New data processing technology provides new answers
Among all the stars in the heavens, Betelgeuse poses a special mystery for astronomers. One of its many secrets is its high rotation speed, which is incommensurable for a supergiant star. If we moved it to the position where the Sun is, then the visible layer, the photosphere, would cover the orbit of Jupiter and move at a speed of 5 km/s. New research hints that this is due not so much to the speed of rotation as to the intense «boiling» on the surface of the star, which was erroneously interpreted as rapid rotation.
It is one of the first stars that astronomy lovers notice in the heavens. Betelgeuse is recognizable by its characteristic reddish glow in the upper left corner of the constellation Orion. It is easy to detect and identify, and can also serve as a reference point for orientation in the night sky. It is known that stars — large objects, but Betelgeuse takes this feature to a new level with its gigantic size: its diameter is 1.2 billion kilometers, which is about 2000 times the diameter of the Sun. Stars of this size are usually assumed to rotate slowly, but observations indicate a high rotation rate, higher than expected for a star at this stage of evolution.
To measure the rotation speed of Betelgeuse, a powerful radio interferometer was used — Large Atacama millimeter grille. This system consists of 66 antennas that combine their signals to produce more accurate data. Using ALMA, astronomers concluded that one hemisphere of the star is approaching while the other is moving away, causing a rotation speed estimated at 5 km/s. It was natural to assume that if Betelgeuse were a sphere, then this would be a logical conclusion. However, its surface — non-spherical.
Like all stars, convection — This is an important process in the photosphere that brings heat from the interior of the star. In the case of Betelgeuse, the convection cells are gigantic in size, sometimes reaching the size of the Earth's orbit. These cells rise and fall at a speed of about 30 km/s, which is faster than the speed at which the Earth moves around the Sun in space.
Dr. Jing-Jie Ma of the Max Planck Institute for Astrophysics has put forward a hypothesis that may provide an explanation for Betelgeuse's mysterious rotation rate. According to his theory, the dipolar velocity map, previously used to determine the approaching and receding hemispheres, could actually record convection cells rising on one side of the star and sinking on the other. ALMA's limited resolution did not allow these cells to be clearly differentiated, leading to misinterpretation of the observed rotation rates. This new understanding calls into question previous ideas about Betelgeuse and opens up the possibility of further research into convection processes in this star.
To test this hypothesis, a team of astronomers developed a new data processing technique and obtained high-resolution synthetic data. In 90% of cases, the movement of the convection cells was not distinct and could be perceived as a high rotation speed. Further observations will be required to investigate this possibility more deeply, but this requires more precise tools. For this purpose, observations with a higher resolution have already been carried out in 2022, and the data obtained are now being analyzed. However, it is hoped that these data will help reveal even more details about the nature and characteristics of Betelgeuse.