A new theory has emerged regarding the “Great Dimming” period of Betelgeuse. Known as one of the biggest and most luminous stars in the night sky (it is located in the Orion constellation), it is also very mysterious.
Between October 2019 and March 2020, this red supergiant star’s brightness dimmed 2.5 times which was the biggest drop in 50 years. Known as the “Great Dimming”, the decrease in brightness caused a drop in surface temperature of about 300 degrees Fahrenheit (149 degrees Celsius).
While scientists scrambled to figure out what was causing such a dim in the star, several theories emerged, such as a giant dust cloud that moved between Earth and Betelgeuse that temporarily blocked us from seeing the light; it was about to go supernova; and “cool star spots” that covered about 70% of the star’s surface. Even though the star’s luminosity had dipped dramatically, the theory of it going supernova was dismissed when it started brightening up again.
And now, there is a new theory that suggests a large dark spot is covering parts of the star’s surface. While this is another interesting hypothesis, experts can’t confirm or deny the idea as a large dark spot has never been directly observed on the star.
The research team studied Betelgeuse’s temperature by analyzing the high-resolution near-infrared spectra of the star on four specific dates -- January 31, March 19, April 4, and April 6, 2020. These four dates coincide with the dimming and post-dimming phases of the star.
Dr. Sofya Alexeeva explained their research in further detail, “Our method is based on the measurement of titanium oxide (TiO) and cyanide (CN) molecular lines in stellar spectra.” “The cooler a star is, the more these molecules can form and survive in its atmosphere and the molecular lines are stronger in the stellar spectrum.” “In a hotter atmosphere, these molecules dissociate easily and do not survive.”
Since the decrease in brightness caused a surface temperature drop of about 300 degrees Fahrenheit, the researchers realized that the results of an earlier study predicting that 70% of the star’s surface was covered in spots was similar to their findings. However, they believe that it is just one gigantic dark spot that is actually quite common on red supergiants.
While this is just the most recent of several theories regarding Betelgeuse’s “Great Dimming” period, the mysterious red supergiant star will continue to amaze and baffle us at the same time. (More pictures of Betelgeuse can be seen here.)
The study was published in the journal Nature Communications where it can be read in full.