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We propose a cosmological model in which Bose-Einstein condensation works as Dark Energy. We obtain a novel mechanism of inflation, very early formation of highly non-linear objects, and log-z periodicity in the BEC collapsing time.

Relativistic outflows represent one of the best-suited tools to probe the physics of AGN. Numerical modelling of internal structure of the relativistic outflows on parsec scales provides important clues about the conditions and dynamics of the material in the immediate vicinity of the central black holes in AGN. We investigate possible causes of the structural patterns and regularities observed in the parsec-scale jet of the well known quasar 3C 273. We compare the model with the radio structure observed in 3C 273 on parsec scales using very long baseline interferometry (VLBI) and constrain the basic properties of the flow. Our results show that Kelvin-Helmholtz instabilities are the most plausible mechanism to generate the observed structures.

Nuclear activity in galaxies is closely connected to galactic mergers and supermassive black holes (SBH). Galactic mergers perturb substantially the dynamics of gas and stellar population in the merging galaxies, and they are expected to lead to formation of supermassive binary black holes (BBH) in the center of mass of the galaxies merged. A scheme is proposed here that connects the peak magnitude of the nuclear activity with evolution of a BBH system. The scheme predicts correctly the relative fractions of different types of active galactic nuclei (AGN) and explains the connection between the galactic type and the strength of the nuclear activity. It shows that most powerful AGN should result from mergers with small mass ratios, while weaker activity is produced in unequal mergers. The scheme explains also the observed lack of galaxies with two active nuclei, which is attributed to effective disruption of accretion disks around the secondary in BBH systems with masses of the primary smaller than ~ 10 M⊙.

Blazars produce a large fraction of the observed extragalactic gamma ray background between 100 MeV and 100 GeV. The average spectrum of the resolved blazars in the 3rd EGRET catalogue is too steep to be consistent with the shape of the background spectrum above 1 GeV. The most proliferant emitters above 100 GeV, the high-peaked blazars, which are too faint to have been detected with EGRET, but of which an increasing number is now being detected with imaging air Cherenkov telescopes such as MAGIC, H.E.S.S., and VERITAS, could supply a substantial contribution to the background above GeV energies. We show that dark matter annihilation in clumpy halos could naturally produce an emission component peaking at ~20 GeV. Adding this to the blazar-origin component, a best-fit model for the extragalactic gamma ray background is obtained.

X–ray deep field observations of the Lockman hole reveal a wealth of active supermassive black holes at large distances. All these AGN together contribute to a significant and strong relativistic iron K feature around 6.5 keV rest frame energy. This XMM–observation is modeled by superimposing line emission of standard disks around Kerr black holes. The simulation is based on relativistic ray tracing techniques accounting for radial drift motion of the infalling plasma in the plunging region. This work shows that it is in principle possible to explain the observed feature by a superposition of line emission from a number of disks. Thereby, low inclined disks seem to dominate the feature – a diagnosis that is in contradiction to simple AGN unification schemes based on orientation effects.

Large spectroscopic samples of active galactic nuclei (AGNs), combined with improved methods for calculating black hole mass and accretion rate, enable a eaningful statistical investigation of the mass, accretion rate and metallicity of such sources as a function of redshift. The results shown here are based on the study of about 10,000 < 0.75 radio-quiet SDSS AGNs and about 30 $z=2.3-3.4$ high redshift, very high luminosity AGNs. Their combination suggests that: 1. The fraction of more massive active black holes is larger at earlier times. 2. The normalized accretion rate (L/L) is an increasing function of redshift for black holes of all masses. 3. The slope of the accretion rate vs. redshift correlation is similar to the slope of the cosmic star formation rate over the redshift interval 0–0.75. 4. Metallicity as measured by the Nλ 1240/CIVλ 1549 line ratio at high redshifts, and by FeII/H at low redshifts, is an increasing function of L/L. 5. Most AGNs do not have enough time to grow to their present size given their present (observed) accretion rate. 6. There must have been several episodes of increased broad line gas metallicity, as well as of low metallicity, in the history of most active black holes. Thus, the BLR metallicity goes through cycles and is likely correlated with the large scale galactic star formation history.

The propagation of electromagnetic signals of pulsars through the non-stationary gravitational field of the stellar globular clusters formed by an ensemble of arbitrarily distributed stars are discussed. The expression for the relativistic time delay of pulsars radiation in such fields are derived taking into account the negligible aberration corrections. The obtained results are considered in the application to the globular cluster NGC 104 (Tucanae 47) for the cases of the small and large impact parameters.

We propose a cosmological model in which Bose-Einstein condensation works as Dark Energy. We obtain a novel mechanism of inflation, very early formation of highly non-linear objects, and log-z periodicity in the BEC collapsing time.

Recent progress in modeling type Ia supernovae by means of 3-dimensional hydrodynamic simulations as well as several of the still open questions are addressed in this article. It will be shown that the new models have considerable predictive power which allows us to study observable properties such as light curves and spectra without adjustable non-physical parameters. This is a necessary requisite to improve our understanding of the explosion mechanism and to settle the question of the applicability of SNe Ia as distance indicators for cosmology. We explore the capabilities of the models by comparison with observations and show in a preliminary approach, how such a model can be applied to study the origin of the diversity of SNe Ia which could be a source of considerable systematic errors in their distances.

Relativistic outflows (mainly observed in the radio) are a characteristic feature of both Galactic stellar mass black holes and supermassive black holes (SMBHs). Simultaneous radio and X-ray observations of Galactic sources have shown that the outflow is strong at low accretion rates, but it weakens dramatically or disappears completely at high accretion rates, manifesting structural changes in the accretion flow. If the outflow is quenched in SMBHs at high accretion rates similarly to the behavior of galactic sources, then rapidly accreting SMBHs may grow without very strong impact on the gas in the host galaxy. At much lower accretion rates the system switches to a stable state corresponding to passively evolving ellipticals, when the power of the outflow is high and it keeps the gas hot.