Binary neutron stars in general relativity: Quasiequilibrium models

We perform fully relativistic calculations of binary neutron stars in quasiequilibrium circular orbits. We integrate Einstein’s equations together with the relativistic equation of hydrostatic equilibrium to solve the initial-value problem for equal-mass binaries of arbitrary separation. We construct sequences of constant rest mass and identify the innermost stable circular orbit and its angular velocity. We find that the quasiequilibrium maximum allowed mass of a neutron star in a close binary is slightly larger than in isolation.