TIDAL DISRUPTION EVENTS IN THE ERA OF MULTIMESSENGER ASTRONOMY

Tidal Disruption Events (TDEs) occur when a star, wandering too close to a black hole (BH), is torn apart by BH tides. After the disruption, roughly half of the stellar debris is expected to circularize around the BH and eventually form an accretion disc. These events represent a unique way to detect BHs through the universe since they emit both electromagnetic (EM) radiation and gravitational waves (GWs). In fact, after returning to the pericenter, the stellar material accretes onto the central object, producing very luminous EM flares. To date, around 50 robust TDEs have been detected in different bands of the EM spectrum (optical, X-ray, radio). Furthermore, these events also produce GWs during the whole process: while the star is stretched and compressed by BH tides, when the star is disrupted at pericenter and during the circularization process. So far, these gravitational signals have been inaccessible to us since they are low-frequency signals. Hence, these events will be seen by the future space-based detectors (like LISA and deci-Hertz observatories). In the upcoming future, thanks to the synergy between the spatial GW observatories and new and more performant telescopes, we will observe these events both via GWs and EM radiation. This will provide us a unique and more complete way to study BHs. Given these premises, this Thesis aims to study the main features of TDE gravitational emission, both through analytical and numerical studies. In particular, I explore the signal from an individual TDE, focussing on the emission generated at later stages during the circularization of the debris. Then, I investigate the signal produced by the entire cosmic population of tidal disruptions. Finally, I illustrate a catalogue of gravitational waveforms from TDEs built with a numerical tool implemented by myself during the PhD.