Abstract

This project aims at studying several effects related to rotation and magnetic fields, mostly in neutron stars (NSs), but with some extension to other stars: 1. Rotation-induced reheating processes in old NSs: Standard, passive cooling models predict that NSs will be very cold a few million years after their birth. However, at that point, their rotation still decreases progressively, which can induce at least two dissipative processes that affect the thermal evolution, possibly keeping the stars at a detectable temperature: rotochemical heating, predicted by the present PI, and vortex friction, proposed by other authors. The resulting thermal emission appears to have been detected in one object so far, and we have an approved HST program to observe another three. This will allow us to compare to the two models and constrain various parameters in the NS interiors. 2. Magnetic fields in NSs: There are various pieces of observational evidence suggesting that NS magnetic fields evolve in time. I propose to study the hypothesis that, at the birth of the NS, the magnetic field organizes into a stable ideal-MHD equilibrium configuration, which later evolves by non-ideal-MHD processes such as Hall drift in the crust and ambipolar diffusion and weak interactions in the core, stressing the NS crust, which might break violently, and releasing energy to power magnetars. The relatively short time scales and high energy release of magnetars and the weak, but non-zero magnetic fields of millisecond pulsars might be natural consequences of this scenario, which we intend to study through analytical calculations and numerical simulations in 2 and 3 dimensions. 3. Differential rotation and magnetic torques in stars: I propose to study how a pre-existing radial magnetic field can couple different layers within a rotating star, transporting angular momentum between them, and thus impeding differential rotation. This is likely to prevent any significant differential rotation inside neutron stars (except for a possibly decoupled neutral superfluid component) and to explain the relatively slow rotation of red giant cores recently measured by Kepler satellite asteroseismology.