On a clear winter night, it’s difficult to miss Orion the Hunter, who holds his shield in one hand and stretches his other arm high into the sky. Betelgeuse, a bright red dot on Orion’s shoulder, has captivated sky gazers for thousands of years with its strange dimming. Aboriginal Australians may have even worked it into their oral histories.
Today, astronomers know that Betelgeuse varies in brightness because it’s a dying, red supergiant star with a diameter some 700 times larger than our Sun. The star will eventually explode as a supernova, providing humanity with a celestial show before vanishing from our night sky forever.
That eventual explosion explains why astronomers were so excited in 2019 when Betelgeuse began to dim dramatically. The brightness of the 11th brightest star decreased by two-and-a-half magnitude. Could Betelgeuse have reached the end of its life? While unlikely, the idea of a supernova appearing in Earth’s skies caught the public’s attention.
And now, thanks to new simulations, astronomers have a better idea of what humans will see when Betelgeuse explodes in the next 100,000 years.
Supernova seen from Earth
With all the speculation about how a Betelgeuse supernova would appear from Earth, astronomer Andy Howell of the University of California, Santa Barbara, got tired of the back-of-the-envelope calculations. He entrusted the problem to Jared Goldberg and Evan Bauer, two UCSB graduate students, who created more precise simulations of the star’s final days.
The astronomers say there’s still uncertainty over how the supernova would play out, but they were able to augment their accuracy using observations taken during Supernova 1987A, the closest known star to explode in centuries.
The Earth’s life will be unaffected. But that isn’t to say it will go unnoticed. Goldberg and Bauer discovered that when Betelgeuse explodes, it will shine as bright as the half-Moon — nine times fainter than the full Moon — for more than three months.
“All this brightness would be concentrated into one point,” Howell says. “So it would be this incredibly intense beacon in the sky that would cast shadows at night, and that you could see during the daytime. Everyone all over the world would be curious about it, because it would be unavoidable.”
Humans would be able to see the supernova in the daytime sky for roughly a year, he says. And it would be visible at night with the naked eye for several years, as the supernova aftermath dims.
“By the time it fades completely, Orion will be missing its left shoulder,” adds Sarafina Nance, a University of California, Berkeley, graduate student who’s published several studies of Betelgeuse.
Ongoing observations of Betelgeuse reveal that we still have much to learn about its structure.
Observations of the red giant revealed that gas that is leaving the star is colder than astronomers thought it would be. Scientists aren’t sure how so much mass left the star, while not generating a lot of heat, they said in a 2016 study. Possible explanations include magnetic fields, or shockwaves, but more work will be needed to confirm the models. Astronomers are also doing comparison studies with another red supergiant star, Antares, to better understand the situation.
Meanwhile, scientists remain puzzled by Betelgeuse’s ultra-fast rotation, which is about 150 times faster than expected. This may have happened if the star swallowed a sun-mass star about 100,000 years ago, according to a 2016 study. Given Betelgeuse’s huge size — it’s 1,000 times wider than our sun, or 860 million miles (1.4 billion kilometers) across — it should be spinning much more slowly, astronomers suggest.
In 2017, the Atacama Large Millimeter/submillimeter Array Telescope (ALMA) took its first image of Betelgeuse’s surface (image below), which astronomers said was the highest-resolution image yet obtained of the star.