Shedding light on the black hole mass spectrum

The mass spectrum of stellar black holes (BHs) is highly uncertain. Theoretical models of BH formation strongly depend on the efficiency of stellar winds of the progenitor star and on the supernova (SN) explosion mechanism. We discuss the BH mass spectrum we obtain using SEVN, a new public population-synthesis code that includes up-to-date stellar-wind prescriptions and several SN explosion models. Our models indicate a sub-solar metallicity environment for the progenitors of the gravitational wave source GW150914. We show that our models predict substantially larger BH masses (up to ~100 Msun) than other population synthesis codes, at low metallicity. In this proceeding, we also discuss the impact of pair-instability SNe on our previously published models.