Francesco De Paolis

Black Holes in Bulk Viscous Cosmology

We investigate the effects of the accretion of phantom energy with non-zero bulk viscosity onto a Schwarzschild black hole and show that black holes accreting viscous phantom energy will lose mass rapidly compared to the non-viscous case. When matter is incorporated along with the phantom energy, the black holes meet with the same fate as bulk viscous forces dominate matter accretion. If the phantom energy has large bulk viscosity, then the mass of the black hole will reduce faster than in the small viscosity case.

Search for exoplanets in M31 with pixel-lensing and the PA-99-N2 event revisited

Several exoplanets have been detected towards the Galactic bulge with the microlensing technique. We show that exoplanets in M31 may also be detected with the pixel-lensing method, if telescopes making high cadence observations of an ongoing microlensing event are used. Using a Monte Carlo approach we find that the mean mass for detectable planetary systems is about 2 MJ. However, even small mass exoplanets (

Periastron shift in Weyl class spacetimes

{M_{\rm P} < 20 M_{\oplus}}

Dark matter and dark energy or alternative theories of gravity and cosmology

) can cause significant deviations, which are observable with large telescopes. We reanalysed the POINT-AGAPE microlensing event PA-99-N2. First, we test the robustness of the binary lens conclusion for this light curve. Second, we show that for such long duration and bright microlensing events, the efficiency for finding planetary-like deviations is strongly enhanced with respect to that evaluated for all planetary detectable events.

∞-RADIATION FROM THE GALACTIC CENTER: DARK MATTER ANNIHILATION OR MORE CONSERVATIVE ASTROPHYSICAL MODELS?

The emission of gravitational waves from a system of massive objects interacting on hyperbolic orbits is studied in the quadrupole approximation. Analytic expressions are derived for the gravitational radiation luminosity, the total energy output and the gravitational radiation amplitude. An estimation of the expected number of events towards different targets (i.e. globular clusters and the center of the Galaxy) is also given. In particular, for a dense stellar cluster at the galactic center, a rate up to one event per year is obtained.

Radiation from fast rotating neutron stars

The periastron position advance for geodesic motion in axially symmetric solutions of the Einstein field equations belonging to the Weyl class of vacuum solutions is investigated. Explicit examples corresponding to either static solutions (single Chazy-Curzon, Schwarzschild and a pair of them), or stationary solutions (single rotating Chazy-Curzon and Kerr black hole) are discussed. The results are then applied to the case of S2-SgrA* binary system of which the periastron position advance will be soon measured with a great accuracy.

3rd Italian–Pakistani Workshop on Relativistic Astrophysics (IPWRA2011)

After exactly a century since the formulation of the general theory of relativity, the phenomenon of gravitational lensing is still an extremely powerful method for investigating in astrophysics and cosmology. Indeed, it is adopted to study the distribution of the stellar component in the Milky Way, to study dark matter and dark energy on very large scales and even to discover exoplanets. Moreover, thanks to technological developments, it will allow the measure of the physical parameters (mass, angular momentum and electric charge) of supermassive black holes in the center of ours and nearby galaxies.

The astrometric signal of microlensing events caused by free floating planets

One could call 2006 as the year of cosmology since in the year two US scientists were awarded by the Nobel prize for their studies of Cosmic Microwave Background (CMB) spectrum and anisotropy. Studies of CMB anisotropy done with the Soviet spacecraft Prognoz‐9 by the Relikt‐1 team are reminded. Problems of modern cosmology are outlined. We discuss conformal cosmology parameters from supernovae data in brief. Two approaches to solve the basic problems of cosmology, such as dark matter and dark energy, are discussed, the first (standard) possibility is to introduce new particles, fields etc, the second possibility is to try to change a gravity law to fit observational data. We discuss advantages and disadvantages of the second choice.