A well-known star in the constellation of Orion—the one that makes up Orion's right shoulder—has been the subject of an 18-month mystery that has now been solved. Betelgeuse rapidly dimmed in late 2019 and early 2020 to a degree that had never been recorded before and one that could be seen with the naked eye, per a press release. That spurred fears that the red supergiant was on the verge of exploding. Astronomers in Chile used the European Southern Observatory's Very Large Telescope, which is powerful enough to image the star's surface, to check things out. After analyzing images taken before, during, and after the loss of brightness and doing some modeling, they arrived at an answer, which they outlined in a study published in Nature: blame a dust cloud and a cool spot on the star's surface.
"Our overall idea is that there was a cool spot on the star which, because of the local drop in temperature, then caused gas ejected previously to condense into dust," study author Emily Cannon told the BBC. "So, the cool spot on the surface would initially make the star look dimmer to us. But then this condensation of dust would add to the rapid drop in brightness of the star." But she did express a sliver of sadness that Betelgeuse is unlikely to go supernova anytime soon (its the brightness was back to normal by April 2020). "I was kind of wishing it myself!" she said. The study notes that "red supergiants are the most common final evolutionary stage of stars that have initial masses between 8 and 35 times that of the Sun," which Betelgeuse does. As the BBC explains, the last supernova seen in our Milky Way Galaxy happened in 1604. Astronomers of the time wrote that when Kepler's Star went supernova, the event could be seen during the day for more than three weeks. (Read more discoveries stories.)