A Global Threedimensional Radiation Magnetohydrodynamic Simulation of SuperEddington Accretion Disks
Abstract
We study superEddington accretion flows onto black holes using a global threedimensional radiation magnetohydrodynamical simulation. We solve the timedependent radiative transfer equation for the specific intensities to accurately calculate the angular distribution of the emitted radiation. Turbulence generated by the magnetorotational instability provides selfconsistent angular momentum transfer. The simulation reaches inflow equilibrium with an accretion rate ~220 L _{Edd}/c ^{2} and forms a radiationdriven 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 _{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 Xray sources.
 Publication:

The Astrophysical Journal
 Pub Date:
 December 2014
 DOI:
 10.1088/0004637X/796/2/106
 arXiv:
 arXiv:1410.0678
 Bibcode:
 2014ApJ...796..106J
 Keywords:

 accretion;
 accretion disks;
 magnetohydrodynamics: MHD;
 methods: numerical;
 radiative transfer;
 Astrophysics  High Energy Astrophysical Phenomena
 EPrint:
 15 pages, 16 figures, 1 table, accepted to ApJ