The mysterious dimming observed in the giant star Betelgeuse last year may be due to massive sunspots and temperature fluctuations. Astronomers in a new study suggest that it will take hundreds of years for Betelgeuse to temporarily cool down.
A recent study reveals a “large dark spot” leading to a drop in Betelgeuse’s surface temperature, contributing to the temporary reduction in brightness or the inherent brightness of the red giant star.
Betelgeuse in a material ejection event from its atmosphere that caused it to temporarily dim a few years ago – Image: ESO
This significant decline made headlines worldwide in 2020, sparking speculations about what was happening. Although science is not entirely clear, astronomers have blamed everything from gas emissions to dust and the oscillation of stars before Betelgeuse eventually explodes as a supernova.
The new study, led by the Chinese Academy of Sciences, examined molecules in Betelgeuse’s spectrum to understand what was occurring. To do this, they used the Uighur Observatory (based at Sun Yat-sen University) four times in 2020 during the dimming and brightening periods: on January 31, March 19, April 4, and April 6.
To estimate the star’s temperature, astronomers examined the molecules of titanium oxide and cyanide, which tend to form more easily in colder star environments.
“The colder the star, the more these molecules can form and exist in its atmosphere, and the stronger molecular lines in the star’s spectrum,” said lead author Sofya Alexeeva in a statement on August 5.
From late 2019 to early 2020, Betelgeuse dimmed more than 2.5 times, the most significant dimming observed in decades.
However, when the star returned to its normal brightness, measurements showed a nearly 5% increase in temperature to 3,646 Kelvin (about 3,370 degrees Celsius).
Astronomers stated in a research paper published on August 5 in the journal Nature Communications that Betelgeuse may take hundreds of years to temporarily cool down. Instead, it may be a sunspot or more accurately a “stellar spot” blocking some of Betelgeuse’s radiation from escaping.
Stellar spots, similar to sunspots on the Sun’s surface, are believed to be common on red giant stars like Betelgeuse. The dim spots form due to turbulence in the star’s magnetic flow, or the observable surface of the star. Sunspots are typically clusters of activity from large magnetic fields and can lead to bright spots or the emission of solar mass ejections – the source of solar winds in our solar system.
While this temperature study focused on Betelgeuse’s dimming, the research group noted that future studies in this field may provide better information for research on all red giant stars – the primary source of heavy elements in the universe, given their propensity to explode and eject matter into space.