Astrometry for Earth-sized Exoplanets and Dark Matter

<v Speaker 1>Welcome to Bedtime Astronomy. Explore the wonders of the cosmos
<v Speaker 1>with our soothing Bedtime Astronomie podcast. Each episode offers a
<v Speaker 1>gentle journey through the stars, planets, and beyond, perfect for
<v Speaker 1>unwinding after a long day. Let's travel through the mysteries
<v Speaker 1>of the universe as you drift off into a peaceful
<v Speaker 1>slumber under the night sky.
<v Speaker 2>We are starting today with a pretty cosmic mandate, really
<v Speaker 2>trying to find our closest earthlike neighbors out there. And
<v Speaker 2>for this deep dive, we're looking into the future of
<v Speaker 2>space explorations, specifically at the machine designed to do just that,
<v Speaker 2>the Habitable World's Observatory. You'll hear it called HWO. Now.
<v Speaker 2>HWO is slated to be the next great observatory, you know,
<v Speaker 2>following the footsteps of giants like Hubble and Web. But
<v Speaker 2>it has this incredibly specific central mission. It needs to
<v Speaker 2>analyze the atmospheres of at least twenty five exoplanets earth
<v Speaker 2>like ones, searching for biosignature basically signs of life. For
<v Speaker 2>a long time, the main strategy for HWO has really
<v Speaker 2>hinged on using an extremely powerful coronagraph that's well the
<v Speaker 2>specialized tool designed to block out the overwhelming light of
<v Speaker 2>a star so you can actually see hopefully the faint
<v Speaker 2>little planet orbiting next to it. But here's the snag.
<v Speaker 2>Finding twenty five worlds like that, especially when you don't
<v Speaker 2>even know for sure where most of them are hiding.
<v Speaker 2>That's a massive targeting problem.
<v Speaker 3>It absolutely is. It's an issue of well efficiency and
<v Speaker 3>just sheer astronomical legwork. You could waste so much time
<v Speaker 3>pointing at the wrong places, and that difficulty, that strategic
<v Speaker 3>challenge is exactly what Fibiu Malbad and his colleagues are
<v Speaker 3>tackling in some new research. They're proposing that hw needs
<v Speaker 3>a bit of an upgrade, really a powerful secondary instrument,
<v Speaker 3>one that could frankly revolutionize how HWO picks its targets
<v Speaker 3>for that crucial atmospheric analysis. Yeah, the big idea is
<v Speaker 3>adding a cutting edge, super high precision astrometry instrument to
<v Speaker 3>hwo's toolkit. And this isn't just like a minor tweak.
<v Speaker 3>It's a genuine leap in capability. If they do this,
<v Speaker 3>this instrument could potentially identify confirmed Earth sized planets orbiting
<v Speaker 3>hundreds of nearby stars. Think about that. It would instantly
<v Speaker 3>feed the HWO chronograph. This like perfectly curated list of
<v Speaker 3>prime targets.
<v Speaker 2>Okay, wow, let's unpack that straight away, because I mean
<v Speaker 2>the implications they are pretty stunning. So this add on
<v Speaker 2>dramatically boosts hwo's chances of hitting its main goal finding
<v Speaker 2>those biosignatures, obviously, but you're saying it also gives us
<v Speaker 2>this remarkable, almost separate scientific bonus that this incredibly precise
<v Speaker 2>planet hunter could actually double as a tool for cosmology,
<v Speaker 2>helping us map, maybe even solve, one of the biggest
<v Speaker 2>riddles out there, how cold dark matter CDM is spread
<v Speaker 2>out precisely.
<v Speaker 3>That's the unexpected twist. So for you listening, what we'll
<v Speaker 3>do in this dive is unpack the amazing tech precision
<v Speaker 3>needed for this. We're talking measurements down to half of
<v Speaker 3>micro arc second, just incredibly fine. We'll explore why that
<v Speaker 3>jump in sensitivity so critical, the kind of engineering tricks
<v Speaker 3>that might make it possible, and you know what discovering
<v Speaker 3>all these plans and potentially mapping dark matter could mean
<v Speaker 3>for understanding our place in the cosmos and the universe's
<v Speaker 3>basic structure.
<v Speaker 2>All right, let's start with HWO itself and its core
<v Speaker 2>job it's a biosignature hunter. Fundamentally, that means it needs
<v Speaker 2>to gather light from a planet potentially dozens of light
<v Speaker 2>years away, break that light down and look for the
<v Speaker 2>chemical fingerprints of things like oxygen, methane, water, vapor, things
<v Speaker 2>that could indicate life. And doing that takes a long time,
<v Speaker 2>hours and hours of telescope time focused on just one
<v Speaker 2>single target. So picking the right targets efficiently, that's everything.
<v Speaker 3>It really is. The coronagraph, as amazing as it is,
<v Speaker 3>needs good intel beforehand. It needs to know exactly where
<v Speaker 3>to point and ideally know the planet's orbit pretty well
<v Speaker 3>so it can track it effectively. And that leads us
<v Speaker 3>right into this, well, this significant gap in what we
<v Speaker 3>currently know about planets right here in our own stellar backyard.
<v Speaker 3>Just think about the stars within say sixty five light
<v Speaker 3>years of Earth. That's our immediate cosmic neighborhood, right These
<v Speaker 3>are prime candidates for HWO to look at. But of
<v Speaker 3>the sun like stars in that local bubble, we currently
<v Speaker 3>only know if planet's orbiting about twelve percent of them.
<v Speaker 2>Only twelve percent, And that low number isn't even the
<v Speaker 2>most critical part of the story, is it, No, not
<v Speaker 2>at all?
<v Speaker 3>The really crucial detail is the kind of planets we've
<v Speaker 3>found so far around those nearby stars. Every single one
<v Speaker 3>of the confirmed planets in that local sixty five light
<v Speaker 3>year zone is a gas giant. We're talking worlds like
<v Speaker 3>Jupiter or even bigger. As of today, we haven't confidently
<v Speaker 3>identified a single rocky Earth sized exoplanet orbiting a nearby
<v Speaker 3>Sun like star.
<v Speaker 2>Not one, right, So let me just make sure I'm
<v Speaker 2>getting the straight for everyone listening. In this huge volume
<v Speaker 2>of space right around us, a space where we assume
<v Speaker 2>there should be plenty of smaller rocky worlds, our best
<v Speaker 2>technology so far just hasn't been able to confirm any.
<v Speaker 2>It almost sounds wrong.
<v Speaker 3>It's purely a function of our instruments limitations, not necessarily
<v Speaker 3>a reflection of what's actually out there. It doesn't mean
<v Speaker 3>those Earth sized worlds aren't there. I mean all our
<v Speaker 3>theories of planet formation suggest they should be pretty common. Actually,
<v Speaker 3>it just means the signals they pretty, whether it's their
<v Speaker 3>reflected light or their gravitational tug, are currently getting drowned
<v Speaker 3>out by the noise. You know, if you're trying to
<v Speaker 3>spot a tiny firefly right next to a giant searchlight,
<v Speaker 3>your camera needs incredible contrast and stability.
<v Speaker 2>Same idea here, and that brings us squarely to this
<v Speaker 2>precision problem and the limits of our current best tool
<v Speaker 2>for this kind of work. The Gaya Space Observatory. Guy's
<v Speaker 2>been amazing for mapping stars in the Milky Way, absolutely revolutionary,
<v Speaker 2>but for finding these tiny earth like worlds nearby, it
<v Speaker 2>kind of hits a sensitivity wall.
<v Speaker 3>Guya really is the gold standard for current astrometry. It
<v Speaker 3>measures the positions and movements of stars with phenomenal accuracy,
<v Speaker 3>but its absolute best precision, its limit is around twenty
<v Speaker 3>to thirty micro arc seconds. We usually write that as ice.
<v Speaker 2>Okay, twenty or thirty micro arc seconds. That sounds incredibly
<v Speaker 2>tiny already. Why does that still fall short for finding
<v Speaker 2>an Earth? Twin? What's the physical scale here that we're missing?
<v Speaker 3>Well, to grasp the challenge, you need to visualize the
<v Speaker 3>star's actual movement. It's wobble. See when a planet orbits
<v Speaker 3>a star, they both actually orbit a common center of mass.
<v Speaker 3>It's called the Barry center. Now, a really massive planet
<v Speaker 3>like Jupiter makes our Sun move quite a bit, pulls
<v Speaker 3>the Sun around and a loop that's what about two
<v Speaker 3>million kilometers across even from sixty five light years away.
<v Speaker 3>That's a relatively large angular displacement on the sky. It's
<v Speaker 3>something Guy that can measure, and that's why Guy is
<v Speaker 3>great at finding gas giants. Okay, but now picture an
<v Speaker 3>Earth mass planet orbiting a sun like star. That tiny
<v Speaker 3>planet only makes it star wobble by maybe a few
<v Speaker 3>thousand kilometers let's say enter ten thousand kilometers over its
<v Speaker 3>whole orbit. Now translate that tiny physical movement into an
<v Speaker 3>angle on the sky as seen from sixty five light
<v Speaker 3>years away. That angular shift, the wobble we need to
<v Speaker 3>detect it works out to be less than one micro second.
<v Speaker 2>Ah. Okay, So Guya's best measurement twenty to thirty onens
<v Speaker 2>is just way too coarse. It's like trying to measure
<v Speaker 2>something a millimeter wide with a ruler marked only in centimeters.
<v Speaker 2>We're hunting for a wiggle that might be, say, thirty
<v Speaker 2>times smaller than the inherent error the noise level in
<v Speaker 2>our current best.
<v Speaker 3>Instruments exactly that twenty to thirty on's level is effectively
<v Speaker 3>the noise floor of today's technology for this specific task.
<v Speaker 3>And hiding beneath that noise floor we think are potentially
<v Speaker 3>hundreds of habitable Earth sized worlds right next door. So
<v Speaker 3>the only way to really enable hwo's primary mission to
<v Speaker 3>give it those targets is to dramatically, drastically lower that
<v Speaker 3>noise floor.
<v Speaker 2>Right. So, if the coronagraph is the tool for the
<v Speaker 2>deep dive, the detailed atmospheric sniffing, then astrometry, this wobble
<v Speaker 2>measuring technique sounds like the perfect tool for the initial
<v Speaker 2>survey for finding the worlds and figuring out their basic properties. First,
<v Speaker 2>can you give us a quick, clear definition of astrometry
<v Speaker 2>against specifically how it helps us find exoplanet sure?
<v Speaker 3>At its heart, astrometry is simply the science of measuring
<v Speaker 3>the precise positions and motions of stars over time very accurately.
<v Speaker 3>When we apply it to finding exoplanets, we're looking for
<v Speaker 3>that tiny, repetitive periodic shift in a star's parent position
<v Speaker 3>on the sky. That shift is caused by the gravitational
<v Speaker 3>pull of an orbiting planet tugging the star back and
<v Speaker 3>forth as they both orbit that common center of mass,
<v Speaker 3>the Barry Center. We're basically tracking the star's side of
<v Speaker 3>that orbital.
<v Speaker 2>Dance, and the beauty of it is the size of
<v Speaker 2>that wobble directly relates to the mass of the planet
<v Speaker 2>doing the tugging right, bigger wobble, bigger planet.
<v Speaker 3>Mass exactly right. And that's the huge advantage of astrometry
<v Speaker 3>because that gravitational relationship is so well understood based on physics.
<v Speaker 3>If you can measure that wobble with extremely high precision,
<v Speaker 3>you can calculate the exoplanet's entire orbital solution, its orbital period,
<v Speaker 3>how far it is from the star on average, a
<v Speaker 3>semi major axis, even how elliptical its orbit is. You
<v Speaker 3>basically get a complete map of its path, which tells
<v Speaker 3>you exactly where that planet will be at any given time.
<v Speaker 3>And that's absolutely critical for pointing the coronograph later on.
<v Speaker 2>Okay, so that's the practical benefit better targeting knowing where
<v Speaker 2>to look makes sense. But you also mention a fundamental
<v Speaker 2>scientific advantage, something that other main planet finding methods like
<v Speaker 2>the transit method or radial velocity can't quite deliver with
<v Speaker 2>the same certainty.
<v Speaker 3>Yes, and this is key. Astrometry allows you to determine
<v Speaker 3>the exo planet's absolute mass, not just a minimum mass,
<v Speaker 3>but it's actual mass. See the radio velocity method, which
<v Speaker 3>measures the stars wobble towards and away from us only
<v Speaker 3>gives you a minimum possible mass for the planet. That's
<v Speaker 3>because the signal depends on the tilt of the planet's
<v Speaker 3>orbit relative to our line of sight, and usually we
<v Speaker 3>don't know that tilt precisely. Astrometry, though, measures the side
<v Speaker 3>to side wobble on the sky. That measurement directly gives
<v Speaker 3>you the true, unambiguous mass of the planet. And why
<v Speaker 3>is knowing the true mass so important? We'll think about
<v Speaker 3>Hwo's goal finding life. To assess if a planet could
<v Speaker 3>host life, we first need to know if it's even rocky. Right.
<v Speaker 3>If you can combine that absolute mass from astrometry with
<v Speaker 3>the planet's radius, which you might get if you're lucky
<v Speaker 3>and the planet also happens to transit passing in front
<v Speaker 3>of it star from our view, then mass plus radius
<v Speaker 3>gives you density. And density is the killer metric. It's
<v Speaker 3>what fundamentally tells you if you're looking at a dense,
<v Speaker 3>rocky world like Earth or Venus, or a puffy, low
<v Speaker 3>density gas or ice giant like Jupiter or Neptune, which are,
<v Speaker 3>let's face it, much less likely places to find life
<v Speaker 3>as we know it. So astramistry provides that foundational piece
<v Speaker 3>of the puzzle for figuring out if the planet is
<v Speaker 3>even potentially habitable in the first place.
<v Speaker 2>Okay, so it all comes back to the main challenge
<v Speaker 2>getting sensitive enough to measure that incredibly tiny wobble from
<v Speaker 2>an Earth mass planet Gia. Our current best is stuck
<v Speaker 2>at around twenty thirty oins. What's the leap in precision
<v Speaker 2>that doctor Malbat's proposal is calling for. How much better
<v Speaker 2>do we need to be?
<v Speaker 3>The instrument they're suggesting aims for an operational precision of
<v Speaker 3>I get this zero point five micro arc seconds.
<v Speaker 2>Half of microrost. Wow. Okay, just comparing that to Gaya,
<v Speaker 2>which is already state of the area. You're talking about
<v Speaker 2>making this new instrument on EAHWO something like four hundred
<v Speaker 2>to six hundred times more sensitive than Guya. That's that's
<v Speaker 2>not just like the next step up. That's like skipping
<v Speaker 2>two whole generations of technology. It completely changes the game
<v Speaker 2>for hwo's mission.
<v Speaker 3>It really does. Just to give you a sense of scale,
<v Speaker 3>foer point five targets, that's roughly the angular size of
<v Speaker 3>a single human hair viewed from about five hundred miles away.
<v Speaker 3>It's an unbelievably fine measurement we're talking about making from
<v Speaker 3>space and achieving that level of sensitivity that point five
<v Speaker 3>tarrets is the absolute key. It's what unlocks potentially hundreds
<v Speaker 3>of new Exo Earth candidates right in our solar neighborhood.
<v Speaker 3>It means hwo's giant coronagraph doesn't have to waste precious
<v Speaker 3>time searching blindly or inefficiently. Instead, it gets handed this
<v Speaker 3>highly optimized, pre vetted list of confirmed targets, complete with
<v Speaker 3>their masses and orbital details, making it much much easier
<v Speaker 3>to efficiently tick off that primary mission goal finding those
<v Speaker 3>twenty five biosignatures.
<v Speaker 2>Okay, boosting precision by a factor of say four hundred
<v Speaker 2>or six hundred, that obviously means you have to overcome
<v Speaker 2>some equally huge technical challenges. If doing astronotry at point
<v Speaker 2>five highs was easy, presumably we'd have done it by now.
<v Speaker 2>So what's the main weakness? What makes these astrometers so
<v Speaker 2>prone to error that we need to fix?
<v Speaker 3>Well, even out in the relative stability of space, astronomers
<v Speaker 3>are inherently susceptible to what we call systematic errors. You're
<v Speaker 3>trying to measure an angular shift on the sky. That's
<v Speaker 3>smaller than the width of a virus. Right, So, every
<v Speaker 3>tiny physical imperfection in the instrument itself, whether it's in
<v Speaker 3>the detector chip, tiny misalignments in the mirrors, slight changes
<v Speaker 3>do to temperature, all these things can combine and create
<v Speaker 3>noise that swamps the signal you're looking for. The main
<v Speaker 3>offenders are usually imperfections in the detector and just thermal instability.
<v Speaker 3>The sensor, typically a CMOS chip like in your phone camera,
<v Speaker 3>but much more advanced, isn't mathematically perfect. The pixels aren't
<v Speaker 3>all identical squares. They have tiny variations and how sensitive
<v Speaker 3>they are, their exact size, their electrical behavior. That's due
<v Speaker 3>to the manufacturing process, and it's called fixed pattern noise. Now,
<v Speaker 3>if that sensor shifts even minutely relative to the incoming starlight,
<v Speaker 3>or if it's temperature fluctuates by even a tiny fraction
<v Speaker 3>of a degree, those built in imperfections create errors in
<v Speaker 3>your position measurement, and those errors very quickly add up
<v Speaker 3>and overwhelm the sub microarc second signal you're desperately trying
<v Speaker 3>to detect. That inherent instrumental noise floor is basically why
<v Speaker 3>we've been stuck around that twenty thirty oin limit for
<v Speaker 3>so long.
<v Speaker 2>Okay, So to break through that barrier and actually hit
<v Speaker 2>zero point five noise, Malvot's team is proposing a kind
<v Speaker 2>of two pronged attack, right, a strategy to cancel out
<v Speaker 2>both those predictable systematic errors from the hardware itself and
<v Speaker 2>also the unpredictable random noise from the environment. Let's start
<v Speaker 2>with the first part, the clever bit of technology, the
<v Speaker 2>detector calibration unit or DCU. What does that do?
<v Speaker 3>The DCU is a really neat piece of engineering. It's
<v Speaker 3>designed specifically to tackle that fixed pattern noise problem on
<v Speaker 3>the CMOS sensor head on. So you've got your sensor,
<v Speaker 3>which is basically this grid of millions of tiny light
<v Speaker 3>collecting pixels. The DCU generates a set of extremely precise,
<v Speaker 3>stable reference patterns, think of them like light and dark
<v Speaker 3>interference fringes, or a super high resolution grid pattern, and
<v Speaker 3>it projects these known patterns directly onto the face of
<v Speaker 3>the CMO sensor itself while you're observing.
<v Speaker 2>Ah. Okay, so it's like shining a perfect unchanging calibration
<v Speaker 2>ruler directly onto the detector every time you take a
<v Speaker 2>picture exactly.
<v Speaker 3>That's a great analogy the DCU allows the system to
<v Speaker 3>isolate and map the precise physical location and the specific
<v Speaker 3>response characteristics of every single pixel in that detector array.
<v Speaker 3>And this calibration isn't just done once. It's done constantly
<v Speaker 3>or very frequently. It effectively corrects for all those tiny
<v Speaker 3>pixel to pixel variations, any slight geometric distortions introduced by
<v Speaker 3>the telescope's optics, and even tiny changes in the detector's
<v Speaker 3>own internal shape or geometry caused by minute thermal expansions
<v Speaker 3>or vibrations. What it does basically is create a perfectly
<v Speaker 3>stable internal coordinate system right on the detector itself, so
<v Speaker 3>when the light from the target star hits that sensor,
<v Speaker 3>the DCU calibration ensures that any measured shift in the
<v Speaker 3>star's apparent position is a real angular movement due to
<v Speaker 3>its gravitational wobble, and not just some artifact caused by
<v Speaker 3>the telescope hardware warming up by a thousandth of a
<v Speaker 3>degree or a pixel behaving slightly differently than its neighbor.
<v Speaker 3>It aims to drive that systematic air contribution down to
<v Speaker 3>almost zero.
<v Speaker 2>Okay, that sounds like it tackles the predictable flaws in
<v Speaker 2>the hardware pretty effectively. But even with a perfect DCU,
<v Speaker 2>you're still going to have some residual fuzziness, right, random
<v Speaker 2>errors from things like stray background light, maybe a cosmic
<v Speaker 2>ray hitting the detector, tiny thermal jitters. So this requires
<v Speaker 2>the second ingredient in the recipe, basically statistical brute force.
<v Speaker 2>You need lots and lots of data.
<v Speaker 3>You need a massive amount of data. The estimate they
<v Speaker 3>provide to the paper suggests that to really nail down
<v Speaker 3>the conformation of an Earth mass planet and to average
<v Speaker 3>down all those random errors to achieve that overall zero
<v Speaker 3>point five arrow precision goal, HWO would probably need to
<v Speaker 3>collect over one hundred separate high precision measurements of that
<v Speaker 3>particular star system.
<v Speaker 2>And these aren't just one hundred snapshots taken one after another.
<v Speaker 2>I assume you need to spread them out over time
<v Speaker 2>to actually see the orbit absolutely correct.
<v Speaker 3>These hundred plus measurements would need to be distributed over
<v Speaker 3>the course of hwo's planned operational lifetime, which is typically
<v Speaker 3>expected to be around three to four years. You need
<v Speaker 3>that longtime baseline to actually track this are through a
<v Speaker 3>significant portion, ideally more than one full cycle of its
<v Speaker 3>gravitational wobble caused by the planet. That's how you confirm
<v Speaker 3>the orbital period accurately, and the reason for needing so
<v Speaker 3>many images. The statistics part is pretty straightforward. Even the
<v Speaker 3>brilliant DCU can't stop every single random, unpredictable error. A
<v Speaker 3>stray photon here, a tiny vibration there. These are stochastic events.
<v Speaker 3>But the magic happens when you take a hundred or
<v Speaker 3>maybe one hundred and fifty of these individual measurements. The
<v Speaker 3>central limit theorem from statistics starts to work in your favor.
<v Speaker 3>Random errors are by definition random. They scatter. So if
<v Speaker 3>what measurement happens to have a random error that nudges
<v Speaker 3>the stars measure positions slightly to the north, it's likely
<v Speaker 3>that another measurement taken later will have a roughly equal
<v Speaker 3>and opposite random error that nudges the position slightly to
<v Speaker 3>the south right.
<v Speaker 2>So by combining and averaging all those hundreds of measurements together,
<v Speaker 2>you effectively force those random plus and minus errors to
<v Speaker 2>statistically cancel each other out over the long run, leaving
<v Speaker 2>behind only the consistent underlying signal that tiny, stable, repeatable
<v Speaker 2>gravitational wobble of the star caused by the planet.
<v Speaker 3>That's exactly the rationale. It's this combination, this marriage of
<v Speaker 3>highly sophisticated real time technical calibration that's the DCU with
<v Speaker 3>the sheer power of statistical averaging from taking lots and
<v Speaker 3>lots of pictures that gives us confidence we can actually
<v Speaker 3>stabilize the final result down to that incredibly demanding zero
<v Speaker 3>point five a's of precision level. It transforms a mission
<v Speaker 3>initially conceived around just a coronagraph into potentially the definitive
<v Speaker 3>surveyor of nearby planetary masses as well.
<v Speaker 2>Okay, now we pivot to the part that for me,
<v Speaker 2>really elevates this whole proposal. It goes beyond just making
<v Speaker 2>HWO better at its main job. The idea that an
<v Speaker 2>instrument fine tuned to measure a star wobbling by just
<v Speaker 2>a few thousand kilometers could also give us real leverage
<v Speaker 2>on one of the universe's biggest mysteries, cold dark matter.
<v Speaker 2>That's pretty amazing.
<v Speaker 3>It is a truly remarkable example of how pushing the
<v Speaker 3>technological envelope in one area of science can suddenly unexpectedly
<v Speaker 3>on block brand new capabilities in a completely different field.
<v Speaker 3>Hwo's proposed astrometer if built to this point five and
<v Speaker 3>spec could provide crucial observational data to directly test the
<v Speaker 3>standard model of cold dark matter. Specifically, it could help
<v Speaker 3>resolve a long standing puzzle about how dark matter is
<v Speaker 3>actually distributed right in the centers of galaxies.
<v Speaker 2>Right, and this gets into the famous cusp versus core debate,
<v Speaker 2>doesn't it? If dark matter is cold, meaning it moves
<v Speaker 2>slowly and mostly non interacting except through gravity, which is
<v Speaker 2>the standard CDM picture, what should happen to it near
<v Speaker 2>the super dense center of a galaxy? What does theory predict?
<v Speaker 3>The standard CDM theory is pretty unequivocal on this. It
<v Speaker 3>should form a cusp because dark matter particles in this
<v Speaker 3>model only really feel gravity. They should just keep getting
<v Speaker 3>pulled deeper and deeper into the galaxies gravitational Well, this
<v Speaker 3>process should cause the density of dark matter to continuously
<v Speaker 3>increase the closer you get to the very center, creating
<v Speaker 3>a really steep, sharp spike in density right at the core,
<v Speaker 3>like a pointy cut.
<v Speaker 2>Okay, so theory predicts this sharp density peak, But what
<v Speaker 2>do our observations actually show us, Especially when we look
<v Speaker 2>at smaller dwarf galaxies where the dark matter signal is
<v Speaker 2>often clearer, less mixed up with normal matter.
<v Speaker 3>Well, that's where the tension arises. Observations, particularly from studying
<v Speaker 3>how stars orbit in the outer parts of galaxies, and
<v Speaker 3>especially in these smaller dwarf galaxies, they frequently suggest something different.
<v Speaker 3>The data often indicates that the dark matter density profile
<v Speaker 3>tends to flatten out in the very center. Instead of
<v Speaker 3>that sharp cusp, we seem to see a core, basically
<v Speaker 3>a region where the dark matter density is more or
<v Speaker 3>less constant, or at least doesn't spike up dramatically right
<v Speaker 3>at the galactic heart.
<v Speaker 2>So theory predicts a steep point. Observation suggests more of
<v Speaker 2>a flat plateau in the middle. That's a pretty significant disagreement,
<v Speaker 2>and the existence of these apparent cores implies something's going
<v Speaker 2>on that isn't in the simplest CDM model right. Either
<v Speaker 2>are assumptions about dark matter or wrong, or something else
<v Speaker 2>is messing with its distribution exactly.
<v Speaker 3>These cores are real and common. It means something must
<v Speaker 3>be acting to sort of smooth out or push that
<v Speaker 3>dark matter away from the very center. What could it be, Well,
<v Speaker 3>one possibility is astrophysical feedback from normal matter things like
<v Speaker 3>massive bursts of star formation and powerful supernova explosions. These
<v Speaker 3>events can violently expel gas and energy, potentially pushing the
<v Speaker 3>dark matter outwards too, dynamically creating a core over time.
<v Speaker 3>Or maybe point to something fundamental about the dark matter
<v Speaker 3>particles themselves. Perhaps dark matter isn't completely non interacting. Maybe
<v Speaker 3>it's self interacting dark matter or SIDM, where dark matter
<v Speaker 3>particles can actually collide and scatter off each other occasionally.
<v Speaker 3>That kind of self interaction would naturally tend to smooth
<v Speaker 3>out the central density peak, turning a CUSP into a core.
<v Speaker 2>And this is where hwo's super precise astrometer comes back
<v Speaker 2>into the picture. We're not looking for a star's wobble anymore.
<v Speaker 2>We're talking about using that same incredible point five visos
<v Speaker 2>precision to detect the subtle gravitational effects of those predicted
<v Speaker 2>dark matter cusps themselves, if they exist. How does that work?
<v Speaker 2>How does measuring star positions help us see? A dark
<v Speaker 2>matter cusp.
<v Speaker 3>Would use the phenomenon called gravitational lensing, or more specifically,
<v Speaker 3>gravitational deflection of light. Any concentration of mass like the
<v Speaker 3>dense dark matter cusp predicted by CDM theory will bend
<v Speaker 3>the path of light that passes near it. Now we
<v Speaker 3>can't see the dark manner directly, of course, but we
<v Speaker 3>can see distant background stars or quasars whose light has
<v Speaker 3>to travel past or through these potential dark matter concentrations
<v Speaker 3>in nearby galaxies on its way to us. If a
<v Speaker 3>dense dark matter cusp is sitting there between HWO and
<v Speaker 3>some distant background star, the gravity of that cusp will
<v Speaker 3>slightly deflect the light from the background star. This deflection
<v Speaker 3>causes a tiny, tiny shift in the apparent position of
<v Speaker 3>that background star as seen by HWO. That predicted shift
<v Speaker 3>caused by the lengthening effect of a standard CDM cusp
<v Speaker 3>is incredibly small. Calculation suggests it's right around the level
<v Speaker 3>of you guessed a zero point five micro arc seconds.
<v Speaker 3>Only an instrument with the kind of precision being proposed
<v Speaker 3>for hw a's astrometer would actually be sensitive enough to
<v Speaker 3>reliably detect these minute skilled deflections caused specifically by the
<v Speaker 3>presence of a dark matter.
<v Speaker 2>Cusp ah I see. So the logic is if this
<v Speaker 2>astrometer looks at millions of background stars shining through the
<v Speaker 2>centers of nearby galaxies, and it consistently fails to find
<v Speaker 2>those tell tale point five thitdistic positional shifts that a
<v Speaker 2>cusp should produce. Then that provides strong evidence that the
<v Speaker 2>cusps aren't there and the dark matter must be arranged
<v Speaker 2>in cores instead.
<v Speaker 3>It would provide potentially definitive, clean observational evidence. Yes, that
<v Speaker 3>kind of data. A null result across many targets would
<v Speaker 3>really force cosmologists to seriously re evaluate the standard, simplest
<v Speaker 3>CDM model. It would lend powerful support either to alternative
<v Speaker 3>dark matter theories like self interacting dark matter, or to
<v Speaker 3>models where astrophysical feedback processes are extremely efficient at flattening
<v Speaker 3>alcocentral densities. So this one instrument, borne out of the
<v Speaker 3>very practical need to find nearby Earth like planets suddenly
<v Speaker 3>becomes this fundamental probe for understanding the distribution of dark
<v Speaker 3>matter and the very structure of galaxies.
<v Speaker 2>It really is quite something, the solution to a tricky
<v Speaker 2>planetary measurement problem potentially unlocking answers to a deep cosmological mystery. Now,
<v Speaker 2>this proposal sounds incredibly powerful, almost essential, giving these potential
<v Speaker 2>twins scientific payoffs better exoplanet hunting and insights into dark matter.
<v Speaker 2>But space missions are notoriously complex, incredibly expensive, and take
<v Speaker 2>decades to plan and build. So let's put this idea
<v Speaker 2>into context a bit. How developed is this concept? Is
<v Speaker 2>it brand new or does it have some history? And
<v Speaker 2>why does it make sense to try and tack it
<v Speaker 2>onto HWO.
<v Speaker 3>Now, well, that's a good point, and the idea is
<v Speaker 3>actually highly mature technically speaking. It didn't just spring up
<v Speaker 3>out of nowhere for HWO. Doctor Malbitt, who led the
<v Speaker 3>recent paper, was also a key figure behind a much earlier,
<v Speaker 3>very detailed mission proposal called THEA.
<v Speaker 2>THEA I remember hearing about that. That was basically envisioned
<v Speaker 2>as a dedicated space telescope whose entire purpose was going
<v Speaker 2>to be ultra high precision astrometry. Right, using essentially the
<v Speaker 2>same core technology concept.
<v Speaker 3>That's exactly right. THEO was designed from the ground up
<v Speaker 3>as a standalone mission, completely separate from the lineage at
<v Speaker 3>the great observatories like Hubble Web or HWO. The THEA
<v Speaker 3>team spent years meticulously developing the concept, working through the
<v Speaker 3>incredibly demanding error budgets, figuring out how to control systematic errors,
<v Speaker 3>and designing the specialized hardware needed, including crucial calibration systems
<v Speaker 3>like that detector calibration unit of the DCU we discussed. Now,
<v Speaker 3>ultimately THEA wasn't selected by the funding agencies to move
<v Speaker 3>forward and actually launch, but all that detailed engineering work,
<v Speaker 3>the simulations, the technical solutions, that knowledge base still exists
<v Speaker 3>and is highly valuable.
<v Speaker 2>Okay, So if you look at it strategically, then since
<v Speaker 2>the really hard groundwork for achieving this kind of super
<v Speaker 2>precision astrometry has largely already been done for THEA, it
<v Speaker 2>seems incredibly logical, maybe even efficient, to try and incorporate
<v Speaker 2>that already developed capability into HDI. You avoid the huge
<v Speaker 2>cost and complexity of launching a whole, separate, dedicated mission
<v Speaker 2>like THEO was planned to be, while at the same
<v Speaker 2>time you significantly boost hwo's ability to achieve its own
<v Speaker 2>primary goal. Kind of a win win.
<v Speaker 3>It really does look like a way to maximize the
<v Speaker 3>scientific return on investment for a single major flagship mission
<v Speaker 3>like HWO. I mean, any instrument that can quickly and
<v Speaker 3>definitively find and confirm potentially hundreds of Earth mass planets
<v Speaker 3>right in our solar neighborhood. That directly makes hwo's main
<v Speaker 3>job getting those twenty five biosignatures far more achievable within
<v Speaker 3>its likely mission lifetime and budget. It feels like perhaps
<v Speaker 3>the smartest way to leverage all that prior R and
<v Speaker 3>D investment from the CIA effort and frankly reduce the
<v Speaker 3>overall risk for hwo's core science.
<v Speaker 2>However, we should probably ground ourselves and you the listener,
<v Speaker 2>in the actual timeline here. HWO isn't launching next year
<v Speaker 2>or even this decade.
<v Speaker 3>Oh far from it. HWO development is still very much
<v Speaker 3>in the early study and planning phases. Serious hardware can
<v Speaker 3>instruction and detailed engineering work aren't really expected to kick
<v Speaker 3>off in earnest until sometime in the twenty thirties, and
<v Speaker 3>the most optimistic launch window for HWO itself is probably
<v Speaker 3>somewhere in the early to mid twenty forties. We're talking
<v Speaker 3>twenty years out, maybe more. But interestingly, that long lead
<v Speaker 3>time is actually a major advantage for this astrometry proposal.
<v Speaker 3>It means there's still plenty of time, well over a
<v Speaker 3>decade potentially to fully finalize the instrument design, build and
<v Speaker 3>thoroughly test prototypes of things like the detector calibration unit,
<v Speaker 3>and figure out how to integrate the whole astrometry package
<v Speaker 3>smoothly into the larger HWO observatory architecture without causing major
<v Speaker 3>delays or disruptions to the primary coronagraph instrument, which is
<v Speaker 3>still the centerpiece.
<v Speaker 2>So the underlying science case seems solid. The core technology
<v Speaker 2>is apparently quite mature thanks to the earlier THEO work,
<v Speaker 2>and the long HWO timeline actually provides a feasible window
<v Speaker 2>for implementation. So the final decision really comes down to
<v Speaker 2>the HWO project managers, the scientific advisory committees, and ultimately
<v Speaker 2>the funding aidies. Like Massa, it sounds like a classic
<v Speaker 2>strategic decision. Do you stick rigidly to the original highly
<v Speaker 2>focused mission plan for HWO centered on the coronograph, or
<v Speaker 2>do you allow the mission's scope its scientific ambition to
<v Speaker 2>grow a bit to incorporate this incredibly powerful dual purpose
<v Speaker 2>astrometry capability. Given the groundwork already laid, it.
<v Speaker 3>Really is a choice between perhaps maximizing the potential scientific
<v Speaker 3>discovery space versus maintaining programmatic simplicity and sticking to the
<v Speaker 3>original baseline. Integrating the astrometer undoubtedly adds complexity to the
<v Speaker 3>overall instrument package and the mission operations. There's no denying that,
<v Speaker 3>but the potential scientific payoff having hundreds of confirmed exo
<v Speaker 3>Earth masses to feed the chronograph, plus getting unique observational
<v Speaker 3>constraints on the nature of dark matter, that payoff is
<v Speaker 3>arguably multiplicatid it could be huge. It's definitely a major
<v Speaker 3>decision point that will likely shape hwo's ultimate scientific legacy
<v Speaker 3>long before it ever leaves the ground.
<v Speaker 2>It certainly seems to shift the perception of HWO, doesn't
<v Speaker 2>it from being primarily a specialized machine for analyzing atmospheres
<v Speaker 2>to becoming potentially a much more versatile foundational observatory for
<v Speaker 2>broad areas of space physics as well well. This has
<v Speaker 2>been a really fascinating look into the kind of high
<v Speaker 2>stakes planning and technological innovation that goes into shaping the
<v Speaker 2>next generation of big space science missions. We started with
<v Speaker 2>this fundamental need just finding a better and more efficient
<v Speaker 2>way to locate those small, rocky worlds that HBO is
<v Speaker 2>ultimately designed to study up close, and that let us
<v Speaker 2>down this path exploring an incredibly complex technological leap, combining
<v Speaker 2>that sophisticated detector calibration unit with the need for maybe
<v Speaker 2>over one hundred statistical measurements, all just to reach that
<v Speaker 2>almost unbelievable point five microarc second precision target, and.
<v Speaker 3>Then we discovered this amazing bonus that this hyper precision,
<v Speaker 3>initially conceived just for measuring planet masses accurately, it simultaneously
<v Speaker 3>gives us this completely new, powerful way to probe the
<v Speaker 3>universe on a much grander scale. It provides exactly the
<v Speaker 3>kind of leverage needed to observe vationally test competing theories
<v Speaker 3>about how cold dark matter behaves in the hearts of galaxies,
<v Speaker 3>potentially resolving that cusp versus core puzzle has been nagging
<v Speaker 3>cosmologists for years. So this proposed astrometer, it really isn't
<v Speaker 3>just some minor add on. It feels like it could
<v Speaker 3>fundamentally shift the scientific identity of the habital world's observatory.
<v Speaker 3>It potentially transforms it from being a highly specialized, though
<v Speaker 3>important coronagraph mission into more of a foundational, dual purpose
<v Speaker 3>powerhouse for both incredibly precise exoplanet characterization and fundamental deep
<v Speaker 3>space physics. It just seems to maximize the potential science
<v Speaker 3>you get out of one enormous public.
<v Speaker 2>Investment, and thinking about that dual use potential if one
<v Speaker 2>instrument developed primarily to measure a star moving just a
<v Speaker 2>tiny bit because of a planet sixty five light years away.
<v Speaker 2>If that same instrument could also potentially help resolve one
<v Speaker 2>of the deepest mysteries we have about the fundamental structure
<v Speaker 2>of the entire universe, it really prompts a final question
<v Speaker 2>for you, the listener, to maybe mull over. As we
<v Speaker 2>continue to pour billions into developing ever more sensitive, ever
<v Speaker 2>more precise scientific tools for space, what other profound, perhaps
<v Speaker 2>completely unintended discoveries might already be lurking, waiting to be
<v Speaker 2>made within the designs and development pipelines from missions that
<v Speaker 2>haven't even launched yet. Often the biggest scientific leaps seem
<v Speaker 2>to happen almost by accident, when instrument's built for one
<v Speaker 2>very specific purpose turn out to have an even grander
<v Speaker 2>application in a completely different scientific domain we hadn't anticipated.
<v Speaker 3>It's that kind of beautiful, unforeseen synergy that often drives
<v Speaker 3>scientific discovery forward in surprising ways.
<v Speaker 2>Absolutely well, thank you for joining us for this deep
<v Speaker 2>dive into the exciting future of space exploration and the
<v Speaker 2>potential of the habitable world's observatory. We'll catch you on
<v Speaker 2>the next one.
<v Speaker 3>Last DA