Thesis (Ph. D.)--Ohio State University, 2002. / Title from first page of PDF file. Document formatted into pages; contains xxix, 171 p. Includes abstract and vita. Advisor: Andrew P. Gould, Dept. of Astronomy. Includes bibliographical references (p. 153-157).

Thesis (M.S. in physics)--Washington State University, December 2005. / Includes bibliographical references.

Approximate gravitational field equations in an alternative theory of gravity are solved for a class of boundary conditions. The generation of gravitational radiation from spatially bounded sources is analyzed, and it is found that the theory predicts the emission of dipole gravitational radiation. However, the dipole radiation vanishes for slow-motion post-Newtonian sources. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

No description available.

It has been customary practice in galactic dynamics to implicitly assume that the corresponding N-body problem is (near) integrable. After a review of some relevant ideas from non-linear dynamics, I discuss the evidence suggesting that the above assumption is not generally satisfied and the consequences of such a situation. Next, I discuss the characterization of such "chaotic" behaviour. A geometric method-which I argue is best suited for measuring the instability properties of N-body systems-is tested on systems of 231 particles integrated with high precision and displaying "obvious" instabilities like violent relaxation and collective processes. The predicted instability time-scales show good agreement with those inferred from the spatial evolution. As a further test I study closed systems which relax towards definite equilibrium states. The times of relaxation towards such states are then compared to the exponential instability time-scales in an attempt to identify the physical interpretation of the exponential instability that appears to be always present in N -body systems. As an application of the method, the variation of the exponential divergence time-scales in N -body Plummer models with particle number, rotation, softening, and central mass is studied. I also study the extent of chaotic behaviour in some non-axisymmetric but smooth potentials representing galaxies with triaxial halos. This is done with the aid of Liapunov exponents, Poincare maps, and stability analysis of resonant orbits. It is found that a significant amount of chaos is usually present and increases dramatically with the addition of rotating bar perturbations, or of central masses. The degree of instability may also depend on the presence of external noise. It is also shown that dissipative perturbations have the important effect of producing an inflow of matter to the central areas. The consequences of the above processes are then discussed and it is suggested that they may explain some aspects of the observed relative bulge-disk-halo contributions to galaxy rotation curves.

No description available.

No description available.

No description available.

Soft gamma repeaters (SGRs) and anomalous X-ray pulsars are thought to be neutron stars with strong magnetic fields, called magnetars, which emit intermittent bursts of hard X-rays and soft gamma rays. Three highly energetic bursts, known as giant flares, have been observed originating from three different SGRs, the latest and most energetic of which occurred on December 27, 2004, from the SGR with the largest estimated magnetic field, SGR 1806-20. Modulations in the X-ray tails of giant flares may be caused by global seismic oscillations. Non-radial oscillations of the dense neutron star matter could emit gravitational waves powered by the magnetar's magnetic energy reservoir. This analysis searched for long-duration transient gravitational waves associated with three magnetar bursts that occurred during LIGO's sixth science run, from July 7, 2009 to October 20, 2010. The search results were consistent with the calculated background, and 90% confidence upper limits on the possible undetected gravitational wave energy were found.

No description available.