A mystery has been plaguing scientists concerning why exactly Betelgeuse has dimmed. New observations by NASA and the ESA using the Hubble Space Telescope have given a possible answer to that mystery. The observation suggests that Betelgeuse, a supergiant star, unexpectedly dimmed because of an immense amount of hot material ejected into space. The material formed a dust cloud that blocked starlight coming from the surface of the star.
Betelgeuse is a red supergiant star that has massively swollen in size. Scientists say if Betelgeuse was placed at the center of our solar system, it’s so large that its outer surface would extend past the orbit of Jupiter. Starting in October 2019, the star dimmed so noticeably that it could be seen with the naked eye.
By February 2020, the brightness of the star had dropped by a factor of three. Researchers believe that a dust cloud around the star formed when super-hot plasma was unleashed from an upwelling of a large convection cell on the star’s surface. As the material passed through the hot atmosphere to the colder outer layers, it cooled and formed dust.
The dust cloud blocked about 25% of the light from the star’s surface beginning in late 2019. By April 2020, the start had returned to its normal brightness. Hubble was able to see through its observations dense heated material moving through the star’s atmosphere in September, October, and November 2019.
Scientists began using Hubble early last year to analyze Betelgeuse. The analysis was part of a three-year study to monitor variations in the outer atmosphere of the star. Hubble’s sensitivity to ultraviolet light also allowed researchers to probe the layers above the surface of the star that are so hot they’re mostly in the ultraviolet region and can’t be seen in visible light. One of the most interesting aspects is that the star is about 725 light-years away from us. That means it would’ve taken the light so long to reach us, the dimming event would’ve happened around the year 1300.