The recent bizarre dimming of the star Betelgeuse was caused by spots that temporarily covered at least half of the star’s massive surface, a new study suggests.
Betelgeuse, which forms the shoulder of the Orion constellation, is one of the most famous and familiar stars in the night sky, and one of the most extreme.
Betelgeuse is a “red supergiant” 11 times more massive than our sun and 900 times wider. If transported to the center of our solar system, Betelgeuse would gobble up Mercury, Venus, Earth, Mars, and the asteroid belt. (That would be a long-distance trip for the red supergiant, which is about 500 light-years from Earth.)
Related: The brightest stars in the sky: a starry countdown
The bloated state of the star shows that Betelgeuse is in the final stages of its life, which will end in a violent supernova explosion. And last fall, the supergiant began to fade significantly, which led some astronomers to speculate that it is dramatic death may be imminent.
But Betelgeuse emerged from depression this spring, regaining its usual shine in May. This brilliant recovery led some astronomers to claim that the attenuation of the star had been caused by a dust cloud, which scientists thought may have blocked a large part of Betelgeuse’s light before reaching Earth.
But the new study suggests that attenuation was inherent in Betelgeuse. The researchers examined the supergiant in January, February, and March this year using the James Clerk Maxwell Telescope (JCMT) in Hawaii, which sees the cosmos in submillimeter light, a wavelength invisible to the human eye.
The team then compared these data with Betelgeuse’s observations made over the past 13 years, including images obtained by the Atacama Pathfinder Experiment, a telescope in Chile that also observes in sub-millimeter light.
“What surprised us was that Betelgeuse became 20% darker during its dimming event even in submillimeter light,” said study lead author Thavisha Dharmawardena, a postdoctoral researcher at the Max Planck Institute for Astronomy in Germany, he said in a statement.
“This behavior is not entirely consistent with the presence of dust,” said Dharmawardena. “It was very exciting to realize that the star herself had undergone this massive change.”
The combined data suggests that Betelgeuse’s attenuation was associated with a drop in mean surface temperature of around 360 degrees Fahrenheit (200 degrees Celsius), the researchers said. (The star’s usual temperature is about 5,840 degrees F, or 3,230 C.)
But this drop in temperature is unlikely to occur symmetrically across the star, given that Betelgeuse’s high-resolution images collected in December 2019 show brightness intensities that are decidedly irregular.
“Along with our result, this is a clear indication of huge stars that cover between 50% and 70% of the visible surface, each with a lower temperature than the rest of the surface,” said Dharmawardena.
Star dots are relatively cool dark patches of time on a star’s surface that have very strong magnetic fields. Our own sun has them; astronomers have been counting Sunspots for hundreds of years as a way to measure stellar activity. (Sunspots serve as launching pads for solar storms like flares and huge plasma flares known as coronal mass ejections.)
These researchers will continue to study Betelgeuse with the JCMT over the next year or so to learn more about the supergiant, whose disappearance will have a major impact on its cosmic neighborhood.
“Previous generations of stars like Betelgeuse have physically manufactured most of the elements we find on Earth, and in fact in our bodies, distributing them throughout the galaxy en masse supernova explosions“JCMT Chief Scientist Steve Mairs said in the same statement.
“While we can’t predict when the star will explode, tracking its brightness will not only allow us to better understand the evolution of an interesting class of stars, but it also helps write a page in our own cosmic history,” said Mairs.
The new study was published online Monday (June 29) in The letters of the astrophysical journal.
Mike Wall is the author of “Out There” (Grand Central Publishing, 2018; illustrated by Karl Tate), a book on the search for extraterrestrial life. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or Facebook.
