Netherlands Astronomy Conference 2026

We present the development of a resistive-MHD (RMHD) module within the ideal-GRMHD code GRaM-X. GRaM-X (General Relativistic accelerated Magnetohydrodynamics on AMReX) is a new, GPU-accelerated, dynamical-spacetime ideal-GRMHD code that extends the capabilities of the Einstein Toolkit to GPU-based exascale platforms. It features three-dimensional adaptive mesh refinement (AMR) on GPUs through the CarpetX AMR driver.
In this work, we have developed a Maxwell solver that evolves the electric and magnetic fields independently. Coupling this solver with the hydrodynamic equations yields a complete resistive GRMHD code. Resistive Maxwell's equations are stiff, and we use a second-order implicit-explicit Runge–Kutta scheme for stable numerical evolution. We validate the accuracy of our implementation through a series of tests in both static and dynamical spacetimes, including 1D magnetohydrodynamic shock tubes, the 2D cylindrical explosion, and the oscillations of a 3D Tolman-Oppenheimer-Volkoff star. We then apply the GRRMHD code to simulations of neutron star mergers and core-collapse supernovae (CCSNe). In particular, we investigate the role of finite resistivity in these systems, examining its impact on magnetic-field amplification, jet formation, and jet strength in CCSN models.