Numerical Simulations of Optically Thick Accretion Onto a Black Hole. I. Spherical Case

Abstract

Modeling the radiation generated by accreting matter is an important step towards realistic simulations of black hole accretion disks, especially at high accretion rates. To this end, we have recently added radiation transport to the existing general relativistic magnetohydrodynamic code, Cosmos++. However, before attempting to model radiative accretion disks, we have tested the new code using a series of shock tube and Bondi (spherical inflow) problems. The four radiative shock tube tests, first presented by Farris et al. (2008), have known analytic solutions, allowing us to calculate errors and convergence rates for our code. The Bondi problem only has an analytic solution when radiative processes are ignored, but is pertinent because it is closer to the physics we ultimately want to study. In our simulations, we include Thomson scattering and thermal bremsstrahlung in the opacity, focusing exclusively on the super-Eddington regime. Unlike accretion onto bodies with solid surfaces, super-Eddington accretion onto black holes does not produce super-Eddington luminosity. In our examples, despite accreting at up to 300 times the Eddington rate, our measured luminosity is always several orders of magnitude below Eddington.

Double Compton and Cyclo-Synchrotron in Super-Eddington Discs, Magnetized Coronae, and Jets

“…Model M6 would be like many existing radiative transfer simulations (Fragile et al 2012;Jiang et al 2014a;Fragile et al 2014;Takahashi et al 2016) except those by Fragile & Meier (2009) ;Kawashima et al (2009);Jiang et al (2014b) and ourselves McKinney et al 2014).…”

“…Similar GR (Fragile et al 2012;Takahashi et al 2013;Sadowski et al 2014;McKinney et al 2014;Fragile et al 2014;Ryan et al 2015;Takahashi et al 2016) and non-GR (Jiang et al 2014a) schemes have been developed.…”

An Algorithm for Radiation Magnetohydrodynamics Based on Solving the Time-Dependent Transfer Equation

“…While GRMHD flows including radiation using FLD or the M1 closure have recently been reported (Fragile et al 2012;Saadowski et al 2013;McKinney et al 2013), developing algorithms based on the formal solution of the RT equation in general relativity (GR) is a formidable challenge. Instead, in this paper we describe an intermediate step.…”

General relativistic radiation-hydrodynamics of accretion flows

“…Based on this, a number of specific physical systems in the optically thick regime have been investigated. [2][3][4] In addition, the presence of stiff source terms in the radiation hydrodynamic equations has been successfully treated via an IMEX RungeKutta scheme 5 and the transition between the optically thick and the optically thin regime, sometimes referred to as the grey regime, has also been accounted for by means of the so-called "M1 closure" [6][7][8][9] . In this work, we study the grey regime of radiation hydrodynamics by combining a stiff source solver with the truncated moment formalism of Thorne, which has been recently formulated in the full general relativistic framework 10 .…”