paper

Phase transitions in dense matter and the maximum mass of neutron stars

arXiv:1205.0983 · doi:10.1051/0004-6361/201220986

Abstract

The recent precise measurement of the mass of pulsar PSR J16142230, as well as observational indications of even more massive neutron stars, has revived the question of the composition of matter at the high densities prevailing inside neutron-star cores. We study the impact on the maximum possible neutron-star mass of an "exotic" core consisting of non-nucleonic matter. For this purpose, we study the occurrence of a first-order phase transition in nucleonic matter. Given the current lack of knowledge of non-nucleonic matter, we consider the stiffest possible equation of state subject only to the constraints of causality and thermodynamic stability. The case of a hadron-quark phase transition is discussed separately. The purely nucleonic matter is described using a set of unified equations of state that have been recently developed to permit a consistent treatment of both homogeneous and inhomogeneous phases. We then compute the mass-radius relation of cold nonaccreting neutron stars with and without exotic cores from the Tolman-Oppenheimer-Volkoff equations. We find that even if there is a significant softening of the equation of state associated with the actual transition to an exotic phase, there can still be a stiffening at higher densities closer to the center of the star that is sufficient to increase the maximum possible mass. However with quarks the maximum neutron-star mass is always reduced by assuming that the sound speed is limited by as suggested by QCD calculations. In particular, by invoking such a phase transition, it becomes possible to support PSR J16142230 with a nucleonic equation of state that is soft enough to be compatible with the kaon and pion production in heavy-ion collisions.

9 pages, 8 figures

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