Even if you don’t know it by name, the red supergiant star Betelgeuse is one of the most familiar sights in the heavens above—a gleaming ruddy dot at the shoulder of the constellation Orion. Although already quite difficult to overlook, Betelgeuse has become even more eye-catching across the past few years because of major changes in its appearance—unexpected fluctuations in its brightness that remain poorly understood. In recent weeks, the star has at times shone more than 50 percent brighter than normal, drawing renewed attention from amateur sky watchers and professional astronomers alike. These individuals hopefully await a historic celestial event. Someday, you see, Betelgeuse will explosively end its life in a supernova—and from our planetary perch just 650 light-years away, we Earthlings will have front-row seats to this spectacular cosmic cataclysm.
But does the current bout of brightening presage Betelgeuse blowing its top? And what would such a nearby supernova look like?
Despite the fervent wishes of astronomers, it’s vanishingly unlikely that anyone alive today will get to see Betelgeuse’s big boom. Based on the star’s brightness, color, size and estimated age, scientists believe Betelgeuse is still early in the process of fusing helium into carbon—which it must then fuse into oxygen, followed by silicon and finally iron. At this point, Betelgeuse’s core will no longer be able to reap energy from further fusion reactions, leading the star to collapse under its own weight and blow itself to smithereens.
“We know that Betelgeuse will explode soon, but ‘soon’ is sometime within the next 10,000 to 100,000 years,” says Jared Goldberg, an astrophysicist at the Flatiron Institute in New York City. “I’m not gonna bet my career on Betelgeuse exploding…right now.”
When the day comes, however, it will be astonishing. The supernova’s first harbinger would be subtle but unmistakable—a flood of ghostly neutrinos emitted during the star’s collapse that would suddenly wash over Earth, lighting up detectors around the globe. Shortly thereafter, as high-energy photons burrowed out from the dense expanding cloud of stellar debris, the real fireworks would begin. “What we would see is Betelgeuse getting really bright—like 10,000, 100,000 times brighter than it normally is—on a timescale of a week,” Goldberg says. Depending on exactly how powerful the explosion turns out to be, the supernova remnant could become perhaps one quarter or half as bright as the full moon, concentrated into a single point of light—sufficiently luminous to be visible during the day and to cast stark shadows at night.
And the spectacle would linger long enough for everyone to see. “It stays really bright for a really long time—I mean, long for a news cycle, short for a human lifetime, infinitely short for a star’s lifetime,” Goldberg says. For astronomers, the explosion and its aftermath would be a watershed event, offering a unique opportunity for up-close observations that are bound to reveal a rich bounty of surprising discoveries.
Conveniently, Betelgeuse is far enough away that we humans wouldn’t suffer any harmful effects from the explosion itself. But humanity’s long history of supernova observations makes it clear that the event would still have consequences. “The sky would change so dramatically, and it would be so visible to everyone, that it would really cause a huge reaction around the world,” says Bryan Penprase, an astronomer at Soka University of America.
Stargazers of yore tended to perceive supernovae as bad omens, Penprase says, and in today’s climate of misinformation and science denialism, Betelgeuse’s demise could prompt some concerning responses. “In our time, when people are already a little bit unstable, having a star like that erupt would definitely trigger a lot of amusing, interesting and perhaps even alarming speculation from different sections of our population,” he says.
Although we’ve become rather disconnected from the heavens, Betelgeuse’s supernova would be impossible to ignore. “To be sort of jolted out of that complete unawareness of the sky by something as dramatic as this would have a huge impact,” Penprase says. “Maybe it could even rekindle a civilization-wide interest in astronomy.”
Betelgeuse’s modern-day antics don’t need to end with a bang to be intriguing, however, Goldberg argues. Its curious oscillation between dimming and flaring “is still evidence of some really cool physics out there,” he says. “The fact that stars are pulsating on human timescales is very cool.”
Astronomers have long known that Betelgeuse periodically brightens and fades—in fact, records from Aboriginal Australians and ancient Greeks alike suggest this cycle was already clear to various cultures across the planet millennia ago. In modern times that cycle has lasted around 400 days—but right now the star’s brightness is fluctuating much more rapidly, on the order of 130 days, says Andrea Dupree, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics, who tracks the star.
And Betelgeuse’s current dynamics seem to be connected to its so-called Great Dimming in late 2019 and early 2020, which scientists ascribe to the star’s ejection of a massive blob of gas and dust. “Just imagine if you take a hunk of the material out. Then everything else is going to swish in, and it’s going to slosh around,” Dupree says. The resulting mire of turbulent plasma and magnetic fields could help explain why the star is currently much brighter than the 400-day cycle would predict.
Dupree compares the off-schedule brightening to an unbalanced washing machine rattling around. “I think what’s happening is that the top layers are having a problem coming back to normal,” she says. “It’s going to eventually, we hope, come back to its 400 days, but right now it’s struggling.”