Related papers: Quasars vs. Microquasars: Scaling and Particle Acc…
We have assembled a sample of 37 RLQs that have been imaged with the HST in order to investigate their black hole masses, accretion rates, and the structure of their accretion disks. The black hole masses were estimated from the…
Quasars emission is highly variable, and this variability gives us clues to understand the accretion process onto supermassive black holes. We can expect variability properties to correlate with the main physical properties of the accreting…
According to a currently popular paradigm, nuclear activity in quasars is sustained via accretion of material onto super-massive black holes located at the quasar nuclei. A useful tracer of the gravitational field in the vicinity of such…
It has long been believed that accretion onto supermassive black holes powers quasars, but there has been relatively few observational constraints on the spins of the black holes. We address this problem by estimating the average radiative…
We analysed the optical and radio properties of lobe-dominated giant-sized (> 0.72 Mpc) radio quasars and compared the results with those derived for a sample of smaller radio sources to determine whether the large size of some…
The low-frequency power spectra of the X-ray and radio emission from four microquasars suggest that two distinct modes of energy output are at work: (i) the `coupled' mode in which the X-ray and radio luminosities are closely coupled and…
A non-negligible fraction of quasars are red at optical wavelengths, indicating (in the majority of cases) that the accretion disc is obscured by a column of dust which extinguishes the shorter-wavelength blue emission. In this paper, we…
A solid theoretical understanding of how inflowing, accreting plasma around black holes and other compact objects gives rise to outflowing winds and jets is still lacking, despite decades of observations. The fact that similar processes and…
The majority of quasars are weak in their radio emission, with flux densities comparable to those in the optical, and energies far lower. A small fraction, about 10%, are hundreds to thousands of times stronger in the radio. Conventional…
The results of a comprehensive study of the cluster environments and black-hole masses of an optically matched sample of radio-loud and radio-quiet quasars are presented. No evidence is found for a difference in large-scale environments,…
We use the microlensing variability observed for nine gravitationally lensed quasars to show that the accretion disk size at 2500 Angstroms is related to the black hole mass by log(R_2500/cm) = (15.6+-0.2) + (0.54+-0.28)log(M_BH/10^9M_sun).…
Microquasars are compact objects (stellar-mass black holes and neutron stars) that mimic, on a smaller scale, many of the phenomena seen in quasars. Their discovery provided new insights into the physics of relativistic jets observed…
A key argument in favor of orientation based unification schemes is the finding that among the most powerful 3CRR radio sources the (apparent) median linear size of quasars is smaller than that of radio galaxies, which supports the idea…
To some extent, all Galactic binary systems hosting a compact object are potential `microquasars', so much as all galactic nuclei may have been quasars, once upon a time. The necessary ingredients for a compact object of stellar mass to…
We use the integrated spectrum of the X-ray background and quasars Spectral Energy Distribution to derive the contribution of quasars to the energy output of the Universe. We find a lower limit for the energy from accretion onto black holes…
We present a model for the cosmological evolution of quasars (QSOs) under the assumption that they are powered by massive accreting black holes. Accretion flows around massive black holes make a transition from high radiative efficiency…
In order to investigate the dependence of quasar optical-UV variability on fundamental physical parameters like black hole mass, we have matched quasars from the QUEST1 variability survey with broad-lined objects from the SDSS. Black hole…
We present evidence for the presence of a transition in the accretion properties of radio-loud sources. For a sample of radio galaxies and radio-loud quasars, selected based on their extended radio properties, the accretion rate is…
Quasars, powered by gas accretion onto supermassive black holes, rank among the most energetic objects of the Universe. While they are thought to be ignited by galaxy mergers and affect the surrounding gas, observational constraints on both…
We use the microlensing variability observed for eleven gravitationally lensed quasars to show that the accretion disk size at a rest-frame wavelength of 2500 Angstroms is related to the black hole mass by log(R_{2500}/cm)=(15.78\pm0.12) +…