A Nobel in Ice: Unveiling the Secrets of the IceCube Neutrino Observatory

0:00 Anna: Hello and welcome back to Astronomy daily. It's Friday the 9th of October 2026. This is series five, episode 201. And I'm Anna. Avery: And, um, I'm Avery. It is very good to be back. We've been off air for a little over two weeks. Our producer, Huw, needed some time away for surgery and we're very glad to report that it went well and he's on the mend. Anna: Welcome back, Huw. And to everyone who wrote in over the past fortnight asking where we'd got to, thank you. It meant a lot to know you'd noticed we were gone.

0:31 Avery: It really did. And there's plenty to catch up on today. A Nobel Prize for a telescope buried two kilometres down in Antarctic ice. The most distant fast radio burst ever pinned down. With a Sydney astronomer leading the paper, and a planet that may have been built from the ashes of a dead star. Anna: Plus everything that happened while we were away. Starship reaching orbit. Crew 13 at the station. Everything. And the end of a story you, our listeners, asked us to follow. Avery: Let's go. Anna: On Tuesday, the Royal Swedish Academy of sciences awarded the 2026 Nobel Prize in Physics to one person, Frances Halsen of the University of Wisconsin, Madison, for decisive contributions to the IceCube Neutrino Observatory and the discovery of high energy neutrinos of astrophysical origin.

1:25 Avery: Halsin is 82, born in Tinan in Belgium. In 1944, when the call came, he was travelling in Italy, giving talks. And the instrument he's being honoured for is one of the strangest telescopes ever built, because it has no mirror, no lens, and it sits at the bottom of the world. The problem? A messenger that won't stop. Anna: To see why it matters, start with the particle. A, uh, neutrino is almost nothing, nearly massless, no electric charge, and it barely interacts with anything. Roughly 65 billion of them from the sun pass through every square centimetre of you every second, about the size of your fingernail.

2:09 And essentially none of them notice you're there. Avery: Which is exactly what makes them valuable. Light gets absorbed by dust, bent by magnetic fields, blocked by gas. Charged cosmic rays get deflected so badly we can't tell where they came from. A neutrino just keeps going in a straight line. So if you catch one, it points straight back at, uh, whatever made it. Anna: The catch is the catching. If almost nothing stops a neutrino, you need an enormous amount of material and the patience to wait for the rare one that does hit an atom.

2:43 That's the problem. Halsin took on in 1988, his idea Avery: was to use the ice at the South Pole. Very occasionally, a, ah, neutrino collides with an atomic nucleus in the ice and produces a charged particle that moves faster than light does in ice. That throws off a faint cone of blue lightcherenkov light. The same glow you see in the water around the nuclear reactor core. Anna: And the deep Antarctic ice is extraordinarily clear, dark and stable. So you drill holes, lower light sensors on cables, freeze them in and use a cubic kilometre of glacier as the detector.

3:21 Avery: That's what IceCube is 5,160 sensors on 86 cables sitting between 1,450 and 2,450 metres down near the Ahmanson Scott South Pole Station. It came out of an earlier, smaller experiment called Amanda, and it was completed in 2011. Anna: Hm. Here's the Part I. The overwhelming majority of what IceCube sees isn't cosmic neutrinos at all. It's particles from cosmic ray showers in the atmosphere above Antarcticamore than 100 million a day. One of the cleanest tricks for rejecting them is to look down.

4:01 A particle track coming up through the Earth can only have been made by a neutrino, because nothing else can cross the planet. Avery: So the telescope at the South Pole uses the whole Earth as a filter, which means for that technique, its best view is of the northern sky, straight through the planet. The most southerly observatory on Earth looking north through rock. Anna: It's worth remembering how unlikely that sounded in 1988. Nobody had built a particle detector out of a natural glacier and the early prototype work in the ice was slow going.

4:37 Halsin's own reaction to Tuesday's call was that it was a great surprise and he obviously didn't expect it. After nearly four decades of pushing the Avery: idea and the shape of the light tells you what happened. A neutrino that makes a muon leaves a long, straight track of light through the array. That's the one that points back well to its source. Other interactions make a roughly spherical flash, a cascade which measures the energy well, but the direction only roughly. Different events, different strengths.

5:10 An ice cube uses both. Then there's the question it was really built for cosmic rays. Charged particles hitting Earth with enormous energies were discovered in 1912. And more than a century later, we still can't say for sure where the most energetic ones are accelerated. Wherever cosmic rays are being sped up and crash into gas or light, they make neutrinos. So find the neutrino sources and you've found the particle accelerators. Anna: And it worked. By 2013, two years into full operation, IceCube had collected 28 high energy events that couldn't be explained by the atmosphere.

5:49 The first evidence of neutrinos from beyond the solar system. That's the discovery the prize names. Avery: Then it started pointing to sources. In September 2017, a single high energy neutrino triggered an alert, and telescopes found a Flaring Blazar TXS0506 0.56 in the same patch of sky. In 2022, IceCube reported neutrinos from the active galaxy NGC 10, UM68. And in 2023, it mapped high energy neutrinos coming from the plane of our own Milky Way. Anna: That last one has a southern twist. The heart of our galaxy sits in the southern sky, which is exactly the part IceCube's track method struggles with, because those neutrinos come down through the ice along with all the atmospheric junk.

6:40 The galactic plane result leaned on the cascade events instead and on, um, machine learning to pick them out. Avery: And NGC 1068 is a nice one for listeners. It's about 47 million light years away in Cetus the Whale, right on the celestial equator, so it can be found from both hemispheres. And it shares a constellation with Saturn this month. More, um, on that in Skywatch. Anna: Each of those opened a door optical astronomy can't. Neutrinos come from the deep interiors of the most violent places.

7:13 The core of an active galaxy, the region close to a black hole, places light can't escape cleanly. Avery: Now, one thing we should say plainly, a Nobel in physics can go to, uh, at most, three people. And this year it went to one. IceCube itself is the work of a large international collaboration, plus the engineers who drilled it and the winter over crews who keep it running through the polar night when it's too cold for aircraft to land. Anna: And the committee said so the chair, Mark Pierce, put it this way.

7:45 Halsin has led an international team of researchers and engineers who have provided us with a fantastic instrument. The prize is for the vision and the leadership. The instrument belongs to a lot of people. Avery: It also fits a lineage. Raymond Davis and Masatoshi Koshiba shared a Nobel in 2002 for catching neutrinos from the sun and from supernova 1987a, the explosion in the Large Magellanic Cloud we talked about just a few weeks ago. Still the only supernova whose neutrinos we've ever detected.

8:18 In 2015, it was Takaki Kajita and Arthur McDonald for showing neutrinos change flavour. Anna: The next step is bigger ice. IceCube Gen 2 is planned at roughly 8 times the volume, and the field is no longer only in Antarctica. The KM3 net detectors on the floor of the Mediterranean use seawater the same way, and early last year that collaboration reported the most energetic neutrino yet seen. Avery: So from a 1988 proposal that sounded faintly absurd, let's turn a glacier into a telescope. We now have neutrino astronomy as a working branch of the science, with the southernmost lab on Earth at its centre.

9:02 Anna: Congratulations to Frances Halsin and to everyone who has ever frozen a sensor into the ice at the pole. Avery: Avery from one kind of cosmic messenger to another In a story led out of Sydney, astronomers have pinned down the most distant fast radio burst yet seen, and the paper was published on Thursday in the journal Science, led by Manisha Kaleb of the University of Sydney. Anna: Quick refresher Fast radio bursts are flashes of radio emission lasting about a millisecond from far outside our galaxy.

9:34 The first was found in 2007 in archival data from Parkes Moraing in New South Wales, and we still don't know for certain what makes them. Avery: This one, FRB2024O3 04B, was caught on 4th March 2024 by the Meer TRAP system on the Meerkat radio telescope in South Africa. The radio signal suggested it was extremely far away. The problem was that the world's largest ground based telescopes could see no galaxy at all at that precise spot. Anna: How can a radio flash tell you its distance? As, uh, the burst crosses space, free electrons slow the longer wavelength slightly, so the low frequencies arrive a fraction of a second late.

10:19 That delay, the dispersion measure, grows with the amount of gas crossed. So with distance, the link between the two is called the McQuart relation, after JP McQuart of ICRAR Curtin, whose team pinned it down with Australia's ASCAP in 2020. This burst's dispersion measure was huge, around 2,300, which is why the team expected it to be so far away. So the team turned to the James Webb Space Telescope. Webb's camera found a faint galaxy in exactly the right place, and its spectrograph measured a redshift of 2.148 light.

10:55 That left when the universe was about 3 billion years old. Avery: And the host was a surprise. Most fast radio burst hosts are big star forming galaxies. This one is a small dwarf galaxy about a thousand times less massive than expected, forming stars hard with most of its stars perhaps made within about 30 million years. Anna: That matters for the origin. One idea is that bursts come from merging neutron stars, but that takes billions of years to happen. Another is a young intensely magnetic neutron star, a magnetar, which can form fast.

11:32 A young host fits the magnetar picture and Caleb says the team thinks a uh, merger origin for this burst is very unlikely. Avery: There's a bonus. A burst like this is a flashlight shining through everything between it and us. Its signal carries the imprints of a previously unknown galaxy cluster about three and a half billion light years away and of the nearby Virgo cluster. Anna: One thing to be clear about this is the peer reviewed version of a result first posted as a preprint in August last year and the record distance was reported then.

12:08 What's new this week is publication in Science after review along with NASA's release. It's one burst and one burst doesn't settle the origin question for the whole Avery: population, but the team estimates meerkat could catch several bursts a year from beyond redshift 1. Meerkat is a precursor to the SKA and its low frequency sibling is going up in Western Australia. Expect more of these next. Anna: A cold case from the Hubble archive in 1999 Hubble took an ultraviolet spectrum of a white dwarf called HS02090832 about 270 light years away.

12:50 It contained roughly 100 absorption features nobody could identify. Avery: Jamie Williams, a doctoral candidate at the University of Warwick, went back to that spectrum with an updated atomic database and found that many of the mystery lines matched niobium, an element never before seen in a white dwarf. The paper was published on Monday in Nature Astronomy. Anna: Why is niobium a clue? Elements heavier than iron mostly aren't forged in a star's core. Niobium is made in the late swollen stage of a dying sun like star and then expelled.

13:24 And this star's surface is also rich in zinc and copper, while it's nearly bare of the silicon and iron you'd expect from an ordinary rocky planet. Avery: Falling in that contrast is the point astronomers have found plenty of so called polluted white dwarfs. Stars whose surfaces are dusted with the remains of rocky asteroids and planets from the original system. First generation debris with silicon and iron in it. This one's surface chemistry looks nothing like that. Anna: Then there's tess. Over four months it saw ah, the white dwarf's brightness wobble on a cycle of about 4.4 days.

14:03 The team reads that as a Jupiter sized planet orbiting about 6 million kilometres out far closer than Mercury is to the Sun. Avery: Put it together. And the proposal is remarkable. The planet didn't survive from the system's birth. It formed afterwards out of material the star shed as it died. A second generation planet, the white dwarf, is still around 35,000 degrees. So it's stripping that planet's atmosphere. And the niobium rich gas is raining back down onto the star where Hubble saw it. Anna: If that sounds familiar, it's the flip side of a story we ran last month.

14:41 Bataygin and colleagues arguing that when a star like the sun becomes a white dwarf, it its planets get scattered. This suggests a star's death can also build something new. Three caveats and the team states them itself. First, Williams says plainly it is not a confirmed planet. The test signal is indirect. Second, keeping the ejected material close enough to form a planet probably needs a companion star to pull it back. Third, this work was first presented as a conference poster in July last year.

15:14 This week's news is the peer reviewed paper. Avery: Williams plans to use Hubble over the next several years to find out whether planets like this are rare or common. Either way, a 27 year old spectrum just told us something new. Now, while we were away, four stories we'd been following came to a head. So here's to catch up. Anna: First Starship Flight 14 launched from Starbase on 28 September late that evening in eastern Australia and became the first starship to reach orbit. It deployed 26 of the larger Starlink V3 satellites, the first ever delivered to orbit by starship.

15:51 It wasn't clean. One booster engine shut down on the way up and so did one of the ship's vacuum engines. The ship still had enough to fire one sea level engine and insert itself into orbit. But in SpaceX's words, out of an abundance of caution, controllers cut the planned roughly 10 hour mission short, fired the first ever Starship deorbit burn after about two orbits and brought it down in the northern Pacific a little over three hours after launch. Not off Chile as we previewed. So orbit achieved payload delivered and an engine reliability question to answer before flight 15.

16:25 Avery: Second crew um, 13 after the oxidizer leak that uh, grounded it in September. Crew 13 launched on Thursday 1 October from Cape Canaveral aboard the Dragon Grace and docked with the station the same evening. Commander Jessica Watkins became the first NASA astronaut to fly Dragon twice with Luke Delaney, Canada's Joshua Kutryk and Russia's Sergei Tetericio. Anna: Third juice ESA's Jupiter mission swung past at 8,640 kilometres over the Indian Ocean on the 28th, gaining 3 1/2 kilometres per second and bending its path by about 20 degrees.

17:04 Its monitoring cameras sent back views of Africa, Madagascar and the moon. The high resolution science camera images are still being processed. One more Earth Flyby comes in January 2029, then Jupiter in 2031. Avery: ESA says flying through the tail of Earth's magnetic field was a useful dress rehearsal. Juice has 35 flybys of Ganymede, Europa and Callisto ahead of it once it arrives. And fourth, the one you asked us to follow. The Link spacecraft sent to boost NASA's ageing Swift observatory re entered the atmosphere on 25 September after losing two of its three reaction wheels.

17:43 It never had the fuel to attempt to capture, but its team did fly it to within 12 to 15 kilometres of swift and practised moving its robot arms. NASA paid Catalyst $30 million for the attempt and the spacecraft was built in under a year. Swift itself launched in 2004 and has spent more than two decades catching gamma ray bursts within seconds and swinging around to look at them. Work that made it a first responder for half the observatories on Earth. Anna: Swift is expected to follow it down in early November.

18:12 Until then, it's back observing a gamma ray lookout working through its final weeks. Thank you to everyone who wrote in about this one. We'll mark Swift's end when it comes Avery: and one to watch. Japan's MMX mission, aiming to bring back the first samples ever from a moon of Mars, is set to launch on an H3 rocket from Tanegashima at 06:41 on the morning of Tuesday 20th October Sydney time. That's the afternoon of Monday the 19th on the US east coast. Anna: Time for the sky and it's a good weekend for it.

18:46 New moon arrives at 15:50 Universal Time on Saturday. That's Saturday in the Americas and Europe, but 2:50 on Sunday morning in Sydney. Either way, the next several evenings are Avery: properly dark, which makes it prime time for the zodiacal light. A faint cone of sunlight scattered off dust in the plane of the planets. The trick is the angle of that plane to your horizon. And right now the two hemispheres get Anna: opposite ends of the day. From Sydney, after astronomical Twilight ends around 8:30 in the evening, the ecliptic stands about 75 degrees from the western horizon, nearly upright.

19:29 Look west from a dark site for a tilted, tapering glow. A false dusk from Los Angeles. At the same stage it's about 38 degrees from New York, 32 from London, only 23. So in the evening the north mostly misses out. Avery: But in the morning, it flips before astronomical dawn around half past five in Los Angeles and, uh, New York. The ecliptic stands about 79 degrees from the eastern horizon in LA, 73 in New York, 62 in London. That's your false dawn. In the east from Sydney, it's only 33 degrees in the morning.

20:09 Anna: Same geometry as the steep evening Venus we described last month. It's all about how the plane of the planets meets your horizon. One practical note, for Australians, daylight saving began last Sunday in New South Wales, Victoria, the act, Tasmania and South Australia. So all our Sydney times are now daylight time. Southern listeners also get a rare twilight treat. Mercury is near its greatest distance from the sun, magnitude 0, sitting 24 degrees up at sunset from Sydney. Actually higher than Venus, which is 22 degrees up at magnitude -4.3 and sets almost two hours after the sun from the north.

20:53 Avery: Sorry. At Sunset, Venus is 4 degrees up in Los Angeles, under 2 in New York and already below the horizon in London. And Venus is now sliding quickly towards the sun. So southern viewers catch it this week. Anna: And because both planets are close to the Sun, a safety line we never skip. Never look at the sun with your eyes, binoculars or a telescope. And never sweep binoculars across the western sky until the sun is fully down. Any solar viewer must meet the ISO 123122 standard and a filter goes over the front of any optics, never at the eyepiece.

21:35 Avery: Northern listeners, your reward is before dawn. Mars is passing through the Beehive Star cluster, closest little more than a tenth of a degree on the 11th Universal Time and within half a degree either side. Binoculars make it lovely. At nautical dawn on Monday, Mars is about 57 degrees up from LA 55 from New York, 49 from London against 23 from Sydney. Jupiter is nearby, 15 degrees away and closing. The two will be just over a degree apart in mid November. Anna: Southern predawn watchers can see the pair too, just lower.

22:13 Mars about 23 degrees up at nautical dawn from Sydney and Jupiter 17. Mars is at magnitude plus 1.1 and Jupiter at minus 1.8, so the colour contrast is easy even in a bright sky. Avery: Saturn, just past opposition, is magnitude 0.35 and, um, well placed for everyone. Highest around half past midnight local time. 54 degrees up from Sydney, 58 from LA 51 from New York, 40 from London. The rings are tilted only about 7 degrees, so they look unusually, um, thin. Anna: While you're with Saturn, remember NGC 1068.

22:52 From the lead, the neutrino galaxy is in Cetus II. A, uh, small telescope target near the star Delta Ceti. Asteroid Vesta also reaches opposition on Tuesday the 13th in Cetus within reach of binoculars. And the Orionid meteor shower peaks on the night of the 21st into the 22nd. There will be a fat waxing moon early in the night, so the hours before dawn are best from both hemispheres. The Orionids are dust from Hallie's comet, so it's a chance to catch a little of Hallie ahead of its return in 2061.

23:25 Avery: Um, and that's the show. Thank you for your patience over the past couple of weeks. It's good to be back. A Nobel for a telescope made of ice, the most distant fast radio burst, a planet that may have been built from a dying star, and a lot of catching up. Get WOL soon, Huw. And as ever, the credit for this show belongs to the whole team behind it. If you've got a question you'd like us to chase the way you did with Link and Swift, use the contact [email protected] you'll find us on socials.

23:56 Astrodaily pod and the show notes have every source. Anna: I'm Anna. Avery: And I'm Avery. Clear Skies.