A radiation hydrodynamics scheme on adaptive meshes using the Variable Eddington Tensor (VET) closure

TL;DR

This paper introduces a novel radiation hydrodynamics algorithm that combines a Variable Eddington Tensor closure with adaptive mesh refinement, enabling more accurate simulations of gas-radiation interactions in complex astrophysical environments.

Contribution

The paper presents a new RHD scheme using a non-local VET closure with AMR, a time-implicit Godunov method, and a fixed-point iteration for nonlinear energy exchange, improving accuracy over traditional methods.

Findings

Accurately models energy and momentum transfer between gas and radiation.

Successfully handles complex radiation fields where simpler closures fail.

Demonstrates correctness and improved accuracy in test problems.

Abstract

We present a new algorithm to solve the equations of radiation hydrodynamics (RHD) in a frequency-integrated, two-moment formulation. Novel features of the algorithm include i) the adoption of a non-local Variable Eddington Tensor (VET) closure for the radiation moment equations, computed with a ray-tracing method, ii) support for adaptive mesh refinement (AMR), iii) use of a time-implicit Godunov method for the hyperbolic transport of radiation, and iv) a fixed-point Picard iteration scheme to accurately handle the stiff nonlinear gas-radiation energy exchange. Tests demonstrate that our scheme works correctly, yields accurate rates of energy and momentum transfer between gas and radiation, and obtains the correct radiation field distribution even in situations where more commonly used -- but less accurate -- closure relations like the Flux-limited Diffusion and Moment-1 approximations fail. Our scheme presents an important step towards performing RHD simulations with increasing spatial and directional accuracy, effectively improving their predictive capabilities.