Massive Stars as Progenitors of Supernovae and GRBs

The evolutionary fate of massive stars in our Milky Way is thought to be reasonably well understood: stars above Eœ 8 M_o produce neutron stars and supernovae, while those above Eœ 20...30 M_o are presumed to form black holes. At metallicities below that of the SMC, however, our knowledge becomes poor. We show that, possibly, a type of supernova dominates in the low-Z universe which hardly occurs at solar metallicity, and that stars of only 10 M_o initially may form black holes rather than neutron stars.