A Giant Star Is Dimming, Which Could Be a Sign It Is About to Explode

A long time ago in a constellation not that far away, a bright star rapidly dimmed—and 600 years later, astronomers detected the change on Earth.

The star Betelgeuse comprises the shoulder of the constellation Orion, and its abrupt change in brightness hints that it may be on the brink of death. If this star is indeed at the end of its life, it will not go gently into that good night. Before Betelgeuse blips out for good, it will explode in a supernova—a violent stellar cataclysm that could outshine the moon and make it visible even in daylight, reports Deborah Byrd for EarthSky.

The chances of this stellar explosion happening anytime soon are pretty low, says Jackie Faherty, an astrophysicist at the American Museum of Natural History, on Twitter. But the star’s recent spate of symptoms has prompted some speculation. Once among the ten brightest stars in the sky, Betelgeuse has grown progressively dimmer since October, dropping out of even the top 20, reports Nadia Drake for National Geographic. A supernova, some say, could be nigh.

The star’s brightness has flickered before. Betelgeuse is a red supergiant about 700 times as wide as the sun, positioned about about 600 light-years from Earth. The giant is a variable star, meaning it regularly experiences dips in brightness. It's recent bout of faintness could be part of this regular cycle, but the star has dimmed more than at any other point in the last century.

When massive stars like Betelgeuse start to sound their death knells, their brightness is thought to ebb and flow more erratically as they eject enormous amounts of mass that can obscure their light, Sarafina Nance, who studies stellar explosions at the University of California, Berkeley, tells Drake. But humankind has never had the opportunity to closely observe a star in its final stages before—and whether this is what’s currently happening to Betelgeuse is far from guaranteed.

Astronomers are unsure what will happen next. Perhaps Betelgeuse will perk back up in a matter of weeks. But “if it keeps getting fainter, then all bets are off,” Edward Guinan, an astronomer at Villanova University, tells Drake.

Don’t hold your breath, though. Astronomers have known for decades that Betelgeuse is eventually going to go supernova—and, because of its distance from us, perhaps it already has. At 600 light-years away, Betelgeuse’s light takes 600 years to reach us. Perhaps the star blew its top in medieval times, and we have yet to see witness the aftermath.

The far likelier case, though, is that Betelgeuse’s end is still a long way off. Most astronomical predictions put its demise within a million years of present day, Elizabeth Howell reported for Space.com in 2017.

Still, that doesn’t mean you should shelve your telescope. Dying or not, Betelgeuse is worth a glimpse. And who knows? If it does boom out soon, this may be one of our last shots to glimpse the glowing red behemoth.

Katherine J. Wu | | READ MORE

Katherine J. Wu is a Boston-based science journalist and Story Collider senior producer whose work has appeared in National Geographic, Undark magazine, Popular Science and more. She holds a Ph.D. in Microbiology and Immunobiology from Harvard University, and was Smithsonian magazine's 2018 AAAS Mass Media Fellow.