# The Strange Galaxy That Reveals Millions of Years of Cosmic Activity

An episode of [Bedtime Astronomy](https://invisiblenetwork.ai/podcast/1736397134), 3 Oct 2026, 33 min.

Audio: https://dts.podtrac.com/redirect.mp3/api.spreaker.com/download/episode/75419501/radiogalp.mp3

Astronomers have uncovered an extraordinary radio galaxy stretching nearly four million light-years across. Its unusual structure contains clues to a complex history of activity around its central supermassive black hole, offering a rare glimpse into how these cosmic giants evolve over millions of years. Thank you for listening to Bedtime Astronomy — your guide to the cosmos. New episodes on space exploration, NASA missions & the latest astronomy breakthroughs. This episode includes AI-generated content.

## Transcript

[0:03] Speaker 1: Welcome to Bedtime Astronomy. Explore the wonders of the cosmos
[0:07] Speaker 1: with our soothing Bedtime Astronomy podcast. Each episode offers a
[0:12] Speaker 1: gentle journey through the stars, planets and beyond. Perfect for
[0:16] Speaker 1: unwinding after a long day. Let's travel through the mysteries
[0:20] Speaker 1: of the universe as you drift off into a peaceful
[0:22] Speaker 1: slumber under the night sky.
[0:27] Speaker 2: Imagine an explosion so incredibly violent that it shoots this
[0:32] Speaker 2: highly magnetized jet of plasma, basically from Chicago to Los Angeles.
[0:36] Speaker 3: Right, which is already a terrifying thought.
[0:39] Speaker 2: Yeah, but now imagine that exact same explosion is happening
[0:42] Speaker 2: across a distance of 23 quadrillion miles.
[0:45] Speaker 3: It is just, I mean, it's unfathomable.
[0:48] Speaker 2: It really is. And the engine that is actually driving
[0:51] Speaker 2: this thing has been turning on and off, you know,
[0:53] Speaker 2: kind of like a cosmic lighthouse for 20.5 million years.
[0:58] Speaker 3: So we aren't just talking about some singular localized event
[1:02] Speaker 3: that flares up and then just fades away into nothing.
[1:05] Speaker 2: Exactly. We are talking about this massive, eruptive landscape operating
[1:10] Speaker 2: on scales of time and distance that just completely shatter
[1:13] Speaker 2: our earthbound intuitions.
[1:15] Speaker 3: It forces us to entirely reevaluate the stability and really
[1:19] Speaker 3: the mechanics of what we consider to be the most
[1:21] Speaker 3: destructive forces in the universe. Because we're looking at this
[1:25] Speaker 3: engine of creation and destruction that possesses a bizarre, almost
[1:29] Speaker 3: mechanical rhythm.
[1:31] Speaker 2: And that is our mission for you today. We are
[1:34] Speaker 2: journeying out to a massive elliptical galaxy sitting at a
[1:37] Speaker 2: redshift of 0.372.
[1:40] Speaker 3: Which puts us looking back roughly four billion years into
[1:43] Speaker 3: the history of the cosmos. Right.
[1:45] Speaker 2: Four billion years. And we are staring down a supermassive
[1:48] Speaker 2: black hole that has basically acted as a multi-stage cosmic volcano.
[1:53] Speaker 3: It's incredible.
[1:54] Speaker 2: It has reliably blown its top four distinct times. And
[1:59] Speaker 2: it left this perfect fossil record of its eruptions just
[2:02] Speaker 2: written across the intergalactic medium.
[2:05] Speaker 3: Which is a completely unprecedented discovery. I mean, it fundamentally
[2:09] Speaker 3: challenges the standard continuous flow models of active galactic nuclei.
[2:13] Speaker 2: Because it introduces a level of episodic complexity that we
[2:17] Speaker 2: have just never confirmed before. Exactly. So let me introduce
[2:21] Speaker 2: the massive elliptical galaxy in question. It goes by the
[2:25] Speaker 2: catalog name J023721. 13- 010528. 5. Catchy name.
[2:30] Speaker 3: Oh, yeah.
[2:33] Speaker 2: Rules right off the tongue. But what we are looking
[2:35] Speaker 2: at is a highly specific, incredibly powerful class of active
[2:39] Speaker 2: galactic nucleus known as an FR2 radio galaxy.
[2:44] Speaker 3: Right. The Fenneroff-Riley classifications.
[2:47] Speaker 2: Exactly. For those of you tracking that, you already know
[2:51] Speaker 2: that FR2s are the edge-brightened monsters.
[2:54] Speaker 3: They are absolute beasts.
[2:56] Speaker 2: They really are. The central supermassive black hole isn't just
[2:59] Speaker 2: accreting mass. It is aggressively converting the rotational energy of
[3:03] Speaker 2: that mass and its own spin into these twin diametrically
[3:07] Speaker 2: opposed jets of relativistic particles.
[3:10] Speaker 3: And I think the distinction between an FR-1 and an
[3:12] Speaker 3: FR-2 is absolutely critical here for why we can even
[3:16] Speaker 3: observe this phenomenon in the first place.
[3:18] Speaker 2: Go ahead and break that down for us. Sure.
[3:20] Speaker 3: So in an FR-1 galaxy, the jets are what we
[3:23] Speaker 3: call edge-darkened. They start out incredibly bright right near the
[3:26] Speaker 3: black hole, but they gradually lose their collimation.
[3:29] Speaker 2: They sort of spread out.
[3:31] Speaker 3: Exactly. They fluff out into these large, diffuse plumes as
[3:35] Speaker 3: they interact with the interstellar medium of their host galaxy.
[3:38] Speaker 3: So all that energy dissipates relatively close to home.
[3:41] Speaker 2: But JO23721 is very much an FR-2.
[3:46] Speaker 3: It is a classic FR-2.
[3:48] Speaker 2: Which means its jets are highly collimated.
[3:51] Speaker 3: They remain tightly bound by these intense, helical magnetic fields.
[3:55] Speaker 2: Like a straight laser beam.
[3:57] Speaker 3: Right. They punch straight through their host galaxy's interstellar medium
[4:00] Speaker 3: without losing much momentum at all. They really don't dissipate
[4:03] Speaker 3: their energy until they slam into the much thinner intergalactic medium,
[4:07] Speaker 3: millions of light years away.
[4:08] Speaker 2: Just blasting through local space.
[4:11] Speaker 3: Yeah, and that kinetic energy dump at the terminal shock
[4:14] Speaker 3: creates what we call hot spots, those violently bright, edge-brightened
[4:18] Speaker 3: lobes that define the FR2 class.
[4:20] Speaker 2: OK, so let's unpack the sheer mind-boggling scale of these jets,
[4:25] Speaker 2: because the numbers associated with this particular galaxy just border
[4:29] Speaker 2: on the absurd. They really do. The entire physical structure
[4:32] Speaker 2: of this galaxy's output, from the terminal shock of the
[4:35] Speaker 2: northern jet all the way down to the terminal shock
[4:37] Speaker 2: of the southern jet, it stretches roughly 3.9 million light
[4:42] Speaker 2: years across.
[4:43] Speaker 3: I mean, that is a structure so vast, it's traversing
[4:46] Speaker 3: a significant fraction of its entire local galaxy cluster.
[4:49] Speaker 2: Yeah, I ran the conversion just before this to look
[4:51] Speaker 2: at the raw mileage. It's roughly 23 quadrillion miles. Wow.
[4:56] Speaker 2: That is 23 followed by 15 zeros. But human brains
[5:00] Speaker 2: aren't built to process quadrillions.
[5:02] Speaker 3: No, not at all.
[5:03] Speaker 2: So let's ground this for you. Our Milky Way's galactic disk,
[5:07] Speaker 2: containing every single star we can see in the night sky,
[5:10] Speaker 2: is roughly 100,000 light years across.
[5:13] Speaker 3: Give or take, yeah. Right.
[5:14] Speaker 2: If we shrink the entire Milky Way down to the
[5:17] Speaker 2: size of a standard city block, The span of this
[5:20] Speaker 2: single radio galaxy's jets would cover the entire North American continent.
[5:24] Speaker 3: That is such a wild visual.
[5:26] Speaker 2: Isn't it? You have a central engine the size of
[5:28] Speaker 2: a grain of sand on this scale, commanding real estate
[5:31] Speaker 2: from New York all the way to California.
[5:33] Speaker 3: And you have to think about the physics required to
[5:35] Speaker 3: maintain a tightly collimated beam of plasma over a 3.9
[5:38] Speaker 3: million light-year trajectory. It's staggering.
[5:42] Speaker 2: Because it's not just flying through empty space.
[5:44] Speaker 3: Right. We have to consider the mechanics of intergalactic resistance.
[5:47] Speaker 3: The intergalactic medium, or the IGM, is incredibly tenuous.
[5:52] Speaker 2: Like what? One atom per cubic meter, maybe?
[5:55] Speaker 3: Exactly. Almost a pure vacuum. But when you are pushing
[5:58] Speaker 3: plasma into it at a significant fraction of the speed
[6:01] Speaker 3: of light, that near vacuum hits back. Right.
[6:03] Speaker 2: You're dealing with ram pressure.
[6:05] Speaker 3: Exactly. The ram pressure scales with the square of the
[6:08] Speaker 3: jet's velocity. So the jet head, the actual working surface,
[6:12] Speaker 3: is acting like a cosmic snowplow.
[6:14] Speaker 2: Pushing everything out of the way.
[6:16] Speaker 3: Violently pushing it. It is shocking the IGM, heating it
[6:19] Speaker 3: to tens of millions of degrees and sweeping it aside.
[6:22] Speaker 2: So this isn't just a cool light show for our
[6:24] Speaker 2: radio telescopes.
[6:25] Speaker 3: Not at all. This is active galactic feedback. A jet
[6:28] Speaker 3: this powerful is literally terraforming the local universe.
[6:32] Speaker 2: Wow.
[6:32] Speaker 3: By injecting all that entropy and thermal energy into the
[6:35] Speaker 3: surrounding gas, it prevents that gas from cooling and collapsing
[6:39] Speaker 3: into new stars.
[6:40] Speaker 2: So it's basically a sterilization beam on a megaparsec scale.
[6:45] Speaker 3: It can be. Or, depending on the specific density profiles
[6:48] Speaker 3: it hits, the shockwave can actually over-compress certain cold gas
[6:52] Speaker 3: clouds and actively trigger starbursts.
[6:54] Speaker 2: Oh, so it could create stars, too.
[6:57] Speaker 3: Yes, the black hole is fundamentally dictating the star-forming destiny
[7:01] Speaker 3: of the cosmos for millions of light-years in every direction.
[7:05] Speaker 2: Which makes total sense for a continuous, unbroken beam of energy.
[7:09] Speaker 2: But that brings us to the real anomaly of JO23721.
[7:13] Speaker 3: The multi-episode nature of it.
[7:15] Speaker 2: Exactly. We aren't looking at a galaxy with a single
[7:18] Speaker 2: massive set of jets. We're looking at a galaxy that
[7:22] Speaker 2: turns those jets on and off.
[7:25] Speaker 3: Which is incredibly rare.
[7:26] Speaker 2: It is. And I want to contextualize how statistically bizarre
[7:30] Speaker 2: that is by looking at the numbers across the known universe.
[7:33] Speaker 3: OK, let's hear them.
[7:35] Speaker 2: So when astronomers find a galaxy where the black hole
[7:37] Speaker 2: has erupted twice, leaving two distinct pairs of hotspots, an
[7:42] Speaker 2: inner pair and an outer pair. It's classified as a
[7:45] Speaker 2: double-double radio galaxy.
[7:46] Speaker 1: Right.
[7:47] Speaker 3: A DDRG. Yeah.
[7:49] Speaker 2: Out of the billions of observable galaxies out there, there
[7:52] Speaker 2: are only about 192 known double-doubles.
[7:56] Speaker 3: Because they require a highly specific convergence of factors to
[7:59] Speaker 3: even happen, let alone be seen.
[8:01] Speaker 2: What kind of factors?
[8:02] Speaker 3: Well, you need a black hole with a distinctly episodic
[8:05] Speaker 3: accretion cycle, obviously. Right. But you also need the IgM
[8:08] Speaker 3: to be uniform enough to actually preserve the terminal shocks
[8:12] Speaker 3: of the previous episode without them just dissipating entirely.
[8:14] Speaker 2: Oh, so the medium has to hold the shape of
[8:17] Speaker 2: the old explosion.
[8:18] Speaker 3: Exactly. And on top of that, you need our line
[8:22] Speaker 3: of sight and the timing from Earth to be absolutely
[8:24] Speaker 3: perfect so we can observe both pairs simultaneously.
[8:28] Speaker 2: That is a lot of hoops to jump through.
[8:30] Speaker 1: It is.
[8:31] Speaker 2: So 192 double-doubles. Then you step up to the triple-doubles.
[8:36] Speaker 2: a supermassive black hole that has erupted three times, leaving
[8:39] Speaker 2: three concentric pairs of hotspots.
[8:41] Speaker 3: And those numbers drop off a cliff.
[8:43] Speaker 2: Big time. There are only seven known or candidate examples
[8:47] Speaker 2: of triple-double radio galaxies in the entire universe. Seven.
[8:52] Speaker 3: It's a vanishingly small sample size.
[8:54] Speaker 2: But a team of researchers, led by Pavan Vijay Kadikar
[8:58] Speaker 2: at the Indian Institute of Science Education and Research in Pune,
[9:01] Speaker 2: just broke the scale completely.
[9:03] Speaker 3: They absolutely did.
[9:04] Speaker 2: They discovered the very first confirmed quadruple-double radio galaxy, a QDRG.
[9:11] Speaker 3: The holy grail of episodic AGN.
[9:13] Speaker 2: Four separate, distinct episodes of jet activity from a single
[9:17] Speaker 2: supermassive black hole, preserved as four pairs of radio hotspots.
[9:21] Speaker 3: The discovery of a QDRG forces a massive paradigm shift
[9:25] Speaker 3: in how we model these active galactic nuclei.
[9:27] Speaker 2: How so?
[9:28] Speaker 3: Well, we are moving from viewing these engines as having
[9:31] Speaker 3: just a single active and quiescent phase to viewing them
[9:35] Speaker 3: as cyclical, almost oscillating systems.
[9:38] Speaker 2: But, you know, I have a real problem with the
[9:40] Speaker 2: mechanics of this intermittent feeding model.
[9:42] Speaker 3: What's the sticking point?
[9:44] Speaker 2: If you have a supermassive black hole sitting in the
[9:47] Speaker 2: gravitational center of a massive elliptical galaxy, it is sitting
[9:50] Speaker 2: at the bottom of the deepest gravity well in the neighborhood. Sure.
[9:53] Speaker 2: It is constantly surrounded by this massive reservoir of cold gas, dust,
[9:59] Speaker 2: orbiting stars. The fuel supply is ubiquitous. Gravity doesn't have
[10:04] Speaker 2: an off switch.
[10:05] Speaker 3: That is true.
[10:06] Speaker 2: So why would the jet turn off? I mean, why
[10:09] Speaker 2: does this engine behave like a faulty faucet instead of
[10:12] Speaker 2: just generating a continuous steady stream of plasma?
[10:16] Speaker 3: It is highly counterintuitive if you only consider gravity, but
[10:19] Speaker 3: you have to realize that accretion dynamics are dictated by
[10:22] Speaker 3: a violent tug of war.
[10:24] Speaker 2: A tug of war between what?
[10:26] Speaker 3: Between gravity, radiation pressure, and magnetic fields.
[10:29] Speaker 2: Okay, walk me through that.
[10:31] Speaker 3: So the material falling toward the black hole forms an
[10:34] Speaker 3: accretion disk, right? But for material to actually cross the
[10:37] Speaker 3: event horizon, it has to shed an immense amount of
[10:40] Speaker 3: angular momentum. Right.
[10:41] Speaker 2: It has to slow its orbit down enough to actually
[10:43] Speaker 2: fall in.
[10:44] Speaker 3: Precisely. Which happens via friction and magnetic viscosity within the disk.
[10:48] Speaker 3: It's a process driven by what we call the magneto-rotational instability,
[10:52] Speaker 3: or MRI. As the gas spirals in, it heats up tremendously.
[10:57] Speaker 3: And when the black hole goes into a feeding frenzy,
[10:59] Speaker 3: say a large molecular cloud was perturbed and dumped into
[11:03] Speaker 3: the inner parsec, the accretion rate spikes.
[11:06] Speaker 2: It gets flooded with material.
[11:07] Speaker 3: Yeah, and the inner disk becomes incredibly hot, and the
[11:10] Speaker 3: magnetic fields threading the black hole's ergosphere become tightly wound.
[11:14] Speaker 2: Because everything is spinning so fast.
[11:16] Speaker 3: Right. And this extracts the rotational energy of the black hole,
[11:20] Speaker 3: launching the relativistic jets via the Blanford-Zniak process.
[11:24] Speaker 2: So the volcano erupts.
[11:25] Speaker 3: Yes. But that eruption carries the seeds of its own shutdown.
[11:29] Speaker 2: Oh, really?
[11:30] Speaker 3: How? There are two primary mechanisms that can choke the flow.
[11:33] Speaker 3: First is radiation pressure. The accretion disk gets so hot
[11:37] Speaker 3: that the outward pressure of the photons it emits literally
[11:39] Speaker 3: exceeds the inward pull of gravity.
[11:41] Speaker 2: Wait, light can push harder than the gravity of a
[11:44] Speaker 2: black hole?
[11:45] Speaker 3: Yes, it's a state known as exceeding the Eddington limit.
[11:48] Speaker 3: The radiation physically blows the inner accretion disk apart, essentially
[11:52] Speaker 3: starving the black hole.
[11:53] Speaker 2: So it eats so fast it blows its food away. Precisely.
[11:56] Speaker 3: It's a self-regulating mechanism. The second mechanism is magnetic flux accumulation.
[12:01] Speaker 2: Okay, what is that?
[12:03] Speaker 3: As plasma falls into the black hole, it drags its
[12:06] Speaker 3: magnetic field lines with it. If too much magnetic flux
[12:09] Speaker 3: accumulates at the event horizon, the outward magnetic pressure pushes
[12:13] Speaker 3: back against the infalling gas.
[12:15] Speaker 2: So it creates a barrier. Exactly.
[12:18] Speaker 3: This creates a magnetically arrested disk, or MAD state. The
[12:22] Speaker 3: accretion is completely halted, the jet launching mechanism collapses, and
[12:26] Speaker 3: the black hole enters a dormant phase.
[12:28] Speaker 2: Until the magnetic field diffuses, I guess. Or more gas
[12:31] Speaker 2: cools and falls back down to build up the pressure
[12:33] Speaker 2: and start the whole cycle over again. Yes, exactly.
[12:36] Speaker 3: And what J023721 shows us is that this gorge and
[12:40] Speaker 3: starve cycle isn't just some random one-off event.
[12:43] Speaker 2: No, it has happened four times.
[12:46] Speaker 3: Four times. With enough regularity to leave this massive segmented
[12:50] Speaker 3: fossil record in the intergalactic medium.
[12:53] Speaker 2: Which brings us to the detective work, because, you know,
[12:55] Speaker 2: you can't just point an optical telescope at the sky
[12:57] Speaker 2: and see four pairs of ancient plasma clouds four billion
[13:00] Speaker 2: light years away.
[13:01] Speaker 3: Definitely not. You need radio astronomy for this. Right.
[13:04] Speaker 2: To pull this off, the team utilized an incredible array
[13:08] Speaker 2: of radio interferometers.
[13:09] Speaker 3: They brought out the big guns.
[13:10] Speaker 2: They really did. They used the upgraded giant meter wave
[13:13] Speaker 2: radio telescope, the UGMRT, in India. They utilized the Meerkat
[13:18] Speaker 2: array in South Africa.
[13:19] Speaker 3: Both incredible facilities.
[13:20] Speaker 2: And they brought in the very large array, the VLA,
[13:23] Speaker 2: in New Mexico.
[13:24] Speaker 3: Using multiple interferometers like that isn't just about getting a
[13:27] Speaker 3: clearer or sharper picture, though. No?
[13:30] Speaker 2: What's the main goal, then?
[13:31] Speaker 3: It's about synthesizing multi-frequency data.
[13:34] Speaker 2: Okay.
[13:35] Speaker 3: In radio astronomy, different frequencies are fundamentally different temporal windows
[13:39] Speaker 3: into the plasma's history.
[13:41] Speaker 2: Okay, let's dig into that, because they used a very
[13:43] Speaker 2: specific spread of frequencies here.
[13:45] Speaker 3: They did.
[13:46] Speaker 2: The UGMRT captured the low-frequency bands, like Band 3 at
[13:49] Speaker 2: 400 MHz and Band 4 at 700 MHz.
[13:52] Speaker 3: Right, the lower end of the spectrum.
[13:54] Speaker 2: Then Meerkat captured the mid-range at 1,280 MHz. And the
[13:58] Speaker 2: VLA Sky Survey provided the high-frequency data at 3 GHz.
[14:02] Speaker 3: Which is a brilliant setup.
[14:04] Speaker 2: But why is that massive spread from 400 MHz up
[14:07] Speaker 2: to 3 GHz necessary to prove this is a quadruple-double?
[14:11] Speaker 3: It all comes down to the physics of synchrotron emission.
[14:14] Speaker 2: Walk us through that.
[14:15] Speaker 3: So when the jet hits the IGM, the terminal shock
[14:18] Speaker 3: accelerates electrons to ultra-relativistic speeds. These electrons spiral around the
[14:24] Speaker 3: magnetic field lines within the hotspot, emitting synchrotron radiation. Now,
[14:28] Speaker 3: the frequency of the radiation an electron emits is proportional
[14:32] Speaker 3: to the square of its energy.
[14:34] Speaker 2: Meaning the highest energy electrons emit the highest frequencies. Exactly.
[14:38] Speaker 3: The most energetic electrons emit at those high frequencies, like
[14:40] Speaker 3: the 3 gigahertz band observed by the VLA.
[14:44] Speaker 2: But those high energy electrons are kind of burning the
[14:46] Speaker 2: candle at both ends, right?
[14:48] Speaker 3: They absolutely are. The rate at which an electron loses
[14:51] Speaker 3: energy to synchrotron radiation is also proportional to the square
[14:54] Speaker 3: of its energy.
[14:55] Speaker 2: Oh, so the brighter they shine, the faster they burn out.
[14:58] Speaker 3: Precisely. This means the highest energy electrons cool down and
[15:02] Speaker 3: deplete their kinetic energy much, much faster than the lower
[15:05] Speaker 3: energy electrons.
[15:06] Speaker 2: So the high frequency radio emission acts as a highly
[15:09] Speaker 2: sensitive clock because it fades so quickly. Exactly.
[15:12] Speaker 3: If a hotspot was created, say, 20 million years ago,
[15:15] Speaker 3: and the jet subsequently turned off, the injection of fresh,
[15:19] Speaker 3: high-energy particles ceases completely.
[15:21] Speaker 2: So the supply gets cut off.
[15:23] Speaker 3: Right. The existing high-energy electrons rapidly cool down via synchrotron losses,
[15:28] Speaker 3: and also by scattering off cosmic microwave background photons.
[15:31] Speaker 2: Which is the inverse Compton effect, right? Yes.
[15:34] Speaker 3: So within just a few million years, that 3 gigahertz
[15:36] Speaker 3: emission completely vanishes.
[15:38] Speaker 2: It's gone. Wow.
[15:40] Speaker 3: But the lower energy electrons, the ones emitting at 400 megahertz,
[15:43] Speaker 3: they cool much more slowly. Their emission persists for tens
[15:47] Speaker 3: of millions of years.
[15:48] Speaker 2: So let me get this straight. If you only looked
[15:51] Speaker 2: at the VLA's 3 gigahertz data, you would only see
[15:54] Speaker 2: the newest, hottest pair of hotspots nearest to the core.
[15:57] Speaker 3: You'd see the most recent eruption and nothing else.
[16:00] Speaker 2: The entire outer structure, the ancient history of the black hole,
[16:04] Speaker 2: would be completely invisible to you.
[16:06] Speaker 3: Yes. You'd just log it as a standard single-eruption FR2
[16:10] Speaker 3: galaxy and move on to the next object.
[16:12] Speaker 2: It is wild. You literally need the low-frequency sensitivity of
[16:16] Speaker 2: the UGM-RT and Meerkat to detect the ghostly, steep-spectrum remnants
[16:21] Speaker 2: of those older episodes.
[16:22] Speaker 3: You absolutely do. And when they finally combined these multi-frequency maps,
[16:27] Speaker 3: the structure was undeniable.
[16:29] Speaker 2: Four distinct pairs of hotspots.
[16:31] Speaker 3: Yes, labeled N1 through N4 on the northern side— and
[16:35] Speaker 3: S1 through S4 on the southern side, radiating outward symmetrically
[16:39] Speaker 3: from the active galactic nucleus.
[16:41] Speaker 2: Though, you know, I think symmetrically is doing a bit
[16:43] Speaker 2: of heavy lifting there, because the universe is rarely that clean.
[16:47] Speaker 2: Fair point.
[16:48] Speaker 3: It is definitely not a perfect mirror image.
[16:51] Speaker 2: Yeah, when you look at the actual data mapping, the
[16:54] Speaker 2: northern jet side is incredibly crisp. The boundaries are sharp,
[16:57] Speaker 2: the emission gradients are clear.
[16:59] Speaker 3: It's beautiful data on that side.
[17:01] Speaker 2: But the southern side is noticeably messier. The emission is fainter,
[17:06] Speaker 2: and the S3 hotspot in particular suffers from very poor
[17:10] Speaker 2: observation quality.
[17:11] Speaker 3: Which is frustrating for researchers, but very common.
[17:14] Speaker 2: Right, forcing them to deal with much larger uncertainty margins
[17:17] Speaker 2: on that half of the galaxy. Why the big difference
[17:20] Speaker 2: between the two sides?
[17:21] Speaker 3: Which is a classic hallmark of deep space observation, honestly.
[17:24] Speaker 3: You are almost never dealing with a perfectly isotropic, perfectly
[17:28] Speaker 3: uniform environment. Right. The jets are being launched with equal
[17:31] Speaker 3: power from the black hole, but they are propagating through
[17:34] Speaker 3: entirely different environments on either side.
[17:37] Speaker 2: Because the IGM isn't just a smooth, featureless fog.
[17:40] Speaker 3: Far from it. It is highly clumpy. It's turbulent. If
[17:45] Speaker 3: the southern jet is propagating into a region of the
[17:47] Speaker 3: IGM with a significantly lower gas density, the ram pressure
[17:51] Speaker 3: at the terminal shock is reduced.
[17:53] Speaker 2: Which leads to a fainter hotspot because there's less material
[17:56] Speaker 2: to slam into. Exactly.
[17:58] Speaker 3: Furthermore, we always have to consider foreground effects.
[18:01] Speaker 2: Like things getting in the way of the telescope?
[18:03] Speaker 3: Yes. As the radio waves travel 4 billion light years
[18:07] Speaker 3: to reach us, they pass through intervening magnetic fields and plasma,
[18:11] Speaker 3: which can cause Faraday rotation and depolarization.
[18:14] Speaker 2: Oh, so the signal itself gets scrambled on the way here. Exactly.
[18:19] Speaker 3: If there happens to be a denser foreground screen of
[18:22] Speaker 3: magnetized plasma along our line of sight to the southern lobe,
[18:25] Speaker 3: it will smear and degrade that signal significantly more than
[18:28] Speaker 3: the northern lobe.
[18:30] Speaker 2: Honestly, it's a miracle we can resolve it at all.
[18:32] Speaker 3: It really is a testament to modern interferometry.
[18:35] Speaker 2: But having the image isn't enough. In astrophysics, an image
[18:39] Speaker 2: is usually just an invitation to an argument.
[18:42] Speaker 3: Oh, inevitably.
[18:43] Speaker 2: When this quadruple-double was proposed, the immediate counter theory was
[18:47] Speaker 2: the knots-in-a-jet hypothesis.
[18:49] Speaker 3: Right, the continuous flow alternative.
[18:51] Speaker 2: And I want to plead devil's advocate here because, honestly,
[18:53] Speaker 2: the continuous jet model makes a lot of intuitive sense.
[18:56] Speaker 1: It does.
[18:57] Speaker 2: Plasma jets are fluid dynamics taken to the absolute extreme.
[19:01] Speaker 2: They suffer from Kelvin-Helmholtz instabilities. They encounter recolumation shocks where
[19:06] Speaker 2: the magnetic fields kind of pinch the plasma flow.
[19:09] Speaker 3: All of which create bright spots. Right.
[19:11] Speaker 2: So if I have a single continuous fire hose of
[19:14] Speaker 2: plasma blasting out for 20 million years, internal traffic jams
[19:18] Speaker 2: are going to form. Why couldn't this just be one
[19:20] Speaker 2: unbroken jet that is clumped up into four bright knots?
[19:23] Speaker 3: It is the essential alternative hypothesis that must be mathematically
[19:27] Speaker 3: destroyed before you can claim a multi-episode discovery.
[19:30] Speaker 2: So how do you destroy it? Because distinguishing a recolumation
[19:34] Speaker 2: knot and a continuous flow from a terminal hotspot of
[19:37] Speaker 2: a deceased episode seems immensely difficult. It is.
[19:41] Speaker 3: A continuous jet will indeed create bright knots. So you
[19:45] Speaker 3: map the temporal gradient of the plasma.
[19:47] Speaker 2: Meaning you figure out how old each part is. Exactly.
[19:50] Speaker 3: The team utilized two independent chronometers to do this, kinematic
[19:54] Speaker 3: aging and spectral aging.
[19:56] Speaker 2: Let's start with kinematic age.
[19:58] Speaker 3: Kinematic age is fairly straightforward astrophysics. We measure the projected
[20:02] Speaker 3: physical distance of each hotspot from the core.
[20:04] Speaker 2: Okay, so just how far away it is.
[20:07] Speaker 3: Right. And by analyzing the ambient IGM density and assuming
[20:11] Speaker 3: a standard advanced speed for an FR-2 jet head, which
[20:14] Speaker 3: is typically between 0.01 and 0.1 times the speed of light,
[20:19] Speaker 3: you can calculate the kinematic age.
[20:21] Speaker 2: Just simple math. Time equals distance divided by velocity. Exactly.
[20:25] Speaker 2: So if hotspot N4 is, say, 1.9 million light years out,
[20:30] Speaker 2: you run the velocity math and get a baseline estimate
[20:32] Speaker 2: of when it was actually launched.
[20:34] Speaker 3: Yes.
[20:35] Speaker 2: But kinematic age is highly dependent on assuming the density
[20:38] Speaker 2: of the intergalactic medium is uniform, which we just established
[20:42] Speaker 2: it definitely isn't.
[20:43] Speaker 3: Which is exactly why kinematic age alone is never enough.
[20:47] Speaker 3: They needed the spectral age to lock it down. All right.
[20:49] Speaker 2: What makes spectral age so much better?
[20:51] Speaker 3: The spectral age is where the multi-frequency data becomes the
[20:55] Speaker 3: absolute arbiter of truth. To calculate a spectral age, astrophysicists
[20:59] Speaker 3: use specific mathematical models of how electron populations cool over time. Like?
[21:04] Speaker 2: Tracking that high-frequency fade we talked about.
[21:07] Speaker 3: Exactly. Kodaker's team likely utilized models like the Jaffe-Parola or
[21:11] Speaker 3: JP model, which accounts for the pitch-angle scattering of electrons
[21:15] Speaker 3: in the magnetic field.
[21:16] Speaker 2: What does that model actually track in the data?
[21:19] Speaker 3: It tracks the spectral break frequency.
[21:22] Speaker 2: The break frequency? Yeah.
[21:24] Speaker 3: So when a jet first creates a hotspot, the power
[21:27] Speaker 3: law distribution of the radio spectrum is relatively flat. It
[21:30] Speaker 3: emits strongly across all the frequencies.
[21:33] Speaker 2: Because it's fresh and full of high-energy electrons.
[21:36] Speaker 3: Right. But as those high-energy electrons cool, the spectrum develops
[21:40] Speaker 3: a break, literally a specific frequency above which the emission
[21:44] Speaker 3: drops off precipitously.
[21:46] Speaker 2: So the spectrum steepens. Yes.
[21:48] Speaker 3: And as the plasma ages, that break frequency marches steadily
[21:51] Speaker 3: down toward the lower frequencies.
[21:54] Speaker 1: Wow.
[21:54] Speaker 2: Okay.
[21:55] Speaker 3: By measuring the flux density of the hotspots across the
[21:57] Speaker 3: 400 megahertz 700 MHz, 1.2 GHz, and 3 GHz bands,
[22:02] Speaker 3: the researchers mapped the exact curvature of the spectrum.
[22:06] Speaker 2: So they can see exactly where that break is happening
[22:08] Speaker 2: for each spot.
[22:09] Speaker 3: Precisely. They found the break frequency for each specific hotspot
[22:13] Speaker 3: and converted that into a highly precise spectral age.
[22:15] Speaker 2: And the timeline they extracted from that data is just breathtaking.
[22:20] Speaker 3: It really is.
[22:22] Speaker 2: They proved that the four hotspot pairs range in age
[22:25] Speaker 2: from 4.5 million years old to 20.5 million years old.
[22:30] Speaker 3: A massive span of time.
[22:32] Speaker 2: But the raw ages aren't the actual smoking gun, are they?
[22:36] Speaker 2: It's the gradient.
[22:37] Speaker 3: The gradient completely precludes the continuous jet hypothesis.
[22:40] Speaker 2: Why is that?
[22:42] Speaker 3: Because if these four structures were simply knots in a
[22:44] Speaker 3: single flowing jet, they would all be continually replenished with fresh,
[22:49] Speaker 3: ultra-relativistic electrons injected from the active core.
[22:52] Speaker 2: So they would all look new.
[22:53] Speaker 3: Exactly. Their spectral ages would be nearly identical, all registering
[22:57] Speaker 3: as relatively young because that high-frequency emission is constantly being restocked.
[23:01] Speaker 2: By the flow. But the data showed the exact opposite
[23:04] Speaker 2: of that.
[23:05] Speaker 3: It did.
[23:06] Speaker 2: The ages, definitively and smoothly, increase the further away you
[23:10] Speaker 2: get from the core.
[23:12] Speaker 1: Yes.
[23:12] Speaker 2: The innermost pair, N1 and S1, are the youngest at
[23:16] Speaker 2: roughly 4.5 million years. Then, stepping outward to the second pair,
[23:21] Speaker 2: the age jumps. The third pair is older still.
[23:24] Speaker 3: It's a perfect chronological record.
[23:26] Speaker 2: And the outermost pair, N4 and S4, clock in at 20.5
[23:31] Speaker 2: million years old. The outer structures are these ancient decaying relics,
[23:36] Speaker 2: and the inner structures are freshly accelerated plasma.
[23:39] Speaker 3: Which proves the engine fired, shut down for millions of years,
[23:43] Speaker 3: fired again, and repeated the cycle.
[23:45] Speaker 2: The spectral steepening from the inner core out to the
[23:47] Speaker 2: outer lobes is basically the undeniable signature of an episodic
[23:51] Speaker 2: active galactic nucleus.
[23:53] Speaker 3: It is undeniable.
[23:54] Speaker 2: And to quantify just how undeniable it is, the team
[23:57] Speaker 2: ran a Bayesian statistical analysis comparing the continuous injection model
[24:02] Speaker 2: against the episodic model.
[24:04] Speaker 3: Oh, the Bayes factor analysis.
[24:05] Speaker 2: Yes. They mapped the likelihood space of the spectral indices
[24:09] Speaker 2: and the age gradients. And the resulting Bayes factor showed
[24:13] Speaker 2: that the four separate episodes model is roughly 3 million
[24:16] Speaker 2: times more likely to explain the observed data than the
[24:19] Speaker 2: continuous knots model.
[24:20] Speaker 3: 3 million to 1 million. Yeah.
[24:23] Speaker 2: In the realm of astrophysics, a 3 million to 1
[24:26] Speaker 2: statistical likelihood is an absolute knockout punch.
[24:29] Speaker 3: The continuous jet hypothesis is mathematically untenable here. JO23721 is
[24:35] Speaker 3: definitively a quadruple-double.
[24:37] Speaker 2: Which is just an incredible triumph for the team. But,
[24:40] Speaker 2: you know, proving the timeline actually highlights an even stranger
[24:43] Speaker 2: physical anomaly.
[24:45] Speaker 3: The geometry.
[24:46] Speaker 2: Exactly. We have this 20-million-year timeline of eruptions, but when
[24:51] Speaker 2: you look at the geometric map of the galaxy... These
[24:53] Speaker 2: eruptions aren't firing in a straight line.
[24:55] Speaker 3: No, they are not.
[24:56] Speaker 2: The entire 3.9 million light-year structure is shaped like a
[25:01] Speaker 2: giant cosmic S.
[25:03] Speaker 3: It is stunning to look at.
[25:04] Speaker 2: It is currently the second largest S-shaped radio source ever discovered.
[25:08] Speaker 3: In astronomical literature, this is referred to as an S-shaped
[25:12] Speaker 3: or a Z-symmetric morphology, and it provides a massive clue
[25:16] Speaker 3: about the dynamic state of the central black hole itself.
[25:19] Speaker 2: Because the jets themselves aren't just curving in midair on
[25:21] Speaker 2: their own. Right?
[25:23] Speaker 3: No, definitely not.
[25:24] Speaker 2: When a jet is launched at a fraction of the
[25:25] Speaker 2: speed of light, its momentum is so immense, it travels
[25:29] Speaker 2: in a ballistic straight line until it hits the terminal shock.
[25:32] Speaker 3: Right. It doesn't bend without a reason.
[25:34] Speaker 2: So the S-shape is being created because the cannon firing
[25:37] Speaker 2: the jets is actually moving.
[25:39] Speaker 3: The launch axis of the supermassive black hole is undergoing
[25:42] Speaker 3: progressive rotation, or precession.
[25:45] Speaker 2: Explain that precession.
[25:46] Speaker 3: When the researchers drew axes through the successive hotspot pairs,
[25:50] Speaker 3: they found severe misalignments. The axis connecting the oldest outermost pair,
[25:55] Speaker 3: N4 and S4, does not align with the axis of
[25:58] Speaker 3: the inner youngest pair.
[26:00] Speaker 2: The rotational shifts are massive. Moving backward in time from
[26:04] Speaker 2: the core, the axis of the second pair, N2S2, is
[26:07] Speaker 2: shifted by negative 7 degrees. Okay. The third pair, N3S3,
[26:12] Speaker 2: is shifted by negative 16 degrees. And the ancient fourth pair, N4S4,
[26:17] Speaker 2: is shifted by a staggering negative 24 degrees.
[26:20] Speaker 3: Which is just a huge sweep.
[26:22] Speaker 2: The black hole's spin axis is rotating counterclockwise by increasing
[26:26] Speaker 2: amounts over that entire 20.5 million year timeline.
[26:29] Speaker 3: Which presents a profound physical puzzle.
[26:32] Speaker 2: Why is it such a puzzle?
[26:33] Speaker 3: Because we are talking about a supermassive black hole, likely
[26:37] Speaker 3: billions of times the mass of our sun. And it
[26:39] Speaker 3: is spinning at a significant fraction of the speed of light.
[26:42] Speaker 2: The inertia must be insane.
[26:44] Speaker 3: The angular momentum bound up in that singularity is nearly incomprehensible.
[26:48] Speaker 3: A 24 degree shift in its spin axis over 20
[26:51] Speaker 3: million years... requires an external torque of unimaginable power. Right.
[26:56] Speaker 2: What could possibly apply that kind of torque? You can't
[26:59] Speaker 2: just gently bump a supermassive black hole and tilt it
[27:03] Speaker 2: 24 degrees.
[27:04] Speaker 3: No, you absolutely cannot. But there are a few primary
[27:07] Speaker 3: mechanisms that can induce that level of precession.
[27:09] Speaker 2: Okay. Lay them out for us.
[27:12] Speaker 3: The most likely culprit is a galactic merger.
[27:14] Speaker 2: Two galaxies crashing into each other.
[27:17] Speaker 3: Exactly. When two massive galaxies collide, Their respective central supermassive
[27:21] Speaker 3: black holes will eventually sink to the dynamical center of
[27:24] Speaker 3: the newly merged system via dynamical friction.
[27:27] Speaker 2: So they meet in the middle.
[27:28] Speaker 3: Yes, and they form a supermassive black hole binary.
[27:31] Speaker 2: Two singularities orbiting each other at the center of the galaxy. Exactly.
[27:36] Speaker 3: And the gravitational interaction between the primary accreting black hole
[27:39] Speaker 3: and the secondary orbiting black hole is immense.
[27:42] Speaker 2: I can imagine.
[27:43] Speaker 3: If the orbital plane of the binary is misaligned with
[27:46] Speaker 3: the accretion disk of the primary black hole, the secondary
[27:49] Speaker 3: black hole will exert a huge gravitational torque on the
[27:52] Speaker 3: outer edges of the primary's disk.
[27:54] Speaker 2: It's just tugging on the disk constantly.
[27:56] Speaker 3: Right. And through a phenomenon known as the Bardeen-Peterson effect,
[28:00] Speaker 3: this torque propagates inward, ultimately causing the central black hole's
[28:04] Speaker 3: spin axis to precess.
[28:06] Speaker 2: So it's kind of like a gyroscope mounted on a
[28:08] Speaker 2: gimbal that's being pulled by an offset or gravity field.
[28:11] Speaker 3: That's a perfect analogy.
[28:13] Speaker 2: As the black hole wobbles, it fires its jet in
[28:15] Speaker 2: a slightly different direction during each episodic outburst.
[28:18] Speaker 3: Exactly.
[28:19] Speaker 2: And over 20 million years, it carves that giant S-shape
[28:23] Speaker 2: into the intergalactic medium. But what if it's not a
[28:27] Speaker 2: binary system? Are there mechanisms for a solitary black hole
[28:31] Speaker 2: to process that violently?
[28:32] Speaker 3: Yes, there is another leading theory. The alternative is asymmetrical
[28:37] Speaker 3: or chaotic cold accretion.
[28:39] Speaker 2: Chaotic cold accretion.
[28:40] Speaker 3: Yeah. In a massive elliptical galaxy, cooling flows from the
[28:44] Speaker 3: hot circumgalactic medium can precipitate these massive cold gas clouds
[28:49] Speaker 3: that fall toward the center.
[28:50] Speaker 2: Okay.
[28:51] Speaker 3: If a truly massive cloud falls in with an angular
[28:54] Speaker 3: momentum vector that is significantly tilted relative to the black
[28:57] Speaker 3: hole's current spin axis, it forms a totally misaligned accretion disk.
[29:02] Speaker 2: So it's coming in sideways, basically.
[29:04] Speaker 3: Right. Now, the Lenz-Thuring effect, which is the physical frame
[29:07] Speaker 3: dragging of spacetime caused by the rotating.
[29:09] Speaker 2: Black hole itself, The black hole is literally twisting space
[29:12] Speaker 2: around it.
[29:13] Speaker 3: Yes. So that twisting will try to force the inner
[29:16] Speaker 3: edge of the disk to align with the black hole's equator.
[29:19] Speaker 2: But Newton's third law still applies, right? If the black
[29:22] Speaker 2: hole is pulling on the disk, the disk is pulling
[29:25] Speaker 2: on the black hole.
[29:26] Speaker 3: Precisely. If the mass of the accreting gas is high enough,
[29:30] Speaker 3: the angular momentum of the infalling material will eventually force
[29:34] Speaker 3: the black hole's spin axis to tilt and realign with
[29:37] Speaker 3: the incoming flow.
[29:39] Speaker 2: So the black hole... gets torqued by an incredibly massive
[29:42] Speaker 2: off-axis meal?
[29:44] Speaker 3: Exactly. It eats a weirdly angled cloud, and it literally
[29:47] Speaker 3: tilts the entire black hole.
[29:50] Speaker 2: It is a staggering sequence of events to visualize.
[29:53] Speaker 3: It really is.
[29:55] Speaker 2: We started by looking at a string of catalog numbers. J023721. 13- 01052. 5.
[30:04] Speaker 3: Just another dot in the sky initially.
[30:06] Speaker 2: Right. But what the multi-frequency radio astronomy revealed is a
[30:11] Speaker 2: masterpiece of cosmic mechanics.
[30:13] Speaker 3: We found a supermassive black hole that has reliably and
[30:17] Speaker 3: violently erupted four distinct times.
[30:20] Speaker 2: We mapped a 20.5 million year timeline of accretion disk instability,
[30:25] Speaker 2: where the engine gorged itself, fired a relativistic jet choked
[30:30] Speaker 2: on its own magnetic and radiation pressure and went dormant.
[30:33] Speaker 3: Only to reawaken millions of years later.
[30:36] Speaker 2: Yeah, and while it was undergoing this massive thermodynamic cycle,
[30:40] Speaker 2: the entire engine was progressively wobbling due to the gravitational
[30:44] Speaker 2: torque of maybe a galactic merger or a massive asymmetric
[30:48] Speaker 2: gas cloud.
[30:49] Speaker 3: Carving a 23 quadrillion mile S-shape into the void.
[30:54] Speaker 2: It's just brilliant. And this discovery provides an incredibly clear
[30:58] Speaker 2: roadmap for future observational astrophysics, doesn't it?
[31:02] Speaker 3: It absolutely does. Katika's team has effectively demonstrated that giant
[31:06] Speaker 3: S-shaped radio galaxies are the ultimate hunting ground for episodic AGN.
[31:11] Speaker 2: Because the wobble and the stuttering are connected? Exactly.
[31:14] Speaker 3: The precession that causes the S-shape and the instabilities that
[31:17] Speaker 3: cause the intermittent feeding appear to be deeply linked.
[31:21] Speaker 2: So if we want to find the next quadruple double or,
[31:24] Speaker 2: you know, push the boundaries to find a quintuple double.
[31:28] Speaker 3: The targeted search needs to focus directly on these processing
[31:32] Speaker 3: z-symmetric giants.
[31:34] Speaker 2: It is literally a treasure map written in radio waves.
[31:36] Speaker 3: It is.
[31:37] Speaker 2: But as we synthesize all of this, I want to
[31:40] Speaker 2: leave you with one final thought. We have spent this
[31:43] Speaker 2: entire time analyzing a system four billion light years away.
[31:48] Speaker 3: Very, very far from home.
[31:49] Speaker 2: But the implications of an episodic 20 million year life
[31:52] Speaker 2: cycle hit much closer to home. It forces us to
[31:56] Speaker 2: realize that the universe operates on physiological rhythms that completely
[32:01] Speaker 2: dwarf human perception.
[32:02] Speaker 3: We view the cosmos as static, you know, because of
[32:05] Speaker 3: our short lifespans, but it is deeply cyclical.
[32:08] Speaker 2: Look at the center of our own Milky Way galaxy,
[32:10] Speaker 2: Sagittarius A star.
[32:12] Speaker 3: Right.
[32:12] Speaker 2: Right now, it is a dormant, quiet, supermassive black hole.
[32:16] Speaker 3: Barely a whisper.
[32:17] Speaker 2: But we know it has massive Fermi bubbles of gamma
[32:20] Speaker 2: ray and X-ray emission expanding outward from the galactic pole.
[32:24] Speaker 3: Which are the remnants of a past eruption.
[32:26] Speaker 2: Exactly. So if a black hole can sleep for 10
[32:29] Speaker 2: million years, only to suddenly violently reawaken and blast a
[32:33] Speaker 2: jet across quadrillions of miles of space, it really begs
[32:39] Speaker 2: the question, Are the dormant monsters at the centers of
[32:43] Speaker 2: the galaxies in our local group truly dead? Or are
[32:47] Speaker 2: they simply in the off-phase of a 20-million-year clock, quietly
[32:51] Speaker 2: gathering magnetic flux, waiting in the dark for their next eruption?
[32:57] Speaker 2: It's a sobering thought. The cosmic mountains are not dead.
[33:01] Speaker 2: They're just sleeping. Something for you to mull over the
[33:04] Speaker 2: next time you look up at the stars.

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