Why did red supergiant Betelgeuse dim last year mysteriously? 'Traumatic outburst' could be the reason: NASA

The Hubble space telescope has given scientists a peek into the past, allowing them to reconstruct the events that led up to the dimming


                            Why did red supergiant Betelgeuse dim last year mysteriously? 'Traumatic outburst' could be the reason: NASA
(Getty Images)

When Betelgeuse — one of the brightest stars in the sky — went dim in 2019, it left astronomers intrigued. Now, NASA's Hubble telescope has revealed a possible explanation for the red supergiant's mysterious behavior. According to the theory, an outburst of hot and dense material emanating from the star led to the dimming. 

This, however, is not the first theory. Previously, some scientists thought that the loss of brightness signaled an impending death. Others believed that cosmic dust was behind the fading. More recently, scientists proposed that Betelgeuse may have had large starspots — similar to our Sun's spots — covering 50% to 70% of its surface, leading to the subsequent dimness. According to NASA, Betelgeuse, which is 725 light-years away, is an aging star that has swelled in size due to reactions at the core. "The star is so huge now that if it replaced the Sun at the center of our solar system, its outer surface would extend past the orbit of Jupiter," the space agency said.

The Hubble space telescope has given scientists a peek into the past, allowing them to reconstruct events that led up to the dimming. The observation suggested that Betelgeuse is likely to have expelled hot material from its surface. It was two to four times brighter than the star's usual brightness, Andrea Dupree, associate director of the Center for Astrophysics, Harvard & Smithsonian (CfA), said in a statement. This, in turn, may have generated a dust cloud, keeping starlight from reaching the Earth.

This four-panel graphic illustrates how the southern region of the rapidly evolving, bright, red supergiant star Betelgeuse may have suddenly become fainter for several months during late 2019 and early 2020
(NASA, ESA, and E Wheatley (STScI))

 

The hot, dense material was moving from the star's surface into its outer atmosphere at about 200,000 miles per hour. It continued its journey outwards. As it reached millions of miles away from the giant, the material cooled down to become dust, the researchers said. Hubble captured material getting out from the red supergiant through September, October and November 2019. Then, in December, telescopes on Earth detected a drop in brightness. By mid-February 2020, the supergiant had lost more than two-thirds of its sheen.

The monster returned to its former glory by April 2020. But, new observations from NASA's space-based observatory, STEREO, showed it is dimming again. Typically, the star undergoes a 420-day cycle between two states: brightening and dimming. "The previous minimum [occured] in February 2020, meaning this dimming is happening unexpectedly early," NASA said. "This is an intriguing phenomenon that scientists will study with additional Earth-orbiting and ground-based observatories when Betelgeuse returns to the night sky in late August," they added.

Is Betelgeuse going supernova? Dupree is unsure. "No one knows what a star does right before it goes supernova because it's never been observed," she explained. "Astronomers have sampled stars maybe a year ahead of them going supernova, but not within days or weeks before it happened. But the chance of the star going supernova anytime soon is pretty small." Next, the researchers will use STEREO to closely watch the supergiant's behavior, including investigating whether an outburst repeats next year.

The study is published in The Astrophysical Journal.

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