The entropy distribution of the intracluster medium and the shape of its confining potential well completely determine the X-ray properties of a relaxed cluster of galaxies, motivating us to explore the origin of intracluster entropy and to describe how it develops in terms of some simple models. We present an analytical model for smooth accretion, including both preheating and radiative coolin...

We consider the implications of recent infrared and radio observations of the nucleus of NGC 4258. There is no direct evidence that the nucleus has been steadily accreting on the viscous timescale of the outer masing disk, which is ∼> 10 9 yr. Thus the mass accretion rate in the outer disk need not be the same as in the inner accretion flow where most of the gravitational binding energy is rele...

A high angular resolution study of the nucleus of the FR I galaxy IC4296 using Chandra ACIS-S and VLBA observations is presented, with the aim of studying the nature of the accretion process. Pointlike and hard X-ray emission is found, well described by a moderately absorbed power law of Γ = 1.48 −0.34; no iron fluorescence line from cold material is detected. The 0.3–10 keV luminosity is 2.4 ×...

It is argued that there is a linear correlation between star formation rate (SFR) and accretion rate for normal bright active galactic nuclei (AGNs). However, it is still unclear whether this correlation holds for LINERs, of which the accretion rates are relatively lower than those of normal bright AGNs. The radiatively inefficient accretion flows (RIAFs) are believed to be present in these LIN...

The classical Bondi-Hoyle formula gives the accretion rate onto a point particle of a gas with a uniform density and velocity. However, the Bondi-Hoyle problem considers only gas with no net vorticity, while in a real astrophysical situation accreting gas invariably has at least a small amount of vorticity. We therefore consider the related case of accretion of gas with constant vorticity, for ...

Low-resolution spectra from 3000–9000 Å of young low-mass stars and brown dwarfs were obtained with LRIS on Keck I. The excess UV and optical emission arising in the Balmer and Paschen continua yields mass accretion rates ranging from 2×10 to 10 M⊙ yr . These results are compared with HST/STIS spectra of roughly solar-mass accretors with accretion rates that range from 2× 10 to 5 × 10 M⊙ yr . T...

We analyze three-dimensional magnetohydrodynamic (MHD) simulations of a nonradiative accretion flow around a black hole using a pseudo-Newtonian potential. The flow originates from a torus initially centered at 100 gravitational (Schwarzschild) radii. Accretion is driven by turbulent stresses generated selfconsistently by the magnetorotational instability. The resulting flow has three well-defi...

Relativistic jets are a fundamental aspect of accretion onto black holes on all scales. They can carry away a large fraction of the available accretion power in collimated flows which later energise particles in the ambient medium. The removal of this accretion power and angular momentum must have a dramatic effect on the overall process of accretion. In their most spectacular form they are ass...

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...

Observations have revealed that most stars are born in clusters. As these clusters typically contain more mass in gas than in stars, accretion can play an important role in determining the final stellar masses. Numerical simulations of gas accretion in stellar clusters have found that the stars compete for the available reservoir of gas. The accretion rates are highly nonuniform and are determi...