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This episode includes AI-generated content.
00:00:00 --> 00:00:02 Anna: Welcome back, everyone. Lovely to have you.
00:00:02 --> 00:00:05 Join us for today's episode. 12 billion
00:00:05 --> 00:00:08 years ago, the Milky Way was not the thin,
00:00:08 --> 00:00:10 elegant spiral we pictured. It was
00:00:10 --> 00:00:13 puffed up, turbulent and restless.
00:00:14 --> 00:00:16 Avery: And now, thanks to some extraordinarily
00:00:16 --> 00:00:19 precise stellar ages, astronomers can tell us
00:00:19 --> 00:00:22 when it calmed down and how fast.
00:00:23 --> 00:00:26 Anna: Welcome to Astronomy AstroDailyPod. I'm Anna.
00:00:26 --> 00:00:29 Avery: And I'm avery. It's Wednesday 21st
00:00:29 --> 00:00:31 October, 2026, and this is
00:00:31 --> 00:00:34 episode 210 of series five
00:00:34 --> 00:00:35 today,
00:00:35 --> 00:00:38 Anna: how our galaxy's disc settled in two very
00:00:38 --> 00:00:41 different stages. Then the gas around the
00:00:41 --> 00:00:43 black hole at the centre of the Milky Way
00:00:43 --> 00:00:45 turns out to be rich in metals.
00:00:45 --> 00:00:47 Avery: We'll meet two of the largest simulated
00:00:47 --> 00:00:50 universes ever built, find shadows
00:00:50 --> 00:00:53 shaping the chemistry of a stellar nursery in
00:00:53 --> 00:00:55 Orion. And it's Orionid Night, so
00:00:55 --> 00:00:56 we'll tell you when to look.
00:00:57 --> 00:00:58 Anna: Let's get into it.
00:00:58 --> 00:01:01 Avery: Okay, let's get stuck into our first story,
00:01:01 --> 00:01:01 then.
00:01:01 --> 00:01:04 Anna: Let's start with a picture of our own galaxy.
00:01:05 --> 00:01:07 If you could fly out of the Milky Way and
00:01:07 --> 00:01:10 look at it edge on, most of its stars would
00:01:10 --> 00:01:13 sit in a flat disc. But it's really
00:01:13 --> 00:01:15 two discs, one inside the other.
00:01:16 --> 00:01:19 Avery: A fin disc and a thick disc.
00:01:19 --> 00:01:22 Anna: Exactly. The thin disc holds the younger
00:01:22 --> 00:01:25 stars, including the sun, packed close to the
00:01:25 --> 00:01:28 galactic plane. The thick disc is older,
00:01:28 --> 00:01:30 puffier, and its stars wander much
00:01:30 --> 00:01:32 further above and below the plane.
00:01:33 --> 00:01:35 Jerry Gilmore and Neil Reed identified it
00:01:35 --> 00:01:38 from star counts back in 1983. And
00:01:38 --> 00:01:41 ever since, the question has been, how did
00:01:41 --> 00:01:43 the galaxy end up with two?
00:01:43 --> 00:01:45 Avery: And there are two main stories, aren't, uh,
00:01:45 --> 00:01:45 there.
00:01:46 --> 00:01:48 Anna: There are. Story one.
00:01:49 --> 00:01:51 Stars are always born in a thin,
00:01:51 --> 00:01:54 orderly disc. And over billions of years,
00:01:54 --> 00:01:55 they get shaken up.
00:01:55 --> 00:01:58 Encounters with giant gas clouds, spiral
00:01:58 --> 00:02:01 arms, the central bar. Each one
00:02:01 --> 00:02:03 kicks a star a little further from the plane.
00:02:04 --> 00:02:06 In that picture, the thick disc is just the
00:02:06 --> 00:02:08 old, well shaken part of
00:02:08 --> 00:02:11 Avery: the thin disc, like a stack of paper that
00:02:11 --> 00:02:13 gets messier the longer it sits on a busy
00:02:13 --> 00:02:14 desk.
00:02:14 --> 00:02:17 Anna: Nice. Story two is called the
00:02:17 --> 00:02:20 upside down model. Here, the disc
00:02:20 --> 00:02:23 is born thick because the gas that forms the
00:02:23 --> 00:02:25 first stars is wildly turbulent.
00:02:26 --> 00:02:28 As that gas calms and settles towards the
00:02:28 --> 00:02:31 plane, each new generation of stars forms in
00:02:31 --> 00:02:34 a thinner layer. So the galaxy builds
00:02:34 --> 00:02:37 itself from the top down, thick first,
00:02:37 --> 00:02:37 then later.
00:02:38 --> 00:02:40 Avery: And, um, simulations can produce both.
00:02:41 --> 00:02:43 Anna: That's been the frustrating part. Both
00:02:43 --> 00:02:46 scenarios work in computer models. To
00:02:46 --> 00:02:48 tell them apart. In the real Milky Way, you
00:02:48 --> 00:02:50 need to know how the thickness of the disc
00:02:50 --> 00:02:52 changed with time. And that means knowing the
00:02:52 --> 00:02:55 ages of a lot of stars very precisely,
00:02:55 --> 00:02:58 including the oldest Ones, which is famously
00:02:58 --> 00:02:58 hard.
00:02:59 --> 00:03:01 Avery: So how did this team do it?
00:03:01 --> 00:03:03 Anna: The study comes from David Mirabal, a, uh,
00:03:03 --> 00:03:06 pre doctoral researcher at the Instituto de
00:03:06 --> 00:03:08 Astrophysica de Canarias and and the
00:03:08 --> 00:03:11 University of La Laguna with Carme Gillart
00:03:11 --> 00:03:14 and colleagues in Spain, Italy and Canada.
00:03:14 --> 00:03:17 It was published online on 16 October in the
00:03:17 --> 00:03:20 Astrophysical journal Letters, with the
00:03:20 --> 00:03:21 Institute's release on Monday.
00:03:21 --> 00:03:22 Avery: And the data?
00:03:23 --> 00:03:26 Anna: Gaia, the European Space Agency's
00:03:26 --> 00:03:28 star mapping mission, which measured the
00:03:28 --> 00:03:30 positions, motions and brightness of more
00:03:30 --> 00:03:32 than a billion stars.
00:03:32 --> 00:03:35 But Gaia doesn't hand you ages directly.
00:03:35 --> 00:03:37 That's where a project called Chronogal comes
00:03:37 --> 00:03:40 in. Instead of dating stars one at a time,
00:03:40 --> 00:03:43 it fits the whole colour magnitude diagram
00:03:43 --> 00:03:45 of a, uh, complete sample of stars in the
00:03:45 --> 00:03:48 solar neighbourhood, essentially reading the
00:03:48 --> 00:03:51 population's history from how its stars are
00:03:51 --> 00:03:52 spread across that diagram.
00:03:53 --> 00:03:55 Avery: Give me an everyday version of that.
00:03:55 --> 00:03:58 Anna: Think of a national census. You can't
00:03:58 --> 00:04:00 interview everyone about their birthday, but
00:04:00 --> 00:04:02 if you know how many people of each age a
00:04:02 --> 00:04:04 population should have depends on, and how
00:04:04 --> 00:04:06 births and deaths shape the numbers, the
00:04:06 --> 00:04:09 overall age pyramid tells you a great deal
00:04:09 --> 00:04:11 about the country's history. Chronogal does
00:04:11 --> 00:04:14 something similar with stars, using models of
00:04:14 --> 00:04:16 how stars of different ages and compositions
00:04:16 --> 00:04:18 should be spread across the diagram and
00:04:18 --> 00:04:21 fitting the real distribution Gaia measured.
00:04:21 --> 00:04:23 Avery: And, um, how precise is that?
00:04:24 --> 00:04:27 Anna: Better than 5% for the oldest
00:04:27 --> 00:04:30 stars. That's an uncertainty of around half
00:04:30 --> 00:04:33 a billion years, but which at an age of
00:04:33 --> 00:04:35 11 or 12 billion years is
00:04:35 --> 00:04:36 remarkable.
00:04:36 --> 00:04:39 The team grouped stars into what they call
00:04:39 --> 00:04:42 quasi monoage populationsstars
00:04:42 --> 00:04:45 of nearly the same age and chemistry, and
00:04:45 --> 00:04:47 then measured how far each group spreads
00:04:47 --> 00:04:50 above and below the plane. Astronomers call
00:04:50 --> 00:04:51 that the scale height.
00:04:51 --> 00:04:53 Avery: So which story won?
00:04:53 --> 00:04:56 Anna: The data show a, uh, clear. The younger the
00:04:56 --> 00:04:59 stars, the closer they hug the plane. But the
00:04:59 --> 00:05:02 rate isn't steady. There's a turning point
00:05:02 --> 00:05:04 about 10.8 billion years ago.
00:05:05 --> 00:05:06 Avery: Before and after.
00:05:07 --> 00:05:09 Anna: Before it, the disc flattened very
00:05:09 --> 00:05:12 fast. In just 2 billion years, the scale
00:05:12 --> 00:05:15 height dropped from more than 4
00:05:15 --> 00:05:18 light years to about 1.
00:05:18 --> 00:05:21 After the turning point, the thinning became
00:05:21 --> 00:05:24 very gradual, down to around 400
00:05:24 --> 00:05:26 light years for the youngest stars today.
00:05:26 --> 00:05:29 Avery: And why does that point to upside down?
00:05:29 --> 00:05:32 Anna: Because slow, steady heating can't do
00:05:32 --> 00:05:35 that. If stars were all born thin
00:05:35 --> 00:05:38 and gradually kicked upward, you'd expect the
00:05:38 --> 00:05:40 disc's thickness to change slowly and
00:05:40 --> 00:05:43 smoothly with age. A, uh, collapse that
00:05:43 --> 00:05:46 steep, that early in a young galaxy that
00:05:46 --> 00:05:48 was regularly colliding with smaller ones
00:05:49 --> 00:05:51 fits gas that started turbulent and then
00:05:51 --> 00:05:53 settled in the Author's words.
00:05:53 --> 00:05:56 An initial highly turbulent epoch gave
00:05:56 --> 00:05:59 birth to the thick disc and a calmer
00:05:59 --> 00:06:02 period of gradual gas settling built the thin
00:06:02 --> 00:06:02 disc.
00:06:03 --> 00:06:04 Avery: Mirabal's pretty confident about it.
00:06:04 --> 00:06:07 Anna: He says the result resolves a classic
00:06:07 --> 00:06:10 problem in astrophysics and calls it the
00:06:10 --> 00:06:13 first clear observational evidence favouring
00:06:13 --> 00:06:15 one of the two models for the galaxy's early
00:06:15 --> 00:06:15 stages.
00:06:16 --> 00:06:18 Avery: This lines up with a few things we've
00:06:18 --> 00:06:18 covered.
00:06:19 --> 00:06:19 Anna: It does.
00:06:20 --> 00:06:23 Back in episode 199, we looked at Andromeda,
00:06:23 --> 00:06:25 where clustered supernovae turned out to be
00:06:25 --> 00:06:28 enough to keep a, ah, galaxy's gas turning.
00:06:28 --> 00:06:30 This is the other half of that story. What
00:06:30 --> 00:06:32 happens to a disc as that turbulence dies
00:06:32 --> 00:06:35 down? And in episode 205 we covered the
00:06:35 --> 00:06:38 Sagittarius dwarf galaxy and its own disc
00:06:38 --> 00:06:40 history. The Milky Way's neighbours are being
00:06:40 --> 00:06:41 dated the same way.
00:06:41 --> 00:06:44 Avery: 10.8 billion years ago. Isn't M that
00:06:44 --> 00:06:46 around when the Milky Way swallowed a big
00:06:46 --> 00:06:46 neighbour?
00:06:47 --> 00:06:50 Anna: It's in the right neighbourhood. Gaia data
00:06:50 --> 00:06:52 showed years ago that the young Milky Way
00:06:52 --> 00:06:54 merged with a sizable dwarf galaxy,
00:06:55 --> 00:06:58 usually called Gaia Enceladus, or the
00:06:58 --> 00:07:00 Gaia sausage, somewhere around 10
00:07:00 --> 00:07:03 billion years ago, or a bit earlier.
00:07:04 --> 00:07:06 It's tempting to say the merger ended the
00:07:06 --> 00:07:09 turbulent phase, but this paper doesn't make
00:07:09 --> 00:07:10 that claim.
00:07:10 --> 00:07:12 And the dating of the merger has its own
00:07:12 --> 00:07:15 error bars. So we'll leave it as an open
00:07:15 --> 00:07:18 question and a good one for the next study to
00:07:18 --> 00:07:18 test.
00:07:18 --> 00:07:20 Avery: And, um, the sovereign angle.
00:07:21 --> 00:07:23 Anna: Honestly, there's no Australian team on this
00:07:23 --> 00:07:26 one. But two things are worth knowing.
00:07:26 --> 00:07:28 Gaia's data came home partly through the
00:07:28 --> 00:07:31 European Space Agency's 35 metre
00:07:31 --> 00:07:34 antenna at New NORSHA in Western Australia.
00:07:35 --> 00:07:37 And the same question is being attacked from
00:07:37 --> 00:07:40 the chemical side by gala, the survey run on
00:07:40 --> 00:07:42 the Anglo Australian Telescope at Siding
00:07:42 --> 00:07:44 Spring, which measures the makeup of hundreds
00:07:44 --> 00:07:47 of thousands of stars. Ages and
00:07:47 --> 00:07:49 chemistry together are, um, how galactic
00:07:49 --> 00:07:50 archaeology gets done.
00:07:51 --> 00:07:52 Avery: What should we be careful about?
00:07:53 --> 00:07:56 Anna: Three things. First, this is the
00:07:56 --> 00:07:58 solar neighbourhood, a complete local sample,
00:07:58 --> 00:08:01 not the whole disc. Other parts of the galaxy
00:08:01 --> 00:08:04 may have settled differently. Second, the
00:08:04 --> 00:08:06 authors strongly support the upside down
00:08:06 --> 00:08:09 scenario. That's not the same as ruling
00:08:09 --> 00:08:11 heating out entirely. Later heating still
00:08:11 --> 00:08:13 happened. It just can't explain the steep
00:08:13 --> 00:08:16 early collapse. And third, everything
00:08:16 --> 00:08:19 rests on those ages. They're the best
00:08:19 --> 00:08:21 available, but they come from stellar models.
00:08:21 --> 00:08:23 And the next test is whether independent age
00:08:23 --> 00:08:26 methods like astroseismology find the same
00:08:26 --> 00:08:27 turning point.
00:08:27 --> 00:08:30 Avery: So, born thick, settled, thin.
00:08:31 --> 00:08:33 Anna: Born thick, settled, thin.
00:08:34 --> 00:08:37 Our galaxy's calm, flat disc is the
00:08:37 --> 00:08:39 end of a much messier beginning.
00:08:39 --> 00:08:42 Avery: From the whole disc to Its very centre.
00:08:43 --> 00:08:45 Sagittarius A, the 4 million
00:08:45 --> 00:08:48 solar mass black hole about 26
00:08:48 --> 00:08:51 light years away, is surrounded by streamers
00:08:51 --> 00:08:54 of hot gas called the telescope to work
00:08:54 --> 00:08:56 out what that gas is made of.
00:08:56 --> 00:08:58 Anna: And it's rich in metals.
00:08:58 --> 00:09:01 Avery: Metals in the astronomer's sense, anything
00:09:01 --> 00:09:03 heavier than hydrogen and helium.
00:09:03 --> 00:09:06 Nicole Ford, a PhD student in Daryl Haggard's
00:09:06 --> 00:09:08 group, led the study in the Astronomical
00:09:08 --> 00:09:10 Journal. Webb's mid infrared
00:09:10 --> 00:09:13 spectrograph picked out the separate gas
00:09:13 --> 00:09:15 structures, the bar, the northern arm
00:09:15 --> 00:09:18 and several compact blobs within about a
00:09:18 --> 00:09:20 tenth of a light year of the black hole, some
00:09:20 --> 00:09:23 racing towards us at more than 600 kilometres
00:09:23 --> 00:09:25 per second. And the composition
00:09:26 --> 00:09:28 measured from neon, argon, sulphur,
00:09:28 --> 00:09:31 nickel and iron. The gas comes out mildly
00:09:31 --> 00:09:34 super Solar, around 1.8 times the
00:09:34 --> 00:09:35 sun's metal content.
00:09:36 --> 00:09:39 The team says the enrichment probably comes
00:09:39 --> 00:09:41 from stars that exploded and seeded the
00:09:41 --> 00:09:43 region over time. And the gas looks a lot
00:09:43 --> 00:09:46 like the stars orbiting the black hole, so
00:09:46 --> 00:09:47 they may have formed together.
00:09:49 --> 00:09:51 They also found nickel and iron being freed
00:09:51 --> 00:09:54 from dust. And the compact blobs show signs
00:09:54 --> 00:09:55 of fast shocks.
00:09:56 --> 00:09:59 Anna: Why does metal content matter for a black
00:09:59 --> 00:09:59 hole?
00:10:00 --> 00:10:02 Avery: Because metals help gas cool. Cooler gas
00:10:02 --> 00:10:05 clumps and clumps can fall inward. And
00:10:05 --> 00:10:08 Sagittarius A is a strangely light
00:10:08 --> 00:10:11 eater. Ford puts it neatly. The black hole
00:10:11 --> 00:10:13 is eating a lot less material than other
00:10:13 --> 00:10:15 supermassive black holes and more slowly.
00:10:16 --> 00:10:18 Knowing what's on the menu is part of working
00:10:18 --> 00:10:21 out why. Caveats two,
00:10:21 --> 00:10:23 A companion paper led by Mayura
00:10:23 --> 00:10:26 Balakrishanan found these infrared lines are
00:10:26 --> 00:10:29 shaped by local conditions, so the gas
00:10:29 --> 00:10:32 can't serve as a reliable record of the black
00:10:32 --> 00:10:34 hole's past outbursts. And um, the
00:10:34 --> 00:10:36 preprint first appeared in May, so this is
00:10:36 --> 00:10:39 the journal version arriving rather than a
00:10:39 --> 00:10:42 brand new result. Next step, the team says,
00:10:42 --> 00:10:44 is matching the observations to long
00:10:44 --> 00:10:45 timescale simulations.
00:10:46 --> 00:10:48 Anna: And there is a southern angle you can see for
00:10:48 --> 00:10:48 yourself.
00:10:49 --> 00:10:52 Avery: There is. The galactic centre is a
00:10:52 --> 00:10:55 southern sky object. From Sydney it climbs to
00:10:55 --> 00:10:57 about 85 degrees nearly overhead.
00:10:58 --> 00:11:00 From Los Angeles it peaks, uh, at 27
00:11:00 --> 00:11:03 degrees, New York 20 and London
00:11:03 --> 00:11:06 under 10. Tonight at the end of civil
00:11:06 --> 00:11:08 twilight, it's 52 degrees up from Sydney.
00:11:09 --> 00:11:11 You won't see the black hole of course, but
00:11:11 --> 00:11:12 you can point at it
00:11:13 --> 00:11:16 Anna: now to a universe that doesn't exist. Or
00:11:16 --> 00:11:19 rather two of them. Researchers at the
00:11:19 --> 00:11:21 US Department of Energy's Argonne National
00:11:21 --> 00:11:24 Laboratory have completed two of the largest
00:11:24 --> 00:11:26 cosmological simulations ever run.
00:11:27 --> 00:11:27 Avery: How large?
00:11:28 --> 00:11:31 Anna: Each one follows 13.4 trillion
00:11:31 --> 00:11:33 dark matter particles across a region
00:11:33 --> 00:11:36 28.6 billion light years wide.
00:11:36 --> 00:11:38 They ran on Aurora, one of the world's
00:11:38 --> 00:11:41 largest supercomputers. Each run used about
00:11:42 --> 00:11:44 8 nodes and roughly
00:11:44 --> 00:11:47 50 graphics processors. And the
00:11:47 --> 00:11:50 simulations, plus much of the analysis took
00:11:50 --> 00:11:51 about four days.
00:11:51 --> 00:11:52 Avery: Um, and the data?
00:11:52 --> 00:11:55 Anna: The two runs wrote more than 85
00:11:55 --> 00:11:58 petabytes, mostly as restart
00:11:58 --> 00:12:01 checkpoints in case something crashed. About
00:12:01 --> 00:12:03 eight petabytes were kept for science.
00:12:03 --> 00:12:04 Avery: What's it for?
00:12:04 --> 00:12:07 Anna: Cosmic inflation. The brief burst
00:12:07 --> 00:12:10 of extreme expansion in the first instant of
00:12:10 --> 00:12:13 the universe. The standard picture says
00:12:13 --> 00:12:15 inflation left behind density ripples with a
00:12:15 --> 00:12:18 simple Gaussian kind of randomness. If
00:12:18 --> 00:12:20 the real ripples depart from that even
00:12:20 --> 00:12:22 slightly, what's called primordial non
00:12:22 --> 00:12:25 gaussianity, it could point to extra fields
00:12:25 --> 00:12:27 or physics at work during inflation.
00:12:28 --> 00:12:30 Avery: And the signal is tiny.
00:12:31 --> 00:12:33 Anna: Tiny and hidden on the largest
00:12:33 --> 00:12:36 scales, where cosmic variance,
00:12:36 --> 00:12:39 the fact that we only have one universe to
00:12:39 --> 00:12:41 samplemuddies everything. So you
00:12:41 --> 00:12:44 need enormous volume and enough
00:12:44 --> 00:12:47 resolution to see the dark matter halos that
00:12:47 --> 00:12:48 host galaxies.
00:12:48 --> 00:12:49 That's the hard bit.
00:12:50 --> 00:12:51 Avery: Here's the clever part, though.
00:12:52 --> 00:12:54 Anna: Two clever parts. The two runs are
00:12:54 --> 00:12:57 statistical mirror images. Same
00:12:57 --> 00:12:59 physics, but with their initial ripples
00:12:59 --> 00:13:02 flipped. Analyse them together and a lot
00:13:02 --> 00:13:05 of the random noise cancels out. And the
00:13:05 --> 00:13:07 strength of the non Gaussian signal planted
00:13:07 --> 00:13:10 inside is blinded. Teams working on
00:13:10 --> 00:13:12 DESI, the Dark Energy Spectroscopic
00:13:12 --> 00:13:15 Instrument and NASA's SPHERE X mission, can
00:13:15 --> 00:13:17 build mock skies from it and test whether
00:13:17 --> 00:13:19 their pipelines recover the hidden answer
00:13:20 --> 00:13:22 before they go anywhere near the real data.
00:13:22 --> 00:13:25 Avery: Like marking an exam where you don't know the
00:13:25 --> 00:13:27 answer key exactly.
00:13:28 --> 00:13:30 Anna: A quick note on what this is and isn't.
00:13:31 --> 00:13:33 It's a computing milestone announced by
00:13:33 --> 00:13:36 Argonne on 19 October. Not a
00:13:36 --> 00:13:38 published scientific result. The science
00:13:38 --> 00:13:40 comes when survey teams use it, but it fits a
00:13:40 --> 00:13:43 theme on this show. In episode 193, we
00:13:43 --> 00:13:46 covered the dark energy supernova compilation
00:13:46 --> 00:13:49 and how much of modern cosmology is about not
00:13:49 --> 00:13:52 fooling yourself. Line tests are how you do
00:13:52 --> 00:13:52 that.
00:13:52 --> 00:13:54 Avery: Since it's Orionid night, let's stay in
00:13:54 --> 00:13:57 Orion. About 1350
00:13:57 --> 00:14:00 light years away, inside the Orion Nebula
00:14:00 --> 00:14:03 sits a ridge of gas called the Orion Bar.
00:14:03 --> 00:14:05 It's where ultraviolet light from young
00:14:05 --> 00:14:07 massive stars is eating into the molecular
00:14:07 --> 00:14:08 cloud.
00:14:08 --> 00:14:10 Anna: They were born from a, uh, photo
00:14:10 --> 00:14:12 dissociation region, right?
00:14:12 --> 00:14:15 Avery: A zone where starlight breaks molecules
00:14:15 --> 00:14:18 apart. And we see the Orion Bar almost
00:14:18 --> 00:14:21 edge on, so its layers line up like a cross
00:14:21 --> 00:14:24 section. That makes it the textbook
00:14:24 --> 00:14:26 test case. The trouble is that Alma and
00:14:26 --> 00:14:29 Webb images show the layers don't behave Like
00:14:29 --> 00:14:32 a textbook. The front where hydrogen
00:14:32 --> 00:14:34 molecules are destroyed overlaps the front
00:14:34 --> 00:14:37 where ionised carbon recombines and the
00:14:37 --> 00:14:39 emission comes in arcs and filaments.
00:14:40 --> 00:14:42 Anna: And the models were one dimensional?
00:14:42 --> 00:14:45 Avery: Mostly, yes. Tidy layers in a row.
00:14:45 --> 00:14:48 M A team led by brank gaetjes@ uh, the
00:14:48 --> 00:14:50 University of Duisburg Essen with colleagues
00:14:50 --> 00:14:53 at Zhejiang Lab in China has now built what
00:14:53 --> 00:14:55 they describe as the first fully three
00:14:55 --> 00:14:58 dimensional high resolution model of an Orion
00:14:58 --> 00:15:01 bar like region. It's in Astronomy and
00:15:01 --> 00:15:03 Astrophysics, published online on 16 October.
00:15:04 --> 00:15:06 Anna: What does 3D change?
00:15:07 --> 00:15:10 Avery: Shadows. Real clouds are clumpy. Dense
00:15:10 --> 00:15:12 knots block the incoming radiation and leave
00:15:12 --> 00:15:15 shielded pockets behind them where molecules
00:15:15 --> 00:15:18 survive and the chemistry runs differently in
00:15:18 --> 00:15:20 the Model A uh, box about a tenth of a light
00:15:20 --> 00:15:23 year across with cells around 160 times
00:15:23 --> 00:15:26 the Earth's sun distance. Those shadows
00:15:26 --> 00:15:28 naturally produce the overlapping fronts and
00:15:28 --> 00:15:30 the arc like hydrogen emission Webb Cs
00:15:32 --> 00:15:34 it's an analogue, not a reconstruction.
00:15:35 --> 00:15:37 The team uses statistically realistic
00:15:37 --> 00:15:40 fractal clouds rather than the actual Orion
00:15:40 --> 00:15:41 bar's shape.
00:15:41 --> 00:15:44 So it shows the mechanism works, not that
00:15:44 --> 00:15:47 every filament is explained. And Orion
00:15:47 --> 00:15:49 is one of the few deep sky targets both
00:15:49 --> 00:15:51 hemispheres share up after midnight from
00:15:51 --> 00:15:53 everywhere this month. Upside down from
00:15:53 --> 00:15:55 Sydney Quick hits.
00:15:56 --> 00:15:58 Anna: ESA's Hira spacecraft fires its second
00:15:58 --> 00:16:01 braking burn, BRM M2 on Thursday.
00:16:02 --> 00:16:04 It's a shorter follow up to last week's 93
00:16:04 --> 00:16:05 minute BRM1.
00:16:06 --> 00:16:08 Fine tuning Hira's approach to Didymos and
00:16:08 --> 00:16:10 Dimorphos. The asteroid's dart hit in
00:16:10 --> 00:16:13 2022. Close in characterization
00:16:13 --> 00:16:16 from about 25 to 30 kilometres follows in
00:16:16 --> 00:16:18 November and December with tracking through
00:16:18 --> 00:16:20 ESA's new Norsha Station in Western
00:16:20 --> 00:16:20 Australia.
00:16:21 --> 00:16:24 Avery: Uzbekistan has signed the Artemis Accords,
00:16:24 --> 00:16:27 the 77th nation to do so at a ceremony
00:16:27 --> 00:16:28 in Samarkand on Monday.
00:16:29 --> 00:16:31 Anna: And NASA will give an update on Artemis on
00:16:31 --> 00:16:33 Thursday at 2pm Eastern.
00:16:33 --> 00:16:36 That's 5am Friday in Sydney. Including
00:16:36 --> 00:16:39 Artemis 3, which NASA now plans as a
00:16:39 --> 00:16:42 2027 crewed test in Earth orbit of
00:16:42 --> 00:16:44 rendezvous with its commercial lunar landers
00:16:44 --> 00:16:47 ahead of a landing attempt targeted for 2028.
00:16:47 --> 00:16:49 We'll bring you what said Skywatch.
00:16:50 --> 00:16:52 Avery: And tonight is the peak of the Orionid meteor
00:16:52 --> 00:16:55 shower. Dust from Hallie's Comet.
00:16:55 --> 00:16:58 Under dark skies it typically gives up to
00:16:58 --> 00:17:00 about 20 metres an hour. The catch this year
00:17:00 --> 00:17:03 is the moon. It's waxing gibbous, around
00:17:03 --> 00:17:05 3/4 lit, so you'll want to wait until it
00:17:05 --> 00:17:06 sets.
00:17:06 --> 00:17:09 Anna: Remind us why Hallie's dust makes good
00:17:09 --> 00:17:11 Avery: meteors speed
00:17:12 --> 00:17:14 Orionids hit the atmosphere at around 66
00:17:14 --> 00:17:17 kilometres per second, among the fastest of
00:17:17 --> 00:17:18 any annual shower.
00:17:18 --> 00:17:21 So the brighter ones often leave glowing
00:17:21 --> 00:17:24 trains that linger for a second or two. And
00:17:24 --> 00:17:26 Earth crosses Hallie's debris twice a year.
00:17:26 --> 00:17:29 In May we get the Eta Aquarids, which
00:17:29 --> 00:17:31 favour the southern hemisphere. And in
00:17:31 --> 00:17:34 October the Orionids, which this year favour
00:17:34 --> 00:17:35 the north.
00:17:35 --> 00:17:37 Anna: And when do they set?
00:17:37 --> 00:17:40 Avery: On Thursday morning, 3:38am in
00:17:40 --> 00:17:43 Sydney, 3:22 in Los Angeles,
00:17:43 --> 00:17:46 3:12 in New York and 2:49 in
00:17:46 --> 00:17:48 London. After that you've got dark sky until
00:17:48 --> 00:17:49 dawn.
00:17:49 --> 00:17:51 Anna: And this one favours the north?
00:17:52 --> 00:17:54 Avery: It does. And it's worth being straight about
00:17:54 --> 00:17:54 it.
00:17:55 --> 00:17:57 From Los Angeles you get more than two hours
00:17:57 --> 00:18:00 of dark sky after moonset with the radiant
00:18:00 --> 00:18:03 near orion's raised club, 59 to 70
00:18:03 --> 00:18:05 degrees up. New York is similar.
00:18:05 --> 00:18:08 London gets nearly three hours with the
00:18:08 --> 00:18:10 radiant 43 to 54 degrees up
00:18:11 --> 00:18:13 from Sydney. There's only about an hour
00:18:13 --> 00:18:15 between moonset and astronomical dawn at
00:18:15 --> 00:18:18 4:37 and the radiant sits 35
00:18:18 --> 00:18:21 to 40 degrees up in the northeast. Still
00:18:21 --> 00:18:23 worthwhile, just shorter.
00:18:23 --> 00:18:26 Lie back, look about 45 degrees away
00:18:26 --> 00:18:29 from the radiant and give your eyes 20
00:18:29 --> 00:18:29 minutes.
00:18:30 --> 00:18:31 Anna: What does the south get?
00:18:31 --> 00:18:34 Avery: The evening Mercury is about 16 and a half
00:18:34 --> 00:18:37 degrees up at the end of civil twilight from
00:18:37 --> 00:18:40 Sydney around 7:39 and sets
00:18:40 --> 00:18:42 just after 9. From Los Angeles it's 4
00:18:42 --> 00:18:45 degrees up, New York too. And from London
00:18:45 --> 00:18:46 it's already gone.
00:18:47 --> 00:18:49 And as we said earlier, the centre of The
00:18:49 --> 00:18:51 Galaxy is 52 degrees up from Sydney at uh,
00:18:51 --> 00:18:54 dusk. Sagittarius and Scorpius high in the
00:18:54 --> 00:18:57 west against 21 from Los Angeles and
00:18:57 --> 00:18:58 16 from New York.
00:18:58 --> 00:18:59 Anna: And Venus.
00:19:00 --> 00:19:02 Avery: Venus reaches inferior conjunction on
00:19:02 --> 00:19:05 Saturday the 24th, passing between us
00:19:05 --> 00:19:08 and the sun only about 6.5
00:19:08 --> 00:19:11 degrees from the Sun's direction. So not one
00:19:11 --> 00:19:12 to hunt for.
00:19:12 --> 00:19:14 And never um, look anywhere near the sun with
00:19:14 --> 00:19:17 your eyes or any optics unless you're using a
00:19:17 --> 00:19:19 certified solar filter that meets the ISO
00:19:19 --> 00:19:22 123122 standard.
00:19:22 --> 00:19:24 Anna: Anything for the weekend?
00:19:24 --> 00:19:27 Avery: On Saturday evening the nearly full moon sits
00:19:27 --> 00:19:30 close to Saturn, about 6 degrees apart from
00:19:30 --> 00:19:32 Sydney and London. Eight from New York,
00:19:32 --> 00:19:34 nearly 10 from Los Angeles.
00:19:35 --> 00:19:38 Full moon follows on Monday the 26th at
00:19:38 --> 00:19:39 4:11am, UM Universal Time.
00:19:40 --> 00:19:43 That's 3:11 in the afternoon in Sydney. So
00:19:43 --> 00:19:45 it'll look full on both Sunday and Monday
00:19:45 --> 00:19:48 nights. And in the pre dawn east,
00:19:48 --> 00:19:51 Mars and Jupiter keep closing in 10 degrees
00:19:51 --> 00:19:53 apart now about 7 by the 28th and 4 by
00:19:53 --> 00:19:54 the 5th of November.
00:19:55 --> 00:19:56 Anna: And a uh, practical note for our
00:19:56 --> 00:19:59 Avery: northern listeners clocks,
00:19:59 --> 00:20:02 the UK moves back to Greenwich Mean Time
00:20:02 --> 00:20:04 early on Sunday the 25th, and the United
00:20:04 --> 00:20:07 States follows on Sunday the 1st of November.
00:20:08 --> 00:20:10 So for a week, the gap between London and New
00:20:10 --> 00:20:13 York shrinks by an hour. If you're planning a
00:20:13 --> 00:20:15 pre dawn session next week, check which time
00:20:15 --> 00:20:18 your app is showing. Here in Australia, we're
00:20:18 --> 00:20:20 already on daylight time, so nothing changes.
00:20:21 --> 00:20:23 Plenty to see, which is
00:20:23 --> 00:20:24 always a good thing.
00:20:25 --> 00:20:27 Anna: That's Astronomy daily for Wednesday,
00:20:27 --> 00:20:28 21 October.
00:20:29 --> 00:20:32 Today, the Milky Way's disc was born thick
00:20:32 --> 00:20:35 and settled thin. The gas around our central
00:20:35 --> 00:20:38 black hole is rich in metals. Two
00:20:38 --> 00:20:40 mirror image universes are ready to test the
00:20:40 --> 00:20:43 next generation of surveys and shadows are
00:20:43 --> 00:20:45 shaping the chemistry of the Orion Bar.
00:20:46 --> 00:20:48 Avery: Find show notes, sources and the Fullback
00:20:48 --> 00:20:51 Catalogue at astronomydaily IO and
00:20:51 --> 00:20:53 you can reach us through the contact form
00:20:53 --> 00:20:55 there. Your questions really do shape what we
00:20:55 --> 00:20:56 cover.
00:20:56 --> 00:20:58 We're astrodaily pod on social media.
00:20:59 --> 00:21:01 Anna: Tomorrow we'll check in on Hera's second
00:21:01 --> 00:21:04 breaking burn and anything else the universe
00:21:04 --> 00:21:05 throws at us.
00:21:05 --> 00:21:06 Avery: I'm Avery.
00:21:06 --> 00:21:09 Anna: And I'm Anna. Uh, thanks for listening.
00:21:09 --> 00:21:11 And if you're up for the Orionids, clear
00:21:11 --> 00:21:12 skies.