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: If you look up at the Milky Way tonight, you know,
Speaker 2: you might think you're looking at a peaceful, eternal home.
Speaker 3: Oh, absolutely right, like just a.
Speaker 2: Quiet neighborhood of stars that has well always been there,
Speaker 2: totally untouched and unchanging.
Speaker 3: Yeah, that is the common assumption.
Speaker 2: But you aren't. You are looking at, honestly, a cosmic
Speaker 2: crime scene. It is built entirely from the shredded corpses
Speaker 2: of other galaxies.
Speaker 3: That is a beautifully grim way to put it, but yeah,
Speaker 3: it's totally accurate.
Speaker 2: Today our mission is to act as galactic forensic investigators.
Speaker 2: We are tracking down the ghost of a lost, ancient
Speaker 2: dwarf galaxy that astronomers are calling Loki.
Speaker 3: And the most unsettling part is that it isn't millions
Speaker 3: of light years away.
Speaker 2: No, it's not.
Speaker 3: It is hiding right here, like completely embedded within the
Speaker 3: structure of our own milky Way, right above our heads.
Speaker 2: It's wild. It completely reframes how you look at the.
Speaker 3: Night sky, it really does. And I want to establish
Speaker 3: the stakes here right at the outset, because trekking down
Speaker 3: Loki isn't just about you know, cataloging a few anomalous.
Speaker 2: Stars, right, It's bigger than that.
Speaker 3: Way bigger. It is about fundamentally rewriting our understanding of
Speaker 3: how galaxies actually grow.
Speaker 2: So we are literally reading the forensic evidence left behind
Speaker 2: by the universe's earliest building blocks exactly.
Speaker 3: We're looking at this groundbreaking work by Federico Sostino and
Speaker 3: his colleagues. Yeah, and this is really about peering back
Speaker 3: to the most violent epochs of the cosmos to understand
Speaker 3: the literal architecture of our own existence.
Speaker 2: Well, let's start with that architecture, because to even comprehend
Speaker 2: where this lost galaxy Loki came from, we have to
Speaker 2: kind of shatter the illusion of the Milky.
Speaker 3: Way, the majestic spiral illusion, right.
Speaker 2: The idea that it just I don't know, popped into existence,
Speaker 2: is this solitary, majestic thing. The harsh reality is that
Speaker 2: our galaxy is a cannibal. A cannibal add to eat
Speaker 2: to grow.
Speaker 3: Cannibal is definitely the most accurate, if slightly gruesome, way
Speaker 3: to describe it. In extra physics, we call it hierarchical
Speaker 3: galaxy formation, right, because the Milky Way did not form
Speaker 3: an isolation as this gargante wind structure we see today.
Speaker 3: It grew over billions.
Speaker 2: Of years by eating smaller guys.
Speaker 3: Exactly by consuming smaller galaxies. Astronomers politely refer to this
Speaker 3: as merging, but.
Speaker 2: I feel like that term is doing a lot of
Speaker 2: heavy lifting.
Speaker 3: Oh, it wildly misrepresents the physics involved.
Speaker 2: Right, because merging makes it sound like, I don't know,
Speaker 2: two companies shaking hands into green to share an office.
Speaker 3: Building, the very peaceful corporate merger.
Speaker 2: Yeah, a neat mutual agreement. But I imagine the mechanics
Speaker 2: of these earthactic gatbox where anything but neat.
Speaker 3: Far from it. When we look back at the early universe,
Speaker 3: we see these smaller systems, these dwarf.
Speaker 2: Galaxies, the little guys.
Speaker 3: The little guys. Yeah, and they served as the foundational
Speaker 3: building blocks of the cosmos.
Speaker 2: Okay, So as.
Speaker 3: The Protomilky Way began to grow. Its immense gravitational well
Speaker 3: would essentially catch these smaller galaxies like a spider web
Speaker 3: sort of, but much more violent, because when a dwarf
Speaker 3: galaxy falls in, it doesn't just slide neatly into a
Speaker 3: designated orbit.
Speaker 2: What happens to.
Speaker 3: It It encounters something called tidal forces.
Speaker 2: Wait, like the tides on Earth, like the Moon pulling
Speaker 2: the oceans.
Speaker 3: Exactly like that, but on a massive, terrifying galactic scale.
Speaker 3: The gravity on the side of the dwarf galaxy closest
Speaker 3: to the Milky Way is pulled significantly harder than the
Speaker 3: side facing away.
Speaker 2: Oh wow, so it's literally being.
Speaker 3: Stretched, stretched, until it hits a critical breaking point.
Speaker 2: Yes, that sounds intense.
Speaker 3: It is. The immense tidal forces of our growing galaxy
Speaker 3: would literally tear the incoming dwarf galaxy apart. It is
Speaker 3: a complete dissolution of the original structure.
Speaker 2: So they don't survive the fall, not at all.
Speaker 3: They disperse everything they have. They're stellar populations, they're vast
Speaker 3: reservoirs of interstellar gas. They're halos of dark matter just
Speaker 3: gone violently stripped away and scattered directly into the chaotic
Speaker 3: swirling mass of our forming proto galaxy.
Speaker 2: I'm trying to picture the sheer scale of that.
Speaker 3: It's hard to wrap your head around.
Speaker 2: It's like, Okay, imagine having a sprawling metropolis, let's say
Speaker 2: Tokyo or London. Okay, good analogy, and this city slowly
Speaker 2: expands outward over the centuries. As it grows, it swallows
Speaker 2: up all these independent neighboring farming towns. Right, But it
Speaker 2: doesn't just annex them, you know. It bulldozes their town halls,
Speaker 2: rips up their roads, and completely disperses their populations into the.
Speaker 3: City grid until you can't even tell where the original
Speaker 3: city ended and the farming towns began exactly.
Speaker 2: The city just absorbs the raw materials and the people
Speaker 2: and completely erases the original borders.
Speaker 3: The structural integrity of those independent towns is just gone forever.
Speaker 2: Okay, let's unpack this, because here is where I really
Speaker 2: struggle with the whole galactic archaeology concept.
Speaker 3: Okay, lagh it on me.
Speaker 2: If the Milky Way completely shredded these smaller galaxies, if
Speaker 2: it pays over those farming towns and violently mixed everything
Speaker 2: into a metropolitan soup, right, how is it even physically
Speaker 2: possible to recognize what used to be a separate galaxy.
Speaker 3: Ah, that is the million dollar question.
Speaker 2: Like, if I'm looking at one hundred billion stars in
Speaker 2: the Milky Way, how can astronomer's point to a specific
Speaker 2: star and definitively say that one right there used to
Speaker 2: belong to a completely different ancient galaxy.
Speaker 3: It's a brilliant question, honestly, because looking at the Milky
Speaker 3: Way today, it really does just look like a homogeneous soup.
Speaker 2: Just a big glowing disc exactly.
Speaker 3: But it turns out the universe leaves indelible fingerprints.
Speaker 2: Fingerprints.
Speaker 3: Yes, the initial violent shredding destroys the galaxy's overall structure,
Speaker 3: but it doesn't actually just droy the individual stars themselves.
Speaker 2: Oh, I see, the buildings are gone, but the people
Speaker 2: are still walking.
Speaker 3: Around precisely, and astronomers hunt for these absorbed alien stars
Speaker 3: using two incredibly powerful, highly specific clues, which are the
Speaker 3: eccentricities of their galactic orbits and their chemical composition orbit
Speaker 3: in chemistry, orbit in chemistry.
Speaker 2: Okay, let's tackle the orbit first, because I think the
Speaker 2: common assumption, at least for me, is that all the
Speaker 2: stars in the Milky Way are essentially just swirling around
Speaker 2: the galactic center in one big, flat, orderly carousel.
Speaker 3: And for the vast majority of stars born natively within
Speaker 3: our galaxy's disc, that is generally true.
Speaker 2: They behave themselves, right.
Speaker 3: They form out of the same rotating disc of gas,
Speaker 3: and because of the conservation of angular momentum, they move together.
Speaker 2: They travel in relatively predictable circular paths around the galactic center.
Speaker 3: Exactly. They are the native population.
Speaker 2: So going back to the city thing, they are like
Speaker 2: cars driving smoothly along a multi lane highway. Yes, everyone
Speaker 2: is going the same direction, staying in their lanes, moving
Speaker 2: with the general flow.
Speaker 3: Of traffic, exactly. But when you meticulously map the billions
Speaker 3: of stars moving through our galaxy, which by the way,
Speaker 3: requires measuring not just their two dimensional position in the
Speaker 3: sky but their three D velocity and.
Speaker 2: Trajectory, which is an insane amount of data.
Speaker 3: It is. But when you do that you occasionally find
Speaker 3: glaring anomalies, like what you find stars with highly eccentric orbits.
Speaker 2: Now eccentric in this context doesn't mean the star has
Speaker 2: a quirky personality.
Speaker 3: No, No, we are talking about the physical geometry of
Speaker 3: its path, right, Instead of a nice flat circular orbit
Speaker 3: that stays neatly within the galactic plane, these stars are
Speaker 3: on wildly irregular, highly elliptical paths.
Speaker 2: What does that look like in three D space?
Speaker 3: Well, they might plunge straight down vertically through the galactic.
Speaker 2: Disk, just straight through the carousel exactly.
Speaker 3: Or they might sweep incredibly far out into the distant,
Speaker 3: sparse galactic halo before diving aggressive back toward the intensely
Speaker 3: crowded center.
Speaker 2: So, going back to the highway analogy, an eccentric orbit
Speaker 2: isn't just a car changing lanes.
Speaker 3: No, not at all.
Speaker 2: It is a car completely ignoring the existence of the road.
Speaker 2: It's swerving perpendicularly across the median, cutting straight through the
Speaker 2: flow of.
Speaker 3: Traffic, completely disconnected from the direction everyone else is traveling.
Speaker 3: That is terrifying, right, And if you see a vehicle
Speaker 3: doing that on a highway, your immediate logical conclusion is
Speaker 3: that the car didn't merge onto this road normally.
Speaker 2: It definitely didn't accelerate down the on ramp exactly.
Speaker 3: Something must have violently thrown it across the lanes. A crash,
Speaker 3: a cosmic crash. In galactic kinematics, a highly eccentric orbit
Speaker 3: is the lingering kinetic scar of an ancient outside collision. Wow,
Speaker 3: what's fascinating here is that it is a dead giveaway
Speaker 3: that the star did not originate from the peaceful native disk.
Speaker 2: The scale of that investigation is staggering to me. You
Speaker 2: are literally looking at a catalog of billions of moving
Speaker 2: points of life billions. Yeah, trying to isolate the few
Speaker 2: dozen that are driving across the median.
Speaker 3: It takes meticulous patients.
Speaker 2: You have to track their current x, y, and z
Speaker 2: coordinates in a three dimensional map of space, measure their
Speaker 2: radio velocity, and then what rewind their mathematical packs millions
Speaker 2: of years into the past just to.
Speaker 3: See where they came from. Yes, the kinematic mapping is
Speaker 3: a monumental achievement in modern astronomy.
Speaker 2: But wait, didn't you say orbit was only one clue
Speaker 2: I did?
Speaker 3: Orbit alone isn't enough to secure a conviction?
Speaker 2: Why not? If a star is plunging vertically through the disc,
Speaker 2: isn't that proof enough that it's an alien interloper?
Speaker 3: Well not necessarily, Yeah, no, because a native star could
Speaker 3: theoretically be violently kicked into a bizarre orbit by a
Speaker 3: localized internal event.
Speaker 2: Oh like a domestic dispute instead of a foreign invasion.
Speaker 3: That's a great way to put it, like a nearby
Speaker 3: supernova explosion could blast a native star off course, right,
Speaker 3: or a gravitational interaction with a passing giant molecular.
Speaker 2: Cloud or a black hole, or a.
Speaker 3: Close encounter with a black hole exactly any of those
Speaker 3: could disrupt a native star's circular path.
Speaker 2: Okay, so a weird orbit makes it a suspect, but
Speaker 2: not definitely guilty.
Speaker 3: Exactly. So to definitively prove a star is an alien
Speaker 3: artifact from a consumed dwarf galaxy like Loki, that wild
Speaker 3: orbit has to be paired with our second clue.
Speaker 2: The chemical forensics.
Speaker 3: The chemical forensics, right.
Speaker 2: The chemistry, and to understand why chemical forensics can identify
Speaker 2: a star as an ancient outsider, I feel like we
Speaker 2: need to take a detour.
Speaker 3: Let's do it.
Speaker 2: We need to look at the universe's heavy metal forges,
Speaker 2: because it's not just about what elements are in.
Speaker 3: The star, right, It's about what elements aren't.
Speaker 2: There, which brings us to stellar nuclear synthesis.
Speaker 3: It does. It is the fundamental process by which the
Speaker 3: universe creates the periodic table.
Speaker 2: Okay, let's bypass the absolute basics here, because we know
Speaker 2: the early universe was just hydrogen.
Speaker 3: And helium, just a very boring, simple soup.
Speaker 2: Right, And we know stars act as fusion actors, But
Speaker 2: the concept of chemical generations is what matters here, right.
Speaker 3: Yes, the generational aspect is crucial.
Speaker 2: So the universe essentially has a family tree.
Speaker 3: Exactly. Think about the very first generation of stars that ignited.
Speaker 2: In the cosmos, the granddaddies.
Speaker 3: The Granddaddy's of the universe. They were forged purely out
Speaker 3: of pristine, primordial hydrogen and helium. There was nothing else available.
Speaker 3: And these stars were massive. They burned fast, and when
Speaker 3: they died, they died in violent supernova explosions. And when
Speaker 3: they exploded, they blasted newly forged heavier elements things they
Speaker 3: cooked up in their cores, like carbon, oxygen, and iron,
Speaker 3: out into the surrounding gas clouds.
Speaker 2: So they basically seeded the surrounding space with a brand
Speaker 2: new recipe of elements.
Speaker 3: They did they polluted the pristine gas.
Speaker 2: So the next generation of stars that formed out of
Speaker 2: those enriched gas clouds inherited a tiny fraction of those
Speaker 2: heavier elements.
Speaker 3: Exactly. They started life with a slightly more complex chemical
Speaker 3: makeup of.
Speaker 2: Their lives fused even heavier elements exploded and handed an
Speaker 2: even richer chemical cocktail down to the third generation.
Speaker 3: It is an ongoing multi billion year cosmic recycling program.
Speaker 3: Every generation gets more chemically complex.
Speaker 2: Our sun is a beneficiary of this recycling rye a
Speaker 2: huge beneficiary.
Speaker 3: It's a relatively late generation.
Speaker 2: Star, which is why if you look at its chemical spectrum,
Speaker 2: it is loaded with heavier elements.
Speaker 3: Exactly, But astronomers use a specific, somewhat idiosyncratic terminology to
Speaker 3: describe this.
Speaker 2: Oh no, what do they call it?
Speaker 3: Well, in astrophysics, anything heavier than helium on the periodic
Speaker 3: table is simply referred to as a metal, which.
Speaker 2: Is completely wild. No, I know, like to a chemist,
Speaker 2: calling oxygen or neon a metal is grounds for having
Speaker 2: your degree revoked.
Speaker 3: Oh it drives chemists absolutely crazy, But for us, it
Speaker 3: gives us a vital shorthand.
Speaker 2: Okay, so if everything heavier than helium is a metal,
Speaker 2: how does that help us find old stars?
Speaker 3: Because astronomers refer to stars with relatively small amounts of
Speaker 3: these heavier elements, specifically elements like iron, as metal.
Speaker 2: Poor, metal poor. So what does this all mean for
Speaker 2: our investigation?
Speaker 3: Well, this is the crux of the chemical fingerprint, because
Speaker 3: if you find a star that is extremely metal poor.
Speaker 2: It means it didn't get the good stuff exactly.
Speaker 3: It means it did not have the benefit of many
Speaker 3: previous generations of cosmic orcyclice.
Speaker 2: So it must be incredibly old.
Speaker 3: It must have formed very very early in the universe's
Speaker 3: history out of gas that was still mostly pristine.
Speaker 2: That is so cool. An extremely metal poor star is
Speaker 2: essentially a rough draft of a star.
Speaker 3: A rough draft. Yes, it is a literal fossil from
Speaker 3: the dawn of time, sitting right there in our galaxy,
Speaker 3: virtually untouched by the billions of years of chemical evolution
Speaker 3: that happened everywhere else.
Speaker 2: Wow.
Speaker 3: And those early metal poor dwarf galaxies were the exact
Speaker 3: raw materials that merged together to form the massive gas
Speaker 3: galaxies we see today.
Speaker 2: Okay, so we have the two pieces of our forensic toolkit.
Speaker 3: We do.
Speaker 2: We are hunting for ancient fossilized metal poor stars, and
Speaker 2: we need them to be flying around of bizarre, highly
Speaker 2: eccentric orbits. Check. The next hurdle, though, is the sheer
Speaker 2: geography of the Milky Way.
Speaker 3: The spatial problem.
Speaker 2: Yes, where do you even begin sweeping for them? The
Speaker 2: galaxy is one hundred thousand light years across.
Speaker 3: Right, and geography and timing are intrinsically linked in galaxy formation. Well,
Speaker 3: if we consider the timeline of how the Milky Way
Speaker 3: was assembled, those earliest building blocks, those ancient metal poor
Speaker 3: dwarf galaxies like Loki, they merged into the forming proto
Speaker 3: galaxy at the very beginning of the process.
Speaker 2: They were the first bricks in the foundation.
Speaker 3: Right. And because they were drawn into the gravitational well
Speaker 3: so early, the remnants of those systems, they're dispersed.
Speaker 2: Stars should logically sink toward the bottom.
Speaker 3: Exactly, they should populate the deepest inner regions of the
Speaker 3: Milky Way. They should be trapped in the dense core
Speaker 3: or what we call the galactic bulge, and deeply embedded
Speaker 3: within the inner galactic plane.
Speaker 2: That makes perfect physical sense. The material that falls in
Speaker 2: first ends up clustered in the middle under the weight
Speaker 2: of everything that piles on top of it later.
Speaker 3: It's just gravity doing its job.
Speaker 2: Conversely, the dwarf galaxies that were consumed much later on,
Speaker 2: long after the main structure of the Milky Way was
Speaker 2: already spinning, they would likely be scattered out in the
Speaker 2: expansive spherical outer.
Speaker 3: Halo because they couldn't penetrate as deeply.
Speaker 2: So the geographical rule of thumb should be early building
Speaker 2: blocks and the dense inner plane late arrivals scattered in
Speaker 2: the sparse outer halo.
Speaker 3: That was the standard model.
Speaker 2: Yes, but I hear a butt coming.
Speaker 3: Oh, a massive butt. When astronomers actually conducted massive surveys
Speaker 3: of the galaxy looking for these extremely metal poor stars,
Speaker 3: they ran headfirst into a massive, frustrating anomaly.
Speaker 2: The map didn't match the territory at all.
Speaker 3: Not even slightly.
Speaker 2: What did they find.
Speaker 3: Well, they found very much metal poor star, sure, but frustratingly,
Speaker 3: almost all of them were being found far out in
Speaker 3: the outer halo. Wait what Yeah, astronomers were desperately searching
Speaker 3: the inner galactic plane, where the oldest building blocks fundamentally
Speaker 3: should be, and they just weren't finding them, not.
Speaker 2: In the numbers that their hierarchical models predicted exactly.
Speaker 3: It was a severe mismatch.
Speaker 2: It's like, Okay, imagine excavating the foundation of an ancient ruin. Okay,
Speaker 2: you dig down expecting to find Roman bricks, but you
Speaker 2: find absolutely nothing but modern concrete. And then you realize
Speaker 2: all the oldest original Roman bricks are inexplicably scattered out
Speaker 2: in the surrounding grassy fields miles away.
Speaker 3: It completely upends the logic of how the structure was built.
Speaker 2: It makes no sense.
Speaker 3: It was a literal crisis for galactic archaeologists, and it
Speaker 3: forced the scientific community to start making some very complex,
Speaker 3: somewhat strain assumptions to explain the discrepancy.
Speaker 2: Because scientists hate a vacuum, we really do.
Speaker 3: We need an explanations.
Speaker 2: So what was the strained assumption.
Speaker 3: Well, astronomers noticed that the few metal poor stars they
Speaker 3: did manage to find deep in the galactic plane often
Speaker 3: had retrograde orbits.
Speaker 2: Retrograde meaning they are orbiting the center of the galaxy backward. Yes,
Speaker 2: they're moving in complete opposition to the general rotational flow
Speaker 2: of the Milky Way's.
Speaker 3: Disc exactly so, because they needed an explanation for why
Speaker 3: these ancient stores were so rare in the plane, the
Speaker 3: prevailing theory became that retrograde stars in the plane were
Speaker 3: the true rare remnants of early violent assembly.
Speaker 2: Because you'd have to hit the galaxy pretty hard to
Speaker 2: end up going backwards.
Speaker 3: That was the logic. The idea was that an early
Speaker 3: merger would be chaotic and violent enough to throw the
Speaker 3: consumed stars into reverse.
Speaker 2: Okay, and what about the ones going forward?
Speaker 3: Oh? Meanwhile, pro grade stars, the ones moving forward harmoniously
Speaker 3: with the disc's rotation, were assumed to have been added
Speaker 3: much later by gentler accretion events that just naturally aligned
Speaker 3: with the spinning disk.
Speaker 2: Wow, So they were basically forcing the puzzle pieces together
Speaker 2: because they didn't have enough data.
Speaker 3: They absolutely were. They looked at the few retrograde stars
Speaker 3: they found and essentially declared a universal rule.
Speaker 2: Prograde means one type of origin. Retrograde means a completely
Speaker 2: different type of origin.
Speaker 3: Exactly, they assumed you couldn't possibly have forward moving and
Speaker 3: backward moving ancient stars originating from the same early event.
Speaker 2: They thought it was physically impossible.
Speaker 3: The assumption was incredibly rigid. Prograde and retrograde meant totally
Speaker 3: different epochs and completely different progenitor galaxies.
Speaker 2: And that rigid assumption that forced geographic disconnect is exactly
Speaker 2: what makes this new study by Federico Ccido and his
Speaker 2: team so monumental. It really is because they didn't just
Speaker 2: find a missing puzzle piece. They found a puzzle piece
Speaker 2: that completely breaks the previous picture of how our galaxy
Speaker 2: was built.
Speaker 3: It is a remarkable paradigm shifting finding. Cistito's team focused
Speaker 3: specifically on sweeping the Milky Way's galactic plane, using highly
Speaker 3: advanced spectroscopic surveys.
Speaker 2: Looking deep in the concrete foundation.
Speaker 3: Exactly and against the odds of all previous searches, they
Speaker 3: successfully isolated a sample of twenty strictly metal poor stars
Speaker 3: located right there, deep in the plane.
Speaker 2: Twenty ancient heavy metal deficient fossil stars, yes, existing exactly
Speaker 2: where the original gravitational theory said they should be, but
Speaker 2: where actual observational surveys had previously failed to find them.
Speaker 3: Finding them at all was a massive triumph.
Speaker 2: But their mere presence wasn't the real shock, was it.
Speaker 3: No, it wasn't the shocking detail. The data point that
Speaker 3: completely upended the models is how these twenty stars actually
Speaker 3: behave kinematically, how they move, how they move. Here's where
Speaker 3: it gets really interesting.
Speaker 2: Okay, lay it on me.
Speaker 3: When Cistido's team looked at the orbital dynamics of these
Speaker 3: twenty stars, they realized these fossils utterly defy what past
Speaker 3: theories demanded in what way, well they all share those
Speaker 3: high eccentricities we discussed, Right.
Speaker 2: They're all swooping and plunging on wild nonsen circular paths
Speaker 2: cutting across the medium.
Speaker 3: Yes, but within this tight, exclusive group of twenty planar stars,
Speaker 3: the team found both prograde stars orbiting with the galaxy's
Speaker 3: rotation andy retrograde stars orbiting backward. Wait, really, yes, both
Speaker 3: within the exact same sample.
Speaker 2: That is insane. It completely shatters that deeply held assumption
Speaker 2: that retrobrade and prograde planar stars must have come from
Speaker 2: different epochs.
Speaker 3: Totally shatters it. Here they are side by side, highly eccentric, ancient,
Speaker 3: and moving in complete diametric opposition.
Speaker 2: To one another. Imagine you're standing in the center of
Speaker 2: a massive circular racetrack where millions of cars are all
Speaker 2: driving clockwise. Okay, and you managed to spot a fleet
Speaker 2: of twenty incredibly old vintage.
Speaker 3: Cars the metal poor stars.
Speaker 2: Right, and they're swerving wildly across the lanes. But the
Speaker 2: crazy part is some of these vintage cars are driving
Speaker 2: clockwise and some of them are driving counterplockwise, accelerating street
Speaker 2: into oncoming traffic.
Speaker 3: It would be terrifying to watch.
Speaker 2: But then when you look closely at their intricate paint jobs.
Speaker 2: You realize they all belong to the exact same racing team.
Speaker 3: It is a perfect visualization of the kinematic chaos, and
Speaker 3: you have to stop and imagine the sheer, unfathomable magnitude
Speaker 3: of the gravitational violence required to create that reality.
Speaker 2: It bends the mind.
Speaker 3: You have a single cohesive dwarf galaxy are racing team Loki.
Speaker 3: It falls into the terrifying gravitational well of the early
Speaker 3: Milky Way.
Speaker 2: And it hits the tidal forces right.
Speaker 3: The collision is so catastrophic that it doesn't just shred Loki.
Speaker 3: It rips the dwarf galaxy apart so violently that half
Speaker 3: of its stars are violently flung forward into prograde orbits,
Speaker 3: and the other half are whipped brutally backward into retrograde orbits,
Speaker 3: scattering them across the entire galactic plane.
Speaker 2: Okay, wait, slow down, I have to push back here.
Speaker 2: So for it, How does finding stars moving in completely
Speaker 2: opposite directions prove they are from the same galaxy?
Speaker 3: What do you mean?
Speaker 2: Well, if I see a car driving north in a
Speaker 2: driving south, my first instinct is not, oh, they obviously
Speaker 2: came from the same driveway.
Speaker 3: Fairpoint.
Speaker 2: It makes no intuitive physical sense. How did the gravity
Speaker 2: of the Milky Way actually accomplish that? How does one
Speaker 2: single object split into opposite orbital directions?
Speaker 3: It is deeply counterintuitive, I agree, until you look at
Speaker 3: the mechanics of tidal stripping during a galactic impact.
Speaker 2: Walk me through it.
Speaker 3: When a dwarf galaxy like Loki approaches the Milky Way,
Speaker 3: it isn't a point mass, right, It isn't a single
Speaker 3: solid rock.
Speaker 2: No, It's a huge collection of stuff.
Speaker 3: It is a sprawling collection of stars with its own
Speaker 3: internal rotation and a massive halo of dark matter. As
Speaker 3: it plunges into the Milky Way's gravitational field, the side
Speaker 3: of Loki closest to the Milky Way is accelerated faster
Speaker 3: than the side further away.
Speaker 2: That's the stretching effect we talked to it earlier.
Speaker 3: Yes, but it is also interacting with the angular momentum
Speaker 3: of the Milky Way's massive spinning disk.
Speaker 2: So the disk is dragging on it.
Speaker 3: Essentially.
Speaker 2: Yes.
Speaker 3: If Loki impacts the dis at a specific angle, what
Speaker 3: astrophysicists call the inclination angle, the immense title shock can
Speaker 3: literally unbind Loki's internal structure in a highly asymmetrical way.
Speaker 2: Okay, so what happens to the stars on the front.
Speaker 3: The stars on the leading edge of Loki get accelerated
Speaker 3: forward by the disk spin, adopting prograde orbits that align
Speaker 3: with the Milky Way's rotation.
Speaker 2: And the stars in the back, the.
Speaker 3: Stars on the trailing edge lose angular momentum due to
Speaker 3: dynamical friction. They get violently yanked backward, falling into retrograde orbits. Wow,
Speaker 3: a single structural entity is essentially smeared completely across the
Speaker 3: kinematic spectrum.
Speaker 2: It is chaos, total, absolute chaos in the early Milky.
Speaker 3: Way, It really was. But your skepticism is exactly the
Speaker 3: right scientific response. Well, thank you, because if you are
Speaker 3: going to make the extraordinary claim that these diametrically opposed
Speaker 3: stars actually belong to the same original dwarf galaxy, you
Speaker 3: cannot rely on orbital models alone.
Speaker 2: You need the paint job from the race cars.
Speaker 3: Yeah, exactly, to prove these cars belong to the same
Speaker 3: race team, Cistino's team had to look past the orbital
Speaker 3: paradox and conduct a rigorous elemental chemical.
Speaker 2: Autopsy, right, because the retrograde prograde split makes them look
Speaker 2: totally unrelated. On the surface.
Speaker 3: Absolutely so, the researchers had to compare the deep chemical
Speaker 3: signatures of these twenty stars not just to each other,
Speaker 3: but to stars out in the halo, to other known
Speaker 3: consumed dwarf galaxies, and to highly complex simulated stellar populations.
Speaker 2: That sounds like an incredible amount of processing.
Speaker 3: Power, oh massive amounts of data. And this chemical autopsy
Speaker 3: revealed a fascinating, deeply violent story about how the environment
Speaker 3: that birthed these specific stars was enriched.
Speaker 2: What does they find.
Speaker 3: When they analyzed the elemental abundances, the specific ratios of
Speaker 3: elements like carbon, magnesium, and calcium compared to iron, They
Speaker 3: found a very distinct, incredibly aggressive chemical fingerprint.
Speaker 2: What exactly does that fingerprint look like? What makes a
Speaker 2: chemical signature aggressive?
Speaker 3: The chemical enrichment of these twenty stars points exclusively lead
Speaker 3: to extreme, highly energetic events. We are talking about the
Speaker 3: ashes of high energy core collapse supernovae, which are the
Speaker 3: explosive deaths of extremely massive stars.
Speaker 2: The ones that live fast and die young.
Speaker 3: Yes, we are also talking about hypernovae, which are even
Speaker 3: more energetic explosions often associated with the core of a
Speaker 3: massive star collapsing directly into a black hole. While the
Speaker 3: eider layers detonate a hypernova.
Speaker 2: That just sounds terrifying.
Speaker 3: It is, And they also found signatures from fast rotating
Speaker 3: massive stars that shed heavily enriched material into space at
Speaker 3: incredible velocities, and even the catastrophic element forging collisions of
Speaker 3: neutron stars.
Speaker 2: So the environment that breth Loki wasn't some quiet stellar nursery.
Speaker 3: No, it was essentially a cosmic war.
Speaker 2: Zone, just continuous, devastating, high energy detonations rapidly seating the
Speaker 2: gas clouds with these specific heavy elements.
Speaker 3: Yes, but in a forensic autopsy sometimes what is missing
Speaker 3: is just as critical as what present. What was missing
Speaker 3: in the complex chemical signature of these twenty stars there
Speaker 3: is a crucial, glaring absence. There is absolutely no chemical
Speaker 3: evidence of white dwarf explosions.
Speaker 2: H Okay, stop. Why is that specific absence so important?
Speaker 3: It's a huge clue.
Speaker 2: What makes a white dwarf explosion chemically different from a
Speaker 2: massive star going supernova? And why does its absence matter
Speaker 2: to low key story.
Speaker 3: It all comes down to the cosmic timeline and the
Speaker 3: specific elements these explosions produce. The high energy events we
Speaker 3: just talked about, massive core collapse, supernovae and hypernovae. Those
Speaker 3: happen very very quickly on a cosmic scale because.
Speaker 2: The massive stars burn their fuels so fast.
Speaker 3: Exactly, massive stars burned through their nuclear fuel at an
Speaker 3: astronomical rate. They live incredibly fast, and they die young,
Speaker 3: usually detonating within just a few million years of forming.
Speaker 2: They were the rock stars of the universe. Fast die young.
Speaker 2: We have a brilliant.
Speaker 3: Explosion exactly, and when they explode, they primarily produce what
Speaker 3: we call alpha elements oxygen, magnesium, silicon, calcium.
Speaker 2: Okay, so that's the fast stuff. What about the white dwarfs.
Speaker 3: A white dwarf explosion, known as a type IA supernova,
Speaker 3: is a completely different beast, both chemically and temporarily.
Speaker 2: Because they come from smaller stars. Right.
Speaker 3: A white dwarf is the incredibly dense, glowing remnant of
Speaker 3: a smaller, less massive star, much like our own sun.
Speaker 2: So for a star to even become a white dwarf,
Speaker 2: it has to slowly burn through its fuel over billions
Speaker 2: of years.
Speaker 3: Right, Yes, it gently puffs off its outer layers and
Speaker 3: leaves behind that dense core. It takes billions of years
Speaker 3: just to form the white dwarf In the first place,
Speaker 3: and then it explodes well eventually. For that white dwarf
Speaker 3: to actually explode, it usually has to be locked in
Speaker 3: a binary system, slowly agonizingly siphoning gas off a companion.
Speaker 2: Star like a vampire star.
Speaker 3: Exactly like a vampire, it pulls material onto its surface
Speaker 3: until it reaches a precise mathematical threshold called the chaundrasecar.
Speaker 2: Limit, and then boom.
Speaker 3: Once it hits that mass, the entire white dwarf detonates
Speaker 3: in a massive thermonuclear explosion.
Speaker 2: Which produces a different chemical signature.
Speaker 3: Yes, Type EA supernovae are the primary producers of iron
Speaker 3: in the universe. But the crucial point is the delay
Speaker 3: time distribution.
Speaker 2: The delay time distribution meaning the time it takes for
Speaker 2: all this to happen.
Speaker 3: Yes, it takes hundreds of millions, often billions of years
Speaker 3: for a stellar population to start producing type IO white
Speaker 3: dwarf explosion.
Speaker 2: Oh wow, I see it now. The timeline is baked
Speaker 2: into the chemistry precisely.
Speaker 3: The fact that Loki stars show all the chemical ashes
Speaker 3: of fast massive core collapse supernovae but completely lack the
Speaker 3: distinct iron rich chemical ashes of slow white dwarf explosions
Speaker 3: gives us a definitive, indisputable timeline.
Speaker 2: It means Loki didn't survive long enough to see its
Speaker 2: smaller stars turn into white dwarfs and explode.
Speaker 3: Exactly, Loki was incredibly short lived. It formed its initial
Speaker 3: bursts of stars. Those massive stars detonated and enriched the
Speaker 3: local environment with alpha elements, and then, and then, before
Speaker 3: the slower white dwarfs had time to evolve, reach critical
Speaker 3: mass and contribute their unique iron signatures, the entire dwarf
Speaker 3: galaxy was swallowed and violently ripped apart by the Milky Way.
Speaker 2: It's star forming days were over.
Speaker 3: Its ability to hold onto its gas and cook new
Speaker 3: elements was abruptly and permanently terminated.
Speaker 2: It lived fast, died violently, and was completely dismantled before
Speaker 2: even had a chance to reach middle age.
Speaker 3: It's sad when you think about it.
Speaker 2: It is, but that is such a tragic, beautiful piece
Speaker 2: of forensic deduction. The absence of an element tells you
Speaker 2: the exact moment the galaxy died.
Speaker 3: It really is elegant physics. But you know, Cistuido's team
Speaker 3: had to push the autopsy even deeper.
Speaker 2: Why wasn't that enough?
Speaker 3: Because they didn't just look at the types of explosions.
Speaker 3: They looked at the precise uniformity of the resulting chemistry
Speaker 3: across all twenty of these scattered stars.
Speaker 2: Okay, this brings us to what the study refers to
Speaker 2: as the closed system clue. Yes, because even with the
Speaker 2: lack of white dwarf signatures and the presence of hypernovae,
Speaker 2: a hardened skeptic might still say, so what right?
Speaker 3: They might ask, could these twenty stars just be a
Speaker 3: massive cosmic coincidence?
Speaker 2: Yeah? Could they have formed in totally different parts of
Speaker 2: the early universe that just happened to have similarly violent,
Speaker 2: short lived conditions and then randomly ended up crossing paths
Speaker 2: in the Milky Way's plane.
Speaker 3: It's the essential devil's advocate question. We have to rule
Speaker 3: out coincidence.
Speaker 2: How do you do that?
Speaker 3: To answer it, the researchers looked at the statistical dispersion,
Speaker 3: the mathematical spread of what we call the XFA ratio
Speaker 3: in these stars.
Speaker 2: Okay, xface sounds intimidating. I need you to translate that
Speaker 2: out of astrophysics notation for us.
Speaker 3: Fair enough, I can do that. In astronomical notation, XFA
Speaker 3: is simply a way of expressing the abundance of a
Speaker 3: specific element let's call it X, like magnesium, right, which
Speaker 3: could be magnesium or calcium or titanium, and you compare
Speaker 3: it to the abundance of iron.
Speaker 2: Which is f okay, So it's a ratio.
Speaker 3: The brackets denote a logarithmic skill compared to our sun.
Speaker 3: But essentially it is a highly specific recipe.
Speaker 2: A recipe.
Speaker 3: Yes, it tells us the exact microscopic proportions of heavy
Speaker 3: ingredients that went into making the star.
Speaker 2: So they are looking at the specific recipe of heavy
Speaker 2: elements compared to iron in each of these twenty stars
Speaker 2: and looking for variations.
Speaker 3: And what they found was truly startling. With the exception
Speaker 3: of just one single star out of the twenty, the
Speaker 3: targets show a noticeably mathematically narrower dispersion in their EXSEV
Speaker 3: ratios compared to stars in the broader galactic halo or
Speaker 3: the bulch.
Speaker 2: Even at similar overall metallicity levels.
Speaker 3: Exactly, the recipe was unbelievably consistent.
Speaker 2: Let me try to put this into human terms to
Speaker 2: make sure I grasp just how definitive this is.
Speaker 3: Go for it.
Speaker 2: Imagine you walk into a massive stadium filled with hundreds
Speaker 2: of thousands of people.
Speaker 3: Okay, that represents the galactic halo.
Speaker 2: Right, You are trying to find people who are secretly related,
Speaker 2: so you look at their blood.
Speaker 3: Types, a good starting point for a search.
Speaker 2: You find twenty people scattered throughout the massive crowd, who
Speaker 2: all have an incredibly rare blood type, say AB negative.
Speaker 3: Okay, that's our rare, violent chemical signature without white dwarfs exactly.
Speaker 2: But having the same rare blood type doesn't guarantee you're
Speaker 2: from the same family.
Speaker 3: No, it doesn't.
Speaker 2: You could just be randomly scattered strangers who happen to
Speaker 2: share a broad biological trait.
Speaker 3: Right, the skeptic could still argue it's a coincidence.
Speaker 2: But then you sequence their DNA, You look past the
Speaker 2: blood type at the microscopic underlying genetic markers. Yes, and
Speaker 2: you realize that these twenty people don't just share a
Speaker 2: rare blood type, they share the exact same, microscopic, highly
Speaker 2: specific genetic mutations down to the most infinitesmal detail.
Speaker 3: The dispersion is zero, Right.
Speaker 2: The dispersion or variation in their genetics is incredibly narrow.
Speaker 2: They aren't strangers who look alike. They are definitively, undeniably siblings.
Speaker 3: That is a brilliant analogy. The exceptionally narrow XPA dispersion
Speaker 3: is the DNA test that proves they are siblings.
Speaker 2: So they have to be from the same galaxy.
Speaker 3: The researchers stated explicitly that the elemental dispersions in these
Speaker 3: targets are so remarkably small that they are virtually identical
Speaker 3: to what you would mathematically expect to see in a
Speaker 3: closed system.
Speaker 2: Okay, define a closed system in this context. Do you
Speaker 2: mean a single isolated bubble where the gas was perfectly
Speaker 2: mixed before the stars formed.
Speaker 3: Yes, exactly that. In astrophysics, a closed system means the
Speaker 3: dwarf galaxy had a deep enough gravitational well to hold
Speaker 3: on to its.
Speaker 2: Gas despite the supernova going off.
Speaker 3: Exactly, it held onto the gas, allowing the violent supernovae
Speaker 3: to explode and thoroughly mix their newly forged elements evenly
Speaker 3: throughout the galaxy's interstellar medium before the next generation of
Speaker 3: stars formed.
Speaker 2: Think of stirring a massive vat of soup until the
Speaker 2: spices are perfectly distributed. Yes.
Speaker 3: If these twenty stars had come from two different formation sites,
Speaker 3: two different dwarf galaxies that fell into the milky way independently,
Speaker 3: the gas in those two separate systems would have had
Speaker 3: slightly different mixing histories.
Speaker 2: Because they'd have different amounts of supernovae going off at
Speaker 2: different times.
Speaker 3: Exactly the chemical dispersion. The variance in the recipe from
Speaker 3: star to star would be noticeably wider.
Speaker 2: But it isn't.
Speaker 3: But it isn't that the data is definitive. These stars
Speaker 3: formed in a single perfectly mixed, isolated vat they formed
Speaker 3: in Loki.
Speaker 2: The data is undeniable. We have the chemical proof of
Speaker 2: a closed system. We do. But wait if we accept
Speaker 2: that this brings us violently back to the massive glaring
Speaker 2: paradox we introduced.
Speaker 3: Earlier, ah, the kinematic paradox.
Speaker 2: Yes, we just proved chemically beyond a shadow of a
Speaker 2: doubt that this is a single closed system. But we
Speaker 2: also note that half these stars are orbiting forward and
Speaker 2: half are orbiting backward.
Speaker 3: It is a staggering contradiction on the surface.
Speaker 2: Now, you explained how tidal forces could do this, but
Speaker 2: did the astronomers actually verify it couldn't just be too
Speaker 2: identical galaxies?
Speaker 3: They absolutely did.
Speaker 2: How can we be mathematically certain a single closed system
Speaker 2: produced stars orbiting in totally opposite directions.
Speaker 3: Well, the orbital paradox sits at the very heart of
Speaker 3: this discovery, and the astronomers absolutely questioned this themselves. It
Speaker 3: is the natural scientific response to such bizarre data. They
Speaker 3: had to ask, despite the incredibly tight chemical similarities, is
Speaker 3: there any mathematical loophole where this could actually be a
Speaker 3: pair of systems?
Speaker 2: Could Loki actually be Loki and say thor.
Speaker 3: Yes, one prograde dwarf galaxy and one retrograde dwarf galaxy
Speaker 3: that just miraculously happened to have identical chemistry.
Speaker 2: Because if it's two separate systems, the orbital problem is
Speaker 2: neatly solved. One hit the milky Way from the left,
Speaker 2: one hit from the right, prograde and retrograde. Explained, without
Speaker 2: needing extreme title unbinding.
Speaker 3: It would elegantly solve the kinematic problem. Yes, but Cistito's
Speaker 3: team didn't just guess. They ran the mass models of
Speaker 3: the star and gas material.
Speaker 2: What does that mean?
Speaker 3: They used complex nd body simulations and mathematical frameworks like
Speaker 3: genes modeling to reconstruct the mass required to produce these.
Speaker 2: Stars, oh like working backwards from the wreckage.
Speaker 3: Exactly, and the physics simply they do not support the
Speaker 3: two system theory.
Speaker 2: Why not break down the math for me? Why does
Speaker 2: the two system theory fail?
Speaker 3: If you assume these stars came from two separate systems,
Speaker 3: one pro grade one retrograde, the total buryonic mass, which
Speaker 3: is the total mass of all the normal visible matter
Speaker 3: like gas and stars needed to form them would have
Speaker 3: to be exactly double what we calculate for a single
Speaker 3: system scenario.
Speaker 2: Okay, so you'd need twice as much raw material falling
Speaker 2: into the Milky Way at the exact same time.
Speaker 1: Yes.
Speaker 3: Furthermore, and this is the mathematical nail in the coffin
Speaker 3: for the two system theory, those two completely separate dwarf
Speaker 3: galaxies would have to share a nearly identical mirror image
Speaker 3: chemical history and evolution, which is just too much of
Speaker 3: a coincidence, way too much. They would have to have
Speaker 3: the exact same rate of high energy hypernovae the exact
Speaker 3: same precise timeline, resulting in the exact same lack of
Speaker 3: white dwarfs, and perfectly match that incredibly narrow X dispersion
Speaker 3: we just talked about.
Speaker 2: To go back to my stadium analogy, that would be
Speaker 2: like finding two completely unrelated families from opposite sides of
Speaker 2: the world, throwing them into the stadium and discovering their
Speaker 2: microscopic D and A mutations are completely identical.
Speaker 3: Yes, it's not just unlikely, it's statistically absurd.
Speaker 2: It is statistically impossible.
Speaker 3: The mass models and the chemical forensics trap us into
Speaker 3: only one viable physical reality. Loki was a single, unified
Speaker 3: dwarf galaxy.
Speaker 2: There's a closed system.
Speaker 3: And it was subjected to an ancient accretion event so
Speaker 3: spectacularly violent, so profoundly disruptive, that the Milky Way ripped
Speaker 3: the galaxy's internal structure entirely apart.
Speaker 2: Scattering its constituent stars across the massive plane of our
Speaker 2: galaxy and completely opposing orbital directions.
Speaker 3: It's breathtaking, isn't it.
Speaker 2: It really is. It completely rewires how I picture the
Speaker 2: space above our heads. Same here, the Milky Way isn't
Speaker 2: just a slow, gentle accumulation of dust. It is a
Speaker 2: violent history of catastrophic collisions. And by looking at chemical
Speaker 2: recipes in backward orbits, we have just successfully pieced together
Speaker 2: the brief life and the violent death of one of
Speaker 2: those victims.
Speaker 3: We have we have isolated the ghost of Loki. Incredible,
Speaker 3: but you know, The most exciting part of Cistido's paper
Speaker 3: isn't just what they found, It is what this implies
Speaker 3: for the future. There's more, oh much more. The search
Speaker 3: for the Milky Way's violent history is really just beginning.
Speaker 3: The study explicitly notes that while this sample of twenty
Speaker 3: planar stars is enough to prove the concept and break
Speaker 3: old models, it is still a relatively small sample size.
Speaker 2: It's a tip of the iceberg. It proves the ghosts
Speaker 2: are there, hiding in.
Speaker 3: The plane exactly. The future of galactic archaeology is incredibly
Speaker 3: bright because we are standing on the precipice of a
Speaker 3: massive data explosion.
Speaker 2: What's coming next?
Speaker 3: The study point specifically to the next generation of larger
Speaker 3: homogeneous spectroscopic surveys that are coming online soon. Facilities and
Speaker 3: instruments like Weave and Foremost explain.
Speaker 2: What Weave and Foremost are going to do. Differently.
Speaker 3: These are highly advanced multi object spectrographs attached to mass
Speaker 3: of telescopes. Instead of looking at a few stars at
Speaker 3: a time, they use thousands of optical fibers positioned by
Speaker 3: robots to simultaneously capture the light from thousands of stars
Speaker 3: at once.
Speaker 2: Oh wow, so they can survey the sky much.
Speaker 3: Faster, exponentially faster. They are going to survey millions of
Speaker 3: stars across the galactic plane with a level of chemical
Speaker 3: and kinematic precision we've never had access to before.
Speaker 2: That's huge.
Speaker 3: If Lokia is out there, represented by these twenty scattered stars,
Speaker 3: Weave and Foremost are going to find hundreds, maybe thousands
Speaker 3: more of its siblings.
Speaker 2: They will map the full extent of its shredded remains.
Speaker 3: They are going to illuminate the entire cosmic graveyard. They
Speaker 3: will clarify the origins of planar metal poor stars, and
Speaker 3: undoubtedly uncover the ghosts of other dwarf galaxies we don't
Speaker 3: even have names for yet.
Speaker 2: It will be a golden age for understanding the violent
Speaker 2: assembly of our home.
Speaker 3: It is just spectacular science.
Speaker 2: So the next time you are out on a clear
Speaker 2: night and you look up at that glowing, milky band
Speaker 2: of light stretching across the blackness, I want you to
Speaker 2: change how you see it.
Speaker 3: Think of the violence.
Speaker 2: Right. You aren't just looking at our galaxy. You aren't
Speaker 2: looking at a peaceful, static home. You're looking at the
Speaker 2: ultimate cosmic graveyard.
Speaker 3: You are looking at the ghostly remains of countless ancient
Speaker 3: dwarf galaxies shredded billions of years ago, with their constituent
Speaker 3: stars still swirling in chaotic, invisible orbits right above our heads.
Speaker 2: And if we really want to push that thought to
Speaker 2: its absolute limit, let's do consider the geometry of what
Speaker 2: we just discussed. If the stars of Loki and other
Speaker 2: consumed systems like it were scattered so violently that they
Speaker 2: are still currently plunging across the galactic plane in wildly opposing,
Speaker 2: highly eccentric directions, is it possible that our own relatively
Speaker 2: young solar system, on its quiet circular path through the
Speaker 2: disc will eventually cross paths with or even be subtly
Speaker 2: gravitationally nudged by the silent ancient ghosts of an entirely
Speaker 2: different lost galaxy.
Speaker 3: Now, that is something to think about.