Tesi di laurea magistrale
For whom the black hole tolls: from ringdown to tests of general relativity
Corso di studi
relatore Dott. Del Pozzo, Walter
- Gravitational Waves
- Tests of general relativity
Data inizio appello
The several observations of gravitational waves, generated by binary black holes coalescences as<br>well as by binary neutron stars mergers, officially ushered the observational era of observational<br>gravitational waves physics. Access to the most violent stages of the coalescence provides unprecedented<br>insights in the general relativistic strong-field dynamics.<br>The information contained inside such signals has already been used by the LIGO and Virgo<br>collaborations to estimate the parameters of such binaries and to produce some of the most<br>stringent tests of general relativity .<br>However, current methods are not suited to fully extract information about the black hole born<br>at the end of the coalescence process.<br>In fact, the remnant black hole mass and spin are inferred from measurements of the initial stages<br>of the coalescence in conjunction with predictions from numerical relativity simulations.<br>In this thesis, we show that, using recent models of the latest stage of the coalescence, known as<br>the “ringdown”, the final parameters of the coalescence can be directly extracted from the signal.<br>Combining numerical simulations and parameter estimation methods, we provide a procedure<br>to measure the parameters of the remnant black hole. For the first time, we demonstrate that<br>ground-based gravitational waves observatories will allow the direct measurement of the mass<br>and the spin of the remnant black hole, exclusively from the analysis of the ringdown part of the<br>signal.<br>We are also able to determine the “effective start time” of the ringdown, as well as the mass ratio<br>of the initial black holes, thanks to the imprint it leaves on the ringdown regime.<br>Independent methods from numerical relativity confirm our results (see ).<br>The start of the ringdown indicates the transition from the non-linear to the linear regime of the<br>theory of gravity, where perturbation methods can be applied. Its knowledge allows to test for<br>the presence of violations of general relativity that can be searched for only in the quasi-linear<br>regime. We quantify the constraints on parametric violations of general relativity with single<br>ringdown observations and show their improvements as the number of observed events increases.