Phase Diagram for Spinning and Accreting Neutron Stars

Abstract

Neutron star configurations are considered as thermodynamical systems for which a phasediagram in the angular velocity ( phi ) - baryon number (N) plane isobtained with a dividing line N crit (phi) for quark coreconfigurations. Trajectories of neutron star evolution in this diagramare studied for different scenarios defined by the external torqueacting on the star due to radiation and/or mass accretion. They show acharacteristic change in the rotational kinematics when the star enters thequark core regime. For isolated pulsars the braking index signalfor deconfinement has been studied in its dependence on the massof the star. Model calculations of the spin evolution of accretinglow-mass X-ray binaries in the phase diagram have been performed fordifferent values of the initial magnetic field, its decay time as wellas initial mass and mass accretion rate. Population clustering ofthese objects at the line N crit (phi) in the phase diagramis suggested as an observable signal for the deconfinement phasetransition if it exists for spinnning and accreting neutron stars.