Massive stars and gravitational waves: Bridging the gap with a new method for rapid stellar evolution

The evolution of stars more massive than about ten times the mass of the sun is riddled with several uncertainties. However, recent observations, such as the detection of gravitational waves, have renewed interest in exploring the lives and deaths of these stars. In this thesis, I examine models of massive stars from different stellar codes, including developing my own set of detailed models, and find their predictions to be highly divergent. Furthermore, I have developed a new method of rapid stellar evolution to test the impact of these models on the simulations of stellar multiples and star clusters.