2012MNRAS.423.2203P

Stars with helium cores between ∼64 and 133 M_☉ are theoretically predicted to die as pair-instability supernovae. This requires very massive progenitors, which are theoretically prohibited for Pop II/I stars within the Galactic stellar mass limit due to mass-loss via line-driven winds. However, the runaway collision of stars in a dense, young star cluster could create a merged star with sufficient mass to end its life as a pair-instability supernova, even with enhanced mass-loss at non-zero metallicity. We show that the predicted rate from this mechanism is consistent with the inferred volumetric rate of roughly ∼2 {x} 10^–9/Mpc3/yr of the two observed pair-instability supernovae, SN 2007bi and PTF 10nmn, neither of which has metal-free host galaxies. Contrary to prior literature, only pair-instability supernovae at low redshifts z < 2 will be observable with the Large Synoptic Survey Telescope. We estimate that the telescope will observe ∼10² such events per year that originate from the collisional runaway mergers in clusters.