Astronomy and Astrophysics – Astronomy
Scientific paper
Feb 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001pasj...53l...1m&link_type=abstract
Publications of the Astronomical Society of Japan, vol.53, no. 1, p. L1-L4.
Astronomy and Astrophysics
Astronomy
41
Accretion, Accretion Disks, Black Holes, Convection, Magnetohydrodynamics, Outflow
Scientific paper
Two-dimensional (2D) and three-dimensional (3D) hydrodynamical simulations have been intensively performed recently to clarify the accretion-flow structure in the low-radiation-efficiency limit. However, the results depend critically on the parameterized magnitude of the viscosity, which, in principle, should be determined self-consistently by MHD simulations. We analyzed the structure of 3D MHD accretion flows initially threaded by weak toroidal magnetic fields, and found for the first time large-scale convective motions dominating near to the black hole. Radial profiles of each physical quantity include: the density, p alpha r-0.5; radial velocity, vr/alpha r-1.5; temperature, T /alpha r-1.0; and B2/alpha r -1.5 field strength, . Although the flow structure, itself, appears to be similar to those obtained by hydrodynamic simulations, the observational appearance is distinct. Unlike non-magnetic models, in which radiation is dominant at the outermost convective zones because of outward energy flow by convection, substantial accretion energy can be released in the vicinity of a black hole in MHD flow via magnetic reconnection. Such reconnection leads to sporadic flare events, thus producing variability in out-going radiation, as is commonly observed in objects with black-hole accretion.
Machida Mami
Matsumoto Ryoji
Mineshige Shin
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