementary school science class, how does reading the
Speaker 2: light actually tell us what is happening near a black
Speaker 2: hole one point three billion light years away?
Speaker 3: Well, think about Isaac Newton passing sunlight through a glass
Speaker 3: prism and seeing a rainbow. Spectroscopy is essentially the advanced
Speaker 3: version of that. When astronomers pass the light from a
Speaker 3: distinct galaxy through a spectrograph attached to a telescope, it
Speaker 3: breaks that light down into its constituent wavelengths, creating a spectrum.
Speaker 2: Okay, so a very detailed rainbow.
Speaker 3: Right, But it's not a perfectly smooth, continuous rainbow. When
Speaker 3: you look closely, you see specific distinct bright lines at
Speaker 3: very precise wavelengths. These are called emission lines.
Speaker 2: And these lines act as a barcode for the universe.
Speaker 3: Don't they exactly like a barcode. Every chemical element hydrogen, helium, carbon,
Speaker 3: iron has a unique atomic structure. When the electrons and
Speaker 3: these atoms are heated up by the intense energy of
Speaker 3: the black hole, they jump to higher.
Speaker 2: Energy level, They get excited, right, and.
Speaker 3: When they fall back down, they release a photon of
Speaker 3: light at a very specific unchanging wavelength. So by looking
Speaker 3: at where these bright lines appear on our spectrum, we
Speaker 3: know exactly what kind of gas is glowing in that
Speaker 3: distant galaxy.
Speaker 2: That's incredible.
Speaker 3: But the spectrum tells us more than just chemistry. It
Speaker 3: tells us velocity.
Speaker 2: Oh right, this is where the Doppler effect comes in.
Speaker 2: I think most of us understand the Doppler effect when
Speaker 2: it comes to sound. You hear an ambulance coming towards you,
Speaker 2: and the siren sounds high pitch because the sound waves
Speaker 2: are being compressed as it passes and drives away. The
Speaker 2: pitch drops noticeably because the sound waves are being stretched out.
Speaker 2: But how does that apply to light?
Speaker 3: It works the exact same way. If a cloud of
Speaker 3: glowing gas and space is moving rapidly toward our telescopes
Speaker 3: on Earth light waves, it emits get slightly compressed. We
Speaker 3: call this blue shift because the light is shifted toward
Speaker 3: the shorter, bluer end of the spectrum. And if the
Speaker 3: gas is moving rapidly away from us, the light waves
Speaker 3: are stretched out, shifting them toward the longer, redder wavelength.
Speaker 3: This is red shift. Now apply this to a swirling
Speaker 3: accretion disk and the clouds of gas orbiting the black hole.
Speaker 2: Well, the gas on one side of the black hole
Speaker 2: is rotating toward us YEA and the gas on the
Speaker 2: other side is rotating away.
Speaker 3: Right. Let's start with a type one ag in. When
Speaker 3: we look at a type one, the spectrograph shows us
Speaker 3: two types of emission lines, broad lines and.
Speaker 2: Narrow lines broad and narrow.
Speaker 3: The physical reality behind this is fascinating. The broad lines
Speaker 3: are created by gas that is swirling extremely fast, very
Speaker 3: very close to the supermassive black hole, in a region
Speaker 3: heavily dominated by the black hole's immense.
Speaker 2: Gravity, so deep in the gravity.
Speaker 3: Well, yes, according to Kepler's laws of orbital motion, things
Speaker 3: closer to a massive body must orbit faster. We are
Speaker 3: talking about gas moving at thousands of kilometers per second.
Speaker 2: Wow.
Speaker 3: Because the gas is moving so incredibly rapidly, the Doppler
Speaker 3: effect severely smears the wavelength of the light it emits.
Speaker 3: The light from the gas moving toward us is heavily
Speaker 3: blue shifted, and the light moving away is heavily red shifted.
Speaker 3: When you combine all that light into one signal, it
Speaker 3: creates a wide, fat, broad peak on our spectrograph.
Speaker 2: Ah. So when an astronomer sees a broad line, they
Speaker 2: know they are looking at incredibly fast gas deep in
Speaker 2: the danger zone right next to the engine.
Speaker 3: Yes, and the narrow lines and a type one spectrum
Speaker 3: come from clouds of gas that are located much further.
Speaker 2: Away from the black hole, where it's safer.
Speaker 3: Where the gravitational pull is significantly weaker. Yeah, the gas
Speaker 3: is moving much slower, maybe just hundreds of kilometers per
Speaker 3: second because the velocity is lower, the Doppler shifting is minimal.
Speaker 3: The light isn't smeared out.
Speaker 2: It's a sharper peak exactly.
Speaker 3: It creates a sharp, tall, narrow peak on the graph.
Speaker 3: So a type one AGN shows both the fast broad
Speaker 3: inner gas and the slow narrow outer.
Speaker 2: Gas, and a type two.
Speaker 3: A type two AGN shows only the narrow emission lines.
Speaker 3: The broad lines are completely absent from the barcode.
Speaker 2: Interesting.
Speaker 3: This means we are only seeing the slow moving gas
Speaker 3: far away from the black hole. We aren't detecting the
Speaker 3: fast moving gas right next to the engine at all.
Speaker 2: Okay, hold on to a late person. Classifying a galaxy
Speaker 2: as type one or type two makes total sense. Either
Speaker 2: you see the fast inner gas or you don't. But
Speaker 2: the universe rarely deals in just black and white.
Speaker 3: Very true.
Speaker 2: Astronomers have these micromeasurements. We have intermediate subtypes sitting right
Speaker 2: in between, like type one point two, one point five,
Speaker 2: one point eight, and one point nine. I gotta say
Speaker 2: arguing over a one point eight versus a one point
Speaker 2: nine sounds like splitting cosmic hares. Why does this micro
Speaker 2: level classification actually matter to our understanding of how the
Speaker 2: black hole.
Speaker 3: Operates because it reveals the thermodynamics of the engine shutting down.
Speaker 3: The intermediate types are where the taxonomy gets incredibly precise.
Speaker 3: They are ranked purely by how strong the broad emission
Speaker 3: lines are relative to the narrow ones. Okay, and astronomers
Speaker 3: look for very specific chemical signatures to make this judgment,
Speaker 3: particularly two specific hydrogen emission lines known as hydrogen alpha
Speaker 3: or H alpha, and hydrogen beta or H beta.
Speaker 2: Let's break this down. Why focus on those two hydrogen
Speaker 2: lines specifically.
Speaker 3: Well, hydrogen is the most abundant element in the universe,
Speaker 3: so its signals are the loudest. In the atomic structure
Speaker 3: of hydrogen, an electron jumping from the third energy level
Speaker 3: down to the second produces the H alpha line, which
Speaker 3: is a specific shade of red. An electron jumping from
Speaker 3: the fourth energy level down to the second produces the
Speaker 3: H beta line, which is a specific shade of blue. Green.
Speaker 3: Here's the crucial physical difference. It takes significantly more energy
Speaker 3: from the black holes radiation to kick an electron up
Speaker 3: to that fourth level to make H beta than it
Speaker 3: does to kick it to the third level to make
Speaker 3: H alpha.
Speaker 2: Ah. So the H beta line requires a hotter, more
Speaker 2: energetic engine to exist.
Speaker 3: Precisely, so, as an AGN starts to lose power the
Speaker 3: environment cools down, it doesn't have the intense energy required
Speaker 3: to excite the hydrogen atoms to that fourth energy level anymore.
Speaker 3: So what happens the broad H beta line starts to
Speaker 3: fade away. First, in a type one point eight AGN,
Speaker 3: you can still clearly see one broad line, the hydrogen
Speaker 3: alcil line, because the engine still has enough juice for that.
Speaker 3: But the broad hydrogen beta line has become very weak.
Speaker 3: It's just barely hanging on.
Speaker 2: It's like watching a city experience a rolling blackout. The
Speaker 2: most power hungry industrial sector shut down first, while the
Speaker 2: residential lights stay on a little longer.
Speaker 3: That is a highly accurate way of view it. Actually,
Speaker 3: as the temperature continues to drop, the power hungry H
Speaker 3: beta line vanishes entirely. When you show just the broad
Speaker 3: H offal line, you are classified as a type one.
Speaker 2: Point nine is one broad line left yep.
Speaker 3: If the engine cools even further and that final broad
Speaker 3: h Alfha line disappears because there isn't even enough energy
Speaker 3: to excite electrons to the third level, you've arrived at
Speaker 3: a type two. The fast inner gas has gone completely dark.
Speaker 2: Which brings us to the changing look identity of h
Speaker 2: E one two three seven twenty two fifty two. This
Speaker 2: galaxy didn't just sit comfortably in one category, It moved
Speaker 2: through them right.
Speaker 3: What's fascinating here is that shifting between these highly specific
Speaker 3: classifications reveals the real time physical transformation of the space
Speaker 3: immediately surrounding the black hole. Historically, based on archival data,
Speaker 3: HG one two three seven twenty two fifty two was
Speaker 3: classified as a type one point zero.
Speaker 2: To one point two, so it was running hot.
Speaker 3: Very hot. It had strong, clear broad lines for both
Speaker 3: H alpha and N beta. The engine was roaring at
Speaker 3: high temperatures.
Speaker 2: But then when astronomers observed it in twenty twenty two,
Speaker 2: the spectrum had shifted all the way down to a
Speaker 2: type one point eight. The broad H beta line had
Speaker 2: almost entirely vanished. The power hungry sector of the gas
Speaker 2: near the black hole had effectively gone dark.
Speaker 3: And the story didn't end there. By late twenty twenty four,
Speaker 3: observation showed its spectral lines had fully recovered. Wow, the
Speaker 3: broad H alpha and H beta lines were back in
Speaker 3: full force, returning the galaxy to a type one point
Speaker 3: zero classification. Now over one hundred and fifty of these
Speaker 3: changing up AGNs or Cliegen's have been confirmed to date,
Speaker 3: so it's not the only one. No, they're usually found
Speaker 3: through repeat optical spectroscopy over many years, or by scanning
Speaker 3: large photometric surveys. But catching one shifting so dramatically and
Speaker 3: capturing the entire cycle of dimming and recovering in such
Speaker 3: a brutally short window of eighteen months, that is a
Speaker 3: rare treasure for astrophysicists.
Speaker 2: So we know the engine throttled down, we know the
Speaker 2: spectral fingerprints shifted, proving the gas physically cool than then reheated.
Speaker 2: But how did humanity actually coordinate the tracking of this
Speaker 2: massive event? I mean, we are talking about something one
Speaker 2: point three billion light years away. You don't just point
Speaker 2: a single backyard telescope at it and call it a day.
Speaker 3: No, absolutely not.
Speaker 2: This required an astronomical stakeout across multiple wavelengths of light.
Speaker 3: The coordination required to monitor an event like this is
Speaker 3: a massive logistical triumph for modern astronomy. Getting time on
Speaker 3: major space telescopes is incredibly competitive. I can imagine you
Speaker 3: have thousands of astronomers writing proposals waiting years for a
Speaker 3: few hours of observation time. But when an event like
Speaker 3: this happens, it triggers what are called target of opportunity protocols.
Speaker 2: Physical was skipping the line.
Speaker 3: Exactly, allowing astronomers to essentially interrupt the scheduled programming of
Speaker 3: humanity's most expensive satellites.
Speaker 2: So the initial spotting of this dramatic dimming happened in
Speaker 2: January twenty twenty two. It was detected using an instrument
Speaker 2: called ROSITA.
Speaker 3: Yes, the discovery was led by a stronomer named Alex
Speaker 3: Markowitz and his team at the Nicholas Copernicus Astronomical Center.
Speaker 3: eROSITA stands for the Extended Rumpchin Survey with an Imaging
Speaker 3: telescope array. It is an X ray telescope in orbit,
Speaker 3: basically scanning the entire sky.
Speaker 2: Let's talk about how an X ray telescope actually works,
Speaker 2: because it is fundamentally different from a ground based optical telescope,
Speaker 2: isn't it. You can't just use a normal mirror.
Speaker 3: You absolutely cannot. If you try to use a standard
Speaker 3: curved glass mirror like the ones in the Hubble Space
Speaker 3: telescope or ground based observatories, the X rays would just
Speaker 3: blast straight through the glass or be completely absorbed.
Speaker 2: By it because they have too much energy.
Speaker 3: Right. X rays carry far too much energy to be
Speaker 3: reflected at a direct angle. So to focus X rays,
Speaker 3: astronomers use what are called grazing incidence mirrors. Think of
Speaker 3: skipping a stone across a pond. Okay, if you throw
Speaker 3: the stone straight down, it sinks, but if you throw
Speaker 3: it at a very shallow grazing angle, it skips off
Speaker 3: the surface.
Speaker 2: So they build a telescope that is in skips X
Speaker 2: rays into a detector.
Speaker 3: Precisely, they use nested cylindrical mirrors coated with heavy metals
Speaker 3: like gold or iridium. The X rays entered the tube
Speaker 3: skip off the shallow angles of the mirrors and are
Speaker 3: slowly guided down into a focal point.
Speaker 2: At the detector. That is brilliant engineering.
Speaker 3: It is so Arosiita surveys the sky in soft X rays,
Speaker 3: and when the team analyzed the data for h E
Speaker 3: one two three, seven, twenty two fifty two from January
Speaker 3: twenty twenty two, they saw that the soft X ray
Speaker 3: flux had simply collapsed compared to previous archival observations from
Speaker 3: years prior, and once.
Speaker 2: That alarm was sounded the bureaucracy, as space astronomy, had
Speaker 2: to move at lightning speed. They triggered a global and
Speaker 2: orbital coordination effort to track the galaxy across the entire
Speaker 2: electromagnetic spectrum. They essentially aimed every lens humanity has at
Speaker 2: this one spot in.
Speaker 3: The sky pretty much from late twenty twenty two all
Speaker 3: the way through early twenty twenty five. They brought in
Speaker 3: an absolute arsenal of instruments for a follow up campaign
Speaker 3: in space. They didn't just rely on Arosita. They brought
Speaker 3: in the XMM Newton X ray Observatory, which is one
Speaker 3: of the most powerful X ray telescopes ever built. They
Speaker 3: utilized this swift observatory, which specializes in rapidly pointing at
Speaker 3: transient events and X ray and ultraviolet light. They also
Speaker 3: tasked the Neo Wise satellite, which maps the sky in
Speaker 3: infrared light.
Speaker 2: And down here on Earth. They had ground based optical
Speaker 2: photometry networks stepping into right.
Speaker 3: Yes, specifically the LCO, Thelas Koumber's Observatory, and the PROMPT
Speaker 3: telescope networks, as well as the Atlas Survey, which normally
Speaker 3: looks for near Earth asteroids but sweeps the sky so
Speaker 3: frequently it's fantastic for spotting changing galaxies.
Speaker 2: Why do they need all of that? I mean, why
Speaker 2: is that multi wavelength approach so essential?
Speaker 3: That multi wavelength approach is non negotiable for understanding black holes?
Speaker 3: A single telescope only gives you a tiny slice of reality.
Speaker 3: Different types of light tell you what is happening in
Speaker 3: physically different parts of the black holes environment.
Speaker 2: Oh I see.
Speaker 3: We established that the X rays come from the very
Speaker 3: innermost region, the incredibly hot magnetized corona right next to
Speaker 3: the event horizon. Ultraviolet and optical light the kind we
Speaker 3: can see with our eyes or standard telescopes, come from
Speaker 3: the main body of the accretion disk spreading outward, and
Speaker 3: infrared light comes from massive clouds of dust and gas
Speaker 3: located much further out, essentially measuring the ambient heat generated
Speaker 3: by the inner engine.
Speaker 2: Which leads us to a massive discrepancy in the recovery
Speaker 2: rates they observed. This is a core piece of the mystery.
Speaker 2: The dimming wasn't just happening in X rays. The infrared
Speaker 2: brightness had dipped significantly as well. Yes, it did, But
Speaker 2: when the black hole started to reignite, the different types
Speaker 2: of light didn't come back at the same time. The
Speaker 2: timeline of the recovery was highly stratified, very stratified.
Speaker 3: The highest energy light from the innermost region, the X
Speaker 3: ray flux, bounced back incredibly quickly. It recovered in a
Speaker 3: mere three months. The engines sparked back to life.
Speaker 2: Three months is nothing, right, But the.
Speaker 3: Optical the ultraviolet and the infrared bands, the light coming
Speaker 3: from further out in the system, took a sluggish three
Speaker 3: years to fully recover.
Speaker 2: So what does this all mean? Why would the X
Speaker 2: rays snap back in three months while the infrared or
Speaker 2: the UV light takes three years. If the engine turns
Speaker 2: back on, the whole thing just light up at once.
Speaker 3: It comes down to the sheer physical distance of the
Speaker 3: structures involved and the hard speed limit of the universe,
Speaker 3: the speed of light. Think of it like a massive
Speaker 3: industrial stovetop.
Speaker 2: Okay, I like this analogy, Walk me through it.
Speaker 3: The X rays are the red hot, glowing electric coils
Speaker 3: in the center of the stove. They are the direct
Speaker 3: source of the extreme heat got it. The optical and
Speaker 3: UV light represent a heavy iron pan sitting on those coils.
Speaker 3: The infrared light represents the ambient air warming up in
Speaker 3: the kitchen. If you crank the dial and turn the
Speaker 3: stove on, the electric coils, the innermost corona get hot
Speaker 3: and glow almost instantly. The X rays flare up, but
Speaker 3: it takes time for that heat to physically conduct through
Speaker 3: the heavy iron pan. It takes even longer for that
Speaker 3: heat to radiate out.
Speaker 4: And warm up the entire kitchen, So it is literally
Speaker 4: a delay and cause and effect across the physical distance.
Speaker 2: Of the disk.
Speaker 3: Exactly when the central feeding process restarts, the innermost region
Speaker 3: gets hot instantly, generating X rays, but the signal that
Speaker 3: the engine is back on the intense radiation heating the
Speaker 3: outer disc takes months to physically travel from the center
Speaker 3: to those outer edges. The ultraviolet and optical light take
Speaker 3: time to ramp back up, and.
Speaker 2: The infrared light takes even longer.
Speaker 3: Because the infrared light originates from a massive doughnut shaped
Speaker 3: structure called a dust torus that surrounds the entire agen
Speaker 3: system located light years away from the center O light years. Yes,
Speaker 3: the X ray and UV light have to travel from
Speaker 3: the black hole traverse that vast distance, hit that cold
Speaker 3: distant dust, heated up, and then the dust re emits
Speaker 3: that energy as infrared light. That light travel time creates
Speaker 3: a natural delay, a sluggish, multi year echo of the
Speaker 3: central event.
Speaker 2: Okay, I have to play the role of the skeptical
Speaker 2: observer here for a second. Please do we are talking
Speaker 2: about complex thermal waves, magnetic reconnections, and light speed time
Speaker 2: delays across secretion disks. But couldn't there be a much simpler,
Speaker 2: more intuitive, everyday explanation for why something far away might
Speaker 2: suddenly look dim to us.
Speaker 3: Science requires testing all hypotheses, especially the simplest ones Okham's razor.
Speaker 3: What is the alternative theory?
Speaker 2: What if a massive rogue dust cloud simply drifted across
Speaker 2: our line of sight?
Speaker 3: Oh, the dust cloud theory.
Speaker 2: Yeah, space is full of dust, gas, and stellar debris.
Speaker 2: The galaxy is rotating. What if an incredibly dense clump
Speaker 2: of material just happened to pass exactly between our telescopes
Speaker 2: on Earth and the center of h E one two
Speaker 2: three seven, twenty two fifty two. It would be like
Speaker 2: someone holding their hand over a flashlight. Right, The flashlight
Speaker 2: didn't turn off, it's just physically blocked. Could an obscuring
Speaker 2: cloud explain the dimming we saw?
Speaker 3: It is a vital question to ask. In fact, in
Speaker 3: the early days of studying changing look AGNs, before we
Speaker 3: had such robust multi wavelengths cored nation obscuration by a
Speaker 3: passing cloud was actually the prevailing theory in astronomy makes sense.
Speaker 2: It's simple and mechanically sound.
Speaker 3: However, the multi wavelength data we just outlined completely dismantles
Speaker 3: this dust cloud theory. For this specific event, we can
Speaker 3: definitively prove the flashlight actually turned off.
Speaker 2: Was the smoking gun that proves it wasn't just a
Speaker 2: rogue cloud acting as a filter.
Speaker 3: There are two major pillars of evidence based entirely on
Speaker 3: how different wavelengths of light interact with physical matter. Reason
Speaker 3: number one lies in the X ray data from Arosida
Speaker 3: and XMM Newton. Okay, if a massive dust cloud had
Speaker 3: passed in front of the black hole, we wouldn't just
Speaker 3: see a clean, uniform drop in the overall amount of
Speaker 3: X rays. We would see distinct telltale signs of absorption.
Speaker 2: What does X ray absorption actually look like in astronomical data?
Speaker 3: Think about a medical X ray at the doctor's office. Sure,
Speaker 3: the X rays pass easily through your soft tissue, which
Speaker 3: is why your skin and muscles look transparent on the film.
Speaker 3: But the X rays are absorbed by the denser calcium
Speaker 3: in your casting a shadow. Right in space, dust clouds
Speaker 3: act similarly. They are highly effective at blocking lower energy
Speaker 3: or soft X rays, but they are relatively transparent to
Speaker 3: higher energy or hard X rays, which just punch right through.
Speaker 2: So if the cloud was blocking our view of the
Speaker 2: black hole, the spectrographs would have recorded a massive drop
Speaker 2: in the soft X rays, but the hard X rays
Speaker 2: would have mostly remained steady.
Speaker 3: Exactly, The spectrum would look skewed. It would look artificially filtered.
Speaker 3: But that is not what the observatories recorded. They saw
Speaker 3: a uniform collapse across the board. Soft X rays, hard
Speaker 3: X rays, all of it vanished simultaneously. The X rays
Speaker 3: weren't being filtered by a cloud, they simply weren't being produced.
Speaker 2: No, the stove coils were actually turned off.
Speaker 3: They were turned off.
Speaker 2: What is the second reason?
Speaker 3: Reason Number two is the infrared data from the Neo
Speaker 3: YSE satellite. We talked about how the distant dust torus
Speaker 3: generates infrared light by absorbing energy from the center. Think
Speaker 3: about what happens if you shine a tremendously bright hot
Speaker 3: spotlight onto a thick dark curtain.
Speaker 2: Okay, shining a spotlight on a curtain.
Speaker 3: The visible light doesn't just disappear into nothingness. The curtain
Speaker 3: absorbs that energy, heats up, and radiates that heat away.
Speaker 2: It essentially becomes the giant thermal blanket.
Speaker 3: Exactly in space, if an active black hole is shining
Speaker 3: intensely behind a massive rogue dust cloud, the dust in
Speaker 3: that cloud absorbs the extreme optical and ultraviolet radiation, It
Speaker 3: gets hot, and it glows brightly in the infrared.
Speaker 2: So if a cloud moved in and blocked the visible light,
Speaker 2: the infrared brightness we detect from Earth should have actually
Speaker 2: stayed steady or even spiked, because the cloud itself is
Speaker 2: catching all that heat and glowing exactly.
Speaker 3: The infrared output would remain high because the hidden engine
Speaker 3: is still pumping energy into the obscuring cloud. But Neowise
Speaker 3: showed us the exact opposite. The infrared brightness dropped significantly
Speaker 3: right alongside the X rays and the optical light.
Speaker 2: The flashlight wasn't blocked, it genuinely lost power.
Speaker 3: The conclusion is inescapable because both the X ray spectrum
Speaker 3: collapsed without the specific signatures of absorption and the infrared
Speaker 3: ambient heat dropped. This was an intrinsic change. The black
Speaker 3: hole was genuinely producing less energy. The engine itself was failing,
Speaker 3: which brings.
Speaker 2: Us to the ultimate question the thermodynamics of the void.
Speaker 2: If nothing was blocking or view, what actually happened inside
Speaker 2: that plasma accretion disk to cause a supermassive black hole
Speaker 2: to suddenly lose its appetite?
Speaker 3: That is the million dollar crawl done right.
Speaker 2: What physically causes an engine light months across to fail
Speaker 2: in eighteen months and then restart.
Speaker 3: This is where we reached the cutting edge of modern
Speaker 3: theoretical astrophysics. The leading explanation for what happened inside h
Speaker 3: E one two three seven, twenty two fifty two involves
Speaker 3: the propagation of cold and warm fronts traveling through the
Speaker 3: accretion disk itself.
Speaker 2: Are we talking about weather patterns on a galactic scale.
Speaker 3: In a fluid dynamic sense. Yes, we have to stop
Speaker 3: thinking of the accretion disk as a solid, flat dinner plate,
Speaker 3: it is a highly volatile, fluid turbulent plasma. The dominant
Speaker 3: theory suggests that a local instability, likely related to the
Speaker 3: magnetic fields that provide the friction, a phenomenon called magneto
Speaker 3: rotational instability, triggered a sudden collapse in the heating mechanism. Okay,
Speaker 3: this created a cooling wave that rapidly traveled outward through
Speaker 3: the inner regions of the disc.
Speaker 2: Mechanically, what happens when a cooling wave hits superheated plasma
Speaker 2: or moving at relativistic.
Speaker 3: Speeds well as this cooling front propagase. It drastically lowers
Speaker 3: the temperature of the plasma, and when that happens, the
Speaker 3: physics changed dramatically. Cooler plasma means less turbulent magnetic friction.
Speaker 3: Less friction means the material isn't radiating as much extreme energy. Crucially,
Speaker 3: as it cools, the vertical height of the disc shrinks.
Speaker 3: It deflates from a puffed up doughnut like shape into
Speaker 3: a thin, razor flat disk.
Speaker 2: Like a balloon, losing air.
Speaker 3: Exactly, and this thin structure is incredibly inefficient at feeding
Speaker 3: material inward. The physical flow of gas into the innermost corona,
Speaker 3: chokes off the cooling wave temporarily suppresses the entire disc's
Speaker 3: energy output.
Speaker 2: That explains the eighteen month drop. The cooling waves swept
Speaker 2: through deflated the disc choke the fuel line and shut
Speaker 2: the X ray corona down.
Speaker 3: But a black hole's gravity is relentless. The system will
Speaker 3: always attempt to re establish.
Speaker 2: Equilibrium because the mass is still there.
Speaker 3: Yes, as the material continues to pile up in the
Speaker 3: deflated disc, the density increases. Eventually the friction must reignite.
Speaker 3: This triggers a warming wave, a wave of heating that
Speaker 3: slowly propagates back through materials pushes back right. This warming
Speaker 3: wave gradually restores the extreme temperatures, puffing the disk back up,
Speaker 3: reigniting the intense magnetic friction and forcefully pushing material back
Speaker 3: toward the event horizon. The brilliant luminosity is slowly.
Speaker 2: Restored, and astronomers actually saw hard evidence of this reignition.
Speaker 2: PHAs didn't they As the black hole roared back to
Speaker 2: life in late twenty twenty four, researchers detected something highly
Speaker 2: distinct in the spectral data.
Speaker 3: They did as the galaxy returned to its type one
Speaker 3: point zero status, meaning the broad emission lines returned. The
Speaker 3: researchers detected a highly distinct double peaked pattern in the
Speaker 3: hydrogen emission lines.
Speaker 2: A double peak pattern, What does that imply about the
Speaker 2: geometry of what we're looking at?
Speaker 3: It is a beautiful geometric clue. When you see a
Speaker 3: single broad peak, you are generally looking at a turbulent,
Speaker 3: messy cloud of gas swirling around. But when you see
Speaker 3: a distinct double peak in an emission line, it usually
Speaker 3: means you are looking at a highly organized, rotating ring
Speaker 3: of gas. Yes, one peak is the side of the
Speaker 3: ring rotating rapidly toward you, which is blue shifted. The
Speaker 3: other peak is the side rotating rapidly away, which is
Speaker 3: red shifted. There is a dip in the middle. The
Speaker 3: implication here is stunning. It hints that as the inner
Speaker 3: corona of the black hole suddenly flared back to life,
Speaker 3: its intense X ray radiation reached out into the darkness
Speaker 3: and illuminated a brilliant ring like structure of gas residing
Speaker 3: just above the.
Speaker 2: Disc building on that is it sounds exactly like turning
Speaker 2: on a stadium spotlight in pitch blackness.
Speaker 3: Exactly like that, you flip the.
Speaker 2: Switch and suddenly the intense beam of light catches the
Speaker 2: curved rim of the bleachers.
Speaker 3: Huh huh.
Speaker 2: We only saw the ring of gas because the central
Speaker 2: light finally turned back on to illuminate it.
Speaker 3: The recovering corona acted as a massive cosmic flashbulb, revealing
Speaker 3: the hidden architecture of the space immediately surrounding the black hole.
Speaker 3: And this specific discovery, the sudden appearance of this double
Speaker 3: peaked ring, ties directly into a much broader, long standing
Speaker 3: debate currently raging in astrophysics.
Speaker 2: Regarding the fundamental nature of that broadline gas we talked
Speaker 2: about earlier. Yeah, the fast moving gas that creates the
Speaker 2: type one signature. Why is there a debate about it?
Speaker 2: Don't we know it's just gas ordering the black hole?
Speaker 3: The argument is really about permanence and origins. Is the
Speaker 3: broad line gas region a permanent, massive structural reservoir of
Speaker 3: material that just sits there orbiting the black hole, essentially
Speaker 3: waiting to be illuminated, okay? Or is it not a
Speaker 3: permanent structure at all, but rather a dynamic.
Speaker 2: Wind, a wind like being blown away, an outflow.
Speaker 3: Of gas that is continuously being blown off the surface
Speaker 3: of the accretion disk. Entirely dependent on the black hole
Speaker 3: feeding above a certain threshold.
Speaker 2: Oh wow, that is a massive physical distinction. Are we
Speaker 2: looking at a permanent physical structure like a belt of asteroids? Yeah?
Speaker 2: Or a temporary weather phenomenon like a hurricane created solely
Speaker 2: by the heat of the engine.
Speaker 3: Right, And if we connect this to the bigger picture
Speaker 3: of how galaxies evolve, you can see why HG one
Speaker 3: two three seven tweet two fifty two is so incredibly important.
Speaker 3: If the engine drops below a specific power level, does
Speaker 3: the wind just stop blowing, causing the broad line region
Speaker 3: to literally cease to exist?
Speaker 2: And then when it turns back on, does it have
Speaker 2: to blow a brand new wind exactly?
Speaker 3: This galaxy serves as a real time laboratory to test
Speaker 3: these exact models. By watching the broad lines vanish as
Speaker 3: the cooling wave hits and then reappear with that double
Speaker 3: peaked ring signature as the warming wave restores power, researchers
Speaker 3: can measure exactly how the gas reacts to the turning
Speaker 3: off and turns of the central engine.
Speaker 2: It's like turning the machine on and off to see
Speaker 2: which parts move.
Speaker 3: It provides the hard observational data needed to finally resolve
Speaker 3: these theoretical debates about how black holes interact with their
Speaker 3: host galaxies.
Speaker 2: It is just phenomenal to think about. We set out
Speaker 2: to understand the scale of a changing look agn and
Speaker 2: the journey we just took is staggering.
Speaker 3: It really is.
Speaker 2: We have tracked a super massive black hole one point
Speaker 2: three billion light years away. We watched it mysteriously dim
Speaker 2: its X ray output by a massive factor of seventeen
Speaker 2: in just eighteen months, effectively choking off its own fuel line.
Speaker 2: We saw a massive coordinated network of Earth and space
Speaker 2: based telescopes a Rosita, XMM, Newton NEO wis Atlas, all
Speaker 2: point at the same spot to prove beyond a shadow
Speaker 2: of a doubt, that wasn't just a passing dust cloud,
Speaker 2: definitely not a cloud. It was an intrinsic catastrophic failure
Speaker 2: of the black hole's feeding mechanism. And finally we mapped
Speaker 2: out how fluid thermodynamics cold and warm waves rippling through
Speaker 2: a relativistic plasma decretion disc can temporarily starve a black hole,
Speaker 2: only to watch it slowly come back to life, acting
Speaker 2: as a flash bulb to illuminate a hidden ring of
Speaker 2: gas in the process.
Speaker 3: And this event is a loud, clear signal to the
Speaker 3: astronomical community. The researchers who publish this detailed analysis have
Speaker 3: a specific, urgent call for the future of astrophysics. To
Speaker 3: truly unravel the physics of these changing look agians, astronomy
Speaker 3: needs more high cadence optical and UV monitoring campaigns. We
Speaker 3: cannot rely on archival data taken years apart.
Speaker 2: We can't just check in every decade exactly.
Speaker 3: We need telescopes checking in on these active galaxies frequently,
Speaker 3: not once a decade, but constantly, a week after week.
Speaker 2: We need to watch the movie, not just look at
Speaker 2: isolated polaroids from a family album.
Speaker 3: Precisely, If we monitor them continuously, we can catch these
Speaker 3: cooling and warming waves as they initiate in real time.
Speaker 3: We can map the propagation of the thermal fronts across
Speaker 3: the accretion disks, and finally understand the exact triggers that
Speaker 3: cause these supermassive ends to stall out.
Speaker 2: Yeah, and that leaves us with a final thought. I
Speaker 2: want you listening right now to ponder when you look
Speaker 2: up at the night sky, it is so easy to
Speaker 2: fall into the trap of thinking of the universe as
Speaker 2: a slow, static painting a quiet, unchanging backdrop to our
Speaker 2: frantic human lives. But it's not no h I one
Speaker 2: two three seven, two, two fifty two proves that the
Speaker 2: cosmos is fiercely violently active. If a super massive black hole,
Speaker 2: an object containing the mass of millions of suns anchoring
Speaker 2: an entire galaxy, can effectively turn off and on in
Speaker 2: the time it takes a human being to finish a
Speaker 2: college degree, it begs a massive.
Speaker 3: Question, a very exciting question
Speaker 2: What other immense, rapid cosmic engines are throttling up or
Speaker 2: down right now hidden in the dark, just waiting for
Speaker 2: us to finally point a telescope in their direction.