Towards a self-consistent relativistic model of the exterior gravitational field of rapidly rotating neutron stars

We present a self-consistent, relativistic model of rapidly rotating neutron stars describing their exterior gravitational field. This is achieved by matching the new solution of Einstein's field equations found by Manko et al. (2000) and the numerical results for the interior of neutron stars with different equations of state calculated by Cook et al. (1994). This matching process gives constraints for the choice of the five parameters of the vacuum solution. Then we investigate some properties of the gravitational field of rapidly rotating neutron stars with these fixed parameters.Comment: 11 pages, 18 figures, accepted for publication in MNRA

Braneworlds with timelike extra-dimension

In this work, we consider a braneworld model with a timelike extra-dimension. There are strong constraints to the parameter values of such a model resulting from the claim that there must be a physical solution to the Friedmann equation at least between now and the time of recombination. We fitted the model to supernova type Ia data and checked the consistency of the result with other observations. For parameter values that are consistent with observations, the braneworld model is indistinguishable from a LambdaCDM universe as far as the considered cosmological tests are concerned.Comment: 7 pages, 8 figures, matches version accepted by Phys. Rev.

Evolution of the ISM and Galactic Activity

We study the effects of time-dependent mass injection and heating on the evolution of the interstellar medium (ISM) in elliptical galaxies. As the large and luminous ellipticals have supermassive black holes at their cores, which were probably much less massive in the young universe, feeding these black holes is essential. We examine steady state solutions and describe the impact of the initial starburst on the evolution of the ISM and consequences for galactic activity, based on results from Starburst99.Comment: 6 pages, 5 figures, poster contribution for the 1st Arizona/Heidelberg Symposium "The High Redshift Frontier", November 30 - December 3, 2004, Tucson, AZ, USA. Proceedings available at http://highz.ita.uni-heidelberg.de/Proceedings.pd

Hydrodynamical simulations of the jet in the symbiotic star MWC 560 I. Structure, emission and synthetic absorption line profiles

We performed hydrodynamical simulations with and without radiative cooling of jet models with parameters representative for the symbiotic system MWC 560. For symbiotic systems we have to perform jet simulations of a pulsed underdense jet in a high density ambient medium. We present the jet structure resulting from our simulations and calculate emission plots which account for expected radiative processes. In addition, our calculations provide expansion velocities for the jet bow shock, the density and temperature structure in the jet, and the propagation and evolution of the jet pulses. In MWC 560 the jet axis is parallel to the line of sight so that the outflowing jet gas can be seen as blue shifted, variable absorption lines in the continuum of the underlying jet source. Based on our simulations we calculate and discuss synthetic absorption profiles. Based on a detailed comparison between model spectra and observations we discuss our hydrodynamical calculations for a pulsed jet in MWC 560 and suggest improvements for future models.Comment: 17 pages, 26 figures, accepted for publication in A &

Compact Objects in Astrophysics: White Dwarfs, Neutron Stars and Black Holes

Compact objects are an important class of astronomical objects in current research. Supermassive black holes play an important role in the understanding of the formation of galaxies in the early Universe. Old white dwarfs are nowadays used to calibrate the age of the Universe. Mergers of neutron stars and black holes are the sources of intense gravitational waves which will be measured in the next ten years by gravitational wave detectors. Camenzind's Compact Objects in Astrophysics gives a comprehensive introduction and up-to-date overview about the physical processes behind these objects, covering the field from the beginning to most recent results, including all relevant observations. After a presentation of the taxonomy of compact objects, the basic principles of general relativity are given. The author then discusses in detail the physics and observations of white dwarfs and neutron stars (including the most recent equations of state for neutron star matter), the gravitational field of rapidly rotating compact objects, rotating black holes (including ray tracing and black hole magnetospheres), gravitational waves, and the new understanding of accretion processes by means of the magnetorotational instability of accretion disks. This modern treatise of compact object astrophysics uses the 3+1 split approach to Einstein's equations, and to relativistic hydrodynamics and magnetohydrodynamics. In each chapter problems and solutions help deepen the understanding of the subject. Both advanced students and researchers will appreciate this book as an advanced textbook and reference on this fascinating field of astrophysics