KU Leuven: KU Leuven astronomers find explanation for eclipse of giant star Betelgeuse

Betelgeuse’s luminosity dip, visible even to the naked eye, prompted Miguel Montargès and his team to aim the Very Large Telescope at this immense star in late 2019. Immense in this is no exaggeration: if you put Betelgeuse in the place of the sun, the star would almost swallow the planet Jupiter. A comparison of images at the beginning and end of 2019 showed that the star surface had darkened considerably, especially the southern part, but the astronomers were not sure why.

The team continued to observe the star during its “great eclipse,” shooting Betelgeuse in January and March of 2020 with unparalleled resolution. In April 2020, Betelgeuse returned to its normal brightness. “It is very rare that we see the appearance of a star change on a time scale of several weeks,” says Montargès of the Paris Observatory and at the time of the study working at KU Leuven. “The instruments of ESO’s Very Large Telescope enabled us to able to not only observe the star as a point, but also see the details on its surface and monitor it throughout the event.’ The new images are the only ones to show how Betelgeuse’s surface is changing.

Direct witness of stardust
In a new study, published today in Nature , the team reveals that the mysterious eclipse was caused by a veil of dust that shadowed the star. That dust cloud, in turn, was the result of a drop in temperature on the surface of Betelgeuse.

Betelgeuse’s surface is regularly changed by the movements of giant shrinking and swelling gas bubbles that bubble up from its interior, similar to the bubbles in a pot of boiling water. The team concluded that the star had ejected a large gas bubble shortly before the “great eclipse,” which then moved further away from the star. When part of the star’s surface cooled shortly afterwards, the gas condensed into solid particles.

“We witnessed the formation of so-called stardust directly,” says Montargès. The new results show that dust can form very quickly and close to a star’s surface. emissions that we have recently witnessed may later serve as building material for terrestrial planets and living organisms’, adds co-researcher Emily Cannon from KU Leuven.

End of speculation
The internet has speculated that Betelgeuse’s luminosity dip could be a harbinger of a spectacular supernova explosion, as the red supergiant is nearing the end of its life in astronomical terms. No supernova has been observed in our galaxy since the 17th century, so it is not known how a star would behave in the run-up to such an event. However, this new research confirms that the “great eclipse” was not an early omen of Betelgeuse’s catastrophic end.

“It was exciting to witness the dimming of such a well-known star, for us as researchers, but also for amateur astronomers,” Emily Cannon said. “When you look at the stars at night, these tiny, twinkling points of light seem unperturbed. The eclipse of Betelgeuse shatters this illusion.”

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