Choking of optically thin spherical accretion by dissipative heating

Details Choking of optically thin spherical accretion by dissipative heating Choking of optically thin spherical accretion by dissipative heating

May 1981

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981apj...246l..15s&link_type=abstract

Astrophysical Journal, Part 2 - Letters to the Editor, vol. 246, May 15, 1981, p. L15-L19.

Astronomy and Astrophysics

Astronomy

9

Black Holes (Astronomy), Heat Sources, Mass Flow, Quasars, Stellar Mass Accretion, Supersonic Flow, Active Galactic Nuclei, Compton Effect, Energy Dissipation, Flow Equations, Flow Velocity, Interstellar Magnetic Fields, Mach Number, Numerical Integration, Optical Thickness, Time Dependence

Scientific paper

Dissipative heating is shown to be sufficient to reduce the Mach number of supersonic spherical accretion to unity in the optically thin part of the flow - at a radius of order 100-1000 Schwarzschild radii. It is pointed out that if the flow at a larger radius is forced to be supersonic and cold, by some cooling process like collisional excitation of line radiation, the flow cannot be time-independent. The critical accretion rates are determined below which accretion flows either are forced to be time dependent or become optically thick before the minimum in the Mach number is reached. The implication for the time variability of quasars and active galactic nuclei is discussed. It is pointed out that the dissipation of magnetic fields carried by the accreting matter can also provide a heat source ('dissipative heating') sufficient to prohibit stationary flow. This point is considered to be of particular relevance to accretion onto a black hole, when the central object itself does not provide any luminosity to heat the matter at a large radius by Compton scattering.

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