The hosts explain gravitational microlensing as a way to find exoplanets that the transit method misses. Most known exoplanets, like those from Kepler, are found because a planet crosses in front of its star and dips the star's brightness, which only works if that solar system happens to be edge-on to Earth. Microlensing instead uses general relativity: when a foreground star (and any orbiting planet) passes in front of a background star, its gravity bends and brightens that background star's light, with the planet producing a small extra spike, letting astronomers detect planets regardless of orbital orientation. They also mention a recent, still-uncertain news report claiming a possible direct detection of a dark matter particle, noting the statistical significance is low and that a coincident detection at another underground dark matter experiment, such as those in Japan or Italy, would be needed before it counts as a real discovery.
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The hosts reference a separate FFP episode with astrophysicist Dan Gilman, recorded during a co-host's paternity leave, that covers strong gravitational lensing as a tool for studying dark matter.
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Dan Gilman is noted as organizing a 'dark matter physics in the era of large surveys' conference at the University of Chicago's Kavli Institute for Cosmological Physics (KICP).
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The hosts say a coincident dark matter detection matching mass and energy scale across multiple experiments, such as ones in South Dakota, Japan, and Italy, would be significant enough to warrant a Nobel Prize.
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46:22really excited because it's going to answer questions about dark energy and dark matter. Me personally, if you were to ask me, I am very excited about this idea of microl lensing. >> And you're going to like this idea because >> so most of the planets, most of the exoplanets that we know about are from Kepler. And Kepler was a transiting observatory, right? which means that the planet has to go in front of the star and then the stars light is going to dip. And if that dip is rhythmic, then we know that the planet has gone in front and it's gone in front and it's gone in front and we know that there's a planet there. And then we can do all sorts of um nice analyses about the
47:02atmospheric retrieval. >> Retrie, yes, atmospheric retrieval. What is the atmosphere on this planet? And so on and so forth. But in order to find those types of planets, you have to get very lucky, >> right? >> Because the angle of that solar system, the axis or the the plane of rotation of that solar system has to be in line with however the Earth is looking at that star, >> our line of sight to the star, >> right? Yeah. Like if if the star is over there, then the solar system better be rotating this way such that the plate is like edge on, right? If the star is over there, then it better be edge on and so on and so forth. Um, and that's because it relies on the transit method.
47:44>> What about solar systems that are oblique right? >> For example, the star is like this and the solar the planet is revolving this way. >> Meaning the planet is not going to uh uh revolve in front of its parent star. There's no eclipse in our line of sight. >> Yeah. So there's no dip in the brightness >> in the brightness. Um, what about then? That's where this microl lensing techniques comes in. Okay. What they're using is piggybacking off of Einstein's general relativity to say that when there's a star, let's say the star is right here and there's a background star behind it. If the star moves in front, it's going to gravitationally lens that light and the background star is going to get a little bit brighter. Mhm.
48:25[clears throat] >> Well, if there's a star and a planet right in front, >> then I'm going to see a sort of spike in that gravitational lensing, right? And so now this is a technique where we can start having access to solar systems, exoplanets that no longer have that constraint, you know. And if you're interested in this topic, we actually talked to a friend of the pod astrophysicist Dan Gilman. Yes. While you were on paternity leave about how scientists actually study dark matter. And we talked in depth about this concept of strong gravitational
49:06lensing. But it'll at least be somewhat adjacent or t you know to this idea which is very interesting. And again to your point I is a is a very important distinction between the transit method in terms of how we do exoplanet detection. >> Yeah. >> Um his reference point for um this idea of gravitational lensing is for dark matter detection. >> Yes. And it's an incredible episode. Um and this one is you know you can use gravitational lensing for exoplanets itself. And also shout out to Dan. He's actually organizing a conference right now at the university >> at the University of Chicago at the KICP. Um it's a dark matter physics in the era of large surveys conference. So
49:48best of luck to you Dan. Um hopefully the the conference goes well. >> Uh there's some news headline I just saw the other day about uh Slack finding figuring out something about dark matter and I don't remember what the headline was but it was >> Oh yeah. Um I don't think it was Slack. It it was well maybe it was select but it was it was direct detection >> correct >> of dark matter. There was a news headline. Um I was tempted to do a story on it but I want to >> it's a little early. >> It's a little early is let's let them cook. >> The sigma is not that high and um it's a notoriously hard measurement to make. I mean, all power to them. If if
50:30we get a coincident measurement at another direct detection dark matter, like Japan has one, Italy has one in these mines. The South Dakota one is in a mine and they, you know, they purport to have found a dark matter particle. Um, if there is a coincident detection with the same mass and the same energy scale, that's a Nobel Prize waiting to happen, right? So, um, >> immediately. >> Yeah. And yeah, that is an immediate [laughter] immediately. Yes. immediately. Immediately. Yeah. So, we're not going to wait until you're on your deathbed for that one. >> Yeah. So, um I'm I'm waiting for this type of coincident detection. If it does happen, we will 100% cover it. It's very exciting. >> Uh to stay tuned for future news there.
51:14Uh we just have two more in our fall season update to cover. Uh and we thought this was going to be a short episode, but like always, we find a way to yap away. Uh, so our next one, uh,
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