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We analyse the effects of central AGN heating on the formation of galaxy clusters by means of hydrodynamical simulations. Besides self-gravity of dark matter and baryons, our approach includes radiative cooling and heating processes of the gas component and a multiphase model for a self-consistent treatment of star formation and SNe feedback [1]. Additionally, we incorporate a periodic feedback mechanism in the form of hot buoyant bubbles, injected into the ICM during the active phases of accreting central AGN. We find that AGN heating can substantially affect the properties of the stellar and gaseous components, in particular reducing the mass deposition rate onto the central cD galaxy, thereby offering an energetically plausible solution to the cooling flow problem.

We present the results of the first multi-scale N-body+hydrodynamical simulations of merging galaxies containing central supermassive black holes (SMBHs) and having a spatial resolution of only a few parsecs. Strong gas inflows associated with equal-mass mergers produce non-axisymmetric nuclear disks with masses of order 10, resolved by about 10 SPH particles. Such disks have sizes of several hundred parsecs but most of their mass is concentrated within less than 50 pc. We find that a close pair of supermassive black holes forms after the merger, and their relative distance then shrinks further owing to dynamical friction against the predominantly gaseous background. The orbits of the two black holes decay down to the minimum resolvable scale in a few million years after the merger for an ambient gas temperature and density typical of a region undergoing a starburst. The conditions necessary for the eventual coalescence of the two holes as a result of gravitational radiation emission appear to arise naturally from the merging of two equal-mass galaxies whose structure and orbits are consistent with the predictions of the LCDM model. Our findings have important implications for planned gravitational wave detection experiments such as .

We compare all the available observational data on the redshift evolution of the total stellar mass and star formation rate density in the Universe with the mass and accretion rate density evolution of supermassive black holes, estimated from the hard X-ray selected luminosity function of quasars and active galactic nuclei (AGN). We find that on average black hole mass must have been higher at higher redshift for given spheroid stellar mass. Moreover, we find negative redshift evolution of the disk/irregulars to spheroid mass ratio. The total accretion efficiency is constrained to be between 0.06 and 0.12, depending on the exact value of the local SMBH mass density, and on the critical accretion rate below which radiatively inefficient accretion may take place.

We have placed an upper limit on the magnitude of the rotation measure of 7 × 10^5 rad m for the putative Faraday screen (magnetized plasma) in front of Sgr A*, the radio source associated with the black hole in the Galactic Center. There is evidence that the actual rotation measure is about -5 ×10 rad m. With a simple model of equipartition of energy and reasonable inner radius for the screen, the accretion rate is estimated to be less than 10Myr. In addition, we have detected, for the first time, intra-day variability in the polarization of Sgr A*, which may be due to either intrinsic variations in Sgr A* or variations in the composition of the Faraday screen.

In this contribution I review the mechanism proposed earlier for producing a gamma-ray burst from the rapidly spinning neutron star in an X-ray binary (Spruit 1999), with a discussion of some more recent developments and outstanding issues.

Supermassive black holes (SMBHs) are nowadays believed to reside in most local galaxies, and the available data show an empirical correlation between bulge luminosity - or stellar velocity dispersion - and black hole mass, suggesting a single mechanism for assembling black holes and forming spheroids in galaxy halos. The co-evolution between galaxies and quasars is indicated by the observation of quiescent SMBHs in nearby normal (i.e. not active) galactic centers. The inferred mass density of the inactive black holes is in good agreement with the estimate of the total mass accreted by quasars, through integration of their luminosity function over time. In hierarchical models of galaxy formation major mergers are responsible for forming bulges and elliptical galaxies. Galactic interactions also trigger gas inflows, and the cold gas may be eventually driven into the very inner regions, fueling an accretion episode and the growth of the nuclear SMBH. In cold dark matter cosmogonies, small-mass subgalactic systems form first to merge later into larger and larger structures. In this paradigm galaxy halos experience multiple mergers during their lifetime. If every galaxy with a bulge hosts a SMBH in its center, and a local galaxy has been made up by multiple mergers, then a BH binary is a natural evolutionary stage. The evolution of the supermassive black hole population clearly has to be investigated taking into account both the cosmological framework and the dynamical evolution of SMBHs and their hosts.

We use two models in order to deal with a rotating universe. The first one is a thin rotating spherical shell. When we introduce in this shell an Hydrogen atom we found that the gravitomagnetic field of this universe can split the energy levels of the atom in a way analogous to the Zeeman effect.

The second model is the Gödel universe. There we use the solution of the Dirac equation on an arbitrary spacetime to find the shifts on energy levels of Hydrogen atoms caused by the rotation of the universe.

In both cases the interaction energy is very small, so we have to study the effect of cosmic rotation on Hydrogen atoms in a rotating expanding universe.

We use two models in order to deal with a rotating universe. The first one is a thin rotating spherical shell. When we introduce in this shell an Hydrogen atom we found that the gravitomagnetic field of this universe can split the energy levels of the atom in a way analogous to the Zeeman effect.

The second model is the Gödel universe. There we use the solution of the Dirac equation on an arbitrary spacetime to find the shifts on energy levels of Hydrogen atoms caused by the rotation of the universe.

In both cases the interaction energy is very small, so we have to study the effect of cosmic rotation on Hydrogen atoms in a rotating expanding universe.

A semi-analytic approach to the relativistic transport equation with isotropic diffusion and consistent radiative losses is presented. It is based on the eigenvalue method first introduced in Kirk & Schneider [5]and Heavens & Drury [3]. We demonstrate the pitch-angle dependence of the cut-off in relativistic shocks.

We analyse the effects of central AGN heating on the formation of galaxy clusters by means of hydrodynamical simulations. Besides self-gravity of dark matter and baryons, our approach includes radiative cooling and heating processes of the gas component and a multiphase model for a self-consistent treatment of star formation and SNe feedback [1]. Additionally, we incorporate a periodic feedback mechanism in the form of hot buoyant bubbles, injected into the ICM during the active phases of accreting central AGN. We find that AGN heating can substantially affect the properties of the stellar and gaseous components, in particular reducing the mass deposition rate onto the central cD galaxy, thereby offering an energetically plausible solution to the cooling flow problem.