Population III binary black holes: effects of convective overshooting on formation of GW190521

ABSTRACT GW190521 is a merger of two black holes (BHs), wherein at least one BH lies within the pair-instability (PI) mass gap, and it difficult to form because effects PI supernovae pulsational (PPI). In this study, we examined formation GW190521-like BH-BHs under Population (Pop) III environments by binary population synthesis calculations. We reveal that convective overshooting in stellar evolution strongly affects BH-BHs. A model with small overshoot parameter (similar GENEC) can The derived rate 4 × 10?2 yr?1 Gpc?3 redshift ?0.82, which comparable inferred gravitational wave (GW) observations. model, ?90 M? star collapses avoiding PPI PISN even if member star. This expands up 102 R?, lose only little through evolution. However, large Stern) cannot all. Thus, conclude Pop system origin determination involves highly uncertain. If GW190521, including 100–135 substantially smaller than will be assessed GW observations near future.