It is usually proposed that hyperaccretion disks surrounding stellar-mass black holes at an accretion rate of a fraction of one solar mass per second, which are produced during the mergers of double compact stars or the collapses of massive stars, are central engines of gamma-ray bursts (GRBs). In some origin/afterglow models, however, newborn compact objects are invoked to be neutron stars rat...

The proposed Laser Interferometer Space Antenna is expected to detect gravitational waves from neutron stars and stellar-mass black holes spiraling into supermassive black holes in distant galactic nuclei. Analysis of the inspiral events will require careful comparison of the observed signals with theoretical waveform templates. The comparison could be seriously compromised if non-gravitational...

These lectures provide an overview of the theory of accretion disks with application to bright sources containing black holes. I focus on the fundamental physics of these flows, stressing modern developments and outstanding questions wherever possible. After a review of standard Shakura-Sunyaev based models and their problems and uncertainties, I describe the basic principles that determine the...

The assumption that black hole accretion disks possess an untorqued inner boundary, the so-called zero torque boundary condition, has been employed by models of black hole disks for many years. However, recent theoretical and observational work suggests that magnetic forces may appreciably torque the inner disk. This raises the question of the effect that a time-changing magnetic torque may hav...

Discerning the likelihood of the so-called runaway instability of thick accretion disks orbiting black holes is an important issue for most models of cosmic gamma-ray bursts. To this aim we investigate this phenomenon by means of time-dependent, hydrodynamical simulations of black hole plus torus systems in general relativity. The evolution of the central black hole is assumed to be that of a s...

Geometrically thick disks may form after tidal disruption events, and rapid accretion may lead to short flares followed by long-term, lower-level emission. Using a novel accretion disk code which relies primarily on global conservation laws and the assumption that viscosity is everywhere positive, a broad range of physically allowed evolutionary sequences of thick disks is investigated. The mai...

We investigate the possibility that stellar mass black holes, with masses in the range of 3.8M⊙ and 6M⊙, respectively, could be in fact quark stars in the Color-Flavor-Locked (CFL) phase. Depending on the value of the gap parameter, rapidly rotating CFL quark stars can achieve much higher masses than standard neutron stars, thus making them possible stellar mass black hole candidates. Moreover,...

We present results of several numerical simulations of two dimensional axisymmetric accretion flows around black holes using the Smoothed Particle Hydrodynamics (SPH). We consider both stellar black holes and as well as supermassive black holes. We assume bremsstrahlung to be the only source of cooling as it is simpler to implement in numerical simulations. We observe that due to both radial an...

— Ten years have passed since the global solutions of advective accretion disks around black holes and neutron stars were first discovered. Since then they are enjoying support from observers almost on a daily basis, more so in recent days with the launching of very high resolution satellites. This review presents the development of the subject of advective accretion in last twenty five years l...

This article reviews the current status of black hole astrophysics, focusing on topics of interest to a physics audience. Astronomers have discovered dozens of compact objects with masses greater than 3M⊙, the likely maximum mass of a neutron star. These objects are identified as black hole candidates. Some of the candidates have masses ∼ 5− 20M⊙ and are found in X-ray binaries, while the rest ...