CAMBRIDGE, Massachusetts — New radio images of Betelgeuse show the red supergiant has largely recovered from its dramatic fading of late 2019 and early 2020 — but they also reveal something stranger: the shape of the giant star's outer atmosphere stretches and relaxes in step with the orbit of a hidden companion, Siwarha, which circles so close that it passes through the star's extended atmosphere.
The findings come from a study led by Dr. Lynn D. Matthews of the MIT Haystack Observatory, with colleagues from the Center for Astrophysics | Harvard & Smithsonian, the University of Manchester and the European Southern Observatory. Published in The Astronomical Journal, it is based on observations from 2021 to 2026 at seven radio frequencies, 22 to 485 gigahertz, using the Karl G. Jansky Very Large Array in New Mexico and the Atacama Large Millimeter/submillimeter Array, known as ALMA, in Chile.
According to the National Radio Astronomy Observatory, which announced the results on Monday, 26 October 2026, the images offer the sharpest radio view yet of the gas around one of the brightest stars in the night sky — and the clearest evidence so far that Betelgeuse is not solitary, even though its companion was never seen directly in these radio data.
Illustration: The red supergiant Betelgeuse with its hidden companion star Siwarha moving through its outer atmosphere, leaving faint ripples in the surrounding gas.
What Happened
Betelgeuse, a red supergiant in Orion about 640 light-years from Earth, is so large that if it were placed at the centre of our solar system, its surface would reach beyond Jupiter's orbit. Like many ageing giant stars, it is surrounded by a vast envelope of gas stretching far beyond its visible surface. The new study set out to map that envelope and see how it had changed since the Great Dimming.
The team observed Betelgeuse at seven radio frequencies between 22 and 485 gigahertz, combining five years of data from the Very Large Array and ALMA. Different frequencies probe different depths of the atmosphere, building a layered picture of the gas, from the hotter regions near the star to the cooler, distant material.
The first headline result is reassuring: the extended atmosphere has largely recovered from the Great Dimming, when the star faded in late 2019 and early 2020 to its faintest in more than a century. Brightness temperatures at 22 and 44 gigahertz — the lowest frequencies, probing the outermost layers — have returned to typical levels. Peak temperatures reach about 3,500 kelvin at roughly 2.7 stellar radii, falling to about 2,200 kelvin nearer in, at around 1.2 stellar radii.
The second result is more surprising. The radio images show Betelgeuse does not always look the same shape: at times it appears more elongated, with an ellipticity of up to 10 percent; at other times it looks rounder. The pattern is not random. The star looks most elongated when Siwarha is predicted to be at its greatest apparent separation — its widest distance from the star as seen from Earth — and rounder when the companion should be passing in front of or behind Betelgeuse.
That correlation is the heart of the new paper. The researchers argue it is consistent with Siwarha gravitationally disturbing the gas as it moves through it, stretching the atmosphere towards the companion. The effect is subtle — a shape change of at most about one tenth — but it recurs across five years of observations, in line with its predicted orbit.
Matthews put it vividly in the announcement. "This companion is orbiting so close to the star that it actually passes through its extended atmosphere," she said. Such a passage, she suggested, could leave a wake in the gas, "much as a boat leaves one as it moves through water" — or like "a jet boat tearing through a lake".
Precision matters here. Siwarha was not directly detected in these radio observations: the researchers calculated it is tens to hundreds of times too faint at radio wavelengths to show up, and the images reveal no wake trailing behind it. What the study reports is a correlation between the shape of Betelgeuse's atmosphere and Siwarha's predicted position — evidence supporting the companion, but not proof that Siwarha is causing the changes. More observations, covering more of its orbit, are needed to confirm the picture.
Illustration: The Very Large Array radio telescopes in New Mexico observing Betelgeuse under a starry night sky.
Background
Betelgeuse has been one of the most watched stars in the sky for centuries. It marks the right shoulder of Orion, the hunter, one of the most recognisable constellations in the Northern Hemisphere winter sky, and one of the brightest stars visible to the naked eye. Its name comes from the Arabic for "the hand of al-Jawza".
The star seized the world's attention in late 2019, when it began to dim dramatically. By early 2020 it had faded to its faintest in over a century, losing roughly two-thirds of its visible brightness and setting off speculation that it might be about to explode as a supernova. Astronomers cautioned that no explosion was imminent; later work found a simpler explanation: the star had ejected a cloud of hot gas — about a billion tons of material — which cooled into dust, blocking some of its light.
As the dust cleared, Betelgeuse brightened again, and by 2023 it was back near its usual brilliance. But the episode left questions about the star's outer layers. The new radio study was designed in part to answer them, by mapping the atmosphere years after the event. The answer appears to be yes: the outer atmosphere's brightness temperatures have returned to expected levels.
A second thread goes back further, to a puzzle in the brightness record: for decades, astronomers have known that Betelgeuse's brightness rises and falls on a cycle of about 2,100 days — roughly five and three-quarter years — far longer than its other, shorter pulsations. No explanation based on the star alone fitted the data.
In 2024, researchers proposed an answer: a companion star, orbiting Betelgeuse at only about twice the star's radius, deep inside its extended atmosphere. Such a companion could stir up the surrounding gas and dust as it moved, producing the long brightness cycle. The idea gained support from direct imaging and spectroscopy, and the companion was named Siwarha — from the Arabic for "her bracelet".
The new study is the most detailed radio test of the companion idea so far. Watching Betelgeuse's shape change over five years — covering much of Siwarha's roughly 2,100-day orbit — let the team check whether the atmosphere's stretching matched where the companion was supposed to be. According to the researchers, it does.
The Very Large Array — 27 dishes across the high desert of New Mexico — and ALMA — 66 antennas on a high plateau in the Chilean Andes — are among the most powerful radio telescopes in the world. The study was published in The Astronomical Journal as Matthews et al., volume 172, issue 3, article 184, and posted to arXiv as arXiv:2608.02847.
Illustration: Betelgeuse shining brightly in the constellation Orion after its Great Dimming, with the hunter's familiar shape in the night sky.
Why It Matters
The study matters first for what it says about Betelgeuse itself. Red supergiants are stars in the final stages of their lives, burning through their remaining fuel before eventually exploding as supernovae. Understanding how they shed mass is central to understanding how they evolve and what kind of explosion they will produce. Betelgeuse is the nearest red supergiant to Earth — the best laboratory for studying that process up close.
The new results show that mass loss around Betelgeuse is not smooth or symmetrical. If a companion is ploughing through the star's atmosphere, the gas is being stirred, stretched and shaped by a second gravitational influence — and any model treating the star as single and isolated will miss part of the picture. The same may be true of other red supergiants, whose companions may be more common than assumed.
The study also closes a chapter that began with the Great Dimming. The new measurements show a star recovered from that episode, its outer atmosphere back to normal temperatures, still shining steadily in Orion's shoulder. The study says nothing about an imminent supernova.
What Happens Next
The most important next step is more observation. The team says additional radio observations, covering more of Siwarha's orbit, are needed to confirm the shape changes really do track the companion and to rule out other explanations. Each new set of images will test whether the atmosphere keeps stretching and relaxing in step with its predicted position.
Astronomers will also want to look for the wake itself. If Siwarha is truly ploughing through Betelgeuse's atmosphere like a boat through water, the disturbance should be detectable in sensitive observations — in gas motions, or in the dust around the star. Finding a wake would be strong evidence the companion is actively shaping its surroundings; not finding one would push researchers to reconsider the picture.
Other telescopes and wavelengths will play a part too. Direct imaging and spectroscopy have already supported the companion's existence, and further work in visible and infrared light could pin down Siwarha's mass, temperature and orbit — completing the picture of a binary system in which one star lives inside the atmosphere of another.
Betelgeuse will keep being watched. For now, the star that startled the world six years ago appears back to its old self — a brilliant red supergiant in Orion, with a hidden companion circling inside its glowing layers.
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Frequently Asked Questions
What is Betelgeuse?
Betelgeuse is a red supergiant star in Orion, about 640 light-years from Earth, and one of the brightest stars in the night sky. It marks Orion's right shoulder. It is an ageing, massive star in the final stages of its life, so large that its surface would extend beyond Jupiter's orbit if it were placed at the centre of our solar system. Its name comes from the Arabic for "the hand of al-Jawza".
What is Siwarha?
Siwarha is a companion star proposed in 2024 to explain Betelgeuse's brightness cycle of about 2,100 days. According to the proposal, it orbits at only about twice Betelgeuse's radius, deep inside the giant star's extended atmosphere. The name comes from the Arabic for "her bracelet". The companion has been supported by direct imaging and spectroscopy, but it was not directly detected in the new radio observations — it is tens to hundreds of times too faint at radio wavelengths to show up.
What did the new study find?
Led by Dr. Lynn D. Matthews of the MIT Haystack Observatory and published in The Astronomical Journal, the study used the Very Large Array in New Mexico and ALMA in Chile to observe Betelgeuse at seven radio frequencies, 22 to 485 gigahertz, from 2021 to 2026. It found the star's extended atmosphere has largely recovered from the Great Dimming, with temperatures back to typical levels, peaking at about 3,500 kelvin. It also found Betelgeuse appears more elongated, by up to 10 percent, when Siwarha is predicted to be at its greatest apparent separation, and rounder when the companion should be passing in front of or behind the star.
Did astronomers actually see Siwarha ploughing through the atmosphere?
Not directly. The radio images show Betelgeuse's atmosphere changing shape in step with Siwarha's predicted orbit, consistent with the companion disturbing the gas as it moves — but the companion itself was too faint at radio wavelengths to be detected, and the images show no wake behind it. The correlation supports the companion idea but does not prove Siwarha is causing the changes; more observations covering more of its orbit are needed to confirm it.
Is Betelgeuse about to explode as a supernova?
There is no evidence in this study that Betelgeuse is about to explode, and the study says nothing about an imminent supernova. The Great Dimming of late 2019 and early 2020, which sparked speculation about an explosion, was later explained by a dust cloud from ejected material, and the new observations show the star's atmosphere has largely recovered since then.
Sources
- Phys.org, "Radio images reveal disturbances in Betelgeuse's atmosphere", 27 October 2026 — phys.org
- SciTechDaily, "A Hidden Star May Be Plowing Through Betelgeuse's Giant Atmosphere", 3 November 2026 — scitechdaily.com
- The Daily Galaxy, "Betelgeuse's recovery and strange shape", 3 November 2026 — dailygalaxy.com
- Cosmic Herald, "Betelgeuse companion Siwarha radio atmosphere VLA ALMA October 2026" — cosmicherald.com
- Daily Inference, "Betelgeuse's shape shifts with its suspected companion's orbit", 4 November 2026 — dailyinference.news
- National Radio Astronomy Observatory, "What Lurks Within the Shadows of Betelgeuse?", 26 October 2026 (via Newswise) — newswise.com
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