Atmosphere of Betelgeuse before and during the Great Dimming event revealed by tomography

Vol. 650
1. Letters to the Editor

Atmosphere of Betelgeuse before and during the Great Dimming event revealed by tomography

Between October 2019 and February 2020, Betelgeuse exhibited a rapid and unprecedented decrease in brightness that has been widely dubbed as "the Great Dimming". This has been the subject of numerous studies, and several, sometimes inter-related hypotheses have been put forward to explain this behavior. These have ranged from the formation of a dust cloud, to a temperature change in the atmosphere, to a cool spot covering about half of the stellar surface. Some have even suggested that the dimming could signal imminent core collapse, which could make Betelgeuse the first observable supernova in our Galaxy for over 400 years. However, a key piece of the puzzle relates the brightness changes to the atmospheric dynamics. In this study, Kravchenko et al. use a high signal-to-noise time series of spectra spanning about 5 years, which bracket the Great Dimming event. This allowed them to probe the conditions as a function of depth in the stellar atmosphere. They uncovered the presence of multiple shocks that occurred in 2018 and 2019 that were amplified by the underlying 400-day pulsation cycle, resulting in an outflow and a corresponding increase in opacity that led to the dimming.