Astronomers find strongest evidence yet that Betelgeuse star has a companion | ESO
At long last, astronomers have firm evidence that Betelgeuse, one of the most famous stars in the night sky, is not alone. Using the European Southern Observatory’s Very Large Telescope (ESO's VLT), a team led by French researcher Miguel Montargès obtained the clearest image ever of what likely is Betelgeuse B, the star orbiting Betelgeuse. “This is the conclusion of a century-long quest,” says Montargès.
“We have shown that Betelgeuse is not single, it is accompanied by a faint stellar companion,” says Montargès, astronomer at the Observatoire de Paris - PSL, France, and lead author of the study published today in Astronomy & Astrophysics. Betelgeuse—a reddish star in the Orion constellation that is easily visible with the naked eye and is known to change in brightness—has been observed for millennia. However, it still surprises astronomers.
“I jumped from my chair when I saw the processed images,” recalls Montargès. Astronomers have looked for the potential companion, originally proposed to explain Betelgeuse’s brightness changes, for about a century, but without success. Two studies published in 2024 robustly predicted that in December that year, the companion would be furthest from Betelgeuse and hence easier to spot. Montargès and his team got to work, observing the star with ESO’s VLT in December 2024 and spending several months processing the data.
“Honestly, I thought we did not have the sensitivity to detect Betelgeuse B as it was predicted,” explains Montargès. “Because it is more massive than predicted, we see it!” Originally thought to be about as massive as the Sun, the new observations reveal that Betelgeuse B has instead around two to three times the mass of the Sun. “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,” says Montargès. “These are among the best moments in science: seeing something new, unexpected.”
Betelgeuse B was directly imaged, meaning the light from the star itself was detected, using the SPHERE instrument on ESO’s VLT in Chile’s Atacama Desert. While there was evidence for the existence of this companion star, including a possible direct detection with the Gemini North Telescope in Hawaiʻi, USA, this is the strongest evidence for, and clearest image yet of, Betelgeuse B. “It is remarkable to see how SPHERE and advanced post-processing techniques, originally developed to find exoplanets, also excel at detecting a companion around a massive, evolved star like Betelgeuse," says co-author Anthony Boccaletti, also an astronomer at the Observatoire de Paris.
“To be certain that the companion is really there, we still need to observe it in one year on the other side of the star, but there is very little space left for doubt,” adds Montargès.
A few years back, Betelgeuse was the subject of attention from astronomers and non-astronomers alike when it visibly started dimming. As an evolved supergiant star, Betelgeuse is expected to die in a supernova explosion, and the dimming led to speculations it could be about to explode. A group of astronomers led by Montargès studied the star with ESO’s VLT, finding it was instead obscured by a cloud of dust.
The potential detection of Betelgeuse B will prompt astronomers to investigate how the companion could affect Betelgeuse's anticipated supernova explosion. “The question is truly opened whether this companion is going to have an impact on the evolution of the red supergiant,” concludes Montargès.
https://www.eso.org/public/archives/releases/sciencepapers/eso2611/eso2611a.pdf
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