PRODUCTION OF ALL THE r-PROCESS NUCLIDES IN THE DYNAMICAL EJECTA OF NEUTRON STAR MERGERS

By S. Wanajo, Yuichiro Sekiguchi, N. Nishimura, Kentaro Kiuchi, K. Kyutoku, M. Shibata. 2014

376 citations recorded by the source corpus.

Recent studies suggest that binary neutron star (NS–NS) mergers robustly produce heavy r-process nuclei above the atomic mass number A ∼ 130 because their ejecta consist of almost pure neutrons (electron fraction of Ye < 0.1). However, the production of a small amount of the lighter r-process nuclei (A ≈ 90–120) conflicts with the spectroscopic results of r-process-enhanced Galactic halo stars. We present, for the first time, the result of nucleosynthesis calculations based on the fully general relativistic simulation of a NS–NS merger with approximate neutrino transport. It is found that the bulk of the dynamical ejecta are appreciably shock-heated and neutrino processed, resulting in a wide range of Ye (≈0.09–0.45). The mass-averaged abundance distribution of calculated nucleosynthesis yields is in reasonable agreement with the full-mass range (A ≈ 90–240) of the solar r-process curve. This implies, if our model is representative of such events, that the dynamical ejecta of NS–NS mergers could be the origin of the Galactic r-process nuclei. Our result also shows that radioactive heating after ∼1 day from the merging, which gives rise to r-process-powered transient emission, is dominated by the β-decays of several species close to stability with precisely measured half-lives. This implies that the total radioactive heating rate for such an event can be well constrained within about a factor of two if the ejected material has a solar-like r-process pattern.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/120ec3fa25cb79f9a41bbc58c721a36044992207

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Citations in the corpus

NEUTRINO-DRIVEN WINDS IN THE AFTERMATH OF A NEUTRON STAR MERGER: NUCLEOSYNTHESIS AND ELECTROMAGNETIC TRANSIENTS (2015, methodology): “…physics input, this type of ejecta yields a very robust, “strong r-process” (Sneden et al. 2008) pattern due to efficient fission cycling (Panov et al. 2008; Goriely et al. 2011; Korobkin et al. 2012; Petermann et al. 2012; Bauswein et al. 2013; Wanajo et al. 2014; Goriely 2015; Just et al. 2015a).”
r-PROCESS LANTHANIDE PRODUCTION AND HEATING RATES IN KILONOVAE (2015, methodology): “The dynamical ejecta from the contact region sits somewhere in between, as it is ejected rapidly but shocked to high temperatures and irradiated strongly by neutrinos, which can significantly alter the initial electron fraction (Wanajo et al. 2014; Goriely et al. 2015).”
The Emergence of a Lanthanide-rich Kilonova Following the Merger of Two Neutron Stars (2017, background): “…the initial focus has been on the extremely neutronrich, low electron fraction (Ye), “tidal” ejecta component, recent studies (Perego et al. 2014; Wanajo et al. 2014; Just et al. 2015; Radice et al. 2016) have highlighted that this material is likely complemented by higher Ye material that…”
Constraining the Maximum Mass of Neutron Stars from Multi-messenger Observations of GW170817 (2017, background): “Matter from the shocked interface expands into the polar direction and possesses a higher Ye & 0.25 (Wanajo et al. 2014; Sekiguchi et al. 2016).”
Mass Ejection from the Remnant of a Binary Neutron Star Merger: Viscous-radiation Hydrodynamics Study (2017, methodology): “We performed a nucleosynthesis calculation as a postprocess to the ejecta as done in Wanajo et al. (2014).”
Neutron-powered precursors of kilonovae (2014, background): “…eff cts of weak interactions on the ejecta electron fraction must also be explored using merger calcultions that include self-consistent neutrino transport, although preliminary work in this direction by Wanajo et al. (2014) finds that the outermost ejecta hasYe increased to only∼ 0.1 − 0.2.”
Impact of ejecta morphology and composition on the electromagnetic signatures of neutron star mergers (2017, background): “However, if the distribution of lanthanides has a quasi-toroidal morphology due to preferentially equatorial ejection or neutrino irradiation in polar regions (Wanajo et al. 2014), there is a possibility of detecting an additional blue component from the lanthanide-free "polar caps".”
Production of the entire range of r-process nuclides by black hole accretion disc outflows from neutron star mergers (2016, background): “As a result, lighter r-process elements with 90 ∼< A ∼< 130 are generated in addition to third-peak elements (Wanajo et al. 2014).”
The Intermediate r-process in Core-collapse Supernovae Driven by the Magneto-rotational Instability (2016, background): “It has also been shown that other theoretical β-decay rates provide different abundance features (e.g. Goriely et al. 2011; Wanajo et al. 2014; Wu et al. 2016).”
The cocoon emission - an electromagnetic counterpart to gravitational waves from neutron star mergers (2017, background): “…et al. 2011; Fernández & Metzger 2013; Hotokezaka et al. 2013b; Bauswein et al. 2013; Rosswog 2013; Perego et al. 2014a; Siegel et al. 2014; Wanajo et al. 2014; Just et al. 2015) suggest that the mergers are accompanied by significant mass ejection from several sources (see e.g. Hotokezaka…”