Special Talk: Efficient general-relativistic simulation: Magnetic field amplification and electromagnetic signals of binary neutron star mergers

First-principles general-relativistic magnetohydrodynamics (GRMHD) simulations are essential for understanding the multi-messenger signatures of binary neutron star (BNS) mergers — including gravitational waves, kilonovae, and short gamma-ray bursts — as seen in GW170817. These signatures arise from highly nonlinear coupling between MHD, nuclear physics, neutrino transport, and strong-field gravity.

We have developed a hybrid numerical framework that combines, through a carefully designed handoff procedure, a fully general-relativistic GRMHD code with a significantly more efficient code based on the conformally flat approximation. This approach yields a 3–4× speedup while preserving accuracy during the post-merger phase, enabling high-resolution, long-term evolutions.

Using this efficient simulation approach, we investigate magnetic field amplification mechanisms and the resulting electromagnetic signatures throughout the evolution of a BNS merger producing a long-lived magnetar remnant. Specifically, we study the Kelvin-Helmholtz instability during the merger phase, and the magneto-rotational instability, magnetic winding, and Parker instability in the post-merger phase, enabling high-resolution.

Anyone interested is welcome to attend.