Semi-implicit scheme for treating radiation under M1 closure in general relativistic conservative fluid dynamics codes

Abstract

A numerical scheme is described for including radiation in multi-dimensional\ngeneral-relativistic conservative fluid dynamics codes. In this method, a\ncovariant form of the M1 closure scheme is used to close the radiation moments,\nand the radiative source terms are treated semi-implicitly in order to handle\nboth optically thin and optically thick regimes. The scheme has been\nimplemented in a conservative general relativistic radiation hydrodynamics code\nKORAL. The robustness of the code is demonstrated on a number of test problems,\nincluding radiative relativistic shock tubes, static radiation pressure\nsupported atmosphere, shadows, beams of light in curved spacetime, and\nradiative Bondi accretion. The advantages of M1 closure relative to other\napproaches such as Eddington closure and flux-limited diffusion are discussed,\nand its limitations are also highlighted.\n