Long-term evolution of neutron-star merger remnants in general relativistic resistive magnetohydrodynamics with a mean-field dynamo term

Long-term neutrino-radiation resistive-magnetohydrodynamics simulations in full general relativity are performed for a system composed of a massive neutron star and a torus formed as a remnant of binary neutron-star mergers. The simulation is performed in axial symmetry incorporating a mean-field dynamo term for a hypothetical amplification of the magnetic-field strength. We first calibrate the mean-field dynamo parameters by comparing the results for the evolution of black hole–disk systems with viscous hydrodynamics results. We then perform simulations for the system of a remnant massive neutron star and a torus. As in the viscous hydrodynamics case, the mass ejection occurs primarily from the torus surrounding the massive neutron star. The total ejecta mass and electron fraction in the new simulation are similar to those in the viscous hydrodynamics case. However, the velocity of the ejecta can be significantly enhanced by magnetohydrodynamics effects caused by global magnetic fields