Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 456, Issue 2, Pages 1332-1345Publisher
OXFORD UNIV PRESS
DOI: 10.1093/mnras/stv2687
Keywords
black hole physics; MHD; plasmas; quasars: supermassive black holes
Categories
Funding
- NSF
- NASA through Einstein Postdoctoral Fellowship - Chandra X-ray Center [PF4-150122]
- NASA [NAS803060]
- Illinois Distinguished Fellowship from the University of Illinois
- NSF [AST-1333612, ACI-1053575]
- Simons Fellowship
- Simons Investigator Award from the Simons Foundation
- David and Lucile Packard Foundation
- visiting fellowship at All Souls College, Oxford
- Direct For Mathematical & Physical Scien [1333682] Funding Source: National Science Foundation
- Direct For Mathematical & Physical Scien
- Division Of Astronomical Sciences [1333091] Funding Source: National Science Foundation
- Division Of Astronomical Sciences [1333682] Funding Source: National Science Foundation
- Division Of Astronomical Sciences
- Direct For Mathematical & Physical Scien [1333612] Funding Source: National Science Foundation
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Black holes accreting well below the Eddington rate are believed to have geometrically thick, optically thin, rotationally supported accretion discs in which the Coulomb mean free path is large compared to GM/c(2). In such an environment, the disc evolution may differ significantly from ideal magnetohydrodynamic (MHD) predictions. We present non-ideal global axisymmetric simulations of geometrically thick discs around a rotating black hole. The simulations are carried out using a new code GRIM, which evolves a covariant extended magnetohydrodynamics model derived by treating non-ideal effects as a perturbation of ideal MHD. Non-ideal effects are modelled through heat conduction along magnetic field lines, and a difference between the pressure parallel and perpendicular to the field lines. The model relies on an effective collisionality in the disc from wave-particle scattering and velocityspace (mirror and firehose) instabilities. We find that the pressure anisotropy grows to match the magnetic pressure, at which point it saturates due to the mirror instability. The pressure anisotropy produces outward angular momentum transport with a magnitude comparable to that of MHD turbulence in the disc, and a significant increase in the temperature in the wall of the jet. We also find that, at least in our axisymmetric simulations, conduction has a small effect on the disc evolution because (1) the heat flux is constrained to be parallel to the field and the field is close to perpendicular to temperature gradients, and (2) the heat flux is choked by an increase in effective collisionality associated with the mirror instability.
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