Neutrino trapping and out-of-equilibrium effects in binary neutron star merger remnants

Right panels: equatorial snapshots of out of equilibrium chemical potentials with and without neutrinos. Left panels: phase space diagrams.
Right panels: equatorial snapshots of out of equilibrium chemical potentials with and without neutrinos. Left panels: phase space diagrams.

In 2311.00031 we study out-of-thermodynamic equilibrium effects in neutron star mergers with 3D general-relativistic neutrino-radiation large-eddy simulations. During merger, the cores of the neutron stars remain cold (a few MeV) and out of thermodynamic equilibrium with trapped neutrinos originating from the hot collisional interface between the stars. However, within ∼2−3 milliseconds matter and neutrinos reach equilibrium everywhere in the remnant. Our results show that dissipative effects, such as bulk viscosity, if present, are only active for a short window of time after the merger.