2017MNRAS.470.4739S

Understanding the link between massive (>=30 M_☉) stellar black holes (BHs) and their progenitor stars is a crucial step to interpret observations of gravitational-wave events. In this paper, we discuss the final fate of very massive stars (VMSs), with zero-age main sequence (ZAMS) mass >150 M_☉, accounting for pulsational pair-instability supernovae (PPISNe) and for pair-instability supernovae (PISNe). We describe an updated version of our population synthesis code SEVN, in which we added stellar evolution tracks for VMSs with ZAMS mass up to 350 M_☉ and we included analytical prescriptions for PPISNe and PISNe. We use the new version of SEVN to study the BH mass spectrum at different metallicity Z, ranging from Z = 2.0 x 10^–4 to 2.0 x 10^–2. The main effect of PPISNe and PISNe is to favour the formation of BHs in the mass range of the first gravitational-wave event (GW150914), while they prevent the formation of remnants with mass 60-120 M_☉. In particular, we find that PPISNe significantly enhance mass-loss of metal-poor (Z <= 2.0 x 10^–3) stars with ZAMS mass 60 <= M_ZAMS/ M_☉ <= 125. In contrast, PISNe become effective only for moderately metal-poor (Z < 8.0 x 10^–3) VMSs. VMSs with m_ZAMS >= 220 M_☉ and Z < 10^–3 do not undergo PISNe and form intermediate-mass BHs (with mass >=200 M_☉) via direct collapse.