Nucleosynthesis in Stars and the Chemical Enrichment of Galaxies

Abstract

After the Big Bang, production of heavy elements in the early Universe takes place starting from the formation of the first stars, their evolution, and explosion. The first supernova explosions have strong dynamical, thermal, and chemical feedback on the formation of subsequent stars and evolution of galaxies. However, the nature of the Universe's first stars and supernova explosions has not been well clarified. The signature of the nucleosynthesis yields of the first stars can be seen in the elemental abundance patterns observed in extremely metal-poor stars. Interestingly, those patterns show some peculiarities relative to the solar abundance pattern, which should provide important clues to understanding the nature of early generations of stars. We thus review the recent results of the nucleosynthesis yields of mainly massive stars for a wide range of stellar masses, metallicities, and explosion energies. We also provide yields tables and examine how those yields are affected by some hydrodynamical effects during supernova explosions, namely, explosion energies from those of hypernovae to faint supernovae, mixing and fallback of processed materials, asphericity, etc. Those parameters in the supernova nucleosynthesis models are constrained from observational data of supernovae and metal-poor stars. Nucleosynthesis yields are then applied to the chemical evolution model of our Galaxy and other types of galaxies to discuss how the chemical enrichment process occurred during evolution.

Nucleosynthesis in Supernovae, Hypernovae/Gamma-ray Bursts and Compact Binary Mergers

“…Interim approaches beyond piston or thermal bomb models [20,34,53,81] try to mimic multi-D neutrino heating in a spherical approach in order to obtain more appropriate predictions of the explosion energy, mass cut between neutron star and ejecta, as well as nucleosynthesis (including the effects of neutrinos on Y e , the proton/nucleon ratio): Fröhlich et al [15] multiplied neutrino-capture rates by a factor, causing additional ν-heating, to obtain observed explosion energies. Ugliano, Ertl, and Sukhbold et al [68] introduced a tuned, time-dependent central neutrino source that approximately captures the essential effects of (3D) neutrino transport (PHOTB).…”

“…A major open question is whether core collapse leads finally to a supernova explosion and neutron star remnant or whether the final outcome is a central black hole. Expectations from observations and their interpretation [53] would argue for a gradual transition between these two regimes as a function of initial stellar mass. PHOTB [68] shows that both results can be obtained within the same mass interval, dependent on the stellar model and its compactness parameter.…”

“…This mixes some Fe-group nuclei to larger radii, while the fallback reduces the ejected amount of Fegroup elements and can this way create C-rich ejecta, as observed in some extremely low metallicity stars. Such behavior is suggested to stem from very massive stars, possible being more frequent in the early Galaxy [53].…”

“…The collapsar model was proposed by Woosley, MacFadyen and others (see also [35,36,46,47,62]), based on neutrino heating from the accretion disk and/or the winding of strong magnetic fields and MHD jets [41,54]. Hydrodynamic simulations (injecting explosion energies artificially) were performed, either by introducing high explosion energies (up to 10 52 erg) in a spherically symmetric way or aspherically in order to understand jet-like explosions [53]. For the role of weak interactions and resulting nucleosynthesis see e.g.…”

“…Detailed reviews on the present understanding of the end stages of massive stars are given e.g. in [10,20,28,53]. CCSNe contribute to galactic evolution via their wind ejecta, and after explosion via (a) ejecta of essentially unburned matter from the outer stellar zones and (b) explosively processed matter from the inner ejecta.…”