The Great Dimming of Betelgeuse: a Surface Mass Ejection (SME) and its Consequences

TL;DR

Betelgeuse experienced a significant surface mass ejection during its 2020 dimming, leading to atmospheric changes, dust formation, and altered stellar oscillations, highlighting episodic mass loss's role in stellar evolution.

Contribution

This study provides detailed observational evidence linking a surface mass ejection to the 2020 dimming event of Betelgeuse, emphasizing episodic mass loss's impact on supergiant behavior.

Findings

Surface mass ejection caused the dimming event.

Mass ejection contributed significantly to the star's mass loss.

Post-event, Betelgeuse showed cooler temperature and altered pulsations.

Abstract

The bright supergiant, Betelgeuse (Alpha Orionis, HD 39801), underwent a historic optical dimming during 2020 January 27 $-$ February 13. Many imaging and spectroscopic observations across the electromagnetic spectrum were obtained prior to, during, and subsequent to this dimming event. These observations of Betelgeuse reveal that a substantial surface mass ejection (SME) occurred and moved out through the extended atmosphere of the supergiant. A photospheric shock occurred in 2019 January - March, progressed through the extended atmosphere of the star during the following 11 months and led to dust production in the atmosphere. Resulting from the substantial mass outflow, the stellar photosphere was left with lower temperatures and the chromosphere with a lower density. The mass ejected could represent a significant fraction of the total annual mass loss rate from the star suggesting that episodic mass loss events can contribute an amount comparable to that of the stellar wind. Following the SME, Betelgeuse was left with a cooler average photosphere, an unusual short photometric oscillation, reduced velocity excursions, and the disappearance of the $\sim$400-day pulsation in the optical and radial velocity for more than two years following the Great Dimming.