Star light, star not so bright
During January 2019, everything with Betelgeuse seemed normal. Then, a short time later, the star began to dim. By February 2020, it was just two-thirds its normal brilliance.
The cause of Betelgeuse’s dip in brightness initially baffled astronomers. But with this new research, they’ve charted a timeline of events leading up to the star’s dramatic dimming. They were able to do this because, beginning in January 2019, the Hubble Space Telescope periodically observed Betelgeuse in the ultraviolet wavelength, revealing new aspects of the stellar monster.
From September to November of 2019, the historic space telescope spotted signs of dense blobs of sizzling material moving through the star’s atmosphere. And by December, ground-based telescopes started to witness the star dimming.
“We think this [ejected] gas cooled down millions of miles outside the star to form the dust that blocked the southern part of the star imaged in January and February," lead author Andrea Dupree said in a press release.
"Only Hubble gives us this evidence [of what] led up to the dimming," Dupree added.
Lingering mysteries for Betelgeuse
Although scientists might have solved the case of Betelguese’s dimming, the goliath star isn’t done confusing astronomers just yet.
For one, the mass ejection that caused the dimming didn’t erupt from one of the star’s poles — which is where gravity should be weakest, thus making it easier for material to escape the star’s clutches. “We don’t know how [star’s like this] loose mass,” Dupree tells Astronomy. “Is it a nice wind that just goes out slowly forever or does it come out in puffs and bursts?”
Furthermore, NASA’s Solar Terrestrial Relations Observatory (STEREO) captured additional observations of Betelgeuse, published July 28 in The Astronomer’s Telegram, that showed another, smaller dip in the star’s brightness. And this one occurred nearly a year before Betelgeuse should be reaching a minimum.
“It shouldn’t be doing this,” Dupree says. “[But] maybe it’s going to be a little bump.” With consistent observations of the star dating back 150 years, it isn’t unusual for Betelgeuse to start getting faint and quickly brighten back up. Nonetheless, Dupree plans to observe Betelgeuse again through August and September, during the star’s expected maximum, to monitor for more unexpected outbursts.