Astronomers using the Hubble Space Telescope have captured the clearest direct image yet of a companion star orbiting Betelgeuse, the famous red supergiant in the constellation Orion. The discovery helps explain one of the most watched mysteries in modern astronomy: why Betelgeuse keeps dimming and brightening in strange ways.
A star hiding in plain sight
Betelgeuse, roughly 650 light-years from Earth, is one of the brightest stars in the night sky. Astronomers first proposed that it might have a companion about 100 years ago, as a way to explain dimming that observers have recorded for more than a thousand years. Over time, other teams gathered indirect evidence for such a star, called Betelgeuse B. But no one had imaged it clearly, until now.
The new observations, made with Hubble and ground-based telescopes, show the companion, named Siwarha, as a small bright point close to the giant star. The data also reveal a trail of dense gas swirling through Betelgeuse's vast extended atmosphere, likely carved by the companion's gravity.
Bigger than expected
The image carries a surprise: Siwarha is much more massive than predicted. Earlier models suggested the companion had about the same mass as the Sun. The new observations indicate it holds two to three times the Sun's mass, making it brighter and easier to spot.
"The fact that we can still discover a nearby companion, more massive and brighter than the sun, around such a well-studied star is remarkable," said Miguel Montargès, an astronomer at the Observatoire de Paris who led the work. "These are among the best moments in science: seeing something new, unexpected."
Clues from a timing gamble
The team timed its search using two papers published in 2024 that predicted the companion would be at its furthest separation from Betelgeuse in December of that year. With that clue, the astronomers set out to catch the star at the right moment. Montargès admitted he doubted the telescope had the sensitivity to detect the predicted companion. "Because it is more massive than predicted, we see it!" he said.
The finding gives scientists a new tool for reading Betelgeuse's moods. Tracking how Siwarha stirs the star's outer layers could clarify what drives its famous dimming events, including the Great Dimming of 2019-2020, and help refine estimates of when the supergiant might one day explode as a supernova.