Differential rotation and magnetic torques in the interior of the Sun

Abstract

The frequencies of solar oscillations can be measured with extreme precision and 5-min oscillations reveal the internal structure of the Sun1–5. In particular, measurements of rotational splitting4 have provided the first reliable indications of the variation of angular velocity with radius6, while recent observations5 have yielded information on the variation with depth of latitudinal differential rotation. These results confirm theoretical predictions that the angular velocity decreases inwards in the convective zone7,8 but raise problems for dynamo models of the solar cycle. The suggestion that the core rotates with roughly twice the surface angular velocity has important implications both for the rotational history of the Sun and for other late-type stars, whose magnetic activity is closely correlated with rotation. Such a rapidly rotating core is hard to reconcile with the presence of any significant magnetic field pervading the entire radiative interior. We can only explain it by suggesting that the core contains a fossil field, unaffected by turbulence in the pre-main sequence Hayashi phase, that is decoupled from the rest of the star.