Impact of Wolf-Rayet stellar winds on compact object formation

Wolf-Rayet (WR) stars are massive stars that have lost their hydrogen envelopes, exposing the underlying helium cores. In the Small Magellanic Cloud (SMC), 12 WR stars have been observed, 7 of which appear to be single. To exist without a binary companion, these stars must have undergone a self-stripping process. Although such a mechanism is theoretically plausible, current models of line-driven stellar winds, combined with the relatively low metallicity of the SMC, fail to fully account for the presence of apparently isolated WR stars. This is primarily due to the reduced strength of stellar winds at low metallicity, which is generally insufficient to remove the hydrogen envelope. In this thesis, I have implemented a new model for radiation-driven stellar winds within the MESA stellar evolution code. This model includes the possibility of activating optically thick winds when a star approaches the Eddington limit. I demonstrate that rapidly rotating stars can enter the thick-wind regime, successfully removing their hydrogen envelopes and evolving into WR stars even at low metallicity. The resulting stellar evolutionary tracks were subsequently used as input for the population synthesis code SEVN, to evaluate the impact of the new wind model on binary star populations. Finally, the output from SEVN was used to estimate the merger efficiency of binary black hole (BBH) systems in this population, with the goal of addressing the persistent overestimation of the BBH merger rate density by theoretical models, compared to that inferred by the LIGO-Virgo-Kagra (LVK) collaboration. Multiple relevant results have been found. Firstly, optically thick winds are able to reduce the hardening of the binary, therefore lowering the merger efficiency. On the other hand, this effect significantly increases the time delay between formation and black hole merger, which on average becomes about 10 Gyr. This means that the mergers observed today through GWs originate from objects formed at cosmic noon or earlier.