Astronomers have used the Very Large Telescope (VLT) in the Atacama Desert region of Northern Chile to discover the strongest evidence yet that the famous star Betelgeuse has a companion star. That means after a century of investigation, scientists are closer than ever before to conclusively identifying Betelgeuse as a binary system composed of two stars, Betelgeuse A and Betelgeuse B.
Betelgeuse is a red colored star visible with the naked eye in the constellation of Orion and located around 650 light-years from Earth. Astronomers initially proposed the existence of another star orbiting Betelgeuse around 100 years ago in an attempt to explain the familiar star's strange dimming, which has been observed for over 1,000 years. While other teams have gathered evidence of the existence of Betelgeuse B, this new image is the clearest ever direct observation of the star. The scientists behind the discovery are thrilled.
"This is the conclusion of a century-long quest," team leader Miguel Montargès of the Observatoire de Paris, France, said in a statement. "We have shown that Betelgeuse is not single; it is accompanied by a faint stellar companion. I jumped from my chair when I saw the processed images."
The discovery of this new evidence of Betelgeuse B follows two papers published in 2024 that suggested this elusive stellar companion would be at its furthest from Betelgeuse A in December of that year. With that clue in hand, Montargès and colleagues set about hunting it.
"Honestly, I thought we did not have the sensitivity to detect Betelgeuse B as it was predicted," Montargès said. "Because it is more massive than predicted, we see it!"
Betelgeuse B had previously been theorized to be around the same mass as the sun, but these new observations reveal that this elusive star has instead around two to three times the mass of our star.
"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," Montargès added. "These are among the best moments in science: seeing something new, unexpected."
Capturing Betelegeuse B was only possible thanks to the VLT's SPHERE instrument, which features a coronagraph that blocks out the light of a planetary system's star. Combined with the advanced optics on the instrument, this allows scientists to measure the wavelength and polarity of light both coming directly from the star and being reflected off of any nearby planets. But that's not all SPHERE can do.
"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," team member Anthony Boccaletti, also an astronomer at the Observatoire de Paris, said.
There are still many questions to answer regarding Betelgeuse B. The team still needs to solidly confirm that what they have seen is actually a companion star, and they would also like to know how the presence of this star could shape the future of Betelgeuse A.
This red supergiant star nearing the end of its evolution gained notoriety a few years ago when its sudden and rapid brightening led to speculation it was about to suffer an explosive death.
"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," Montargès said. "The question is truly open whether this companion is going to have an impact on the evolution of the red supergiant."
The team's research was published on Tuesday (July 28) in the journal Astronomy & Astrophysics.
