Rotochemical Heating in Millisecond Pulsars: Formalism and Nonsuperfluid Case

Abstract

Rotochemical heating originates in a departure from beta equilibrium due to spin-down compression in a rotating neutron star. The main consequence is that the star eventually arrives at a quasi-equilibrium state, in which the thermal photon luminosity depends only on the current value of the spin-down power, which is directly measurable. Only in millisecond pulsars the spin-down power remains high long enough for this state to be reached with a substantial luminosity. We report an extensive study of the effect of this heating mechanism on the thermal evolution of millisecond pulsars, developing a general formalism in the slow-rotation approximation of general relativity that takes the spatial structure of the star fully into account, and using a sample of realistic equations of state to solve the non-superfluid case numerically. We show that nearly all observed millisecond pulsars are very likely to be in the quasi-equilibrium state. Our predicted quasi-equilibrium temperatures for PSR J0437-4715 are only 20% lower than inferred from observations. Accounting for superfluidity should increase the predicted value.