Recoil of Binary Black Hole systems and the multipolar structure of gravitational wave signals

Abstract

[eng] This thesis concerns the gravitational wave signal emitted by merging black holes, as is described by the theory of general relativity, which is our modern theory of gravity. The detection of tens of such gravitational wave signals since 2015 has started the new field of gravitational wave astronomy. The success in the detection of these tiny oscillations on the fabric of the spacetime is a motivation for constant upgrading of the actual ground-based detectors. In the future, spacebased and a third generation of ground-based observatories will join efforts. So improved sensitivity and accuracy to the detected gravitational waves will provide an increase in the the quality and quantity of the observed signals, allowing us to extract more physical information from complex sources. A particularly interesting quantity, which is the subject of this thesis is the gravitational recoil. After an introduction to the theory of general relativity, and the identification of solutions of the linearized equations with gravitational waves, the multipolar structure of the gravitational wave signal is discussed in terms of spin weighted spherical harmonics. A brief introduction is also given to gravitational wave detectors and the process of detecting such waves, and to the theoretical modelling of the signals, which is crucial for the identification of the sources, e.g. for their masses, spins, and location in the sky. Complex gravitational signals require complex waveform models for the efficient detection and accurate measurement of the source parameters. The gravitational wave recoil has proven to be a very useful tool to test and improve the models. The general calculation of the recoil of a binary black hole system from the multipolar structure of the waves is discussed in detail, and an example numerical simulation is presented, where the recoil is computed and discussed. Finally, an outlook is given to the future relevance of the recoil for waveform models