About eight percent of red giants are covered by sunspot-like dark areas.
Starspots are more common among red giant stars than previously thought. In the journal Astronomy & Astrophysics, researchers led by the Max Planck Institute for Solar System Research (MPS) in Germany report that approximately eight percent of red giants exhibit such spots. They are the expression of strong magnetic fields at the stellar surface. These magnetic fields are created deep inside the star in a process that requires, among other things, convection and a fast rotation of the star. Although red giants are generally regarded as slowly rotating stars, those with starspots are apparently an exception. The new publication offers a comprehensive analysis of the reasons for their short rotation periods ranging from forced synchronization with another, closely neighboring star, to the swallowing of a star or planet, to a fast initial rotation speed in an early phase of development.