INFLUENCE OF OHMIC HEATING ON ADVECTION-DOMINATED ACCRETION FLOWS

Advection-dominated, high-temperature, quasi-spherical accretion flow onto a compact object, recently considered by a number of authors, ass umes that the dissipation of turbulent energy of the flow heats the io ns and that the dissipated energy is advected inward. It is suggested that the efficiency of conversion of accretion energy to radiation can be very much smaller than unity. However, it is likely that the hows have an equipartition magnetic field with the result that dissipation of magnetic energy at a rate comparable to that for the turbulence mus t occur by ohmic heating. We argue that this heating occurs as a resul t of plasma instabilities and that the relevant instabilities are curr ent driven in response to the strong electric fields parallel to the m agnetic held. We argue further that these instabilities heat predomina ntly the electrons. We conclude that the efficiency of conversion of a ccretion energy to radiation can be much smaller than unity only for t he unlikely condition that the ohmic heating of the electrons is negli gible.