Betelgeuse’s Ghost Companion: The Hidden Star Stirring Orion’s Giant

[00:00:00] [SPEAKER_01] Hello everyone, thanks for taking the time to listen. Today's headline, there's a star in Orion that's being haunted. Something is moving through its outer atmosphere, stirring it up, pulling it out of shape. And nobody can see the thing doing it. Not in radio anyway.

[00:00:17] [SPEAKER_03] Just in time for Halloween. Today, Betelgeuse and the ghost inside it. How two of the world's great radio telescopes caught a hidden companion by the ripples it leaves behind.

[00:00:28] [SPEAKER_01] Welcome to Astronomy Daily. I'm Anna.

[00:00:32] [SPEAKER_03] And I'm Avery. Also today, crystals that rode around the moon on Artemis 1 and came home carrying the tracks of cosmic rays. A new study that says comets almost certainly didn't seed life on Earth, but might have done better on Mars. And Virgin Galactic's new spaceship gets a name and a home.

[00:00:51] [SPEAKER_01] Plus, Swift's final days, Hubble getting Roman ready, and where to find Betelgeuse tonight. Let's go.

[00:00:58] [SPEAKER_03] It's Halloween, so I'm guessing you have something on theme to get us going?

[00:01:03] [SPEAKER_01] Let's start with the star itself. Because Betelgeuse is not a normal star. It's a red supergiant. The bright orange-red shoulder of Orion. And it is enormous. Put it where the sun is and its surface would reach somewhere out past the orbit of Mars.

[00:01:19] [SPEAKER_03] And it's close enough and big enough that it's one of the very few stars we can actually resolve as a disk rather than a point. It was the first star, other than the sun, ever directly imaged by Hubble back in 1996.

[00:01:34] [SPEAKER_01] It's also famously restless. In late 2019 and early 2020, it went through what's now called the Great Dimming. By February 2020, it had faded to its faintest in more than a century of records. People genuinely wondered whether it was about to go supernova.

[00:01:51] [SPEAKER_03] It didn't. The dimming turned out to be a huge surface mass ejection. A shockwave from deep convection that threw out gas, which cooled and formed dust and blocked our view for a few months.

[00:02:04] [SPEAKER_01] But Betelgeuse has a second, slower rhythm that has puzzled astronomers for a long time. On top of its roughly 400-day pulsation, it brightens and fades over about 2,100 days. Call it 5.8 years.

[00:02:19] [SPEAKER_03] And that's where the ghost comes in. In 2024, two independent teams went back through more than a century of brightness, velocity and position measurements and came to the same conclusion. That long period is a companion star in orbit.

[00:02:35] [SPEAKER_01] Not just in orbit. In orbit, inside Betelgeuse's extended atmosphere. The companion circles at about 2.3 times the radius of the visible star, which, for a star this size, means it's plowing through the giant's outer layers of gas.

[00:02:52] [SPEAKER_03] It now has a name. Siwarha. Betelgeuse comes from an Arabic phrase, usually read as the Hand of Al Jauza. So the companion was named for her bracelet. The International Astronomical Union adopted it this year.

[00:03:06] [SPEAKER_01] And the evidence has been building fast. Speckle imaging gave a tentative detection in 2025. In January this year, a team led by Andrea Dupree at the Center for Astrophysics used Hubble and ground-based spectra to find what looks like a wake, a dense trail of gas left behind the companion as it moves.

[00:03:25] [SPEAKER_01] And then, using the SPHERE instrument on ESO's Very Large Telescope at Paranal in Chile, a team led by Miguel Montargis reported a direct detection of the companion itself at about six sigma.

[00:03:38] [SPEAKER_03] So by now, we're fairly confident it's there. The new question is, what is it doing to Betelgeuse?

[00:03:45] [SPEAKER_01] This is the new paper, led by Lynn Matthews of MIT's Haystack Observatory, with Andrea Dupree, Anita Richards at the University of Manchester, and Bill Dent at ESO and ALMA. It's published in the Astronomical Journal, and the National Radio Astronomy Observatory released it this week.

[00:04:03] [SPEAKER_03] They observed Betelgeuse at seven radio frequencies, from 22 gigahertz up to 485 gigahertz, between 2021 and 2026. The two lowest came from the Very Large Array in New Mexico. The other five came from ALMA, high on the Chajnantor Plateau in Chile.

[00:04:24] [SPEAKER_01] And here's why seven frequencies matter. In radio, a star's atmosphere is opaque. But how opaque depends on the wavelength. Longer wavelengths only let you see the higher, outer layers. Shorter wavelengths let you see deeper in. So stacking seven frequencies is like slicing the atmosphere into layers, from just above the visible surface, out to nearly three times the star's radius.

[00:04:50] [SPEAKER_03] A CT scan of a star, more or less, with a disk only about a twentieth of an arc second across.

[00:04:57] [SPEAKER_01] Three things. First, Betelgeuse has recovered from the Great Dimming. Back in 2019, just before the dimming, Matthews and Dupree had found the outer atmosphere unusually cold in radio, a sign of that shock passing through. Now, at 22 gigahertz, the gas is back to about 3,500 Kelvin, roughly the temperature of the star's own surface.

[00:05:19] [SPEAKER_03] Second, they've pinned down a temperature minimum. Go deeper, with ALMA's highest frequency, to about 1.2 times the star's radius, and the gas drops to about 2,200 Kelvin. That's more than a thousand degrees cooler than the visible surface underneath it.

[00:05:36] [SPEAKER_01] Which sounds backwards. Hotter surface, cooler layer, then hotter again further out where the chromosphere is. But it matches a shell of molecular gas, the so-called mallsphere, that infrared astronomers have inferred for years. The radio measurement says that cool gas really does dominate that region.

[00:05:55] [SPEAKER_03] And third, the ghost. The team fitted the shape of Betelgeuse at every frequency and every date. And the star isn't quite round. It's slightly egg-shaped. What they notice is that how egg-shaped it is seems to track where the companion is in its orbit.

[00:06:10] [SPEAKER_01] When sawarha is at its greatest apparent distance from the star, off to one side, Betelgeuse looks more stretched. When sawarha is passing in front of the star, or hidden behind it, Betelgeuse looks rounder. The clearest single example. In October 2024, near greatest separation, the star was about 10% out of round. In April this year, near the companion's eclipse, it was under 2%.

[00:06:37] [SPEAKER_03] And the companion itself? Completely invisible at these wavelengths. The team worked out it would be tens to hundreds of times too faint to detect. Matthew's summary is that it actually passes through its extended atmosphere, and what they see is the disturbance.

[00:06:54] [SPEAKER_01] Like watching ripples on a pond, and inferring something moving just under the surface.

[00:07:00] [SPEAKER_03] And this needs the honest version. The effect is small. The star is never more than about 10% out of round. The correlation rests on around 9 epochs, and a few of those come from earlier papers by other teams. That's a pattern worth taking seriously, not a close case.

[00:07:17] [SPEAKER_01] There's also a genuine puzzle the authors flag themselves. The direction of the stretch isn't the same at every frequency. The highest ALMA bands, the middle ALMA bands, and the VLA bands all point different ways. One possibility is that different depths are cutting through different parts of a three-dimensional wake. But that's an idea to test, not a result.

[00:07:42] [SPEAKER_03] And what Siwarha actually is remains contested. Estimates of its mass run from around half a solar mass to roughly three. Even the distance to Betelgeuse is uncertain. This paper uses about 720 light years, while the figure you'll usually see is around 650.

[00:08:01] [SPEAKER_01] One more disclosure. A preprint of this work appeared in early August. So the journal publication is what's new this week, not the first side of the data.

[00:08:12] [SPEAKER_03] Why care? Because the companion is orbiting right in the zone where Betelgeuse launches its wind. The region where a red supergiant sheds the mass it loses on the way to its eventual supernova. If a companion is shaping that region, it changes how we model these stars' last stages. And not just for Betelgeuse.

[00:08:31] [SPEAKER_01] And there's a southern thread worth naming. Five of the seven frequencies came from ALMA in the Atacama, including the deepest layer. One of the authors is at ESO, and the direct detection came from Paranal. The northern VLA and the southern dishes together built the picture.

[00:08:48] [SPEAKER_03] The next beat has a date on it, roughly. Siwarha is currently on the far side of Betelgeuse from us. It should swing back into view, on the opposite side, in late 2027. Teams are already planning to be watching. In radio, in the ultraviolet, and with adaptive optics.

[00:09:06] [SPEAKER_00] So the ghost comes back out in a year. Rather fitting.

[00:09:11] [SPEAKER_03] When Artemis 1 flew around the moon in late 2022, there were no astronauts on board. But there were two passengers, mannequins called Helga and Zohor, built to mimic human bone and soft tissue and packed with thousands of radiation detectors. That was the Mare experiment, led by the German Aerospace Center.

[00:09:31] [SPEAKER_01] And some of the most interesting detectors on board were tiny crystals of lithium fluoride, made by the Institute of Nuclear Physics of the Polish Academy of Sciences in Krakow.

[00:09:41] [SPEAKER_03] A new paper, led by Pavel Bilsky in the journal Radiation Measurements, reports how those crystals did. The idea is clever. When a cosmic ray particle tears through the crystal, it knocks electrons loose and leaves a permanent defect along its path. Later, in the lab, you shine a laser through the crystal under a microscope, and the particle's track glows blue.

[00:10:04] [SPEAKER_01] And the advantage over the old method is big. The standard track detectors are plastic. To read them, you soak them for hours in hot caustic soda to etch the tracks out, which destroys the detector and makes hazardous waste. The crystal can be read without destroying it.

[00:10:20] [SPEAKER_03] The team's stacked microscope images taken a micrometer apart and followed each track through the crystal in three dimensions. That let them rebuild the full spectrum of how much energy each particle dumped along its path, which is what matters biologically. Heavy ions dump a lot of energy in a short distance, and that's the dangerous part of deep space radiation.

[00:10:40] [SPEAKER_01] For middling energies, the crystals matched the plastic detectors flying right beside them. For the heaviest hitters, they overestimated the dose by about 30%. The team's explanation is that fast neutrons can knock a lithium nucleus out of place inside the crystal, which leaves a track of its own. Crystals made with lithium-7 reduce that.

[00:11:01] [SPEAKER_03] The broader MARI results are worth hearing, too. Near the moon, the dose was higher than in low Earth orbit, but not by as much as you might expect. In Earth orbit, a big chunk of an astronaut's dose comes from protons trapped in the Van Allen belt. Out by the moon, those are gone, and what's left is galactic cosmic radiation, which is so energetic it passes straight through the body.

[00:11:24] [SPEAKER_01] Which also means the dose was spread more evenly through the mannequins. Less a surface sunburn, more something that goes all the way through. Two caveats.

[00:11:35] [SPEAKER_03] This is a methods paper with preliminary numbers, not a full risk assessment for crews. And Artemis 1 flew near solar maximum when the sun shields us best from galactic cosmic rays. As we said back in episode 193, that shield weakens as the cycle quietens.

[00:11:53] [SPEAKER_01] Which matters for the crews who'll go back to deep space after next year's Artemis 3 test in Earth orbit. They'll be flying as the sun winds down.

[00:12:02] [SPEAKER_03] Next up, a bit of myth-busting?

[00:12:05] [SPEAKER_01] It's one of the most romantic ideas in planetary science, that comets delivered the ingredients for life to the young Earth. And it's not baseless. Rosetta found glycine, an amino acid, and phosphorus at comet 67P. Comets are rich in hydrogen cyanide, which chemists rate as one of the key starting molecules for building life's components.

[00:12:29] [SPEAKER_03] A new study says the delivery almost certainly didn't work. It's led by Richard Anzlo at the University of Cambridge's Institute of Astronomy, published in Scientific Reports. And in Anzlo's own words, it's kind of a romantic idea. But their results suggest it's highly unlikely.

[00:12:47] [SPEAKER_01] The team modeled Earth's whole early comet bombardment, focusing on the slower, short-period comets. Because those give the molecules their best chance. And then they ran into one problem after another.

[00:13:02] [SPEAKER_03] First, the bombardment fell away fast, within roughly the first 500 million years. Second, many small comets tear themselves apart on the way in. Outgassing spins them up until they break. Third, Earth's atmosphere acts as a filter, destroying small comets and those coming in at shallow angles. And fourth, an impact is extremely hot. And earlier work showed only the gentlest strikes keep hydrogen cyanide intact.

[00:13:30] [SPEAKER_01] And even if some survived, there's a final twist. A big impact makes a crater leak, and groundwater rushes in and dilutes whatever arrived far below useful concentrations.

[00:13:42] [SPEAKER_03] Anzlo's verdict is that it would have had to be a one-in-a-million event. At best, a one-off fluke.

[00:13:48] [SPEAKER_01] But here's the part I love. They ran the same numbers for Mars. And comets do about five times better there. Lower impact speeds, because Mars is smaller and further from the sun, and a much thinner atmosphere to filter them out.

[00:14:03] [SPEAKER_03] So if cometary delivery mattered for life anywhere in the inner solar system, Mars was the better target. Anzlo puts it this way. In fact, it would be odd if it happened on Earth and not on Mars. Or perhaps more likely, it didn't happen on either.

[00:14:21] [SPEAKER_01] Caveats. This is modeling, centered on one molecule. It doesn't rule comets out. And it says nothing against comets delivering water or other material. And Anzlo's own earlier work found that in tightly packed planetary systems, comets can bounce between planets, slow down, and deliver intact. So the answer may depend on the system.

[00:14:44] [SPEAKER_03] It pairs nicely with this week's other icy body stories. And with episode 200's Three Floods at Jezero. If you're shopping for a place where life's chemistry got a delivery, Mars keeps looking interesting.

[00:14:57] [SPEAKER_01] Virgin Galactic is back. On Wednesday, the company named its first next-generation space plane. And on the same day, flew it to its home base.

[00:15:09] [SPEAKER_03] The name is a Pyron, chosen in an online contest with votes from more than 80 countries. It's Greek for boundless. And it said Aperon, not Ape Iron.

[00:15:21] [SPEAKER_01] Aperon is the first Delta-class ship. It was carried slung beneath the twin fuselage mothership, Eve, on a 90-minute flight from the company's factory in Mesa, Arizona, to Spaceport America in New Mexico. TEO Michael Cole-Glazier summed up the day. This morning, we gave Aperon a name. This afternoon, Aperon came home.

[00:15:42] [SPEAKER_03] The design principle hasn't changed since Spaceship One won the X Prize in 2004. Drop from the mothership at altitude. Fire the rocket motor to the edge of space. Then feather the wings to fall back stably before gliding to a runway.

[00:15:57] [SPEAKER_01] The road here has been hard. The first spaceship, too, VSS Enterprise, broke up in a test flight in 2014, killing one pilot. The second, VSS Unity, flew more than 30 people, including Richard Branson, before its last commercial flight in 2024. The company then stopped flying to build this new class.

[00:16:18] [SPEAKER_03] The Delta ships are meant to be tougher and quicker to turn around. Better thermal protection, simpler maintenance, a target of two flights a week per ship, and more than 500 missions each.

[00:16:31] [SPEAKER_01] What's next? Software integration and validation, then flight tests. Paying customers, who've paid as much as $750,000 U.S. dollars, are due to fly from mid-2027. A second ship is already being built, and should join in the second half of 2027.

[00:16:48] [SPEAKER_03] And the timing may suit them. Blue Origin paused New Shepard after its 17th crewed flight in January, for at least two years, to focus on the moon. So if the schedule holds, Virgin could have suborbital tourism to itself for a while.

[00:17:04] [SPEAKER_01] As ever with spaceflight, if. Let's move on to a few quick updates from today's news. Swift.

[00:17:12] [SPEAKER_03] NASA's Swift Observatory ended operations on the 20th of October, at about 275 kilometers up, and NASA says re-entry is expected in the next few weeks. Tracking predictions currently point to early November. Most of it is expected to burn up. Swift caught thousands of gamma-ray bursts in 22 years, and the paper we covered on Monday, the burst with a split personality, was one of them.

[00:17:37] [SPEAKER_01] Hubble is helping Roman get ready. NASA has released a Hubble image of a gravitational lens, cataloged as DESI-J194, where a galaxy about 4.5 billion light-years away bends the light of a more distant one into an arc and a counter arc. Roman's wide survey should find around 160,000 lenses like it. And Hubble's sharp single-detector views are helping calibrate how Roman's images will look.

[00:18:06] [SPEAKER_01] This is an image release, not a new paper. And Starship.

[00:18:10] [SPEAKER_03] SpaceX says Flight 15 is targeted for November, with an attempt to catch both the booster and, for the first time, the ship with the tower. Planning documents mention the 8th, but that's not an official date.

[00:18:23] [SPEAKER_01] Now, let's go and find our haunted star. Betelgeuse sits at a declination of about plus 7 degrees, close to the celestial equator, which means this one is genuinely for everyone, north and south.

[00:18:37] [SPEAKER_03] Right now, it's a late evening riser. On Friday night, it comes up at about 10.33 p.m. in Sydney, 9.48 in Los Angeles, 9.46 in New York, and 8.39 in London. It's best before dawn when it's highest, around 4.15 in the morning in Sydney, Los Angeles, and New York, and about 3.20 in London.

[00:18:59] [SPEAKER_01] How high depends on where you are. About 49 degrees up from Sydney, 63 from Los Angeles, 57 from New York, and 46 from London. And a reminder for North America, clocks fall back on Sunday, the 1st of November. So from then on, all of those times arrive an hour earlier by the clock.

[00:19:21] [SPEAKER_03] From Australia, Orion is upside down. The belt is still the three stars in a row, but the red shoulder, Betelgeuse, sits below it, and blue-white Rigel above. Northern listeners get the familiar version, Betelgeuse at upper left. Compare its orange with Rigel's blue. That's 3,500 Kelvin against more than 10,000.

[00:19:43] [SPEAKER_01] Evening planets. Saturn is your easy one after sunset. About 28 degrees up at dusk from Sydney, 15 from Los Angeles, 12 from New York, and only 6 from London. Mercury is making its last appearance of this evening run, and this one belongs to the south. About 11 degrees up at sunset from Sydney, against under 4 from the U.S., and barely 1 from London. It's faint now, so binoculars.

[00:20:12] [SPEAKER_01] And never sweep for it before the sun has fully set.

[00:20:14] [SPEAKER_03] The pre-dawn sky is the north's turn. Mars and Jupiter are closing in. 6.5 degrees apart this weekend, 4 by the 5th of November, and just over 1 degree on the 16th. Jupiter is the bright one, Mars the dimmer orange one beside it. At civil dawn, they're 60 to 69 degrees up from the U.S., 50-odd from London, and about 30 from Sydney.

[00:20:37] [SPEAKER_01] The moon helps out. It reaches last quarter on the 1st of November at 2028 UTC, which is early Monday morning in Sydney. Before that, it passes near Pollux in Gemini. Then, in the pre-dawn of the 2nd and 3rd of November, it slides past Mars and Jupiter, and then Regulus, within about 2 degrees of Regulus on the 3rd.

[00:20:58] [SPEAKER_03] And with the moon out of the evening sky after last quarter, it's a good week for zodiacal light. That faint cone of sunlight scattered by dust in the plane of the solar system. From the southern hemisphere, it's in the west after dusk, the false dusk. From the north, it's in the east before dawn, the false dawn. Dark sight, no moon, and give your eyes 20 minutes.

[00:21:22] [SPEAKER_01] Venus has just slipped past the sun into the morning sky. But it's still only a few degrees up at dawn everywhere. Give it a couple of weeks.

[00:21:32] [SPEAKER_03] And our standing reminder, never look at the sun without proper protection. For any solar viewing, including a partial eclipse, use only filters certified to ISO 12312-2, and never through binoculars or a telescope unless the filter goes over the front.

[00:21:49] [SPEAKER_01] That's Astronomy Daily for today. A haunted supergiant, crystals that went around the moon, comets that probably didn't deliver life to Earth, and a new spaceship with a Greek name.

[00:22:02] [SPEAKER_03] If you head out before dawn this weekend, find Beetlejuice, and remember, there's a companion in there, hidden, stirring things up. It reappears in about a year, and we'll be watching for it.

[00:22:15] [SPEAKER_01] You can find every episode, the show notes, and our newsletter at astronomydaily.io. And you can send us your questions there, too. Some of our best segments started as a listener question. We are at Astro Daily Pod on social media, part of the Bytes.com podcast network. I'm Avery. And I'm Anna. Clear skies and happy Halloween.