Pair-instability supernovae via collision runaway in young dense star clusters

Abstract

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 × 10-9Mpc-3yr-1 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. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.