Physics of quadrupolar and accelerated compact astrophysical objects

Abstract

This thesis analyzes how the properties of space-times containing quadrupoles or acceleration parameters, depending on their values, can be distinguishable from the Schwarzschild or the Kerr solutions in the observational fingerprints or be a black hole mimicker. In fact, the recent window to the gravitational wave has shifted the debate about them from a purely theoretical issue to a phenomenological consideration.

To answer this question, this investigation takes place on two levels: first, constructing a solution containing two quadrupoles describing a non-isolated object to obtain a more realistic model. This metric is new generalization of the Schwarzschild solution containing a quadrupole. On the second level, space-times considered here are investigated in the eyes of the configurations and properties of accretion discs, collision of particles, quasi-periodic oscillations, geodesics, dynamics of uncharged and charged particles with or without a magnetic field, stability of the geodesics, and shadow.

In this work, the analytical and semi-analytical approaches are employed. Although the majority of astrophysical systems are studied via numerical methods and simulations, the analytical techniques always open a window and provide a systematic study as a stepping stone due to their large parameter space. For example, the Event Horizon Telescope findings that provided a new branch in studying characteristics of black holes and their accretion flows were predicted theoretically in 2000, the same for the famous Higgs boson in particle physics.

This study concludes that, first, the resulting generalized metric introduces novel analytical expressions to connect to the observable. For the accretion discs models new properties arose, in particular, enabling to connect the critical behavior of the observation of the quasi-periodic oscillations in observed microquasars to the metric parameters. Second, all space-times considered in this thesis are from the general family of the Weyl space-times including the Schwarzschild, the distorted Schwarzschild, the static and the stationary $\rm q$-metric, characterizing with quadrupole, as the representative of the different classes of the solution in different ways. Thus, the complete discussion on astrophysical systems in these space-times provides the primary reference source for comparisons, particularly with the Kerr space-time. In the outlook, the various future works led by this thesis are listed.