Three-dimensional modeling of red supergiants has allowed an international team of astrophysicists to better understand unusual observational data from Betelgeuse. In their new study, scientists showed that such observations can be explained by boiling, or more precisely, by large-scale convective motion of the star’s atmosphere.

Betelgeuse is one of the brightest stars in the northern hemisphere and one of the closest red supergiants to Earth. Because of its location and size, it was in many respects the first star after the Sun from which astronomers obtained images of the disk and its spots. If Betelgeuse were the home of our star, its atmosphere would reach the orbit of Jupiter.

Recently, Betelgeuse has not attracted much attention from astronomers simply because of the change in brightness that indicates a supernova explosion. Although there was no explosion and the “great extinction” was explained by the birth of a cosmic dust cloud, the miracles did not end there. Observations made by the ALMA radio telescope complex in the Atacama Desert and their interpretations showed that the star was rotating much faster than scientists expected from a red supergiant.

During evolution, most stars gradually expand and slow down to preserve their angular momentum. However, considering ALMA’s observational data, Betelgeuse’s surface should be rotating at a speed of more than five kilometers per second; this is twice as high as theoretical predictions. As possible explanations, researchers hypothesized absorption by a nearby star or a planet.

This interpretation did not sit well with the international group of astrophysicists led by experts from the Max Planck Institute for Astrophysics. Researchers have suggested that Betelgeuse’s “boiling” surface could simulate rotation. To prove this, scientists performed 3D simulations of non-rotating red supergiants, which were then post-processed to predict possible ALMA images.

As a result of modeling and image processing, astrophysicists reproduced the result of real observations in 90 percent of cases. They obtained images of red supergiants with surface rotation speeds of several kilometers per second. The researchers described the results of their study in an article published in a journal. Astrophysics Journal Letters .

According to the authors, a kind of illusion arises because the accumulation of boiling convective flows rises on one side of the star, while another group descends on the other. Due to the limited resolution of the ALMA telescope, such convective motions of the red supergiant atmosphere will be blurred in real observations. This will lead to the emergence of a bipolar velocity field (when one part of the object moves towards the observer, the other moves away from it) and the illusion of rotation of the star.

“There’s still a lot we don’t understand about seething giant stars like Betelgeuse. How do they actually work? How do they lose weight? What molecules can form inside them? Why did Betelgeuse suddenly become less bright? We’re working hard to make our computer simulations better and better. But We also need new, incredibly detailed observations from telescopes like ALMA to test our models,” conclude the authors of the new study.