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Cosmological Black Hole

Taghizadeh Firouzjaee, Javad | 2011

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 42432 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Mansouri, Reza
  7. Abstract:
  8. In the era of precision cosmology it is desirable to know if the collapse of an overdensity region within a FRW cosmological model leads to a black hole similar to that of Schwarzschild. Even the simple question of an event horizon within a dynamical universe is not a trivial one. This subject of studying collapsing over-densities within an expanding universe is called ”cosmological black holes”. Our aim is to construct such a black hole in the simplest possible scenario and study its similarities and differences to the familiar Schwarzschild one in vacuum. Therefore questions of rotating or charged black holes are not dealt with in our work. We insist, however, that the solution is dynamic without any constraint or freeze-out of any degrees of freedom related to the dynamics of the collapsing region. Using a LTB metric, we propose different models for a cosmic collapse within a flat, open, and closed FRW universe. The notion of apparent and event horizons are applied to these cosmological black holes, and their existence and non-equivalence is shown. It is also shown that the singularity in these models is not necessarily a strong one. The general properties of spherically symmetric cosmological black holes are then discussed in detail. Using these cosmological black hole models, we have calculated the quasi-local mass of a collapsing structure within the cosmological setting due to different definitions put forward in the last decades to see how similar or different they are. It has been shown that the mass within the horizon follows the familiar Brown-York behavior. It increases, however, outside the horizon again after a short decrease, in contrast to the Schwarzschild case. Further away, near the void, outside the collapsed region and where the density reaches the background minimum, all the mass definitions roughly coincide. They differ, however, substantially far from it. Given the complexities of solving appropriate field equations in a dynamic metric necessary to calculate Hawking radiation and to formulate the laws of black hole dynamics, we have used two different methods proposed recently arriving at the familiar results. The first law of LTB black hole dynamics and the thermal character of the radiation are then appropriately formulated
  9. Keywords:
  10. Cosmological Black Hole ; Horizon ; Singularity ; Quasi-Local Masses

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