For centuries, Betelgeuse, the iconic red supergiant in Orion, has fascinated astronomers with its changing brightness.
Why does its light vary over a ~6-year cycle?
Thanks to the Gemini North telescope, we now have an answer: Betelgeuse has a companion star!
A research team, led by Steve Howell (NASA Ames Research Center), used the āAlopeke speckle imager on Gemini North to observe Betelgeuse with unprecedented precision. In Dec. 2024, three days after the predicted time of maximum angular separation, a star ~6 magnitudes fainter was detected, which is assumed to be coeval with Betelgeuse with an estimated age of 10 Myr.
This long-awaited discovery confirms recent studies predicting a companion star to explain Betelgeuseās 6-year brightness variations.
The detection has a significance of ~1.5Ļ (a low-confidence detection, requiring further confirmation). The position and angular separation correspond to the predictions of Goldberg et al. (2024) and MacLeod et al. (2025).
Named Siwarha ("Her Bracelet" in Arabic, reflecting Betelgeuseās "Hand of the Giant"), this young, hot starālikely a pre-main-sequence F-dwarf with ~1.6 times the Sunās mass and a temperature of ~7400 Kāorbits Betelgeuse at an estimated physical distance of ~8ā10 au (based on a ~52 milliarcsecond angular separation), though the press release suggests ~4 au, possibly a simplified estimate or the closest orbital distance.
Siwarha was discovered thanks to the speckle imaging technique, which eliminated the distortions of Earth's atmosphere. During the 2019ā2020 "Great Dimming", its companion was unobservable, as expected, because it was located "behind" the red supergiant. But in 2024, it reappeared: its position and brightness matched exactly the predictions based on dynamical analyses.
Siwarha is likely key to understanding long-term brightness variations, which cannot be explained by stellar pulsations alone. Furthermore, it offers a unique glimpse into the life of Betelgeuse, which will eventually explode as a supernova in the "distant" future. Siwarha, influenced by strong tidal forces, could spiral toward the red supergiant and disappear within the next 10,000 years.
This discovery paves the way for new observations. In November 2027, when Siwarha will reach maximum angular separation again, scientists will have another opportunity to study it and confirm its characteristics.
The discovery of Betelgeuse's stellar companion is not only an extraordinary technical achievement, but another piece of the puzzle in understanding red supergiants and their fate.
I have a question: āWhat will Betelgeuseās supernova look like in the distant future?ā
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Image Credit: International Gemini Observatory/NOIRLab/NSF/AURA
Image Processing: M. Zamani (NSF NOIRLab)
Press releaseā”ļø
noirlab.edu/public/news/noirā¦
Research paper: "The Probable Direct-Imaging Detection of the Stellar Companion to Betelgeuse"ā”ļø
arxiv.org/abs/2507.15749
ALT The image shows a vast star field with a faint yellow-orange star, Betelgeuse, at its center. Two white segments radiate from it, converging toward a black box at the upper left. In the box, Betelgeuse appears as a bright orange, almost circular disk, next to its companion, a smaller, less well-defined, dark blue star located slightly to the lower left of Betelgeuse. The companion, detected with the 'Alopeke instrument on the Gemini North telescope, is a hot, young star. This discovery explains Betelgeuse's brightness variability every six years.