Speaker 1: Welcome to Bedtime Astronomy. Explore the wonders of the cosmos
Speaker 1: with our soothing Bedtime Astronomie podcast. Each episode offers a
Speaker 1: gentle journey through the stars, planets, and beyond, perfect for
Speaker 1: unwinding after a long day. Let's travel through the mysteries
Speaker 1: of the universe as you drift off into a peaceful
Speaker 1: slumber under the night sky.
Speaker 2: I want you to visualize a really sprawling modern architectural marvel,
Speaker 2: like a massive glass and steel house pushed right on
Speaker 2: a cliff side.
Speaker 3: Okay, I can picture that.
Speaker 2: Yeah, And it has this incredibly complex foundation, right vaulted ceilings,
Speaker 2: a heavy slate roof. But there is a structural reality
Speaker 2: to this house that totally defies everyday intuition. Eighty five
Speaker 2: percent of the load bearing columns, the rebar, the absolute
Speaker 2: core of its structural integrity, is completely invisible. Okay, touch
Speaker 2: those columns. You can't bounce light off them, but the
Speaker 2: mathematics of tension and compression absolutely dictate they have to.
Speaker 3: Be there, right, because otherwise the whole thing comes down exactly.
Speaker 2: Yeah. If you were to somehow cleanly extract that invisible scaffolding,
Speaker 2: the entire cantilevered structure would just instantaneously succumb to gravity
Speaker 2: and collapse into the review.
Speaker 3: It'd be a disaster.
Speaker 2: Yeah, And that structural dynamic that is the baseline, non
Speaker 2: negotiable reality of how we understand our universe. Specifically, it's
Speaker 2: the foundational rule of galactic.
Speaker 3: Dynamics, because galaxies are held together by this invisible, non
Speaker 3: buryonic scaffolding, what we call dark matter.
Speaker 2: Right, But then imagine you are mapping out a seemingly
Speaker 2: quiet cosmic neighborhood and you stumble across an absolute architectural impossibility.
Speaker 3: You find a house floating perfectly intact.
Speaker 2: Yes, stable, entirely, fully built, without a single one of
Speaker 2: those invisible load bearing columns.
Speaker 3: Which I mean that forces a total re valuation of
Speaker 3: the engineering principles you thought govern the universe, right totally.
Speaker 3: Finding a structure that shouldn't exist doesn't just mean the
Speaker 3: structure is weird. It means your foundational equations regarding cosmic
Speaker 3: architecture have these spectacular, violent exceptions that we're well, we're
Speaker 3: only just beginning to comprehend.
Speaker 2: And that brings us to the monumental data published in
Speaker 2: April of twenty twenty six. Okay, let's unpack this because
Speaker 2: astronomers Mike l. A. Khin, Peter van Dockaman their collaborative
Speaker 2: team at Yale University just dropped an absolute bombshell.
Speaker 3: They really did.
Speaker 2: They confirmed the discovery of a third galaxy designated NNGC
Speaker 2: one oh five to two DF nine or just DF
Speaker 2: nine that appears to be entirely devoid of dark matter.
Speaker 3: Is just incredible.
Speaker 2: It is that cliff side House completely missing its invisible columns,
Speaker 2: just sitting out there, stable in the void.
Speaker 3: And you know, the scientific weight of this really cannot
Speaker 3: be overstated. I mean, finding a single galaxy missing its
Speaker 3: dark matter halo. Back in twenty eighteen, that was DF two,
Speaker 3: right DF two, that was treated by many as a
Speaker 3: statistical anomaly or perhaps even an observational error.
Speaker 2: People were definitely skeptical.
Speaker 3: Highly skeptical, and then finding a second one shortly after
Speaker 3: that elevated it to a real crisis for our theoretical models.
Speaker 2: Yeah, crisis is the right word.
Speaker 3: But confirming a third and critically finding that it perfectly
Speaker 3: aligns with the other two in a highly specific spatial
Speaker 3: and kinematic geometry, that isn't a glitch in the data anymore.
Speaker 2: No, definitely not.
Speaker 3: That is an entirely new class of object. It forces
Speaker 3: us to confront theories of galaxy formation that previously seemed
Speaker 3: well far too chaotic and hydrodynamically violent to be sustainable.
Speaker 2: So we have an incredibly complex physical puzzle to unpack. Today,
Speaker 2: we are going to look closely at the exact mechanics
Speaker 2: of how a galaxy manages to actually decouple from its
Speaker 2: dark matter halo.
Speaker 3: The uncoupling process is fascinating, it really is.
Speaker 2: And we're going to examine the extreme physics of a
Speaker 2: high speed supersonic cosmic collision that triggered this separation billions
Speaker 2: of years ago, right.
Speaker 3: The bullet dwarf scenario exactly.
Speaker 2: And perhaps the most beautiful paradox of this entire discovery,
Speaker 2: we're going to explore how this highly anomaloust galaxy, which
Speaker 2: is defined entirely by its missing dark matter, might actually
Speaker 2: serve as the final crushing mathematical proof that dark matter
Speaker 2: is a distinct physical.
Speaker 3: Entity because we found a place where it was left.
Speaker 2: Behind, precisely because we found the empty spot.
Speaker 3: It's an elegant paradox, isn't it to prove a substance
Speaker 3: is a physical reality rather than just a mathematical tweak
Speaker 3: to our understanding of gravity. You have to find a
Speaker 3: scenario where that substance has been dynamically separated from ordinary matter.
Speaker 2: You have to catch it in the act of not
Speaker 2: being there.
Speaker 3: Yeah, exactly. But to fully appreciate the mechanics of DF nine,
Speaker 3: we really need to look at the kinematic tension that
Speaker 3: defined the Lambda CDM model in the first place. Baseline expectation, right,
Speaker 3: we need to look at the baseline expectation for a
Speaker 3: galaxy's velocity dispersion.
Speaker 2: Let's focus on that kinematic tension then, because within the
Speaker 2: standard model of cosmology, lambda cold dark matter. Yeah, dark
Speaker 2: matter isn't just some fringe component, right.
Speaker 3: Not at all. It represents roughly eighty five percent of
Speaker 3: the universe's total matter content.
Speaker 2: So the baryonic matter, the gas, dust stars, that's just
Speaker 2: the frosting.
Speaker 3: Yeah, a very thin layer of frosting.
Speaker 2: And now the reason we know the cake is there
Speaker 2: even if we can't see it comes down to how
Speaker 2: fast that frosting is spinning.
Speaker 3: That's a great way to put it.
Speaker 2: Like if we look at the rotation curves of typical
Speaker 2: galaxies or the velocity dispersion of stars. Within dwarf galaxies,
Speaker 2: the math just fundamentally doesn't work if you only count
Speaker 2: the luminous matter.
Speaker 3: It fails catastrophically. The foundational tool we use here is
Speaker 3: the virial theorem.
Speaker 2: Okay, break that down for us.
Speaker 3: So, in a stable gravitationally bound system, the kinetic energy
Speaker 3: of the objects moving around inside it.
Speaker 2: The stars, right, the.
Speaker 3: Stars, their kinetic energy has to be balanced by the
Speaker 3: gravitational potential energy holding the whole system.
Speaker 2: Together, otherwise they just fly apart.
Speaker 3: Exactly, if we measure the kinetic energy, which we do
Speaker 3: by observing the velocity dispersion, or you know how fast
Speaker 3: the stars are buzzing around relative to each other, we
Speaker 3: can calculate exactly how much gravitational potential energy is required
Speaker 3: to keep those stars from exceeding escape velocity and just
Speaker 3: boiling off into intergalactic space.
Speaker 2: So the velocity dispersion is really the key metric here, absolutely,
Speaker 2: because if I'm looking at a typical dwarf galaxy, the
Speaker 2: stars are moving incredibly fast. It's like watching a merry
Speaker 2: go round spinning way too fast.
Speaker 3: We are violently fast married around the.
Speaker 2: Kids, or the stars should be flying off. This centripetal
Speaker 2: acceleration required to keep those stars in their orbits is massive.
Speaker 3: It is. And if we calculate the mass of the
Speaker 3: galaxy strictly by counting the starlight, you know, adding up
Speaker 3: the mass of the gas clouds.
Speaker 2: Luminous mass, if we can actually see.
Speaker 3: Right, the resulting gravitational binding energy from just that visible
Speaker 3: stuff is nowhere near enough to counter that kinetic energy.
Speaker 2: The kids should be flying off the merry go round.
Speaker 3: But they aren't, and the disparity is often an order
Speaker 3: of magnet or more. I mean, in typical dwarf spheroidals,
Speaker 3: we see mass to light ratios that are astronomically high.
Speaker 3: So you need invisible seat belts, exactly invisible seat belts.
Speaker 3: The visible matter might only account for ten percent or
Speaker 3: even one percent of the gravity required to keep the
Speaker 3: system virialized.
Speaker 2: That's wild one percent.
Speaker 3: Yeah, the stars are moving with such high velocity dispersions
Speaker 3: that absence some massive, unseen gravitational anchor, the galaxy should
Speaker 3: have dissolved billions of years ago.
Speaker 2: So the dark matter halo provides that deep gravitational potential. Well,
Speaker 2: it is the anchor, Okay, So the baseline rule is
Speaker 2: firmly established. If you have a galaxy of a certain
Speaker 2: stellar mass, you absolutely expect its stars to be moving
Speaker 2: at a relatively high velocity because they are surfing inside
Speaker 2: this massive unseen dark matter gravity.
Speaker 4: Well, that is the universal expectation, yes, which sets the
Speaker 4: state perfectly for the absolute kinematic shockwave the Yale team
Speaker 4: triggered when they aim their instruments at the constellation Seatus Oh.
Speaker 3: It was a massive disruption to the field. So we
Speaker 3: are looking at a field roughly sixty to seventy million
Speaker 3: light years away dominated by a massive elliptical galaxy called
Speaker 3: NNGC one oh fifty two.
Speaker 2: But the focus isn't that central elliptical galaxy.
Speaker 3: Right now, it's the highly unusual population of satellite galaxies
Speaker 3: surrounding it. The initial crack in the dark matter paradigm
Speaker 3: actually occurred a few years earlier, in twenty eighteen.
Speaker 2: Right when Van Dokam's team first identified NNGC one fifty
Speaker 2: two DF.
Speaker 3: Two exactly DF two and DF.
Speaker 2: Two is categorized as an alternate diffuse galaxy. And what's
Speaker 2: wild is they found it using an instrument that frankly
Speaker 2: sounds like it belongs in a commercial photography studio rather
Speaker 2: than a world class observatory.
Speaker 3: You're talking about the Dragonfly telephoto array.
Speaker 2: Yes, Dragonfly. It is a phenomenal piece of engineering, truly
Speaker 2: born out of a very specific observational necessity.
Speaker 3: Why did they need it? Why not just use Hubble
Speaker 3: right away? Well, traditional massive reflectors like the Hubble Space
Speaker 3: Telescope or the Keck observatory, they are unparallel at achieving
Speaker 3: high resolution, but they actually struggle when it comes to
Speaker 3: mapping incredibly faint, low surface brightness objects spread over a
Speaker 3: really wide field of.
Speaker 2: View because of the optics design, right, Yeah, largely, Like
Speaker 2: if you have a massive primary mirror and a secondary
Speaker 2: mirror suspended in front of it, you introduce diffraction exactly.
Speaker 3: You get light scattering off the microscopic imperfections in the
Speaker 3: mirror coatings or the struts holding the secondary mirror, which
Speaker 3: creates a kind of optical noise floor.
Speaker 2: So it's like trying to see a whisper in a
Speaker 2: noisy room.
Speaker 3: That's a perfect analogy. The internal scattering within a traditional
Speaker 3: reflecting telescope creates these broad wings on the point spread
Speaker 3: function of bright stars or central galaxies.
Speaker 2: And that scattered light effectively washes out the exceptionally faint
Speaker 2: diffuse glow of objects like.
Speaker 3: DF two, Right, it just drowns it out. But the
Speaker 3: Dragonfly telephoto array bypassed this entirely by using refractive.
Speaker 2: Optic refractive so lenses instead of mirrors.
Speaker 3: Right. They took commercially ava bill high end cannon telephoto
Speaker 3: camera lenses and literally arrayed them together.
Speaker 2: It literally looks like the compound eye of an insect
Speaker 2: pointing at the sky.
Speaker 3: It really does. And the reason it works so brilliantly
Speaker 3: is because those commercial lenses use proprietary nanocoatings.
Speaker 2: Coatings that were originally designed to reduce glare and ghosting
Speaker 2: for like sports and wildlife photographers.
Speaker 3: Yes, when you stack dozens of these lenses together, they
Speaker 3: mimic the light gathering power of a massive telescope. But
Speaker 3: because there are no secondary mirrors or central obstructions.
Speaker 2: Those struts to bounce light around.
Speaker 3: Exactly, the internal scattering is suppressed by orders of magnitude.
Speaker 3: The noise floor just drops out completely, revealing structures that
Speaker 3: are practically translucent, which is incredible.
Speaker 2: And DF two was one of those translucent structures. It was.
Speaker 2: It has a physical diameter roughly comparable to the Milky Way. Right, Yeah,
Speaker 2: it's huge, but it possesses only about one five hundredth
Speaker 2: of our stellar mass.
Speaker 3: It's basically a ghost.
Speaker 2: The stars are so sparse you can actually see background
Speaker 2: galaxy shining cleanly through the gaps in the galaxy itself.
Speaker 3: Which is so visually striking.
Speaker 2: But the diffuse nature of the galaxy wasn't the headline here.
Speaker 2: The headline was what happened when they pointed the massive
Speaker 2: KEC telescopes at DF two's globular clusters.
Speaker 3: To measure that velocy dispersion we were just talking about, right.
Speaker 2: Because globular clusters are incredibly dense, luminous spirical collections of
Speaker 2: older stars that orbit the galactic center.
Speaker 3: And because they are so bright and compact, they serve
Speaker 3: as excellent kinematic tracers.
Speaker 2: Like tracking lights on a dark highway.
Speaker 3: Exactly by taking specter of these clusters, astronomers can measure
Speaker 3: the Dopplay shift of their light.
Speaker 2: Okay, the Doppler shift.
Speaker 3: Yeah, So they can determine exactly how fast those clusters
Speaker 3: are moving within the gravitational potential of the galaxy.
Speaker 2: And the virial theorem dictates that for a galaxy of
Speaker 2: DF two's size, those globular clusters should be zipping around
Speaker 2: governed by the massive dark matter halo. We just assume there.
Speaker 3: They should be moving fast, but the spectral data told
Speaker 3: a completely different story.
Speaker 2: They weren't moving fast, not at all.
Speaker 3: The velocity dispersion of those clusters was staggeringly low.
Speaker 2: Wow.
Speaker 3: It was so low, in fact, that it perfectly matched
Speaker 3: the gravitational potential of the luminous matter alone.
Speaker 2: Just the visible stars, just the stars.
Speaker 3: The stars and clusters were moving slubbishly, exactly as you
Speaker 3: would expect if there was absolutely no dark matter halo present.
Speaker 2: And the reaction from the astrophysics community to that twenty
Speaker 2: eighteen paper was well, it was not exactly a quiet
Speaker 2: round of applause.
Speaker 3: Oh no, it was intense scrutiny.
Speaker 2: Bordering on outright hostility from certain corners of the theoretical community,
Speaker 2: I imagine, definitely.
Speaker 3: And the primary vector of attack was the distance measurement,
Speaker 3: Which makes sense.
Speaker 2: That is the most rigorous and appropriate scientific response.
Speaker 3: Right it is. In astronomy, distance is the foundational variable
Speaker 3: for almost all derived properties. If you get the distance wrong,
Speaker 3: your entire physical model collapses.
Speaker 2: Right, because OFF two isn't sixty five million light years away,
Speaker 2: but say only thirty million light years away.
Speaker 3: Then it fundamentally changes what the object is.
Speaker 2: It would be intrinsically much smallertrinsically much less luminous, and
Speaker 2: therefore its stellar mass would be drastically lower than they
Speaker 2: originally calculated.
Speaker 3: Exactly. And if the stellar mass is lower, then the
Speaker 3: sluggish velocity dispersion might actually perfectly align with a normal
Speaker 3: standard dark matter halo for a dwarf galaxy of that
Speaker 3: much smaller size.
Speaker 2: I see, So the missing dark matter would just be
Speaker 2: an artifact of putting the decimal point in the wrong
Speaker 2: place on the distance calculation precisely.
Speaker 3: The distance debate absolutely dominated the literature for over a year.
Speaker 3: I remember that teams ran independent analyzes utilizing different calibration methods,
Speaker 3: specifically looking at surface prightness fluctuations.
Speaker 2: Well, what's that.
Speaker 3: It's a statistical method for estimating distance based on the
Speaker 3: pixel to pixel variance in the galaxy's light. And some
Speaker 3: of those initial independent studies suggested DFI was indeed much closer.
Speaker 2: But the Yale team didn't just back down or stand
Speaker 2: by their initial data blindly, did they.
Speaker 3: No, they didn't. They secured highly contested observation time on
Speaker 3: the Hubble space telescope to execute what is really the
Speaker 3: gold standard of cosmic distance measurement.
Speaker 2: The tip of the red giant branch TRGB.
Speaker 3: Yes, the TRGB method is incredibly elegant.
Speaker 2: Walk us through how that works.
Speaker 3: So, when a medium mass star exhausts the hydrogen in
Speaker 3: its core, it expands into a red giant. Right, it
Speaker 3: starts burning hydrogen in a shell around an inert helium core. Okay,
Speaker 3: As the core contracts and heats up, it eventually hits
Speaker 3: a critical temperature and pressure where the helium rapidly ignites.
Speaker 2: That's a helium flash.
Speaker 3: Yes, the helium flash, and that flash, that specific evolutionary
Speaker 3: phase happens at a highly predictable, standardized intrinsic luminosity.
Speaker 2: So it functions as a standard candle.
Speaker 3: Precisely because we know the exact intrinsic absolute magnitude of
Speaker 3: a star at the tip of the red giant branch,
Speaker 3: if we can individually resolve those specific stars in a
Speaker 3: distant galaxy.
Speaker 2: And measure their apparent brightness from.
Speaker 3: Earth, then the inverse square law gives us a highly precise,
Speaker 3: unambiguous geometric distance.
Speaker 2: But it takes an incredible amount of resolving power to
Speaker 2: isolate individual red giant stars in a galaxy millions of
Speaker 2: light years away.
Speaker 3: It's incredibly difficult, but Hubble did it.
Speaker 2: Of course it did.
Speaker 3: They isolated the TRGB for DF two and the results
Speaker 3: were absolutely definitive.
Speaker 2: The distance was correct, It was correct.
Speaker 3: It was roughly twenty two megaparsex away. It was exactly
Speaker 3: as large and as massive as the Yale team originally claimed,
Speaker 3: which meant the velocity dispersion was genuinely anomalous.
Speaker 2: The dark matter was truly missing.
Speaker 3: It was really missing, and that confirmation was immediately followed
Speaker 3: in twenty nineteen by the discovery of.
Speaker 2: DF four, a virtual twin to DF two.
Speaker 3: Exactly located in the same NGC one off fifty two group,
Speaker 3: exhibiting the exact same missing dark matter profile.
Speaker 2: Two impossible structures, which brings us to the April twenty
Speaker 2: twenty six breakthrough. DF nine, the newcomer right the third
Speaker 2: ultraed diffuse galaxy in this specific system devoid of dark matter.
Speaker 2: But what elevates DF nine is the sheer precision of
Speaker 2: the kinematic data they acquired and the spatial relationship it
Speaker 2: shares with the other two.
Speaker 3: The data on DF nine is just beautiful Let's look
Speaker 3: at the instrumentation first.
Speaker 2: Because they utilize the Keck Cosmic Web Imager or CASEWI
Speaker 2: on the Kekit telescope. How did this instrument pull the
Speaker 2: velocity dispersion out of DF nine so precisely?
Speaker 3: KCWI is a spectacular piece of technology. It is an
Speaker 3: integral field spectrograph. Or ifs, how.
Speaker 2: Is that different from a normal spectrograph.
Speaker 3: Well, traditional spectrographs require you to place a narrow slit
Speaker 3: over a specific part of a galaxy, so you only
Speaker 3: get kinematic data for that tiny sliver. Oh I see, Yeah,
Speaker 3: if you want to map the whole galaxy, you have
Speaker 3: to move the slit, take another long exposure, move the
Speaker 3: slit again, and basically piece it together over countless nights of.
Speaker 2: Observation, which is incredile inefficient for a massive diffuse object
Speaker 2: where the light is already so spread.
Speaker 3: Out exactly it would say forever. But an integral field
Speaker 3: spectrograph like KCWI uses an image.
Speaker 2: Slicer and image slicer.
Speaker 3: Yeah, it takes the two dimensional image of the entire
Speaker 3: galaxy optically slices it into dozens of thin strips aligns.
Speaker 3: Those strips end to end into one giant pseudo slit
Speaker 3: feeds that light through the spectrograph grading, and then computer
Speaker 3: software reconstructs it into a three D data cube.
Speaker 2: The data cube right.
Speaker 3: Two axes represent the spatial X and Y coordinates of
Speaker 3: the galaxy, and the third axis represents wavelength.
Speaker 2: So for every single pixel in the image of DF nine,
Speaker 2: you get a full spectrum of light.
Speaker 3: Every single pixel you can see exactly what elements are
Speaker 3: absorbing light and how fast that specific patch of stars
Speaker 3: is moving.
Speaker 2: That's amazing it is.
Speaker 3: And they are looking very closely at absorption lines, specifically
Speaker 3: things like the Calciumer two H and K lines or
Speaker 3: the Bomber series of hydrogen.
Speaker 2: Okay, so when we talk about measuring velocity dispersion, here
Speaker 2: we are just looking at the overall red shift of
Speaker 2: the galaxy moving away from us due to cosmic expansion.
Speaker 1: No.
Speaker 3: No, we are looking at the Doppler broadening of those
Speaker 3: specific absorption.
Speaker 2: Lines, the smearing of the fingerprint, basically.
Speaker 3: Exactly the smearing in a galaxy with a high velocity dispersion.
Speaker 3: Some stars are orbiting rapidly toward our line of sight
Speaker 3: and their light is blue shifted. Other stars are orbiting
Speaker 3: rapidly away from us, and their light is red shifted.
Speaker 3: Because we can't resolve every single star individually, all their
Speaker 3: light blends together.
Speaker 2: So the sharp, narrow absorption line of calcium becomes mathematically broadened.
Speaker 2: It gets fat and smeared out.
Speaker 3: Yes, so if you measure the width of that absorption line,
Speaker 3: it tells you the spread of velocities within that population
Speaker 3: of stars.
Speaker 2: The fatter the line, the higher the velocity dispersion, the
Speaker 2: more mass of the dark matter halo must be to
Speaker 2: contain them.
Speaker 3: You've got it perfectly. And the data from KCWI on
Speaker 3: DF nine was stunning. They calculated the total stellar mass
Speaker 3: of DF nine to be approximately one point four times
Speaker 3: ten to the eighth solar masses.
Speaker 2: Around one hundred and forty million.
Speaker 3: Suns right, and based on standard LAMBDAICDM scaling relations, a
Speaker 3: dwarf galaxy of that stellar mass residing in a typical
Speaker 3: dark matter halo should exhibit a velocity dispersion approximately twenty
Speaker 3: seven kilometers per second.
Speaker 2: So the absorption line should have a very specific calculated
Speaker 2: with corresponding to twenty seven kilometers per second.
Speaker 3: Yes, But when they process the data cube from KEK,
Speaker 3: what do they see the absorption lines were incredibly narrow.
Speaker 3: The measured velocity dispersion was approximately six point four kilometers
Speaker 3: per second.
Speaker 2: Six point four compared to the expected twenty seven kinematic
Speaker 2: energy is just gone.
Speaker 3: It is a profound deficit. Even pushing the margins of
Speaker 3: error to their absolute limits, which maxed out around ten
Speaker 3: point four kilometers per second depending on the specific basion
Speaker 3: modeling framework they applied.
Speaker 2: Even at the absolute maximum of the air.
Speaker 3: Bar, it still falls catastrophically short of the expected dark
Speaker 3: matter profile. A velocity dispersion of six point four kilometers
Speaker 3: aligns perfectly, almost uncomfortably so with the gravitationable potential calculated
Speaker 3: from the luminous stellar mass alone.
Speaker 2: So one hundred and forty million solar asses of stars
Speaker 2: and gas generates just enough gravity to support stars moving
Speaker 2: at six point four kilometers per second exactly. The math
Speaker 2: closes without needing any invisible scaffolding. The dark matter is
Speaker 2: entirely absent.
Speaker 3: Which forces us to address the geometry of the situation.
Speaker 3: Because now we have DF two, D four and DF
Speaker 3: nine threena them three, but they aren't randomly distributed around
Speaker 3: the central elliptical galaxy. They are aligned along a distinct
Speaker 3: spatial linear trail.
Speaker 2: They form a line, a cosmic breadcrumb trail spanning over
Speaker 2: two megapar sects, which is what roughly six and a
Speaker 2: half million light years in length.
Speaker 3: Yes, and that linear alignment is the critical piece of
Speaker 3: forensic evidence here.
Speaker 2: Why is the line so important.
Speaker 3: Because it completely eliminates the possibility that these are primorial
Speaker 3: anomalies that just you know, coincidentally form without dark matter halos.
Speaker 3: The linear structure strongly implies a highly directional, violently dynamical origin.
Speaker 2: We are looking at the splatter pattern of a cosmic car.
Speaker 3: Crash, a very messy car crash.
Speaker 2: Specifically what astrophysicists referred to as a bullet dwarf collision.
Speaker 3: Right. The terminology is a direct nod to the famous
Speaker 3: Bullet Cluster, which was a much larger scale collision between
Speaker 3: two massive galaxy clusters that provided some of the earliest
Speaker 3: empirical evidence for the separation of dark and baryonic matter.
Speaker 3: Oh interesting, what we are seeing in the NNGC twent
Speaker 3: fifty two group is that exact same physical process, but
Speaker 3: scaled down to the interactions of individual dwarf galaxies.
Speaker 2: I want to really dig into the hydrodynamics of this
Speaker 2: collision because my initial intuition when I hear galaxies colliding
Speaker 2: is heavily biased by images of like the Antenna galaxies
Speaker 2: or the impending Milky Way Andromeda merger.
Speaker 3: Beautiful slow gravitational dances.
Speaker 2: Exactly. I picture this slow, billions of years long gravitational
Speaker 2: ballet where tidal forces stretch the galaxies out, their gas
Speaker 2: clouds tangle together, and eventually they coalesce and merge into
Speaker 2: one larger, unified system. Right, but that model doesn't explain
Speaker 2: the creation of a linear debris trail completely stripped of
Speaker 2: dark matter.
Speaker 3: No, it doesn't, because your intuition is describing a low
Speaker 3: velocity collision, which is indeed how the vast majority of
Speaker 3: galaxy merges occur. Okay, the relative velocities in those typical
Speaker 3: mergers are lower than the escape velocity of the combined system,
Speaker 3: so they are gravitationally bound to eventually merge.
Speaker 2: They can't escape each other.
Speaker 3: Right, but the bullet dwarf scenario is an entirely different
Speaker 3: kinematic beast. We are talking about a high velocity, highly supersonic,
Speaker 3: potentially head on collision. Now fast the relative velocity of
Speaker 3: the two progenitor dwarf galaxies exceeded their mutual escape velocity.
Speaker 3: We're talking hundreds of kilometers per second.
Speaker 2: So they aren't merging. They're glowing right through each other.
Speaker 3: They're passing right through one another. But the interaction fundamentally
Speaker 3: alters their composition due to the radically different physical properties
Speaker 3: the matter involved.
Speaker 2: This is where it gets so weird, it really does.
Speaker 3: We have to separate the galaxies into two distinct components,
Speaker 3: the collisionless n body system, which is.
Speaker 2: The dark matter and the existing.
Speaker 3: Stars, yes, and then the collisional fluid, which is the
Speaker 3: interstellar gas.
Speaker 2: Okay, let's start with the dark matter halos, two massive
Speaker 2: invisible gravitational wells rocketing toward each other at perhaps three
Speaker 2: hundred to four hundred kilometers per second. When they intersect.
Speaker 2: What actually happens.
Speaker 3: Physically, well, dark matter is essentially collisionless. It interacts almost
Speaker 3: exclusively via gravity. It doesn't possess electromagnetic charge, so it
Speaker 3: doesn't experience friction or fluid dynamics or ram pressure, so
Speaker 3: it doesn't hit anything exactly. When the two dark matter
Speaker 3: halos overlap, the individual dark matter particles simply pass right
Speaker 3: through each other like ghosts, Like ghosts. Their trajectories might
Speaker 3: be slightly perturbed by the shifting gravitational potential, sure, but
Speaker 3: they do not physically collide or slow down.
Speaker 2: The invisible scaffolding of the first galaxy just ghosts straight
Speaker 2: through the invisible scaffolding of the second galaxy. Percisely, they
Speaker 2: cross the intersection and keep moving at almost their original velocity,
Speaker 2: and the existing stars in those dwarf galaxies behave the
Speaker 2: exact same way they do.
Speaker 3: Because the space between stars is so vast, the odds
Speaker 3: of two stars physically hitting each other are effectively zero.
Speaker 3: They act as collisionless particles too, So.
Speaker 2: The dark matter halos and the older stellar populations essentially
Speaker 2: fly straight through the impact zone and continue on their way,
Speaker 2: largely intact.
Speaker 3: Largely intact, yes, but forever altered by what they leave behind.
Speaker 2: Because the interstellar medium, the vast clouds of cold hydrogen
Speaker 2: and helium gas, experiences a drastically different reality in that intersection.
Speaker 3: A much more violent reality. The gas is baryonic, it
Speaker 3: is a physical fluid.
Speaker 2: It's highly collisional, extremely collisional.
Speaker 3: When these massive gas clouds moving at hundreds of kilometers
Speaker 3: per second smashed into each other, the general immense ram
Speaker 3: pressure like a high speed car crash exactly right, and
Speaker 3: the collision is highly supersonic because the relative velocity of
Speaker 3: the impact drastically exceeds the internal sound speed of the
Speaker 3: cold interstellar gas, which might only be you know, ten
Speaker 3: kilometers per second.
Speaker 2: So they hit and it triggers a massive system wide shock.
Speaker 3: Front, a brutal shock front. The kinetic energy of the
Speaker 3: forward momentum is instantaneously converted into thermal energy through shock heating.
Speaker 2: Things get hot fast, very fast.
Speaker 3: The gas temperature sprit to millions of degrees, radiating away
Speaker 3: energy via brimstrolong or free emission. But mechanically, the critical
Speaker 3: factor is that the ram pressure completely halts the forward
Speaker 3: momentum of the gas. The physical gas clouds slam into
Speaker 3: each other, compress violently, and come to a dead stop
Speaker 3: right in the center of the impact zone.
Speaker 2: Wow, So the gas hits a brick wall, while the
Speaker 2: dark matter halos, being collisionless, just keep flying.
Speaker 3: They just keep going.
Speaker 2: The gas literally gets ripped out of its own gravitational potential. Well,
Speaker 2: the dark matter ghosts drive away, leaving the entire physical
Speaker 2: payload of gas dumped at the intersection.
Speaker 3: It is a complete violent decoupling of baryonic matter from
Speaker 3: dark matter.
Speaker 2: That is insane to picture, it's incredible.
Speaker 3: And as the dark matter halos continue moving apart, the
Speaker 3: immense volume of shocked compressed gas left behind in the
Speaker 3: intergalactic medium begins to.
Speaker 2: Cool, and as it cools, it loses pressure support, allowing
Speaker 2: gravity to take over.
Speaker 3: Yes, but and this is the crucial part. This gravity
Speaker 3: is entirely different. Now. It isn't being guided by a
Speaker 3: massive dark matter well anymore.
Speaker 2: Because the well left exactly.
Speaker 3: The well is gone. The gas has to rely purely
Speaker 3: on its own self gravity.
Speaker 2: Which usually isn't enough to form a galaxy.
Speaker 3: Right normally no, to collapse and form stars without the
Speaker 3: deep potential well of a dark matter halo, the gas
Speaker 3: must exceed the genes mass limit under its own weight alone.
Speaker 2: Okay, the gene's mass.
Speaker 3: Yeah, it's the critical mass where gravity overcomes internal gas pressure.
Speaker 3: Because the collision can press the gas so violently, it
Speaker 3: achieves the extreme densities required to trigger gravitational collapse on
Speaker 3: its own.
Speaker 2: The shockwave forced it past the.
Speaker 3: Limits exactly, the gas fragments and ignites, triggering a massive
Speaker 3: rapid starburst event. Along this two megaparsec debris trail.
Speaker 2: And because it is forming stars entirely out of that
Speaker 2: orphan compressed gas, the resulting galaxies DF two, D four,
Speaker 2: and DF nine are born completely naked, completely naked. They
Speaker 2: are entirely devoid of dark matter from the very moment
Speaker 2: of their creation.
Speaker 3: They condensed directly out of the cosmic shrapnel. And this
Speaker 3: specific hydrodynamical mechanism elegantly explains the other highly unusual features
Speaker 3: of these galaxies too, like the.
Speaker 2: Globular clusters you mentioned earlier that their globular clusters are bizarre.
Speaker 3: Yes, the globular clusters in these galaxies are significantly more
Speaker 3: luminous and massive than the clusters we find in standard
Speaker 3: bwarf galaxies of similar mass.
Speaker 2: Why is that?
Speaker 3: That is a direct signature of the high pressure environment
Speaker 3: of the post collision gas. In a standard dwarf galaxy,
Speaker 3: star formation is a relatively slow, inefficient process regulated by
Speaker 3: the depth of the dark matter. Well, and you know supernova.
Speaker 2: Feedback right to slowburn.
Speaker 3: But in the bullet dwarf scenario, you have a massive
Speaker 3: reservoir of gas that has been shock compressed to extreme densities.
Speaker 2: So it all collapses at once.
Speaker 3: Yes, when it collapses, it does so violently and efficiently,
Speaker 3: forging these over massive, incredibly dense globular clusters all at
Speaker 3: the same time.
Speaker 2: It's like comparing diamonds formed slowly deep in the Earth
Speaker 2: to diamonds forged instantaneously by the explosive pressure of a
Speaker 2: meteorite impact.
Speaker 3: That captures the physics perfectly. It's an explosive formation. Furthermore,
Speaker 3: because this was a single violent starburst event that exhausted
Speaker 3: or expelled the remaining cold gas rapidly, these galaxies are
Speaker 3: now entirely quiescent.
Speaker 2: Meaning they aren't actively forming stars anymore.
Speaker 3: No, they are just aging, quietly drifting along this linear
Speaker 3: trail populated by older, cooler stars. Every one thing we
Speaker 3: observe in DF nine flawlessly matches the predictive models of
Speaker 3: a high velocity dark matter stripping collusion.
Speaker 2: The forensic reconstruction of the bullet dwarf collision is just incredible.
Speaker 2: It paints a picture of a universe that is highly
Speaker 2: dynamic and frankly deeply violent.
Speaker 3: It's a messy place, it really is.
Speaker 2: But the significance of DF nine extends far beyond just
Speaker 2: explaining how a weird linear trail of galaxies formed. This
Speaker 2: specific discovery is fundamentally altering the landscape of theoretical.
Speaker 3: Physics, specifically regarding the most persistent debate and cosmology.
Speaker 2: Exactly does dark matter actually exist as a physical particle
Speaker 2: or is our math just wrong?
Speaker 3: It is the absolute crux of the issue. The existence
Speaker 3: of DF nine serves as a highly robust observational falsification
Speaker 3: of alternative gravity models.
Speaker 2: To understand why finding a galaxy without dark matter proves
Speaker 2: that dark matter is real, we really have to examine
Speaker 2: the mathematical architecture of the alternative modified Newtonian dynamics or MOND.
Speaker 3: Let's really dig into MOD because it's easy to dismiss
Speaker 3: it as a fringe theory, but mathematically it was a
Speaker 3: highly elegant, deeply reasoned response to the rotational curve problem
Speaker 3: we discussed earlier.
Speaker 2: Right If you look at the history, physicists were faced
Speaker 2: with a tough choice. Either of the universe is filled
Speaker 2: with a ghost particle that we cannot interact with, cannot
Speaker 2: directly detect in any collider, and cannot observe despite decades
Speaker 2: of highly funded, incredibly sensitive underground experiments, or Isaac Newton's
Speaker 2: gravitational equations just need a slight adjustment. What applied to
Speaker 2: galactic scales?
Speaker 3: Which is an entirely valid scientific hypothesis. It was first
Speaker 3: proposed by Mordehim Milgrim back in nineteen eighty.
Speaker 2: Three, and what's the core idea of M and D.
Speaker 3: The foundation of MOD is based on the observation that
Speaker 3: the discrepancies in galactic rotation curves do not randomly appear
Speaker 3: based on the size or mass of the galaxy. Rather,
Speaker 3: they appear specifically when the gravitational acceleration drops below a
Speaker 3: certain critical threshold.
Speaker 2: This is the A zero parameter.
Speaker 3: Right exactly the azero parameter. Milgrim proposed a fundamental constant
Speaker 3: of acceleration A zero, which is roughly one point two
Speaker 3: times ten to the negative tenth meters per second.
Speaker 2: Squared, which is an incredibly small acceleration.
Speaker 3: Heine mon D posits that in regimes of high acceleration,
Speaker 3: like our Solar system or the dense inner cores of galaxies,
Speaker 3: Newton's law of universal gravitation, where the force of gravity
Speaker 3: drops off with the square of the distance, holds perfectly true.
Speaker 2: So the mass we use to send probes to Mars
Speaker 2: or calculate the orbit of the Earth remains completely unchanged.
Speaker 3: Yes, unchanged. But Mond theorizes that when you move to
Speaker 3: the extreme outer edges of a galaxy, where the gravitational
Speaker 3: pull from the central mass becomes incredibly weak and the
Speaker 3: acceleration drops below that a zero threshold, the laws of
Speaker 3: physics change exactly. Gravity stops behaving according to the inverse
Speaker 3: square law. Instead, it transitions to a regime where it
Speaker 3: drops off linearly. It scales as one over R instead
Speaker 3: of one over R squared.
Speaker 2: Which means gravity becomes stronger relatively speaking over vast distances
Speaker 2: than Newton predicted.
Speaker 3: Precisely, it modifies the Poisson equation by tweaking how gravity
Speaker 3: behaves at extremely low accelerations. Mo and D mathematically perfectly
Speaker 3: reproduces the flat rotation curves of spiral galaxies and.
Speaker 2: The high velocity dispersions of dwarf galaxies.
Speaker 3: Yes, it explains the missing mass problem without needing to
Speaker 3: invent a single new particle. The extra gravity isn't coming
Speaker 3: from dark matter. It is baked into the fundamental geometry
Speaker 3: of space time at those specific accelerations.
Speaker 2: Okay, but if mon D is a fundamental law of physics,
Speaker 2: it has to be universal, right, It must, It must
Speaker 2: apply to every object in the universe experiencing low acceleration,
Speaker 2: which brings us right back to our anomalous Trio and Cetus.
Speaker 3: And this is exactly where the mon D framework encounters
Speaker 3: a critical structural failure. Because ulteredifuse galaxies like DF two,
Speaker 3: D four, and DF nine are so physically sprawling and
Speaker 3: their stellar mass is so low, their internal gravitational accelerations
Speaker 3: are incredibly.
Speaker 2: So the entirety of DF nine exists deep within the
Speaker 2: low acceleration regime, well below the zero threshold below it,
Speaker 2: which means, under the rules of MD, DF nine should
Speaker 2: be fully experiencing this modified stronger version of gravity.
Speaker 3: Yes, according to Mo and d the velocity dispersion of
Speaker 3: DF nine should be artificially high, driven by the modified
Speaker 3: laws of physics. It should exhibit the exact same kinematics
Speaker 3: as a dark matter dominated dwarf galaxy.
Speaker 2: The stars should be moving fast fast.
Speaker 3: Yes, But the KCWI data showed us unequivocally that they
Speaker 3: are not.
Speaker 2: They are moving at six point four kilometers per second.
Speaker 3: They are behaving exactly perfectly according to standard unmodified Newtonian dynamics.
Speaker 2: Wow.
Speaker 3: The fact that DF nine obeys purely Newtonian kinematics in
Speaker 3: a regime where Mond predicts it shouldn't completely breaks the
Speaker 3: universality of the M and D hypothesis in this context.
Speaker 2: I'm trying to visualize this tension because it feels like
Speaker 2: a massive philosophical shift if M and D were true.
Speaker 2: It's almost like, imagine gravity is the atmosphere. Okay, I'm
Speaker 2: with you, and we keep seeing these empty three p
Speaker 2: suits walking down the street, completely upright, holding their shape
Speaker 2: as if a person is inside them. Em ow D
Speaker 2: theorists look at the empty suits and say, there's no
Speaker 2: invisible man. The fundamental laws of aerodynamics in this specific
Speaker 2: neighborhood dictate that empty suits are supported by air pressure
Speaker 2: and forced to walk upright. The atmosphere is just modified here.
Speaker 3: That captures the deterministic nature of M and and D perfectly.
Speaker 3: The environment dictates the behavior right.
Speaker 2: But then we look at DF nine, we see an
Speaker 2: empty suit crumpled on the sidewalk, not moving, obeying normal,
Speaker 2: unmodified gravity, right in the middle of that exact same neighborhood.
Speaker 2: If the atmosphere itself was fundamentally modified to hold suits upright,
Speaker 2: that suit on the sidewalk should be walking too.
Speaker 3: But it's not, which means the law of aerodynamics isn't
Speaker 3: modified exactly.
Speaker 2: The fact that the suit is crumpled on the ground
Speaker 2: proves that the other suits walking down the street aren't
Speaker 2: being held up by a modified atmosphere. They're being held
Speaker 2: up by invisible men. I love this analogy, and we
Speaker 2: just happen to find the one suit that the invisible
Speaker 2: man took off and left behind. D K nine is
Speaker 2: the crumpled suit. It proves that dark matter isn't a fundamental,
Speaker 2: baked in modification of how gravity works across the universe.
Speaker 2: It proves dark matter is a distinct, physical, separable substance. Yes,
Speaker 2: you can take it away from the baryonic matter and
Speaker 2: the baryonic matter reverts to standard Newtonian behavior.
Speaker 3: That is an absolutely brilliant synthesis. The separability is the
Speaker 3: ultimate proof dark matter is an isolatable component of the universe.
Speaker 2: It's a real thing.
Speaker 3: It is now to be rigorous, we really must acknowledge
Speaker 3: how the M and D community has attempted to address this.
Speaker 3: They have proposed something called the external field effect or EFD.
Speaker 2: Oh I was wondering about that, Yeah, Because theoretically mond
Speaker 2: allows for a loophole if a massive external object is nearby. Right.
Speaker 3: Yes, The external field effect posits that if a low
Speaker 3: acceleration object like our dwarf galaxy DF nine, is deeply
Speaker 3: embedded in the strong grind gravitational field of a massive neighbor,
Speaker 3: in this.
Speaker 2: Case, the giant elliptical NNGC ten Ozho fifty two.
Speaker 3: Right, the external acceleration can override the internal MO and
Speaker 3: D dynamics. Essentially, the strong background gravity of the giant
Speaker 3: neighbor pulls the dwarf galaxy back into the Newtonian regime.
Speaker 2: It violates the strong equivalence principle, but mathematically it offers
Speaker 2: to defense, so does the EFE save m D. In
Speaker 2: the case of DF nine.
Speaker 3: It requires extreme fine tuning for the external field effect
Speaker 3: to perfectly cancel out the m O D behavior and
Speaker 3: result in the exact six point four kilometers velocity dispersion
Speaker 3: we observe. DF nine, DF two, and DF four would
Speaker 3: have to be situated at highly specific, precise distances from
Speaker 3: the central elliptical.
Speaker 2: Galaxy like incredibly lucky positioning.
Speaker 3: Yes, but our three D spatial modeling of the n
Speaker 3: GC one oh fifty two group suggests they are not
Speaker 3: deep enough within that potential well for the EFE to
Speaker 3: fully explain the discrepancy without stretching the parameters to their
Speaker 3: absolute breaking point.
Speaker 2: It requires too many coincidences.
Speaker 3: Exactly. While the bait will certainly continue in the literature,
Speaker 3: the consensus forming around the bullet dwarf collision model provides
Speaker 3: a naturally occurring hydrodynamically sound mechanism that elegantly explains every
Speaker 3: observed anomaly of these galaxies without needing to invent complex
Speaker 3: loopholes in modified gravity.
Speaker 2: Right, the physics just works.
Speaker 3: DF nine strongly reinforces the LAMB to CDM model. Dark
Speaker 3: matter is real. It just isn't there anymore.
Speaker 2: This totally rewrites the textbook on galaxy formation channels. Honestly,
Speaker 2: we've always assumed that dark matter halo was the absolute prerequisite,
Speaker 2: the required foundation before you could pour the concrete of a.
Speaker 3: Galaxy, the required starting point.
Speaker 2: Yeah. DF nine proves you can build the house without
Speaker 2: the foundation, provided the materials are subjected to enough trauma.
Speaker 3: That's a good way to phrase it. It introduces collision
Speaker 3: induced dwarf galaxies as a distinct, viable evolutionary path.
Speaker 2: So, with this new framework established, what is the astrophysics
Speaker 2: community doing right now, where does the cosmic laboratory go next?
Speaker 3: Well, the mobilation is happening across multiple domains, observational and theoretical.
Speaker 3: On the observational front, these objects are now absolute prime
Speaker 3: targets for the James Web Space Telescope.
Speaker 2: Oh, of course JWST.
Speaker 3: Yeah. While KEK provided incredible kinematic data, JWST's near infrared
Speaker 3: camera in ierarc cam and its Near Infrared spectrograph and
Speaker 3: URSPEC offer unparalleled capabilities to resolve the individual stellar populations
Speaker 3: deep within DF nine Because.
Speaker 2: We want to forensically deep the collision. Right, we know
Speaker 2: it happened roughly eight billion years ago, but JWST can
Speaker 2: tighten that timeline dramatically.
Speaker 3: JWUST can map the asymptotic giant branch stars and precisely
Speaker 3: measure the metallicity metallicity.
Speaker 2: Being the ratio of a heavy elements like iron.
Speaker 3: To hydrogen right denoted as FAY over H. They will
Speaker 3: also look really closely at alpha element enhancements. Does that
Speaker 3: tell us so when that violent starburst occurred post collision?
Speaker 3: The massive short lived stars exploded as core collapse supernovae right,
Speaker 3: and the supernova enrich the surrounding gas with alpha elements
Speaker 3: like oxygen and magnesium very rapidly.
Speaker 2: Oh, before the lower mass stars had time to evolve
Speaker 2: and produce iron.
Speaker 3: Precisely, by measuring that specific chemical abundance ratio just can
Speaker 3: pinpoint not just the age of the stars, but the
Speaker 3: exact duration and intensity of the starburst event.
Speaker 2: That's incredible.
Speaker 3: It will tell us exactly how fast that collision compressed
Speaker 3: the gas and how rapidly the star formation quenched afterward.
Speaker 2: And beyond deeply analyzing the three we have, the hunt
Speaker 2: has to be scaling up to find more. Right, a
Speaker 2: two megaparsec debris trail has to contain more surviving fragments.
Speaker 3: Oh, the search space is vast, but we are entering
Speaker 3: the era of extreme wide field surveys. The via C
Speaker 3: Reuben Observatory conducting the Legacy Survey of Space and Time
Speaker 3: or LSST, is going to be revolutionary here.
Speaker 2: With its what three point two gigapixel camera.
Speaker 3: Yes, it will repeatedly image the entire visible sky, specifically
Speaker 3: optimized to detect the incredibly faint, low surface brightness universe
Speaker 3: that traditional surveys just miss.
Speaker 2: It will map the few structures that are essentially invisible
Speaker 2: to us.
Speaker 3: Right now, it is highly probable that the Reuben observatory
Speaker 3: will identify extended tidle features, fainter stellar streams, and potentially
Speaker 3: dozens of smaller dark matter free fragments scattered along the
Speaker 3: NNGC ten fifty two trail.
Speaker 2: And when Reuben identifies those candidates, then the massive ground
Speaker 2: based telescopes, the extremely large telescope currently under construction, and
Speaker 2: the very large telescope will follow up with high resolution
Speaker 2: integral field spectroscopy to confirm their missing dark matter profiles.
Speaker 2: So we're basically building a pipeline to find these ghost galaxies.
Speaker 3: Exactly a dedicated pipeline, and.
Speaker 2: While the observers are mapping the sky, the theorists have
Speaker 2: to be running supercomputer simulations to see how often this
Speaker 2: actually happens. Because a bullet dwarf collision seems like an
Speaker 2: insanely specific alignment.
Speaker 3: It does seem rare, and the theoretical teams are heavily
Speaker 3: invested in running advanced hydrodynamical simulations right now. These are
Speaker 3: incredibly computationally expensive. By the way, I can imagine, you
Speaker 3: can't just run an n body simulation model and gravity alone.
Speaker 3: You have to run Eularian grid based codes or smooth
Speaker 3: particle hydrodynamics to accurately model the shock heating, the ram
Speaker 3: pressure stripping, and the radiative cooling of the gas simultaneously
Speaker 3: with the collisionless dark matter.
Speaker 2: So they're building digital models of the collision, tuning the knobs,
Speaker 2: changing the impact parameter, adjusting the relative velocity to three
Speaker 2: hundred or four hundred klometers per second, altering the initial
Speaker 2: gas fraction of the dwarf galaxies just to see exactly
Speaker 2: what initial conditions yield a DF nine.
Speaker 3: Yes, they're playing with all the variables, and the overarching
Speaker 3: goal of those simulations is to determine the statistical frequency
Speaker 3: of these events across cosmic time.
Speaker 2: Is the NNGC one F two system once in the
Speaker 2: universe anomaly right?
Speaker 3: Or because the early universe was much denser and interactions
Speaker 3: were more frequent, were these high velocity dark matter stripping
Speaker 3: collisions relatively common?
Speaker 2: Wow? If they were common, there could be a massive
Speaker 2: hidden population of dark matter free galaxies out there, fundamentally
Speaker 2: challenging our senses of the cosmos.
Speaker 3: It's a very real possibility.
Speaker 2: It forces us to reevaluate how much of the universe
Speaker 2: is pristine and how much of it is actually just
Speaker 2: surviving wreckage.
Speaker 3: It really does.
Speaker 2: It has been an intensely complex narrative to untangle today.
Speaker 2: We started by examining the mathematical tension inherent in the
Speaker 2: virial theorem, the requirement for dark matter to stabilize the
Speaker 2: high velocity dispersions observed in galactic structures.
Speaker 3: Right the invisible seat celts.
Speaker 2: We then tracked the forensic data from the low surface
Speaker 2: brightness imaging of the Dragonfly array to the highly contested
Speaker 2: distance measurements utilizing the tip of the red Giant branch,
Speaker 2: and ultimately the definitive Keck integral field spectroscopy that recorded
Speaker 2: DF nine's anomalous six point four kilometer per second velocity dispersion.
Speaker 3: And we move from observing the anomaly to uncovering its
Speaker 3: violent origins.
Speaker 2: The bullet Dwarf collision.
Speaker 3: Yes, the hydrodynamics of the highly supersonic bullet Dwarf collision
Speaker 3: demonstrated how collisional bearonic gas can be violently shock heated
Speaker 3: and entirely stripped away from its collisionless dark matter halo,
Speaker 3: collapsing under its own immense pressure to forge massive globular
Speaker 3: clusters and dark matter free galaxies.
Speaker 2: And finally we synthesized how that dynamical separation serves as
Speaker 2: the definitive counter argument to modified gravity theories like Mond
Speaker 2: the crumpled suit the crumpled suit. By demonstrating that DF
Speaker 2: nine behaves precisely according to Newtonian dynamics in the low
Speaker 2: acceleration regime, it isolates dark matter as a distinct physical
Speaker 2: entity that was dynamically left behind, not a universal modification
Speaker 2: of gravity.
Speaker 3: It is a profound demonstration of the scientific process, really,
Speaker 3: where a singular, anomalous observation forces a comprehensive reevaluation of
Speaker 3: both theoretical physics and our models of galaxy formation.
Speaker 2: As we conclude this exploration, I will leave you contemplating
Speaker 2: the structural reality of the night's sky. For decades, we
Speaker 2: have looked up and assumed a universal uniformrmity that every
Speaker 2: glowing collection of stars is cradled securely within a massive,
Speaker 2: invisible gravitational.
Speaker 3: Well the standard model, right.
Speaker 2: But DF nine and its siblings along that violent two
Speaker 2: megaparsek trail shatter that assumption. They are architectural impossibilities that
Speaker 2: survive to cataclysm.
Speaker 3: They are the exceptions that prove the rule exactly so.
Speaker 2: The next time you observe the deep Sky, consider the
Speaker 2: invisible violence required to forge it. How many other seemingly serene,
Speaker 2: quiescent galaxies drifting through the void are actually completely hollowed
Speaker 2: out ghost towns, ghost towns. How much of the universe's
Speaker 2: quiet beauty is actually composed of the faint, orphan shrapnel
Speaker 2: of ancient invisible collisions. How many massive houses are floating
Speaker 2: out there are perfectly intact, entirely missing their invisible columns,
Speaker 2: waiting to be found.