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Ernst Mach (1838-1916) suggested that the origin of gravitational interaction could depend on the presence of all masses in the universe. A corresponding hypothesis of Sciama (1953) on the gravitational constant, c/G = ∑ m/r, is linked to Dicke’s (1957) proposal of an electromagnetic origin of gravitation, a precursor of scalar-tensor-theories. A formula for c depending on the mass distribution is given that reproduces Newton’s law of gravitation. This mass distribution allows to calculate a slightly variable term that corresponds to the ‘constant’ G. The present proposal may supply an alternative explanation to the flatness problem and the horizon problem in cosmology. This is a short form of the author’s paper gr-qc/0511038.

In the century since Einstein’s anno mirabilis of 1905, our concept of the Universe has expanded from Kapteyn’s flattened disk of stars only 10 kpc across to an observed horizon about 30 Gpc across that is only a tiny fraction of an immensely large inflated bubble. The expansion of our knowledge about the Universe, both in the types of data and the sheer quantity of data, has been just as dramatic. This talk will summarize this century of progress and our current understanding of the cosmos.

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.

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.

The gravitational waves (GWs) emitted during the coalescence of supermassive black holes (SMBHs) will be detectable with the future (). The direction and distance can be determined from the accumulated GW signal with a precision that increases rapidly in the final stages of the inspiral. We find that for M = (10 − 10)M near = 1 the angular uncertainty decreases under 1ˆ at least several hours before the plunge, allowing a targeted electromagnetic (EM) observation of the final stages of the merger with a wide field instrument. We then calculate the size of the final, three dimensional error volume. Under the plausible assumption that SMBH-SMBH mergers are accompanied by gas accretion leading to Eddington-limited quasar activity, we find that many cases this error volume will contain at most a single quasar for M = (10 − 10) M near = 1. This will allow a straightforward test of the hypothesis that GW events are accompanied by bright quasar activity. The identification and observation of counterparts would allow unprecedented tests of the physics of MBH accretion, such as precision–measurements of the Eddington ratio. They would clarify the role of gas as a catalyst in SMBH coalescences, and would also offer an alternative method to constrain cosmological parameters.

This first ever double pulsar system consists of two pulsars orbiting the common center of mass in a slightly eccentric orbit of only 2.4-hr duration. The pair of pulsars with pulse periods of 22 ms and 2.8 sec,respectively, confirms the long-proposed recycling theory for millisecond pulsars and provides an exciting opportunity to study the works of pulsar magnetospheres by a very fortunate geometrical alignment of the orbit relative to our line-of-sight. In particular, this binary system represents a truly unique laboratory for relativistic gravitational physics.

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.

We propose degenerate fermionic dark matter to explain the flat-top density profile of the cluster A1689 recently observed.

We use detailed scattering experiments to study the role of 3-body interactions in driving orbital decay of massive black hole binaries (MBHBs) in galactic centers, quantifying also the effect of secondary slingshot on binary shrinking. We find that without invoking other physical mechanisms, such as gas dynamical processes, binaries cannot shrink to the gravitational wave (GW) emission regime in less than a Hubble time, unless they have very small mass ratios. Very unequal mass binaries are therefore a natural target for the planned . The star-binary interactions create a population of hypervelocity stars on nearly radial corotating orbits that is highly flattened in the inspiral plane. Most of the stars are ejected in an initial burst lasting much less then the bulge crossing time.