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00:00:00 --> 00:00:02 Anna: Hello and welcome to Astronomy daily. It's
00:00:02 --> 00:00:05 Thursday the 10th of September 2026.
00:00:06 --> 00:00:08 This is series five, episode 190.
00:00:09 --> 00:00:10 And I'm Anna.
00:00:10 --> 00:00:13 Avery: And I'm Avery. Anna, I want to start with a
00:00:13 --> 00:00:15 number. 109.
00:00:15 --> 00:00:18 Anna: Ah, 109 radio flashes.
00:00:18 --> 00:00:20 Each one lasting about a thousandth of a
00:00:20 --> 00:00:23 second. Each one from a different galaxy.
00:00:23 --> 00:00:26 And together they have just been used to
00:00:26 --> 00:00:29 weigh the ordinary matter of the universe and
00:00:29 --> 00:00:31 to work out how badly galaxies have been
00:00:31 --> 00:00:31 throwing it around.
00:00:32 --> 00:00:35 Avery: A hundred and nine. That's not a lot of
00:00:35 --> 00:00:35 anything.
00:00:36 --> 00:00:38 Anna: It's not. And yet the answer they give is
00:00:38 --> 00:00:41 already as good as what you get from an X ray
00:00:41 --> 00:00:44 survey of the entire sky. Or a microwave
00:00:44 --> 00:00:46 telescope that's been running a decade on the
00:00:46 --> 00:00:49 problem currently standing between cosmology
00:00:49 --> 00:00:52 and a straight answer about dark energy,
00:00:52 --> 00:00:55 dark matter and the mass of the neutrino.
00:00:55 --> 00:00:56 That's our lead.
00:00:56 --> 00:00:59 Avery: After that, 84 objects that have been sitting
00:00:59 --> 00:01:02 in the Chandra archive for years, glowing
00:01:02 --> 00:01:05 in a part of the X ray spectrum nobody was
00:01:05 --> 00:01:08 really looking at. And which may turn out to
00:01:08 --> 00:01:10 be the missing ancestors of the exploding
00:01:10 --> 00:01:12 stars we used to measure the universe.
00:01:13 --> 00:01:16 Anna: A serious worked out plan to fly a spacecraft
00:01:16 --> 00:01:18 alongside Hallie's Comet in 2060,
00:01:18 --> 00:01:21 not past it in a blur alongside it for
00:01:21 --> 00:01:24 for months, using nothing that hasn't already
00:01:24 --> 00:01:25 flown.
00:01:25 --> 00:01:28 Avery: And the US military manoeuvring real
00:01:28 --> 00:01:30 satellites across three orbital regimes
00:01:30 --> 00:01:33 in the first exercise of its kind.
00:01:33 --> 00:01:36 Anna: Plus the sky for both hemispheres. New moon
00:01:36 --> 00:01:38 tomorrow afternoon. So tonight is about as
00:01:38 --> 00:01:41 dark as September gets and there's a run of
00:01:41 --> 00:01:43 solar storms arriving that could put aurora
00:01:43 --> 00:01:44 at both ends of the planet.
00:01:45 --> 00:01:47 Let's start with the flashes before the
00:01:47 --> 00:01:47 result.
00:01:48 --> 00:01:51 Avery: Set it up for me. What is a fast radio burst?
00:01:51 --> 00:01:54 Anna: Actually, a pulse of radio energy that
00:01:54 --> 00:01:56 arrives, does its business in about a
00:01:56 --> 00:01:59 millisecond and is gone in that
00:01:59 --> 00:02:01 thousandth of a second. It can release as
00:02:01 --> 00:02:03 much energy as the sun puts out in a couple
00:02:03 --> 00:02:05 of days. The first one was found in
00:02:05 --> 00:02:08 2007 in archived data from the Parkes
00:02:08 --> 00:02:11 dish in New South Wales. Murrayang by
00:02:11 --> 00:02:13 Dunkley Lorimer and a student going back
00:02:13 --> 00:02:16 through observations from 2001. For
00:02:16 --> 00:02:18 a while, nobody believed it. Reasonably
00:02:18 --> 00:02:21 enough, one burst, one telescope, no
00:02:21 --> 00:02:21 repeat.
00:02:22 --> 00:02:22 Avery: And now.
00:02:23 --> 00:02:25 Anna: Now we know of thousands. And we know at
00:02:25 --> 00:02:28 least some come from magnetars, neutron stars
00:02:28 --> 00:02:30 with absurd magnetic fields. Because in
00:02:30 --> 00:02:33 2020, one went off inside our own
00:02:33 --> 00:02:36 galaxy. But that's not today's storey. And
00:02:36 --> 00:02:37 this is the interesting turn the field has
00:02:37 --> 00:02:40 taken. What a fast radio burst is, has
00:02:40 --> 00:02:42 become less important than what it does on
00:02:42 --> 00:02:45 the way here, which is what it gets
00:02:45 --> 00:02:48 stretched. That millisecond pulse contains a
00:02:48 --> 00:02:51 range of radio frequencies, all leaving at
00:02:51 --> 00:02:53 the same instant. But space between galaxies
00:02:53 --> 00:02:56 isn't, uh, empty. There's a thin haze of free
00:02:56 --> 00:02:58 electrons in it. And free electrons, slow,
00:02:58 --> 00:03:00 low radio frequencies, slightly more than
00:03:00 --> 00:03:01 high ones.
00:03:02 --> 00:03:02 Avery: Like a prism.
00:03:03 --> 00:03:06 Anna: Exactly like a prism. And that's Caltech's
00:03:06 --> 00:03:09 own comparison. The burst leaves
00:03:09 --> 00:03:11 its galaxy as one clean pulse
00:03:11 --> 00:03:14 and arrives here smeared out in time. High
00:03:14 --> 00:03:17 frequencies first, low frequencies trailing
00:03:17 --> 00:03:20 behind. You can measure that smear
00:03:20 --> 00:03:23 precisely. And it has a name, the
00:03:23 --> 00:03:25 dispersion measure. The size of the delay
00:03:25 --> 00:03:27 tells you how many free electrons the pulse
00:03:27 --> 00:03:30 went through, not how far it travelled, how
00:03:30 --> 00:03:33 much stuff it travelled through. Every burst
00:03:33 --> 00:03:35 is a core sample of the universe along one
00:03:35 --> 00:03:36 line of sight.
00:03:37 --> 00:03:38 Avery: And that solved something.
00:03:39 --> 00:03:41 Anna: It solved a real embarrassment first time
00:03:41 --> 00:03:44 out. Ordinary matter, baryons,
00:03:44 --> 00:03:47 the stuff of atoms. We knew from the cosmic
00:03:47 --> 00:03:49 microwave background how much of it the
00:03:49 --> 00:03:51 universe was made with. And when you added up
00:03:51 --> 00:03:54 everything we could actually see, roughly a
00:03:54 --> 00:03:57 third was missing. The suspicion was always
00:03:57 --> 00:03:59 that it sat between the galaxies, spread
00:03:59 --> 00:04:02 impossibly thin and too cool to glow in X
00:04:02 --> 00:04:04 rays, which is exactly what a dispersion
00:04:04 --> 00:04:06 measure is sensitive to, glowing or not.
00:04:07 --> 00:04:09 Avery: And that's where Australia comes in.
00:04:09 --> 00:04:12 Anna: That's where Australia comes in. In 2020,
00:04:12 --> 00:04:14 a team led by Jean Pierre Macquart at the
00:04:14 --> 00:04:17 Curtain node of ICRAR used ASCAP in
00:04:17 --> 00:04:20 Western Australia to localise a handful of
00:04:20 --> 00:04:22 bursts to their host galaxies, compared
00:04:22 --> 00:04:25 dispersion against distance. And there was
00:04:25 --> 00:04:27 the missing matter. It's called the Macart
00:04:27 --> 00:04:30 relation. Now, Makartt himself died that same
00:04:30 --> 00:04:33 year at 45 months after the paper.
00:04:33 --> 00:04:35 And it's the foundation everything today is
00:04:35 --> 00:04:36 built on.
00:04:36 --> 00:04:38 Avery: So we found the missing matter.
00:04:38 --> 00:04:41 Anna: What's left to argue about where it is
00:04:41 --> 00:04:44 in detail? And that's the whole problem,
00:04:44 --> 00:04:46 because galaxies don't sit quietly and hold
00:04:46 --> 00:04:48 onto their gas, they throw it out.
00:04:49 --> 00:04:51 Supernovae. And more importantly,
00:04:51 --> 00:04:53 supermassive black holes, switching on and
00:04:53 --> 00:04:56 driving enormous outflows. Gas that
00:04:56 --> 00:04:58 started concentrated around galaxies gets
00:04:58 --> 00:05:01 pushed into the space between them, sometimes
00:05:01 --> 00:05:02 millions of light years out.
00:05:03 --> 00:05:03 Avery: Feedback.
00:05:04 --> 00:05:07 Anna: Feedback. And Vikram Ravi at Caltech
00:05:07 --> 00:05:09 puts the consequence better than I can. The
00:05:09 --> 00:05:12 process thins the gas around galaxies,
00:05:12 --> 00:05:14 redistributing matter across vast distances.
00:05:15 --> 00:05:18 And it smooths out the clumps in a way, he
00:05:18 --> 00:05:20 says, that looks astonishingly similar to
00:05:20 --> 00:05:23 what massive neutrinos do or what dark energy
00:05:23 --> 00:05:26 or dark matter theories predict. Unless you
00:05:26 --> 00:05:28 can independently measure the feedback, you
00:05:28 --> 00:05:30 can't tell those effects apart.
00:05:30 --> 00:05:33 Avery: Explain why clumpiness is the thing being
00:05:33 --> 00:05:35 Anna: measured, because how lumpy the universe is,
00:05:36 --> 00:05:38 how strongly matter clusters on different
00:05:38 --> 00:05:40 scales, is one of the sharpest tests we have
00:05:40 --> 00:05:43 of what it's made of. Massive neutrinos
00:05:43 --> 00:05:46 wash out small scale structure. Certain
00:05:46 --> 00:05:49 dark energy behaviours change the clustering.
00:05:49 --> 00:05:52 Dark matter that isn't quite cold and inert.
00:05:52 --> 00:05:55 Same thing. And so does gas being blown about
00:05:55 --> 00:05:56 by a black hole.
00:05:56 --> 00:05:58 Avery: So it's a confound.
00:05:58 --> 00:06:00 Anna: It's the confound and it has a name.
00:06:00 --> 00:06:03 This sits at the heart of the S8 tension,
00:06:04 --> 00:06:06 the long running disagreement between how
00:06:06 --> 00:06:08 lumpy the early universe says things should
00:06:08 --> 00:06:11 be and how lumpy the late universe actually
00:06:11 --> 00:06:14 looks. Either that gap is new physics,
00:06:14 --> 00:06:16 which would be enormous, or we simply
00:06:16 --> 00:06:19 don't understand how much gas galaxies throw
00:06:19 --> 00:06:22 around, which is deflating but entirely
00:06:22 --> 00:06:24 plausible. And nobody could settle it because
00:06:24 --> 00:06:26 nobody could measure the diffuse gas
00:06:26 --> 00:06:29 properly. X ray telescopes see the hot
00:06:29 --> 00:06:32 gas and miss the cool. The microwave
00:06:32 --> 00:06:34 technique, the kinetic Sunyaev Zeldovich
00:06:34 --> 00:06:37 effect works, but it's statistical and
00:06:37 --> 00:06:39 hard. You want something that counts
00:06:39 --> 00:06:41 electrons and doesn't care what temperature
00:06:41 --> 00:06:41 they are.
00:06:42 --> 00:06:43 Avery: A dispersion measure.
00:06:44 --> 00:06:46 Anna: A dispersion measure. So the new
00:06:46 --> 00:06:49 work published Tuesday 8 September in Nature
00:06:49 --> 00:06:52 Astronomy, led by Kriti Sharma at Caltech,
00:06:52 --> 00:06:55 with Vikram Ravi, Liam Connor and
00:06:55 --> 00:06:57 Elizabeth Kraus at the University of Arizona.
00:06:57 --> 00:07:00 Among The CO authors, 109
00:07:00 --> 00:07:03 fast radio bursts, each localised to a
00:07:03 --> 00:07:06 host galaxy, so it has a redshift as well as
00:07:06 --> 00:07:08 a dispersion measure out to a redshift of
00:07:08 --> 00:07:11 about 0.3, relatively local,
00:07:11 --> 00:07:13 deliberately, because that's where feedback
00:07:13 --> 00:07:16 effects are most measurable. Most of the
00:07:16 --> 00:07:18 bursts come from the Deep synoptic array, the
00:07:18 --> 00:07:21 DSA110, a Caltech instrument
00:07:21 --> 00:07:23 at Owens Valley in California built to catch
00:07:23 --> 00:07:25 these things and pin them to a galaxy in real
00:07:25 --> 00:07:26 time.
00:07:26 --> 00:07:29 Avery: And what did the hundred and nine tell them?
00:07:29 --> 00:07:32 Anna: Two things. First, they measured how much
00:07:32 --> 00:07:33 feedback has suppressed the clustering of
00:07:33 --> 00:07:36 matter across the range from galaxy group
00:07:36 --> 00:07:39 structures down to individual galaxy halos.
00:07:39 --> 00:07:41 And how much gas is actually sitting in
00:07:41 --> 00:07:43 groups and clusters between 10 to the 13
00:07:43 --> 00:07:46 and 10 to the 15 solar masses.
00:07:46 --> 00:07:48 And there's more of it there than the other
00:07:48 --> 00:07:51 methods we're finding. The gas fractions come
00:07:51 --> 00:07:54 out about 1.9 Sigma higher than
00:07:54 --> 00:07:56 stacking. Erosita's X ray observations of the
00:07:56 --> 00:07:59 same kinds of systems, and a little above
00:07:59 --> 00:08:01 what the Atacama Cosmology Telescope gives
00:08:02 --> 00:08:05 the team reads that the obvious. The bursts
00:08:05 --> 00:08:07 are counting cool gas the X rays can't see
00:08:08 --> 00:08:09 because it isn't hot. Enough to shine.
00:08:10 --> 00:08:12 Avery: So feedback has smoothed things less than we
00:08:12 --> 00:08:13 thought.
00:08:13 --> 00:08:16 Anna: Less than the X ray picture implied. And the
00:08:16 --> 00:08:19 second result is precision Using the bursts
00:08:19 --> 00:08:21 cut the uncertainty on the clustering at
00:08:21 --> 00:08:23 those scales by roughly a factor of eight.
00:08:23 --> 00:08:25 And the constraint is competitive with E.
00:08:25 --> 00:08:28 Rosita and with the Atacama Cosmology
00:08:28 --> 00:08:31 Telescope. Those are enormous experiments.
00:08:31 --> 00:08:34 This is 109 Flashes. Kraus
00:08:34 --> 00:08:37 Line. This is amazing considering we only had
00:08:37 --> 00:08:40 about a hundred FRBs in our sample. It's only
00:08:40 --> 00:08:40 the beginning.
00:08:41 --> 00:08:41 Avery: Caveats?
00:08:42 --> 00:08:45 Anna: Three honest ones. One M hundred nine
00:08:45 --> 00:08:47 is a small sample and the tension with
00:08:47 --> 00:08:50 Erosita at 1.9 Sigma is
00:08:50 --> 00:08:53 interesting, not established. Second
00:08:54 --> 00:08:56 part of every dispersion measure comes from
00:08:56 --> 00:08:58 the host galaxy itself and has to be
00:08:58 --> 00:09:00 modelled. They get an average host
00:09:00 --> 00:09:03 contribution of about 129
00:09:03 --> 00:09:06 in the units the field uses, give or take
00:09:06 --> 00:09:06 nearly 20.
00:09:07 --> 00:09:10 That's the weakest joint in the chain. And
00:09:10 --> 00:09:13 third, it's a low redshift sample. A
00:09:13 --> 00:09:15 lot about the recent universe, much less
00:09:15 --> 00:09:16 about the deep past.
00:09:16 --> 00:09:19 Avery: And the fix is more bursts.
00:09:19 --> 00:09:21 Anna: Many more. And it's being built.
00:09:22 --> 00:09:24 Caltech's next machine, the full Deep
00:09:24 --> 00:09:27 Synoptic Array is planned for a valley in
00:09:27 --> 00:09:29 Nevada with construction targeted around
00:09:29 --> 00:09:32 2029. And should find these in the tens
00:09:32 --> 00:09:35 of thousands. Ravi's assessment is blunt.
00:09:35 --> 00:09:38 It'll be a game changer. Sharma's is that
00:09:38 --> 00:09:40 they've established fast radio bursts as a
00:09:40 --> 00:09:42 leading probe of the distribution of matter
00:09:42 --> 00:09:45 in the universe. And that the data can now
00:09:45 --> 00:09:47 sharpen experiments asking about dark matter,
00:09:48 --> 00:09:50 dark energy and the mass of the neutrino.
00:09:51 --> 00:09:53 For something that was a single unexplained
00:09:53 --> 00:09:56 blip in an Australian archive 19 years ago.
00:09:56 --> 00:09:57 That's quite a promotion.
00:09:58 --> 00:10:00 Avery: And that's the thread back home.
00:10:00 --> 00:10:03 Anna: That's the thread. The technique is southern
00:10:03 --> 00:10:06 in origin and still substantially southern in
00:10:06 --> 00:10:08 practise. The first burst came out of parks.
00:10:08 --> 00:10:11 The McCourt relation came out of Azcap on
00:10:11 --> 00:10:14 Wajari country at Inyarimana Il Ghari
00:10:14 --> 00:10:17 Bundara. And ASCAP is still one of the most
00:10:17 --> 00:10:19 productive burst localising instruments on
00:10:19 --> 00:10:21 the planet. Its Krako upgrade exists
00:10:21 --> 00:10:24 specifically to catch them live and hand a
00:10:24 --> 00:10:26 position to other telescopes fast enough to
00:10:26 --> 00:10:29 chase. Meerkat works the same field.
00:10:29 --> 00:10:32 Both sites are the foundations of the Square
00:10:32 --> 00:10:34 Kilometre Array which we talked about
00:10:34 --> 00:10:37 Avery: five days ago for a completely different
00:10:37 --> 00:10:37 reason.
00:10:38 --> 00:10:40 Anna: The MeerKAT 21 centimetre detection.
00:10:41 --> 00:10:43 A different way of weighing the same universe
00:10:43 --> 00:10:46 with the same kind of dish. Two techniques,
00:10:46 --> 00:10:49 two hemispheres. One question and the
00:10:49 --> 00:10:51 honest summary of today is that 109 flashes
00:10:51 --> 00:10:53 have walked into a fight with the giant
00:10:53 --> 00:10:56 surveys have been having for a decade and
00:10:56 --> 00:10:58 landed a punch storey too.
00:10:58 --> 00:11:01 Avery: And it's a discovery made without a telescope
00:11:01 --> 00:11:04 pointing anywhere. Yesterday, NASA announced
00:11:04 --> 00:11:07 a new class of cosmic object found
00:11:07 --> 00:11:09 in data that Chandra had already collected.
00:11:09 --> 00:11:12 And the reason nobody had noticed is that
00:11:12 --> 00:11:14 they're bright in exactly the place people
00:11:14 --> 00:11:16 don't usually look.
00:11:16 --> 00:11:17 Anna: Which place is that?
00:11:18 --> 00:11:20 Avery: The very bottom of the X ray band
00:11:21 --> 00:11:23 below about 3/10 of a kilo electron
00:11:23 --> 00:11:26 volt, which is the soft edge of what an X
00:11:26 --> 00:11:29 ray telescope can even register. The
00:11:29 --> 00:11:32 team's own criterion is stark. These
00:11:32 --> 00:11:34 things put out more than eight times as many
00:11:34 --> 00:11:37 photons in the lowest slice of the band as
00:11:37 --> 00:11:40 they do in the slice immediately above it.
00:11:40 --> 00:11:43 Look at them in a standard X ray image and
00:11:43 --> 00:11:45 they're there. Look at the same field at
00:11:45 --> 00:11:48 higher energies and they vanished.
00:11:48 --> 00:11:50 Anna: So they're being selected out routinely.
00:11:50 --> 00:11:53 Avery: By the way surveys are built. Mustafa
00:11:53 --> 00:11:56 Muhibullah at the University of Alabama with
00:11:56 --> 00:11:59 Jimmy Irwin there and Roseanne Distefano at
00:11:59 --> 00:12:01 the Centre for Astrophysics went looking
00:12:01 --> 00:12:04 specifically in that soft slice across six
00:12:04 --> 00:12:06 galaxies. Andromeda and the Pinwheel
00:12:07 --> 00:12:10 M M101, plus four ellipticals,
00:12:10 --> 00:12:13 84 of them hypersoft X ray
00:12:13 --> 00:12:15 sources. They're calling them Muhibulla's
00:12:15 --> 00:12:18 line. We've never encountered a group of
00:12:18 --> 00:12:19 objects that act like this.
00:12:20 --> 00:12:21 Anna: What are they?
00:12:21 --> 00:12:24 Avery: Best guess. And the paper keeps it a guess.
00:12:24 --> 00:12:27 A, uh, compact object pulling material off a
00:12:27 --> 00:12:30 companion star. A white dwarf, in
00:12:30 --> 00:12:33 some cases, possibly a black hole. That's
00:12:33 --> 00:12:36 a familiar picture. We know hundreds of X ray
00:12:36 --> 00:12:39 binaries. What isn't familiar is the
00:12:39 --> 00:12:41 combination. More than 10 to the 38
00:12:41 --> 00:12:44 ergs per second in that narrow soft band
00:12:44 --> 00:12:47 alone. And considerably more again in the
00:12:47 --> 00:12:50 extreme ultraviolet. Fierce
00:12:50 --> 00:12:53 ultraviolet paired with unusually feeble X
00:12:53 --> 00:12:55 rays. Nobody's seen those two together in
00:12:55 --> 00:12:56 one population.
00:12:57 --> 00:12:59 Anna: And there are two payoffs.
00:12:59 --> 00:13:02 Avery: Both good accreting, uh, white dwarfs are
00:13:02 --> 00:13:04 the leading candidate for the thing we've
00:13:04 --> 00:13:07 never caught in the act. The progenitor of a
00:13:07 --> 00:13:10 type 1A supernova. A white
00:13:10 --> 00:13:12 dwarf steadily eating a companion until it
00:13:12 --> 00:13:15 crosses a mass threshold and detonates.
00:13:16 --> 00:13:18 Anna: Which is the supernova we use as a standard
00:13:18 --> 00:13:19 candle.
00:13:19 --> 00:13:22 Avery: Exactly the one the explosion, the whole
00:13:22 --> 00:13:24 discovery of cosmic acceleration was built
00:13:24 --> 00:13:27 on. And the one we were talking about a
00:13:27 --> 00:13:29 fortnight ago with the dark energy rebuttal,
00:13:30 --> 00:13:32 we've been calibrating cosmology on a blast
00:13:32 --> 00:13:34 whose ancestors we couldn't identify.
00:13:35 --> 00:13:38 If these 84 are, uh, that population
00:13:38 --> 00:13:41 or part of it, that's a gap closed
00:13:41 --> 00:13:44 and the second ionisation. All
00:13:44 --> 00:13:47 that extreme ultraviolet strips electrons off
00:13:47 --> 00:13:50 surrounding gas and which gas is
00:13:50 --> 00:13:52 ionised feeds straight into how galaxies
00:13:52 --> 00:13:55 cool and form stars. There's been a
00:13:55 --> 00:13:58 persistent shortfall between the ionising
00:13:58 --> 00:14:00 radiation we can account for and what we
00:14:00 --> 00:14:03 actually observe. And here's a population
00:14:03 --> 00:14:05 that's been quietly contributing all along
00:14:06 --> 00:14:09 while staying nearly invisible to the surveys
00:14:09 --> 00:14:11 meant to find it. Caveat the
00:14:11 --> 00:14:14 obvious 184 objects across
00:14:14 --> 00:14:17 six galaxies is a class defined by a
00:14:17 --> 00:14:20 shared X ray signature, not by anyone
00:14:20 --> 00:14:23 knowing what each one is. Some may be several
00:14:23 --> 00:14:25 different things wearing the same colours.
00:14:26 --> 00:14:28 The work now is ultraviolet follow up and
00:14:28 --> 00:14:31 looking for variability. A nova
00:14:31 --> 00:14:34 leaves a very different fingerprint over time
00:14:34 --> 00:14:36 than a steadily accreting binary.
00:14:36 --> 00:14:39 But the headline stands a whole category
00:14:39 --> 00:14:42 of luminous object in nearby galaxies.
00:14:43 --> 00:14:45 In data we already had storey
00:14:45 --> 00:14:46 three
00:14:46 --> 00:14:49 Anna: and it's a plan rather than a result. But
00:14:49 --> 00:14:51 it's a serious one and it has a deadline.
00:14:51 --> 00:14:54 Hallie's comet comes back to perihelion in
00:14:54 --> 00:14:57 2061. A group of researchers
00:14:57 --> 00:14:59 has just published a worked trajectory for
00:14:59 --> 00:15:02 getting a spacecraft alongside it and staying
00:15:02 --> 00:15:02 there.
00:15:02 --> 00:15:05 Avery: Alongside, not passed.
00:15:05 --> 00:15:07 Anna: That's the whole point. Remember what
00:15:07 --> 00:15:10 happened last time? In 1986 we sent
00:15:10 --> 00:15:12 the largest international fleet ever
00:15:12 --> 00:15:15 assembled to one object. The Haley
00:15:15 --> 00:15:18 Armada, ESA's Giotto, the
00:15:18 --> 00:15:21 Soviet Vega 1 and 2, Japan's
00:15:21 --> 00:15:23 Suisei and Sakigake and a
00:15:23 --> 00:15:26 repurposed NASA spacecraft. Giotto
00:15:26 --> 00:15:29 got within about 600 kilometres and returned
00:15:29 --> 00:15:31 the first images of a cometary nucleus and
00:15:31 --> 00:15:32 ever taken.
00:15:32 --> 00:15:34 Avery: And how long did that take?
00:15:34 --> 00:15:37 Anna: Minutes. Giotto went past at, uh, roughly
00:15:37 --> 00:15:40 68 kilometres per second, about
00:15:40 --> 00:15:42 245 kilometres an hour
00:15:42 --> 00:15:45 and was hit by a dust grain and knocked off
00:15:45 --> 00:15:48 its spin axis on the way through. Everything
00:15:48 --> 00:15:50 we learned about Haley up close we learned in
00:15:50 --> 00:15:52 the time it takes to make a cup of tea.
00:15:53 --> 00:15:54 Avery: Why so fast?
00:15:54 --> 00:15:57 Anna: Because Hailey goes the wrong way. Its orbit
00:15:57 --> 00:16:00 is retrograde against the direction the
00:16:00 --> 00:16:02 planets travel and steeply inclined.
00:16:02 --> 00:16:05 So a spacecraft on a normal solar orbit meets
00:16:05 --> 00:16:08 it nearly head on to match velocity.
00:16:08 --> 00:16:10 Instead you'd have to reverse a large
00:16:10 --> 00:16:12 fraction of your own motion around the sun.
00:16:13 --> 00:16:15 And the propellant bill for that has always
00:16:15 --> 00:16:16 been considered fantasy.
00:16:17 --> 00:16:19 Avery: And this paper says otherwise.
00:16:19 --> 00:16:21 Anna: With hardware that has already flown.
00:16:22 --> 00:16:25 Roberto Flores and Elena Fantino at Khalifa
00:16:25 --> 00:16:28 University in Abu Dhabi with Mauro Pontani
00:16:28 --> 00:16:31 at Sapienza in Rome and Ivano Bertini
00:16:31 --> 00:16:33 and Cesare Barbieri at Padua. And
00:16:33 --> 00:16:36 Barbieri is worth a pause because he worked
00:16:36 --> 00:16:39 on the camera that took those 1986 Giotto
00:16:39 --> 00:16:41 images. 50 years on planning the
00:16:41 --> 00:16:42 return trip.
00:16:43 --> 00:16:44 Avery: So what's the trick.
00:16:44 --> 00:16:47 Anna: Two unpowered gravity assists,
00:16:47 --> 00:16:50 Jupiter, then Saturn, stitched together
00:16:50 --> 00:16:52 with long, low thrust arcs in deep space.
00:16:53 --> 00:16:55 The assists do the expensive bending and
00:16:55 --> 00:16:58 slowing for free. And a Hall effect ion
00:16:58 --> 00:17:00 thruster running off a standard radioisotope
00:17:00 --> 00:17:03 generator. Does the patient work in between
00:17:03 --> 00:17:06 their two worked examples? Launch in August
00:17:06 --> 00:17:09 2036 or September 2037 on
00:17:09 --> 00:17:11 an existing launcher at roughly 2
00:17:11 --> 00:17:14 kilogrammes, including propellant. About
00:17:14 --> 00:17:16 750 of that instruments
00:17:16 --> 00:17:19 arriving when? 2060, about
00:17:19 --> 00:17:22 a year before perihelion. Deliberately early,
00:17:22 --> 00:17:24 so it's in place and settled before the comet
00:17:24 --> 00:17:27 warms up and switches on. Then it flies
00:17:27 --> 00:17:30 alongside and watches months instead
00:17:30 --> 00:17:32 of minutes, and the whole transition from a
00:17:32 --> 00:17:35 cold, quiet nucleus to a fully active
00:17:35 --> 00:17:38 comet recorded from a few kilometres away.
00:17:39 --> 00:17:41 Avery: 24 years of flight, which is the real
00:17:41 --> 00:17:42 cost.
00:17:42 --> 00:17:45 Anna: That's a career and then some. But it's a
00:17:45 --> 00:17:48 rendezvous with Hallie's comet using proven
00:17:48 --> 00:17:50 parts, and the launch window is 10 years
00:17:50 --> 00:17:53 away. Somebody has to decide fairly soon.
00:17:54 --> 00:17:56 Avery: And there's a southern footnote, a lovely
00:17:56 --> 00:17:56 one.
00:17:57 --> 00:17:59 Anna: Hallie belongs to us down here in a way it
00:17:59 --> 00:18:02 doesn't to the north. The
00:18:02 --> 00:18:04 1986 apparition was poor from
00:18:04 --> 00:18:07 northern latitudes and much better from the
00:18:07 --> 00:18:10 southern hemisphere. Hallie's dust
00:18:10 --> 00:18:13 gives us the Eta Aquariids. Every May,
00:18:13 --> 00:18:16 a decidedly southern shower. And
00:18:16 --> 00:18:19 Edmond Hallie made his name by sailing to St
00:18:19 --> 00:18:22 Helena at 20 to catalogue the southern
00:18:22 --> 00:18:24 stars no European had properly charted.
00:18:25 --> 00:18:27 He was a southern sky observer before he was
00:18:27 --> 00:18:28 a comet man.
00:18:29 --> 00:18:30 Avery: Last storey.
00:18:30 --> 00:18:32 And it's a change of subject entirely.
00:18:33 --> 00:18:35 On Tuesday, you, US Space Command
00:18:35 --> 00:18:37 announced it had just completed something
00:18:37 --> 00:18:40 called Apollo Manoeuvres 2026,
00:18:41 --> 00:18:44 the first live fly exercise of its kind
00:18:44 --> 00:18:47 using real satellites actually moved
00:18:47 --> 00:18:50 across three different orbital regimes.
00:18:50 --> 00:18:53 Anna: Live fly meaning not a simulation?
00:18:53 --> 00:18:56 Avery: Not a simulation. Which is the
00:18:56 --> 00:18:59 newsworthy part? Space exercises
00:18:59 --> 00:19:02 are almost always tabletop or synthetic.
00:19:02 --> 00:19:05 This one took existing operational satellites
00:19:05 --> 00:19:08 and manoeuvred them in low Earth orbit,
00:19:08 --> 00:19:10 in medium orbit and out at
00:19:10 --> 00:19:13 geosynchronous, 22 miles
00:19:13 --> 00:19:16 up. Allied partners from Operation
00:19:16 --> 00:19:19 Olympic Defender took part, which includes
00:19:19 --> 00:19:21 Australia and commercial operators were
00:19:21 --> 00:19:24 folded in through what Space Command calls
00:19:24 --> 00:19:26 its Commercial Integration Cell.
00:19:26 --> 00:19:28 Anna: Why is that a departure?
00:19:28 --> 00:19:31 Avery: Because of how satellites are normally flown.
00:19:32 --> 00:19:34 A, uh, satellite carries a fuel budget
00:19:34 --> 00:19:37 calculated for one staying
00:19:37 --> 00:19:39 where it was put, Station
00:19:39 --> 00:19:42 keeping, a bit of debris avoidance and a
00:19:42 --> 00:19:45 final nudge to a disposal orbit. At end of
00:19:45 --> 00:19:48 life. Every gramme of propellant is
00:19:48 --> 00:19:50 hoarded because when it runs out, the
00:19:50 --> 00:19:53 satellite's working life is over, regardless
00:19:53 --> 00:19:56 of whether anything on board still functions.
00:19:57 --> 00:19:58 Anna: And this is the opposite philosophy.
00:19:59 --> 00:20:01 Avery: This is treating manoeuvre as something you
00:20:01 --> 00:20:04 do on purpose for position and
00:20:04 --> 00:20:06 accepting the cost. General Stephen
00:20:06 --> 00:20:08 Whiting's framing was that to perform,
00:20:09 --> 00:20:12 survive and gain advantage in the space
00:20:12 --> 00:20:14 domain, they need manoeuvrability and
00:20:15 --> 00:20:17 survivability in their capabilities.
00:20:18 --> 00:20:20 The exercise even borrows its name from
00:20:20 --> 00:20:23 history, the Louisiana manoeuvres of
00:20:23 --> 00:20:26 1941, when the US army
00:20:26 --> 00:20:28 moved several hundred thousand troops around
00:20:28 --> 00:20:31 the American south to work out how
00:20:31 --> 00:20:33 mechanised warfare actually functioned
00:20:33 --> 00:20:35 before it had to.
00:20:35 --> 00:20:37 Anna: And the implication for everyone else in
00:20:37 --> 00:20:40 Avery: orbit, that's the part I'd flag. And
00:20:40 --> 00:20:42 it cuts both ways. If
00:20:42 --> 00:20:45 satellites start manoeuvring routinely rather
00:20:45 --> 00:20:48 than exceptionally, then the catalogues and
00:20:48 --> 00:20:50 conjunction warnings that the whole industry
00:20:50 --> 00:20:53 relies on get harder to keep accurate.
00:20:53 --> 00:20:56 Those systems assume objects follow
00:20:56 --> 00:20:59 predictable paths and are updated on a
00:20:59 --> 00:21:01 schedule. Everyone tracking the sky,
00:21:02 --> 00:21:04 civil and military, has to work with
00:21:04 --> 00:21:07 more uncertainty. There's also a design
00:21:07 --> 00:21:10 consequence coming. Refuelling and
00:21:10 --> 00:21:13 servicing in orbit stop being a nice idea
00:21:13 --> 00:21:16 and start being the thing that determines how
00:21:16 --> 00:21:17 long a satellite
00:21:17 --> 00:21:20 Anna: is useful for, which is a commercial storey
00:21:20 --> 00:21:21 as much as a defence one.
00:21:21 --> 00:21:24 Avery: Very much so, and that's why it's on this
00:21:24 --> 00:21:27 show. Whatever you think about militaries
00:21:27 --> 00:21:30 manoeuvring in orbit, and there are entirely
00:21:30 --> 00:21:32 reasonable views in both directions, the
00:21:32 --> 00:21:35 practical consequence is more moving objects
00:21:35 --> 00:21:38 in a region that is already more crowded than
00:21:38 --> 00:21:40 it has ever been. That affects
00:21:40 --> 00:21:43 observers, operators and astronomers alike,
00:21:43 --> 00:21:46 Anna: and to the sky. This is a good week. And the
00:21:46 --> 00:21:49 reason is simple. New Moon falls Tomorrow,
00:21:49 --> 00:21:52 Friday the 11th, at 27 minutes past
00:21:52 --> 00:21:55 2 in the afternoon. Sydney time. That's
00:21:55 --> 00:21:57 just after 4 in the morning, Universal Time,
00:21:57 --> 00:21:59 which means tonight and tomorrow night are
00:21:59 --> 00:22:02 the darkest of the month. Whatever you have
00:22:02 --> 00:22:04 been meaning to look at, look at it now.
00:22:05 --> 00:22:08 Southern hemisphere first from Sydney and
00:22:08 --> 00:22:10 similar latitudes. The core of the Milky Way
00:22:10 --> 00:22:13 is still high after dark. Sagittarius and
00:22:13 --> 00:22:16 Scorpius up towards the zenith in the early
00:22:16 --> 00:22:18 evening. And on a moonless night away from
00:22:18 --> 00:22:21 town, it is genuinely startling. This
00:22:21 --> 00:22:23 is the last really good fortnight of it for
00:22:23 --> 00:22:26 the year. Binoculars, no plan,
00:22:26 --> 00:22:28 half an hour, that's the whole
00:22:28 --> 00:22:29 recommendation.
00:22:29 --> 00:22:30 Avery: And, um. Venus.
00:22:31 --> 00:22:34 Anna: Venus is the evening object, low in the
00:22:34 --> 00:22:37 west southwest, and it wants dealing with
00:22:37 --> 00:22:39 promptly 45 minutes after sunset.
00:22:39 --> 00:22:42 It's less than 5 degrees up, about three
00:22:42 --> 00:22:45 finger widths at arm's length. So you need a
00:22:45 --> 00:22:48 genuinely flat horizon. The compensation
00:22:48 --> 00:22:50 is that it's brilliant. And Spica sits a bit
00:22:50 --> 00:22:53 over 7 degrees away, both in one
00:22:53 --> 00:22:55 binocular field. Is a nice catch and it's
00:22:55 --> 00:22:58 still brightening. Greatest Brilliancy on the
00:22:58 --> 00:23:00 18th at magnitude -4.8.
00:23:01 --> 00:23:03 This is an apparition where the geometry
00:23:03 --> 00:23:05 favours the south. From mid northern
00:23:05 --> 00:23:08 latitudes, Venus is scraping the horizon in
00:23:08 --> 00:23:10 twilight From Sydney it's a clean
00:23:10 --> 00:23:13 naked eye object. Saturn.
00:23:13 --> 00:23:16 Saturn is the good news for everybody. It
00:23:16 --> 00:23:18 rises in the east about an hour after sunset
00:23:18 --> 00:23:21 and three hours after sunset it's more than
00:23:21 --> 00:23:23 20 degrees up in the east southeast.
00:23:24 --> 00:23:27 Opposition is on the 4th of October, close
00:23:27 --> 00:23:29 enough now to matter. And the rings are only
00:23:29 --> 00:23:32 about 7 degrees from edge on, which makes
00:23:32 --> 00:23:34 this an unusual year to look at it. Any
00:23:34 --> 00:23:37 telescope and quite a few decent binoculars
00:23:37 --> 00:23:39 on a tripod will show it North
00:23:39 --> 00:23:40 America.
00:23:40 --> 00:23:41 Avery: Your turn.
00:23:41 --> 00:23:44 Anna: Saturn is your evening object too for the
00:23:44 --> 00:23:46 same reasons and it's a far better bet for
00:23:46 --> 00:23:48 you than Venus. Venus is technically there in
00:23:48 --> 00:23:51 the west after sunset, but it's a hard low
00:23:51 --> 00:23:54 catch from mid northern latitudes. Worth a
00:23:54 --> 00:23:57 try. With a clear horizon, not worth planning
00:23:57 --> 00:24:00 an evening around. The morning sky though is
00:24:00 --> 00:24:02 where northern observers do well this week.
00:24:02 --> 00:24:04 Before sunrise there are two planets in the
00:24:05 --> 00:24:08 Mars higher moving through Gemini and
00:24:08 --> 00:24:10 Jupiter below it in Cancer. Mars
00:24:10 --> 00:24:13 passes right by Castor on Saturday the 12th
00:24:13 --> 00:24:16 and by Pollux on the 17th. So you can watch
00:24:16 --> 00:24:18 a planet walk past the twins over a week
00:24:19 --> 00:24:21 from southern latitudes. Both are lower and
00:24:21 --> 00:24:23 later. This one belongs to the north
00:24:24 --> 00:24:24 and
00:24:24 --> 00:24:25 Avery: um, there's live weather.
00:24:26 --> 00:24:28 Anna: There is and it's why I'd keep an eye out
00:24:28 --> 00:24:31 tonight. A run of coronal mass ejections
00:24:31 --> 00:24:33 left active region 4524
00:24:34 --> 00:24:37 on the 5th and 6th and has been arriving in
00:24:37 --> 00:24:39 convoy since Tuesday. Two have already
00:24:39 --> 00:24:42 produced minor geomagnetic storming
00:24:43 --> 00:24:45 with G2 possible as the last arrive
00:24:46 --> 00:24:48 and forecasters expect it to settle from
00:24:48 --> 00:24:51 today. Aurora chances have reached the
00:24:51 --> 00:24:53 northern United States, the UK and northern
00:24:53 --> 00:24:56 France. And down here for the
00:24:56 --> 00:24:59 aurora Australis. A uh G1 to G2
00:24:59 --> 00:25:02 storm puts Tasmania in with a real chance.
00:25:02 --> 00:25:04 Coastal southern Victoria if it strengthens.
00:25:05 --> 00:25:07 And the south island of New Zealand well
00:25:07 --> 00:25:10 placed. Look south, get away from town lights
00:25:10 --> 00:25:12 and give your camera a long exposure even if
00:25:12 --> 00:25:15 your eyes see nothing, A phone on night mode
00:25:15 --> 00:25:18 will often pick up colour the eye can't. And
00:25:18 --> 00:25:20 with New Moon there's no moonlight in the
00:25:20 --> 00:25:20 way.
00:25:20 --> 00:25:22 Avery: Safety passage, yes.
00:25:23 --> 00:25:25 Anna: And this one is in every episode for a
00:25:25 --> 00:25:27 reason. With Venus this bright, some people
00:25:27 --> 00:25:29 go looking for it in daylight, which is a
00:25:29 --> 00:25:32 real and rewarding thing to do. And also the
00:25:32 --> 00:25:35 one time of year we get nervous. Venus in
00:25:35 --> 00:25:37 daylight sits close to the sun in the sky.
00:25:38 --> 00:25:40 Never sweep for it with binoculars or a
00:25:40 --> 00:25:42 telescope without a proper solar filter
00:25:42 --> 00:25:44 fitted at the front. A fraction of a second
00:25:44 --> 00:25:47 of direct sunlight through magnifying optics
00:25:47 --> 00:25:50 causes permanent, painless retinal damage.
00:25:50 --> 00:25:52 If you're looking anywhere near the sun with
00:25:52 --> 00:25:55 your eyes alone, use eclipse glasses
00:25:55 --> 00:25:56 certified to ISO
00:25:56 --> 00:25:58 123122.
00:25:59 --> 00:26:01 Cheque them for scratches or pinholes first
00:26:01 --> 00:26:03 and understand what they're for. They are
00:26:03 --> 00:26:06 made for the naked eye only and must never be
00:26:06 --> 00:26:08 used in combination with binoculars, a
00:26:08 --> 00:26:11 telescope or a camera viewfinder. The
00:26:11 --> 00:26:13 safe way to find Venus in daylight is to use
00:26:13 --> 00:26:16 a solid object, a building edge, a
00:26:16 --> 00:26:19 wall to block the sun completely before you
00:26:19 --> 00:26:20 start looking.
00:26:20 --> 00:26:23 Avery: And looking ahead the equinox on the
00:26:23 --> 00:26:25 Anna: 22nd, which is spring for us and autumn for
00:26:25 --> 00:26:27 the north. Then Saturn's opposition on the
00:26:27 --> 00:26:30 4th of October and on the 6th of October
00:26:30 --> 00:26:32 there's a pre dawn lunar occultation of
00:26:32 --> 00:26:35 Jupiter that is being billed as the year's
00:26:35 --> 00:26:37 best. We'll build up to that one properly.
00:26:38 --> 00:26:39 Avery: Something to look forward to.
00:26:40 --> 00:26:42 Anna: That's Astronomy daily for Thursday 10th
00:26:42 --> 00:26:45 September. A hundred and nine radio flashes
00:26:45 --> 00:26:47 weighing the ordinary matter of the universe
00:26:47 --> 00:26:49 and finding more of it than the X rays could
00:26:49 --> 00:26:52 see. 84 new objects that were in the
00:26:52 --> 00:26:55 archive the whole time. A uh, worked plan to
00:26:55 --> 00:26:58 fly alongside Hallie's Comet in 2060 and
00:26:58 --> 00:27:00 satellites being moved around on purpose.
00:27:01 --> 00:27:03 Avery: Everything we covered with links to the
00:27:03 --> 00:27:05 papers and the source releases is in the show
00:27:05 --> 00:27:08 notes and at astronomydaily IO
00:27:08 --> 00:27:10 where you'll also find the full back
00:27:10 --> 00:27:13 catalogue and the newsletter. If you'd rather
00:27:13 --> 00:27:14 have it in your
00:27:14 --> 00:27:17 Anna: inbox and the contact form on the site is
00:27:17 --> 00:27:19 real and we read it. Several of the storeys
00:27:19 --> 00:27:21 we've run in the past fortnight started as a
00:27:21 --> 00:27:24 listener question, so if there's something
00:27:24 --> 00:27:26 you want explained or followed up, tell us.
00:27:26 --> 00:27:28 Avery: You'll find this on X, Facebook,
00:27:29 --> 00:27:32 Instagram, TikTok, YouTube and
00:27:32 --> 00:27:34 Tumblr at astrodaily. Pod
00:27:34 --> 00:27:36 Astronomy AstroDailyPod is part of the
00:27:36 --> 00:27:38 bytes.com podcast network.
00:27:39 --> 00:27:40 Anna: I'm Anna.
00:27:40 --> 00:27:43 Avery: And I'm Avery. Clear skies and
00:27:43 --> 00:27:45 if you're anywhere south tonight, look up.
00:27:45 --> 00:27:47 It's as dark as it gets.
00:27:53 --> 00:27:53 Anna: The.
00:27:58 --> 00:27:58 Storeys.
00:28:06 --> 00:28:07 Avery: We told
00:28:10 --> 00:28:10 Anna: M.