PROGENITOR: PRobing the OriGin of black holes through spectral moNITORing

Through their stellar winds and intense radiation, stars initially heavier than eight solar masses strongly influence their host galaxies throughout the Universe. The death of a massive star is marked by the collapse of its core into a compact object - a neutron star or a black hole - often associated with a violent supernova explosion. Detections of gravitational waves emitted from the merging of black holes placed their PROGENITOR massive stars in the focus of modern astrophysics, revealing huge gaps in our knowledge of key processes governing massive star evolution. As a consequence, the forward evolution of massive stars is hampered with uncertainties. To advance, I propose to obtain empirical constraints on the multiplicity, configuration, and stellar properties of poorly understood evolved stars and binaries. In my project, I will exploit cutting edge observations obtained with the world's largest earth- and space-bound telescopes. Multi-epoch spectra of massive binaries will be analysed using novel analysis and disentanglement tools. I will deliver the properties and bias-corrected multiplicities of populations of evolved massive stars and binaries in our Galaxy and neighbouring galaxies, and derive critical constraints on the upper-mass limit through data obtained for the most massive stars known. Through this, I aim to push our understanding of gravitational wave progenitors and the cosmic role of massive stars to new frontiers.