Collapsar R-Process Yields Can Reproduce [Eu/Fe] Abundance Scatter in Metal-Poor Stars

Abstract

It is unclear if neutron star mergers can explain the observed r-process abundances of metal-poor stars. Collapsars, defined here as rotating massive stars whose collapse results in a rapidly accreting disk around a black hole that can launch jets, are a promising alternative. We find that we can produce a self-consistent model in which a population of collapsars with stochastic europium yields synthesizes all of the r-process material in metal-poor ([Fe/H] < −2.5) stars. Our model reproduces the observed scatter and evolution of scatter of [Eu/Fe] abundances. We find that if collapsars are the dominant r-process site for metal-poor stars, r-process synthesis may be linked to supernovae that produce long γ-ray bursts. Our results also allow for the possibility that core-collapse supernovae beyond those that launch γ-ray bursts also produce r-process material (e.g., potentially a subset of Type Ic-BL supernovae). Furthermore, we identify collapsar jet properties (isotropic energy, engine luminosity, or engine time) which may trace r-process yield and verify that the amount of r-process yield produced per collapsar in our model (∼ 0.07M ) is consistent with other independent estimates. In the future, achieving 0.05 dex precision on distribution scatter or a reliable selection function would further constrain our probe of r-process production. Our model would also hold for another prompt r-process site with a power-law yield, and work is needed to determine if, for example, fast-merging neutron stars can also explain abundance scatter.

Radio Constraints on $r$-process Nucleosynthesis by Collapsars

“…Nevertheless, theoretical and observational uncertainties remain (Kobayashi et al 2020;Siegel 2019;Bartos & Marka 2019a). * imrebartos@ufl.edu Collapsars-rapidly rotating massive stars whose ironcore collapse produces a black hole (Woosley & Mac-Fadyen 1999)-have also been proposed as a major source of heavy r-process elements (Nakamura et al 2013(Nakamura et al , 2015Siegel et al 2019;Brauer et al 2020). This possibility could help explain the observed early enrichment of dwarf galaxies (Ji et al 2016) and the longterm chemical enrichment of the Milky Way (Côté et al 2017;Hotokezaka et al 2018), albeit their low rate is in tension with meteoritic r-process abundances (Bartos & Marka 2019b).…”

The neutron-capture and alpha-elements abundance ratios scatter in old stellar populations. Cosmological simulations of the stellar halo

“…Hence, the study of the scatter among two different n-capture elements can bring important insights both on stellar nucleosynthesis and galaxy assembly (e.g. Cescutti et al 2013;Cescutti & Chiappini 2014;Wehmeyer et al 2015;Wehmeyer et al 2019;Brauer et al 2020; see also review by Cowan et al 2021 and references therein). The fast observational progress in this area urgently calls for informative theoretical models which help the interpretation of chemo-kinematic datasets (with 6D phase space information plus chemistry and, sometimes, age -Valentini et al 2019;Montalbán et al 2021;Miglio et al 2021).…”