Giant Spots Found On The Surface Of The Star Betelgeuse
Observations of the last dimming of Betelgeuse showed that its surface is covered with giant spots. Astronomers believe that they cover 50 to 70% of the star's surface, according to an article describing the research published by the scientific journal Astrophysical Journal Letters.
"We were surprised that the brightness of Betelgeuse decreased by 20% even in the submillimeter range. This suggests that the dimming of this star was hard since its light from us was blocked by a huge cloud of dust. The luminosity of the sun itself has changed," commented one of its authors, an astronomer from the East Asian Observatory (USA), Steve Mairs.
Betelgeuse is one of the largest and brightest stars in the sky, located in the constellation of Orion. Due to its huge size and mass, which is 15-25 times larger than the sun, and the fact that it is located near the Earth, Betelgeuse can be easily seen even with the naked eye. If this star were located in the center of the Solar system, its outer layers would reach the orbits of Mars or Jupiter.
Astronomers believe that Betelgeuse is now at the last stage of stellar evolution – the stage of a red supergiant. This is what scientists call elderly stars that have almost run out of hydrogen; they have expanded dramatically and started dumping the substance of their outer shells into outer space. Because of this, a huge amount of dust is formed and bright gas-dust nebulae are formed.
Some features of Betelgeuse's brightness fluctuations indicate that this star will end its existence in the next few thousand years. It will turn into a supernova, the flash of which on Earth can be seen even during the day. Because of this, both professional astronomers and ordinary people are interested in the fate of Betelgeuse.
At the end of December last year, scientists began to notice that Betelgeuse was rapidly fading. By the beginning of January, its luminous intensity had decreased by about 63%, reaching a record low for the last 25 years of observations; its fading further spurred the interest of astronomers.
The first such observations, as noted by Mairs and his colleagues, were made by scientists using optical telescopes. Because of this, they were not able to determine the exact cause of the fading. Astronomers offered three explanations: a real decrease in the brightness of the entire surface of Betelgeuse, the appearance of spots on it, and the formation of a giant cloud of dust between the Sun and the star.
Mairs and his colleagues tried to find out the real cause of this phenomenon using two microwave observatories – the James Maxwell telescope in the Hawaiian Islands, as well as the APEX telescope, which is installed at the Chilean high-altitude Observatory Chahnantor.
In the range to which these telescopes were tuned, microwave radiation interacts particularly actively with cosmic dust particles. If Betelgeuse was actually blocked by a cloud of dust, then telescopes should have detected an excess of such radiation. A decrease in brightness, in turn, would indicate that the star has dimmed.
The data showed that the second theory was closer to the truth. Despite a large amount of dust in the vicinity of red supergiants, the brightness of Betelgeuse in the microwave range fell by 20%. According to scientists' calculations, something similar would have happened if the surface of this star became colder by 200 Kelvins.
As Mairs and his colleagues point out, this is quite possible. However, another option is more likely, which is indicated by the December photos of Betelgeuse. Researchers suggest that between 50 and 70% of the star is covered by giant spots. Like spots on the Sun, they are points where the magnetic field of the star "breaks out" and slows down the circulation of plasma in the bowels of the star. As a result, the surface at these points becomes colder.
According to the researchers, the dimming of Betelgeuse could be due to the fact that this star has a minimum of stellar activity, which is similar to the one that recently ended on the Sun. Mairs and his colleagues hope to confirm this theory in the course of the next observations when Betelgeuse "wakes up." Then the brightness of the star will grow again.