Speaker 1: Welcome to Bedtime Astronomy. Explore the wonders of the cosmos
Speaker 1: with our soothing Bedtime Astronomie podcast. Each episode offers a
Speaker 1: gentle journey through the stars, planets, and beyond, perfect for
Speaker 1: unwinding after a long day. Let's travel through the mysteries
Speaker 1: of the universe as you drift off into a peaceful
Speaker 1: slumber under the night sky.
Speaker 2: I want you to start by visualizing something with me.
Speaker 2: Picture a massive, heavy velvet tapestry and it's pitch black,
Speaker 2: absolutely lightless. But woven into this black fabric are these
Speaker 2: brilliant shimmering threads of gold and silver. It's a pretty
Speaker 2: classic image, right, Yeah.
Speaker 3: That's the standard metaphor for the universe. People call it
Speaker 3: the cosmic web.
Speaker 2: Right because when we look up at the night sky,
Speaker 2: or you know, we look at those incredible composite images
Speaker 2: from NASA, that is exactly what we see. We see
Speaker 2: the light. We see billions of galaxy whirling in the void,
Speaker 2: glowing with the heat of trillions of stars. We fundamentally
Speaker 2: define the universe by what shines.
Speaker 3: Well, because that is what our eyes are built to do.
Speaker 3: We are biological light detectors. Our entire history of astronomy,
Speaker 3: from the ancient Greeks drawing constellations to Hubble taking deep
Speaker 3: field images has been biased toward luminosity.
Speaker 2: If it glows, it exists exactly.
Speaker 3: And if it doesn't glow, we assume it's just empty
Speaker 3: space the void.
Speaker 2: But and this is why we are here today doing
Speaker 2: this exploration. What if that assumption is fundamentally flawed.
Speaker 3: It's a huge question.
Speaker 2: What if that tapestry is actually full of things woven
Speaker 2: with black thread against a black background, Objects that are massive, complex,
Speaker 2: and gravitationally significant, but effectively invisible.
Speaker 3: It is a really disquieting thought. When you dig into
Speaker 3: the research, it suggests that our map of the universe
Speaker 3: is not actually a map of mass. Oh interesting, Yeah,
Speaker 3: it's merely a map of light bulbs, and we might
Speaker 3: be missing the vast majority of the furniture in the room,
Speaker 3: so to speak.
Speaker 2: That is exactly what we are unpacking today. We're looking
Speaker 2: at a specific discovery from our sources that challenges the
Speaker 2: very definition of what a galaxy is. Yes, we are
Speaker 2: talking about a ghost hiding in the Perseus cluster, a
Speaker 2: galaxy named CDG two.
Speaker 3: CDG two is just a fascinating case study. It's an
Speaker 3: object that breaks the usual rules of galactic formation.
Speaker 2: Breaks the rules, feels like an understatement to me. When
Speaker 2: I was reading the research on this, one statistic jumped
Speaker 2: out and just sat there staring at me.
Speaker 3: The mass ratio, Yes.
Speaker 2: We usually think of galaxies as star factories, right, but
Speaker 2: this thing, this galaxy appears to be ninety nine percent
Speaker 2: dark matter.
Speaker 3: Ninety nine percent. It is an immense figure.
Speaker 2: So if I'm doing the math right, that leaves roughly
Speaker 2: one percent for the stuff we can actually see, you know,
Speaker 2: the stars, the gas, the.
Speaker 3: Dust, the buryonic matter, baryonic right, the normal stuff that
Speaker 3: makes up you, me, the Earth, and the Sun in
Speaker 3: this galaxy, all of that is essentially a rounding era
Speaker 3: that is just wild.
Speaker 2: To think about. But before we get too far into
Speaker 2: the wow factor of it all, I want to push
Speaker 2: back on this a little bit. We talk about dark
Speaker 2: matter a lot. We know our own Milky Way has
Speaker 2: dark matter. We know it's the gravitational glue that keeps
Speaker 2: galaxies from spinning apart. So is ninety nine percent actually
Speaker 2: that weird? What is the standard ratio?
Speaker 3: That is a very important distinction to make you are right?
Speaker 3: Almost every galaxy has a dark matter halo. But typically
Speaker 3: the cosmic ratio is about five to one fave to one,
Speaker 3: five parts dark matter to one part visible matter.
Speaker 2: Okay, so five to one versus ninety nine to one.
Speaker 3: Exactly In a normal galaxy like the Milky Way, the
Speaker 3: dark matter provides the structure that the visible matter, the
Speaker 3: gas and stars, has collapsed into the center to form
Speaker 3: a bright, churning.
Speaker 2: Disc right the spiral we always see.
Speaker 3: Yeah, the baryonic physics are very active. Yeah. In CDG two,
Speaker 3: that process seems to have short circuited.
Speaker 2: Entirely short circuited.
Speaker 3: How well, It's like a house built almost entirely of
Speaker 3: invisible bricks, with just a few effects of dust floating
Speaker 3: inside to prove it's actually.
Speaker 2: There, Which brings us to the definition problem. If you
Speaker 2: have a clump of dark matter with almost no stars,
Speaker 2: is it even a galaxy or is it just a
Speaker 2: halo that failed to do anything?
Speaker 3: That is the existential crisis as strongers are grappling with
Speaker 3: right now.
Speaker 2: Really, oh yeah.
Speaker 3: Traditionally a galaxy is defined by its starlight, but objects
Speaker 3: like CDG two suggest that a galaxy should really be
Speaker 3: defined by its gravitational potential. It's dark matter halo so.
Speaker 2: The stars are just an afterthought exactly.
Speaker 3: The stars are just the ornamentation, they aren't the structure itself.
Speaker 2: So our mission today for you listening is to understand
Speaker 2: this ghost. We aren't just going to gawk at the
Speaker 2: ninety nine percent number. We really need to understand the
Speaker 2: detective work here. The methodology is the best part, because
Speaker 2: finding something that emits almost no light in a universe
Speaker 2: that is incredibly big and incredibly dark seems like an
Speaker 2: impossible task.
Speaker 3: It borders on the impossible. This isn't just an observation,
Speaker 3: it's really a forensic investigation.
Speaker 2: It really is a cosmic crime scene. We have a
Speaker 2: ghost galaxy hiding in a very rough neighborhood called the
Speaker 2: Perseus Cluster, very rough. We have a team of detectives
Speaker 2: using three of the most powerful telescopes ever built. And
Speaker 2: they used a technique that I found absolutely brilliant in
Speaker 2: the source.
Speaker 3: Material, always so clever.
Speaker 2: They didn't look for the galaxy itself. They looked for
Speaker 2: the well, let's call them the ornaments.
Speaker 3: Globular clusters. They were hunting for globular clusters.
Speaker 2: So let's set the scene. We are going to the
Speaker 2: Perseus Cluster.
Speaker 3: Very chaotic noisy place in the universe.
Speaker 2: Let's start with the visual or I guess the lack thereof.
Speaker 2: The research comes from a collaboration evolving NASA, the European
Speaker 2: Space Agency, in the University of Toronto, and they released
Speaker 2: an image from the Hubble Space telescope. Now, usually when
Speaker 2: you see a Hubble press release, you expect fireworks, WAPs,
Speaker 2: you expect nebulas, pillars of creation giants, sweeping spiral arms.
Speaker 3: You expect high contrast, bright whites, deep blacks, vibrant colors
Speaker 3: all over the place, right.
Speaker 2: But I looked at the image for CDG two, specifically
Speaker 2: the crop they provided in the material, there is a
Speaker 2: dashed red circle drawn on the blackness of space, just
Speaker 2: to tell me where to look. And what did you
Speaker 2: see inside that circle? I literally had to wipe my monitor.
Speaker 2: I thought it was a smudge on my screen.
Speaker 3: It is incredibly underwhelming to the naked eye, isn't it.
Speaker 2: It looks like noise. It's just a faint, barely there haze.
Speaker 3: That is what astronomers classify as a low surface brightness galaxy.
Speaker 2: Low surface brightness the term.
Speaker 3: Is quite literal, the surface brightness meaning the amount of
Speaker 3: light emitting from any given square arc second of the
Speaker 3: sky is so low that it's barely distinguishable from the
Speaker 3: background radiation of the universe.
Speaker 2: So let's try to ground this for you listening. If
Speaker 2: I were in a spaceship floating just outside this galaxy
Speaker 2: looking out the window, what would I see? What I see?
Speaker 2: A galaxy?
Speaker 3: Honestly, you wouldn't see a structure. You wouldn't see a
Speaker 3: disk or spiral arms, or a glowing core, nothing like that. No,
Speaker 3: you would see a very sparse scattering of faint stars.
Speaker 3: It wouldn't look like a cohesive object. It would just
Speaker 3: look like you were in a slightly more populated region
Speaker 3: of empty space.
Speaker 2: It's a galaxy running on one percent battery.
Speaker 3: That's a good analogy to put a number on it.
Speaker 3: The paper notes that CDG two has a total luminosity
Speaker 3: equivalent to roughly six million sun like stars.
Speaker 2: Okay, stop there, six million sons. To me and probably
Speaker 2: to you listening, six million suns sounds like a blinding
Speaker 2: amount of light. That sounds huge.
Speaker 3: It sounds massive in human terms. Yes, but we have
Speaker 3: to adjust our scale to galactic terms.
Speaker 2: Okay, adjusted for me.
Speaker 3: For context, the Milky Way contains somewhere between one hundred
Speaker 3: and four hundred billion stars.
Speaker 2: Wow, one hundred to four hundred billion.
Speaker 3: To do the math there, six million versus four hundred
Speaker 3: billion CDG two is putting out less than zero point
Speaker 3: zero one percent of the light of the Milky Way.
Speaker 2: That is nothing.
Speaker 3: It is a whisper compared to a shout.
Speaker 2: And it's not just that it's faint, it's where it is.
Speaker 2: We are looking at an object inside the Percus galaxy cluster.
Speaker 2: How far away is this?
Speaker 3: We are looking at a distance of roughly three hundred
Speaker 3: million light years.
Speaker 2: Three hundred million light years. I want to pause on
Speaker 2: that number because I think we get really numb to
Speaker 2: millions and billions in space talk.
Speaker 3: It's hard for the human brain to process.
Speaker 2: Right. The light we are seeing from this faint smudge
Speaker 2: left the galaxy three hundred million years ago. That's the Palaeozoic.
Speaker 3: Era on Earth, long before the dinosaurs. We are talking
Speaker 3: about the time when the first reptiles were just emerging
Speaker 3: on Earth. The continents were in completely different positions.
Speaker 2: So we are trying to spot a faint collection of
Speaker 2: six million stars, which is basically nothing, from a distance
Speaker 2: that is incomprehensibly far away. It's like trying to see
Speaker 2: a candle in the moon, but the candle is behind
Speaker 2: a giant searchlight, the searchlight being.
Speaker 3: The rest of the Perseus cluster. You have to understand,
Speaker 3: Perseus is one of the most massive objects in the
Speaker 3: entire known universe. Really, Oh yeah, it contains thousands of galaxies.
Speaker 3: It is full of hot X ray emitting gas. It
Speaker 3: is bright, it is crowded, and it is gravitationally noisy.
Speaker 3: Finding CDG two in there is statistically nightmarish.
Speaker 2: And that leads me to the how if you can't
Speaker 2: just stand the sky and see it, Because as we establish,
Speaker 2: it looks like nothing, how do you find it? You
Speaker 2: can't just zoo in on every single pixel of the sky.
Speaker 3: Now you would never finish. Yeah, the universe is too big.
Speaker 3: You need a marker, you need a proxy.
Speaker 2: Entered David Lai. He's the lead researcher from the University
Speaker 2: of Toronto on this project. Yes, and his team didn't
Speaker 2: start by looking for the galaxy itself. They started by
Speaker 2: hunting for those ornaments we mentioned earlier.
Speaker 3: They went looking for globular clusters.
Speaker 2: Okay, let's unpack globular clusters because to me, it sounds
Speaker 2: like a type of candy or maybe a geology term.
Speaker 2: What exactly is a globular cluster In this astronomical context,
Speaker 2: it is.
Speaker 3: One of the most ancient and fundamental structures in the cosmos.
Speaker 3: A globular cluster is a very compact, spherical group of stars. Spherical, right,
Speaker 3: Imagine a ball maybe ten to thirty light years across,
Speaker 3: but packed with tens of thousands, sometimes even millions of stars.
Speaker 2: So it's a super dense city of stars.
Speaker 3: Extremely dense. In the solar neighborhood where we are, stars
Speaker 3: are light years apart in the core of a globular cluster.
Speaker 3: They are packed cheek by jowl, and the key characteristic
Speaker 3: for this study is that globular clusters are typically found
Speaker 3: orbiting normal.
Speaker 2: Galaxies, orbiting them like moons around a planet.
Speaker 3: Kind of The Milky Way has about one hundred and
Speaker 3: fifty of them. They swarm around the galacticiclo like bees
Speaker 3: around a hive.
Speaker 2: Okay, so the clusters are the bees.
Speaker 3: The galaxy is the high right now, imagine you are
Speaker 3: looking at a hive at night from a mile away.
Speaker 2: It's pitch black.
Speaker 3: You can't see the hive itself. It blends completely into
Speaker 3: the darkness of the trees. But suppose the bees are bioluminescent.
Speaker 3: Suppose they glow.
Speaker 2: Ah, if I see a swarm of glowing bees hovering
Speaker 2: in a specific tight formation, I can safely assume the
Speaker 2: hive is sitting right in the middle of them.
Speaker 3: That is precisely the logic. This is the big breakthrough.
Speaker 3: CDG two is the first galaxy detected solely through its
Speaker 3: globular cluster population.
Speaker 2: I want to make sure I really get the difficulty
Speaker 2: of this though. At three hundred million light years away,
Speaker 2: does a globular cluster look like a ball of stars
Speaker 2: in a telescope?
Speaker 3: No, even with hubble at that immense distance, a globular
Speaker 3: cluster is what we call a point source, meaning it
Speaker 3: looks like a single pixel, looks exactly like a single
Speaker 3: faint star in our own milky way that just happens
Speaker 3: to be in the foreground. Yeah. Or it looks like
Speaker 3: a very distant background galaxy.
Speaker 2: So you have a field of view full of thousands
Speaker 2: of tiny dots. Some are foreground stars, some are background galaxies,
Speaker 2: and a very small few are these globular clusters exactly?
Speaker 2: How do you know which a witch?
Speaker 3: That is the real trick of this whole endeavor. You
Speaker 3: can't just look at the dots individually. You have to
Speaker 3: look at the statistics of the dots. Statistics explain that
Speaker 3: this is where David Lye's work is so incredibly impressive.
Speaker 3: They used a sophisticated algorithm to scan the overall distribution
Speaker 3: of these points of light. Okay, random noise, meaning your
Speaker 3: foreground stars and your background galaxies, tends to be distributed
Speaker 3: somewhat uniformly across the sky, or at least randomly scattered.
Speaker 2: This is a general spread.
Speaker 3: Right, But globular clusters that belong to a single galaxy
Speaker 3: aren't random at all. They're gravitationally bound to each other
Speaker 3: and to the host galaxy. They cluster together.
Speaker 2: So they were specifically looking for a tight grouping of dots.
Speaker 3: Exactly, they were looking for a statistical anomaly. The algorithm
Speaker 3: essentially asks, is there a region in this patch of
Speaker 3: sky where I see three or four of these specific
Speaker 3: point sources huddled together in a way that is highly
Speaker 3: unlikely to happen just by random chance.
Speaker 2: I see. It's like walking into a crowded sports stadium.
Speaker 2: You can't tell who knows who just by looking at
Speaker 2: the giant sea of faces.
Speaker 3: No, you can't.
Speaker 2: But if you see four people standing in a tight
Speaker 2: little circle facing each other, ignoring everyone else, you assume
Speaker 2: they are a group. They came together.
Speaker 3: That's a perfect analogy. The algorithm flagged these friends. It said, Hey,
Speaker 3: at these specific coordinates, there are four objects that seem
Speaker 3: to be hanging out together.
Speaker 2: And because gravity works the way it does, yes.
Speaker 3: If you have four massive star clusters hanging out in
Speaker 3: the tight group, there must be something massive in the
Speaker 3: middle holding them there.
Speaker 2: And that unseen massive something is the dark matter halo
Speaker 2: of CDG two.
Speaker 3: Correct Using this method, they identified ten previously confirmed low
Speaker 3: surface brightness.
Speaker 2: Galaxies, which prove the math works exactly.
Speaker 3: It validated the tool, and then using that validated tool,
Speaker 3: they found two new candidates. CGG two was one of them.
Speaker 2: I love that so much. They didn't see the galaxy,
Speaker 2: they calculated that it absolutely must be there. It's a
Speaker 2: triumph of math as much as it is observation.
Speaker 3: Which is really where modern astronomy is heading. As a field.
Speaker 3: We are rapidly moving from point and shoot astronomy to
Speaker 3: massive data mining.
Speaker 2: But as with any good detective investigation, just having a
Speaker 2: suspect isn't enough. You can't publish a paper saying the
Speaker 2: math says there's a galaxy here.
Speaker 3: Trust us, you definitely cannot. You need to verify it
Speaker 3: and see the body to keep the crime scene metaphor going.
Speaker 2: And that requires the heavy artillery. It does verification triad.
Speaker 2: I really like the sound of that from the research.
Speaker 3: It does sound official, doesn't it. It refers to the
Speaker 3: three major observatories they used in tandem to confirm this candidate,
Speaker 3: because no single telescope on Earth or in space could
Speaker 3: do the whole job.
Speaker 2: Let's break down why that is. Why did they need
Speaker 2: three different telescopes. Let's start with the most famous one
Speaker 2: of the bunch, NASA's Hubble Space telescope.
Speaker 3: Hubble is the sniper of the group.
Speaker 2: The sniper.
Speaker 3: Yes, it has incredible pinpoint resolution. They needed Hubble to
Speaker 3: confirm that those four suspicious dots were actually globular clusters
Speaker 3: and not just something else masquerading A Is that?
Speaker 2: So Hubble gives you the fine detail.
Speaker 3: Hubble provided the sharpness to resolve the immediate local environment
Speaker 3: of those four points.
Speaker 2: Okay, so Hubble confirms the ornaments are real. Who is
Speaker 2: next in the triad?
Speaker 3: Next is ESA's EUCLID Space Observati Tory, the European Space Agency.
Speaker 3: This is a newer mission and it's critical for a
Speaker 3: totally different reason. Hubble has a very, very narrow field
Speaker 3: of view. It basically looks at a tiny straw hole
Speaker 3: of the sky at any given moment. EUCLID, on the
Speaker 3: other hand, is wide angle. It surveys huge swaths of
Speaker 3: the cosmos all at once.
Speaker 2: But why do you need a wide angle to see
Speaker 2: a tiny, faint galaxy.
Speaker 3: You need context. You need to know that this tight
Speaker 3: grouping of four clusters is truly isolated in space. Oh,
Speaker 3: I see, you need to see the surrounding neighborhood to
Speaker 3: ensure these clusters aren't just the far outskirts of some other,
Speaker 3: much bigger galaxy nearby. EUCLID confirms the isolation.
Speaker 2: Got it. Hubble zooms in to check the details. EUCLID
Speaker 2: zooms out to check the neighborhood. And the third telescope.
Speaker 3: The Subreu telescope. This is a ground based monster located
Speaker 3: on Monachia in Hawaii.
Speaker 2: Now, why do we need a ground telescope if we
Speaker 2: already have two amazing space telescopes. Usually we think space
Speaker 2: is better because there's no atmosphere to distort the image.
Speaker 3: Space gives you clarity. Yes, the ground gives you size.
Speaker 3: You can build much bigger things on the ground.
Speaker 2: Size matters here very much.
Speaker 3: The Subaru telescope has a primary mirror that is over
Speaker 3: eight meters wide. Hubble's mirror is only two point four meters.
Speaker 2: That's a huge difference.
Speaker 3: It is. Think of it like catching rain. A bigger
Speaker 3: bucket catches more rain. In this case, the rain is
Speaker 3: light photons.
Speaker 2: So Subro is essentially a giant light bucket exactly.
Speaker 3: They needed Subru's immense light gathering power to try and
Speaker 3: detect the incredibly faint glow between those clusters the actual
Speaker 3: galaxy itself.
Speaker 2: And this is the real moment of truth in the story.
Speaker 2: They combine the data from the sniper, the wide angle,
Speaker 2: and the light bucket. What did they actually find.
Speaker 3: They found the ghost when they process the deep imaging,
Speaker 3: specifically looking at the empty space between those four colobular clusters.
Speaker 2: Yeah, they detected a signal, a signal like a radio
Speaker 2: sign row.
Speaker 3: An optical signal, a faint, diffuse structural glow. It wasn't
Speaker 3: just empty black space, was a very very weak stellar
Speaker 3: population surrounding those clusters.
Speaker 2: That is the body of the galaxy.
Speaker 3: That is the body. It confirmed once and for all
Speaker 3: the clusters weren't just randomly floating in the void. They
Speaker 3: were embedded in a dark matter halo. They were anchoring
Speaker 3: a hidden stellar population.
Speaker 2: So the Christmas tree analogy holds up perfectly. They saw
Speaker 2: the glowing ornaments, they did the math to prove they
Speaker 2: were a group, and when they turned up the exposure
Speaker 2: time with the big telescope, they finally saw the faint
Speaker 2: outline of the trees branches precisely.
Speaker 3: And David Lay makes a very conservative, but very interesting
Speaker 3: point here in the findings.
Speaker 2: What's that?
Speaker 3: He notes they given the mass calculations of the halo,
Speaker 3: these four clusters likely represent the entire globular cluster population
Speaker 3: of CDG two.
Speaker 2: Wait only four? You just said our Milky Way has
Speaker 2: one hundred and fifty.
Speaker 3: Yes, CDG two is hanging onto these four clusters for
Speaker 3: dear life. They're the only major structural features it has left.
Speaker 2: That brings us to the why. This is the part
Speaker 2: of the exploration that really hooked me. We have a
Speaker 2: gaps galaxy that is ninety nine percent dark matter, has
Speaker 2: almost no stars and only four Measley clusters.
Speaker 3: It's a barren place.
Speaker 2: Why is it so empty? Did it form this way
Speaker 2: right after the Big Bang? Or does something terrible happen
Speaker 2: to it?
Speaker 3: Now we are moving from detection to forensics. We're looking
Speaker 3: at the cause of death, or perhaps more accurately, the
Speaker 3: cause of sterility.
Speaker 2: Sterility, that's a strong word for a galaxy.
Speaker 3: Well, a galaxy lives in astronomical terms, as long as
Speaker 3: it forms new stars. Ok, deform stars. You need fuel,
Speaker 3: and the fuel of the universe is hydrogen gas, cold,
Speaker 3: dense hydrogen gas.
Speaker 2: And the research says CDG two has none.
Speaker 3: Of this gas. It is completely depleted. It is what
Speaker 3: we call gas poor. This means it stopped forming stars
Speaker 3: a very long time ago. It's a dormant system.
Speaker 2: So where did the gas go? Did it use it
Speaker 2: all up?
Speaker 3: No, The culprit is the environment, the Perseus cluster itself.
Speaker 3: We mentioned earlier that Perseus is a rough neighborhood. Let's
Speaker 3: dig into what that actually means physically.
Speaker 2: Yeah, you mentioned it's chaotic and noisy.
Speaker 3: A galaxy cluster isn't just a collection of galaxies floating
Speaker 3: in a vacuum. The space between the galaxies is filled
Speaker 3: with something called the intracluster medium or.
Speaker 2: Icm intracluster medium.
Speaker 3: This is a plasma, a superheated gas that permeates the
Speaker 3: entire volume of the cluster.
Speaker 2: So space there is not a vacuum.
Speaker 3: It's not a vacuum in the way we usually think
Speaker 3: of deep space. It's very diffuse, sure, but it is
Speaker 3: physically there, and it's hot, millions of degrees hot. Now,
Speaker 3: I want you to imagine CDG two falling into this
Speaker 3: cluster from the outside. Okay, it is moving at thousands
Speaker 3: of kilometers per second.
Speaker 2: Thousands of kilometers per second, so it's moving incredibly fast
Speaker 2: through this plasma soup exactly.
Speaker 3: Yeah, And even though the plasma is thin, when you
Speaker 3: hit it at two thousand kilometers per second, it creates
Speaker 3: a massive amount of drag. It creates a physical.
Speaker 2: Wind, a cosmic headwind.
Speaker 3: We call this ram pressure.
Speaker 2: Yeah.
Speaker 3: The standard analogy we used to teach this is driving
Speaker 3: a convertible down the highway with a top down.
Speaker 2: Okay, I'm in the car, top is down.
Speaker 3: You have a stack of loose paper sitting on the
Speaker 3: passenger seat next to you. Those papers represent the hydrogen
Speaker 3: gas in the galaxy. Okay, it's fluffy, it's light, it's
Speaker 3: not gravitationally bound very tightly to the center.
Speaker 2: I can see exactly where this is going.
Speaker 3: You hit the gas pedal, you go out to one
Speaker 3: hundred miles per hour. The wind, the ramp pressure whips
Speaker 3: inside the car and rips the loose papers right out.
Speaker 2: The papers go flying out the back of the.
Speaker 3: Car right but the car itself, the head, steel chassis,
Speaker 3: in the engine.
Speaker 2: The car keeps moving forward.
Speaker 3: The car represents the dark matter halo and the existing stars.
Speaker 3: They are massive and gravitationally down tightly enough where they
Speaker 3: simply don't interact with the wind, so they just plow
Speaker 3: right through the plasma. But the gas, the future potential
Speaker 3: for new stars, is violently stripped away.
Speaker 2: That is such a violent image. The galaxy is essentially
Speaker 2: being flayed alive as it falls into the cluster.
Speaker 3: It is a violent process. It's called ram pressure stripping.
Speaker 3: It effectively kills the galaxy. It completely removes its ability
Speaker 3: to grow or evolve.
Speaker 2: But wait a minute, here's the plot hole for me.
Speaker 2: What's that If the cosmic wind is strong enough to
Speaker 2: rip out all the gas, why are those four globular
Speaker 2: clusters still there? Why didn't the ornaments get blown off
Speaker 2: the tree with the leaves.
Speaker 3: This is a fantastic question, and it all comes down
Speaker 3: to density. Physics is all about density contrasts. Do you
Speaker 3: remember how I described a globular cluster a few minutes ago.
Speaker 2: A super dense ball of.
Speaker 3: Stars keywords there, super dense. A globular cluster is not
Speaker 3: a stack of loose papers. It is a bowling ball.
Speaker 2: Ah, the bowling ball on the passenger seat.
Speaker 3: Right. If you have a twelve pound bowling ball on
Speaker 3: the passenger seat of your convertible and you drive one
Speaker 3: hundred miles per hour, does the wind blow it out?
Speaker 2: No, it just sits there. The wind flows right over.
Speaker 3: It, exactly. The globular clusters are gravitationally tightly bound. They
Speaker 3: are tough little knots of.
Speaker 2: Matter, so they survive.
Speaker 3: They are highly resistant to gravitational tidal disruption, and they
Speaker 3: are way too dense to be pushed around by the
Speaker 3: ram pressure wind.
Speaker 2: So the galaxy gets stripped of the gas, but the
Speaker 2: bowling ball the globular clusters stay behind.
Speaker 3: Precisely, they are ultimate survivors. They act as reliable tracers
Speaker 3: for us because they are the only things tough enough
Speaker 3: to survive the extreme environment of the Perseus cluster.
Speaker 2: That really paints a picture of CDG two not just
Speaker 2: as a weird scientific object, but almost as a survivor
Speaker 2: character in a story.
Speaker 3: It is.
Speaker 2: It's been battered, it's been stripped, and it's been starved
Speaker 2: to fuel for millions of years, but its dark matter
Speaker 2: skeleton and its four toughest star clusters are still hanging on.
Speaker 3: It's a ghost with a history. It tells the story
Speaker 3: of its own abuse just by its current state.
Speaker 2: This brings us to the bigger picture of our deep
Speaker 2: look today. We found this one ghost. We used this
Speaker 2: amazing new method finding the clusters to find the galaxy.
Speaker 2: We verified it with the triad of telescopes. What does
Speaker 2: this mean for the future of astronomy. Is CDG two
Speaker 2: a unicorn, a one off anomaly, or are we about
Speaker 2: to find a whole herd of these things?
Speaker 3: The general consensus in the field is that we are
Speaker 3: definitely about to find a herd. This discovery is a
Speaker 3: proof of concept.
Speaker 2: It proves the tools work.
Speaker 3: It shows that the statistic method works in the real universe,
Speaker 3: and we are entering a golden age for this specific
Speaker 3: kind of low surface brightness detective work.
Speaker 2: The source material mentions some specific upcoming missions that are
Speaker 2: going to blow this wide open.
Speaker 3: Yes, there are several. We are currently in the era
Speaker 3: of EUCLID, which is great, as we discussed, but coming
Speaker 3: up very soon, we have NASA's Nancy Grace Roman Space Telescope.
Speaker 2: The Roman Telescope. I've heard this described by astronomers as
Speaker 2: Hubble with a panoramic lens.
Speaker 3: That is a very fair and accurate description. Roman has
Speaker 3: the same visual resolution as Hubble, so it can see
Speaker 3: those tiny faint point source dots, but its field of
Speaker 3: view is one hundred times larger.
Speaker 2: One hundred times larger at the exact same sharpness.
Speaker 3: Yes, so instead of looking at a tiny patch of
Speaker 3: the Perseus cluster and hoping to get lucky, it can
Speaker 3: map the whole cluster and high resolution in one go.
Speaker 3: You'll be able to spot these globular class populations across
Speaker 3: huge swaths of the sky.
Speaker 2: That's incredible. And there's another one mentioned in the research too,
Speaker 2: the Verisi Reuben Observatory.
Speaker 3: The Ruben Observatory is a massive ground based project currently
Speaker 3: being built in Chile. It is going to conduct what's
Speaker 3: called the Legacy Survey of Space.
Speaker 2: And time legacy survey of space and time. What does
Speaker 2: that actually mean.
Speaker 3: Basically, it's going to make a high definition movie of
Speaker 3: the entire Southern sky, scanning the whole thing repeatedly every
Speaker 3: few nights.
Speaker 2: Every few nights, So we are going to go from
Speaker 2: having a few static snapshots to having a continuous moving
Speaker 2: stream of data.
Speaker 3: We are going to be drowning in data, petabytes of it.
Speaker 3: And that leads to the final necessary piece of the puzzle.
Speaker 3: We can't do this with human eyes anymore.
Speaker 2: The source mentions astronomers turning to artificial intelligence.
Speaker 3: It's inevitable. As we mentioned, finding CDG two required complex
Speaker 3: statistical analysis a relatively small area. Now imagine doing that
Speaker 3: for billions of objects detected by Reuben and Roman over
Speaker 3: the entire sky.
Speaker 2: A human astronomer cannot manually scan the sky for these
Speaker 2: tiny mathematical patterns. It would take lifetimes.
Speaker 3: You need a machine to find the needle in the haystack, more.
Speaker 2: Like you need a machine to find the needle in
Speaker 2: a stack of needle Exactly.
Speaker 3: We are actively training machine learning algorithms to recognize the
Speaker 3: specific statistical fingerprint of these globular clustered groupings.
Speaker 2: So the AI will flag it.
Speaker 3: The AI will scan the data and say, hey, look
Speaker 3: at these specific coordinates, there is a ninety five percent
Speaker 3: probability of a dark batter dominated galaxy hiding there. And
Speaker 3: then the human astronomers will turn the big telescopes like
Speaker 3: subru or James Web there to verify the body.
Speaker 2: So we are literally building machines to hunt for ghosts.
Speaker 3: We are automating the discovery of the invisible universe.
Speaker 2: It feels like we are on the edge of a
Speaker 2: major paradigm shift. For so long, we've thought of the
Speaker 2: universe as just the stuff we can see, but this
Speaker 2: suggests the universe is much much more crowded than we thought.
Speaker 3: I think that is the inevitable conclusion here. We were
Speaker 3: realizing that our cosmic map has huge blank spots, not
Speaker 3: because nothing is there, but simply because we were wearing
Speaker 3: the wrong glasses.
Speaker 2: So let's bring this all together for you listening. We
Speaker 2: started with a wild headline, a galaxy that is ninety
Speaker 2: nine percent dark matter CDG two. We learned that it's
Speaker 2: nearly invisible, just a faint scattering of stars three hundred
Speaker 2: million light years away.
Speaker 3: A textbook low surface brightness galaxy.
Speaker 2: We learned that the way David Laie and his team
Speaker 2: found it was sheer cleverness. They didn't look for the galaxy,
Speaker 2: They looked for its ornaments, four globular clusters huddled together
Speaker 2: in the background noise.
Speaker 3: Using advanced statistical clustering algorithms, we.
Speaker 2: Verified it with the avengers of astronomy Hubble, Euclid, and subru,
Speaker 2: proving that there was indeed a faint diffuse glow holding
Speaker 2: those clusters together, confirming.
Speaker 3: The presence of the massive dark matter halo.
Speaker 2: And we learned that this galaxy is essentially a victim
Speaker 2: of its environment. It was stripped of its star making
Speaker 2: gas by the ram pressure of the Perseus cluster, leaving
Speaker 2: only the dark matter skeleton and the tough dense clusters behind.
Speaker 3: A cosmic skelet left on the wind.
Speaker 2: So what is the big takeaway here? Why does this
Speaker 2: matter to the person listening right now on their commute
Speaker 2: or doing dishes?
Speaker 3: It matters because it fundamentally changes how we perceive reality
Speaker 3: on a cosmic scale. For all of human history, seeing
Speaker 3: is believing. In astronomy, light is matter. This discovery tells
Speaker 3: us that the map is dangerously incomplete. There are massive
Speaker 3: continents on this cosmic map that we haven't drawn yet
Speaker 3: simply because they are dark. We are moving from a
Speaker 3: light based cartography of the universe to a gravity based one.
Speaker 2: We are finally seeing the bones of the universe, not
Speaker 2: just the glowing skin.
Speaker 3: Exactly, and that gives us a much more accurate picture
Speaker 3: of how the universe actually works and how it evolved.
Speaker 2: I want to leave you the listener with a thought
Speaker 2: that's been sticking with me since we started prepping this research.
Speaker 2: We found CDG two, this massive dark matter dominated object,
Speaker 2: by spotting just four faint clusters, just four tiny ambiguous
Speaker 2: dots in the darkness.
Speaker 3: It really was a needle in a haystack.
Speaker 2: So if we found this one ghost using just four
Speaker 2: faint clues, how many billions of invisible galaxies are sitting
Speaker 2: right in front of our faces right now?
Speaker 3: It's a staggering thought.
Speaker 2: How many times have we looked at a pitch black
Speaker 2: patch of empty sky thinking it was the void when
Speaker 2: really we were staring directly at a massive galaxy just
Speaker 2: waiting for the right algorithm to reveal it.
Speaker 3: The universe is likely a lot more crowded and a
Speaker 3: whole lot darker than it looks to our eyes.
Speaker 2: Thanks for exploring the dark with us today.
Speaker 3: It's always a pleasure to be here.
Speaker 2: Keep looking up everyone, even at the empty parts. Catch
Speaker 2: it next time.
Speaker 3: The station
Speaker 2: Se