Betelgeuse’s bizarre dimming caused by eruption

In the autumn of 2019, red giant Betelgeuse began dimming significantly, losing about two-thirds of its brightness by February. This dramatic dip spurred speculation that the star’s demise may have been imminent – perhaps just weeks away, from our perspective, anyway. Betelgeuse lies about 500 light years from Earth, so everything we’re seeing with the star today happened centuries ago.

But the dramatic sky show didn’t happen: Betelgeuse powered through the dimming episode and returned to its normal brightness by May of this year. The recovery sparked a new round of speculation, this time about the dimming’s cause. Some scientists attributed the doldrums to a light-blocking dust cloud, whereas others said big starspots on Betelgeuse’s surface were likely to blame. The dust hypothesis adds a twist – Betelgeuse itself apparently coughed up the cloud.

Researchers studied the star in 2019 and 2020 using the iconic Hubble Space Telescope. Hubble’s observations from September through November 2019 revealed huge amounts of material moving from Betelgeuse’s surface to its outer atmosphere at tremendous speeds – about 320,000 kilometres (200,000 miles) per hour. During this three-monthlong outburst, Betelgeuse lost about twice as much material to space from its southern hemisphere as it normally does. Betelgeuse’s background shedding rate is significant – about 30 million times that of our Sun’s.