Dynamics and Energetics of Turbulent, Magnetized Disk Accretion around Black Holes: A First‐Principles Approach to Disk‐Corona‐Outflow Coupling

Abstract

We present an analytic description of turbulent, magnetohydrodynamic (MHD) disk accretion around black holes that specifically addresses the relationship between radial and vertical mean field transport of mass, momentum, and energy, thereby complementing and extending numerical simulations. The azimuthal-vertical component of the magnetic stress is fundamental to an understanding of disk-corona-outflow coupling: when it is important for driving the angular momentum transport and mass accretion in the disk, it also has an important influence on the disk-corona-outflow energy budget. The Poynting flux derived from the product of this term with the Keplerian velocity also dominates the Poynting flux into the corona. The ratio of the coronal Alfven velocity to the Keplerian velocity is an important parameter in disk-corona-outflow physics. If this parameter is greater than unity, then energetically significant winds and Poynting flux into the corona occur. However, significant effects could also occur when this parameter is much less than unity. A limiting solution describing the case of angular momentum transport solely by the vertical-azimuthal stress has the property that all of the accretion power is channeled into a wind, some of which would be dissipated in the corona. More realistic solutions in which there is both radial and vertical transport of angular momentum would have different fractions of the accretion power emitted by the disk and corona, respectively. These results have important implications for existing accretion disk theory and for our interpretation of high-energy emission and nuclear outflows from the central engines of active galactic nuclei and galactic black hole candidates.