A fraction of neutrino emission from GRB accretion disks annihilates above the disk, creating e+plasma that can drive GRB explosions. We calculate the efficiency of this annihilation using the recent detailed model of hyper-accretion disks around Kerr black holes. Our calculation is fully relativistic and based on a geodesic-tracing method. We find that the efficiency is a well-defined function...

This review covers the main aspects of black hole accretion disk theory. We begin with the view that one of the main goals of the theory is to better understand the nature of black holes themselves. In this light we discuss how accretion disks might reveal some of the unique signatures of strong gravity: the event horizon, the innermost stable circular orbit, and the ergosphere. We then review,...

Radiation pressure-dominated accretion disks are predicted to exhibit strong density inhomogeneities on scales much smaller than the disk scale height, due to the nonlinear development of photon bubble instability. Radiation would escape from such a “leaky” disk at a rate higher than that predicted by standard accretion disk theory. The disk scale height is then smaller than that of a similar d...

Black holes are most often detected by the radiation produced when they gravitationally pull in surrounding gas, in a process called accretion. The efficiency with which the hot gas radiates its thermal energy strongly influences the geometry and dynamics of the accretion flow. Both radiatively efficient thin disks and radiatively inefficient thick disks are observed. When the accreting gas get...

We consider a subset of the physical processes that determine the spin j ≡ a/M of astrophysical black holes. These include: (1) Initial conditions. Recent models suggest that the collapse of supermassive stars are likely to produce black holes with j ∼ 0.7. (2) Major mergers. The outcome of a nearly equal mass black hole-black hole merger is not yet known, but we review the current best guesses...

We consider observational tests for the nature of Ultraluminous X-ray sources (ULXs). These must distinguish between thermal–timescale mass transfer on to stellar–mass black holes leading to anisotropic X-ray emission, and accretion on to intermediate–mass black holes. We suggest that long–term transient behavior via the thermal–viscous disk instability could discriminate between these two poss...

Recently, reliable mass estimates for the central black holes in AGN became feasible due to emission-line reverberation techniques. Using this method as a calibrator, it is possible to determine black hole masses for a wide range of AGN, in particular NLS1s. Do NLS1s have smaller black holes than ordinary Seyfert 1 galaxies? Are their black holes smaller compared to the sizes of their host gala...

We study nucleosynthesis in low accretion rate hot advective flows around black holes. We find that matter is generally photo-dissociated into protons and neutrons inside the disk. These neutrons stay around black holes for longer time because they are not coupled to magnetic fields while the protons accrete into the hole. We find the nature of the resulting neutron disks and estimate the rate ...

It is well known that the outer parts of QSO accretion disks are prone to selfgravity if heated solely by orbital dissipation. Such disks might be expected to form stars rather than accrete onto the black hole. The arguments leading to this conclusion are reviewed. Conversion of a part of the gas into high-mass stars or stellar-mass black holes, and the release of energy in these objects by fus...

We use three dimensional hydrodynamical simulations to show that a highly misaligned accretion disk around one component of a binary system can exhibit global Kozai–Lidov cycles, where the inclination and eccentricity of the disk are interchanged periodically. This has important implications for accreting systems on all scales, for example, the formation of planets and satellites in circumstell...