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00:00:00 --> 00:00:02 Anna: A galaxy should be quiet. Stir
00:00:02 --> 00:00:05 a cloud of gas and the churning dies away in
00:00:05 --> 00:00:08 a few million years, like ripples going flat
00:00:08 --> 00:00:11 on a pond. And yet every spiral
00:00:11 --> 00:00:13 galaxy we look at is still churning.
00:00:13 --> 00:00:15 Something keeps stirring the pot.
00:00:16 --> 00:00:18 Avery: Today, a survey of the galaxy next door that
00:00:18 --> 00:00:21 catches a spoon in the act, plus the
00:00:21 --> 00:00:23 ghostly particles that may decide which stars
00:00:23 --> 00:00:26 explode at all. A planet with an expiry
00:00:26 --> 00:00:28 date and the sun goes blank for the first
00:00:28 --> 00:00:29 time since February.
00:00:30 --> 00:00:31 Anna: The I'm Anna.
00:00:31 --> 00:00:34 Avery: And I'm Avery. This is astronomy daily,
00:00:34 --> 00:00:36 episode 199.
00:00:36 --> 00:00:39 Anna: Start with a problem that has sat in the
00:00:39 --> 00:00:42 background of galaxy science for about 50
00:00:42 --> 00:00:45 years, and that has the useful quality of
00:00:45 --> 00:00:48 being easy to state and very hard to
00:00:48 --> 00:00:51 answer. The gas between the stars in a
00:00:51 --> 00:00:53 galaxy is turbulent. It is not sitting still
00:00:53 --> 00:00:56 and it is not flowing smoothly. It is
00:00:56 --> 00:00:59 churning on every scale from a few light
00:00:59 --> 00:01:02 years up to thousands, with gas moving at
00:01:02 --> 00:01:04 something like 10 kilometres a second
00:01:04 --> 00:01:06 relative to its neighbours. We have measured
00:01:06 --> 00:01:09 this in our own galaxy and in every nearby
00:01:09 --> 00:01:12 galaxy we can resolve it is simply how
00:01:12 --> 00:01:15 interstellar gas behaves. Here is the
00:01:15 --> 00:01:18 problem. Turbulence dies. That is
00:01:18 --> 00:01:20 the one thing turbulence reliably does.
00:01:21 --> 00:01:24 Energy cascades from big eddies down to
00:01:24 --> 00:01:26 small eddies, and at the bottom it turns into
00:01:26 --> 00:01:29 heat and it gone. In
00:01:29 --> 00:01:31 1999, an astrophysicist named
00:01:31 --> 00:01:34 Mordecai Mark Macklow put a number on
00:01:34 --> 00:01:36 how fast that happens in interstellar
00:01:36 --> 00:01:39 conditions. And the number was brutal.
00:01:40 --> 00:01:42 Turbulence in a galaxy's gas should decay
00:01:42 --> 00:01:45 away in roughly the time it takes the gas to
00:01:45 --> 00:01:48 cross itself once a few tens of
00:01:48 --> 00:01:50 millions of years on a galactic clock.
00:01:50 --> 00:01:53 That's an afternoon. So the churning
00:01:53 --> 00:01:56 we see should not be there unless
00:01:56 --> 00:01:58 something is putting the energy back
00:01:58 --> 00:02:01 continuously for billions of years.
00:02:01 --> 00:02:03 Avery: And there has never been a shortage of
00:02:03 --> 00:02:04 suspects.
00:02:04 --> 00:02:07 Anna: No shortage at all. Supernovae are
00:02:07 --> 00:02:10 the obvious one. But gravity itself can
00:02:10 --> 00:02:13 drive turbulence. As the disc shears and
00:02:13 --> 00:02:16 clumps, there is the magnetorotational
00:02:16 --> 00:02:18 instability, which wrings energy out of the
00:02:18 --> 00:02:21 galaxy's rotation through its magnetic field.
00:02:21 --> 00:02:23 There is gas falling in from outside, and
00:02:23 --> 00:02:26 massive stars blow winds long before they
00:02:26 --> 00:02:29 explode. All of these are real. The
00:02:29 --> 00:02:31 question was never whether supernovae
00:02:31 --> 00:02:34 contribute. It was whether they are enough
00:02:34 --> 00:02:37 on their own to pay the whole bill.
00:02:37 --> 00:02:39 Avery: Uh, and to answer that, you need to do
00:02:39 --> 00:02:41 something nobody had managed. You need to
00:02:41 --> 00:02:44 count the receipts. When massive stars in a
00:02:44 --> 00:02:46 cluster explode, and they do it in batches,
00:02:46 --> 00:02:49 because massive stars are born in groups and
00:02:49 --> 00:02:51 die within a few million years of one
00:02:51 --> 00:02:54 another, the blasts merge. Instead of
00:02:54 --> 00:02:56 a single expanding remnant you get a super
00:02:56 --> 00:02:59 bubble, an enormous cavity blown in the
00:02:59 --> 00:03:01 neutral hydrogen, its edge still pushing
00:03:01 --> 00:03:04 outwards. Superbubbles are the fingerprints
00:03:04 --> 00:03:07 each one carries in its size and its
00:03:07 --> 00:03:10 expansion speed, a record of how much energy
00:03:10 --> 00:03:11 went into it and roughly when.
00:03:12 --> 00:03:15 Anna: So a, uh, complete, dynamically resolved
00:03:15 --> 00:03:17 census of superbubbles across an entire
00:03:17 --> 00:03:20 galaxy would let you add up the energy
00:03:20 --> 00:03:23 supernovae have actually delivered and then
00:03:23 --> 00:03:25 compare it against how fast the turbine
00:03:25 --> 00:03:27 turbulence in that same galaxy is bleeding
00:03:27 --> 00:03:30 energy away. If the two numbers match,
00:03:30 --> 00:03:33 you have your answer. If supernovae falls
00:03:33 --> 00:03:35 short, something else is doing the work.
00:03:36 --> 00:03:38 Avery: Nobody had that senses for a reason. That's
00:03:38 --> 00:03:41 almost funny. We can't do it for the Milky
00:03:41 --> 00:03:43 Way because we live inside it. Mapping
00:03:43 --> 00:03:46 bubbles in our own galaxy is like surveying a
00:03:46 --> 00:03:48 forest from the base of one tree. And for
00:03:48 --> 00:03:51 other galaxies we have the sensitivity or the
00:03:51 --> 00:03:53 resolution, never both.
00:03:53 --> 00:03:56 Anna: Which is where two telescopes on opposite
00:03:56 --> 00:03:59 sides of the world come in. Exactly
00:03:59 --> 00:04:02 that. The paper is in Nature astronomy,
00:04:02 --> 00:04:05 published on 17 September. Led by
00:04:05 --> 00:04:07 Fan Yi Meng of Tsinghua University,
00:04:07 --> 00:04:10 with Zhao Wei Tsai and Jingwen Wu,
00:04:10 --> 00:04:13 and with D Li, Jinghua's head of
00:04:13 --> 00:04:15 astronomy and the former chief scientist of
00:04:15 --> 00:04:18 the FAST telescope as corresponding
00:04:18 --> 00:04:21 authority, they combined two instruments.
00:04:21 --> 00:04:24 FAST is the 500 metre aperture
00:04:24 --> 00:04:26 spherical telescope sitting in a natural
00:04:26 --> 00:04:29 limestone bowl in Guizhou Province in
00:04:29 --> 00:04:32 southern China, the most sensitive single
00:04:32 --> 00:04:34 dish on Earth. At these wavelengths, what it
00:04:34 --> 00:04:37 gives you is faint, diffuse, large
00:04:37 --> 00:04:40 scale structure, the outskirts of bubbles,
00:04:40 --> 00:04:43 the gas nobody else can see. What it
00:04:43 --> 00:04:46 cannot give you is fine detail. For
00:04:46 --> 00:04:48 that they used archival observations from the
00:04:48 --> 00:04:51 Jansky Very Large array in New Mexico,
00:04:52 --> 00:04:54 27 dishes spread across the desert.
00:04:54 --> 00:04:57 Working as one instrument, the array
00:04:57 --> 00:05:00 resolves the sharp edges fast,
00:05:00 --> 00:05:03 fills in everything. The array's spacing
00:05:03 --> 00:05:06 makes it blind to stitch them together, and
00:05:06 --> 00:05:08 you get a map that is both deep and sharp,
00:05:08 --> 00:05:11 which is exactly what this problem has always
00:05:11 --> 00:05:12 needed.
00:05:13 --> 00:05:15 Avery: They pointed that combination at Messier 31,
00:05:16 --> 00:05:18 the Andromeda Galaxy, the nearest big
00:05:18 --> 00:05:21 spiral, 2 1/2 million light years away
00:05:21 --> 00:05:23 and close enough that we can see the whole
00:05:23 --> 00:05:26 disc laid out from the outside. They mapped
00:05:26 --> 00:05:28 it in the 21 centimetre line of neutral
00:05:28 --> 00:05:31 hydrogen, the radio signal that traces
00:05:31 --> 00:05:33 cold atomic gas.
00:05:33 --> 00:05:35 Anna: From that map, they pulled
00:05:35 --> 00:05:38 365 candidate cavities
00:05:38 --> 00:05:40 and after classification, confirmed
00:05:40 --> 00:05:43 118 genuine super bubbles
00:05:43 --> 00:05:45 across the entire disc.
00:05:45 --> 00:05:46 Avery: And the result?
00:05:47 --> 00:05:49 Anna: The first thing worth noticing is the ages.
00:05:50 --> 00:05:52 Measured from their sizes and expansion
00:05:52 --> 00:05:55 speeds, the bubbles run up to 40 million
00:05:55 --> 00:05:58 years old. That is not an arbitrary number.
00:05:58 --> 00:06:01 It is almost exactly how long a star
00:06:01 --> 00:06:03 cluster keeps producing Supernovae from its
00:06:03 --> 00:06:06 first massive star dying to its last.
00:06:07 --> 00:06:09 The ages line up with the clock you would
00:06:09 --> 00:06:12 predict if clusters are uh, what makes them B
00:06:12 --> 00:06:14 Lee put the scale plainly. Those
00:06:14 --> 00:06:17 118 bubbles correspond to
00:06:17 --> 00:06:19 thousands of supernova explosions over the
00:06:19 --> 00:06:22 past 40 million years. Then the actual
00:06:22 --> 00:06:25 test from the bubbles they calculated the
00:06:25 --> 00:06:28 rate at which supernovae are injecting
00:06:28 --> 00:06:30 kinetic energy between 10 to the
00:06:30 --> 00:06:33 49th to 10 to the 51.5
00:06:33 --> 00:06:36 ergs per cubic kiloparsec per
00:06:36 --> 00:06:39 million years. Separately and this is the
00:06:39 --> 00:06:42 part that makes the paper work. They derived
00:06:42 --> 00:06:44 the rate at which turbulence is dissipating
00:06:44 --> 00:06:47 energy from the same data using the
00:06:47 --> 00:06:49 observed motions of the gastwo
00:06:49 --> 00:06:52 independent numbers. They match match
00:06:52 --> 00:06:55 how closely in magnitude. And
00:06:55 --> 00:06:58 this is the stronger claim in spatial
00:06:58 --> 00:06:58 distribution.
00:06:59 --> 00:07:01 It's not just that the galaxy wide totals
00:07:01 --> 00:07:04 happen to agree, which could be coincidence
00:07:04 --> 00:07:06 between two quantities that both scale with
00:07:06 --> 00:07:09 how many stars a ah galaxy has. It's that
00:07:09 --> 00:07:12 where the supernovae energy goes in is
00:07:12 --> 00:07:14 where the turbulent energy comes out
00:07:15 --> 00:07:17 region by region across the disc. The
00:07:17 --> 00:07:20 supply map matches the demand map.
00:07:20 --> 00:07:23 That's much harder to get by accent. The
00:07:23 --> 00:07:25 conclusion the authors draw is carefully
00:07:25 --> 00:07:27 worded and I want to keep their wording.
00:07:27 --> 00:07:30 Clustered supernova feedback is
00:07:30 --> 00:07:32 sufficient to sustain galactic scale
00:07:32 --> 00:07:35 turbulence. Why this matters beyond
00:07:35 --> 00:07:37 bookkeeping is turbulence is not a detail
00:07:37 --> 00:07:40 of galaxies, it's one of the controls.
00:07:40 --> 00:07:43 Turbulent pressure helps hold a ah gas disc
00:07:43 --> 00:07:46 up against its own gravity. And turbulence is
00:07:46 --> 00:07:49 what stops molecular clouds collapsing all at
00:07:49 --> 00:07:51 once. A large part of why galaxies
00:07:51 --> 00:07:54 convert gas into stars. So slowly
00:07:54 --> 00:07:57 change the turbulence and you change the star
00:07:57 --> 00:08:00 formation rate. So this closes a loop.
00:08:00 --> 00:08:03 Gas collapses and forms stars. The biggest
00:08:03 --> 00:08:06 of those stars explode. The explosions
00:08:06 --> 00:08:08 stir the remaining gas. The stirring
00:08:08 --> 00:08:11 regulates how readily the next generation
00:08:11 --> 00:08:13 forms. Galaxies are partly self
00:08:13 --> 00:08:16 governing and this is the first time both
00:08:16 --> 00:08:18 ends of that loop have been measured in the
00:08:18 --> 00:08:21 same galaxy from the same data and found
00:08:21 --> 00:08:22 to balance.
00:08:22 --> 00:08:25 Avery: And um, the caveat now the honest
00:08:25 --> 00:08:27 Anna: limits and there are three first,
00:08:27 --> 00:08:30 sufficient is not the same as sole
00:08:30 --> 00:08:32 showing supernovae can pay the whole bill
00:08:32 --> 00:08:35 does not prove nothing else. Chips in
00:08:35 --> 00:08:37 gravity and the magneto rotational
00:08:37 --> 00:08:40 instability have not been eliminated. They
00:08:40 --> 00:08:43 have been made unnecessary, which is a weaker
00:08:43 --> 00:08:46 and more interesting result. Second, this
00:08:46 --> 00:08:49 is neutral atomic hydrogen. It does not
00:08:49 --> 00:08:51 directly trace the molecular gas where
00:08:51 --> 00:08:54 stars actually form or the hot
00:08:54 --> 00:08:56 ionised gas and the energy budget in those
00:08:56 --> 00:08:59 phases could behave differently. And third,
00:08:59 --> 00:09:02 this is one galaxy, a large,
00:09:02 --> 00:09:05 fairly quiet spiral that has not formed stars
00:09:05 --> 00:09:08 vigorously in a long while. Whether the books
00:09:08 --> 00:09:11 balance the same way in a starburst or in a
00:09:11 --> 00:09:13 small, irregular, uh, galaxy where bubbles
00:09:13 --> 00:09:14 can blow straight out.
00:09:14 --> 00:09:17 The top is exactly the next question.
00:09:17 --> 00:09:20 Two footnotes I enjoyed Bordechai Mark
00:09:20 --> 00:09:23 McClo, the man whose 1999
00:09:23 --> 00:09:26 paper showed this turbulence should have died
00:09:26 --> 00:09:29 long ago, is a co author here. His own
00:09:29 --> 00:09:31 result is referenced too, in the paper that
00:09:31 --> 00:09:34 answers it. And because Nature Astronomy
00:09:34 --> 00:09:37 publishes its referee reports, we know one
00:09:37 --> 00:09:39 of the two reviewers was Christoph Federath
00:09:40 --> 00:09:42 at the Australian National University, who
00:09:42 --> 00:09:45 has spent a career on this exact question.
00:09:45 --> 00:09:48 The Australian fingerprint is on the scrutiny
00:09:48 --> 00:09:51 rather than the data. Regular listeners will
00:09:51 --> 00:09:54 hear an echo here. Two weeks ago we ran
00:09:54 --> 00:09:56 the finding that black hole outflows can
00:09:56 --> 00:09:59 trigger star formation as well as shut it
00:09:59 --> 00:10:02 down. Feedback that builds as well as
00:10:02 --> 00:10:05 breaks. This is the same lesson one
00:10:05 --> 00:10:07 rung down the letter. At stellar scale,
00:10:07 --> 00:10:10 feedback is not simply destructive, it is
00:10:10 --> 00:10:12 a galaxy's thermostat.
00:10:13 --> 00:10:15 Avery: Anna's Storey takes supernovae as given and
00:10:15 --> 00:10:18 asks what they do to a galaxy. This one
00:10:18 --> 00:10:21 asks a question one step which
00:10:21 --> 00:10:24 stars actually managed to explode? You would
00:10:24 --> 00:10:27 think that was settled. It is not. We
00:10:27 --> 00:10:29 see fewer supernovae than our models say we
00:10:29 --> 00:10:32 should. And there's a related puzzle, the red
00:10:32 --> 00:10:35 supergiant problem. When astronomers go back
00:10:35 --> 00:10:38 through archival images to identify the star
00:10:38 --> 00:10:40 that blew up, they never find 1 above about
00:10:40 --> 00:10:43 16 to 18 solar masses. Even
00:10:43 --> 00:10:46 though plenty of stars are heavier, something
00:10:46 --> 00:10:48 is quietly removing the most massive stars
00:10:48 --> 00:10:51 from the exploding population. A new paper in
00:10:51 --> 00:10:54 Physical Review D from Mariam Gogilashvili
00:10:54 --> 00:10:56 and Irene Tambora at the Niels Bohr Institute
00:10:56 --> 00:10:59 in Copenhagen Contorm points at an
00:10:59 --> 00:11:02 unlikely culprit. Neutrinos changing
00:11:02 --> 00:11:04 identity Quick refresher When a
00:11:04 --> 00:11:07 Anna: massive star's core collapses, about
00:11:07 --> 00:11:10 99% of the energy released leaves
00:11:10 --> 00:11:13 as neutrinos. And the explosion depends on
00:11:13 --> 00:11:15 a small fraction of that flood being
00:11:15 --> 00:11:18 reabsorbed by the gas just outside the
00:11:18 --> 00:11:20 core, heating it enough to revive the
00:11:20 --> 00:11:23 stalled shock wave. It's a narrow margin.
00:11:24 --> 00:11:26 Neutrinos also come in three flavours
00:11:26 --> 00:11:29 electron, muon and tau and
00:11:29 --> 00:11:31 oscillate between them, which is Nobel
00:11:31 --> 00:11:33 winning physics from 1998.
00:11:34 --> 00:11:37 Avery: Here's the catch. Only the electron flavour
00:11:37 --> 00:11:39 deposits heat efficiently. Muon and tau
00:11:39 --> 00:11:42 neutrinos mostly sail straight out. So
00:11:42 --> 00:11:45 if flavour conversion happens deep inside a
00:11:45 --> 00:11:47 collapsing core, it takes energy earmarked
00:11:47 --> 00:11:50 for the explosion and redistributes it into
00:11:50 --> 00:11:52 flavours that simply leave. Most state of the
00:11:52 --> 00:11:55 art simulations leave this out on the old
00:11:55 --> 00:11:57 assumption that conversion happens too far
00:11:57 --> 00:11:59 out to matter. Recent work says
00:11:59 --> 00:12:02 otherwise, so Maryam Gogilashvili and
00:12:02 --> 00:12:05 Irene Tambora put it in schematically and
00:12:05 --> 00:12:08 ran the collapse of 195 stars
00:12:08 --> 00:12:11 from 9 to 120 solar masses
00:12:12 --> 00:12:14 without flavour conversion. About 27%
00:12:14 --> 00:12:17 of their stars fail to explode and collapse
00:12:17 --> 00:12:20 straight to black holes. That matches both
00:12:20 --> 00:12:22 the literature and observations. Switch
00:12:22 --> 00:12:25 flavour conversion on and the failure rate
00:12:25 --> 00:12:28 climbs to somewhere between 48 and
00:12:28 --> 00:12:30 88% depending on how deep in the
00:12:30 --> 00:12:33 core you let it happen. And the stars most
00:12:33 --> 00:12:36 affected sit between 16 and 30
00:12:36 --> 00:12:37 solar masses, which is
00:12:37 --> 00:12:40 Anna: precisely the missing mass range. In the red
00:12:40 --> 00:12:41 supergiant problem.
00:12:42 --> 00:12:44 Avery: There is a second quieter result I like more.
00:12:45 --> 00:12:47 And the stars that do still explode. Flavour
00:12:47 --> 00:12:50 conversion revives the shock earlier so less
00:12:50 --> 00:12:52 material rains back onto the newborn neutron
00:12:52 --> 00:12:55 star. The neutron stars come out lighter,
00:12:55 --> 00:12:58 closer to the 1.2 to 1.4 solar
00:12:58 --> 00:13:00 masses we actually measure in pulsars.
00:13:00 --> 00:13:03 A model that was running heavy now matches
00:13:03 --> 00:13:06 the honest handling. Here is the range. 48
00:13:06 --> 00:13:09 to 88% is not a measurement. It is a span
00:13:09 --> 00:13:11 across assumptions. And the authors say
00:13:11 --> 00:13:13 plainly that their upper valleys look to be
00:13:13 --> 00:13:16 in tension with observations. This is one
00:13:16 --> 00:13:18 dimensional modelling with a deliberately
00:13:18 --> 00:13:20 simplified switch for the neutrino physics.
00:13:20 --> 00:13:23 What it establishes is not a number. It is
00:13:23 --> 00:13:25 that this effect is too big to keep leaving
00:13:25 --> 00:13:28 out. The preprint went up in mid
00:13:28 --> 00:13:30 May, so the work has been circulating about
00:13:30 --> 00:13:32 four months. It is the journal version that
00:13:32 --> 00:13:32 is
00:13:32 --> 00:13:34 Anna: new and a southern footnote that is not a
00:13:34 --> 00:13:36 stretch. We have caught neutrinos from
00:13:36 --> 00:13:39 exactly one supernova SN
00:13:39 --> 00:13:42 1987A in the Southern Magellanic
00:13:42 --> 00:13:45 Cloud cloud 20 dozen particles over about 13
00:13:45 --> 00:13:47 seconds in February 1987.
00:13:48 --> 00:13:50 Every word of this debate traces back to that
00:13:50 --> 00:13:53 1 handful of detections from a galaxy only
00:13:53 --> 00:13:56 southern observers see properly. The next
00:13:56 --> 00:13:58 galactic supernova settles a great deal of
00:13:58 --> 00:13:58 it.
00:13:59 --> 00:14:00 Avery: Okay, moving on to storey 3.
00:14:01 --> 00:14:03 Most exoplanet discoveries come with an open
00:14:03 --> 00:14:06 ended invitation. Go and study it whenever
00:14:06 --> 00:14:08 you like. This one comes with a deadline.
00:14:09 --> 00:14:11 Published on 18 September in the publications
00:14:11 --> 00:14:14 of the Astronomical Society of Japan from
00:14:14 --> 00:14:16 Noriharu Watanabe and Norio
00:14:16 --> 00:14:18 Narita at the University of Tokyo with a
00:14:18 --> 00:14:21 large international team. The discovery of
00:14:21 --> 00:14:24 TOI 1355b, a
00:14:24 --> 00:14:27 hot Jupiter and a strange one on three counts
00:14:27 --> 00:14:30 count one is the star. TOI
00:14:30 --> 00:14:33 1355 is an A type star about twice
00:14:33 --> 00:14:36 the Sun's mass with a surface near 8
00:14:36 --> 00:14:39 Kelvin, um, some 3 degrees hotter than
00:14:39 --> 00:14:41 the Sun. It's around 800 light years away
00:14:41 --> 00:14:44 and it spins fast better than 80
00:14:44 --> 00:14:46 kilometres a second against our Sun's
00:14:46 --> 00:14:49 leisurely two count two is the
00:14:49 --> 00:14:52 planet. Nearly six Jupiter masses. About
00:14:52 --> 00:14:55 1.4 Jupiter radii whipping around
00:14:55 --> 00:14:57 that star every 2.17 days.
00:14:57 --> 00:15:00 But its orbit is not a circle. The
00:15:00 --> 00:15:03 eccentricity is about 0.22 a
00:15:03 --> 00:15:04 properly lopsided orbit.
00:15:04 --> 00:15:07 Anna: Why is that surprising for a hot Jupiter?
00:15:07 --> 00:15:09 Avery: Because they're almost never lopsided sitting
00:15:09 --> 00:15:12 that close in tides should round off an orbit
00:15:12 --> 00:15:15 quickly. Of the roughly 20 hot Jupiters known
00:15:15 --> 00:15:17 around hot stars, the measured eccentricities
00:15:17 --> 00:15:20 are essentially zero, some to four decimal
00:15:20 --> 00:15:22 places. And there's exactly one other
00:15:22 --> 00:15:24 eccentric case on record. These worlds are
00:15:24 --> 00:15:27 thought to be flung inward on wild elliptical
00:15:27 --> 00:15:29 orbits by gravitational bullying from other
00:15:29 --> 00:15:32 planets. Then have those orbits ground down
00:15:32 --> 00:15:34 to circles by tides. TOI
00:15:34 --> 00:15:37 1355B is partway through the grinding,
00:15:37 --> 00:15:40 which we rarely gets. Watch count three
00:15:40 --> 00:15:42 is the deadline. Comparing transits across
00:15:42 --> 00:15:45 TESS observations from 2019, 2020,
00:15:46 --> 00:15:48 2022 and 2024. The team
00:15:48 --> 00:15:50 found the planet crossing the star at a
00:15:50 --> 00:15:53 steadily different height each time. The
00:15:53 --> 00:15:55 orbit's plane is swinging nodal precession
00:15:55 --> 00:15:58 driven by the bulge of that rapidly spinning
00:15:58 --> 00:16:01 star. Wind it forward and the planet stops
00:16:01 --> 00:16:03 crossing the star's face from our point of
00:16:03 --> 00:16:05 view around the middle of 2033.
00:16:05 --> 00:16:08 Anna: After that, no transits for centuries. The
00:16:08 --> 00:16:09 planet is fine.
00:16:09 --> 00:16:12 Our line of sight is what runs out. There is
00:16:12 --> 00:16:15 a lovely methodological wrinkle too.
00:16:15 --> 00:16:17 You normally weigh a planet by watching the
00:16:17 --> 00:16:20 star wobble. But this star spins
00:16:20 --> 00:16:23 so fast its spectral lines are smeared
00:16:23 --> 00:16:26 and that does not work. So they weighed it
00:16:26 --> 00:16:28 from the light curve instead from M. The way
00:16:28 --> 00:16:31 the planet's gravity distorts the star into
00:16:31 --> 00:16:33 a faint rugby ball shape. And from the
00:16:33 --> 00:16:36 subtle brightening as the star is tugged
00:16:36 --> 00:16:39 towards us. The mass came out of the shape of
00:16:39 --> 00:16:41 the light, not the shift of the lines. And
00:16:41 --> 00:16:43 the supporting cast is worth naming.
00:16:44 --> 00:16:47 Alongside TESS and the 3.8 metre
00:16:47 --> 00:16:49 SEMI telescope in Okayama, this
00:16:49 --> 00:16:52 paper leans on a 91 centimetre
00:16:52 --> 00:16:55 telescope on the slopes of Matt Etna,
00:16:55 --> 00:16:58 a 40 centimetre in Switzerland and a
00:16:58 --> 00:17:00 28 centimetre at a private observatory in
00:17:00 --> 00:17:03 Germany. Backyard scale instruments on the
00:17:03 --> 00:17:06 Discovery paper for a six Jupiter mass
00:17:06 --> 00:17:09 world. The preprint went up in August, so
00:17:09 --> 00:17:12 about a month ahead of the journal. And for
00:17:12 --> 00:17:14 our southern listeners the star sits at Ah,
00:17:14 --> 00:17:17 Declination 67, which means
00:17:17 --> 00:17:20 it never rises from Sydney. Northern
00:17:20 --> 00:17:22 listeners can find the field in Cepheus. The
00:17:22 --> 00:17:25 team is already preparing a follow up on how
00:17:25 --> 00:17:27 tilted the orbit is and wants
00:17:27 --> 00:17:30 JWST time to low
00:17:30 --> 00:17:31 ETH
00:17:31 --> 00:17:32 Avery: orbit now and the business end of
00:17:32 --> 00:17:33 spaceflight.
00:17:33 --> 00:17:36 On 18 September, NASA exercised a UH
00:17:36 --> 00:17:39 contract modification with SpaceX for three
00:17:39 --> 00:17:41 additional crew rotation missions to the
00:17:41 --> 00:17:44 International Space Crew 1 5, Crew
00:17:44 --> 00:17:47 16 and Crew 1 7. The value
00:17:47 --> 00:17:50 is $946 million for all
00:17:50 --> 00:17:52 three covering ground launch in
00:17:52 --> 00:17:54 orbit and return and recovery operations,
00:17:55 --> 00:17:58 cargo on each mission and lifeboat capability
00:17:58 --> 00:18:00 while docked. That takes SpaceX to
00:18:00 --> 00:18:03 17 crew missions under the commercial crew
00:18:03 --> 00:18:06 transportation contract and that contract's
00:18:06 --> 00:18:08 running total to $5.92
00:18:08 --> 00:18:11 billion. Period of performance runs through
00:18:11 --> 00:18:13 2030 with mission readiness dates in
00:18:13 --> 00:18:16 2027 and 2028. NASA
00:18:16 --> 00:18:18 flagged its intent to buy back in May and
00:18:18 --> 00:18:21 calls this a sole source modification that
00:18:21 --> 00:18:23 does not pre further purchases later.
00:18:24 --> 00:18:26 Anna: One line in that release is worth reading
00:18:26 --> 00:18:29 carefully. NASA says the change helps
00:18:29 --> 00:18:32 it maintain access to the station with quote,
00:18:32 --> 00:18:34 two unique commercial crew industry
00:18:34 --> 00:18:37 partners. The award itself goes to one
00:18:37 --> 00:18:40 of them. The original 2014
00:18:40 --> 00:18:42 contracts went to both Boeing and SpaceX
00:18:43 --> 00:18:46 and Boeing appears in this release exactly
00:18:46 --> 00:18:48 once in that history. NASA does
00:18:48 --> 00:18:51 not say anything here about when its second
00:18:51 --> 00:18:53 provider next flies people.
00:18:53 --> 00:18:55 We'll report that when they do say.
00:18:55 --> 00:18:57 Avery: Meanwhile, the near term mission is moving.
00:18:58 --> 00:19:00 The four astronauts of Crew 13 entered
00:19:00 --> 00:19:02 quarantine late on Thursday at UH Johnson
00:19:02 --> 00:19:05 Space Centre in Houston. NASA's Jessica
00:19:05 --> 00:19:08 Watkins and Luke Delaney, the Canadian Space
00:19:08 --> 00:19:10 Agency's Yoshua Kutryk and
00:19:10 --> 00:19:12 Roscosmos cosmonaut Sergey
00:19:12 --> 00:19:15 tatariotnikov. NASA and SpaceX
00:19:15 --> 00:19:18 are still targeting early October. Before
00:19:18 --> 00:19:20 quarantine. They finished training at SpaceX
00:19:20 --> 00:19:22 in Hawthorne and ran a crew equipment
00:19:22 --> 00:19:25 interface test at Cape Canaveral. Suits on
00:19:25 --> 00:19:28 into the Dragon leak cheques, seat fit
00:19:28 --> 00:19:31 comms cheques, my favourite detail. They sit
00:19:31 --> 00:19:33 in the capsule and listen to its fans and
00:19:33 --> 00:19:35 pumps so that none of the sounds are
00:19:35 --> 00:19:37 unfamiliar on launch day.
00:19:37 --> 00:19:40 Anna: The quarantine itself is an Apollo era
00:19:40 --> 00:19:43 invention still doing its job. Keeping a head
00:19:43 --> 00:19:45 cold on the ground where it belongs. That
00:19:45 --> 00:19:47 closes out an arc we tracked since the
00:19:47 --> 00:19:50 oxidizer leak stood. Crew 13 down
00:19:50 --> 00:19:53 valve replaced. Crew in quarantine early
00:19:53 --> 00:19:55 October. We still want a date.
00:19:55 --> 00:19:57 Quick hit, closing a thread. We opened on
00:19:57 --> 00:20:00 Friday. It happened on the 18th of
00:20:00 --> 00:20:02 September. The earth facing sun went
00:20:02 --> 00:20:05 completely spotless. No numbered active
00:20:05 --> 00:20:08 regions at all. It's the first spotless day
00:20:08 --> 00:20:11 since the 24th of February and the
00:20:11 --> 00:20:13 19th was spotless too, making it two in a
00:20:13 --> 00:20:16 row. By the 20th, a small new region
00:20:16 --> 00:20:19 had rotated up and the run ended. Which is
00:20:19 --> 00:20:21 exactly how the descent from a solar maximum
00:20:21 --> 00:20:24 goes. Not a switch, but a flicker that
00:20:24 --> 00:20:27 Avery: lengthens for scale on how far we have come
00:20:27 --> 00:20:27 down.
00:20:27 --> 00:20:30 The busiest single day of the Solar cycle
00:20:30 --> 00:20:33 was 8 August 2024, with
00:20:33 --> 00:20:35 an estimated 337
00:20:35 --> 00:20:38 sunspots. That was the highest daily count
00:20:38 --> 00:20:41 since March 2001. Cycle
00:20:41 --> 00:20:44 25 peaked in late 2024
00:20:44 --> 00:20:46 and minimum is not expected before about
00:20:46 --> 00:20:47 2030.
00:20:47 --> 00:20:50 Anna: But do not put the aurora gear away. A
00:20:50 --> 00:20:53 coronal hole is rotating into position and
00:20:53 --> 00:20:55 its fast solar wind stream should reach us
00:20:55 --> 00:20:58 around the 23rd, with forecasters flagging a
00:20:58 --> 00:21:01 chance of minor geomagnetic storming. If
00:21:01 --> 00:21:03 it lands, best chances are the far north,
00:21:03 --> 00:21:06 northern Scotland and the far south, southern
00:21:06 --> 00:21:09 New Zealand. It arrives right on the equinox,
00:21:09 --> 00:21:11 which is the most aurora friendly moment of
00:21:11 --> 00:21:14 the year. For reasons of geometry and the
00:21:14 --> 00:21:16 standing point we keep making. A, uh, quiet
00:21:16 --> 00:21:19 sun means fewer auroras, but it also means
00:21:19 --> 00:21:22 a weaker shield against galactic cosmic rays.
00:21:22 --> 00:21:25 So that background quietly rises same
00:21:25 --> 00:21:27 dial opposite end to the sky.
00:21:27 --> 00:21:30 Avery: And this week the calendar does something
00:21:30 --> 00:21:32 that only makes sense if you remember. The
00:21:32 --> 00:21:35 Earth is tilted first to equinox,
00:21:35 --> 00:21:37 five minutes past midnight universal time on
00:21:37 --> 00:21:40 the 23rd. An equinox is an instant,
00:21:40 --> 00:21:43 not a day. So where you stand decides the
00:21:43 --> 00:21:45 date. That is Tuesday evening in the
00:21:45 --> 00:21:48 Americas, just after five in Los Angeles,
00:21:48 --> 00:21:50 just after eight in New York, one in the
00:21:50 --> 00:21:53 morning in London and five past ten on
00:21:53 --> 00:21:56 Wednesday morning in Sydney. Spring here,
00:21:56 --> 00:21:58 autumn there, same instant.
00:21:58 --> 00:22:01 Anna: Then on Saturday the 26th, the full
00:22:01 --> 00:22:04 moon, the harvest moon. The full moon falling
00:22:04 --> 00:22:07 closest to the September equinox. And here's
00:22:07 --> 00:22:09 where it gets interesting. Because the
00:22:09 --> 00:22:11 harvest moon's entire reputation is a
00:22:11 --> 00:22:13 northern hemisphere phenomenon.
00:22:13 --> 00:22:15 Avery: Explain that, because I think most people
00:22:15 --> 00:22:16 assume it's just a name.
00:22:17 --> 00:22:19 Anna: It's not just a name. The moon Normally
00:22:19 --> 00:22:22 rises about 50 minutes later each night.
00:22:22 --> 00:22:24 Around the northern autumn equinox. The
00:22:24 --> 00:22:26 Moon's path meets the eastern horizon at a
00:22:26 --> 00:22:29 shallow angle. So successive moon rises,
00:22:29 --> 00:22:32 bunch up and you get several evenings running
00:22:32 --> 00:22:34 with bright moonlight arriving just after
00:22:34 --> 00:22:37 sunset, which was the whole point. Extra
00:22:37 --> 00:22:38 light to finish the harvest.
00:22:39 --> 00:22:41 Avery: We ran the numbers for this week. On the
00:22:41 --> 00:22:44 nights around full moon, moonrise comes later
00:22:44 --> 00:22:46 by about 12 minutes a night. In London,
00:22:46 --> 00:22:49 22 minutes in New York, 27 in Los
00:22:49 --> 00:22:51 Angeles and in Sydney,
00:22:51 --> 00:22:53 62 minutes.
00:22:53 --> 00:22:56 Anna: So we get the opposite of a harvest moon.
00:22:56 --> 00:22:59 Avery: We get the anti harvest moon. The effect the
00:22:59 --> 00:23:01 thing is named for is more than five times
00:23:01 --> 00:23:04 weaker here than in London. Same moon,
00:23:04 --> 00:23:07 same week, geometry simply reversed. In
00:23:07 --> 00:23:10 spring it's the same ecliptic angle that
00:23:10 --> 00:23:13 gives us a brilliant high Venus and one
00:23:13 --> 00:23:14 hugging the horizon.
00:23:14 --> 00:23:17 One wrinkle for Australian listeners The full
00:23:17 --> 00:23:20 moon Instant lands at 2:48 on Sunday
00:23:20 --> 00:23:22 morning our time, so our calendars say
00:23:22 --> 00:23:25 27th and northern ones say
00:23:25 --> 00:23:27 26th. It looks full on both nights.
00:23:27 --> 00:23:28 Anna: And the planets?
00:23:28 --> 00:23:30 Avery: Venus is still the show in the west after
00:23:30 --> 00:23:33 sunset. At uh magnitude -4.5
00:23:34 --> 00:23:37 from Sydney it stands 37 degrees high as
00:23:37 --> 00:23:40 the sun sets and hangs on for more than three
00:23:40 --> 00:23:42 hours. From New York, 13 degrees
00:23:42 --> 00:23:45 from London, 2 1/2 degrees about
00:23:45 --> 00:23:48 25 minutes with a dead flat western horizon
00:23:48 --> 00:23:51 in the north. Look early and low through a
00:23:51 --> 00:23:54 telescope. It's a big thin crescent, a
00:23:54 --> 00:23:57 quarter lit but 42 arcseconds across.
00:23:57 --> 00:24:00 Larger than Jupiter's disc. Below it
00:24:00 --> 00:24:03 Mercury is having a genuinely good Southern
00:24:03 --> 00:24:05 apparition. Magnitude
00:24:05 --> 00:24:08 0.2, 18 degrees up from Sydney
00:24:08 --> 00:24:11 at sunset and setting an hour and a half
00:24:11 --> 00:24:14 after the Sun. From London it's 3 degrees
00:24:14 --> 00:24:16 up and effectively out of reach for the
00:24:16 --> 00:24:17 north.
00:24:17 --> 00:24:19 Anna: The compensation is the morning at the start
00:24:19 --> 00:24:22 of nautical Twilight. Mars stands 49
00:24:22 --> 00:24:25 degrees high from Los Angeles, 47 from
00:24:25 --> 00:24:28 New York, 42 from London and just
00:24:28 --> 00:24:30 21 from Sydney. Jupiter is
00:24:30 --> 00:24:33 28 degrees up from Los Angeles against 10
00:24:33 --> 00:24:34 from here.
00:24:34 --> 00:24:37 The pre dawn sky belongs to the north right
00:24:37 --> 00:24:39 now and it is worth getting up for.
00:24:39 --> 00:24:42 Saturn rises mid evening and is highest
00:24:42 --> 00:24:45 just after midnight, better than 50 degrees
00:24:45 --> 00:24:47 up from Sydney at magnitude plus
00:24:47 --> 00:24:50 0.3. It is heading for opposition
00:24:50 --> 00:24:53 in early October and you will see listings
00:24:53 --> 00:24:55 disagree about the date. Some um, say the
00:24:55 --> 00:24:57 fourth, some the fifth. Both are right.
00:24:58 --> 00:25:00 Opposition measured by ecliptic longitude
00:25:00 --> 00:25:03 falls on the 4th, measured by right ascension
00:25:03 --> 00:25:06 the 5th. Saturn's brightness and size are
00:25:06 --> 00:25:08 identical across that whole week so you
00:25:08 --> 00:25:11 cannot pick the wrong night and our lead
00:25:11 --> 00:25:13 storey. Can anyone actually see
00:25:13 --> 00:25:14 Andromeda?
00:25:15 --> 00:25:17 Avery: Depends entirely where you are. From New
00:25:17 --> 00:25:19 York, Andromeda passes almost overhead,
00:25:20 --> 00:25:23 89 degrees up around half past one in the
00:25:23 --> 00:25:25 morning from Los Angeles, 83 from
00:25:25 --> 00:25:28 London, 80 from Sydney. It scrapes to
00:25:28 --> 00:25:31 under 15 degrees low in the north through the
00:25:31 --> 00:25:34 thickest part of our atmosphere. Binocular is
00:25:34 --> 00:25:36 in a clear northern horizon after midnight
00:25:36 --> 00:25:39 we'll find it but it is a smudge rather than
00:25:39 --> 00:25:41 the showpiece. It is up north which is the
00:25:41 --> 00:25:44 storey of tonight really. The north gets the
00:25:44 --> 00:25:46 deep sky, the predawn planets and the lunar
00:25:46 --> 00:25:49 occultation of Jupiter on 6 October
00:25:49 --> 00:25:51 that sits below our horizon entirely.
00:25:52 --> 00:25:55 We get Venus, Mercury and the better half of
00:25:55 --> 00:25:56 the geometry.
00:25:56 --> 00:25:57 Some weeks it runs the other way
00:25:58 --> 00:26:00 Anna: and the standing reminder because we are
00:26:00 --> 00:26:03 talking about a sun with almost nothing on it
00:26:03 --> 00:26:05 and people will be tempted to look. Never
00:26:05 --> 00:26:07 look at the sun without proper protection.
00:26:08 --> 00:26:10 Solar viewers and eclipse glasses must meet
00:26:10 --> 00:26:11 the ISO
00:26:12 --> 00:26:14
00:26:14 --> 00:26:17 international safety standard, and that is
00:26:17 --> 00:26:20 not the same as ordinary sunglasses, no
00:26:20 --> 00:26:22 matter how dark they are. And stacking
00:26:22 --> 00:26:24 sunglasses does not help.
00:26:24 --> 00:26:26 Cheque your filters for damage before use,
00:26:26 --> 00:26:29 and discard any that are scratched, punctured
00:26:29 --> 00:26:32 or peeling. If you're using a telescope or
00:26:32 --> 00:26:34 binoculars, the filter goes on the front of
00:26:34 --> 00:26:37 the instrument, never on the eyepiece, where
00:26:37 --> 00:26:39 focused sunlight can crack it without
00:26:39 --> 00:26:42 warning. There is no safe way to improvise
00:26:42 --> 00:26:42 this.
00:26:43 --> 00:26:45 Avery: That's astronomy daily for today.
00:26:45 --> 00:26:48 118 Bubbles in Andromeda that bounce a
00:26:48 --> 00:26:51 galaxy's energy books neutrinos that may
00:26:51 --> 00:26:53 quietly decide which stars are allowed to
00:26:53 --> 00:26:56 explode a planet. We have until
00:26:56 --> 00:26:58 2033 to study three more
00:26:58 --> 00:27:00 dragonflights on the books and a crew in
00:27:00 --> 00:27:03 quarantine and a sun with nothing on its face
00:27:03 --> 00:27:05 for the first time since February.
00:27:05 --> 00:27:08 Anna: A note for tomorrow this was episode
00:27:08 --> 00:27:10 199, which makes the next one
00:27:10 --> 00:27:13 200, and we would like to mark it
00:27:13 --> 00:27:15 properly. If there's a storey from this
00:27:15 --> 00:27:17 series you want revisited or a question
00:27:17 --> 00:27:20 you've been sitting on the contact form at
00:27:20 --> 00:27:22 astronomydaily IO is the place.
00:27:23 --> 00:27:25 We do read them, and listener questions have
00:27:25 --> 00:27:27 set our running order more than once.
00:27:27 --> 00:27:29 Avery: All our sources are linked in the show notes,
00:27:29 --> 00:27:32 as always, along with the full references for
00:27:32 --> 00:27:33 today's papers.
00:27:33 --> 00:27:36 You'll find us at astronomydaily IO until
00:27:36 --> 00:27:36 tomorrow.
00:27:36 --> 00:27:37 Anna: Clear skies.
00:27:49 --> 00:27:50 The storeys.
00:27:57 --> 00:27:58 Avery: Were told.