Current theoretical models for the outflows/jets from AGN, X-ray binaries and young stellar objects involve large-scale magnetic fields threading an underlying accretion disk. We suggest that such a disk is subjected to warping instability and retrograde precession driven by magnetic torques associated with the outflow. The growth timescale for the disk warp and the precession period are of ord...

We consider the classic MHD turbulent dynamo operating in a thin, Keplerian accretion disk powered by turbulent viscous stress. The character of the turbulence is encapsulated into two constant parameters: the Shakura-Sunyaev dimensionless viscosity, SS , and the Coriolis number, = 2 corr. The dependence of the total electromotive force on SS and is derived and the dynamo-generated magnetic eld...

We discuss the solution of accretion disk when the black hole is chosen to be rotating. We study, how the fluid properties get affected for different rotation parameters of the black hole. We know that no cosmic object is static in Universe. Here the effect of the rotation of the black hole to the space-time is considered following an earlier work of the author, where the pseudo-Newtonian poten...

We present new numerical simulations in the thin-disk approximation which characterize the burst mode of protostellar accretion. The burst mode begins upon the formation of a centrifugally balanced disk around a newly formed protostar. It is comprised of prolonged quiescent periods of low accretion rate (typically . 10M⊙ yr ) which are punctuated by intense bursts of accretion (typically & 10M⊙...

We model the UV/optical spectrum of the black hole binary Nova Muscae as a sum of black body emissions from the outer region of an accretion disk. We show for self-consistency that scattering effects in this region are not important. The black hole mass (M ≈ 6M⊙), the inclination angle (μ ≈ 0.5) and the distance to the source (D ≈ 5 kpc) have been constrained by optical observations during quie...

The efficiency of thin disk accretion onto black holes depends on the inner boundary condition, specifically the torque applied to the disk at the last stable orbit. This is usually assumed to vanish. I estimate the torque on a magnetized disk using a steady magnetohydrodynamic inflow model originally developed by Takahashi et al. 1990. I find that the efficiency ǫ can depart significantly from...

We show that the irradiated accretion disk model can account for all the optical and infrared observations of the anomalous X-ray pulsars in the persistent state. While placing an upper limit on the inner disk radii, and thus on the strength of the dipole component of the stellar magnetic field, the model fits do not constrain the outer disk radii. And while magnetar fields ( G) in higher multi...

We show that the irradiated accretion disk model can account for all the optical and infrared observations of the anomalous X-ray pulsars in the persistent state. Model fits do not constrain the outer disk radii, while placing an upper limit to the inner disk radii, and thus to the strength of the dipole component of the stellar magnetic field. While magnetar fields (B∗ > 10 14 G) in higher mul...

Establishing the origin of accretion powered winds from forming stars is critical for understanding angular momentum evolution in the star-disk interaction region. Here, the high velocity component of accretion powered winds is launched and accreting stars are spun down, in defiance of the expected spin-up during magnetospheric accretion. T Tauri stars in the final stage of disk accretion offer...

We have studied numerically the evolution of protostellar disks around intermediate and upper mass T Tauri stars (0.25 M⊙ < M∗ < 3.0 M⊙) that have formed self-consistently from the collapse of molecular cloud cores. In the T Tauri phase, disks settle into a self-regulated state, with low-amplitude nonaxisymmetric density perturbations persisting for at least several million years. Our main find...