Energy release associated with a first-order phase transition in a rotating neutron star core

¹ N. Copernicus Astronomical Center, Polish Academy of Sciences, Bartycka 18, 00-716 Warszawa, Poland e-mail: [jlz;bejger;haensel]@camk.edu.pl
² LUTH, UMR 8102 du CNRS, Observatoire de Paris, 92195 Meudon Cedex, France e-mail: Eric.Gourgoulhon@obspm.fr

Received: 6 October 2006
Accepted: 2 January 2007

Abstract

Aims.We calculate energy release associated with a first order phase transition at the center of a rotating neutron star. This quantity is equal to the difference in mass-energies between the initial normal phase configuration and the final configuration containing a superdense matter core, with total baryon number and angular momentum kept constant.

Methods.The calculations of the energy release are based on precise numerical 2D calculations, in which both the polytropic equations of state (EOS) as well as realistic EOS of the normal phase are used. Presented results are obtained for a broad range of metastability of initial configuration and size of the new superdense phase core in the final configuration. When the equatorial radius of the dense core of the superdense phase is much smaller than the stellar equatorial radius, analytical expressions for the energy release are obtained.

Results.For a fixed “overpressure”, , defined as the relative excess of central pressure of a collapsing metastable star over the pressure of the equilibrium first-order phase transition, the energy release remarkably does not depend on the stellar angular momentum and coincides with that for nonrotating stars with the same . The energy release is proportional to  for small , when sufficiently precise brute force 2D numerical calculations are not possible. At higher , results of 1D calculations of for non-rotating stars are shown to reproduce, with very high precision, the exact 2D results for rotating stars.