Phase Diagram for Spinning and Accreting Neutron Stars

Neutron star configurations are considered as thermodynamicalsystems for which a phase diagram in the angular velocity (Ω)— baryon number (N) plane is obtained with a dividing line Ncrit(Ω) for quark core configurations. Trajectories of neutron star evolution in this diagram are studied for different scenarios defined by the externaltorque acting on the star due to radiation and/or mass accretion. They show a characteristic change in the rotationalkinematics when the star enters the quark core regime. For isolated pulsars the braking index signal for deconfinement has been studied in its dependence on the mass of the star. Model calculations of the spin evolution of accreting low-mass X-ray binaries in the phase diagram have been performed for different values of the initial magnetic field, its decay time as well as initial mass and mass accretion rate. Population clustering of these objects at the line N crit(Ω) in the phase diagram is suggested as an observable signal for the deconfinement phase transition if it exists for spinnning and accreting neutron stars.