Graphical depiction of Betelgeuse and the Betelbuddy. Credit: Lucy Reading-Ikkanda/ Simons Foundation.

Orion’s Betelgeuse could have a ‘Betelbuddy’ stellar companion, rather than being on the verge of becoming a supernova.

Betelgeuse’s brightening and dimming over the years convinced some that it could be close to becoming a supernova.

However, a new study suggests that these unexplained changes are due to a companion star that ploughs light-blocking dust out of its way.

The tenth-brightest star in the night sky, Betelgeuse, may not be on the brink of exploding as a supernova, according to a new study of the star’s brightening and dimming.

Instead, recent research shows that the observed pulsing of the starlight is probably caused by an unseen companion star orbiting Betelgeuse.

Formally named Alpha Ori B, the ‘Betelbuddy’ acts like a snowplough as it orbits Betelgeuse, pushing light-blocking dust out of the way and temporarily making Betelgeuse seem brighter.

Lead author Jared Goldberg, a Flatiron research fellow at the Flatiron Institute’s Center for Computational Astrophysics, said: “We ruled out every intrinsic source of variability that we could think of as to why the brightening and dimming was happening in this way.

“The only hypothesis that seemed to fit is that Betelgeuse has a companion.”

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

Infographic describing how the Betelbuddy affects Betelgeuse’s apparent brightness. Credit: Lucy Reading-Ikkanda/ Simons Foundation.

Uncovering the ‘Betelbuddy’

Betelgeuse is a red giant star around 100,000 times the brightness of our Sun and more than 400 million times the volume.

The star is nearing the end of its life span, and when it dies, the resulting explosion will be bright enough to see during the day for weeks.

Astronomers can predict when Betelgeuse will die by effectively ‘checking its pulse.’

It’s a variable star, meaning it gets brighter and dimmer, pulsing like a heartbeat.

In Betelgeuse’s case, there are two heartbeats: one that pulses on a timescale a little longer than a year, and one that pulses on a timescale of about six years.

One of these heartbeats is Betelgeuse’s fundamental mode, a pattern of brightening and dimming that’s intrinsic to the star itself.

If the star’s fundamental mode is its long-scale heartbeat, then Betelgeuse could be ready to blow 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 a long secondary period. In that 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 one leading theory is that they arise when a star has a companion that circles it and barrels through the cosmic dust that is produced and expelled by the star.

The displaced dust alters how much starlight reaches Earth, changing the star’s apparent brightness.

The researchers explored whether other processes may have caused the long secondary period, such as the 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 that simulate the star’s activity, the team concluded that the Betelbuddy is by far the most likely explanation.

Goldberg said: “Nothing else added up. Basically, if there’s no Betelbuddy, then that means there’s something way weirder going on — something impossible to explain with current physics.”

The team has yet to determine exactly what the Betelbuddy is, but they assume it’s a star of up to twice the sun’s mass.

Joyce said: “It is difficult to say what the companion actually is beyond providing mass and orbital constraints.  sunlike star is the most probable type of companion, but that is by no means conclusive.”

She added: “A more exotic hypothesis I personally like, though the opinions of my co-authors may differ, is that the companion is a neutron star — the core of a star that has already gone supernova.

“However, in that case, we would expect to see evidence of this with X-ray observations, and we haven’t. I think we should look again.”

Betelgeuse’s position in the constellation Orion. Credit: Lucy Reading-Ikkanda/ Simons Foundation.

A new view of an old star

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

Molnár said: “We need to confirm that Betelbuddy actually exists, since our result is based on inference, not on direct detection. So we’re working on observation proposals now.”

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

Joyce said: “Without each of us considering this problem from very different angles — László as an expert in space-based observations and data analysis, Jared as someone who studies and simulates massive stars, and myself as a 1D modeller — the work wouldn’t have been possible.”

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

Molnár said Betelgeuse: “has been the target of countless studies since the dawn of modern astrophysics, and yet there’s still room to make significant new discoveries: in this case, a sunlike star hiding in plain sight, in the immense glare of a red supergiant.

“That is what excites me the most.”

The research is published in The Astrophysical Journal.