Links & sources Southwest Research Institute — SwRI-led modeling identifies new scenarios for Moon formation — https://www.swri.org/newsroom/press-releases/swri-led-modeling-identifies-new-scenarios-moon-formation Denton, Canup, Asphaug et al. — The Astrophysical Journal Letters (DOI) — https://doi.org/10.3847/2041-8213/ae91e9 Space.com — Earth's moon could have formed in just 5 hours after giant impact — https://www.space.com/astronomy/moon/earths-moon-could-have-formed-in-just-5-hours-after-giant-impact Buchner et al. — A large population of overmassive black hole quasars at z=0.3–0.8 revealed by eROSITA, A&A 713, A11 — https://www.aanda.org/articles/aa/full_html/2026/09/aa59356-26/aa59356-26.html Astronomy & Astrophysics — 2026 press releases — https://www.aanda.org/2026-press-releases Zhang, Garay et al. — An eccentric massive protobinary assembled via a core-merger parabolic encounter, Nature Astronomy — https://www.nature.com/natastron/articles?year=2026 Universidad de Chile coverage of the IRAS 07299-1651 result — https://www.radiofestival.cl/la-danza-nupcial-de-estrellas-masivas-astronomo-de-la-universidad-de-chile-participa-de-historico-hallazgo/ NASA / APL — Dragonfly Gets Wired Up While Titan Landing Area Is Named — https://science.nasa.gov/blogs/dragonfly/2026/09/02/nasas-dragonfly-gets-wired-up-while-titan-landing-area-is-named/ Sky & Telescope — Tuesday's daytime Jupiter occultation, a warm-up for the 'big one' — https://skyandtelescope.org/astronomy-news/tuesdays-daytime-jupiter-occultation-a-warm-up-for-the-big-one/ Universe Today — September's lunar occultations: circumstances and visibility — https://www.universetoday.com/articles/penultimate-lunar-occultations-inbound-for-jupiter-venus-and-more-in-september NASA — What's Up: September 2026 skywatching tips — https://science.nasa.gov/solar-system/skywatching/whats-up-september-2026-skywatching-tips-from-nasa/ EarthSky — Visible planets and night sky guide for September — https://earthsky.org/astronomy-essentials/visible-planets-tonight-mars-jupiter-venus-saturn-mercury/
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This episode includes AI-generated content.
00:00:00 --> 00:00:02 Anna: Hello and welcome to Astronomy daily.
00:00:02 --> 00:00:04 It's Tuesday, September 8,
00:00:05 --> 00:00:08 2026. I'm Anna and this is series
00:00:08 --> 00:00:10 five, episode 188.
00:00:11 --> 00:00:14 Avery: And I'm Avery. Anna, uh, how long did
00:00:14 --> 00:00:15 it take to build the moon?
00:00:16 --> 00:00:18 Anna: Depending on which model you read, anywhere
00:00:18 --> 00:00:20 from a month to a few hundred years.
00:00:21 --> 00:00:24 Avery: And the paper we're leading with today says
00:00:24 --> 00:00:24 five hours.
00:00:25 --> 00:00:28 Anna: Five hours. Not the debris settling, not
00:00:28 --> 00:00:31 the first draught. An intact moon in
00:00:31 --> 00:00:34 orbit five hours after the collision that
00:00:34 --> 00:00:36 made it. And the reason nobody found that
00:00:36 --> 00:00:38 before is almost comically mundane.
00:00:39 --> 00:00:41 Everyone had been modelling rock as if it
00:00:41 --> 00:00:42 were water.
00:00:42 --> 00:00:45 Avery: That's our lead, and it comes from Southwest
00:00:45 --> 00:00:46 research institute.
00:00:47 --> 00:00:49 Anna: Then three more eight quasars whose
00:00:49 --> 00:00:52 black holes are 10 times too big for the
00:00:52 --> 00:00:54 galaxies they live in and are still eating.
00:00:55 --> 00:00:57 A pair of massive stars that didn't form
00:00:57 --> 00:00:59 together at all, but fell past each other and
00:00:59 --> 00:01:02 got caught. And Dragonfly, NASA's
00:01:02 --> 00:01:05 nuclear powered helicopter for Titan, which
00:01:05 --> 00:01:07 just got its wiring and a name for the place
00:01:07 --> 00:01:08 it's going
00:01:08 --> 00:01:10 Avery: to land, plus the sky for both
00:01:10 --> 00:01:13 hemispheres. And if you're in North America,
00:01:13 --> 00:01:16 put the show on and then go outside because
00:01:16 --> 00:01:18 the moon is going to hide Jupiter this
00:01:18 --> 00:01:20 afternoon in broad daylight.
00:01:21 --> 00:01:23 Anna: In daylight. We'll tell you how to do that
00:01:23 --> 00:01:24 safely later on.
00:01:24 --> 00:01:27 Let's start with the Moon and the five hours.
00:01:27 --> 00:01:30 Avery: Alright? Before the new result. Give
00:01:30 --> 00:01:33 me the version we've all been taught, because
00:01:33 --> 00:01:35 I want to know exactly what's being
00:01:35 --> 00:01:36 challenged.
00:01:36 --> 00:01:39 Anna: The giant impact hypothesis. The standard
00:01:39 --> 00:01:42 model. Since the mid-70s, roughly four and
00:01:42 --> 00:01:44 a half billion years ago, a body about the
00:01:44 --> 00:01:47 size of Mars hit the young Earth. We call it
00:01:47 --> 00:01:50 Theia. Not head on. A glancing
00:01:50 --> 00:01:50 blow.
00:01:51 --> 00:01:52 Avery: And that produces the Moon. How?
00:01:53 --> 00:01:56 Anna: In the classical picture, it doesn't produce
00:01:56 --> 00:01:58 the Moon, it produces a mess. Theia
00:01:58 --> 00:02:01 is destroyed. A chunk of Earth's mantle goes
00:02:01 --> 00:02:04 with it and all of that ends up as a disc of
00:02:04 --> 00:02:06 vaporised and molten rock circling the Earth.
00:02:07 --> 00:02:09 A ring system made of magma. Then
00:02:10 --> 00:02:12 over anywhere from about a month to a couple
00:02:12 --> 00:02:14 of hundred years, depending on whose
00:02:14 --> 00:02:17 simulation you read. That disc cools and
00:02:17 --> 00:02:19 clumps and builds a moon.
00:02:19 --> 00:02:22 Avery: So the moon is assembled out of debris
00:02:22 --> 00:02:24 slowly after the fact.
00:02:24 --> 00:02:26 Anna: Assembled out of debris after the fact.
00:02:27 --> 00:02:29 That's the model in every textbook. And it
00:02:29 --> 00:02:32 works beautifully, except for one thing that
00:02:32 --> 00:02:35 has bothered people for about 25 years, which
00:02:35 --> 00:02:37 is the Moon looks too much like Earth.
00:02:38 --> 00:02:40 If you take a lunar sample and measure its
00:02:40 --> 00:02:42 oxygen isotopes, the ratio of
00:02:42 --> 00:02:45 oxygen 17 to oxygen 16, say
00:02:45 --> 00:02:48 you get a number that is indistinguishable
00:02:48 --> 00:02:51 from Earth's. Same for titanium, same
00:02:51 --> 00:02:53 for chromium. Now everybody in the solar
00:02:53 --> 00:02:56 system has its own isotopic fingerprint.
00:02:56 --> 00:02:59 Mars is measurably different. The meteorites
00:02:59 --> 00:03:01 we have from the asteroid belt are different.
00:03:01 --> 00:03:04 Everything has its own signature because
00:03:04 --> 00:03:06 everything formed in a slightly different
00:03:06 --> 00:03:07 part of the disc.
00:03:07 --> 00:03:09 Avery: But the Moon doesn't.
00:03:09 --> 00:03:11 Anna: And that's a problem, because in the
00:03:11 --> 00:03:13 classical model, the disc and therefore the
00:03:13 --> 00:03:16 moon is mostly theia, something
00:03:16 --> 00:03:19 like 60 to 80% theia.
00:03:20 --> 00:03:22 So the Moon should carry Theia's fingerprint,
00:03:22 --> 00:03:25 not Earth's. And it doesn't. People call it
00:03:25 --> 00:03:28 the isotopic crisis. And the fixes on
00:03:28 --> 00:03:31 offer all work, but none of them is clean.
00:03:31 --> 00:03:33 Make the impact violent enough to mix
00:03:33 --> 00:03:36 everything into one vapour cloud or, or make
00:03:36 --> 00:03:38 Thea, uh, a chemical twin of Earth. Which is
00:03:38 --> 00:03:40 possible, but is a coincidence you have to
00:03:40 --> 00:03:41 buy.
00:03:41 --> 00:03:42 Avery: Okay, so what's new?
00:03:43 --> 00:03:45 Anna: What's new is that a team led by a Dean
00:03:45 --> 00:03:48 Denton at Southwest Research Institute with
00:03:48 --> 00:03:51 Robin Canop, who is one of the architects of
00:03:51 --> 00:03:54 the modern giant impact model, and Eric
00:03:54 --> 00:03:56 Asfalg at the University of Arizona
00:03:56 --> 00:03:59 went back and changed one assumption. Not
00:03:59 --> 00:04:02 the speed, not the angle, not the size,
00:04:02 --> 00:04:03 the strength.
00:04:03 --> 00:04:05 Avery: The strength of what?
00:04:05 --> 00:04:08 Anna: Of rock. In essentially every giant
00:04:08 --> 00:04:10 impact simulation ever run, the two
00:04:10 --> 00:04:13 colliding bodies are treated as strengthless
00:04:13 --> 00:04:15 fluids. Which sounds mad, but there's a good
00:04:15 --> 00:04:18 reason. At those energies, rock genuinely
00:04:18 --> 00:04:20 does behave more like a liquid than a solid.
00:04:20 --> 00:04:23 The pressures are so far beyond anything it
00:04:23 --> 00:04:25 can resist that its own material strength,
00:04:26 --> 00:04:28 the thing that makes a boulder a boulder
00:04:28 --> 00:04:30 rather than a puddle, is negligible.
00:04:31 --> 00:04:33 So you ignore it and you save an enormous
00:04:33 --> 00:04:34 amount of computing time.
00:04:34 --> 00:04:37 Avery: And the assumption turns out to be wrong.
00:04:37 --> 00:04:39 Anna: The assumption turns out to be incomplete.
00:04:39 --> 00:04:41 Which is more interesting, because strength
00:04:41 --> 00:04:44 isn't a fixed property. It depends on
00:04:44 --> 00:04:46 temperature. Hot rock is weak,
00:04:47 --> 00:04:49 cold rock is strong. And these bodies were
00:04:49 --> 00:04:52 not all at the same temperature. A young
00:04:52 --> 00:04:54 protoplanet, still hot from its own formation
00:04:54 --> 00:04:57 and full of short lived radioactive isotopes,
00:04:57 --> 00:05:00 is a soft object. An older one that's had a
00:05:00 --> 00:05:02 hundred million years to cool is a much
00:05:02 --> 00:05:03 tougher one.
00:05:03 --> 00:05:05 Avery: So they put temperature dependent strength
00:05:05 --> 00:05:06 into the model.
00:05:07 --> 00:05:09 Anna: They put temperature dependent strength into
00:05:09 --> 00:05:11 the model, ran the canonical impact,
00:05:11 --> 00:05:13 the same parameters as the original
00:05:13 --> 00:05:16 modelling, nothing exotic. And out of one of
00:05:16 --> 00:05:19 those runs came an intact moon. Not a
00:05:19 --> 00:05:22 disc, a satellite. In about five hours,
00:05:23 --> 00:05:25 five hours from impact to moon,
00:05:25 --> 00:05:28 five hours from impact to a self gravitating
00:05:28 --> 00:05:31 body in orbit around the Earth. Deton's own
00:05:31 --> 00:05:32 description is that she used the same
00:05:32 --> 00:05:35 parameters as the Original impact modelling
00:05:35 --> 00:05:38 and within around five hours, an intact moon
00:05:38 --> 00:05:40 emerged. And I want to be careful here,
00:05:40 --> 00:05:41 because this is the bit the headlines
00:05:41 --> 00:05:44 flatten. The point is not that we now know
00:05:44 --> 00:05:47 the moon formed in five hours. The point is
00:05:47 --> 00:05:49 that a variable everybody had reasonably
00:05:49 --> 00:05:52 ignored turns out to swing the outcome from
00:05:52 --> 00:05:54 one formation pathway to a completely
00:05:54 --> 00:05:55 different one.
00:05:55 --> 00:05:57 Avery: So it's a sensitivity result.
00:05:58 --> 00:06:00 Anna: It's a sensitivity result and it's a
00:06:00 --> 00:06:03 genuinely uncomfortable one, because it means
00:06:03 --> 00:06:04 a lot of previous work may have been
00:06:04 --> 00:06:06 exploring only half the possibility space.
00:06:07 --> 00:06:09 Avery: You said one of the runs. What did the others
00:06:09 --> 00:06:10 do?
00:06:10 --> 00:06:13 Anna: This is the part I find lovely. They got
00:06:13 --> 00:06:16 two distinct outcomes, and which
00:06:16 --> 00:06:19 one you land in depends on how hot Theia was,
00:06:19 --> 00:06:21 which is really a question about when the
00:06:21 --> 00:06:24 impact happened, if Theia was young and
00:06:24 --> 00:06:27 hot. The paper puts that at an impact less
00:06:27 --> 00:06:29 than about 60 million years after the solar
00:06:29 --> 00:06:32 system started forming. It's a weak body,
00:06:32 --> 00:06:34 it comes apart completely. You get the
00:06:34 --> 00:06:37 immediate moon made overwhelmingly of Thea's
00:06:37 --> 00:06:38 mantle.
00:06:38 --> 00:06:40 Avery: And if it was older, if the
00:06:40 --> 00:06:43 Anna: impact came later, 100 to 150
00:06:43 --> 00:06:46 million years in Theia has cooled,
00:06:46 --> 00:06:49 it's stronger and it holds together better.
00:06:49 --> 00:06:52 More of it survives the encounter and ends up
00:06:52 --> 00:06:55 merging into the Earth. And what's left? Over
00:06:55 --> 00:06:58 goes the classical route a disc and
00:06:58 --> 00:06:59 a moon that assembles gradually.
00:07:00 --> 00:07:02 Avery: So the moon's own history is a clock.
00:07:03 --> 00:07:05 Anna: The moon's initial state becomes a clock. And
00:07:05 --> 00:07:08 that's the real prize here, because the date
00:07:08 --> 00:07:10 of the giant impact is one of the genuinely
00:07:10 --> 00:07:13 open numbers in planetary science. The
00:07:13 --> 00:07:15 estimates span something like a hundred
00:07:15 --> 00:07:17 million years. If the state the moon started
00:07:17 --> 00:07:20 in depends on when it was hit, then in
00:07:20 --> 00:07:22 principle you can run that backwards. You
00:07:22 --> 00:07:24 look at what the moon is actually made of and
00:07:24 --> 00:07:26 you read off the timing.
00:07:26 --> 00:07:27 Avery: Can we do that yet?
00:07:27 --> 00:07:30 Anna: Not from where we're standing. To separate
00:07:30 --> 00:07:32 these two scenarios properly, you want deep
00:07:32 --> 00:07:35 material, mantle or close to it.
00:07:35 --> 00:07:37 And that is an argument for the sample return
00:07:37 --> 00:07:40 Artemis is building towards and for the
00:07:40 --> 00:07:43 Chinese South Pole missions. This paper has
00:07:43 --> 00:07:45 just made that argument considerably sharper.
00:07:46 --> 00:07:48 Avery: What's the caveat? There's always a
00:07:48 --> 00:07:49 caveat.
00:07:49 --> 00:07:52 Anna: 2 and the authors are upfront about both.
00:07:52 --> 00:07:55 This is a simulation, not an observation.
00:07:55 --> 00:07:57 A better simulation, because it includes
00:07:57 --> 00:08:00 physics that was missing. But the strength
00:08:00 --> 00:08:02 model for rock at those pressures is itself
00:08:02 --> 00:08:05 an approximation. And they ran the canonical
00:08:05 --> 00:08:07 case, one region of parameter space.
00:08:08 --> 00:08:11 The full survey, every angle, every speed,
00:08:11 --> 00:08:13 every temperature is somebody's next several
00:08:13 --> 00:08:14 years.
00:08:14 --> 00:08:16 Avery: Does it fix the isotope problem?
00:08:16 --> 00:08:19 Anna: It nudges it in a helpful direction. The
00:08:19 --> 00:08:22 paper argues that Earth and theia most likely
00:08:22 --> 00:08:23 formed from similar regions of the
00:08:23 --> 00:08:26 protoplanetary disc, near neighbours,
00:08:26 --> 00:08:28 chemically speaking, which is what you'd want
00:08:28 --> 00:08:30 to explain the match. And it distinguishes
00:08:30 --> 00:08:32 both of them from Mars, which formed
00:08:32 --> 00:08:35 somewhere different. So it's not a solution
00:08:35 --> 00:08:37 to the isotopic crisis, so much as a
00:08:37 --> 00:08:39 reframing of what a solution has to look
00:08:39 --> 00:08:39 like.
00:08:39 --> 00:08:42 Avery: Alright, Southern hemisphere angle.
00:08:42 --> 00:08:45 Anna: You've got one, I've got one. And it's about
00:08:45 --> 00:08:47 400 kilometres inland from Geraldton.
00:08:48 --> 00:08:50 Because if the timing of the giant impact is
00:08:50 --> 00:08:52 the number in play, then the hard floor under
00:08:52 --> 00:08:54 that number is sitting in Western Australia,
00:08:55 --> 00:08:57 the Jack Hills in the Narrier. Nice terrain.
00:08:58 --> 00:09:00 That's where the oldest known pieces of the
00:09:00 --> 00:09:03 Earth are zircon crystals. Tiny,
00:09:03 --> 00:09:06 a fraction of a millimetre, dated to about
00:09:06 --> 00:09:07 4.4 billion years.
00:09:08 --> 00:09:10 Avery: And zircons survive things.
00:09:10 --> 00:09:13 Anna: Zircons survive almost everything. You can
00:09:13 --> 00:09:15 lose the rock that contained them and the
00:09:15 --> 00:09:18 crystal keeps its date. And what those Jack
00:09:18 --> 00:09:20 Hills grains tell you is that by 4.4
00:09:20 --> 00:09:23 billion years ago, the Earth had a solid
00:09:23 --> 00:09:26 crust. And on the isotopic evidence,
00:09:26 --> 00:09:29 probably liquid water. Which means the
00:09:29 --> 00:09:31 moon forming impact, an event that turns the
00:09:31 --> 00:09:34 entire surface into a magma ocean, has to be
00:09:34 --> 00:09:35 older than that.
00:09:36 --> 00:09:38 Avery: So the late branch of this new model is up
00:09:38 --> 00:09:40 against a hard deadline.
00:09:40 --> 00:09:43 Anna: And the deadline is a handful of grains of
00:09:43 --> 00:09:45 sand from the Western Australian outback.
00:09:46 --> 00:09:48 I love that the constraint on how the Moon
00:09:48 --> 00:09:51 was born is sitting in a creek bed in the
00:09:51 --> 00:09:52 Murchison.
00:09:53 --> 00:09:55 Avery: That's a good line to move on from Storey
00:09:55 --> 00:09:58 2, published yesterday in Astronomy and
00:09:58 --> 00:10:01 Astrophysics. And it's about black holes that
00:10:01 --> 00:10:04 are the wrong size. Anna, uh, what's the rule
00:10:04 --> 00:10:05 they're breaking?
00:10:05 --> 00:10:08 Anna: The rule is co evolution. Every
00:10:08 --> 00:10:10 big galaxy has a supermassive black hole at
00:10:10 --> 00:10:13 its centre. And the mass of the black hole
00:10:13 --> 00:10:15 tracks the mass of the galaxy's stars
00:10:15 --> 00:10:18 remarkably tightly. Typically, the black
00:10:18 --> 00:10:20 hole is a few tenths of a percent of the
00:10:20 --> 00:10:23 stellar mass. Not 1%, a
00:10:23 --> 00:10:24 few tenths of one.
00:10:25 --> 00:10:27 Avery: And that ratio holds across enormous
00:10:27 --> 00:10:28 ranges
00:10:28 --> 00:10:31 Anna: across a factor of a thousand in galaxy mass,
00:10:31 --> 00:10:34 which is why people take it seriously. The
00:10:34 --> 00:10:36 interpretation has always been that the two
00:10:36 --> 00:10:38 grow together and regulate each other. The
00:10:38 --> 00:10:41 black hole feeds, it blazes as a quasar,
00:10:41 --> 00:10:44 it blows gas out of the galaxy that shuts
00:10:44 --> 00:10:46 down both its own supply and the galaxy's
00:10:46 --> 00:10:48 star formation. A thermostat.
00:10:49 --> 00:10:52 Avery: So here's the result. Johannes Buchner at the
00:10:52 --> 00:10:55 Max Planck Institute for Extraterrestrial
00:10:55 --> 00:10:57 Physics, with colleagues at Penn State,
00:10:57 --> 00:11:00 Illinois, Cal Poly, the Centre for
00:11:00 --> 00:11:02 Astrophysics and the Space Telescope Science
00:11:02 --> 00:11:05 institute went through 140 square
00:11:05 --> 00:11:08 degrees of the E Rosita X ray survey.
00:11:09 --> 00:11:11 They picked out 200 quasars
00:11:11 --> 00:11:14 selected on hard X rays, which is the honest
00:11:14 --> 00:11:16 way to do it because. Because dust can hide a
00:11:16 --> 00:11:19 growing black hole at optical wavelengths,
00:11:19 --> 00:11:21 but not in hard X rays.
00:11:21 --> 00:11:23 Anna: And eight of the 200 are wrong.
00:11:24 --> 00:11:27 Avery: Eight are badly wrong. Black hole to
00:11:27 --> 00:11:29 host galaxy mass ratios above
00:11:29 --> 00:11:32 5%. That's roughly 10 times
00:11:32 --> 00:11:35 what the relation says they should be. The
00:11:35 --> 00:11:37 black holes themselves run from about a
00:11:37 --> 00:11:39 hundred million to three billion solar
00:11:39 --> 00:11:41 masses. They're, uh, at redshifts between
00:11:42 --> 00:11:44 0.3 and 0.8.
00:11:45 --> 00:11:47 So we're looking at them as they were between
00:11:47 --> 00:11:49 about three and a half and seven billion
00:11:49 --> 00:11:52 years ago. And they are all still actively
00:11:52 --> 00:11:55 feeding some of them at close to the
00:11:55 --> 00:11:56 theoretical maximum rate.
00:11:57 --> 00:11:59 Anna: So they're not fossils. They're not objects
00:11:59 --> 00:12:01 that finished growing early and then had
00:12:01 --> 00:12:02 their galaxy stripped away.
00:12:03 --> 00:12:05 Avery: That's the key point. They're still eating.
00:12:06 --> 00:12:08 And they're not rare freaks, either. The
00:12:08 --> 00:12:11 team put a floor on their space density of at
00:12:11 --> 00:12:13 least 4 per cubic gigaparsec.
00:12:14 --> 00:12:17 Which sounds tiny, but for objects this
00:12:17 --> 00:12:19 extreme, it's a population, not an
00:12:19 --> 00:12:20 accident.
00:12:21 --> 00:12:22 Anna: So what does it mean?
00:12:22 --> 00:12:25 Avery: The author's phrase is an accretion channel
00:12:25 --> 00:12:28 disconnected from the stellar population.
00:12:28 --> 00:12:31 Some way of feeding a black hole that doesn't
00:12:31 --> 00:12:33 involve and doesn't disturb the
00:12:33 --> 00:12:36 galaxy's ability to make stars. And
00:12:36 --> 00:12:39 there's a bonus. You'll remember that
00:12:39 --> 00:12:42 JWST has been finding black holes
00:12:42 --> 00:12:44 that look far, far too massive for their
00:12:44 --> 00:12:46 galaxies in the very early universe.
00:12:46 --> 00:12:49 And the explanation people reached for was
00:12:49 --> 00:12:52 exotic seeds. Direct collapse of
00:12:52 --> 00:12:55 enormous gas clouds. Special conditions
00:12:55 --> 00:12:57 that only existed at cosmic dawn.
00:12:58 --> 00:13:01 Anna: And if you find the same thing halfway to the
00:13:01 --> 00:13:03 present day, then maybe
00:13:03 --> 00:13:06 Avery: you don't need the special conditions. Maybe
00:13:06 --> 00:13:08 it's a channel that operates whenever the
00:13:08 --> 00:13:10 circumstances allow. Including now.
00:13:11 --> 00:13:14 That's a much less dramatic explanation, and
00:13:14 --> 00:13:16 it's the kind that tends to be right.
00:13:17 --> 00:13:17 Anna: Caveats.
00:13:18 --> 00:13:21 Avery: Eight objects. And measuring a black
00:13:21 --> 00:13:24 hole's mass from a single spectrum carries
00:13:24 --> 00:13:27 real systematic uncertainty. You're
00:13:27 --> 00:13:29 using the width of an emission line as a
00:13:29 --> 00:13:32 proxy for orbital speed and calibrating
00:13:32 --> 00:13:33 that is an entire field.
00:13:34 --> 00:13:37 Separating a galaxy's starlight from the
00:13:37 --> 00:13:39 quasar's glare is also hard.
00:13:39 --> 00:13:42 The team knows all of this. That's why the
00:13:42 --> 00:13:45 headline number is a floor rather than a
00:13:45 --> 00:13:45 count.
00:13:46 --> 00:13:48 Anna: And it's erosita again. Two episodes
00:13:48 --> 00:13:51 running, it's erosita again.
00:13:51 --> 00:13:54 Avery: The same all sky X ray survey that gave us
00:13:54 --> 00:13:57 that six minute white dwarf binary yesterday.
00:13:58 --> 00:14:00 It has been extraordinarily productive for a
00:14:00 --> 00:14:03 telescope that has been sitting silent since
00:14:03 --> 00:14:04 2022.
00:14:04 --> 00:14:07 Anna: Storey3 also published yesterday,
00:14:08 --> 00:14:10 this time in Nature Astronomy. And
00:14:10 --> 00:14:13 it's a birth storey. Avery. About
00:14:13 --> 00:14:16 90% of massive stars are not alone.
00:14:16 --> 00:14:19 They come in pairs or triples or
00:14:19 --> 00:14:20 more.
00:14:20 --> 00:14:23 Avery: 90%. So the single massive
00:14:23 --> 00:14:25 star is the exception.
00:14:25 --> 00:14:28 Anna: The single massive star is the oddity. And
00:14:28 --> 00:14:31 that matters enormously because massive stars
00:14:31 --> 00:14:33 in pairs are, uh, are what eventually become
00:14:33 --> 00:14:35 the neutron star and black hole binaries that
00:14:35 --> 00:14:38 LIGO and Virgo hear merging. The question
00:14:38 --> 00:14:40 has always been how the pairs form in the
00:14:40 --> 00:14:43 first place. And there have been two answers.
00:14:43 --> 00:14:44 Avery: Give me both.
00:14:45 --> 00:14:48 Anna: One, disc fragmentation. A
00:14:48 --> 00:14:50 single star forms. It has a big accretion
00:14:50 --> 00:14:53 disc around it. The disc is heavy enough to
00:14:53 --> 00:14:56 become unstable and it breaks up and a piece
00:14:56 --> 00:14:58 of it collapses into a second star. That
00:14:58 --> 00:15:01 gives you a close pair orbiting more or less
00:15:01 --> 00:15:03 in the same plane with their discs neatly
00:15:03 --> 00:15:06 aligned because they came from the same disc.
00:15:06 --> 00:15:09 And two core fragmentation.
00:15:09 --> 00:15:12 The cloud core that's collapsing splits early
00:15:12 --> 00:15:15 before the stars really get going. And you
00:15:15 --> 00:15:18 get two protostars far apart. Both
00:15:18 --> 00:15:20 processes are in the models. Nobody had a
00:15:20 --> 00:15:23 clean example of a third possibility, which
00:15:23 --> 00:15:25 is two separate cores forming
00:15:25 --> 00:15:28 independently that happen to fall past each
00:15:28 --> 00:15:31 other and don't escape a
00:15:31 --> 00:15:33 capture. And that's what this team says
00:15:33 --> 00:15:36 they're watching. The object is IRAS
00:15:36 --> 00:15:38
00:15:38 --> 00:15:40 1651, about
00:15:40 --> 00:15:43 1 parsecs away.
00:15:43 --> 00:15:46 Call it five and a half thousand light years.
00:15:46 --> 00:15:49 The work is led by Yi Chen Zhang at Shanghai
00:15:49 --> 00:15:52 Jiaotong University with Guido Garay at the
00:15:52 --> 00:15:54 Universidad uh de Chile. And it's built on
00:15:54 --> 00:15:57 eight years of observations from 2016 to
00:15:57 --> 00:15:58 2024.
00:15:58 --> 00:16:01 Avery: Eight years. What's in the data set?
00:16:01 --> 00:16:04 Anna: ALMA, the Jansky Very Large Array
00:16:04 --> 00:16:07 and JWST. And the picture they
00:16:07 --> 00:16:10 build is two massive protostars about
00:16:10 --> 00:16:13 200 astronomical units apart. So
00:16:13 --> 00:16:16 five times the sun to Pluto distance on a
00:16:16 --> 00:16:17 violently eccentric orbit.
00:16:18 --> 00:16:20 Avery: And the eccentricity is the evidence.
00:16:21 --> 00:16:23 Anna: The eccentricity is half the evidence.
00:16:24 --> 00:16:26 The other half is the discs. Each
00:16:26 --> 00:16:29 protostar has its own and they're tilted with
00:16:29 --> 00:16:31 respect to each other. If these two had
00:16:31 --> 00:16:34 formed from a single fragmenting disc, they'd
00:16:34 --> 00:16:37 share its plane. They don't. They look
00:16:37 --> 00:16:39 like two objects that formed somewhere else
00:16:39 --> 00:16:42 on their own terms and then met on
00:16:42 --> 00:16:44 what the paper calls a parabolic encounter,
00:16:45 --> 00:16:47 which is the astronomer's phrase for a flyby
00:16:47 --> 00:16:49 that was just barely slow enough to end in
00:16:49 --> 00:16:51 capture rather than a miss.
00:16:52 --> 00:16:54 Avery: How do you get captured. Two body gravity
00:16:54 --> 00:16:56 doesn't let you do that.
00:16:56 --> 00:16:57 Anna: It doesn't.
00:16:57 --> 00:17:00 Two bodies on a parabolic path fall past each
00:17:00 --> 00:17:02 other and separate again. You need somewhere
00:17:02 --> 00:17:05 to dump the energy. In this case the
00:17:05 --> 00:17:07 candidates are gas. There's plenty of it in a
00:17:07 --> 00:17:09 star forming core. And drag is very
00:17:09 --> 00:17:12 effective. And the cores themselves which are
00:17:12 --> 00:17:14 not points, they're extended, they're
00:17:14 --> 00:17:17 squishy and they can absorb orbital energy by
00:17:17 --> 00:17:20 deforming. That's the merger part of the
00:17:20 --> 00:17:21 paper's title.
00:17:21 --> 00:17:23 Avery: Southern hemisphere angle.
00:17:23 --> 00:17:26 Anna: It's baked in. The bulk of this is Alma
00:17:26 --> 00:17:29 66 dishes on the Chagnantor Plateau in
00:17:29 --> 00:17:32 northern Chile. 5000 metres up in the
00:17:32 --> 00:17:34 driest desert on Earth. Looking at
00:17:34 --> 00:17:36 wavelengths that only work if there's almost
00:17:36 --> 00:17:38 no water vapour above you. And there's a
00:17:38 --> 00:17:41 Chilean co author on the paper. Which is
00:17:41 --> 00:17:43 exactly how that investment is supposed to
00:17:43 --> 00:17:45 pay off. This is a southern sky object
00:17:46 --> 00:17:48 studied from the southern hemisphere. And the
00:17:48 --> 00:17:50 result is a new way of making the binaries
00:17:50 --> 00:17:53 whose collisions we eventually detect as
00:17:53 --> 00:17:54 gravitational waves.
00:17:54 --> 00:17:57 Avery: Last storey today and it's a progress report
00:17:57 --> 00:18:00 on my favourite mission that nobody has
00:18:00 --> 00:18:02 launched yet. Anna Dragonfly
00:18:02 --> 00:18:04 in one sentence.
00:18:04 --> 00:18:07 Anna: A nuclear powered eight rotor helicopter
00:18:07 --> 00:18:10 about the size of a small car that will fly
00:18:10 --> 00:18:12 around on Saturn's moon Titan.
00:18:12 --> 00:18:14 Avery: Which sounds absurd until you look at the
00:18:14 --> 00:18:17 numbers. Titan's air at the surface is
00:18:17 --> 00:18:20 about four times as dense as ours and the
00:18:20 --> 00:18:23 gravity is about 1/7 thick
00:18:23 --> 00:18:26 air, weak gravity. It is the easiest
00:18:26 --> 00:18:28 place in the solar system to fly. A person
00:18:28 --> 00:18:31 in a decent set of strapped on wings could
00:18:31 --> 00:18:32 manage it.
00:18:32 --> 00:18:33 Anna: So what's the news?
00:18:33 --> 00:18:36 Avery: Two things both from NASA and Johns
00:18:36 --> 00:18:39 Hopkins APL on 2 September.
00:18:39 --> 00:18:42 The first is an assembly milestone. Back in
00:18:42 --> 00:18:44 July the team installed the harness on the
00:18:44 --> 00:18:47 flight fuselage. The harness is the
00:18:47 --> 00:18:50 wiring. Every cable that connects every
00:18:50 --> 00:18:53 instrument, every rotor, every computer.
00:18:53 --> 00:18:55 It's the vehicle's nervous system. And it's
00:18:55 --> 00:18:58 one of those steps that isn't glamorous but.
00:18:58 --> 00:19:00 But does mark the transition from building
00:19:00 --> 00:19:03 parts to building a spacecraft. And the
00:19:03 --> 00:19:05 second, the landing area has a name.
00:19:06 --> 00:19:08 The International Astronomical Union has
00:19:08 --> 00:19:11 approved Amaqeek Undae for the dune field
00:19:11 --> 00:19:13 where Dragonfly will touch down.
00:19:14 --> 00:19:16 Undae is just the IAU's Latin term
00:19:16 --> 00:19:19 for dunes. Amakique comes from Mayan
00:19:19 --> 00:19:22 tradition. It's a name for a protective
00:19:22 --> 00:19:24 deity. And the meaning given in the
00:19:24 --> 00:19:26 announcement is. Is one who locks up the wind
00:19:27 --> 00:19:28 Anna: for a mission that flies.
00:19:29 --> 00:19:31 Avery: For a mission whose entire existence depends
00:19:31 --> 00:19:34 on air moving over rotors. Titan's
00:19:34 --> 00:19:36 dune fields are named after wind gods by
00:19:36 --> 00:19:39 convention. So it's a legitimate naming, but
00:19:39 --> 00:19:42 you could not have scripted it better. The
00:19:42 --> 00:19:44 field is about 500 miles across,
00:19:45 --> 00:19:47 800 kilometres, and it sits just south
00:19:47 --> 00:19:49 of Selk crater.
00:19:49 --> 00:19:51 Anna: And Selk is the destination that actually
00:19:51 --> 00:19:53 matters scientifically.
00:19:53 --> 00:19:56 Avery: Selk is the prize. It's an impact
00:19:56 --> 00:19:59 crater. And an impact on Titan means
00:19:59 --> 00:20:01 heat enough to melt water ice into
00:20:01 --> 00:20:04 liquid water and hold it liquid for a while.
00:20:05 --> 00:20:07 Titan has liquid water underneath as an
00:20:07 --> 00:20:10 ocean and complex organic chemistry on
00:20:10 --> 00:20:13 the surface in the form of those dunes which
00:20:13 --> 00:20:16 are made of organic sand, not silicate
00:20:16 --> 00:20:18 sand. What Selk gives you is a place where
00:20:18 --> 00:20:21 those two things were mixed together. Liquid
00:20:21 --> 00:20:24 water and complex organics in the same place
00:20:24 --> 00:20:27 at the same time. That is the setup for
00:20:27 --> 00:20:30 prebiotic chemistry. And Dragonfly is
00:20:30 --> 00:20:32 designed to fly from the dunes to the crater
00:20:32 --> 00:20:35 and sample both. Timeline
00:20:35 --> 00:20:37 launch in the summer of 2028,
00:20:38 --> 00:20:40 arrival at Titan in late 2034,
00:20:41 --> 00:20:44 and a 3.3 year primary mission after
00:20:44 --> 00:20:46 that. So this is a long game.
00:20:47 --> 00:20:49 If you're listening to this and you're in
00:20:49 --> 00:20:51 high school, you'll be well into your career
00:20:51 --> 00:20:53 before Dragonfly lands.
00:20:53 --> 00:20:56 Anna: And there's an Australian footnote to Titan.
00:20:57 --> 00:20:59 Avery: There is. When Huygens descended through
00:20:59 --> 00:21:01 Titan's atmosphere in January
00:21:01 --> 00:21:04 2005, one of its two data
00:21:04 --> 00:21:06 channels failed. And a, uh, set of radio
00:21:06 --> 00:21:09 telescopes on Earth, including Parkes,
00:21:09 --> 00:21:11 listened directly for the probe's faint
00:21:11 --> 00:21:14 carrier tone to, to reconstruct its descent.
00:21:14 --> 00:21:17 Titan sits low in the northern sky from here
00:21:17 --> 00:21:20 now, but when Dragonfly starts sending,
00:21:20 --> 00:21:22 southern dishes will be part of how we hear
00:21:22 --> 00:21:22 it.
00:21:23 --> 00:21:26 Anna: And that brings us to the sky and North
00:21:26 --> 00:21:28 America. This one is yours. And it is
00:21:28 --> 00:21:29 happening this afternoon.
00:21:29 --> 00:21:32 Avery: The moon occults, uh, Jupiter in
00:21:32 --> 00:21:33 daylight.
00:21:33 --> 00:21:36 Anna: In daylight, the Moon passes in front of
00:21:36 --> 00:21:38 Jupiter and blots it out. It, it's visible
00:21:38 --> 00:21:41 across most of the continental United States.
00:21:41 --> 00:21:43 The exception is California and the
00:21:43 --> 00:21:45 southwestern states, plus Canada, the
00:21:45 --> 00:21:48 Caribbean, Greenland, most of Alaska and
00:21:48 --> 00:21:51 eastern Siberia for most of the lower
00:21:51 --> 00:21:54 48. It happens in the early to mid afternoon.
00:21:54 --> 00:21:57 Avery: And the moon is a 7% crescent
00:21:57 --> 00:21:59 about 30 degrees from the sun, which
00:21:59 --> 00:22:02 Anna: is what makes it both wonderful and genuinely
00:22:02 --> 00:22:04 hazardous. So let's do the safety properly.
00:22:05 --> 00:22:07 You are pointing binoculars into a bright
00:22:07 --> 00:22:09 blue sky within 30 degrees of the sun.
00:22:10 --> 00:22:12 Never sweep binoculars or a telescope near
00:22:12 --> 00:22:15 the sun. Put a solid object between you and
00:22:15 --> 00:22:17 it, the corner of a building, the eaves of a
00:22:17 --> 00:22:20 roof, so the sun is physically blocked before
00:22:20 --> 00:22:23 you raise the glass. Do not look for the Moon
00:22:23 --> 00:22:26 by scanning across. Find it first with the
00:22:26 --> 00:22:26 sun hidden,
00:22:27 --> 00:22:29 Avery: then hold your position and the Eye
00:22:29 --> 00:22:30 safety standard.
00:22:31 --> 00:22:33 Anna: The standard for looking anywhere near the
00:22:33 --> 00:22:34 sun is ISO
00:22:34 --> 00:22:37 123122.
00:22:38 --> 00:22:40 That's the specification for solar viewers
00:22:40 --> 00:22:43 and eclipse glasses. Sunglasses do not
00:22:43 --> 00:22:46 meet it, smoked glass does not meet it, and
00:22:46 --> 00:22:49 exposed film does not meet it. And a filter
00:22:49 --> 00:22:51 of any kind belongs on the front of a
00:22:51 --> 00:22:53 telescope or binoculars, never on the
00:22:53 --> 00:22:56 eyepiece end. This is a daytime event next to
00:22:56 --> 00:22:59 the sun and it deserves the same discipline
00:22:59 --> 00:22:59 as an eclipse.
00:23:00 --> 00:23:02 Avery: Once you're on it, what do you see?
00:23:02 --> 00:23:05 Anna: Jupiter takes somewhere between one and three
00:23:05 --> 00:23:07 minutes to slide behind the bright edge of
00:23:07 --> 00:23:09 the crescent and about the same to come back
00:23:09 --> 00:23:12 out. And it reappears from the dark limb,
00:23:12 --> 00:23:14 which is the better half of the show because
00:23:14 --> 00:23:17 the planet just materialises out of empty sky
00:23:17 --> 00:23:19 with nothing visible next to it.
00:23:19 --> 00:23:21 Avery: And, um, this is the warm up act.
00:23:21 --> 00:23:24 Anna: Indeed it is. Sky and Telescope are billing
00:23:24 --> 00:23:27 the 6 October occultation as the one
00:23:27 --> 00:23:30 to wait for. That one's before dawn in a dark
00:23:30 --> 00:23:33 sky. And it will be the more spectacular of
00:23:33 --> 00:23:36 the pair by a distance. Consider today the
00:23:36 --> 00:23:38 rehearsal southern hemisphere.
00:23:38 --> 00:23:41 Avery: You don't get this afternoon's event, what do
00:23:41 --> 00:23:41 you get?
00:23:42 --> 00:23:44 Anna: You get the best part of the year. Still from
00:23:44 --> 00:23:47 Sydney, the centre of the galaxy is close to
00:23:47 --> 00:23:49 overhead as darkness falls. Scorpius and
00:23:49 --> 00:23:52 Sagittarius up high. The Milky Way running
00:23:52 --> 00:23:55 the length of the sky. And it's drifting west
00:23:55 --> 00:23:57 a little more each night. So this is the run
00:23:57 --> 00:24:00 out of the season. And New Moon falls on the
00:24:00 --> 00:24:03 11th at 27 minutes past 3
00:24:03 --> 00:24:06 UTC, which means the week either side of it
00:24:06 --> 00:24:08 is properly dark. If you're going to get out
00:24:08 --> 00:24:10 of town for one night this month, make it
00:24:10 --> 00:24:11 that week.
00:24:11 --> 00:24:13 Avery: Planets for the south.
00:24:13 --> 00:24:15 Anna: Venus low in the west after sunset.
00:24:16 --> 00:24:19 And it builds to greatest Brilliancy on the
00:24:19 --> 00:24:21 18th at magnitude
00:24:21 --> 00:24:24 -4.8. You'll see
00:24:24 --> 00:24:27 the 22nd quoted elsewhere. That's a different
00:24:27 --> 00:24:29 definition of the same event. And we're using
00:24:29 --> 00:24:32 the 18th. Saturn is up in the
00:24:32 --> 00:24:34 northeast by about 9 o' clock and it's the
00:24:34 --> 00:24:37 storey of the next month opposition on 4
00:24:38 --> 00:24:40 October. And the rings have opened back up to
00:24:40 --> 00:24:43 around 7 degrees, which after the near edge
00:24:43 --> 00:24:45 on view of last year, is a genuine
00:24:45 --> 00:24:48 improvement in a small telescope. And the
00:24:48 --> 00:24:50 Harvest Moon rides past Saturn at the end of
00:24:50 --> 00:24:53 the month. The 26th in the Americas,
00:24:53 --> 00:24:55 the 27th here.
00:24:55 --> 00:24:56 Avery: Morning sky.
00:24:56 --> 00:24:58 Anna: Both hemispheres get Jupiter and Mars before
00:24:58 --> 00:25:01 dawn. Jupiter unmistakable,
00:25:01 --> 00:25:04 closing on Regulus by mid month. And Mars
00:25:04 --> 00:25:06 fainter up near Castor and Pollux.
00:25:07 --> 00:25:09 And the equinox lands on the 23rd of
00:25:09 --> 00:25:12 September at 6 minutes past 12am in M
00:25:12 --> 00:25:14 UTC. That's 10 past 10 on the Wednesday
00:25:14 --> 00:25:17 morning in Sydney and 6 minutes past 8 on the
00:25:17 --> 00:25:20 Tuesday evening in New York. Spring for us,
00:25:20 --> 00:25:21 autumn for the north.
00:25:21 --> 00:25:24 Avery: And that's Astronomy daily for Tuesday,
00:25:24 --> 00:25:24
00:25:24 --> 00:25:27 Anna: September a moon that may have been built in
00:25:27 --> 00:25:30 five hours instead of five centuries, eight
00:25:30 --> 00:25:32 black holes that outgrew their galaxies and
00:25:32 --> 00:25:34 haven't stopped eating, two massive stars
00:25:34 --> 00:25:37 that fell past each other and got caught, and
00:25:37 --> 00:25:39 a helicopter for Titan that now has both its
00:25:39 --> 00:25:41 wiring and an address.
00:25:41 --> 00:25:43 Avery: Every paper and release we've mentioned is
00:25:43 --> 00:25:46 linked in the show notes, along with the full
00:25:46 --> 00:25:47 episode transcript.
00:25:47 --> 00:25:50 Anna: That's astronomydaily IO the whole back
00:25:50 --> 00:25:52 catalogue is there, plus the newsletter if
00:25:52 --> 00:25:54 you'd rather read it, and the contact form if
00:25:54 --> 00:25:56 you want to ask us something. We do read
00:25:56 --> 00:25:58 them, and they've been shaping segments
00:25:58 --> 00:25:58 lately.
00:25:59 --> 00:26:01 Avery: You'll find us on X, at astrodaily Pod
00:26:02 --> 00:26:04 and wherever you get your podcasts. A
00:26:04 --> 00:26:07 rating genuinely helps other people find us.
00:26:08 --> 00:26:10 Anna: We're back tomorrow. Until then, clear skies
00:26:10 --> 00:26:13 and North America. Be careful out there this
00:26:13 --> 00:26:13 afternoon.
00:26:14 --> 00:26:16 Avery: Clear skies, everyone. See you tomorrow.