A Hundred and Nine Flashes

0:00 Anna: Hello and welcome to Astronomy daily. It's Thursday the 10th of September 2026. This is series five, episode 190. And I'm Anna. Avery: And I'm Avery. Anna, I want to start with a number. 109. Anna: Ah, 109 radio flashes. Each one lasting about a thousandth of a second. Each one from a different galaxy. And together they have just been used to weigh the ordinary matter of the universe and to work out how badly galaxies have been throwing it around. Avery: A hundred and nine. That's not a lot of anything.

0:36 Anna: It's not. And yet the answer they give is already as good as what you get from an X ray survey of the entire sky. Or a microwave telescope that's been running a decade on the problem currently standing between cosmology and a straight answer about dark energy, dark matter and the mass of the neutrino. That's our lead. Avery: After that, 84 objects that have been sitting in the Chandra archive for years, glowing in a part of the X ray spectrum nobody was really looking at. And which may turn out to be the missing ancestors of the exploding stars we used to measure the universe.

1:13 Anna: A serious worked out plan to fly a spacecraft alongside Hallie's Comet in 2060, not past it in a blur alongside it for for months, using nothing that hasn't already flown. Avery: And the US military manoeuvring real satellites across three orbital regimes in the first exercise of its kind. Anna: Plus the sky for both hemispheres. New moon tomorrow afternoon. So tonight is about as dark as September gets and there's a run of solar storms arriving that could put aurora at both ends of the planet.

1:45 Let's start with the flashes before the result. Avery: Set it up for me. What is a fast radio burst? Anna: Actually, a pulse of radio energy that arrives, does its business in about a millisecond and is gone in that thousandth of a second. It can release as much energy as the sun puts out in a couple of days. The first one was found in 2007 in archived data from the Parkes dish in New South Wales. Murrayang by Dunkley Lorimer and a student going back through observations from 2001. For a while, nobody believed it.

2:17 Reasonably enough, one burst, one telescope, no repeat. Avery: And now. Anna: Now we know of thousands. And we know at least some come from magnetars, neutron stars with absurd magnetic fields. Because in 2020, one went off inside our own galaxy. But that's not today's storey. And this is the interesting turn the field has taken. What a fast radio burst is, has become less important than what it does on the way here, which is what it gets stretched. That millisecond pulse contains a range of radio frequencies, all leaving at the same instant.

2:52 But space between galaxies isn't, uh, empty. There's a thin haze of free electrons in it. And free electrons, slow, low radio frequencies, slightly more than high ones. Avery: Like a prism. Anna: Exactly like a prism. And that's Caltech's own comparison. The burst leaves its galaxy as one clean pulse and arrives here smeared out in time. High frequencies first, low frequencies trailing behind. You can measure that smear precisely. And it has a name, the dispersion measure. The size of the delay tells you how many free electrons the pulse went through, not how far it travelled, how much stuff it travelled through.

3:32 Every burst is a core sample of the universe along one line of sight. Avery: And that solved something. Anna: It solved a real embarrassment first time out. Ordinary matter, baryons, the stuff of atoms. We knew from the cosmic microwave background how much of it the universe was made with. And when you added up everything we could actually see, roughly a third was missing. The suspicion was always that it sat between the galaxies, spread impossibly thin and too cool to glow in X rays, which is exactly what a dispersion measure is sensitive to, glowing or not.

4:07 Avery: And that's where Australia comes in. Anna: That's where Australia comes in. In 2020, a team led by Jean Pierre Macquart at the Curtain node of ICRAR used ASCAP in Western Australia to localise a handful of bursts to their host galaxies, compared dispersion against distance. And there was the missing matter. It's called the Macart relation. Now, Makartt himself died that same year at 45 months after the paper. And it's the foundation everything today is built on. Avery: So we found the missing matter.

4:38 Anna: What's left to argue about where it is in detail? And that's the whole problem, because galaxies don't sit quietly and hold onto their gas, they throw it out. Supernovae. And more importantly, supermassive black holes, switching on and driving enormous outflows. Gas that started concentrated around galaxies gets pushed into the space between them, sometimes millions of light years out. Avery: Feedback. Anna: Feedback. And Vikram Ravi at Caltech puts the consequence better than I can. The process thins the gas around galaxies, redistributing matter across vast distances.

5:15 And it smooths out the clumps in a way, he says, that looks astonishingly similar to what massive neutrinos do or what dark energy or dark matter theories predict. Unless you can independently measure the feedback, you can't tell those effects apart. Avery: Explain why clumpiness is the thing being Anna: measured, because how lumpy the universe is, how strongly matter clusters on different scales, is one of the sharpest tests we have of what it's made of. Massive neutrinos wash out small scale structure.

5:45 Certain dark energy behaviours change the clustering. Dark matter that isn't quite cold and inert. Same thing. And so does gas being blown about by a black hole. Avery: So it's a confound. Anna: It's the confound and it has a name. This sits at the heart of the S8 tension, the long running disagreement between how lumpy the early universe says things should be and how lumpy the late universe actually looks. Either that gap is new physics, which would be enormous, or we simply don't understand how much gas galaxies throw around, which is deflating but entirely plausible.

6:22 And nobody could settle it because nobody could measure the diffuse gas properly. X ray telescopes see the hot gas and miss the cool. The microwave technique, the kinetic Sunyaev Zeldovich effect works, but it's statistical and hard. You want something that counts electrons and doesn't care what temperature they are. Avery: A dispersion measure. Anna: A dispersion measure. So the new work published Tuesday 8 September in Nature Astronomy, led by Kriti Sharma at Caltech, with Vikram Ravi, Liam Connor and Elizabeth Kraus at the University of Arizona.

6:57 Among The CO authors, 109 fast radio bursts, each localised to a host galaxy, so it has a redshift as well as a dispersion measure out to a redshift of about 0.3, relatively local, deliberately, because that's where feedback effects are most measurable. Most of the bursts come from the Deep synoptic array, the DSA110, a Caltech instrument at Owens Valley in California built to catch these things and pin them to a galaxy in real time. Avery: And what did the hundred and nine tell them? Anna: Two things.

7:30 First, they measured how much feedback has suppressed the clustering of matter across the range from galaxy group structures down to individual galaxy halos. And how much gas is actually sitting in groups and clusters between 10 to the 13 and 10 to the 15 solar masses. And there's more of it there than the other methods we're finding. The gas fractions come out about 1.9 Sigma higher than stacking. Erosita's X ray observations of the same kinds of systems, and a little above what the Atacama Cosmology Telescope gives the team reads that the obvious.

8:04 The bursts are counting cool gas the X rays can't see because it isn't hot. Enough to shine. Avery: So feedback has smoothed things less than we thought. Anna: Less than the X ray picture implied. And the second result is precision Using the bursts cut the uncertainty on the clustering at those scales by roughly a factor of eight. And the constraint is competitive with E. Rosita and with the Atacama Cosmology Telescope. Those are enormous experiments. This is 109 Flashes. Kraus Line. This is amazing considering we only had about a hundred FRBs in our sample.

8:39 It's only the beginning. Avery: Caveats? Anna: Three honest ones. One M hundred nine is a small sample and the tension with Erosita at 1.9 Sigma is interesting, not established. Second part of every dispersion measure comes from the host galaxy itself and has to be modelled. They get an average host contribution of about 129 in the units the field uses, give or take nearly 20. That's the weakest joint in the chain. And third, it's a low redshift sample. A lot about the recent universe, much less about the deep past.

9:16 Avery: And the fix is more bursts. Anna: Many more. And it's being built. Caltech's next machine, the full Deep Synoptic Array is planned for a valley in Nevada with construction targeted around 2029. And should find these in the tens of thousands. Ravi's assessment is blunt. It'll be a game changer. Sharma's is that they've established fast radio bursts as a leading probe of the distribution of matter in the universe. And that the data can now sharpen experiments asking about dark matter, dark energy and the mass of the neutrino.

9:51 For something that was a single unexplained blip in an Australian archive 19 years ago. That's quite a promotion. Avery: And that's the thread back home. Anna: That's the thread. The technique is southern in origin and still substantially southern in practise. The first burst came out of parks. The McCourt relation came out of Azcap on Wajari country at Inyarimana Il Ghari Bundara. And ASCAP is still one of the most productive burst localising instruments on the planet. Its Krako upgrade exists specifically to catch them live and hand a position to other telescopes fast enough to chase.

10:27 Meerkat works the same field. Both sites are the foundations of the Square Kilometre Array which we talked about Avery: five days ago for a completely different reason. Anna: The MeerKAT 21 centimetre detection. A different way of weighing the same universe with the same kind of dish. Two techniques, two hemispheres. One question and the honest summary of today is that 109 flashes have walked into a fight with the giant surveys have been having for a decade and landed a punch storey too. Avery: And it's a discovery made without a telescope pointing anywhere.

11:02 Yesterday, NASA announced a new class of cosmic object found in data that Chandra had already collected. And the reason nobody had noticed is that they're bright in exactly the place people don't usually look. Anna: Which place is that? Avery: The very bottom of the X ray band below about 3/10 of a kilo electron volt, which is the soft edge of what an X ray telescope can even register. The team's own criterion is stark. These things put out more than eight times as many photons in the lowest slice of the band as they do in the slice immediately above it.

11:40 Look at them in a standard X ray image and they're there. Look at the same field at higher energies and they vanished. Anna: So they're being selected out routinely. Avery: By the way surveys are built. Mustafa Muhibullah at the University of Alabama with Jimmy Irwin there and Roseanne Distefano at the Centre for Astrophysics went looking specifically in that soft slice across six galaxies. Andromeda and the Pinwheel M M101, plus four ellipticals, 84 of them hypersoft X ray sources. They're calling them Muhibulla's line.

12:16 We've never encountered a group of objects that act like this. Anna: What are they? Avery: Best guess. And the paper keeps it a guess. A, uh, compact object pulling material off a companion star. A white dwarf, in some cases, possibly a black hole. That's a familiar picture. We know hundreds of X ray binaries. What isn't familiar is the combination. More than 10 to the 38 ergs per second in that narrow soft band alone. And considerably more again in the extreme ultraviolet. Fierce ultraviolet paired with unusually feeble X rays.

12:53 Nobody's seen those two together in one population. Anna: And there are two payoffs. Avery: Both good accreting, uh, white dwarfs are the leading candidate for the thing we've never caught in the act. The progenitor of a type 1A supernova. A white dwarf steadily eating a companion until it crosses a mass threshold and detonates. Anna: Which is the supernova we use as a standard candle. Avery: Exactly the one the explosion, the whole discovery of cosmic acceleration was built on. And the one we were talking about a fortnight ago with the dark energy rebuttal, we've been calibrating cosmology on a blast whose ancestors we couldn't identify.

13:35 If these 84 are, uh, that population or part of it, that's a gap closed and the second ionisation. All that extreme ultraviolet strips electrons off surrounding gas and which gas is ionised feeds straight into how galaxies cool and form stars. There's been a persistent shortfall between the ionising radiation we can account for and what we actually observe. And here's a population that's been quietly contributing all along while staying nearly invisible to the surveys meant to find it. Caveat the obvious 184 objects across six galaxies is a class defined by a shared X ray signature, not by anyone knowing what each one is.

14:22 Some may be several different things wearing the same colours. The work now is ultraviolet follow up and looking for variability. A nova leaves a very different fingerprint over time than a steadily accreting binary. But the headline stands a whole category of luminous object in nearby galaxies. In data we already had storey three Anna: and it's a plan rather than a result. But it's a serious one and it has a deadline. Hallie's comet comes back to perihelion in 2061. A group of researchers has just published a worked trajectory for getting a spacecraft alongside it and staying there.

15:02 Avery: Alongside, not passed. Anna: That's the whole point. Remember what happened last time? In 1986 we sent the largest international fleet ever assembled to one object. The Haley Armada, ESA's Giotto, the Soviet Vega 1 and 2, Japan's Suisei and Sakigake and a repurposed NASA spacecraft. Giotto got within about 600 kilometres and returned the first images of a cometary nucleus and ever taken. Avery: And how long did that take? Anna: Minutes. Giotto went past at, uh, roughly 68 kilometres per second, about 245,000 kilometres an hour and was hit by a dust grain and knocked off its spin axis on the way through.

15:47 Everything we learned about Haley up close we learned in the time it takes to make a cup of tea. Avery: Why so fast? Anna: Because Hailey goes the wrong way. Its orbit is retrograde against the direction the planets travel and steeply inclined. So a spacecraft on a normal solar orbit meets it nearly head on to match velocity. Instead you'd have to reverse a large fraction of your own motion around the sun. And the propellant bill for that has always been considered fantasy. Avery: And this paper says otherwise.

16:19 Anna: With hardware that has already flown. Roberto Flores and Elena Fantino at Khalifa University in Abu Dhabi with Mauro Pontani at Sapienza in Rome and Ivano Bertini and Cesare Barbieri at Padua. And Barbieri is worth a pause because he worked on the camera that took those 1986 Giotto images. 50 years on planning the return trip. Avery: So what's the trick. Anna: Two unpowered gravity assists, Jupiter, then Saturn, stitched together with long, low thrust arcs in deep space. The assists do the expensive bending and slowing for free.

16:56 And a Hall effect ion thruster running off a standard radioisotope generator. Does the patient work in between their two worked examples? Launch in August 2036 or September 2037 on an existing launcher at roughly 2,000 kilogrammes, including propellant. About 750 of that instruments arriving when? 2060, about a year before perihelion. Deliberately early, so it's in place and settled before the comet warms up and switches on. Then it flies alongside and watches months instead of minutes, and the whole transition from a cold, quiet nucleus to a fully active comet recorded from a few kilometres away.

17:39 Avery: 24 years of flight, which is the real cost. Anna: That's a career and then some. But it's a rendezvous with Hallie's comet using proven parts, and the launch window is 10 years away. Somebody has to decide fairly soon. Avery: And there's a southern footnote, a lovely one. Anna: Hallie belongs to us down here in a way it doesn't to the north. The 1986 apparition was poor from northern latitudes and much better from the southern hemisphere. Hallie's dust gives us the Eta Aquariids. Every May, a decidedly southern shower.

18:16 And Edmond Hallie made his name by sailing to St Helena at 20 to catalogue the southern stars no European had properly charted. He was a southern sky observer before he was a comet man. Avery: Last storey. And it's a change of subject entirely. On Tuesday, you, US Space Command announced it had just completed something called Apollo Manoeuvres 2026, the first live fly exercise of its kind using real satellites actually moved across three different orbital regimes. Anna: Live fly meaning not a simulation?

18:53 Avery: Not a simulation. Which is the newsworthy part? Space exercises are almost always tabletop or synthetic. This one took existing operational satellites and manoeuvred them in low Earth orbit, in medium orbit and out at geosynchronous, 22,000 miles up. Allied partners from Operation Olympic Defender took part, which includes Australia and commercial operators were folded in through what Space Command calls its Commercial Integration Cell. Anna: Why is that a departure? Avery: Because of how satellites are normally flown.

19:32 A, uh, satellite carries a fuel budget calculated for one staying where it was put, Station keeping, a bit of debris avoidance and a final nudge to a disposal orbit. At end of life. Every gramme of propellant is hoarded because when it runs out, the satellite's working life is over, regardless of whether anything on board still functions. Anna: And this is the opposite philosophy. Avery: This is treating manoeuvre as something you do on purpose for position and accepting the cost. General Stephen Whiting's framing was that to perform, survive and gain advantage in the space domain, they need manoeuvrability and survivability in their capabilities.

20:18 The exercise even borrows its name from history, the Louisiana manoeuvres of 1941, when the US army moved several hundred thousand troops around the American south to work out how mechanised warfare actually functioned before it had to. Anna: And the implication for everyone else in Avery: orbit, that's the part I'd flag. And it cuts both ways. If satellites start manoeuvring routinely rather than exceptionally, then the catalogues and conjunction warnings that the whole industry relies on get harder to keep accurate.

20:53 Those systems assume objects follow predictable paths and are updated on a schedule. Everyone tracking the sky, civil and military, has to work with more uncertainty. There's also a design consequence coming. Refuelling and servicing in orbit stop being a nice idea and start being the thing that determines how long a satellite Anna: is useful for, which is a commercial storey as much as a defence one. Avery: Very much so, and that's why it's on this show. Whatever you think about militaries manoeuvring in orbit, and there are entirely reasonable views in both directions, the practical consequence is more moving objects in a region that is already more crowded than it has ever been.

21:39 That affects observers, operators and astronomers alike, Anna: and to the sky. This is a good week. And the reason is simple. New Moon falls Tomorrow, Friday the 11th, at 27 minutes past 2 in the afternoon. Sydney time. That's just after 4 in the morning, Universal Time, which means tonight and tomorrow night are the darkest of the month. Whatever you have been meaning to look at, look at it now. Southern hemisphere first from Sydney and similar latitudes. The core of the Milky Way is still high after dark.

22:12 Sagittarius and Scorpius up towards the zenith in the early evening. And on a moonless night away from town, it is genuinely startling. This is the last really good fortnight of it for the year. Binoculars, no plan, half an hour, that's the whole recommendation. Avery: And, um. Venus. Anna: Venus is the evening object, low in the west southwest, and it wants dealing with promptly 45 minutes after sunset. It's less than 5 degrees up, about three finger widths at arm's length. So you need a genuinely flat horizon.

22:46 The compensation is that it's brilliant. And Spica sits a bit over 7 degrees away, both in one binocular field. Is a nice catch and it's still brightening. Greatest Brilliancy on the 18th at magnitude -4.8. This is an apparition where the geometry favours the south. From mid northern latitudes, Venus is scraping the horizon in twilight From Sydney it's a clean naked eye object. Saturn. Saturn is the good news for everybody. It rises in the east about an hour after sunset and three hours after sunset it's more than 20 degrees up in the east southeast.

23:24 Opposition is on the 4th of October, close enough now to matter. And the rings are only about 7 degrees from edge on, which makes this an unusual year to look at it. Any telescope and quite a few decent binoculars on a tripod will show it North America. Avery: Your turn. Anna: Saturn is your evening object too for the same reasons and it's a far better bet for you than Venus. Venus is technically there in the west after sunset, but it's a hard low catch from mid northern latitudes. Worth a try. With a clear horizon, not worth planning an evening around.

23:58 The morning sky though is where northern observers do well this week. Before sunrise there are two planets in the Mars higher moving through Gemini and Jupiter below it in Cancer. Mars passes right by Castor on Saturday the 12th and by Pollux on the 17th. So you can watch a planet walk past the twins over a week from southern latitudes. Both are lower and later. This one belongs to the north and Avery: um, there's live weather. Anna: There is and it's why I'd keep an eye out tonight. A run of coronal mass ejections left active region 4524 on the 5th and 6th and has been arriving in convoy since Tuesday.

24:38 Two have already produced minor geomagnetic storming with G2 possible as the last arrive and forecasters expect it to settle from today. Aurora chances have reached the northern United States, the UK and northern France. And down here for the aurora Australis. A uh G1 to G2 storm puts Tasmania in with a real chance. Coastal southern Victoria if it strengthens. And the south island of New Zealand well placed. Look south, get away from town lights and give your camera a long exposure even if your eyes see nothing, A phone on night mode will often pick up colour the eye can't.

25:17 And with New Moon there's no moonlight in the way. Avery: Safety passage, yes. Anna: And this one is in every episode for a reason. With Venus this bright, some people go looking for it in daylight, which is a real and rewarding thing to do. And also the one time of year we get nervous. Venus in daylight sits close to the sun in the sky. Never sweep for it with binoculars or a telescope without a proper solar filter fitted at the front. A fraction of a second of direct sunlight through magnifying optics causes permanent, painless retinal damage.

25:50 If you're looking anywhere near the sun with your eyes alone, use eclipse glasses certified to ISO 123122. Cheque them for scratches or pinholes first and understand what they're for. They are made for the naked eye only and must never be used in combination with binoculars, a telescope or a camera viewfinder. The safe way to find Venus in daylight is to use a solid object, a building edge, a wall to block the sun completely before you start looking. Avery: And looking ahead the equinox on the Anna: 22nd, which is spring for us and autumn for the north.

26:26 Then Saturn's opposition on the 4th of October and on the 6th of October there's a pre dawn lunar occultation of Jupiter that is being billed as the year's best. We'll build up to that one properly. Avery: Something to look forward to. Anna: That's Astronomy daily for Thursday 10th September. A hundred and nine radio flashes weighing the ordinary matter of the universe and finding more of it than the X rays could see. 84 new objects that were in the archive the whole time. A uh, worked plan to fly alongside Hallie's Comet in 2060 and satellites being moved around on purpose.

27:01 Avery: Everything we covered with links to the papers and the source releases is in the show notes and at astronomydaily IO where you'll also find the full back catalogue and the newsletter. If you'd rather have it in your Anna: inbox and the contact form on the site is real and we read it. Several of the storeys we've run in the past fortnight started as a listener question, so if there's something you want explained or followed up, tell us. Avery: You'll find this on X, Facebook, Instagram, TikTok, YouTube and Tumblr at astrodaily.

27:34 Pod Astronomy AstroDailyPod is part of the bytes.com podcast network. Anna: I'm Anna. Avery: And I'm Avery. Clear skies and if you're anywhere south tonight, look up. It's as dark as it gets.

27:53 Anna: The.

27:58 Storeys.

28:06 Avery: We told

28:10 Anna: M.