Betelgeuse Betelgeuse? Bright star Betelgeuse likely has stellar companion ‘Betelbuddy’

One of the brightest stars in the night sky, Betelgeuse, may not be about to explode in a supernova, according to a new study of the star’s brightening and dimming. Instead, recent research shows that the observed pulsations of starlight are likely caused by an invisible companion star orbiting Betelgeuse.

Formally named Alpha Ori B, the “Betelbuddy” (as astrophysicist Jared Goldberg calls it) acts like a snowplow as it orbits Betelgeuse, pushing away light-blocking dust and temporarily making Betelgeuse brighter. Goldberg and colleagues present their simulations of this process in a paper accepted for publication in The Astrophysics Journal. The results are published on the arXiv preprint server.

“We excluded every intrinsic source of variability that we could think of to explain why the brightening and dimming were occurring in this way,” says Goldberg, lead author of the study and a Flatiron Researcher at the Center for Computational Astrophysics at Flatiron Institute. “The only hypothesis that seemed valid was that Betelgeuse would have a mate.”

Goldberg co-authored the study with Meridith Joyce of the University of Wyoming and László Molnár of the Konkoly Observatory at the HUN-REN Research Center for Astronomy and Earth Sciences in Hungary.

Discovering the “Betelbuddy”

Betelgeuse is a red giant star whose luminosity is approximately 100,000 times that of our sun and whose volume is more than 400 million times greater. The star is nearing the end of its lifespan and when it dies, the resulting explosion will be bright enough to be visible during the day for weeks.

Astronomers can predict when Betelgeuse will die by “checking its pulse.” It’s a variable star, meaning it gets brighter and dimmer, pulsing like a heartbeat. In the case of Betelgeuse, there are two heartbeats: one that beats on a time scale of just over a year, and one that beats on a time scale of about six years .

One of these heartbeats is Betelgeuse’s fundamental mode, a pattern of brightening and dimming intrinsic to the star itself. If the star’s fundamental mode is its long-scale heartbeat, then Betelgeuse could be ready to explode sooner than expected. However, if its fundamental mode is its short-scale heartbeat, as several studies suggest, then its longer heartbeat is a phenomenon called the long secondary period. In this case, this longer brightening and dimming would be caused by something external to the star.

Scientists still don’t know for sure what causes long secondary periods, but a leading theory is that they occur when a star has a companion that orbits it and passes through cosmic dust produced and expelled by the star . The displaced dust changes the amount of starlight reaching Earth, thereby changing the star’s apparent brightness.

The researchers investigated whether other processes could be causing this long secondary period, such as churning of the star’s interior or periodic changes in the star’s powerful magnetic field. After combining data from direct observations of Betelgeuse with advanced computer models simulating the star’s activity, the team concluded that Betelbuddy is by far the most likely explanation.

“Nothing else adds up,” Goldberg says. “Basically, if there’s no Betelbuddy, that means there’s something much stranger going on, something impossible to explain with current physics.”

The team hasn’t yet determined exactly what Betelbuddy is, but they suspect it’s a star weighing up to twice the mass of the sun.

“It’s hard to say what the companion actually is beyond the constraints of mass and orbit,” says Joyce. “A sun-like star is the most likely type of companion, but it is by no means conclusive.”

“A more exotic hypothesis that I personally like, although my co-authors’ opinions may differ, is that the companion would be a neutron star, the core of a star that has already gone supernova,” she says. . “However, in this case we would expect to see evidence of it with X-ray observations, and that’s not the case. I think we should look again.”

A new vision of an old star

Next, the team will play paparazzi, trying to take images of the Betelbuddy with telescopes, as there will be a potential window of visibility around December 6.

“We need to confirm that Betelbuddy actually exists, since our result is based on inference and not direct detection,” explains Molnár. “So we are currently working on observation proposals.”

The researchers note that this study was only possible thanks to team science.

“Without each of us considering this problem from very different perspectives – László as an expert in space observations and data analysis, Jared as someone who studies and simulates massive stars, and myself as a modeler 1D – the work would not have been possible. possible,” says Joyce. “I would like to particularly thank the Flatiron Center for Computational Astrophysics for creating an environment in which it is possible to bring together such a diverse range of scientists.”

The team is also excited to have new information about a long-studied celestial body.

Betelgeuse “has been the target of countless studies since the dawn of modern astrophysics,” says Molnár. “And yet it is still possible to make significant new discoveries: in this case, a sun-like star is hiding in plain sight, in the immense brilliance of a red supergiant. This is what I excites the most.”