Red supergiant star Betelgeuse has a new excuse for its bad behavior: an accomplice.
The star, pronounced "Beetlejuice" (just like the Michael Keaton character), sits like a little devil on the shoulder of the Orion constellation about 700 light-years away in space. It has long-perplexed scientists, with some convinced it was on the brink of a supernova.
More recently, astronomers have proposed a theory for its volatile nature, which explains the star's seemingly erratic changes in brightness. They've suggested an unseen companion star orbiting Betelgeuse is periodically clearing dust out of the giant star's way to reveal more of its starlight.
Now a NASA-led team of scientists has made a direct detection of a companion. Using the 8.1-meter Gemini North telescope in Hawaii, the team found a faint star beside the supergiant’s brilliant glare — in the exact location previously predicted by computer simulations. The new evidence is a technological feat that some believed impossible due to its proximity to the luminous giant.
In the past, researchers have referred to the hypothetical companion star as Alpha Ori b or "Betelbuddy." But this team has proposed its own name (and, shockingly, didn't take the 2024 recommendation of this reporter, "Otho").
"The name Betelgeuse means 'Hand of the Giant,' with 'Elgeuse' being a historical Arabic name of the Orion constellation and a feminine name in old Arabian legend," the authors wrote in their paper, which will be published in The Astrophysical Journal Letters on Thursday. "Given that α Ori B orbits the hand of the giant, we suggest that the companion star be named Siwarha, or 'Her Bracelet.'"
Betelgeuse is about 100,000 times brighter than the sun. Because it's in the twilight of its life, the variable star has puffed up. Scientists say it's so large — hundreds of millions of miles in diameter — that if it were swapped with the sun, it would reach Jupiter in the outer solar system. By comparison, the sun is about 865,000 miles across.
Beginning in 2019, there was a dramatic decrease in Betelgeuse’s brightness — an event referred to as the "Great Dimming." Some believed this was a sign that stellar death was imminent, but scientists were able to determine the fading was the result of a large dust cloud temporarily blocking light from the star. About a year later, the star returned to its previous brightness.
But that event led to renewed interest in Betelgeuse, with some astronomers seeking answers to why Betelgeuse has two pulses — one that "beats" about every year and another on a six-year cycle. Some theorized the less-frequent pulse could be caused by another star.
A team of astrophysicists, headed by NASA Ames Research Center's Steve Howell, observed Betelgeuse in late 2024, when the hypothesized companion star was predicted to be at its maximum distance from its sibling. That's when they saw a faint light — located about four times the Earth-sun distance from Betelgeuse but still well within the supergiant's outer atmosphere.
The team ruled out the possibility that the new detection was just a background or foreground star. Betelgeuse’s motion through space would have revealed such interlopers in earlier images — but no such object was visible in observations about four years earlier.
The companion star is much fainter than Betelgeuse, perhaps just 1.5 times heavier than the sun. It appears to be a hot, blue-white star that has not yet started burning hydrogen in its core, according to the team's findings. But it's ill-fated, the researchers say. In about 10,000 years, it'll likely spiral into its supergiant sibling. At that point, in the words of Beetlejuice, it'll be "dead, dead, deadski."
Astronomers now hope to catch the smaller companion again when it reaches its next greatest separation from Betelgeuse in late 2027. Further studies could shed light on why similar red supergiant stars may undergo periodic changes in their brightness over many years.
"This detection was at the very extremes of what can be accomplished with Gemini in terms of high-angular resolution imaging, and it worked," Howell said in a statement. "This now opens the door for other observational pursuits of a similar nature.”
