Related papers: Spherical Accretion in Nearby Weakly Active Galaxi…
In order to find an explanation for the radiative quiescence of supermassive black holes in the local Universe, for a sample of nearby galaxies the most accurate estimates are collected for the mass of a central black hole M_BH, the nuclear…
We present a new model for low-luminosity X-ray sources in globular clusters, with L_x < 10^34 erg/s. The model we propose is that of a single neutron star accreting from cluster gas that has accumulated as a natural product of stellar…
We use new central stellar velocity dispersions and nuclear X-ray and Halpha luminosities for the Palomar survey of nearby galaxies to investigate the distribution of nuclear bolometric luminosities and Eddington ratios for their central…
Our X-ray study of the nuclear activity in a new sample of six quiescent early-type galaxies, and in a larger sample from the literature, confirmed (Soria et al., Paper I) that the Bondi accretion rate of diffuse hot gas is not a good…
We develop an analytic, steady-state model for the gas environment in quiescent galactic nuclei. We assume that the mass is constantly supplied by a spherically symmetric distribution of wind emitting stars, and that gravity is solely due…
We analytically study the dynamical and thermal properties of the optically-thin gases at the parsec-scale when they are spherically accreted onto low luminous active galactic nuclei (LLAGNs). The falling gases are irradiated by the central…
We present an analysis of the XMM-Newton and Chandra ACIS-S observations of the LINER nucleus of the Sombrero galaxy and we discuss possible explanations for its very sub-Eddington luminosity by complementing the X-ray results with high…
The discovery of hard, power-law X-ray emission from a sample of six nearby elliptical galaxies, including the dominant galaxies of the Virgo,Fornax and Centaurus clusters (M87, NGC 1399 and NGC 4696, respectively), and NGC 4472, 4636 and…
Accretion onto central massive black holes in galaxies is often modelled with the Bondi solution. In this paper we study a generalization of the classical Bondi accretion theory, considering the additional effects of the gravitational…
Two possible explanations for the low luminosity of the supermassive black hole at the center of our galaxy are (1) an accretion rate of order the canonical Bondi value (roughly 10^{-5} solar masses per year), but a very low radiative…
We have studied the nuclear activity in a sample of six quiescent early-type galaxies, with new Chandra data and archival HST optical images. Their nuclear sources have X-ray luminosities ~ 10^{38} - 10^{39} erg/s (L_X/L_Edd ~ 10^{-8} -…
Compact objects are expected to exist in the accretion disks of supermassive black holes (SMBHs) in active galactic nuclei (AGNs), and in the presence of such a dense environment ($\sim 10^{14}\,{\rm cm^{-3}}$), they will form a new kind of…
(Abridged) We propose a new method to estimate the Bondi (hot gas) accretion rates, \dot M_B, onto the supermassive black holes (SMBHs) at the centres of elliptical galaxies. It can be applied even if the Bondi radius is not well-resolved…
The classical Bondi model is adopted to study accretion onto the finite luminous region around the central massive black hole (MBH) in an elliptical galaxy. Unlike Bondi (1952), we define the boundary conditions at a certain finite radius…
A large number of neutron stars (NSs), ~10^9, populate the Galaxy, but only a tiny fraction of them is observable during the short radio pulsar lifetime. The majority of these isolated NSs, too cold to be detectable by their own thermal…
This paper presents a study of quasi-steady spherical accretion in the early Universe, before the formation of the first stars and galaxies. The main motivation is to derive the basic formulas that will be used in a companion paper to…
Hermann Bondi's 1952 paper "On spherically symmetrical accretion" is recognized as one of the foundations of accretion theory. Although Bondi later remarked that it was "not much more than an examination exercise", his mathematical analysis…
We use Chandra X-ray data and Very Large Array radio observations for a sample of 20 nearby, massive, X-ray bright, early-type galaxies to investigate the relation between the Bondi accretion rates and the mechanical jet powers. We find a…
Nearby galactic nuclei are observed to be very much dimmer than active galactic nuclei in distant galaxies. The Chandra X-ray Observatory has provided a definitive explanation for why this is so. With its excellent angular resolution,…
Bondi accretion assumes that there is a sink of mass at the center -- which in case of a black hole (BH) corresponds to the advection of matter across the event horizon. Other stars, such as a neutron star (NS), have surfaces and hence the…