The most massive stars in the Gaia/Gravitational Wave era through spectroscopy and interferometry.

Massive stars, stars with masses higher than eight times the mass of the Sun, have strong winds, yearly blowing away a significant amount of mass from their stellar surface. Together with the supernova explosion accompanying their death, they chemically enrich their host galaxies and increase star formation rates in their surroundings. Unfortunately, our massive star evolution theories lack in fundamental elements such as the understanding of their winds and mixing processes within the star. Most massive stars are found in pairs, called binaries, and are expected to interact with their companion. Still, binary interactions such as mass transfer, are not well established. As opposed to single star evolution, it can change the evolution of the binary components drastically. To improve our understandings on binary evolution, we have to constrain every phase in this evolution. In this fellowship, the focus is on analyzing massive binaries with a black hole component, a stage in the binary evolution that has not yet been studied. This will provide the needed information to tune binary evolution models. Specifically, by combining the techniques of spectroscopy and interferometry with the new Gaia data release, this phase in binary evolution can be constrained. As binaries also serve as a means to obtain accurate masses, I will tenfold the number of known massive stars with accurately determined masses. This will also help us understand the single evolution of massive stars.