One Flash in the Xenon: The Dark Matter Event Nobody Can Explain

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Anna: Welcome back to Astronomy daily. It's Friday,

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September 4th, 2026. I'm

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Anna and this is series five, episode

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185.

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Avery: And I'm Avery. Anna.

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I want to start today with a number.

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2.6.

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Anna: 2.6 Sigma, which is not a

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discovery.

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Avery: M. You said that very fast.

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Anna: I said it fast because it's the most

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important sentence in the storey. But here's

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the rest of it. A dark matter detector a mile

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underground in South Dakota recorded a single

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flash of light in exactly the place a dark

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matter particle was supposed to show up. And

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the collaboration spent months trying to make

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that flash go away and could not do it.

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Avery: One event.

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Anna: One event. That's our lead.

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Including why we can't explain it. And

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we found dark matter are very different

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sentences.

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Avery: Then India has put its first imaging

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satellite into geostationary orbit. A,

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uh, real first and a capability nobody

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else in the region has.

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Anna: The first private mission to Venus has been

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grounded. Not by Venus, but by a

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rocket that hasn't flown yet.

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Avery: And a lovely piece of physics out of

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Syracuse. Why a star that keeps getting

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torn apart by a black hole puts on a fainter

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show every time.

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Anna: Plus the sky this weekend, both hemispheres

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and a new sunspot worth knowing about.

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Avery: Let's get into it.

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Start me at the beginning. Who announced what

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and where?

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Anna: The LZ collaboration, Lux Zeppelin,

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presented a result this week at TEV Particle

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Astrophysics 2026 in Chiba, Japan, which

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wraps up today. Brown University released it

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on Tuesday. The U.S. department of Energy has

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published its own account. And. And the paper

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has gone to Physical Review Letters.

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Avery: And LZ is the big Xenon one.

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Anna: LZ is the big Xenon one. 10

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tonnes of ultra pure liquid xenon in a tank

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at the Sanford Underground Research facility

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in Lead, South Dakota. That's the old home

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state gold mine. And the detector sits about

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a mile down, roughly 1480

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metres of rock overhead.

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Avery: Why underground?

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Anna: Because the enemy isn't darkness. It's noise.

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At the surface, you're rained on constantly

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by cosmic rays. A mile of rock filters

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nearly all of that out. Then they wrap the

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xenon in a water tank and a veto detector for

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stray neutrons and build it all from

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materials screened for radioactivity to

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absurd levels. The art of this field

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is subtraction. You spend 20 years

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removing every signal you can explain, then

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look at what's left.

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Avery: And what are they hoping is left?

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Anna: A, uh, wimp, weakly interacting massive

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particle. The leading dark matter candidate

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for about 40 years. A heavy particle left

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over from the early universe. That has mass,

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so it pulls on galaxies gravitationally, but

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ignores light and ignores ordinary matter.

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Almost all of the time.

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Avery: Almost all of the time being the operative

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phrase.

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Anna: That's the whole bet. If a WIMP occasionally

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bumps into an atomic nucleus, a big enough

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tub of xenon sitting quietly for long enough

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should eventually record one. The nucleus

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recoils and you get two flashes. A

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prompt one, then a second, from electrons

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drifting up through the liquid. Together they

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tell you where in the tank it happened and

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whether you hit a nucleus or just knocked an

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electron loose.

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Avery: Okay, tell me about the event.

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Anna: It's in data taken between March 2023

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and April 2024.

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220 live days. That

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dataset has been analysed before. LZ

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published world leading limits from it.

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What's new is that a team went back and

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searched a much wider range of possible

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interactions than the standard analysis

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covers, including higher energies.

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And one event turned up, uh, a nuclear

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recoil in a region where the expected

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background is very close to zero.

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Avery: Higher energy. Is that where you'd expect

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dark matter?

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Anna: No. And that's the first genuinely odd

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thing. The simplest WIMP models put your

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first signal at low energies. This is up the

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other end. Taken at face value, it points to

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a particle of at least 200 giga electron

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volts, more than 200 times the mass of a

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proton, interacting in a way the simplest

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models don't predict.

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Avery: So it's not the WIMP anyone ordered.

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Anna: It is not the WIMP anyone ordered.

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Which cuts both ways. And we'll come back to

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that.

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Avery: Give me the statistics. Honestly.

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Anna: 2.6- Sigma globally, 3.4-

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Sigma locally. And the difference between

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those two numbers is the most useful thing I

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can teach anyone today.

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Avery: Go on.

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Anna: LocalSignificants asks at this

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exact energy for this exact mass,

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how surprising is this event? Fairly

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surprising. Global significance asks the

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fairer question. I searched a whole range of

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masses and energies. So how surprising is it

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that somewhere in that range I found one odd

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thing? Account for the haystack and the

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surprise drops. That's the look elsewhere

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effect. Honest experiments quote both

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and LZ did

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Avery: M and 2.6 Sigma means what? In

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plain terms?

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Anna: Roughly a half a percent chance known

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backgrounds produced it. Which sounds

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compelling until you remember the bar.

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Particle physics calls something a discovery

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at five sigma, about one in three and

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a half million. 2.6 is nowhere near

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it. And physicists have watched three sigma

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results evaporate for decades.

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Avery: Did they try to kill it for months?

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Anna: Cosmic rays, neutrons from the rock,

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radioactivity in the detector materials,

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instrumental artefacts all modelled.

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Aaron Manalaise at Berkeley Lab, who chairs

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LZ's institutional board, said it's the first

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example in any experiment he's worked on of

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an outlier that appears valid in every way.

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That's a striking thing for an

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experimentalist to say out loud.

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Avery: What does the spokesperson say?

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Anna: Rick Gates, skull at Brown, is the

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spokesperson and he's been about as

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disciplined as you can be. His. His line

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with only one event. We don't want to get

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ahead of ourselves. We are not claiming to

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have seen dark matter and separately

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we're very intrigued to see this event in the

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data in the region where we expect dark

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matter to show up and the competing

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backgrounds are very low.

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Avery: Both things at once.

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Anna: Both things at once. And that's the correct

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posture. Sam Erickson at Bristol led the

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analysis and made the point that matters.

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Dark matter events are expected to be so rare

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that only a handful could mark the first

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detection. You can't dismiss one event for

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being single, but you can't build a discovery

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on it either.

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Avery: Is there a UK end um, to this?

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Anna: A significant one. Imperial College

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London did much of the work characterising

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the event and Henrique Araujo there put

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it beautifully. We need to analyse more data

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to be sure, but. But these are certainly

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interesting times.

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Avery: Now you promised the caveat about it not

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being the expected wimp.

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Anna: Two ways to read an unexpected signal.

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The generous one. Nature isn't obliged to

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be simple and 40 years of not finding dark

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matter may be exactly because we searched the

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tidiest places first. The unkind one,

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when a result lands where no model predicted,

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an unmodeled background is a very live

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explanation. The reason you haven't modelled

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it is that you didn't know it was there.

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Avery: Has this field been burned before?

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Anna: Repeatedly. DAMA in Italy has claimed an

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annual dark matter signal for over 20 years

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that nobody else can reproduce.

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Xenon1T reported an excess in 2020

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that caused enormous excitement and was most

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likely tritium contamination. A hydrogen

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isotope at a level almost too small to

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measure. That's the standard to hear this

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week against. To LZ's credit, they've

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published this as an anomaly, not a

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discovery.

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Avery: So what settles it?

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Anna: More xenon and more time. LZ has

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already banked substantially more data than

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went into this analysis and is running toward

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a thousand live days. If it's real,

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the rate is set by physics and more events

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follow. The significance climbs. If it's

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a fluke, it decays as exposure grows

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and A proposed successor, XLZD,

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would hold 10 times the xenon. This

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resolves itself in data, not argument.

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Avery: Southern hemisphere angle. Because dark

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matter feels like a Northern Hemisphere

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sport.

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Anna: It has been. And that's changing for a

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genuinely clever reason. There's now an

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underground lab in Australia, supl.

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The Stawell Underground Physics Laboratory, a

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kilometre down. A working gold mine in

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western Victoria. It's the first underground

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physics lab in the Southern hemisphere, built

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by the University of Melbourne with the ARC

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Centre of Excellence for Dark Matter Particle

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Physics and Ansto. And its first

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experiment, Sabre south, moves in late

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this year.

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Avery: And why does the hemisphere matter for dark

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matter of all things?

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Anna: Because of dama. Its claim is

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that the signal rises and falls once a year

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as Earth's motion around the sun adds to and

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subtracts from the solar system's motion

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through the galaxy's dark matter halo. The

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trouble is that plenty of ordinary things

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cycle annually too. Temperature,

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radon, cosmic ray rates. And

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in Italy they all peak in summer alongside

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the claimed signal.

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Avery: And in Victoria, the seasons are flipped.

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Anna: The seasons are flipped and the dark matter

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signal isn't. Run a near identical

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detector in the Southern hemisphere and a

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real galactic signal peaks in the same

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calendar month it does in Italy, while a

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seasonal artefact peaks six months out.

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Elegant piece of experiment design. And the

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only place on Earth you can do it is the one

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we happen to broadcast from.

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Avery: So what should people take away from today?

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Anna: Three things. LZ has found something it

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cannot explain in the right place and

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said so honestly. One event is one event and

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2.6 Sigma is a long way from a discovery.

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And the answer is already being collected.

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The detector is running right now. The honest

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headline is dark matter hunters find

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something they can't explain and refuse to

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overclaim it a good day for science, even if

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it isn't the day.

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Avery: On to our second storey today and this one

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is a genuine national first.

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Overnight, our time, 2:55 in the

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morning, Indian Standard Time on the 4th,

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which was 5:25 yesterday evening,

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US Eastern ISRO

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00:10:57.590 --> 00:10:59.950
launched EOS05 on a

266
00:10:59.950 --> 00:11:02.790
GSLV Mark 2 out of Srihari

267
00:11:02.790 --> 00:11:03.430
Kota.

268
00:11:03.750 --> 00:11:06.350
Anna: And it's the orbit that's the storey, not the

269
00:11:06.350 --> 00:11:06.870
rocket.

270
00:11:07.350 --> 00:11:10.150
Avery: Exactly. EOS05

271
00:11:10.230 --> 00:11:12.630
is India's first dedicated imaging

272
00:11:12.630 --> 00:11:15.350
satellite headed for geosynchronous orbit.

273
00:11:16.110 --> 00:11:18.030
Everything India has flown for Earth

274
00:11:18.030 --> 00:11:20.590
observation until now has been in low

275
00:11:20.590 --> 00:11:23.230
orbit a few hundred kilometres up.

276
00:11:23.710 --> 00:11:25.920
Anna: Spell out the difference for people, a,

277
00:11:25.920 --> 00:11:28.150
Avery: uh, low orbit imaging satellite is a

278
00:11:28.150 --> 00:11:30.910
sprinter. It races around the planet in

279
00:11:30.910 --> 00:11:33.310
90 minutes and gives you a superb,

280
00:11:33.710 --> 00:11:36.710
very high resolution snapshot of a strip of

281
00:11:36.710 --> 00:11:39.710
ground and then it's gone. And you wait.

282
00:11:40.110 --> 00:11:42.350
Depending on the orbit, you might get another

283
00:11:42.350 --> 00:11:44.490
look in a day or, or several days.

284
00:11:45.130 --> 00:11:47.530
Anna: Whereas geostationary is a stair.

285
00:11:48.090 --> 00:11:49.930
Avery: Geostationary is a stair

286
00:11:50.570 --> 00:11:53.330
36,000 kilometres up, matching

287
00:11:53.330 --> 00:11:56.130
Earth's rotation. So from the ground, the

288
00:11:56.130 --> 00:11:58.610
satellite appears to hang motionless over the

289
00:11:58.610 --> 00:12:01.250
same piece of the planet permanently. You

290
00:12:01.250 --> 00:12:03.570
don't get a revisit time because you never

291
00:12:03.570 --> 00:12:04.010
leave.

292
00:12:04.490 --> 00:12:06.330
Anna: And that changes what you can use it for

293
00:12:06.970 --> 00:12:07.610
completely.

294
00:12:08.330 --> 00:12:11.170
Avery: Isro's framing is persistent

295
00:12:11.170 --> 00:12:13.580
coverage of the subcontinent and the

296
00:12:13.580 --> 00:12:15.900
applications are obvious once you say it that

297
00:12:15.900 --> 00:12:18.420
way. A, uh, cyclone forming in the Bay of

298
00:12:18.420 --> 00:12:20.620
Bengal. You watch it develop

299
00:12:20.620 --> 00:12:23.300
continuously instead of getting one frame a

300
00:12:23.300 --> 00:12:26.100
day. A flood, you see the water

301
00:12:26.100 --> 00:12:29.020
advance, a fire front, a landslide,

302
00:12:29.099 --> 00:12:31.980
a border. It's a dual use satellite,

303
00:12:32.060 --> 00:12:34.900
civil and military, and India hasn't been

304
00:12:34.900 --> 00:12:35.820
shy about that.

305
00:12:36.140 --> 00:12:38.100
Anna: There's a trade off though, surely there

306
00:12:38.100 --> 00:12:40.700
Avery: is, and it's worth being honest about it.

307
00:12:41.290 --> 00:12:43.290
You are imagining from a hundred times

308
00:12:43.370 --> 00:12:45.850
further away than a low orbit satellite,

309
00:12:46.170 --> 00:12:48.730
so the resolution is inevitably coarser.

310
00:12:49.050 --> 00:12:51.050
You are not reading number plates from

311
00:12:51.050 --> 00:12:53.810
geostationary orbit. What you're

312
00:12:53.810 --> 00:12:56.530
buying is time, not detail. And

313
00:12:56.530 --> 00:12:59.490
for disaster response, time is usually the

314
00:12:59.490 --> 00:13:00.570
thing you're short of.

315
00:13:01.210 --> 00:13:03.530
Anna: How did the launch go clean?

316
00:13:04.010 --> 00:13:05.410
Avery: The Spacecraft is about

317
00:13:05.410 --> 00:13:07.770
2,367

318
00:13:07.770 --> 00:13:10.660
kilogrammes, and ISRO chairman V

319
00:13:10.660 --> 00:13:13.060
Narayanan said it was successfully and

320
00:13:13.060 --> 00:13:15.820
precisely injected into its planned orbit.

321
00:13:16.140 --> 00:13:19.060
From here, EOS05 works

322
00:13:19.060 --> 00:13:21.300
its way up to its final station over the

323
00:13:21.300 --> 00:13:21.900
coming days.

324
00:13:22.700 --> 00:13:24.700
Anna: And the GSLV has had a mixed history.

325
00:13:25.660 --> 00:13:28.460
Avery: It has, which is part of why this matters to

326
00:13:28.460 --> 00:13:31.140
ISRO. The GSLV

327
00:13:31.140 --> 00:13:33.980
MK2 has now flown 12 times for

328
00:13:33.980 --> 00:13:36.720
10 successes. That's a vehicle that has

329
00:13:36.720 --> 00:13:39.280
visibly matured and it's the one carrying

330
00:13:39.280 --> 00:13:41.840
India's heavier missions to high orbit.

331
00:13:42.400 --> 00:13:43.360
Anna: Small country club.

332
00:13:43.360 --> 00:13:45.280
Avery: This very small,

333
00:13:45.840 --> 00:13:48.320
dedicated, high resolution imaging from

334
00:13:48.320 --> 00:13:50.960
geostationary orbit is a capability

335
00:13:51.200 --> 00:13:54.080
only a handful of nations have ever fielded.

336
00:13:54.400 --> 00:13:57.320
India has just joined that list and it did

337
00:13:57.320 --> 00:13:59.160
it with its own rocket from its own

338
00:13:59.160 --> 00:13:59.760
spaceport.

339
00:14:00.890 --> 00:14:03.850
Anna: Third storey, and it's a frustrating one. The

340
00:14:03.850 --> 00:14:05.930
first privately funded mission to another

341
00:14:06.010 --> 00:14:08.850
planet is still on the ground and it's going

342
00:14:08.850 --> 00:14:10.170
to stay there for a while yet.

343
00:14:10.810 --> 00:14:13.290
Avery: This is the Venus Life Finder.

344
00:14:13.770 --> 00:14:16.410
Anna: That's it. It's an MIT led mission

345
00:14:16.570 --> 00:14:19.250
driven by Sarah Seager, flying in partnership

346
00:14:19.250 --> 00:14:21.730
with Rocket Lab, and it is beautifully,

347
00:14:21.730 --> 00:14:24.570
almost aggressively simple. A small

348
00:14:24.570 --> 00:14:27.430
probe, one instrument, a few minutes of

349
00:14:27.430 --> 00:14:28.110
useful life.

350
00:14:29.070 --> 00:14:30.750
Avery: One instrument. That's it.

351
00:14:31.470 --> 00:14:33.270
Anna: One instrument. It's called an

352
00:14:33.270 --> 00:14:36.030
autofluorescence nifalometer, which is a

353
00:14:36.030 --> 00:14:38.830
mouthful for a fairly elegant idea. You

354
00:14:38.830 --> 00:14:40.990
fire an ultraviolet laser into the cloud

355
00:14:40.990 --> 00:14:43.390
droplets. As you fall through them, certain

356
00:14:43.390 --> 00:14:45.830
organic molecules absorb ultraviolet light

357
00:14:45.830 --> 00:14:47.870
and re emit it at a different wavelength.

358
00:14:48.030 --> 00:14:50.870
They fluoresce. So the instrument is looking

359
00:14:50.870 --> 00:14:53.030
for a glow that ordinary sulfuric acid

360
00:14:53.030 --> 00:14:54.720
chemistry shouldn't produce.

361
00:14:55.360 --> 00:14:57.360
Avery: And why the clouds, specifically?

362
00:14:58.080 --> 00:15:00.280
Anna: Because the surface of Venus is out of the

363
00:15:00.280 --> 00:15:02.880
question. 460 odd

364
00:15:02.880 --> 00:15:05.720
degrees, 90 atmospheres, but

365
00:15:05.720 --> 00:15:08.560
between about 45 and 60 kilometres up,

366
00:15:08.720 --> 00:15:10.720
the temperature and pressure are, uh, close

367
00:15:10.720 --> 00:15:12.800
to conditions at sea level on Earth.

368
00:15:13.280 --> 00:15:16.280
Extremely acidic, but not thermodynamically

369
00:15:16.280 --> 00:15:18.920
hopeless. That's the only plausible

370
00:15:18.920 --> 00:15:21.390
habitable niche on the planet. And it's what

371
00:15:21.390 --> 00:15:23.830
the 2020 phosphine claim put back on the

372
00:15:23.830 --> 00:15:26.230
table. A result that is still genuinely

373
00:15:26.230 --> 00:15:28.550
disputed and which this mission is designed

374
00:15:28.550 --> 00:15:30.590
to go and settle rather than argue about.

375
00:15:31.630 --> 00:15:33.230
Avery: So why isn't it flying?

376
00:15:34.030 --> 00:15:36.750
Anna: Neutron. The mission moved onto Rocket

377
00:15:36.750 --> 00:15:39.550
Lab's new medium lift rocket and Neutron

378
00:15:39.550 --> 00:15:42.030
hasn't flown yet. It was originally talked

379
00:15:42.030 --> 00:15:44.150
about for 2024, slipped to

380
00:15:44.150 --> 00:15:46.990
2026 and it's still in qualification.

381
00:15:47.670 --> 00:15:49.910
The launch date on Rocket Lab's own website

382
00:15:49.910 --> 00:15:51.990
now simply says to be confirmed.

383
00:15:52.710 --> 00:15:54.230
Avery: How is Seeger taking it?

384
00:15:54.310 --> 00:15:57.070
Anna: With more grace than I would. Her

385
00:15:57.070 --> 00:16:00.030
line was, we are awaiting neutron

386
00:16:00.030 --> 00:16:02.470
readiness. And she went on to say she

387
00:16:02.470 --> 00:16:04.710
continues to have high hopes for the mission

388
00:16:04.790 --> 00:16:07.070
and for its role in demonstrating what

389
00:16:07.070 --> 00:16:08.990
private enterprise can do in space

390
00:16:08.990 --> 00:16:09.750
exploration.

391
00:16:10.550 --> 00:16:12.630
Avery: There's an irony in there somewhere.

392
00:16:13.190 --> 00:16:15.430
Anna: There's a real one. The whole pitch of this

393
00:16:15.430 --> 00:16:17.670
mission was speed. That a small,

394
00:16:17.910 --> 00:16:20.830
focused, privately funded probe could go

395
00:16:20.830 --> 00:16:23.630
and answer one sharp question years before an

396
00:16:23.630 --> 00:16:26.390
agency flight could be approved, built and

397
00:16:26.390 --> 00:16:28.829
launched. And it's now waiting on launch

398
00:16:28.829 --> 00:16:31.070
capacity, which is the one part of the

399
00:16:31.070 --> 00:16:32.990
problem private industry was supposed to have

400
00:16:32.990 --> 00:16:33.430
solved.

401
00:16:33.990 --> 00:16:36.310
Avery: Meanwhile, Venus is getting crowded.

402
00:16:36.550 --> 00:16:39.310
Anna: It is. NASA's DaVinci and

403
00:16:39.310 --> 00:16:42.200
Veritas and Europe's Envision are all in

404
00:16:42.200 --> 00:16:43.960
the pipeline. For around the end of this

405
00:16:43.960 --> 00:16:46.800
decade, the Venus Life Finder was meant to be

406
00:16:46.800 --> 00:16:49.200
the scrappy one that got there first. And

407
00:16:49.200 --> 00:16:51.840
that lead is quietly evaporating on a launch

408
00:16:51.840 --> 00:16:52.840
pad in Virginia.

409
00:16:53.400 --> 00:16:55.680
Avery: Last news storey and it's pure

410
00:16:55.680 --> 00:16:58.200
astrophysics, published in the

411
00:16:58.200 --> 00:17:01.200
Astrophysical Journal on Tuesday, led by

412
00:17:01.200 --> 00:17:03.880
Ananya Bandopadhyay, a doctoral

413
00:17:03.880 --> 00:17:06.830
student at Syracuse University with Benjamin

414
00:17:06.830 --> 00:17:09.830
Amend and Eric Coughlin, plus collaborators

415
00:17:09.830 --> 00:17:12.550
at Leeds MIT and the Space

416
00:17:12.550 --> 00:17:14.310
Telescope Science Institute.

417
00:17:14.790 --> 00:17:17.590
Anna: And the puzzle is about stars that survive

418
00:17:17.590 --> 00:17:18.550
being eaten.

419
00:17:19.110 --> 00:17:22.109
Avery: Partly eaten. When a star wanders too

420
00:17:22.109 --> 00:17:24.710
close to a supermassive black hole and is

421
00:17:24.710 --> 00:17:27.350
ripped apart entirely, that's a tidal

422
00:17:27.350 --> 00:17:30.150
disruption event. One enormous flare

423
00:17:30.150 --> 00:17:32.880
and it's over. But there's a smaller

424
00:17:32.880 --> 00:17:35.400
class where the star is only partly stripped

425
00:17:35.400 --> 00:17:38.240
on each pass, survives and comes back

426
00:17:38.240 --> 00:17:38.560
around.

427
00:17:39.120 --> 00:17:42.120
Anna: So it flares over and over, over

428
00:17:42.120 --> 00:17:45.120
Avery: and over on a schedule. The

429
00:17:45.120 --> 00:17:48.080
Famous one is Assassin 14 Ko,

430
00:17:48.400 --> 00:17:51.040
which flares roughly every 114

431
00:17:51.200 --> 00:17:53.440
days and has done so for years.

432
00:17:54.240 --> 00:17:56.640
There are now something like seven or eight

433
00:17:56.640 --> 00:17:57.440
of these known.

434
00:17:58.050 --> 00:17:58.930
Anna: And what's the problem?

435
00:17:59.570 --> 00:18:02.450
Avery: The flares get dimmer each time. Which

436
00:18:02.450 --> 00:18:05.410
sounds intuitive. Less star left to strip.

437
00:18:05.890 --> 00:18:07.850
Except the simulations kept saying the

438
00:18:07.850 --> 00:18:10.850
opposite. Strip material from a star and

439
00:18:10.850 --> 00:18:13.649
it puffs up. And a puffier star is

440
00:18:13.649 --> 00:18:15.490
easier to strip next time round.

441
00:18:16.210 --> 00:18:18.410
Models kept producing flares that got

442
00:18:18.410 --> 00:18:21.250
brighter and the sky kept producing flares

443
00:18:21.250 --> 00:18:22.210
that got fainter.

444
00:18:22.690 --> 00:18:24.130
Anna: So what's the missing ingredient?

445
00:18:24.920 --> 00:18:27.040
Avery: Spin. This team ran

446
00:18:27.040 --> 00:18:29.720
hydrodynamic simulations of a high mass

447
00:18:29.720 --> 00:18:32.320
main sequence star being repeatedly

448
00:18:32.320 --> 00:18:34.840
disrupted by a black hole of about a million

449
00:18:34.920 --> 00:18:37.800
solar masses. And the key move was

450
00:18:37.800 --> 00:18:40.359
giving the star a fast rotation before the

451
00:18:40.359 --> 00:18:42.640
first encounter, spinning in the same

452
00:18:42.640 --> 00:18:44.200
direction as its orbit.

453
00:18:44.680 --> 00:18:46.280
Anna: Why does that change the outcome?

454
00:18:46.440 --> 00:18:48.840
Avery: Because ordinarily, the encounter itself

455
00:18:48.840 --> 00:18:51.720
spins the star up. And that spin up is

456
00:18:51.720 --> 00:18:53.920
part of what makes the next pass more

457
00:18:53.920 --> 00:18:56.440
violent. If the star arrives already

458
00:18:56.520 --> 00:18:59.120
rotating at a decent fraction of its breakup

459
00:18:59.120 --> 00:19:01.920
speed, there's very little extra spin to give

460
00:19:01.920 --> 00:19:04.600
it. The debris then falls back to the black

461
00:19:04.600 --> 00:19:07.240
hole, spread over a longer stretch of time

462
00:19:07.560 --> 00:19:10.440
instead of arriving in one lump. And the same

463
00:19:10.440 --> 00:19:13.280
material dribbling in over longer makes a

464
00:19:13.280 --> 00:19:15.400
fainter, more drawn out flare.

465
00:19:16.130 --> 00:19:18.210
Anna: Spread the fuel out and the fire is lower.

466
00:19:18.610 --> 00:19:21.370
Avery: That's it exactly. And with tens of

467
00:19:21.370 --> 00:19:23.970
percent of breakup rotation prograde,

468
00:19:24.210 --> 00:19:27.010
the simulations reproduce the dimming that's

469
00:19:27.010 --> 00:19:28.130
actually observed.

470
00:19:28.610 --> 00:19:30.810
Anna: Does it tell us anything about how the star

471
00:19:30.810 --> 00:19:31.970
got there in the first place?

472
00:19:32.610 --> 00:19:35.330
Avery: It does. And that's the bonus. A

473
00:19:35.330 --> 00:19:38.250
fast spinning star on a tight orbit around a

474
00:19:38.250 --> 00:19:40.970
supermassive black hole fits the Hill's

475
00:19:40.970 --> 00:19:43.880
mechanism. A, uh, binary pair strays too

476
00:19:43.880 --> 00:19:46.640
close. The black hole keeps one star

477
00:19:46.640 --> 00:19:49.640
and flings the other away at enormous speed.

478
00:19:50.040 --> 00:19:52.720
The captured one lands exactly where you need

479
00:19:52.720 --> 00:19:55.400
it. So the spin isn't an arbitrary

480
00:19:55.400 --> 00:19:58.320
knob. It's a fingerprint of how these systems

481
00:19:58.320 --> 00:19:58.840
get built.

482
00:19:59.400 --> 00:20:02.240
Anna: Right, let's get you outside. And the Moon is

483
00:20:02.240 --> 00:20:03.720
doing us a favour this weekend.

484
00:20:04.280 --> 00:20:05.480
Avery: Last quarter today.

485
00:20:06.200 --> 00:20:08.840
Anna: Last quarter today. September 4th. Which

486
00:20:08.840 --> 00:20:10.920
means it doesn't rise until around midnight.

487
00:20:10.920 --> 00:20:13.720
So. So the entire evening is dark. If you

488
00:20:13.720 --> 00:20:15.200
have been waiting for a night to actually

489
00:20:15.200 --> 00:20:17.760
look at something faint, this is the weekend.

490
00:20:18.160 --> 00:20:19.600
Avery: Southern hemisphere first.

491
00:20:20.080 --> 00:20:22.440
Anna: Southern hemisphere first because we get the

492
00:20:22.440 --> 00:20:25.120
best of it from Sydney. The sun sets about 20

493
00:20:25.120 --> 00:20:27.720
to 6 now, and once it's properly Dark. The

494
00:20:27.720 --> 00:20:29.920
centre of the Milky Way is high overhead.

495
00:20:30.400 --> 00:20:32.840
Sagittarius and Scorpius almost directly

496
00:20:32.840 --> 00:20:35.560
above you. From mid southern latitudes, the

497
00:20:35.560 --> 00:20:38.120
galactic core passes near the zenith, so

498
00:20:38.120 --> 00:20:39.680
you're looking through the least possible

499
00:20:39.760 --> 00:20:42.520
atmosphere. Northern listeners get the same

500
00:20:42.520 --> 00:20:44.880
object low and murky above the southern

501
00:20:44.880 --> 00:20:47.520
horizon. It's the one thing we can be smug

502
00:20:47.520 --> 00:20:50.000
about. And September is the last good month

503
00:20:50.000 --> 00:20:51.360
before it sinks westward.

504
00:20:51.680 --> 00:20:53.200
Avery: What do you actually look at?

505
00:20:53.840 --> 00:20:56.400
Anna: Find the teapot of Sagittarius with the naked

506
00:20:56.400 --> 00:20:59.080
eye and let your eye drift up out of the

507
00:20:59.080 --> 00:21:01.720
spout. That steam is the galactic

508
00:21:01.720 --> 00:21:04.720
centre. Binoculars turn it into star clouds

509
00:21:04.720 --> 00:21:07.450
and dark lanes. And the Lagoon Nebula is

510
00:21:07.450 --> 00:21:09.810
sitting right there, along with a dozen

511
00:21:09.810 --> 00:21:10.930
globular clusters.

512
00:21:11.570 --> 00:21:12.130
Avery: Planets.

513
00:21:12.610 --> 00:21:15.370
Anna: Venus in the west after sunset. Brilliant,

514
00:21:15.370 --> 00:21:18.170
unmistakable. Low and building toward

515
00:21:18.170 --> 00:21:20.210
greatest Brilliancy on the 18th.

516
00:21:20.690 --> 00:21:23.090
Saturn is up most of the night in Aquarius,

517
00:21:23.330 --> 00:21:25.730
climbing toward opposition on October 4th.

518
00:21:25.890 --> 00:21:28.690
And from here it passes far higher overhead

519
00:21:28.690 --> 00:21:30.530
than it does for northern observers.

520
00:21:30.930 --> 00:21:31.810
Avery: Pre dawn.

521
00:21:32.290 --> 00:21:35.250
Anna: Jupiter is the predawn showpiece, well up in

522
00:21:35.250 --> 00:21:37.890
the east before sunrise. And on Sunday

523
00:21:37.890 --> 00:21:40.850
morning the 6th, Mars sits just a few

524
00:21:40.850 --> 00:21:43.570
degrees below a thin, waning crescent Moon.

525
00:21:43.890 --> 00:21:45.850
That's a lovely one for a phone camera if

526
00:21:45.850 --> 00:21:46.530
you're up early.

527
00:21:47.090 --> 00:21:49.730
Avery: Now North America, because there's a proper

528
00:21:49.730 --> 00:21:50.610
event coming.

529
00:21:50.770 --> 00:21:53.530
Anna: On Tuesday the 8th, the moon occults

530
00:21:53.530 --> 00:21:56.170
Jupiter. The planet passes behind the

531
00:21:56.170 --> 00:21:58.700
lunar disc. The footprint favours

532
00:21:58.700 --> 00:22:01.140
northeastern Asia, where it happens in the

533
00:22:01.140 --> 00:22:04.060
dawn sky, and eastern North America

534
00:22:04.220 --> 00:22:06.580
where it happens after sunrise in broad

535
00:22:06.580 --> 00:22:08.700
daylight. Daylight,

536
00:22:09.100 --> 00:22:11.500
daylight. Which brings us to the standing

537
00:22:11.500 --> 00:22:13.900
reminder. And it applies directly here.

538
00:22:14.220 --> 00:22:16.540
If you are observing anywhere near the sun,

539
00:22:16.860 --> 00:22:19.340
hunting for Jupiter in a bright sky or

540
00:22:19.340 --> 00:22:21.340
looking at the sunspot. I'm about to mention

541
00:22:21.900 --> 00:22:24.620
any filter you use for direct solar viewing

542
00:22:25.020 --> 00:22:26.900
must be certified to the ISO

543
00:22:26.900 --> 00:22:29.900
123122 standard.

544
00:22:30.220 --> 00:22:32.820
Not sunglasses, not welding glass of unknown

545
00:22:32.820 --> 00:22:35.500
grade, not smoked glass, not a phone screen.

546
00:22:35.820 --> 00:22:36.620
ISO

547
00:22:36.620 --> 00:22:39.100
123122

548
00:22:39.500 --> 00:22:41.260
and cheque. The certification is real.

549
00:22:41.900 --> 00:22:44.260
Sweeping binoculars or a telescope across a

550
00:22:44.260 --> 00:22:46.900
daylight sky is exactly the situation where

551
00:22:46.900 --> 00:22:49.380
people injure themselves permanently and it

552
00:22:49.380 --> 00:22:50.620
takes a fraction of a second.

553
00:22:51.380 --> 00:22:53.700
Avery: And the day after there's one for us.

554
00:22:53.800 --> 00:22:56.140
Anna: M the ninth, the Moon occults

555
00:22:56.140 --> 00:22:59.100
Regulus, the brightest star in Leo. And

556
00:22:59.100 --> 00:23:01.300
that footprint runs across the South Pacific.

557
00:23:01.700 --> 00:23:04.420
New Caledonia, best placed. Not Australia,

558
00:23:04.580 --> 00:23:07.220
unfortunately. But if you're in that track, a

559
00:23:07.220 --> 00:23:09.540
first magnitude star vanishing off the edge

560
00:23:09.540 --> 00:23:11.780
of the Moon is one of the sharpest things

561
00:23:11.780 --> 00:23:14.020
you'll ever see. Instantaneous.

562
00:23:14.740 --> 00:23:17.320
Avery: You mentioned a Sunspot, a new one,

563
00:23:17.640 --> 00:23:20.600
Anna: Active Region 4524, which

564
00:23:20.600 --> 00:23:23.120
rotated into view over the northeastern limb

565
00:23:23.120 --> 00:23:25.890
this week and has been busy. It fired an M

566
00:23:25.890 --> 00:23:28.840
M3 flare peaking at 19:20 Universal

567
00:23:28.840 --> 00:23:31.720
Time on Wednesday the 2nd, plus a stack of

568
00:23:31.720 --> 00:23:34.640
smaller ones. The coronal mass ejection from

569
00:23:34.640 --> 00:23:37.120
that flare isn't aimed at us, but a filament

570
00:23:37.120 --> 00:23:39.360
eruption the same day threw out material that

571
00:23:39.360 --> 00:23:41.720
may deliver a glancing blow around Monday the

572
00:23:41.720 --> 00:23:43.670
7th. Aurora chances

573
00:23:44.390 --> 00:23:47.150
modest and honest quiet conditions through

574
00:23:47.150 --> 00:23:49.390
the weekend, so nothing to promise tonight or

575
00:23:49.390 --> 00:23:52.190
Saturday. Monday is the one to watch. And if

576
00:23:52.190 --> 00:23:54.070
anything comes of it, the people with a shot

577
00:23:54.070 --> 00:23:56.230
are Tasmania and southern New Zealand down

578
00:23:56.230 --> 00:23:58.990
here and the northern tier of the us, Canada

579
00:23:58.990 --> 00:24:01.390
and Scotland up there. Watch the space

580
00:24:01.390 --> 00:24:03.350
weather feeds rather than the headlines.

581
00:24:03.830 --> 00:24:05.750
Avery: And one for northern observers with

582
00:24:05.750 --> 00:24:06.710
binoculars.

583
00:24:07.030 --> 00:24:09.840
Anna: The Double Cluster in Perseus. Two open

584
00:24:09.840 --> 00:24:12.520
clusters side by side in the same binocular

585
00:24:12.520 --> 00:24:15.400
field. Naked eye. It's a smudge in

586
00:24:15.400 --> 00:24:17.520
binoculars. It's one of the best sights in

587
00:24:17.520 --> 00:24:20.320
the sky and a moonless evening is exactly

588
00:24:20.320 --> 00:24:21.120
when to try it.

589
00:24:21.600 --> 00:24:24.000
Avery: And that's episode 185.

590
00:24:24.640 --> 00:24:27.520
A dark matter detector a mile underground

591
00:24:27.680 --> 00:24:30.360
has recorded one flash of light it cannot

592
00:24:30.360 --> 00:24:33.200
explain and has been admirably careful

593
00:24:33.200 --> 00:24:35.700
about what that does and and doesn't mean.

594
00:24:36.260 --> 00:24:38.940
Anna: India has put its first imaging satellite on

595
00:24:38.940 --> 00:24:41.500
station over the subcontinent. The first

596
00:24:41.500 --> 00:24:43.620
private mission to Venus is stuck waiting on

597
00:24:43.620 --> 00:24:46.220
a rocket that hasn't flown. And a star that

598
00:24:46.220 --> 00:24:48.380
keeps surviving a black hole shines a little

599
00:24:48.380 --> 00:24:51.180
fainter each time because of how fast it was

600
00:24:51.180 --> 00:24:51.940
already spinning.

601
00:24:52.420 --> 00:24:55.140
Avery: Full show notes, links to every primary

602
00:24:55.140 --> 00:24:57.660
source and the whole back catalogue are, uh,

603
00:24:57.740 --> 00:24:59.860
@astronomydaily.IO.

604
00:25:00.020 --> 00:25:02.330
Anna: you can find us on X Instagram and

605
00:25:02.330 --> 00:25:04.890
TikTok Strodaily pod.

606
00:25:05.130 --> 00:25:07.450
And if you've got a question or a correction,

607
00:25:07.690 --> 00:25:10.370
we genuinely want it. There's a contact form

608
00:25:10.370 --> 00:25:10.970
on the website.

609
00:25:12.010 --> 00:25:14.890
Avery: And if today's episode was useful, the single

610
00:25:14.890 --> 00:25:17.170
most helpful thing you can do is send it to

611
00:25:17.170 --> 00:25:18.810
one person who'd enjoy it.

612
00:25:19.210 --> 00:25:21.610
Anna: It's the weekend. Get outside and look up

613
00:25:21.610 --> 00:25:22.810
while the Moon's out of the way.

614
00:25:23.130 --> 00:25:24.890
Until tomorrow. Clear skies.

615
00:25:24.970 --> 00:25:25.850
Avery: Clear skies.

616
00:25:26.490 --> 00:25:27.850
Anna: Astronomy Day

617
00:25:29.610 --> 00:25:30.170
storeys

618
00:25:32.570 --> 00:25:32.810
the.

619
00:25:37.530 --> 00:25:37.930
Storey.