Abstract

The standard theory of stellar oscillations focuses primarily on the forces of pressure and buoyancy, while the effects of rotation and magnetic fields are assumed to be weak perturbations and usually ignored. Recent observations of red giants have suggested that in a substantial fraction of these stars the oscillations are subject to a source of damping localised to the core region, but this has neither been anticipated nor accounted for by standard theory. Indirect evidence argues for the role of a deeply buried fossil magnetic field within the core, but so far no convincing mechanism has been proposed that explains how the damping occurs. Here we present a mechanism for damping the observable modes of red giants harbouring magnetised cores that involves resonant interactions with standing Alfven waves of high harmonic index. The damping rates produced by this mechanism are quantitatively on par with those associated with turbulent convection, and in the range required to explain observations, for realistic stellar models and magnetic field strengths. Our results suggest that magnetic fields can provide an efficient means of damping stellar oscillations, and lay the groundwork for an extension of the theory that incorporates these effects.