Betelgeuse, the 10th brightest star in the sky and one of the biggest known stars in our galaxy, has left experts in awe with its unbelievable speed. Scientists are perplexed at how a star so big, roughly 2,000 times bigger than our Sun, can spin so quickly, at roughly 5km (3.1 miles) per second.
A new study suggests that the data supporting the rotational speed could actually be tracking the star’s convection movement rather than its true speed. This red supergiant, floating around 700 light years away in the Orion constellation, is some 2,000 times larger than our Sun, with a 746-million-mile diameter. Betelgeuse’s photosphere—the star’s outer shell—is about the same radius as the orbit of Jupiter in our Solar System.
Despite its size and hypothetical explosive tendency, Betelgeuse’s rotational speed of about 5 kilometers (3.1 miles) a second is two orders of magnitude faster than scientists thought possible at this evolutionary stage. This has led to the question of whether Betelgeuse is doing something unexplainable or if the data gathered by Chile’s Atacama Large Millimeter/submillimeter Array (ALMA) isn’t telling the whole story.
A new study from scientists at the Max Planck Institute for Astrophysics suggests that ALMA may be recording the movement of the star’s convection cells rather than its true rotational speed. The results of the study were published in mid-February in The Astrophysical Journal Letters. According to Selma de Mink, director of the Max Planck Institute for Astrophysics and study co-author, Betelgeuse’s incredibly large and nearby nature allows scientists to observe and study its boiling surface with the very best telescopes.
The study explains that if Betelgeuse was a perfectly round sphere, then ALMA’s data would indeed represent its true rotational speed. However, because the star is not perfectly round, its convection movement may be affecting the data, leading to the misinterpretation of its rotational speed. The study suggests that the movement of the star’s convection cells could be creating an illusion of faster rotation, and further observations and studies are needed to clarify the true rotational speed of Betelgeuse.
