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The weird and mysterious darkening seen last year in the huge star Betelgeuse may be due to giant sunspots and temperature fluctuations.
A new study suggests that a “large dark spot” caused the surface temperature of Betelgeuse to drop, which in turn contributed to a temporary dimming of the luminosity or inherent luminosity of the red giant.
The brutal fading made headlines around the world in 2020 as speculation mounted about what was going on. The science is still unclear, but astronomers blame everything from gas cloud emissions and dust to stellar fluctuations before Betelgeuse finally exploded into a supernova.
Related: Scientists are still stranded on Betelgeuse one year after strange gradation episode
The new study, led by the Chinese Academy of Sciences, looked at molecules in Betelgeuse’s spectrum – or light signature – to try and figure out what was going on. To do this, they used the Weihai Observatory (based at Shandong University in Jinan) four times in 2020 during the dimming and re-lighting period: January 31, March 19, April 4, and April 6.
To estimate the star’s temperature, astronomers looked at molecules of titanium oxide and cyanide, which tend to form more easily in colder star environments.
“The colder a star, the more these molecules can form and survive in its atmosphere – and molecular lines are stronger in the stellar spectrum,” lead author Sofya Alexeeva said in a statement on Thursday (August 5th). “In a warmer atmosphere, these molecules easily dissociate and do not survive,” Alexeeva added.
When Betelgeuse was at its peak on January 31, 2020, its effective temperature – that is, the temperature calculated from its emitted radiation – was measured at 3,476 degrees Kelvin (approximately 5,800 degrees Fahrenheit or 3,200 degrees Celsius .)
But once the star returned to normal brightness, measurements indicated an increase in temperature of almost 5% at 3,646 Kelvin (about 6,100 F or 3,370 degrees C.)
Given that Betelgeuse could still be several hundred years away from becoming a supernova, astronomers said in their research paper, which was published Thursday August 5 in the journal Nature Communications, they concluded that it is unlikely that the entire surface temporarily cools down by this amount. . Rather, it had to be a sunspot – or rather a “star spot” – preventing some of Betelgeuse’s radiation from escaping, they said.
Star spots, like sunspots that appear on the sun, are said to be common on giant red stars such as Betelgeuse. Defects arise as disturbances in the magnetic field flux from a star to the photosphere, or the visible surface of the star. Sunspots tend to be large clusters of magnetic activity and can result in flares or particle emissions known as coronal mass ejections – the source of the solar wind in our solar system.
While this temperature study focused on the gradation of Betelgeuse, the team said future research in this area may better inform our study of all red giants – the main source of heavy elements in the universe, by because of the tendency of stars to explode and spit out matter.
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