We study the evolution of disk accretion during the merger of supermassive black hole binaries in galactic nuclei. In hierarchical galaxy formation models, the most common binaries are likely to arise from minor galactic mergers, and have unequal mass black holes. Once such a binary becomes embedded in an accretion disk at a separation a ∼ 0.1 pc, the merger proceeds in two distinct phases. Dur...

In the 1970s, the standard accretion disk models were constructed to largely explain observations from the binary systems. In these systems, angular momentum supplied at the outer edge is necessarily Keplerian. Viscosity drives the inflow by removing angular momentum outwards and keeping the entire disk Keplerian in the process. Since then these binary disk models are being used also to explain...

Recent observations of the radio and NIR source Sgr A* reinforce the interpretation of the Galactic Center as a scaled down version of an AGN. The discovery of an elongated structure at 43 GHz and increasing evidence for the presence of an accretion disk surrounding a Black Hole lead us to assume that both, an accretion disk and a jet, are present in the Galactic Center and are physically linke...

We present results from fully general relativistic three-dimensional numerical studies of thickdisk accretion onto a rapidly-rotating (Kerr) black hole with a spin axis that is tilted (not aligned) with the angular momentum vector of the disk. We initialize the problem with the solution for an aligned, constant angular momentum, accreting thick disk, which is then allowed to respond to the Lens...

The theory of coronal evaporation predicts the formation of an inner hole in the cool thin accretion disk for mass accretion rates below a certain value (≈ 1/50 of the Eddington mass accretion rate) and the sudden disappearance of this hole when the mass accretion rate rises above that value. The inner edge of the standard thin disk then suddenly shifts inward vvvvfrom about a few hundred Schwa...

We reexamine the hypothesis that the optical/UV/soft X-ray continuum of Active Galactic Nuclei is thermal emission from an accretion disk. Previous studies have shown that fitting the spectra with the standard, optically thick and geometrically thin accretion disk models often led to luminosities which contradict the basic assumptions adopted in the standard model. There is no known reason why ...

We suggest a possible mechanism of efficient transport of the large-scale external magnetic flux inward through a turbulent accretion disk. The outward drift by turbulent diffusion which limits the effectiveness of this process is reduced if the external flux passes through the disk in concentrated patches. Angular momentum loss by a magnetocentrifugal wind from these patches of strong field ad...

If a Kerr black hole is connected to a disk rotating around it by a magnetic field, the rotational energy of the Kerr black hole provides an energy source for the radiation of the disk in addition to disk accretion. The black hole exerts a torque on the disk, which transfers energy and angular momentum between the black hole and the disk. If the black hole rotates faster than the disk, energy a...

Accretion rates of order 10 M⊙yr −1 are observed in young pre–main– sequence (PMS) stars of approximately a solar mass with evidence of circumstellar disks. The accretion rate is significantly lower for PMS stars of smaller mass, approximately proportional to the second power of the stellar mass, Ṁaccr ∝ M . The traditional view is that the observed accretion is the consequence of the angular m...

Three classical modes of accretion are briefly discussed: wind-fed, spherical, and disk. The three modes are illustrated with the mass transfer onto black holes in high-mass X-ray binaries. Then a new regime of mini-disk accretion is described and it is argued that observed wind-fed X-ray sources are likely to accrete in this regime. Switching from one accretion mode to another can cause the ob...