Reconsidering the contribution of massive stars in star cluster simulations

In the last few decades, our view of the cosmos has changed a lot. High-resolution data from both ground- and space-based telescopes have enabled us to observe unprecedented details in stellar systems such as stellar binaries and star clusters. On the theoretical side, however, stellar evolution remains highly approximated in most population synthesis codes. While this may have been sufficient to reproduce observations of stellar systems in the past, an improved and up-to-date treatment of stellar evolution is required for the current and upcoming observations, especially for stars more massive than 9 Msun. In this talk, I will present results from a new approach, the Method of Interpolation for Single Star Evolution (METISSE). It can readily make use of stellar models computed with different stellar evolution codes and approximate evolution parameters for a population of stars. I will further shed light on the lives of massive stars and discuss how various physical ingredients used in modeling their evolution, such as the treatment of their radiation-dominated envelopes, can lead to differences in their evolutionary properties. Finally, I will show that by using METISSE with population synthesis codes, we can better understand the impact of these differences on the evolution of stellar systems and the formation of gravitational-wave progenitors.