Massive neutron stars with a color superconducting quark matter core

Abstract

We construct the equation of state for high-density neutron star matter at zero temperature using the two-flavor Nambu--Jona-Lasinio (NJL) model as an effective theory of QCD. We build nuclear matter, quark matter, and the mixed phases from the same NJL Lagrangian, which has been used to model free and in-medium hadrons as well as nuclear systems. A focus here is to determine if the same coupling constants in the scalar diquark and vector meson channels, which give a good description of nucleon structure and nuclear matter, can also be used for the color superconducting high-density quark matter phase. We find that this is possible for the scalar diquark (pairing) interaction, but the vector meson interaction has to be reduced so that superconducting quark matter becomes the stable phase at high densities. We compare our equation of state with recent phenomenological parametrizations based on generic stability conditions for neutron stars. We find that the maximum mass of a hybrid star, with a color superconducting quark matter core, exceeds $2.01\ifmmode\pm\else\textpm\fi{}0.04\phantom{\rule{0.16em}{0ex}}{M}_{\ensuremath{\bigodot}}$, which is the value of the recently observed massive neutron star PSR $\text{J0348}+0432$. The mass-radius relation is also consistent with gravitational wave observations (GW170817).