Very Massive Stars: Near and Far.

In addition to being spectacular objects, very massive stars (VMS) are suspected to have a tremendous impact on their environment and on the whole cosmic evolution. The nucleosynthesis both during their advanced stages and their final explosion likely contribute greatly to the overall enrichment of the Universe. Their resulting Supernovae are candidates for the most superluminous events and their extreme conditions lead also to very important radiative and mechanical feedback effects, from local to cosmic scale. With the recent implementation of a new equation of state in the GENEC stellar evolution code, appropriate for describing the conditions in the central regions of very massive stars in the advanced phases, we present new results on VMS evolution from Population III to solar metallicity. We explore their evolution and final fate as potential (P)PISNe across the cosmic time. We compare our results to recent spectroscopic observations of VMS in the Large Magellanic Cloud (LMC). We also underline the important radiative feedback of Population III VMS during the reionization epoch and the chemical contribution of these stars at high metallicity, especially for short-lived radionuclei. [ABSTRACT FROM AUTHOR]