Differentially-rotating neutron star models with a parametrized rotation profile

¹ Max-Planck-Institut für Gravitationsphysik, Albert-Einstein-Institut, Am Mühlenberg 1, 14476 Potsdam, Germany
e-mail: filippo.galeazzi@aei.mpg.de
² Department of Earth Science and Astronomy, Graduate School of Arts and Sciences, University of Tokyo, Komaba, Meguro-ku 3-8-1, 153-8902 Tokyo, Japan

Accepted: 23 March 2012

Abstract

We analyze the impact of the rotation law on equilibrium sequences of relativistic differentially-rotating neutron stars in axisymmetry. The maximum allowed mass for each model is strongly affected by the distribution of the angular velocity in the radial direction and by the consequent degree of differential rotation. To study the wide parameter space implied by the choice of the rotation law, we introduce a functional form that generalizes the so-called “j-const. law” adopted in all previous work. We compute equilibrium sequences of differentially rotating stars with a polytropic equation of state starting from the spherically symmetric static case. By analyzing the sequences with decreasing degrees of differential rotation, we find that the maximum value of the ratio T/|W| of rotational kinetic energy to gravitational binding energy, is substantially limited in these cases to a value of 0.128.