Betelgeuse, the red supergiant star that acts as the shoulder of Orion in his constellation, intrigued astronomers when the normally bright star showed signs of unprecedented dimming in December. Many have suggested potential causes for this dimming, including dust or the fact that the star is likely to explode in a supernova between now and 100,000 years from now.
New research has suggested that large star spots, like sunspots on our sun, are on the surface of Betelgeuse and causing the dimming. The researchers said their result rules out the dust scenario, which suggested that Betelgeuse ejected dust and it was obscuring the star.
The study published Monday in The Astrophysical Journal Letters.
Betelgeuse is estimated to be a few million years old and is about 700 light-years away. And the “supergiant” name is no joke: According to NASA, the star is thought to be somewhere between the diameter of Mars and Jupiter’s orbits in size. It’s estimated to be between 11 to 12 times the mass of our sun.
Astronomers expected it to begin dimming in December because the star experiences periods of dimming and subsequent brightening every 425 days.
However, Betelgeuse dropped to 40% of its normal luminosity between October 2019 and April 2020, which surprised astronomers.
Thavisha Dharmawardena, a postdoctoral researcher at the Max Planck Institute for Astronomy in Germany, led a team of international astronomers as they studied Betelgeuse amid this unusual dimming episode. The team’s data showed that temperature variations in the surface of the star caused the drop in brightness. And the most probable cause of this would be gigantic star spots covering 50% to 70% of Betelgeuse’s surface.
“Towards the end of their lives, stars become red giants,” Dharmawardena said in a statement. “As their fuel supply runs out, the processes change by which the stars release energy. As a result, they bloat, become unstable and pulsate with periods of hundreds or even thousands of days, which we see as a fluctuation in brightness.”
The star is so massive that the gravitational pull on the surface is less than that of a smaller star, so any pulsating by the star can actually eject layers of it easily. When this gas released by the star cools, it essentially forms dust.