After a long wait, astronomers have finally seen the stellar companion of the famous star Betelgeuse. This companion star orbits Betelgeuse in an incredibly tight orbit, which could explain one of Betelgeuse’s longstanding mysteries. The star is doomed, however, and the team behind this discovery predicts that Betelgeuse will cannibalize it in a few thousand years.
The fact that Betelgeuse is one of the brightest stars in the sky over Earth, visible with the naked eye, has made it one of the most well-known celestial bodies. And ever since the first astronomers began inspecting this fixture in the night sky, they have been baffled by the fact that its brightness varies over periods of six years.
This mystery is now solved.
The six-year dimming of this red supergiant star is not to be confused with an event that saw it drop sharply in brightness over 2019 and 2020. This event, known as the “Great Dimming,” sparked intense interest across the globe. The Great Dimming was so unexpected that it led some scientists to theorize that it could signal Betelgeuse was approaching the supernova explosion that will one day mark the end of its life.
That supernova speculation was well-founded. After all, though it is only around 10 million years old, the fact that Betelgeuse is 700 times the size of the sun means it has burned through its nuclear fuel much faster than our 4.6 billion-year-old star. That means its supernova death is likely approaching. However, in 2023, the Great Dimming was explained by a giant obscuring cloud of dust emitted by Betelgeuse.
Even though the mystery of the Great Dimming was solved, this event spurred a renewed interest in this ever-so familiar star, the tenth brightest in the night sky. That renewed interest included the desire of astronomers to solve the less dramatic but more regular periodic dimming of Betelgeuse.
The lesser dimming of Betelgeuse
Betelgeuse has a primary period of variability that lasts around 400 days, as well as a second, more extended dimming period lasting around six years.
Unlike the Great Dimming, which perplexed scientists for only a few years, this regular “heartbeat” of Betelgeuse has baffled humanity for millennia!
It was while reviewing archival data that scientists began to theorize that the six-year variability of Betelgeuse could be the work of a hidden companion star. However, deeper investigation with the Hubble Space Telescope and NASA’s X-ray space observatory Chandra left scientists coming up empty-handed in terms of a companion star.
Undeterred, NASA Ames Research Center scientist Steve Howell led a team of astrophysicists who set about investigating Betelgeuse with the Gemini North telescope and its ‘Alopeke (Hawaiian for “fox”) instrument.
“Gemini North’s ability to obtain high angular resolutions and sharp contrasts allowed the companion of Betelgeuse to be directly detected,” Howell said in a statement. “Papers that predicted Betelgeuse’s companion believed that no one would likely ever be able to image it.”
The ‘Alopeke instrument uses a technique in astronomy called “speckle imaging” that uses short exposure times to remove distortions from images that are caused by Earth’s atmosphere. This provided the Gemini North telescope with the high-resolution capability to detect the faint companion of Betelgeuse for the first time ever.
Howell and colleagues were able to do more than just image the companion star of Betelgeuse; they were also able to determine some of its characteristics.
What do we know about Betelgeuse’s companion?
The team thinks the star has a mass around 1.5 times that of the sun and that it is a hot blue-white star orbiting Betelgeuse at a distance equivalent to four times the distance between Earth and the sun, fairly close for binary stars. That means it exists within the extended atmosphere of Betelgeuse. This represents the first time a companion star has been detected so close to a red supergiant.
The team also theorizes that this star has not yet begun to burn hydrogen in its core, the process that defines the main sequence lifetime of a star. Thus, the Betelgeuse system appears to consist of two stars that exist at opposite ends of their lives, despite the fact that both stars formed at the same time!
That’s because larger and more massive stars don’t just burn through their nuclear fuel more rapidly; they also initiate the fusion of hydrogen to helium earlier. However, in this case, this delay doesn’t mean that Betelgeuse’s companion is in for a long life; the intense gravity of Betelgeuse is likely to drag the smaller star into it, devouring it.
The team estimates this cannibalistic event could happen within the next 10,000 years.
In the meantime, astronomers will get another look at the stellar companion of Betelgeuse in November 2027 when it achieves maximum separation from the infamous red supergiant star.
Beyond this research’s implications for Betelgeuse and its ill-fated companion, it tells scientists more about why red supergiants undergo periodic changes in brightness how periods of 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. “This now opens the door for other observational pursuits of a similar nature.”
The team’s research was published on Monday (July 21) across two papers in The Astrophysical Journal.