Accurate models of gravitational wave signals from precessing black holes

Photo: Antoni Costa (UIB)

Photo: Antoni Costa (UIB)

The 28th July of 2022 Hector Estellés present his thesis: Accurate models of gravitational wave signals from precessing black holes


Gravitational waveform modelling is a crucial field for the accurate analysis of gravitational wave events registered by current and futures observatories. To infer properly the physical characteristics of the astrophysical source of an event it is necessary to use accurate and computationally efficient models that could be employed in Bayesian inference methods for parameter estimation. One of the main waveform modelling approaches is the phenomenological framework, which has produced very accurate and efficient models for the signals generated by binary black-hole coalescing systems in quasi-circular orbits, constructed in the Fourier-domain for an optimal efficiency of the models. Nevertheless, the improvements in the sensitivity of the detectors make it necessary to further improve upon the accuracy and efficiency of current models, and to explore new avenues for modelling generic systems. The main goal of this thesis has been the development of a complementary phenomenological framework in the time domain for binary black-hole coalescing signals. Working in the time domain allows to dispense with some of the limitations of the Fourier-domain models, especially regarding the description of generic spin precessing systems, and to establish the foundations for future modelling strategies towards the description of generic systems.

In this thesis, I present a new family of phenomenological waveform models, which is constructed in the time-domain. The core of the modelling framework is a model for the dominant gravitational wave harmonic for aligned-spin systems, IMRPhenomT, which provides closed-form expressions for the amplitude and phase of the dominant mode. The next step is the construction of a model covering sudominant harmonics, IMRPhenomTHM, which are crucial for breaking the inclination-distance degeneracy in the signals and for an accurate description of asymmetric systems. Finally the models are extended to model generic-spin binary systems, IMRPhenomTPHM, via the “twisting-up” approximation, offering several improvements in the description of the precession angles and a more consistent treatment of those during the coalescence and the ringdown of the system. The new models have been calibrated to accurate numerical simulations in the non-precessing sector, where the spins of the system are aligned with the orbital angular momentum of the system, with an accuracy comparable to other state-of-the-art multimode waveform models, allowing an accurate inference of the source parameters for non-precessing systems. The precessing extension, although not yet calibrated, presents several improvements with respect to previous Fourier-domain models; it provides a valuable tool in the validation and systematic study of parameter estimation results, and a complementary basis for the study of future generic calibrations. This thesis also presents the application of the models in the re-analysis of the gravitational wave event GW190521, one of the most interesting detections due to its astrophysical interpretations, performing a detailed study of the impact of several parameter estimation codes and exploiting the flexibility of the models in the physical description of precession.

Author: Hector Estellés
Directors: Sascha Husa and Marta Colleoni
Date: 28 July 2022