Pulsational Pair-instability Supernovae. I. Pre-collapse Evolution and Pulsational Mass Ejection

We calculate the evolution of massive stars, which undergo pulsational pair-instability (PPI) when the O-rich core is formed. The evolution from the main sequence through the onset of PPI is calculated for stars with initial masses of 80-140 M and metallicities of Z = 10−3−1.0 Z . Because of mass loss, Z ≤ 0.5 Z is necessary for stars to form He cores massive enough (i.e., mass >40 M ) to undergo PPI. The hydrodynamical phase of evolution from PPI through the beginning of Fe-core collapse is calculated for He cores with masses of 40−62 M and Z = 0. During PPI, electron-positron pair production causes a rapid contraction of the O-rich core, which triggers explosive O-burning and a pulsation of the core. We study the mass dependence of the pulsation dynamics, thermodynamics, and nucleosynthesis. The pulsations are stronger for more massive He cores and result in a large amount of mass ejection such as 3-13 M for 40−62 M He cores. These He cores eventually undergo Fe-core collapse. The 64 M He core undergoes complete disruption and becomes a pair-instability supernova. The H-free circumstellar matter ejected around these He cores is massive enough to explain the observed light curve of Type I (H-free) superluminous supernovae with circumstellar interaction. We also note that the mass ejection sets the maximum mass of black holes (BHs) to be ∼50 M , which is consistent with the masses of BHs recently detected by VIRGO and aLIGO.