Core-collapse Supernova Explosions Driven by the Hadron-quark Phase Transition as a Rare $r$-process Site

Supernova explosions of massive stars are one of the primary sites for the production of the elements in the universe. Up to now, stars with zero-age main-sequence masses in the range of 35--50~$M_\odot$ had mostly been representing the failed supernova explosion branch. In contrast, it has been demonstrated recently that the appearance of exotic phases of hot and dense matter, associated with a sufficiently strong phase transition from nuclear matter to the quark-gluon plasma at high baryon density, can trigger supernova explosions of such massive supergiant. Here, we present the first results obtained from an extensive nucleosynthesis analysis for material being ejected from the surface of the newly born proto-neutron star of such supernova explosions. These ejecta contain an early neutron-rich component and a late-time high-entropy neutrino-driven wind. The nucleosynthesis robustly overcomes the production of nuclei associated with the second $r$-process peak, at nuclear mass number $A\simeq 130$, and proceeds beyond the formation of the third peak ($A\simeq 195$) to the actinides. These yields may account for metal-poor star observations concerning $r$-process elements such as strontium and europium in the Galaxy at low metalicity, while the actinide yields suggests that this source may be a candidate contributing to the abundances of radioactive $^{244}$Pu measured in deep-sea sediments on Earth.