After nearly a century of astronomers trying to find it, the strongest evidence yet has emerged that Betelgeuse, one of the most famous stars in the sky, is not a solitary star, but is accompanied by a faint star that revolves around it.
An international team led by French astronomer Miguel Montargis of the Paris Observatory captured the clearest direct image of this possible companion using the Very Large Telescope of the European Southern Observatory in Chile's Atacama Desert.
This image is a color composite made from exposures from the Digitized Sky Survey 2 (DSS2). The field of view is approximatelly 2.0 x 1.5 degrees.Credit: ESO/Digitized Sky Survey 2. Acknowledgment: Davide De Martin.
A composite color image showing the region around the star Betelgeuse within a field of view of about two degrees in the sky (European Southern Observatory).
"We have proven that Betelgeuse is not alone, but is accompanied by a faint star," Montargis said in an official press release, describing the result as "the culmination of a century-long search."
A rare opportunity solved the mystery
Scientists had suggested decades ago that the presence of a companion star could help explain some of the changes in the brightness of Betelgeuse, but attempts to observe it have been unsuccessful.
In 2024, two studies predicted that the companion would reach its farthest point from Betelgeuse in December of that year, making it more likely to be observed. Therefore, the Montargis team went to the Very Large Telescope in December 2024 and then spent months processing the data.
This image, taken with ESO's Very Large Telescope (VLT), shows the clearest image ever of what likely is Betelgeuse B, a star orbiting Betelgeuse. The image was taken with the SPHERE instrument in December 2024, when the companion was predicted to be furthest apart from Betelgeuse as seen from Earth. The circle indicates the size of Betelgeuse, which has been removed. The bright source to the left, marked with a crosshair, is consistent with being Betelgeuse B. Credit: ESO/M. Montargès et al.
The clearest image yet of Betelgeuse's companion star, taken by the Very Large Telescope in late 2024, shows the companion to the left of the star (European Southern Observatory).
When the manipulated images appeared, Montargis said, "I jumped out of my seat when I saw the pictures."
The discovery was not easy; the researcher initially thought that the sensitivity of the instruments would not be sufficient to see the faint star, but the surprise was that the companion star was more massive than expected.
A star two or three times larger than the sun
Previous estimates suggested that the companion star, referred to as Betelgeuse "B", had a mass close to that of the Sun. But new images indicate that its mass is about two to three times that of the Sun.
Although there has been previous evidence of the companion, including a possible sighting by the Gemini North telescope in Hawaii, the new image is the clearest and strongest evidence yet.
Anthony Boccaletti of the Paris Observatory said that what was remarkable was that an instrument originally developed to search for planets outside the solar system had also proven capable of detecting a companion star around a giant, evolving star like Betelgeuse.
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