Catálogo de publicaciones - libros

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.

In this paper we have considered a model of modified Chaplygin gas and its role in accelerating phase of the universe. We have assumed that the equation of state of this modified model is valid from the radiation era to ΛCDM model. We have used recently developed statefinder parameters in characterizing different phase of the universe diagrammatically.

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.

The problem of motion in higher dimensions is an intriguing problem. This can be seen by studing path and path deviation equations for charged, spinning and spinning charged objects in higher dimensions. The significance of motion in higher dimensions may yield some physical implications on the effect of the extra dimension on the current motion. In this approach, we apply the Bazanski method to derive path and path deviation equations for different objects in five dimensions.

I describe the theoretical motivation for and possible roles of cosmological scalar fields, focusing on the spacetime variation of fundamental couplings. I then present our recent measurements of the fine-structure constant using quasar spectroscopy data from ESO’s VLT telescope. Finally, I briefly discuss some ongoing and planned work and prospects for future improvements.

We have performed 3-dimensional general relativistic magnetohydrodynamic (GRMHD) simulations of jet formation from an accretion disk with/without initial perturbation around a rotating black hole. We input a sinusoidal perturbation (m=5 mode) in the rotation velocity of the accretion disk. The simulation results show the formation of a relativistic jet from the accretion disk. Although the initial perturbation becomes weakened by the coupling among different modes, it survives and triggers lower modes. As a result, complex non-axisymmetric density structure develops in the disk and the jet. Newtonian MHD simulations of jet formation with a non-axisymmetric mode show the growth of the m=2 mode but GRMHD simulations cannot see the clear growth of the m=2 mode.

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.

We present the light curves of the components of gravitationally lensed source SBS1520+530 in R band, obtained during the interval 2001-2005 with the 1.5 m Russian-Turkish Telescope RTT150 at TÜBİTAK National Observatory of Turkey. The time delay of brightness fluctuations between the two components of the gravitationally double-imaged quasar corresponding to 2001-2002 period of observations is determined. Using all the available data, at least two microlensing events, one of them with long-time linear behavior and second one with duration of a few hundred days, are detected.

The shape and the intensity of the 6.4 keV iron line bring unique information on the geometrical and physical properties of the supermassive black hole and the surrounding accreting gas at the very center of Active Galactic Nuclei. While there is convincing evidence of a relativistically broadened iron line in a few nearby bright objects, their properties at larger distances are basically unknown. We have searched for the presence of iron lines by fully exploiting observations in the deep fields. The line is clearly detected in the average spectra of about 250 sources stacked in several redshift bins over the range z=0.5-4.0. We discuss their average properties with particular emphasis on the presence and intensity of a broad component.