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December 27, 2019
A young, bright star has been acting a little erratic lately.
The star, Betelgeuse, is suddenly dimming. It may be a sign, astronomers say, that the star is about to explode. Another possibility is the red supergiant may just be going through a phase.
Ed Guinan, an astronomy professor at Villanova University, was the lead author on a December 8 paper entitled "The Fainting of the Nearby Supergiant Betelgeuse."
He told CNN that Betelgeuse (pronounced: BAY-tel juice) been declining in brightness sharply since October, and was now about 2.5 times fainter than usual. Once the ninth brightest star in the sky, Betelgeuse has fallen now to about the 23rd brightest.
Guinan and his colleagues have been closely observing the star for decades, with "continuous coverage since 1980," he said.
In the last half-century, the star has never dimmed so aggressively, and that could mean we're on the verge of something extraordinary.
"What causes the supernova is deep inside the star," Guinan said. And because the star is so huge, it's impossible to tell what's going on so far down.
Image above: The red supergiant star Betelgeuse is seen here in a new view from the Herschel Space Observatory.
It could be a prelude to a supernova
Betelgeuse is the star at the shoulder of Orion, the iconic constellation in the shape of a hunter wielding a bow in the night sky. Its name is derived from the Arabic for "hand of Orion."
The star, which is about 700 light years away from Earth, is a relatively close neighbor within our galaxy.
"What's special about this is how close it is," Guinan said.
Guinan said it's the most likely nearby supernova candidate. It's about nine million years old, and stars as large as Betelgeuse don't usually have lifespans past 10 million years. Though its time is nigh, it probably won't explode in your lifetime.
"It'll probably happen in the next 200,000 or 300,000 years," Guinan said.
It's a variable star, which means it regularly dims and brightens, in cycles that can last about 420 days. Betelgeuse has been in a normal dimming period over the past few months, but it's just dramatically accelerated compared to past years.
Herschel Space Observatory
The dimming process should end by mid-January, according to mathematical models. But Betelgeuse often follows its own rules, he says.
"I personally think it's going to bounce back, but it's fun to watch stars change," Guinan said. However, he adds, "If it continues dimming, then all bets are off."
If it exploded, it would be be bright enough to see during the day
That might mean we're on the verge of a brilliant light show, because if a star this close exploded, it would make an impact.
Giant star (supernova) explosion
Stars rapidly fuse various elements in their cores. And if Betelgeuse burns down to an iron core, which won't fuse, that core could collapse rapidly, leading to a supernova.
The red supergiant would glow a vibrant blue for three of four months, and would take about a year to fade out.
"It would be a really bright star visible in the daytime," Guinan said.
There wouldn't be any direct danger to life on earth, but ultraviolet radiation from the celestial blast could scorch ozone in our atmosphere.
Betelgeuse has been acting strangely for years
Betelgeuse's curious behavior has stuck out in other ways over the decades.
In 2009, the late astronomer and Nobel Laureate Charles Townes told CNN he had observed Betelgeuse shrinking 15% since the mid 1990s.
Back then, Townes and his colleagues were puzzled because as stars usually get brighter as they shrink. Betelgeuse, however, was dimming.
The star has been acting differently in the past few months, and it's anyone guess what all the unusual readings may mean.
"It might then be a very small bright star, or it might even be a black hole. An explosion would be very surprising," Townes said at the time.
Herschel Space Observatory: https://www.herschel.caltech.edu/ and https://sci.esa.int/web/herschel
Images, Animation, Text, Credits: NASA/ESA/CNN/By Ryan Prior.