Surrounding the Galactic center is a molecular cloud with a central black hole. This raises the question as to how the hole was formed. While clouds containing HCN are circulating around the Galactic center, they do not all move at the same speed and so collide mutually and should make a more uniform motion and distribution after a period of some 100 kyrs (e.g., Ekers, van Gorkom, Schwartz et al. 1983). Hence some very energetic phenomena must have occurred within that period.

We propose a plausible mechanism for orbital angular momentum loss in black-hole intermediate-mass X-ray binaries, assuming that a small fraction of the transferred mass form a circumbinary disc. The disc can effectively drain orbital angular momentum from the binary, leading to the formation of compact black-hole low-mass X-ray binaries. This scenario also suggests the possible existence of luminous, persistent black hole low-mass X-ray binaries.

Both the X-shaped radio galaxies and double-double radio galaxies (DDRGs) are suggested in the literature to be due to the binary-accretion disk interaction or to the coalescence of SMBBHs. These models suggest some relationship between the two types of radio sources. In this paper, we collected data from literatures for two samples of X-shaped and double-double radio galaxies together with a control sample of FRII radio galaxies and statistically investigate their properties.

We find that the wings of X-shaped radio galaxies and the outer and inner lobes of DDRGs tend to be perpendicular to the major axis of the host galaxy (or dust structures), while the active lobes orient randomly. Both X-shaped and double-double radio galaxies are low luminous FRII or FRI/FRII transitional radio sources with the similar dimensionless accretion rate ṁ ∼ 0.01, which is about the transitional accretion rate given in the literature.

All the statistic results can be reconciled if there is an evolutionary relationship between X-shaped and double-double radio galaxies, in the sense that X-shaped radio galaxies may be due to the interaction of active SMBBHs and accretion disk and DDRGs due to the removal of inner disk region and the coalescence of SMBBHs.

We construct an exact and simple general relativistic model to describe a galactic disc based on a Schwarzschild disc immersed in a six dimensional space-time. The stability of this configuration is studied and we present results for the calculation of circular geodesic orbits.

We show, performing a viable cosmological window, that only the magneto hydrodynamic (MHD) disk model is capable to explain how an intermediate mass black hole (IMBH) (with masses ∼ 103M⊙) grows unto a supermassive black hole (SMBH) (with masses ∼ 107M⊙). We still calculate the supermassive stars sequence of stability. Those stars, with synthetized helium or oxygen cores, collapse to form IMBHs. In our calculation we show that the primordial stars must have rapid rotation if they are in the stable part of the sequence.

At the centre of the Milky Way is Sgr A*, a putative 3 million solar mass black hole with an observed luminosity that is orders of magnitude smaller than that expected from simple accretion theories. The number density of early-type stars is quite high near Sgr A*, so the ensemble of their stellar winds has a significant impact on the black hole's environment.

We present results of 3D hydrodynamic simulations of the accretion of stellar winds onto Sgr A*. Using the LANL/SAIC code, RAGE, we model the central arc-second of the Galaxy, including the central cluster stars (the S-stars) with orbits and wind parameters that match observations. A significant fraction of the winds from the S stars becomes gravitationally bound to the black hole and thus could provide enough hot gas to produce the X-ray emission seen by Chandra. We perform radiative transfer calculations on the 3D hydrodynamic data cubes and present the resulting synthetic X-ray spectrum.

The growth of supermassive black holes (SBHs) appears to be closely linked with the formation of spheroids. There is a pressing need to acquire better statistics on SBH masses, since the existing samples are preferentially weighted toward early-type galaxies with very massive SBHs. With this motivation we started a project aimed at measuring upper limits on the mass of the SBHs in the center of all the nearby galaxies (D < 100 Mpc) for which STIS/G750M spectra are available in the HST archive. These upper limits will be derived by modeling the central emission-line widths observed in the Hα region over an aperture of ∼0.1″. Here we present our results for a subsample of 22 S0-Sb galaxies within 20 Mpc.

We summarize findings from imaging surveys of 143 early-type galaxies in the Virgo and Fornax Clusters. Using deep HST images in the F475W (g) and F850LP (z) band-passes obtained with the Advanced Camera for Surveys (ACS), we have examined the central structure of the program galaxies, finding clear evidence for a compact stellar nucleus in ∼ 75% of the sample. The formation of early-type galaxies of low- and intermediate-mass is often – but not always – accompanied by the formation of a compact stellar nucleus.

We develop a two-flow model of accretion onto a black hole which incorporates the effect of the local magneto-rotational instability. The flow consists of an accretion disk and an accreting corona, and the local dynamo affects the disk/corona mass exchange. The model is aimed to explain the power spectra of the sources in their soft, disk-dominated states. The local perturbations of the magnetic field in the disk are described as in King et al. (2004) and Mayer & Pringle (2006), but the time-dependent local magnetic field is assumed to affect the local supply of the material to the corona. The accreting corona model can reproduce the broad power spectra of Soft State X-ray binaries and AGN. The model, however, predicts that (i) sources undergoing radiation pressure instability (GRS 1915+105) should have systematically steeper power spectra than other sources, (ii) AGN should have systematically steeper power spectra than GBH. More measurements of power spectra of Soft State sources are clearly needed.

We observed a sample of three Brightest Cluster Galaxies (BCGs), Abell 1836-BCG, Abell 2052-BCG, and Abell 3565-BCG, with the Advanced Camera for Surveys (ACS) and the Imaging Spectrograph (STIS) on board the Space Telescope. For each target galaxy we obtained high-resolution spectroscopy of the Hα and [N II] λ6583 emission lines at three slit positions, to measure the central ionized-gas kinematics. ACS images in three different filters (F435W, F625W, and FR656N) have been used to determine the optical depth of the dust, stellar mass distribution near the nucleus, and intensity map. We present supermassive black hole (SBH) mass estimates for two galaxies which show regular rotation curves and strong central velocity gradients, and an upper limit on the SBH mass of the third one. For the SBHs of Abell 1836-BCG and Abell 3565-BCG, we derived M• = 4.8+0.8−0.7 × 109 M⊙ and M• = 1.3+0.3−0.4 × 109 M⊙ at 1 σ confidence level, respectively. For the SBH of Abell 2052-BCG, we found M• ≤ 7.3 × 109 M⊙.

In February 1997 the Japanese radio astronomy satellite HALCA was launched to provide the space-borne element for the VSOP mission. HALCA provided linear baselines three-times greater than that of ground arrays, thus providing higher resolution and higher AGN brightness temperature measurements and limits. Twenty-five percent of the scientific time of the mission was devoted to the “VSOP survey” of bright, compact, extra-galactic radio sources at 5 GHz. A complete list of 294 survey targets were selected from pre-launch surveys, 91% of which were observed during the satellite's lifetime.

The major goals of the VSOP Survey are statistical in nature: to determine the brightness temperature and approximate structure, to provide a source list for use with future space VLBI missions, and to compare radio properties with other data throughout the electro-magnetic spectrum. All the data collected have now been analysed and is being prepared for the final image Survey paper. In this paper we present details of the mission, and some statistics of the images and brightness temperatures.

The polarization from a spot orbiting around Schwarzschild and extreme Kerr black holes is studied. The time dependence of the degree and angle of polarization during the spot revolution is examined as a function of the observer's inclination angle and black hole angular momentum. The gravitational and Doppler shifts, lensing effect as well as time delays are taken into account.

We present the first high resolution optical spectrum of the black hole candidate BG Geminorum, as well as UV spectroscopy from the Hubble Space Telescope, and X-ray data from INTEGRAL. The UV spectra suggest the presence of material in BG Gem with velocities possibly as high as ∼1000 km s−1, suggesting an origin at a distance of ∼0.7 R⊙ from a 3.5 M⊙ object; if real, this would be strong evidence that the primary in BG Gem is indeed a black hole. In contrast, the upper limit provided by the INTEGRAL data gives a maximum X-ray luminosity of only ∼0.1 of the Eddington luminosity.

Evolution of rotating globular clusters with embedded black holes is presented. The interplay between velocity diffusion due to relaxation and black hole star accretion is followed together with cluster rotation, using 2-dimensional, in energy and z-component of angular momentum, Fokker Planck numerical methods. Gravogyro and gravothermal instabilities drive the system to a faster evolution leading to shorter collapse times and a faster cluster dissolution in the tidal field of a parent galaxy.

Angular momentum transport and star accretion support the development of central rotation in relaxation time scales. Two-dimensional distribution (in the meridional plane) of kinematical and structural parameters (density, dispersions, rotation) are reproduced, with the aim to enable the use of set of models for comparison with observational data.

The 3CR catalogue provides a statistical sampling of the most powerful radio galaxies out to z ∼ 0.3. Over the decade and a half of Hubble observations we have amassed a major multi-wavelength dataset on these sources, discovering amongst other things, new jets, hotspots, dust disks, and faint point-like nuclei. We present here the results of our latest snapshot survey, a near-complete sampling of the 3CR host galaxies at z < 0.3 in the near-IR (H-band). This un-extinguished view of the host galaxies has provided us with an accurate measure of the stellar/spheroid masses of the sources, and an unbiased view of their morphologies. We show that they exhibit an identical Kormendy relation to nearby QSO's and the massive Elliptical population, but are distinct from the Brightest Cluster Members, and mergers. We find that while a few sources exhibit signs of a recent or impending major merger, many more sources have remnants consistent with a gas-rich minor merger in their recent history. We detect unresolved nuclear sources in most (∼80%) of FRI, with their IR luminosities correlating linearly with radio core power. This implies that the IR nuclei are synchrotron radiation produced at the base of the relativistic jet, and confirms that no infrared (thermal) radiation in excess to synchrotron is present in FRIs, unlike in other classes of AGN.

We study magnetohydrodynamic (MHD) standing shocks in ingoing plasmas in a black hole (BH) magnetosphere. We find that low or mid latitude (non-equatorial) standing MHD shocks are both physically possible, creating very hot and/or magnetized plasma regions close to the event horizon. We also investigate the effects of the poloidal magnetic field and the BH spin on the properties of shocks and show that both effects can quantitatively affect the MHD shock solutions. MHD shock formation can be a plausible mechanism for creating high energy radiation region above an accretion disk in AGNs.

We used the long term spectroscopic observations of Mrk 110 (Hα and Hβ lines) to investigate the gravitational field influence on spectral line profiles. We found that effects of gravitational field can be measured and that the lines are more intense where the emission is originating close to the central black hole of Mrk 110.

The HyperLeda database (!http://leda.univ-lyon1.fr) is a tool to study the physics of galaxies. It is based on compilations of heterogeneous data (from large surveys and literature) which are cross-identified and homogenized to produce a uniform representation of the galaxies. We have added in the database a characterization of the nuclear and starburst activity from the Véron and Véron catalogue.

It is now possible to retrieve an activity type for the HyperLeda galaxies having this attribute, and to select list of objects from constraints on activity type. For example, one may select all Sy2 galaxies within some magnitude limits and/or redshift.

We report the analysis of the X-ray data for a sample of 48 LINER nuclei with available X-ray Chandra imaging. In González-Martín et al. 2006 21 objects had enough count rate to make the spectral analysis. Here we enlarge the sample performing the spectral analysis of the XMM-Newton observations of 7 additional galaxies. Our aim is to investigate the physical mechanisms which power the nuclear activity of LINERs. The use of multiwavelength information at radio, UV, optical HST and X-ray lead us to conclude that at least 60% of the LINERs are hosting a low luminosity AGN in their nuclei.

We introduce a new, publicly available Monte Carlo radiative transfer code, Stokes, which has been developed to model polarization induced by scattering of free electrons and dust grains. It can be used in a wide range of astrophysical applications. Here, we apply it to model the polarization produced by the equatorial obscuring and scattering tori assumed to exist in active galactic nuclei (AGNs). We present optical/UV modeling of dusty tori with a curved inner shape and for two different dust types. The polarization spectra enable us to clearly distinguish between the two dust compositions. The Stokes code and its documentation can be freely downloaded from http://www.stokes-program.info/.