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00:00:00 --> 00:00:03 Anna: Hello, everyone, and welcome back for another
00:00:03 --> 00:00:05 week's of space and astronomy news.
00:00:06 --> 00:00:08 On 25 April 2016,
00:00:09 --> 00:00:11 NASA's Swift Observatory caught a flash of
00:00:11 --> 00:00:14 gamma rays lasting less than two seconds.
00:00:14 --> 00:00:17 Then nothing. Then, about four
00:00:17 --> 00:00:20 minutes later, from the same patch of sky, a
00:00:20 --> 00:00:22 second burst. This one lasted nearly a
00:00:22 --> 00:00:23 minute.
00:00:23 --> 00:00:26 Avery: Two bursts that by every rule in the
00:00:26 --> 00:00:28 textbook, should come from two completely
00:00:28 --> 00:00:31 different kinds of cosmic catastrophe. The
00:00:31 --> 00:00:34 paper explaining them came out on Friday. The
00:00:34 --> 00:00:36 same week Swift itself fell silent.
00:00:36 --> 00:00:39 Anna: Welcome to Astronomy AstroDailyPod. I'm Anna.
00:00:39 --> 00:00:42 Avery: And I'm Avery. Today, a gamma
00:00:42 --> 00:00:45 ray bursts with a split personality. A
00:00:45 --> 00:00:47 black hole disc that throws its own shade.
00:00:48 --> 00:00:51 The most deuterium rich methane ever measured
00:00:51 --> 00:00:53 from an interstellar comet. And NASA's
00:00:53 --> 00:00:55 psyche putting its foot down.
00:00:55 --> 00:00:58 Anna: Let's start with the rule we just mentioned,
00:00:58 --> 00:01:00 because this whole story is about breaking
00:01:00 --> 00:01:03 it. Gamma ray bursts are the brightest
00:01:03 --> 00:01:06 explosions we know of. For a few seconds,
00:01:06 --> 00:01:09 a single burst can outshine everything else
00:01:09 --> 00:01:12 in the gamma ray sky put together. And since
00:01:12 --> 00:01:15 the early 1990s, astronomers have sorted them
00:01:15 --> 00:01:16 into two piles.
00:01:16 --> 00:01:19 Avery: That goes back to Chris Akuvaliotu and
00:01:19 --> 00:01:22 NASA's BATSEE instrument in a paper from
00:01:22 --> 00:01:25 1993. When you plot how
00:01:25 --> 00:01:28 long thousands of bursts last, you don't get
00:01:28 --> 00:01:31 one hump, you get two. A
00:01:31 --> 00:01:33 short population clustered under about two
00:01:33 --> 00:01:36 seconds and a long population above it.
00:01:36 --> 00:01:39 Anna: And over the next 20 odd years,
00:01:40 --> 00:01:42 those two piles picked up two origin stories.
00:01:43 --> 00:01:46 Long bursts come from the collapse of a
00:01:46 --> 00:01:48 massive, rapidly spinning star, a
00:01:48 --> 00:01:51 collapsar. In the best studied cases,
00:01:51 --> 00:01:54 a supernova turns up in the light a week or
00:01:54 --> 00:01:57 two later. Short bursts come from
00:01:57 --> 00:02:00 mergers. Two neutron stars, or a
00:02:00 --> 00:02:02 neutron star and a black hole spiralling
00:02:02 --> 00:02:05 together. The clincher was August
00:02:05 --> 00:02:08 2017, when gravitational waves from a
00:02:08 --> 00:02:11 neutron star merger arrived about 1.7
00:02:11 --> 00:02:13 seconds before a short gamma ray burst.
00:02:14 --> 00:02:16 Avery: So two seconds became shorthand for
00:02:16 --> 00:02:19 two different kinds of death. Under the
00:02:19 --> 00:02:22 line, a merger. Over it, a
00:02:22 --> 00:02:23 collapsing star.
00:02:24 --> 00:02:26 Anna: Which brings us to 25 April
00:02:26 --> 00:02:27 2016,
00:02:27 --> 00:02:30 Avery: Swift's burst alert telescope triggered on an
00:02:30 --> 00:02:33 event now catalogued as GRB
00:02:33 --> 00:02:35 160425A.
00:02:36 --> 00:02:38 The circular the Swift team sent out that day
00:02:38 --> 00:02:41 called it unusual. That, uh, turned out to be
00:02:41 --> 00:02:42 an understatement.
00:02:42 --> 00:02:45 Anna: Here's the light curve. First, a
00:02:45 --> 00:02:48 single sharply peaked pulse lasting about
00:02:48 --> 00:02:51 1.7 seconds. Then more than
00:02:51 --> 00:02:53 250 seconds of nothing,
00:02:54 --> 00:02:56 no detectable emission at all. And
00:02:56 --> 00:02:59 then a second episode, broader and Messier,
00:03:00 --> 00:03:02 lasting around 51 seconds.
00:03:02 --> 00:03:05 Avery: Short, then quiet, then long,
00:03:05 --> 00:03:05 then.
00:03:06 --> 00:03:08 And both from the same position on the sky
00:03:08 --> 00:03:10 within Swift's error box.
00:03:11 --> 00:03:14 Anna: The follow up was fast, and a lot of it came
00:03:14 --> 00:03:17 from southern telescopes. Within about seven
00:03:17 --> 00:03:19 hours, a team using the European Southern
00:03:19 --> 00:03:22 Observatory's Very Large Telescope at
00:03:22 --> 00:03:25 Paranal in Chile with its X Shooter
00:03:25 --> 00:03:27 spectrograph had a redshift
00:03:27 --> 00:03:30 0. That's light
00:03:30 --> 00:03:32 that set out roughly five and a half billion
00:03:32 --> 00:03:34 years ago, and
00:03:34 --> 00:03:36 Avery: the host galaxy turned out to be two
00:03:36 --> 00:03:39 galaxies, 2 knots of light about
00:03:39 --> 00:03:42 8 kiloparsecs apart, moving within about
00:03:42 --> 00:03:45 180 kilometres per second of each other,
00:03:45 --> 00:03:47 an um interacting pair.
00:03:47 --> 00:03:50 Anna: The afterglow was also tracked by grand
00:03:50 --> 00:03:53 a seven channel camera on the 2.2 metre
00:03:53 --> 00:03:56 telescope at La Silla, by Smarts at
00:03:56 --> 00:03:58 Cerro Tololo and by the Master Robotic
00:03:58 --> 00:04:00 Telescope in South Africa.
00:04:00 --> 00:04:03 Avery: The new paper is led by Liang Li at Ningbo
00:04:03 --> 00:04:06 University and Yu Wang at ICRNET
00:04:06 --> 00:04:09 and Sapienza University in Rome, with Bing
00:04:09 --> 00:04:11 Zhang at the University of Hong Kong among
00:04:11 --> 00:04:14 more than 20 co authors. It came out in
00:04:14 --> 00:04:17 Nature Astronomy on Friday and it takes those
00:04:17 --> 00:04:19 two episodes and treats them as two separate
00:04:19 --> 00:04:20 bursts,
00:04:21 --> 00:04:23 Anna: call them G1 and G2.
00:04:23 --> 00:04:26 Each one goes through the full battery of
00:04:26 --> 00:04:28 classification tests, not just duration,
00:04:28 --> 00:04:31 because duration on its own is a blunt
00:04:31 --> 00:04:32 instrument, right?
00:04:33 --> 00:04:36 Avery: The two second line is a statistical
00:04:36 --> 00:04:38 boundary, not a law of physics. The
00:04:38 --> 00:04:41 two populations overlap, so
00:04:41 --> 00:04:44 astronomers lean on other signatures as well.
00:04:44 --> 00:04:47 Anna: Hardness for one short bursts
00:04:47 --> 00:04:49 tend to put more of their energy into high
00:04:49 --> 00:04:52 energy photons. Then there's
00:04:52 --> 00:04:55 the minimum variability timescale, which
00:04:55 --> 00:04:58 is how quickly the light flickers, and
00:04:58 --> 00:05:00 spectral lag, whether the lower energy
00:05:00 --> 00:05:03 photons arrive later than the higher energy
00:05:03 --> 00:05:03 ones.
00:05:04 --> 00:05:07 Avery: Lag is one of the cleanest separators.
00:05:07 --> 00:05:10 Long bursts usually show the soft photons
00:05:10 --> 00:05:13 trailing behind. Short bursts show
00:05:13 --> 00:05:16 almost none. For G1, the
00:05:16 --> 00:05:19 measured lag is about 38 milliseconds, plus
00:05:19 --> 00:05:21 or minus 39. In other words, consistent with
00:05:21 --> 00:05:24 zero. For G2, it's more than a second.
00:05:25 --> 00:05:27 Anna: There are also two empirical relations,
00:05:28 --> 00:05:30 named after Lorenzo Amati and Jay Norris,
00:05:30 --> 00:05:33 that tie together a burst's energy, its
00:05:33 --> 00:05:36 peak photon energy and its lag.
00:05:36 --> 00:05:39 Short and long bursts sit on different
00:05:39 --> 00:05:42 Avery: tracks, and nearly every test
00:05:42 --> 00:05:45 lands the same way. G1 behaves like
00:05:45 --> 00:05:47 a short merger type burst. G2
00:05:47 --> 00:05:50 behaved like a long collapsar type burst.
00:05:50 --> 00:05:53 Two classifications, one event four
00:05:53 --> 00:05:54 minutes apart.
00:05:54 --> 00:05:57 Anna: Now, regular listeners know this isn't the
00:05:57 --> 00:06:00 first time the two second rule has wobbled.
00:06:00 --> 00:06:02 Avery: Not even close. In
00:06:02 --> 00:06:04 2006, GRB
00:06:05 --> 00:06:07 060614 lasted about
00:06:07 --> 00:06:10 100 seconds, but deep searches found
00:06:10 --> 00:06:13 no supernova. A long burst that
00:06:13 --> 00:06:14 behaved like a merger.
00:06:15 --> 00:06:17 In 2020, GRB
00:06:17 --> 00:06:20 200826A lasted well
00:06:20 --> 00:06:23 under a second, but came from a collapsing
00:06:23 --> 00:06:26 star. And then GRB21
00:06:26 --> 00:06:29 1211A and GRB23
00:06:29 --> 00:06:32 0307A, both long,
00:06:32 --> 00:06:35 both followed by a kilonova, the glow of
00:06:35 --> 00:06:38 freshly forged heavy elements that marks a
00:06:38 --> 00:06:41 merger. Webb even picked up tellurium in
00:06:41 --> 00:06:41 the second one.
00:06:42 --> 00:06:44 Anna: So the field has already accepted that
00:06:44 --> 00:06:46 duration and origin don't line up
00:06:46 --> 00:06:49 perfectly. A merger can make a long burst,
00:06:50 --> 00:06:51 a collapser can make a short one.
00:06:52 --> 00:06:55 Avery: What's different here is that both signatures
00:06:55 --> 00:06:57 turn up in the same event, cleanly separated
00:06:57 --> 00:07:00 in time. It's not one ambiguous burst
00:07:00 --> 00:07:03 sitting on the boundary, it's one burst on
00:07:03 --> 00:07:03 each side of it.
00:07:04 --> 00:07:06 Anna: And there was no bright supernova.
00:07:07 --> 00:07:09 Imaging from Cerro to Lolo over the following
00:07:09 --> 00:07:12 month ruled out anything as luminous as
00:07:12 --> 00:07:14 SN1998BW, the
00:07:14 --> 00:07:17 classic gamma ray burst supernova. If
00:07:17 --> 00:07:20 a supernova was there, it was fainter than
00:07:20 --> 00:07:20 that.
00:07:21 --> 00:07:23 Avery: Which is where we need to be careful, because
00:07:23 --> 00:07:26 the headline writes itself and the paper
00:07:26 --> 00:07:26 doesn't.
00:07:27 --> 00:07:30 Anna: Three caveats. First, it's
00:07:30 --> 00:07:32 one event. Just one. The authors
00:07:32 --> 00:07:35 frame it as a challenge to the classification
00:07:35 --> 00:07:37 scheme, a uh, call to reevaluate it,
00:07:38 --> 00:07:41 not as a new class of burst with a population
00:07:41 --> 00:07:41 behind it.
00:07:42 --> 00:07:45 Avery: Second, the physics is open. The team
00:07:45 --> 00:07:47 discusses scenarios where a merger and a uh,
00:07:47 --> 00:07:50 collapse are both involved. But nobody
00:07:50 --> 00:07:51 watched two stars do this.
00:07:52 --> 00:07:55 Alternatives, like a single central engine
00:07:55 --> 00:07:57 that changed its behaviour between the two
00:07:57 --> 00:07:59 episodes, have to stay on the table until
00:07:59 --> 00:08:01 more events like this turn up.
00:08:01 --> 00:08:03 Anna: And third, timing.
00:08:04 --> 00:08:07 The data are 10 years old and a preprint
00:08:07 --> 00:08:09 of this analysis appeared in March. What's
00:08:09 --> 00:08:11 new this week is the peer
00:08:11 --> 00:08:13 Avery: reviewed version, so the honest summary
00:08:13 --> 00:08:16 is an event. The standard toolkit
00:08:16 --> 00:08:19 splits cleanly in two sitting in a
00:08:20 --> 00:08:23 which brings us back to the telescope that
00:08:23 --> 00:08:25 caught it. Swift launched in November
00:08:25 --> 00:08:28 2004 and for 22 years its
00:08:28 --> 00:08:31 whole job was to spot a burst, swing itself
00:08:31 --> 00:08:34 around within a minute or two and point its X
00:08:34 --> 00:08:36 ray and ultraviolet telescopes at the
00:08:36 --> 00:08:37 afterglow before it faded.
00:08:38 --> 00:08:41 Anna: That's how GRB 160425A
00:08:41 --> 00:08:43 got a position good enough for the VLT to
00:08:43 --> 00:08:46 find its galaxy within seven hours. Without
00:08:46 --> 00:08:49 that fast slew, this is just two blips in a
00:08:49 --> 00:08:50 gamma ray detector.
00:08:51 --> 00:08:53 Avery: Swift ended Science operations on 20
00:08:53 --> 00:08:55 October below about
00:08:55 --> 00:08:58 275 kilometres, where
00:08:58 --> 00:09:00 atmospheric drag means it can no longer hold
00:09:00 --> 00:09:03 steady on a target. Listeners will remember
00:09:03 --> 00:09:05 the rescue attempt we followed through
00:09:05 --> 00:09:07 September with the Lynx spacecraft that
00:09:07 --> 00:09:08 couldn't make the catch.
00:09:09 --> 00:09:11 Anna: NASA expects reentry within weeks
00:09:11 --> 00:09:14 and three days after Swift stopped observing,
00:09:15 --> 00:09:17 its data put a crack in one of the most used
00:09:17 --> 00:09:20 rules in high energy astrophysics.
00:09:20 --> 00:09:21 Not a bad last word.
00:09:22 --> 00:09:24 Avery: The next step is finding more of these.
00:09:25 --> 00:09:28 The Chinese French SVOM M mission and the
00:09:28 --> 00:09:30 Einstein probe now carry much of the fast
00:09:30 --> 00:09:32 response burst work Swift used to do.
00:09:33 --> 00:09:35 If double personality bursts are real,
00:09:35 --> 00:09:35 they'll
00:09:35 --> 00:09:38 Anna: turn up again from a burst that came in
00:09:38 --> 00:09:41 two parts to a disc that hides part
00:09:41 --> 00:09:42 of itself.
00:09:43 --> 00:09:45 In November 2019, Japan's
00:09:45 --> 00:09:48 maxi instrument on the International Space
00:09:48 --> 00:09:51 Station spotted a new X ray source low
00:09:51 --> 00:09:53 in the southern sky. Maxi
00:09:53 --> 00:09:54 J0637
00:09:55 --> 00:09:58 -430. It's a black
00:09:58 --> 00:10:00 hole pulling gas off a companion star,
00:10:01 --> 00:10:03 the pair whipping around each other roughly
00:10:03 --> 00:10:04 every two hours.
00:10:05 --> 00:10:08 Avery: And a new study led by Monserrat Armas um
00:10:08 --> 00:10:11 Padilla at the Instituto de Astrophysica de
00:10:11 --> 00:10:13 Canarias and published in Nature
00:10:13 --> 00:10:16 Astronomy on Thursday found something
00:10:16 --> 00:10:18 odd in its outburst.
00:10:18 --> 00:10:21 Anna: Here's the setup in a textbook black
00:10:21 --> 00:10:24 hole Binary gas spirals in through
00:10:24 --> 00:10:25 a thin, flat disc.
00:10:26 --> 00:10:29 The inner disc glows in X rays, and that X
00:10:29 --> 00:10:31 ray light shines out across the outer disc
00:10:31 --> 00:10:34 and heats it up. Astronomers say the outer
00:10:34 --> 00:10:35 disc is irradiated,
00:10:36 --> 00:10:39 Avery: and theory says the inner disc only puffs up,
00:10:39 --> 00:10:41 becoming thick as the black hole approaches
00:10:41 --> 00:10:44 the Eddington limit. That's the point where
00:10:44 --> 00:10:46 the push of radiation fights gravity to a
00:10:46 --> 00:10:47 standstill.
00:10:47 --> 00:10:50 Anna: The team caught this system at three points
00:10:50 --> 00:10:53 as the outburst faded with ESO's Very Large
00:10:53 --> 00:10:56 Telescope and the X Shooter Spectrograph, the
00:10:56 --> 00:10:58 same instrument from our lead plus the SOAR
00:10:58 --> 00:11:01 telescope at Cerro Pechone. And the
00:11:01 --> 00:11:02 spectra ran backwards.
00:11:03 --> 00:11:04 Avery: Backwards how?
00:11:05 --> 00:11:07 Anna: At the peak, at about a fifth of the
00:11:07 --> 00:11:09 Eddington limit, the outer disc looked cool.
00:11:10 --> 00:11:13 Strong hydrogen and helium emission lines.
00:11:13 --> 00:11:15 This signature of gas that isn't being
00:11:15 --> 00:11:17 blasted by X rays. As the black hole
00:11:17 --> 00:11:20 faded, the spectrum turned hot and almost
00:11:20 --> 00:11:23 featureless, as if the outer disc was
00:11:23 --> 00:11:25 suddenly getting much more X ray heating,
00:11:25 --> 00:11:27 even though less X ray light was coming out.
00:11:28 --> 00:11:31 Avery: So the outer disc got more sunburnt
00:11:31 --> 00:11:32 when the sun dimmed.
00:11:33 --> 00:11:35 Anna: Exactly. And the explanation is shade.
00:11:36 --> 00:11:38 At the peak, the inner disc had swollen
00:11:38 --> 00:11:41 vertically and was shielding the outer disc
00:11:41 --> 00:11:43 from the X rays. As the feeding rate
00:11:43 --> 00:11:46 dropped, the inner disc thinned, the shade
00:11:46 --> 00:11:49 lifted, and the outer disc was suddenly
00:11:49 --> 00:11:52 exposed. X ray spectra taken at the same
00:11:52 --> 00:11:54 time by Nicer, Nustar and Swift
00:11:55 --> 00:11:56 back that picture up.
00:11:56 --> 00:11:59 Avery: Why does this matter beyond one system?
00:12:00 --> 00:12:02 Anna: Because a lot of black hole measurements
00:12:02 --> 00:12:05 assume a thin disc. Spin estimates
00:12:05 --> 00:12:08 X ray polarisation from NASA's IXPE
00:12:08 --> 00:12:10 bottles of the winds blowing off the outer
00:12:10 --> 00:12:13 disc if the disc is thicker than assumed
00:12:13 --> 00:12:15 at a fifth of Eddington.
00:12:15 --> 00:12:18 Some of those numbers need revisiting. The
00:12:18 --> 00:12:20 authors point out that similar behaviour in
00:12:20 --> 00:12:22 other systems suggests it may be common
00:12:23 --> 00:12:25 caveats one source and one
00:12:25 --> 00:12:28 outburst and the data are from 2019 and
00:12:28 --> 00:12:31 2020. The point where the disc puffs up
00:12:31 --> 00:12:33 probably isn't the same for every black hole,
00:12:34 --> 00:12:36 but it sits neatly beside the Goodwin and
00:12:36 --> 00:12:39 Mummery result we covered in September the
00:12:39 --> 00:12:41 idea that accretion changes character at
00:12:41 --> 00:12:43 particular fractions of the Eddington rate.
00:12:43 --> 00:12:45 This is the disc's shape changing at
00:12:45 --> 00:12:48 Avery: one of them and another Southern sky story
00:12:49 --> 00:12:52 declination -43 observed from
00:12:52 --> 00:12:54 Paranal and Cerro Pachon.
00:12:54 --> 00:12:57 Our next story continues a thread we followed
00:12:57 --> 00:12:59 since September the chemistry of 3i
00:12:59 --> 00:13:02 ATLAS only the third object ever seen
00:13:02 --> 00:13:04 passing through the solar system from another
00:13:04 --> 00:13:05 star.
00:13:06 --> 00:13:08 Anna: And this time it's a brand new measurement,
00:13:08 --> 00:13:11 not a reanalysis, right?
00:13:11 --> 00:13:14 Avery: Nathan Roth at NASA Goddard with
00:13:14 --> 00:13:17 Martin Cordiner and an international team
00:13:17 --> 00:13:19 used Webb's Near Infrared Spectrum
00:13:19 --> 00:13:22 Spectrograph to look at 3I ATLAS after
00:13:22 --> 00:13:25 its closest approach to the sun at about
00:13:25 --> 00:13:28 2.4 astronomical units out.
00:13:28 --> 00:13:30 Their paper came out in Nature Astronomy on
00:13:30 --> 00:13:31 Friday.
00:13:32 --> 00:13:34 Anna: They picked out methane and also a heavy
00:13:34 --> 00:13:37 version of methane CH3D,
00:13:37 --> 00:13:39 where one hydrogen atom is swapped for
00:13:39 --> 00:13:40 deuterium.
00:13:40 --> 00:13:43 That's the isotope of hydrogen with an extra
00:13:43 --> 00:13:43 neutron.
00:13:44 --> 00:13:46 Avery: And the ratio of deuterium to hydrogen in
00:13:46 --> 00:13:49 that methane is 3.18%,
00:13:50 --> 00:13:52 give or take about a third of a percent.
00:13:53 --> 00:13:54 Anna: Give me some context for that.
00:13:55 --> 00:13:57 Avery: Earth's ocean water has about
00:13:57 --> 00:14:00 156 deuterium atoms for every million
00:14:00 --> 00:14:01 hydrogen, roughly
00:14:01 --> 00:14:04 0%. This
00:14:04 --> 00:14:07 methane is around 200 times richer than that.
00:14:08 --> 00:14:10 It's higher than any methane value measured
00:14:10 --> 00:14:12 anywhere in the solar system, and about 13
00:14:12 --> 00:14:15 times higher than Comet 67P, the only
00:14:15 --> 00:14:17 other comet where heavy methane has been
00:14:17 --> 00:14:19 detected by Rosetta.
00:14:19 --> 00:14:22 Anna: Why does deuterium tell you anything about
00:14:22 --> 00:14:23 where it came from?
00:14:23 --> 00:14:26 Avery: Because cold concentrates it at
00:14:26 --> 00:14:28 a few tens of degrees above absolute zero.
00:14:29 --> 00:14:32 The chemistry on icy dust grains favours
00:14:32 --> 00:14:34 deuterium, so ices that form
00:14:34 --> 00:14:37 in very cold places end up enriched.
00:14:37 --> 00:14:39 It works like a thermometer with a
00:14:39 --> 00:14:42 Anna: memory, like the nitrogen thermometer from
00:14:42 --> 00:14:44 the three eye story back in September.
00:14:44 --> 00:14:47 Avery: Exactly that, and there's a consistency
00:14:47 --> 00:14:49 check in both 3i and
00:14:49 --> 00:14:52 67pMethane is more deuterated
00:14:52 --> 00:14:55 than water. The same pattern seen in nearby
00:14:55 --> 00:14:57 star forming clouds where organic
00:14:57 --> 00:15:00 molecules can be up to 10 times more
00:15:00 --> 00:15:02 deuterated than water. So
00:15:02 --> 00:15:05 3i Atlas isn't strange in kind.
00:15:05 --> 00:15:07 It's the same chemistry turned up,
00:15:08 --> 00:15:11 Turned uh, up by what the team's reading is a
00:15:11 --> 00:15:14 birthplace that was cold pour in heavy
00:15:14 --> 00:15:17 elements, so probably old and
00:15:17 --> 00:15:18 bathed in cosmic rays.
00:15:19 --> 00:15:21 That fits the earlier water measurements
00:15:21 --> 00:15:23 published in April and June, which also
00:15:23 --> 00:15:26 pointed to a cold ancient origin.
00:15:26 --> 00:15:29 Caveats 3 It's
00:15:29 --> 00:15:32 one object. The gas in a uh, comet's
00:15:32 --> 00:15:34 coma comes from ices that have been through a
00:15:34 --> 00:15:37 lot, including a pass by the sun.
00:15:37 --> 00:15:39 So it's a strong clue, not a birth
00:15:39 --> 00:15:42 certificate. And um, a preprint of this has
00:15:42 --> 00:15:43 been around since March.
00:15:43 --> 00:15:45 It's the peer reviewed version that's new
00:15:46 --> 00:15:49 Anna: and a lovely footnote. The acknowledgments
00:15:49 --> 00:15:52 thank school students in the uk, Spain,
00:15:52 --> 00:15:55 Brazil and Croatia through the Comet Chasers
00:15:55 --> 00:15:57 Outreach programme for position measurements
00:15:57 --> 00:16:00 that helped pin down exactly where to
00:16:00 --> 00:16:02 Avery: point Webb and the southern thread.
00:16:02 --> 00:16:05 3i Atlas was discovered
00:16:05 --> 00:16:08 by the ATLAS survey telescope at Rio
00:16:08 --> 00:16:09 Urtado in Chile.
00:16:10 --> 00:16:13 Anna: Time for some engineering. NASA's Psyche
00:16:13 --> 00:16:15 spacecraft is on its way to a metal rich
00:16:15 --> 00:16:18 asteroid of the same name. And last week the
00:16:18 --> 00:16:20 team announced it has gone, in their words,
00:16:20 --> 00:16:21 pedal to the metal.
00:16:21 --> 00:16:24 Avery: Psyche, launched in October 2023,
00:16:24 --> 00:16:27 swung past Mars in May for a uh, gravity
00:16:27 --> 00:16:29 assist. And since 28 September it,
00:16:29 --> 00:16:30 it's been
00:16:30 --> 00:16:32 Anna: thrusting almost continuously about
00:16:32 --> 00:16:35 90% of the time from now until arrival,
00:16:35 --> 00:16:37 pausing once a week to check in with Earth.
00:16:38 --> 00:16:40 And those check ins like every deep space
00:16:40 --> 00:16:42 missions run through NASA's Deep Space
00:16:42 --> 00:16:44 Network, including the big dishes at
00:16:44 --> 00:16:46 Tidbinbilla outside Canberra.
00:16:47 --> 00:16:49 Avery: Now the thrusters Psyche uses Hall
00:16:49 --> 00:16:52 effect thrusters. Electric and uh, magnetic
00:16:52 --> 00:16:55 fields push ions of xenon gas out the back
00:16:55 --> 00:16:57 with a vivid blue glow.
00:16:57 --> 00:17:00 Anna: And the force is tiny, up to
00:17:00 --> 00:17:02 250 millinewtons.
00:17:02 --> 00:17:05 NASA compares it to the weight of a single AA
00:17:05 --> 00:17:06 battery resting in your hand.
00:17:07 --> 00:17:10 Avery: But it never stops pushing. Over
00:17:10 --> 00:17:12 months that adds up. At its
00:17:12 --> 00:17:14 fastest, Psyche will be moving at uh, more
00:17:14 --> 00:17:17 than 160 kilometres an hour
00:17:17 --> 00:17:18 relative to Earth.
00:17:19 --> 00:17:22 Anna: The fuel budget looks healthy too. It
00:17:22 --> 00:17:24 launched with about 1 kilogrammes of
00:17:24 --> 00:17:27 xenon and after three years it has
00:17:27 --> 00:17:28 used roughly a third.
00:17:29 --> 00:17:31 Avery: There's a catch with solar electric
00:17:31 --> 00:17:33 propulsion though. The further you get from
00:17:33 --> 00:17:36 the sun, the less power you have. The
00:17:36 --> 00:17:38 team says it'll run at full power for about
00:17:38 --> 00:17:41 three months, then gradually throttle back to
00:17:41 --> 00:17:43 around half as the sunlight weakens.
00:17:44 --> 00:17:46 Anna: And here's the bit that caught my eye.
00:17:46 --> 00:17:49 When the thruster expels its ions, the
00:17:49 --> 00:17:51 magnetic field makes them swirl. And that
00:17:51 --> 00:17:54 swirl puts a tiny Twist on the spacecraft.
00:17:54 --> 00:17:57 Avery: A torque too small to measure on the ground.
00:17:57 --> 00:18:00 Anna: Exactly. You can only measure it in space.
00:18:01 --> 00:18:03 The team says this is the first time anyone
00:18:03 --> 00:18:05 has measured that swirl torque on a Hall
00:18:05 --> 00:18:07 thruster across different power levels and
00:18:07 --> 00:18:10 operating times over such a long stretch in
00:18:10 --> 00:18:13 space. They soak it up with reaction wheels
00:18:13 --> 00:18:15 and every few hours they run a different
00:18:15 --> 00:18:17 thruster briefly to dump the built up
00:18:17 --> 00:18:17 momentum.
00:18:18 --> 00:18:21 Avery: So the spacecraft is doing science on its own
00:18:21 --> 00:18:23 engine on the way to doing science on an
00:18:23 --> 00:18:24 asteroid.
00:18:24 --> 00:18:27 Anna: Right, and the target is worth the trip.
00:18:28 --> 00:18:30 Psyche is about 280 kilometres
00:18:30 --> 00:18:33 across at its widest. And it may be part of
00:18:33 --> 00:18:36 the exposed metal core of a planetesimal,
00:18:36 --> 00:18:38 one of the building blocks of planets like
00:18:38 --> 00:18:41 Earth. Arrival is mid-2029,
00:18:41 --> 00:18:43 followed by two years in orbit.
00:18:43 --> 00:18:46 Avery: Uh, a look inside a planet without having to
00:18:46 --> 00:18:46 dig.
00:18:47 --> 00:18:50 Anna: Next, let's have some other news headlines.
00:18:50 --> 00:18:51 Avery: The quick hits.
00:18:52 --> 00:18:54 First, a desk flag we've carried for nearly
00:18:54 --> 00:18:57 two weeks can finally come down. ESA's
00:18:57 --> 00:18:59 HERA spacecraft carried out its second
00:18:59 --> 00:19:02 braking manoeuvre, BRM2, on Thursday the
00:19:02 --> 00:19:04 22nd. In a post on X the next day,
00:19:04 --> 00:19:07 ESA said the burn cut HERA speed relative to
00:19:07 --> 00:19:10 the Didymus and dimorphous pair by 70 metres
00:19:10 --> 00:19:13 per second from about 2 kilometres
00:19:13 --> 00:19:16 out. Hera is now drifting in at about
00:19:16 --> 00:19:17 20 metres per second.
00:19:18 --> 00:19:21 Anna: Three smaller transition manoeuvres this week
00:19:21 --> 00:19:23 should bring that close to zero ahead of
00:19:23 --> 00:19:26 arrival in November and the southern thread.
00:19:26 --> 00:19:29 ESA follows these burns through its deep
00:19:29 --> 00:19:31 space antennas at New Nortia in Western
00:19:31 --> 00:19:31 Australia.
00:19:32 --> 00:19:35 Avery: Second, NASA's Dragonfly flew to
00:19:35 --> 00:19:38 Titan sort of at, uh, the
00:19:38 --> 00:19:40 Applied Physics Laboratory in Maryland. The
00:19:40 --> 00:19:43 team ran its most complete simulation yet of
00:19:43 --> 00:19:45 Dragonfly's first flight. On flight, like
00:19:45 --> 00:19:48 avionics, with navigation, camera images
00:19:48 --> 00:19:51 rendered in real time and simulated lidar
00:19:51 --> 00:19:53 all the way to an autonomous landing,
00:19:54 --> 00:19:57 Dragonfly launches no earlier than 2028
00:19:57 --> 00:19:59 and reaches Titan in 2034.
00:20:00 --> 00:20:02 Anna: And third, happy birthday.
00:20:02 --> 00:20:05 Stereo NASA's twin solar
00:20:05 --> 00:20:08 observatories launched on a Delta II rocket
00:20:08 --> 00:20:10 on the evening of the 25th of October
00:20:10 --> 00:20:13 2006, Florida time. That was
00:20:13 --> 00:20:15 late morning on the 26th in eastern
00:20:15 --> 00:20:18 Australia. So 20 years ago this
00:20:18 --> 00:20:21 week, in February 2011, the
00:20:21 --> 00:20:23 pair gave us our first view of the whole sun
00:20:23 --> 00:20:26 at once. Stereo B fell silent
00:20:26 --> 00:20:29 in 2014, but stereo A is
00:20:29 --> 00:20:30 still working.
00:20:31 --> 00:20:34 Avery: Skywatch, as always, we've run the numbers
00:20:34 --> 00:20:36 for Sydney, Los Angeles, New York and
00:20:36 --> 00:20:37 London.
00:20:37 --> 00:20:40 Anna: Start with the moon. The hunter's moon
00:20:40 --> 00:20:43 was full at 4:11 universal time on
00:20:43 --> 00:20:46 Monday the 26th. That's 3:11
00:20:46 --> 00:20:49 on Monday afternoon in Sydney. So Monday
00:20:49 --> 00:20:52 night looks full here in the
00:20:52 --> 00:20:53 Americas, uh, the instant fell on Sunday
00:20:53 --> 00:20:56 night, the 25th. Either way, it looks full
00:20:56 --> 00:20:57 on both
00:20:57 --> 00:20:59 Avery: nights from here, it's a waning
00:20:59 --> 00:21:02 moon rising later each evening.
00:21:03 --> 00:21:05 On Tuesday, it comes up around
00:21:05 --> 00:21:08 8:45pm in Sydney, about
00:21:08 --> 00:21:10 7pm in Los Angeles,
00:21:10 --> 00:21:13 6:40 in New York. And in
00:21:13 --> 00:21:16 London it rises almost exactly at
00:21:16 --> 00:21:18 sunset at about a quarter to five.
00:21:19 --> 00:21:21 Last quarter is on the 1st of
00:21:21 --> 00:21:23 Anna: November Universal Time and a
00:21:23 --> 00:21:25 clock reminder for the north.
00:21:25 --> 00:21:28 The UK went back to standard time on Sunday
00:21:28 --> 00:21:31 the 25th. The US follows this coming
00:21:31 --> 00:21:33 Sunday the 1st of November. Here in
00:21:33 --> 00:21:36 Australia, we've been on daylight time since
00:21:36 --> 00:21:38 the start of October. If you're in a
00:21:38 --> 00:21:40 different time zone from where you usually
00:21:40 --> 00:21:42 listen, your skywatch times have probably
00:21:42 --> 00:21:43 moved.
00:21:43 --> 00:21:46 Avery: The big show is before dawn and
00:21:46 --> 00:21:49 this week it favours the north. Jupiter
00:21:49 --> 00:21:52 at magnitude -1.8 in Leo
00:21:52 --> 00:21:55 and Mars, a, uh, fainter orange point
00:21:55 --> 00:21:58 at about 0.9 in cancer,
00:21:58 --> 00:22:01 are closing on each other. They're about
00:22:01 --> 00:22:03 seven and a half degrees apart this week,
00:22:03 --> 00:22:05 under six by the first of November,
00:22:06 --> 00:22:08 about three by the eighth. And they reach
00:22:08 --> 00:22:11 their closest just over one degree apart
00:22:11 --> 00:22:13 on the 16th of November Universal Time.
00:22:14 --> 00:22:17 Anna: And the hemisphere gap is big. At, uh,
00:22:17 --> 00:22:19 nautical dawn on Wednesday the 28th.
00:22:20 --> 00:22:23 Mars is about 64 degrees up from Los
00:22:23 --> 00:22:25 Angeles, 60 from New York and
00:22:25 --> 00:22:28 52 from London, with Jupiter just
00:22:28 --> 00:22:31 below it from Sydney. Both are only
00:22:31 --> 00:22:33 about 25 degrees up
00:22:33 --> 00:22:35 Avery: in the northeast, so for northern
00:22:35 --> 00:22:38 listeners, they're high and easy. From the
00:22:38 --> 00:22:40 south, look northeast about an hour before
00:22:40 --> 00:22:43 sunrise. They're lower but still well
00:22:43 --> 00:22:44 clear of the Horizon.
00:22:44 --> 00:22:47 And by the 8th of November, both sit around
00:22:47 --> 00:22:48 28 degrees up from Sydney.
00:22:49 --> 00:22:52 Anna: The evening sky gives some back to the south.
00:22:53 --> 00:22:56 Saturn, at about magnitude half in
00:22:56 --> 00:22:58 Cetus, is a few weeks past opposition
00:22:59 --> 00:23:02 and up. As the sky darkens at the
00:23:02 --> 00:23:04 end of evening twilight on Wednesday, it's
00:23:04 --> 00:23:06 around 31 degrees up from Sydney
00:23:07 --> 00:23:09 against about 19 from Los Angeles,
00:23:10 --> 00:23:13 16 from New York and 11 from London.
00:23:13 --> 00:23:15 Avery: And this is Mercury's last call for the
00:23:15 --> 00:23:17 southern evening sky.
00:23:17 --> 00:23:20 It's fading quickly from about magnitude
00:23:20 --> 00:23:23 1.3 on Tuesday to 3.6
00:23:23 --> 00:23:26 by the first of November and sinking toward
00:23:26 --> 00:23:29 the sun from Sydney. It's around 9 degrees up
00:23:29 --> 00:23:31 in the west at the end of twilight midweek,
00:23:31 --> 00:23:34 lick low with a clear horizon 20 to
00:23:34 --> 00:23:37 40 minutes after sunset. From the north,
00:23:37 --> 00:23:38 it's essentially gone.
00:23:39 --> 00:23:42 Anna: Venus passed between us and the sun on the
00:23:42 --> 00:23:45 24th, about 6 1/2 degrees
00:23:45 --> 00:23:47 from it in the sky, so it's out of sight this
00:23:47 --> 00:23:50 week. It'll start climbing into the morning
00:23:50 --> 00:23:51 sky in November.
00:23:52 --> 00:23:55 Avery: Meteor wise, the Taurids are building toward
00:23:55 --> 00:23:57 their peaks in early and mid November.
00:23:57 --> 00:24:00 Rates are low, only a handful an hour, but
00:24:00 --> 00:24:03 this shower is known for slow, bright
00:24:03 --> 00:24:05 fireballs, and it's visible from both
00:24:05 --> 00:24:07 hemispheres. The Moon will be a thinning
00:24:07 --> 00:24:08 crescent by then, which helps.
00:24:09 --> 00:24:11 Anna: No eclipses this week, but the standing
00:24:11 --> 00:24:14 reminder Never look at the sun directly or
00:24:14 --> 00:24:16 through binoculars or a telescope without
00:24:16 --> 00:24:19 proper solar filters Certified to the
00:24:19 --> 00:24:21 ISO 123122
00:24:21 --> 00:24:24 standard. Ordinary sunglasses won't do.
00:24:25 --> 00:24:28 Avery: So north, get up early for Mars and
00:24:28 --> 00:24:31 Jupiter. South catch Saturn in the evening
00:24:31 --> 00:24:33 and Mercury before it's gone. And everybody
00:24:34 --> 00:24:35 enjoy the bright Moon this week.
00:24:35 --> 00:24:37 Anna: That's Astronomy daily for Monday,
00:24:38 --> 00:24:40 26 October. Today,
00:24:41 --> 00:24:43 a UH gamma ray burst that seems to be two
00:24:43 --> 00:24:46 kinds of explosion at UH once caught by Swift
00:24:46 --> 00:24:49 a decade ago and published the week Swift
00:24:49 --> 00:24:52 went Quiet A black hole disc that shades
00:24:52 --> 00:24:54 itself at a fifth of the Eddington limit.
00:24:54 --> 00:24:57 Record heavy methane from 3i atlas
00:24:57 --> 00:25:00 and psyche pedal to the Metal
00:25:00 --> 00:25:01 Show Notes,
00:25:01 --> 00:25:03 Avery: sources and links to every paper are at
00:25:03 --> 00:25:06 astronomydaily.IO Questions
00:25:06 --> 00:25:09 or story ideas use the contact form there.
00:25:09 --> 00:25:11 Some of our best segments have started with a
00:25:11 --> 00:25:13 listener's question and you'll find us on
00:25:13 --> 00:25:16 social media. Strodailypod
00:25:16 --> 00:25:17 thanks for listening.
00:25:17 --> 00:25:18 Anna: I'm Anna.
00:25:19 --> 00:25:22 Avery: And I'm Avery Clear Skies, and we'll see
00:25:22 --> 00:25:24 you tomorrow. Astronomy Day.
00:25:25 --> 00:25:27 The Stories we told
00:25:29 --> 00:25:29 Anna: Love.
00:25:34 --> 00:25:35 Avery: Story soul.