Betelgeuse!

Environmental & Science Education, STEM, Cosmology, Astrophysics, Earth & Space Sciences, Nature of Science, History of Science

Ed Hessler

The supergiant star Betelgeuse, one of the ten brightest stars in the night sky,located on Orion's "right shoulder," has been a source of speculation for about a year. It was showing signs of an explosive event. 

Astrophysicists went to work and Davide Castelvecchi, reporting for Nature explains the results "Normally, Betelgeuse is one of the ten brightest stars in the night sky. For decades, researchers have known that it undergoes cycles of dimming roughly every 425 days, during which it temporarily loses about one-quarter of its peak brightness. But in February 2020, astronomers noticed that the star’s brightness had dropped by an unprecedented two-thirds — enough to be noticeable with the naked eye.

"The unexplained dimming fueled speculation that the star could be about to explode. Betelgeuse is a red supergiant — a type of star that’s more massive and thousands of times shorter-lived than the Sun — and it is expected to end its life in a spectacular supernova explosion sometime in the next 100,000 years. This event would provide a spectacle the likes of which Earthlings have not seen in centuries: the last supernova in the Milky Way that could be observed from Earth was in 1604, and Betelgeuse is so close to our planet that its supernova will be bright enough to be visible during daytime for weeks. The star is around 168 parsecs (548 light years) away, according to the most current estimates².

"But many astrophysicists warned that the supernova speculation was wishful thinking. They pointed out that the dimming was likely to be caused by more mundane mechanisms, such as a blob of unusually cold matter appearing on the surface of the star in what’s known as a convective cell, or a cloud of dust crossing the line of sight to it.

"Now, astrophysicist Miguel Montargès at the Paris Observatory and his collaborators have found that the reason for the ‘great dimming’ was probably a combination of both of those factors."

Castelvecchi's essay includes a short movie showing the dimming sequence and describes how the mystery was solved.  

Castelvecchi also provides a link to a longer article by Emily M. Levesque with further details on stellar evolution, more details on the research, what this means for Betelgeuse, the contribution of the research for next-generation facilities, and the difficulty of predicting an explosive event. There are two additional images and some links, including to the full paper which is behind a paywall but the abstract may be read. 

Leveque also points out an anomaly that attracted the researcher's attention from the beginning: "A comparison of these images shows that the star hadn’t simply shrunk or dimmed uniformly. Instead, the light loss was concentrated in the star’s southern hemisphere," which you can see in the changing images of Betelegeuse.