Hypernovae and Other Black-Hole-Forming Supernovae

Abstract

During the last few years, a number of exceptional core-collapse supernovae (SNe) have been discovered. Although their properties are rather diverse, they have the common feature that at least some of their basic parameters (kinetic energy of the explosion, mass of the ejecta, mass of the synthesized ⁵⁶Ni), and sometimes all of them, are larger, sometimes by more than an order of magnitude, than the values typically found for this type of SNe. Therefore, these SNe have been given the collective classification of ‘Hypernovae’ . The best known object in this class is SN 1998bw, which owes its fame to its likely association with the gamma-ray burst GRB 980425. In this paper, we first describe how the basic parameters of SN 1998bw can be derived from observations and modeling, and discuss the properties of other hypernovae individually. These hypernovae seem to come from rather massive stars, being more massive than ~ 20 – 25 M _⊙ on the main-sequence, thus forming black holes. On the other hand, there are some examples of massive SNe with only a small kinetic energy. We suggest that stars with non-rotating black holes are likely to collapse “quietly” ejecting a small amount of heavy elements (Faint supernovae). In contrast, stars with rotating black holes are likely to give rise to very energetic supernovae (Hypernovae). We present distinct nucleosynthesis features of these two types of “black-holeforming” supernovae. Nucleosynthesis in Hypernovae are characterized by larger abundance ratios (Zn,Co,V,Ti)/Fe and smaller (Mn,Cr)/Fe. Nucleosynthesis in Faint supernovae is characterized by a large amount of fall-back. We show that the abundance pattern of the recently discovered most Fe deficient star, HE0107 – 5240, and other extremely metal-poor carbon-rich stars are in good accord with those of black-hole-forming supernovae, but not pair-instability supernovae. This suggests that black-hole-forming supernovae made important contributions to the early Galactic (and cosmic) chemical evolution. Finally we discuss the nature of First (Pop III) Stars.