Astronomers have captured the clearest image yet of a companion star orbiting Betelgeuse, a red supergiant star. This discovery potentially concludes a search that began approximately one hundred years ago. The image, obtained using the European Southern Observatory's (ESO) Very Large Telescope (VLT), shows what is believed to be Betelgeuse B.
Miguel Montargès, an astronomer at the Observatoire de Paris – PSL and lead author of the study, confirmed that Betelgeuse is not a single star. The companion star is surprisingly massive. Initial estimates suggested it would be similar in mass to the Sun. New observations indicate Betelgeuse B is two to three times more massive than the Sun.
The possibility of a companion star was first suggested a century ago to explain Betelgeuse's varying brightness. Despite decades of observation, a clear detection remained elusive. Two studies published in 2024 predicted the companion would reach its greatest apparent separation from Betelgeuse in December 2024. This provided an optimal viewing opportunity.
Montargès and his team observed Betelgeuse with the VLT during that period. They then spent several months analyzing the data. The SPHERE instrument on ESO's VLT in Chile's Atacama Desert enabled the direct imaging of Betelgeuse B. This means light from the companion itself was detected.
Previous observations, including a possible detection with the Gemini North Telescope, hinted at the companion's existence. The VLT observations offer the strongest evidence and clearest image to date. Researchers plan further observations to confirm the companion's orbital path.
Betelgeuse garnered significant attention when its brightness dramatically decreased several years ago. This event led to speculation about an impending supernova. Subsequent studies, including those by Montargès' team, determined that a dust cloud caused the dimming. The presence of Betelgeuse B introduces a new factor for astronomers to consider in the red supergiant's evolution and its eventual supernova.
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