Collapsar R-process Yields Can Reproduce [Eu/Fe] Abundance Scatter in Metal-poor Stars
Kaley Brauer, Alexander P. Ji, Maria R. Drout, Anna Frebel
Abstract
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) that may trace r -process yield and verify that the amount of r -process yield produced per collapsar in our model ( ∼ 0.07 M ⊙ ) 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.