HERO: A 3D General Relativistic Radiative Postprocessor for Accretion Discs around Black Holes

TL;DR

HERO is a novel 3D general relativistic radiative transfer code tailored for analyzing radiation from accretion disks around black holes, combining fast and accurate methods to improve simulation fidelity.

Contribution

HERO introduces a hybrid radiative transfer approach combining short and long characteristics methods for efficient and accurate modeling of relativistic accretion disks.

Findings

Successfully tests on 1D, 2D, and 3D problems show good agreement with analytical solutions.

Demonstrates capability to handle relativistic curved spacetime scenarios.

Addresses and mitigates ray-defects in the short characteristics method.

Abstract

HERO (Hybrid Evaluator for Radiative Objects) is a 3D general relativistic radiative transfer code which has been tailored to the problem of analyzing radiation from simulations of relativistic accretion discs around black holes. HERO is designed to be used as a postprocessor. Given some fixed fluid structure for the disc (i.e. density and velocity as a function of position from a hydrodynamics or magnetohydrodynamics simulation), the code obtains a self-consistent solution for the radiation field and for the gas temperatures using the condition of radiative equilibrium. The novel aspect of HERO is that it combines two techniques: 1) a short characteristics (SC) solver that quickly converges to a self consistent disc temperature and radiation field, with 2) a long characteristics (LC) solver that provides a more accurate solution for the radiation near the photosphere and in the optically thin regions. By combining these two techniques, we gain both the computational speed of SC and the high accuracy of LC. We present tests of HERO on a range of 1D, 2D and 3D problems in flat space and show that the results agree well with both analytical and benchmark solutions. We also test the ability of the code to handle relativistic problems in curved space. Finally, we discuss the important topic of ray-defects, a major limitation of the SC method, and describe our strategy for minimizing the induced error.