General Relativistic Magneto-Hydrodynamic Simulations with BAM: Implementation and Code Comparison

TL;DR

This paper extends the BAM code to perform general relativistic magneto-hydrodynamic simulations, compares it with other codes, and demonstrates its effectiveness through standard tests and cross-code validation.

Contribution

The authors implement GRMHD capabilities in the BAM code using divergence cleaning and compare its performance with other established codes.

Findings

BAM performs well in special-relativistic tests.

Good agreement between BAM and SACRA_KK22 in GRMHD simulations.

The code extension enables more realistic neutron star merger modeling.

Abstract

Binary neutron star mergers are among the most energetic events in our Universe, with magnetic fields significantly impacting their dynamics, particularly after the merger. While numerical-relativity simulations that correctly describe the physics are essential to model their rich phenomenology, the inclusion of magnetic fields is crucial for realistic simulations. For this reason, we have extended the BAM code to enable general relativistic magneto-hydrodynamic (GRMHD) simulations employing a hyperbolic `divergence cleaning' scheme. We present a large set of standard GRMHD tests and compare the BAM code to other GRMHD codes, SPRITZ, GRaM-X, and SACRA$_{\rm KK22}$, which employ different schemes for the evolution of the magnetic fields. Overall, we find that the BAM code shows a good performance in simple special-relativistic tests. In addition, we find good agreement and consistent results when comparing GRMHD simulation results between BAM and SACRA$_{\rm KK22}$.