Global simulations of strongly magnetized remnant massive neutron stars formed in binary neutron star mergers

We perform a general-relativistic magnetohydrodynamics simulation for ≈30 ms from the merger of a binary neutron star throughout the formation of a remnant massive neutron star (RMNS) with a high spatial resolution of the finest grid resolution 12.5 m. First, we show that the Kelvin-Helmholtz instability at the merger could amplify the magnetic-field energy at least up to ∼1% of the thermal energy. Then, we show that the magnetorotational instability in the RMNS envelope and torus with ρ