Constraining properties of rapidly rotating neutron stars using data from heavy-ion collisions

Abstract

Properties, structure, and thermal evolution of neutron stars are determined by the equation of state of stellar matter. Recent data on isospin-diffusion and isoscaling in heavy-ion collisions at intermediate energies as well as the size of neutron skin in $^{208}Pb$ have constrained considerably the density dependence of the nuclear symmetry energy and, in turn, the equation of state of neutron-rich nucleonic matter. These constraints could provide useful information about the global properties of rapidly rotating neutron stars. Models of rapidly rotating neutron stars are constructed applying several nucleonic equations of state. Particular emphasis is placed on configurations rotating rigidly at $716$ and $1122Hz$. The range of allowed hydrostatic equilibrium solutions is determined and tested for stability. The effect of rotation on the internal composition and thermal properties of neutron stars is also examined. At a given rotational frequency, each equation of state yields a range of possible neutron stars configurations restricted by the Keplerian (mass-shedding) limit, corresponding to the maximal circumferential radius, and the limit due to the onset of instabilities with respect to axial-symmetric perturbations, corresponding to the minimal equatorial radius of a stable neutron star model. We show that the mass of a neutron star rotating uniformly at $1122Hz$ is between $1.7$ and $2.1M_{\sun}$. Central stellar density and proton fraction decrease with increasing rotational frequency with respect to static models, and depending on the exact stellar mass and angular velocity, can drop below the Direct Urca threshold thus closing the fast cooling channel.