Speaker
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The origin of nuclei heavier than iron is still an unsolved biggest question in nuclear astrophysics. The rapid and slow neutron-capture processes (r- and s-processes) are believed to be the origin of the neutron-rich heavy nuclei in the solar system. In addition to the two processes, recent spectroscopic observations of metal deficient asymptotic giant branch stars have raised the need for an intermediate neutron-capture process (i-process). These processes are considered to operate under distinctive conditions (temperature, neutron density, etc.) in different astrophysical sites. Here we show for the first time that the i- and s-processes in addition to the r-process produce heavy nuclei (100 < A) in the explosive nucleosynthesis of collapsar jets [1] which have recently been identified to be one of the most viable astrophysical sites for the r-process [2]. We find that the i- and s-processes operate at relatively later time as secondary processes, where the primary r-process nuclei are the seeds that capture neutrons produced by fission recycling of neutron-rich heavy actinides. We also find that only the collapsar r-process is followed by the subsequent i- and s-processes by exploring the nucleosyntheses in the magneto-hydrodynamic driven jets from core-collapse supernovae and the dynamical ejecta from binary neutron star mergers. We propose that the pronounced odd-even effect in the mass abundance pattern near $^{151}$Eu and the rare earth elements in metal-deficient halo stars could be observational evidence for the collapsar yield. Since the collapsar is one of the viable astrophysical sites to provide the Milky Way with heavy nuclei, our findings might impact the traditional interpretation of the r-process components of the solar system materials.
[1] Z. He, M. Kusakabe, T. Kajino, et al., in preparation for submittal to Phys. Rev. Lett. (2022).
[2] Y. Yamazaki, Z. He, T. Kajino, et al., Astrophys. J. 933 (2022), 112.
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