Exploring energy extraction from Kerr magnetospheres




Taylor, Kate

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The aim of this thesis is to reconsider energy extraction from black hole magnetospheres, and more specifically the Blandford-Znajek (BZ) process from an effective field theory (EFT) perspective. Superradiant instabilities of scalar and vector bound states in the presence of a rotating black hole will be reviewed when the inverse mass of the black hole is much smaller than the Compton wavelength of the bound state particle. Two different matching calculations will be described for the vector bound state case and the overall decay rate will be compared. Force-free electrodynamics will be motivated and discussed in the context of the BZ process. Using a perturbation expansion, the Blandford-Znajek process will be reviewed up to second order in the rotation parameter. The absolute-space/universal-time (3+1) viewpoint will be discussed and applied to the BZ process and an EFT-like description will be discussed when the black hole horizon is parametrically small. Using differential forms, a simplified framework for the BZ process will be introduced in the (3+1) formalism and the field strength F will be simplified in the slow-rotation limit up to first-order in the rotation parameter. Finally, the Blandford-Znajek process will be considered as a superradiant process in the massive vector limit and the total energy flux in this (new) regime will be compared to the known BZ energy flux.



Superradiance, Black hole, Energy extraction