Stars create magnetic fields through convection, the swirling, Ferris-wheel-like motion of hot, ionized gas (or boiling water, for that matter). Where convection happens in a star depends on how massive the star is: low-mass stars, including the Sun, have convective outer envelopes around a non-convective core, but stars a little bulkier — up to a couple Suns’ worth — do have convective cores.
Recently, Jim Fuller (Caltech) and colleagues found that strong core magnetic fields could explain the oddly weak, on-and-off brightening behavior of a sample of red giant stars. These stars are low- to middle-mass and have stopped fusing hydrogen in their centers, so they don’t have convective hearts. They also often have a mismatched, variable glow, with one hemisphere brightening as the other fades. What was strange about the sample the team looked at was that this group didn’t vary as much in brightness as it should have.
Read the full story at Sky & Telescope
Read the letter by Stello, Dennis et al. “A prevalence of dynamo-generated magnetic fields in the cores of intermediate-mass stars.” Nature. January 21, 2016.