Red supergiant Betelgeuse not so bright, not so giant, not so far away

The red supergiant Betelgeuse. Image: ALMA (ESO/NAOJ/NRAO)/E. O’Gorman/P. Kervella

The red supergiant Betelgeuse in the constellation Orion may not be quite as large or far away as previously thought, new research suggests, but it’s still a prime candidate to end its life in a supernova blast as it burns up the last of its nuclear fuel in the (astronomically speaking) not-too-distant future.

Speculation about just when that fiery blast might be expected ramped up in the wake of the star’s pronounced dimming over the past year. But extensive observations suggest a different explanation: most of that dimming was caused by a huge cloud of dusty debris thrown off by the bloated star along the line of sight to Earth.

A second, less intense episode likely was triggered by pressure waves driving pulsations in the giant star.

“It’s normally one of the brightest stars in the sky, but we’ve observed two drops in the brightness of Betelgeuse since late 2019,” said Meridith Joyce of The Australian National University. “This prompted speculation it could be about to explode. But our study offers a different explanation.

“We know the first dimming event involved a dust cloud. We found the second smaller event was likely due to the pulsations of the star.”

Using hydrodynamic and seismic modelling, the research team “confirmed that pressure waves – essentially, sound waves — were the cause of Betelgeuse’s pulsation,” said Shing-Chi Leung of The University of Tokyo.

The research, published in The Astrophysical Journal, indicates Betelgeuse is “burning helium in its core at the moment, which means it’s nowhere near exploding,” Joyce said. “We could be looking at around 100,000 years before an explosion happens.”

Based on analysis of the pressure waves and their periods, the study indicates Betelgeuse is not quite as large as previously thought. If placed in the centre of Earth’s solar system, the star’s radius would extend about two thirds of the way to Jupiter, not all the way.

Based on those calculations, the researchers conclude Betelgeuse is about 530 light years from Earth, not the 700 light years of earlier estimates. The good news is, that’s still too far from Earth to pose a threat whenever the star finally does, in fact, blow up.