The magnetic field of Betelgeuse: a local dynamo from giant convection cells?

Betelgeuse, one of the apparently brightest stars in the sky, is an M supergiant with a complex extended atmosphere. Its very long rotation period is considered too long to sustain a solar-type dynamo, and any fossil magnetic field from previous evolutionary phases is expected to have been diluted away. The large convection cells observed on Betelgeuse have, on the other hand, been predicted to generate magnetic fields through a local dynamo mechanism, Auriere et al. detect a variable magnetic field, which probably matches that mechanism and which is likely to be dynamically important in the envelope. The INSU has issued a press release based on these results.