Friday, July 5, 2013

1307.1143 (A. Sadowski et al.)

Energy, momentum and mass outflows and feedback from thick accretion discs around rotating black holes    [PDF]

A. Sadowski, R. Narayan, R. Penna, Y. Zhu
A set of long-duration general relativistic magnetohydrodynamic simulations of radiatively inefficient accretion discs around rotating black holes are presented, and are used to estimate the energy, mass and momentum outflow rates from such systems. Outflows occur via two fairly distinct modes: a relativistic jet and a sub-relativistic wind. The jet power depends strongly on the black hole spin and on the magnetic flux at the horizon. Unless these are very small, the energy output in the jet dominates over that in the wind. In the limit of a rapidly spinning black hole accreting in the magnetically arrested limit, when the magnetic flux at the black hole is maximum, the jet power exceeds the total rate of accretion of rest mass energy. However, because of strong collimation, the jet probably does not have a significant effect on its surrounding. In the case of an accreting supermassive black hole, external feedback via a jet is likely important only on the largest galaxy cluster scales. The power in the wind is more modest and shows a weaker dependence on the black spin and magnetic flux. Nevertheless, because the wind subtends a large solid angle, it is expected to provide efficient feedback on a wide range of scales inside the host galaxy. Using the simulation results as a guide, empirical formulae are obtained for the energy outflow rates in the jet and the wind, and also for the respective momentum outflow rates. The mass outflow rates are more uncertain, especially in the case of the wind.
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