Three years ago, a star in Orion inexplicably dimmed. Astronomers finally know why - Salon

So when astronomers noticed in 2019 that Betelgeuse had dimmed, some speculated that the massive star was going to expand into a supernova so large it would be visible from Earth even during the daytime hours.

Novas or supernovas that are visible with the naked eye are rare, and when they do happen, they tend to be generation-defining events: the last time a nearby star went supernova, in 1604, it was so bright that it was visible during the daytime. .

But now, thanks to a group of scientists using the Hubble Space Telescope, we now know the cause of Betelgeuse's Great Dimming: A coronal mass ejection (CME), or a phenomenon in which a star's corona (or crown) erupts with a massive cloud of highly magnetized and energetic plasma.

Yet astronomers "could see material moving out through the star's atmosphere (in the southern part of the star) using the Hubble Space Telescope," Dupree explained