Related papers: Does the circularization radius exist or not for l…
The derivation of the viscosity formula of accretion disks appearing in a number of textbooks is based on a mean free path theory of gas particles. However, this procedure, when followed precisely, leads to the incorrect conclusion that the…
We consider time-dependent models for rotating accretion flows onto black holes, where a transition takes place from an outer cooling-dominated disc to a radiatively inefficient flow in the inner region. In order to allow for a transition…
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…
The inner boundary of a black hole accretion disk is often set to the marginally stable circular orbit (or the innermost stable circular orbit, ISCO) around the black hole. It is important for the theories of black hole accretion disks and…
Non-radiating, advection-dominated, accretion flows are convectively unstable. We calculate the two-dimensional (r-theta) structure of such flows assuming that (1) convection transports angular momentum inwards, opposite to normal viscosity…
We report on the second phase of our study of slightly rotating accretion flows onto black holes. We consider magnetohydrodynamical (MHD) accretion flows with a spherically symmetric density distribution at the outer boundary, but with…
The origin of the spins of giant planets is an open question in astrophysics. As planets and stars accrete from discs, if the specific angular momentum accreted corresponds to that of a Keplerian orbit at the surface of the object, it is…
Accretion flows are fundamentally turbulent systems, yet are classically modelled with viscous theories only valid on length scales significantly greater than the typical size of turbulent eddies in the flow. We demonstrate that, while this…
(Abridged) A new type of self-similar hot viscous radiative accretion flow onto a rapidly spinning neutron star has recently been discovered. This ``hot brake'' flow forms in the two-temperature zone (close to a central object), but at a…
In this chapter, we review the role of gas accretion to the acquisition of angular momentum, both in galaxies and in their gaseous halos. We begin by discussing angular momentum in dark matter halos, with a brief review of tidal torque…
In this paper, we fist consider the shadow radius of a quantum corrected black hole proposed recently, and provide a bound on the correction parameter based on the observational data of Sgr A*. Then, the effects of the correction parameter…
We discuss steady viscous Keplerian decretion discs around rapidly rotating stars. We assume that low frequency modes, which may be excited by the opacity bump mechanism, convective motion in the core, or tidal force if the star is in a…
The radial transport of angular momentum in accretion disk is a fundamental process in the universe. It governs the dynamical evolution of accretion disks and has implications for various issues ranging from the formation of planets to the…
The accretion of hot slowly rotating gas onto a supermassive black hole is considered. Rotation velocities at the Bondi radius r_B are small in comparison with speed of sound c_s. The centrifugal barrier at a depth r_c = l^2/G M_BH << r_B…
Gas accretion and radial flows are key ingredients of the chemical evolution of spiral galaxies. They are also tightly linked to each other (accretion drives radial flows, due to angular momentum conservation) and should therefore be…
We study the global solutions of slowly rotating accretion flows around the supermassive black hole in the nucleus of an elliptical galaxy. The velocity of accreted gas surrounding the black hole is initially subsonic and then falls onto…
We use three dimensional magnetohydrodynamic simulations, in a pseudo-Newtonian potential, to study geometrically thin accretion disc flows crossing the marginally stable circular orbit around black holes. We concentrate on vertically…
We calculate the amount of angular momentum that thermal photons carry out of a viscous black hole accretion disc, due to the strong Doppler shift imparted to them by the high orbital velocity of the radiating disc material. While the…
Axisymmetric accretion disks in vicinity of a central compact body are studied. In the case of non-viscous disk it is proven that all solutions for the midplane circular velocity are unstable. Hence, the pure hydrodynamic turbulence in…
I discuss the stability of accretion disks when the black hole is considered to be rotating. I show, how the fluid properties get changed for different choices of angular momentum of black holes. I treat the problem in pseudo-Newtonian…