New images help solve celestial mystery of Betelgeuse’s great dimming

Betelgeuse, a bright star visible in the Orion constellation in the night sky, has beguiled and puzzled space scientists since late 2019.

The red giant, a star in the last stages of its life, experienced two significant drops in brightness, which caused some astronomers to believe that it was nearing its end and could explode in a supernova — something that was last observed in the 17th century.

However, scientists now believe these dimming events occurred because of dust clouds. New images of the star’s surface clearly show how its brightness changed, helping astronomers fully understand what caused what they describe as a “great dimming.”

“For once, we were seeing the appearance of a star changing in real time on a scale of weeks,” said Miguel Montargès, a postdoctoral research fellow at the Observatoire de Paris, France, and the Institute of Astronomy at KU Leuven, Belgium, in a news statement.

The new images were taken in January and March 2020, using the European Southern Observatory’s Very Large Telescope in Chile’s Atacama Desert. Combined with images previously taken in January and December 2019, they clearly captured how the star’s surface changed and darkened over time, especially in the southern region, the astronomers said.

The latest images were part of a study published on Wednesday in the journal Nature.

Betelgeuse’s surface regularly changes as giant bubbles of gas move, shrink and swell within the star, the researchers said. The team concluded that some time before Betelgeuse started to dim, the star ejected a large gas bubble that moved away from it, in part propelled by the pulsating star.

A patch of the star’s surface cooled down shortly after the release of the bubble. That temperature decrease was enough for the heavier elements, such as silicon, in the gas to condense into solid dust, which veiled the star.

The study showed that dust formation can occur very quickly and close to a star’s surface.

“We have directly witnessed the formation of so-called stardust,” Montargès said.

“The dust expelled from cool evolved stars, such as the ejection we’ve just witnessed, could go on to become the building blocks of terrestrial planets and life,” added Emily Cannon, a doctoral student at the Institute of Astronomy at KU Leuven, who was also involved in the study, in the statement.

The star returned to its normal brightness by April 2020.

The new findings match previous observations of Betelgeuse using the Hubble Space Telescope. Andrea Dupree, an astronomer and associate director at the Center for Astrophysics | Harvard & Smithsonian and a coauthor of the new study, captured signs of dense, heated material moving through the star’s atmosphere in the months leading up to the great dimming.

In the paper published last year, Dupree found that the material moved about 200,000 miles per hour as it traveled from the star’s surface to its outer atmosphere. Once the gas bubble was millions of miles from the hot star, it cooled and formed a dust cloud that temporarily blocked the star’s light.