An international team of astronomers led by researchers from the Max Planck Institute in Germany has offered an explanation for the remarkable rotation speed of Betelgeuse, the giant star in the Orion constellation about 650 light-years from Earth. The team published their findings in the Astrophysical Journal Letters (TAJL).
Betelgeuse ranks among the largest known stars. Its diameter exceeds 1 billion kilometers, dwarfing the Sun by nearly a thousandfold, and its mass is estimated to be 10 to 20 times that of the Sun. If Betelgeuse and the Sun swapped places, Betelgeuse would engulf Mercury, Venus, Earth, and Mars, and its atmosphere would reach out to the orbit of Jupiter.
Typically, stars broaden and slow their spin as they evolve, yet recent observations have shown Betelgeuse rotating at about 5 kilometers per second, a rate roughly 20 times faster than expected for a star of this type.
To study the star in detail, astronomers relied on the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile. Observations reveal a surface that is torrential with turbulence, dotted by boiling bubbles. Some of these bubbles are enormous, with sizes comparable to the Earth’s orbital diameter around the Sun, about 300 million kilometers.
By analyzing how these boiling regions form and dissipate, researchers concluded that Betelgeuse’s unusual spin is likely an illusion created by large-scale turbulent motions within the star’s outer layers. The simulations supported this view in about nine out of ten cases.
The team also notes that alternative explanations could exist for Betelgeuse’s peculiar behavior. One possibility is that the star could accelerate to the observed speed by consuming a smaller companion star, an idea that remains under discussion.
Earlier space observations suggested Betelgeuse exhibited changes in brightness that might indicate a merger with a neighboring star, a process that can briefly alter a red supergiant’s dynamics and appearance.