Scientists have long wondered if Betelgeuse, one of the brightest and most enigmatic stars in the sky, is not alone. Astronomers have finally confirmed that it does indeed have a companion star.
A paper published in the Astrophysical Journal Letters presents new observations from the Gemini North Telescope on Mauna Kea in Hawaiʻi. Gemini North’s images are the first to show Betelgeuse with its companion.
Astronomers have discovered a companion star in an incredibly tight orbit around Betelgeuse. Credit: International Gemini Observatory/NOIRLab/NSF/AURA Image Processing: M. Zamani (NSF NOIRLab).
Betelgeuse has long been a source of scientific interest and wonder.
It is the closest red supergiant to Earth, about 650 light-years away, with a radius about 700 times that of our Sun. Betelgeuse is only 10 million years old – compared to the Sun which is about 5 billion years old – but is near the end of its life.
One day, Betelgeuse will light up the sky in a spectacular supernova death which could be as bright as a half-moon for several months.
When Betelgeuse dimmed in 2019 and 2020, scientists thought that the red supergiant might be about to go supernova. But further analysis showed that the so-called “Great Dimming” was caused by the star’s cooling and condensation by a nearby dust cloud.
Betelgeuse has not only dimmed but has also suddenly increased in brightness.
In fact, the variability in Betelgeuse’s brightness has been seen by people for thousands of years, and it is periodic. The main variability is about 400 days, and there is a second period of variability which lasts about 6 years.
This 6-year period of regular dimming and brightening led astronomers to suggest that Betelgeuse might have a companion, or “Betelbuddy”.
Observations by the Hubble Space Telescope and the Chandra X-Ray Observatory came up empty.
Astrophysicists at NASA’s Ames Research Center suggested another way of spotting the Betelbuddy – a type of telescopic imaging called speckle imaging. This method uses very short exposure times to freeze out distortions in images caused by Earth’s atmosphere.
Gemini North’s ‘Alopeke speckle imager spotted Betelgeuse’s companion star.
“Gemini North’s ability to obtain high angular resolutions and sharp contrasts allowed the companion of Betelgeuse to be directly detected,” says lead researcher Steve Howell. “Papers that predicted Betelgeuse’s companion believed that no one would likely ever be able to image it.”
Howell’s team found that the star is about 6 times fainter than Betelgeuse and is about 1.5 times more massive than the Sun. It is probably a hot, young, blue-white star which has not started hydrogen fusion in its core.
The star is quite close to Betelgeuse – probably just 4 times further than Earth is from the Sun.
Credit: International Gemini Observatory/NOIRLab/NSF/AURA Image Processing: M. Zamani (NSF NOIRLab).
“The speckle capabilities provided by the International Gemini Observatory continue to be a spectacular tool, open to all astronomers for a wide range of astronomy applications,” says Martin Still, National Science Foundation program director for the International Gemini Observatory.
“Delivering the solution to the Betelgeuse problem that has stood for hundreds of years will stand as an evocative highlight achievement.”
Astronomers will try again to image the Betelbuddy in November 2027 when the companion star is at its greatest separation from Betelgeuse.