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Title: A global three-dimensional radiation magneto-hydrodynamic simulation of super-eddington accretion disks

Abstract

We study super-Eddington accretion flows onto black holes using a global three-dimensional radiation magneto-hydrodynamical simulation. We solve the time-dependent radiative transfer equation for the specific intensities to accurately calculate the angular distribution of the emitted radiation. Turbulence generated by the magneto-rotational instability provides self-consistent angular momentum transfer. The simulation reaches inflow equilibrium with an accretion rate ∼220 L {sub Edd}/c {sup 2} and forms a radiation-driven outflow along the rotation axis. The mechanical energy flux carried by the outflow is ∼20% of the radiative energy flux. The total mass flux lost in the outflow is about 29% of the net accretion rate. The radiative luminosity of this flow is ∼10 L {sub Edd}. This yields a radiative efficiency ∼4.5%, which is comparable to the value in a standard thin disk model. In our simulation, vertical advection of radiation caused by magnetic buoyancy transports energy faster than photon diffusion, allowing a significant fraction of the photons to escape from the surface of the disk before being advected into the black hole. We contrast our results with the lower radiative efficiencies inferred in most models, such as the slim disk model, which neglect vertical advection. Our inferred radiative efficiencies also exceed publishedmore » results from previous global numerical simulations, which did not attribute a significant role to vertical advection. We briefly discuss the implications for the growth of supermassive black holes in the early universe and describe how these results provided a basis for explaining the spectrum and population statistics of ultraluminous X-ray sources.« less

Authors:
 [1];  [2];  [3]
  1. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
  2. Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)
  3. Canadian Institute for Theoretical Astrophysics. Toronto, ON M5S3H4 (Canada)
Publication Date:
OSTI Identifier:
22370149
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 796; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCRETION DISKS; ANGULAR DISTRIBUTION; ANGULAR MOMENTUM TRANSFER; BLACK HOLES; COMPUTERIZED SIMULATION; DIFFUSION; EMISSION; EQUILIBRIUM; INSTABILITY; LUMINOSITY; MAGNETOHYDRODYNAMICS; POWER TRANSMISSION; RADIANT HEAT TRANSFER; ROTATION; SPECTRA; SURFACES; TIME DEPENDENCE; TURBULENCE; UNIVERSE; X-RAY SOURCES

Citation Formats

Jiang, Yan-Fei, Stone, James M., and Davis, Shane W. A global three-dimensional radiation magneto-hydrodynamic simulation of super-eddington accretion disks. United States: N. p., 2014. Web. doi:10.1088/0004-637X/796/2/106.
Jiang, Yan-Fei, Stone, James M., & Davis, Shane W. A global three-dimensional radiation magneto-hydrodynamic simulation of super-eddington accretion disks. United States. doi:10.1088/0004-637X/796/2/106.
Jiang, Yan-Fei, Stone, James M., and Davis, Shane W. 2014. "A global three-dimensional radiation magneto-hydrodynamic simulation of super-eddington accretion disks". United States. doi:10.1088/0004-637X/796/2/106.
@article{osti_22370149,
title = {A global three-dimensional radiation magneto-hydrodynamic simulation of super-eddington accretion disks},
author = {Jiang, Yan-Fei and Stone, James M. and Davis, Shane W.},
abstractNote = {We study super-Eddington accretion flows onto black holes using a global three-dimensional radiation magneto-hydrodynamical simulation. We solve the time-dependent radiative transfer equation for the specific intensities to accurately calculate the angular distribution of the emitted radiation. Turbulence generated by the magneto-rotational instability provides self-consistent angular momentum transfer. The simulation reaches inflow equilibrium with an accretion rate ∼220 L {sub Edd}/c {sup 2} and forms a radiation-driven outflow along the rotation axis. The mechanical energy flux carried by the outflow is ∼20% of the radiative energy flux. The total mass flux lost in the outflow is about 29% of the net accretion rate. The radiative luminosity of this flow is ∼10 L {sub Edd}. This yields a radiative efficiency ∼4.5%, which is comparable to the value in a standard thin disk model. In our simulation, vertical advection of radiation caused by magnetic buoyancy transports energy faster than photon diffusion, allowing a significant fraction of the photons to escape from the surface of the disk before being advected into the black hole. We contrast our results with the lower radiative efficiencies inferred in most models, such as the slim disk model, which neglect vertical advection. Our inferred radiative efficiencies also exceed published results from previous global numerical simulations, which did not attribute a significant role to vertical advection. We briefly discuss the implications for the growth of supermassive black holes in the early universe and describe how these results provided a basis for explaining the spectrum and population statistics of ultraluminous X-ray sources.},
doi = {10.1088/0004-637X/796/2/106},
journal = {Astrophysical Journal},
number = 2,
volume = 796,
place = {United States},
year = 2014,
month =
}
  • The results of nonrelativistic radiation-hydrodynamic calculations of axisymmetric supercritical accretion disks around Newtonian quasi-black holes are reported. Anisotropic and isotropic constant kinematic viscosity models are used, with radiation transport described by a gray Thomson scattering opacity and flux-limited diffusion. The resulting solutions have four distinct zones: (1) centered on the disk midplane is a thick, dense region of turbulent convection; (2) above this is an accretion zone in which low angular momentum matter rapidly flows onto the black hole; (3) the accretion zone is bounded by a photocone, in which the matter becomes optically thin; (4) inside the photocone, surroundingmore » the angular momentum axis, is a broad subrelativistic jet of expelled matter. Applications of these results to SS 433 and to extragalactic jets are discussed. 44 references.« less
  • The results of self-consistent, azimuthally symmetric, radiation-hydrodynamic calculations of subcritical accretion disks about a Newtonian pseudo-black hole are reported. Energy generation is described by a kinematic viscosity law and a modified alpha-disk model. A disk with constant kinematic viscosity settles to a nearly steady state which approximates a thin disk solution. Its unstable vertical distribution of entropy leads to mild subsonic correction. The alpha-disk is unstable, as expected, and collapses to a thin cold sheet with low accretion rate and low luminosity. 26 references.
  • We describe a Newtonian version of the theory of thick accretion disks orbiting black holes. In view of the present inadequate knowledge of microscopic viscosity process, this theory adopts a macroscopic approach. All the uncertainties are absorbed in currently arbitrary functions lambda(xi) and f(xi) which describe the (non-Keplerian) angular momentum along the disk, and the outgoing radiation flux in units of the critical flux. Assuming surface distributions of angular momentum and radiation flux, one can construct a model of a thick, non-Keplerian accretion disk with no knowledge of the viscosity mechanism. Thick accretion disks can have luminosities 100 times abovemore » the Eddington limit. We study the self-consistency constraints for the theory of thick accretion disks with super-Eddington luminosities.« less
  • We present full 2{pi} global three-dimensional stratified magnetohydrodynamic (MHD) simulations of accretion disks. We interpret our results in the context of protoplanetary disks. We investigate the turbulence driven by the magnetorotational instability (MRI) using the PLUTO Godunov code in spherical coordinates with the accurate and robust HLLD Riemann solver. We follow the turbulence for more than 1500 orbits at the innermost radius of the domain to measure the overall strength of turbulent motions and the detailed accretion flow pattern. We find that regions within two scale heights of the midplane have a turbulent Mach number of about 0.1 and amore » magnetic pressure two to three orders of magnitude less than the gas pressure, while in those outside three scale heights the magnetic pressure equals or exceeds the gas pressure and the turbulence is transonic, leading to large density fluctuations. The strongest large-scale density disturbances are spiral density waves, and the strongest of these waves has m = 5. No clear meridional circulation appears in the calculations because fluctuating radial pressure gradients lead to changes in the orbital frequency, comparable in importance to the stress gradients that drive the meridional flows in viscous models. The net mass flow rate is well reproduced by a viscous model using the mean stress distribution taken from the MHD calculation. The strength of the mean turbulent magnetic field is inversely proportional to the radius, so the fields are approximately force-free on the largest scales. Consequently, the accretion stress falls off as the inverse square of the radius.« less
  • We present the detailed global structure of black hole accretion flows and outflows through newly performed two-dimensional radiation-magnetohydrodynamic simulations. By starting from a torus threaded with weak toroidal magnetic fields and by controlling the central density of the initial torus, {rho}{sub 0}, we can reproduce three distinct modes of accretion flow. In model A, which has the highest central density, an optically and geometrically thick supercritical accretion disk is created. The radiation force greatly exceeds the gravity above the disk surface, thereby driving a strong outflow (or jet). Because of mild beaming, the apparent (isotropic) photon luminosity is {approx}22L{sub E}more » (where L{sub E} is the Eddington luminosity) in the face-on view. Even higher apparent luminosity is feasible if we increase the flow density. In model B, which has moderate density, radiative cooling of the accretion flow is so efficient that a standard-type, cold, and geometrically thin disk is formed at radii greater than {approx}7 R{sub S} (where R{sub S} is the Schwarzschild radius), while the flow is radiatively inefficient otherwise. The magnetic-pressure-driven disk wind appears in this model. In model C, the density is too low for the flow to be radiatively efficient. The flow thus becomes radiatively inefficient accretion flow, which is geometrically thick and optically thin. The magnetic-pressure force, together with the gas-pressure force, drives outflows from the disk surface, and the flow releases its energy via jets rather than via radiation. Observational implications are briefly discussed.« less