Impact of the nuclear equation of state on the last orbits of binary neutron stars

We present calculations of quasiequilibrium sequences of irrotational binary neutron stars based on realistic equations of state (EOS) for the whole neutron star interior. Three realistic nuclear EOSs of various softness and based on different microscopic models have been joined with a recent realistic EOS of the crust, giving in this way three different EOSs of neutron-star interior. Computations of quasiequilibrium sequences are performed within the Isenberg-Wilson-Mathews approximation to general relativity. All evolutionary sequences are found to be stable (no turning point in the binding energy) up to the mass-shedding limit. The EOS dependence on the last orbits is found to be quite important: for two 1.35 M⊙ neutron stars, the gravitational wave frequency at the mass-shedding limit (which marks the end of the inspiral phase) ranges from 800 Hz to 1200 Hz, depending upon the EOS. Detailed comparisons with 3rd order post-Newtonian results for point-mass binaries reveals a very good agreement until hydrodynamical effects (dominated by high-order function of frequency) become important, which occurs at a frequency ranging from 500 Hz to 1050 Hz, depending upon the EOS.