Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 487, Issue 2, Pages 1745-1753Publisher
OXFORD UNIV PRESS
DOI: 10.1093/mnras/stz1310
Keywords
Galaxy: abundances; Galaxy: evolution; nuclear reactions, nucleosynthesis, abundances; Supernovae: general
Categories
Funding
- Swiss National Science Foundation (SNF)
- Research Corporation for Science Advancement through a Cottrell Scholar Award
- United States Department of Energy, Office of Science, Office of Nuclear Physics [SC0010263, DE-FG02-02ER41216]
- European Research Council (FP7) [321263 - FISH]
- SNF
- 'Lendulet-2014' Programme of the Hungarian Academy of Sciences (Hungary), of STFC, through the University of Hull Consolidated Grant [ST/R000840/1]
- ERC Consolidator Grant (Hungary) funding scheme (project RADIOSTAR) [724560]
- National Science Foundation (USA) [PHY-1430152]
- COST (European Cooperation in Science and Technology) [CA16117]
- STFC [ST/R000840/1] Funding Source: UKRI
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Rapid neutron capture process (r-process) elements have been detected in a large fraction of metal-poor halo stars, with abundances relative to iron (Fe) that vary by over two orders of magnitude. This scatter is reduced to less than a factor of 3 in younger Galactic disc stars. The large scatter of r-process elements in the early Galaxy suggests that the r-process is made by rare events, like compact binary mergers and rare sub-classes of supernovae. Although being rare, neutron star mergers alone have difficulties to explain the observed enhancement of r-process elements in the lowest metallicity stars compared to Fe. The supernovae producing the two neutron stars already provide a substantial Fe abundance where the r-process ejecta from the merger would be injected. In this work we investigate another complementary scenario, where the r-process occurs in neutron star-black hole mergers in addition to neutron star mergers. Neutron star-black hole mergers would eject similar amounts of r-process matter as neutron star mergers, but only the neutron star progenitor would have produced Fe. Furthermore, a reduced efficiency of Fe production from single stars significantly alters the age-metallicity relation, which shifts the onset of r-process production to lower metallicities. We use the high-resolution [(20 pc) 3/cell] inhomogeneous chemical evolution tool 'ICE' to study the outcomes of these effects. In our simulations, an adequate combination of neutron star mergers and neutron star-black hole mergers qualitatively reproduces the observed r-process abundances in the Galaxy.
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