  Binary neutron star mergers are studied using nonlinear 3+1 numerical
relativity simulations and the analytical effective-one-body (EOB) model. The
EOB model predicts quasiuniversal relations between the mass-rescaled
gravitational wave frequency and the binding energy at the moment of merger,
and certain dimensionless binary tidal coupling constants depending on the
stars Love numbers, compactnesses and the binary mass ratio. These relations
are quasiuniversal in the sense that, for a given value of the tidal coupling
constant, they depend significantly neither on the equation of state nor on the
mass ratio, though they do depend on stars spins. The spin dependence is
approximately linear for small spins aligned with the orbital angular momentum.
The quasiuniversality is a property of the conservative dynamics; nontrivial
relations emerge as the binary interaction becomes tidally dominated. This
analytical prediction is qualitatively consistent with new, multi-orbit
numerical relativity results for the relevant case of equal-mass irrotational
binaries. Universal relations are thus expected to characterize neutron star
mergers dynamics. In the context of gravitational wave astronomy, these
universal relations may be used to constrain the neutron star equation of state
using waveforms that model the merger accurately.
