It has been found that a class of optically-thin two-temperature advection-dominated accretion solutions explains many observations of low-luminosity accreting black holes. Here it is shown that these models give a satisfactory description also of higher luminosity systems, provided the viscosity parameter is large. The models reproduce the spectra of black hole X-ray binaries in the Low State,...

Recent X-ray surveys by Chandra and XMM-Newton have revealed a population of X-ray bright, optically normal galaxies (XBONGs) at moderate redshifts. By analogy with nearby low-luminosity active galactic nuclei, we propose that many XBONGs are powered by an inner radiatively inefficient accretion flow (RIAF) plus an outer standard thin accretion disk. The absence of optical/UV activity in XBONGs...

We estimate the masses of massive black holes in BL Lac objects from their host galaxy luminosity. The power of jets and central optical ionizing luminosity for a sample of BL Lac objects are derived from their extended radio emission and the narrow-line emission, respectively. The maximal jet power can be extracted from a standard thin accretion disk/spinning black hole is calculated as a func...

We use a sample of radio-loud active galactic nuclei (AGNs) with estimated central black hole masses to explore their jet formation mechanisms. The jet power of AGNs is estimated from their extended radio luminosity. It is found that the jets in several AGNs of this sample are too powerful to be extracted from the standard thin accretion disks or rapidly spinning black holes surrounded by stand...

Episodic ejection of plasma blobs have been observed in many black hole systems. While steady, continuous jets are believed to be associated with largescale open magnetic fields, what causes the episodic ejection of blobs remains unclear. Here by analogy with the coronal mass ejection on the Sun, we propose a magnetohydrodynamical model for episodic ejections from black holes associated with th...

A newly formed black hole may be directly identified if late-time accretion of material from the base of the ejected envelope generates a luminosity that is observable in the tail of the supernova light curve. In this work we estimate the rate at which events where the black hole “emerges” in the supernova light curve can be detected with present capabilities. Our investigation is based on an a...

The radio source Sgr A at the center of our Galaxy is believed to be a 2.6× 10M⊙ black hole which accretes gas from the winds of nearby stars. We show that limits on the X-ray and infrared emission from the Galactic Center provide an upper limit of ∼ 8 × 10M⊙ yr −1 on the mass accretion rate in Sgr A. The advection-dominated accretion flow (ADAF) model favors a rate <∼ 10 M⊙ yr . In comparison,...

Modeling the late inspiral and merger of supermassive black holes is central to understanding accretion processes and the conditions under which electromagnetic emission accompanies gravitational waves. We use fully general relativistic, hydrodynamics simulations to investigate how electromagnetic signatures correlate with black hole spins, mass ratios, and the gaseous environment in this final...

The discovery of hundreds of young, bright stars within a parsec from the massive black hole Sgr A at the center of the Galaxy presents a challenge to star formation theories. The requisite Roche densities for gravitational collapse of gas clouds are most naturally achieved in accretion disks. The water maser sources in Keplerian rotation in the nuclei of NGC4258, NGC1068, and the Circinus Gala...

We have calculated the structures and the emergent spectra of stationary, geometrically thin accretion disks around 100 and 1000 M⊙ black holes in both the Schwarzschild and extreme Kerr metrics. Equations of radiative transfer, hydrostatic equilibrium, energy balance, ionization equilibrium, and statistical equilibrium are solved simultaneously and consistently. The six most astrophysically ab...