Physics
Scientific paper
Apr 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997mnras.286..358m&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Volume 286, Issue 2, pp. 358-368.
Physics
23
Accretion, Accretion Discs, Black Hole Physics, Convection, Hydrodynamics, Instabilities, Waves
Scientific paper
Radiation hydrodynamic simulations of two-dimensional, optically thick, black hole accretion discs are performed under conditions of varying mass accretion rate, /M//M_Edd, and kinematic viscosity, nu. Specifically, the effects of inertial-acoustic oscillations and convection on disc structure and observable properties are studied. It is found that global oscillations with rms amplitudes of <~0.3 per cent can be present at the maximum epicyclic frequency in the disc. These oscillations are favoured for low accretion rates (/M<~/M_Edd) and large viscosities. Local oscillations at the local epicyclic frequencies are always present with rms amplitudes of <~0.2 per cent. These oscillations yield power spectra with spectral slopes of 0.98 and 1.33. Qualitatively similar behaviour is found for discs described by an alpha law or a constant nu. Oscillations may be present for a restricted range of parameters for any viscosity law in which the shear viscosity (mu=rhonu) increases upon compression, and they may be detectable with the X-ray Timing Explorer. It is also found that for /M>~0.1/M_Edd convection dominates the transfer of energy in the disc. The convection cells generally stretch from the mid-plane to the disc surface at low accretion rates (/M<~/M_Edd), while the cells appear on varying length-scales at high accretion rates (/M>~/M_Edd).
Milsom John A.
Taam Ronald E.
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