We have a disappointing update on Betelgeuse. We are saddened to report that our favorite Red Supergiant shows no signs of going boom. After declining radically in brightness from October through January, Betelgeuse is now re-brightening in a perfectly normal way. New research from astronomers at the University of Washington and Lowell Observatory, and published in the Astrophysical Journal Letters, finds that Betelgeuse’s fainting spell was due to the shedding of a cloud of dust. 

During Betelgeuse’s decline in brightness, folks had speculated that the cause was likely either the effect of massive convective cells in the star’s atmosphere cooling and darkening at the surface, or the formation of dust. Both are perfectly normal behaviors for large stars, which lose bits of their atmospheres the way most of us not so young people lose our reading glasses. Only one measurement was needed to sort which scenario was true, but that one measurement was a doozy – scientists had to measure the temperature of Betelgeuse’s surface. If Betelgeuse was dim and warm – it was dust. Dim and cold, well, that’s convection. It turns out, Betelgeuse is one warm star. The physics of this is kind of cool. The star periodically puffs out parts of its atmosphere, and as this material drifts away from the star it cools and coalesces into dust. If Betelgeuse wasn’t running away from some past event on a rapid track through the galaxy, this dust would form a nebula around Betelgeuse. Instead, it forms a train behind the star, making it impossible for us to determine how much dust this system has lost over time. 

Learn more from the University of Washington press release.