Two-moment scheme for general-relativistic radiation hydrodynamics: a systematic description and new applications

Understand

We provide a systematic description of the steps necessary -- and of the potential pitfalls to be encountered -- when implementing a two-moment scheme within an Implicit-Explicit (IMEX) scheme to include radiative-transfer contributions in numerical simulations of general-relativistic (magneto-)hydrodynamics.

• We make use of the M1 closure, which provides an exact solution for the optically thin and thick limit, and an interpolation between these limits.
• Special attention is paid to the efficient solution of the emerging set of implicit conservation equations.
• In particular, we present an efficient method for solving these equations via the inversion of a $4\times 4$-matrix within an IMEX scheme.