Computational general relativistic force-free electrodynamics

I. Multi-coordinate implementation and testing

¹ Departament d’Astronomia i Astrofísica, Universitat de València, 46100 Burjassot, Valencia, Spain
e-mail: jens.mahlmann@uv.es
² National Center for Computational Sciences, Oak Ridge National Laboratory, PO Box 2008, Oak Ridge, TN 37831-6164, USA
³ Physics Division, Oak Ridge National Laboratory, PO Box 2008, Oak Ridge, TN 37831-6354, USA

Received: 13 July 2020
Accepted: 18 December 2020

Abstract

General relativistic force-free electrodynamics is one possible plasma-limit employed to analyze energetic outflows in which strong magnetic fields are dominant over all inertial phenomena. The amazing images of black hole (BH) shadows from the Galactic Center and the M87 galaxy provide a first direct glimpse into the physics of accretion flows in the most extreme environments of the universe. The efficient extraction of energy in the form of collimated outflows or jets from a rotating BH is directly linked to the topology of the surrounding magnetic field. We aim at providing a tool to numerically model the dynamics of such fields in magnetospheres around compact objects, such as BHs and neutron stars. To do so, we probe their role in the formation of high energy phenomena such as magnetar flares and the highly variable teraelectronvolt emission of some active galactic nuclei. In this work, we present numerical strategies capable of modeling fully dynamical force-free magnetospheres of compact astrophysical objects. We provide implementation details and extensive testing of our implementation of general relativistic force-free electrodynamics in Cartesian and spherical coordinates using the infrastructure of the EINSTEIN TOOLKIT. The employed hyperbolic/parabolic cleaning of numerical errors with full general relativistic compatibility allows for fast advection of numerical errors in dynamical spacetimes. Such fast advection of divergence errors significantly improves the stability of the general relativistic force-free electrodynamics modeling of BH magnetospheres.