# SciPost Thesis Link

Title: | Applications of space-time symmetries to black holes and gravitational radiation | |

Author: | Roberto Oliveri | |

As Contributor: | Roberto Oliveri | |

Type: | Ph.D. | |

Discipline: | Physics | |

Subject area: | Gravitation, Cosmology and Astroparticle Physics | |

Approach: | Theoretical | |

URL: | https://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/276311 | |

Degree granting institution: | UniversitĂ© Libre de Bruxelles (ULB) - Physique Theorique et Mathematique (PTM) | |

Supervisor(s): | Geoffrey CompĂ¨re | |

Defense date: | 2018-08-31 |

### Abstract:

This thesis deals with two classes of space-time symmetries: emergent symmetries in the near-horizon region of rapidly rotating Kerr black holes and residual gauge symmetries. The main aim of the thesis is to investigate consequences and effects of these symmetries on black holes and gravitational radiation. The first class of symmetries is exploited to address questions of astrophysical relevance for force-free magnetospheres, thin accretion discs, and strong magnetic fields around Kerr black holes. We investigate how the dynamics of electromagnetic and matter fields is constrained by global conformal symmetries of the near-horizon geometry. In the context of force-free electrodynamics, we find exact solutions and classify them according to the highest weight representation of the isometry group. We introduce novel criteria to distinguish physical solutions and deduce bounds on conformal weights of electromagnetic fields. For thin accretion discs, within the Novikov-Thorne model, new properties arise in the high spin regime of the Kerr black hole. We find a novel self-similar solution and we explain the critical behaviour of the observables by symmetry arguments. Afterwards, we study an exact analytic solution to the Einstein-Maxwell theory. It describes a black hole immersed in a strong magnetic field and it shares the same near-horizon geometry of extreme Kerr black holes. We compute its total conserved mass by means of the covariant phase space formalism and study its thermodynamics. The second class of symmetries is considered in order to provide a new definition of gravitational multipole moments by means of Noether charges and by adopting the covariant phase space formalism. We show that such a definition in terms of Noether charges reproduces multipole moments in General Relativity. We propose to apply it to an arbitrary generally covariant metric theory of gravity.