Free Astronomy Magazine September-October 2021

24 SEPTEMBER-OCTOBER 2021 ASTRO PUBLISHING Mystery of Betelgeuse’s dip in brightness solved by ESO - Bárbara Ferreira T hese images, taken with the SPHERE instrument on ESO’s Very Large Telescope, show the surface of the red supergiant star Betelgeuse during its unprece- dented dimming, which happened in late 2019 and early 2020. The image on the far left, taken in January 2019, shows the star at its normal brightness, while the remaining images, from December 2019, January 2020, and March 2020, were all taken when the star’s brightness had noticeably dropped, especially in its southern region. The brightness returned to normal in April 2020. [ESO/M. Montargès et al.] B etelgeuse’s dip in brightness — a change noticeable even to the naked eye — led Miguel Montargès and his team to point ESO’s VLT towards the star in late 2019. An image fromDecember 2019, when compared to an earlier image taken in January of the same year, showed that the stellar surface was significantly darker, especially in the southern region. But the as- tronomers weren’t sure why. The team continued observing the star during its Great Dimming, cap- turing two other never-before-seen images in January 2020 and March 2020. By April 2020, the star had re- turned to its normal brightness. “For once, we were seeing the ap- pearance of a star changing in real time on a scale of weeks,” says Montargès, from the Observatoire de Paris, France, and KU Leuven, Belgium. The images now published are the only ones we have that show Betelgeuse’s surface changing in brightness over time. In their new study, published in Nature , the team revealed that the mysterious dim-