Spherical Accretion with Anisotropic Thermal Conduction

Abstract

We study the effects of anisotropic thermal conduction on magnetized spherical accretion flows using global axisymmetric MHD simulations. In low collisionality plasmas, the Bondi spherical accretion solution is unstable to the magnetothermal instability (MTI). The MTI grows rapidly at large radii where the inflow is subsonic. For a weak initial field, the MTI saturates by creating a primarily radial magnetic field, i.e., by aligning the field lines with the background temperature gradient. The saturation is quasilinear in the sense that the magnetic field is amplified by a factor of $\sim 10-30$ independent of the initial field strength (for weak fields). In the saturated state, the conductive heat flux is much larger than the convective heat flux, and is comparable to the field-free (Spitzer) value (since the field lines are largely radial). The MTI by itself does not appreciably change the accretion rate $\dot{M}$ relative to the Bondi rate ${\dot{M}}_B$. However, the radial field lines created by the MTI are amplified by flux freezing as the plasma flows in to small radii. Oppositely directed field lines are brought together by the converging inflow, leading to significant resistive heating. When the magnetic energy density is comparable to the gravitational potential energy density, the plasma is heated to roughly the virial temperature; the mean inflow is highly subsonic; most of the energy released by accretion is transported to large radii by thermal conduction; and the accretion rate $\dot{M}\ll {\dot{M}}_B$. The predominantly radial magnetic field created by the MTI at large radii in spherical accretion flows may account for the stable Faraday rotation measure towards Sgr A* in the Galactic Center.

accepted in MNRAS with some modifications suggested by the referee; 15 pages, 16 figures

References in corpus (11)

• An Unambiguous Detection of Faraday Rotation in Sagittarius A*
• MHD simulations of the magnetorotational instability in a shearing box with zero net flux. II. The effect of transport coefficients
• Electron Heating in Hot Accretion Flows
• Preserving Monotonicity in Anisotropic Diffusion
• Galactic Centre stellar winds and Sgr A* accretion
• Buoyancy Instabilities in Weakly Magnetized Low Collisionality Plasmas
• Saturation of the Magnetothermal Instability in Three Dimensions
• Hot Accretion With Conduction: Spontaneous Thermal Outflows
• The Effects of Thermal Conduction on Radiatively-Inefficient Accretion Flows
• Faraday Rotation in Global Accretion Disk Simulations: Implications for Sgr A*
• Convection and AGN Feedback in Clusters of Galaxies

Cited by in corpus (36)

• Hot Accretion Flows Around Black Holes
• Sagittarius A* Accretion Flow and Black Hole Parameters from General Relativistic Dynamical and Polarized Radiative Modeling
• Plasma diagnostic potential of 2p4f in N${}^{+}$ -- accurate wavelengths and oscillator strengths
• The Power of Imaging: Constraining the Plasma Properties of GRMHD Simulations using EHT Observations of Sgr A*
• Rotating Accretion Flows: From Infinity to the Black Hole
• Time Dependent Models of Flares from Sagittarius A*
• Inflow-Outflow Model with Conduction and Self-Consistent Feeding for Sgr A*
• Bondi flow from a slowly rotating hot atmosphere
• A nonlinear theory of the parallel firehose and gyrothermal instabilities in a weakly collisional plasma
• Numerical Parameter Survey of Nonradiative Black Hole Accretion -- Flow Structure and Variability of the Rotation Measure
• Maximum Spin of Black Holes Driving Jets
• Can conduction induce convection? The non-linear saturation of buoyancy instabilities in dilute plasmas
• Buoyancy Instabilities in Galaxy Clusters: Convection Due to Adiabatic Cosmic Rays and Anisotropic Thermal Conduction
• How important is non-ideal physics in simulations of sub-Eddington accretion onto spinning black holes?
• Low density, radiatively inefficient rotating-accretion flow onto a black hole
• Accurately simulating anisotropic thermal conduction on a moving mesh
• grim: A Flexible, Conservative Scheme for Relativistic Fluid Theories
• The Effect of Anisotropic Conduction on the Thermal Instability in the Interstellar Medium
• Radiatively Inefficient Accretion Flow Simulations with Cooling: Implications for Black Hole Transients
• Spherical accretion: Bondi, Michel and rotating black holes
• Magnetothermal and magnetorotational instabilities in hot accretion flows
• Effects of anisotropic thermal conduction on wind properties in hot accretion flow
• Dynamics of Hot Accretion Flow with Thermal Conduction
• Self-similar structure of a hot magnetized flow with thermal conduction
• Radiation Spectrum of a Magnetized Supercritical Accretion Disc with Thermal Conduction
• Abundance profiles in cooling-core clusters: a fossil record of past AGN-driven convection?
• Magneto-Thermal Instability In Galaxy Clusters I: Theory and Two-Dimensional Simulations
• Suppressing hot gas accretion to supermassive black holes by stellar winds
• Spherical accretion: the influence of inner boundary and quasi-periodic oscillations
• Two-dimensional Inflow-Wind Solution of Hot Accretion Flow. I. Hydrodynamics
• Parker/buoyancy instabilities with anisotropic thermal conduction, cosmic rays, and arbitrary magnetic field strength
• Structure of ADAFs in a general large-Scale B-field: The role of wind and thermal conduction
• Self-similar solutions of viscous and resistive ADAFs with thermal conduction
• On the Efficiency of Thermal Conduction in Galaxy Clusters
• Resistive Hot Accretion Flows with Anisotropic Pressure
• Feeding and Small-scale Feedback in Low-Luminosity AGNs