Relativistic Radiation Magnetohydrodynamics in Dynamical Spacetimes: Numerical Methods and Tests

TL;DR

This paper introduces a comprehensive numerical code for simulating relativistic radiation magnetohydrodynamics in dynamical spacetimes, applicable to various high-energy astrophysical phenomena involving strong gravity, magnetic fields, and radiation.

Contribution

The authors develop and validate a new general relativistic MHD and radiation code capable of evolving in full 3+1 dimensions with coupled Einstein, Maxwell, MHD, and radiation equations, including tests in strong-field scenarios.

Findings

Accurate simulation of radiating shocks and nonlinear waves in Minkowski spacetime.

Successful modeling of black hole formation via Oppenheimer-Snyder collapse with good agreement to analytic solutions.

Abstract

Many systems of current interest in relativistic astrophysics require a knowledge of radiative transfer in a magnetized gas flowing in a strongly-curved, dynamical spacetime. Such systems include coalescing compact binaries containing neutron stars or white dwarfs, disks around merging black holes, core collapse supernovae, collapsars, and gamma-ray burst sources. To model these phenomena, all of which involve general relativity, radiation (photon and/or neutrino), and magnetohydrodynamics, we have developed a general relativistic code capable of evolving MHD fluids and radiation in dynamical spacetimes. Our code solves the coupled Einstein-Maxwell-MHD-Radiation system of equations both in axisymmetry and in full 3+1 dimensions. We evolve the metric by integrating the BSSN equations, and use a conservative, high-resolution shock-capturing scheme to evolve both the MHD and radiation moment equations. In this paper, we implement our scheme for optically thick gases and grey-body opacities. Our code gives accurate results in a suite of tests involving radiating shocks and nonlinear waves propagating in Minkowski spacetime. In addition, to test our code's ability to evolve the relativistic radiation-MHD equations in strong-field dynamical spacetimes, we study "thermal Oppenheimer-Snyder collapse" to a black hole, and find good agreement between analytic and numerical solutions.