Japanese astronomers observed the Great Darkening of Betelgeuse, which occurred in 2019-2020, in an unusual way – using a meteorological satellite. Thanks to the Himawari-8 satellite, scientists have determined that both a dust cloud and a local decrease in the temperature of the star can be responsible for the record drop in brightness. The article was published in the journal Nature Astronomy.
Between late 2019 and early 2020, Betelgeuse dimmed in the optical range by about 1.2 magnitudes, which was a historical minimum brightness and received the designation “Great Darkening”.
Astronomers had several hypotheses to explain the star’s dip in brightness, such as a local decrease in the star’s effective temperature, obscuration by a cloud of dust that had either just formed or passed across the star’s disk, or a change in Betelgeuse’s angular diameter. The dust hypothesis received several confirmations, although there was evidence for versions not related to dust.
A team of astronomers led by Daisuke Taniguchi from the University of Tokyo said they were able to observe the Great Betelgeuse Blackout in an unusual way using Japan’s Himawari-8 geostationary meteorological satellite. It takes pictures of the entire Earth’s disk every 10 minutes using the AHI (Advanced Himawari Imager) instrument, which operates in the optical and infrared wavelengths. At the same time, each time a region of outer space around the edge of the earth’s disk, where a number of stars, including Betelgeuse, is located, enters the frame. Thanks to this, scientists were able to catalog the light curves of Betelgeuse between January 2017 and June 2021, using observational data in the wavelength range of 0.45-13.5 micrometers, and track the dynamics of the Great Darkening.
In addition, it is possible that a shock wave arose in the lower part of the star’s photosphere in January 2019, which propagated into the outer shell of Betelgeuse and passed through a bunch of warm gas outside the star’s photosphere.