NASA's Hubble Space Telescope has captured the reason behind why Betelgeuse, a red supergiant and among the brightest in our night sky, has unexpectedly begun to dim earlier this year.
In a report on the NASA website, a possible explanation for Betelgeuse suddenly dimming is its recent outburst. The star, about 700 light-years from our own Sun, has launched an incredibly large amount of debris into space. This formed a dust cloud that blocked starlight from the star's surface, making it appear dimmer.
Researchers further suggested that this monstrous dust cloud was created after the superhot plasma was ejected from a large convection cell on Betelgeuse's surface. The cloud then went through the atmosphere and to the relatively cooler outer layer, causing the plasma to cool and later form the dust cloud.
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It caused the Betelgeuse to appear dimmer, covering about a quarter of the star, starting back in October 2019. However, by last April 2020, the star is back to its usual brightness. This dimming was so notable that it was visible to the naked eye.
Betelgeuse's Traumatic Outburst
The dimming has caused astronomers to develop theories regarding the phenomenon. Observations from the Hubble Space Telescope were studied by a team of researchers led by Andrea Dupree. Dupree is the associate director for the Harvard-Smithsonian Center for Astrophysics.
The Hubble team has kept ultraviolet-light (UV light) spectroscopic observations of the dimming red supergiant, starting from January 2019. With the available UV-light observations of Betelgeuse, the team was able to create a timeline of Betelgeuse's brightness. These data were used in understanding the mechanism of how and when the star began dimming.
A dense cluster of superhot material began moving through the surface of Betelgeuse from September to November 2019. It was in December that several ground-based telescopes observed the dimming in the star's southern surface.
"With Hubble, we see the material as it left the star's visible surface and moved out through the atmosphere before the dust formed that caused the star to appear to dim," said Dupree in the press release. Dr. Dupree added that the material in the buildup was "two to four times" brighter than Betelgeuse's normal luminosity. "And then, about a month later, the south part of Betelgeuse dimmed conspicuously as the star grew fainter," she continued.
The team's report that details the timeline of Betelgeuse's dimming was published Friday, August 13, on The Astrophysical Journal.
A monstrous cloud of hot material exploding from its surface is most likely what caused the supergiant star Betelgeuse to dim last fall, @NASAHubble/@ESAScience observations suggest.
Our @NASASun spacecraft STEREO witnessed more odd behavior this summer: https://t.co/gvUxgTtOif pic.twitter.com/BmmxhLTVPf — NASA (@NASA) August 13, 2020
A Supergiant Nearing Its End
Betelgeuse is estimated to be twelve times as massive as our sun. Its age is dated to be less than ten million years, owing to its rapid evolution to its size. Astronomers generally agree that this red supergiant will explode into a supernova sometime in the next 100,000 years. This dimming was dated to have happened around the year 1300, but its light has just reached Earth recently.
Dupree also notes that a star turning into a supernova is a phenomenon that has not yet been observed before. However, she said that astronomers have "sampled" stars as close as a year before they went supernova, but not as immediately as a day or a week before.
The NASA press release also reported that Dupree would observe the star through the Hubble Space Telescope in August or September this year when it returns to the night sky. Currently, Betelgeuse is located in the daytime sky.
