Production of the entire range of r-process nuclides by black hole accretion disc outflows from neutron star mergers

By Meng-Ru Wu, R. Fern'andez, G. Mart'inez-Pinedo, B. Metzger. 2016

138 citations recorded by the source corpus.

We consider $r$-process nucleosynthesis in outflows from black hole accretion discs formed in double neutron star and neutron star -- black hole mergers. These outflows, powered by angular momentum transport processes and nuclear recombination, represent an important -- and in some cases dominant -- contribution to the total mass ejected by the merger. Here we calculate the nucleosynthesis yields from disc outflows using thermodynamic trajectories from hydrodynamic simulations, coupled to a nuclear reaction network. We find that outflows produce a robust abundance pattern around the second $r$-process peak (mass number $A \sim 130$), independent of model parameters, with significant production of $A < 130$ nuclei. This implies that dynamical ejecta with high electron fraction may not be required to explain the observed abundances of $r$-process elements in metal poor stars. Disc outflows reach the third peak ($ A \sim 195$) in most of our simulations, although the amounts produced depend sensitively on the disc viscosity, initial mass or entropy of the torus, and nuclear physics inputs. Some of our models produce an abundance spike at $A = 132$ that is absent in the Solar system $r$-process distribution. The spike arises from convection in the disc and depends on the treatment of nuclear heating in the simulations. We conclude that disc outflows provide an important -- and perhaps dominant -- contribution to the $r$-process yields of compact binary mergers, and hence must be included when assessing the contribution of these systems to the inventory of $r$-process elements in the Galaxy.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/55e9ff08b715e0802f06b48a719393b5c90ff6bd

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In Astronomy and Astrophysics

Citations in the corpus

AT 2017gfo: An Anisotropic and Three-component Kilonova Counterpart of GW170817 (2017, methodology): “The properties of secular ejecta are inspired by simulations of disks around a MNS or a BH (Wu et al. 2016; Lippuner et al. 2017; Siegel & Metzger 2017).”
Origin of the heaviest elements: The rapid neutron-capture process (2019, unknown): “opacity (Just et al., 2015a; Wu et al., 2016).”
Neutron Star Mergers Might Not Be the Only Source of r-process Elements in the Milky Way (2018, background): “While the viscous ejecta can still produce the heaviest r-process nuclei (Wu et al. 2016), the neutrino-driven ejecta have been found to produce first-peak elements only (Perego et al. 2014; Martin et al. 2015).”
A kilonova as the electromagnetic counterpart to a gravitational-wave source (2017, background): “The compilation by Wu et al.(65) shows that current simulations predict similar masses of the two components, but uncertainty of a factor few for their mass ratio.”
GW170817: Joint Constraint on the Neutron Star Equation of State from Multimessenger Observations (2017, background): “In these cases, neutrino driven winds and viscous and magnetic processes in the disk are expected to unbind sufficient material to explain the optical and infrared observations for AT2017gfo (Perego et al. 2014; Wu et al. 2016; Siegel & Metzger 2017).”
Three-dimensional GRMHD Simulations of Neutrino-cooled Accretion Disks from Neutron Star Mergers (2017, result): “We find that by including neutrino absorption, the entire range of r-process nuclei from the first to the third r-process peak can be synthesized in the unbound outflows, in agreement with the findings of previous α−disk simulations (e.g. Wu et al. 2016).”
Formation of Double Neutron Star Systems (2017, background): “…systems is a vital source of chemical enrichment of the interstellar medium with heavy r-process elements such as, for example, gold (e.g. Eichler et al. 1989; Freiburghaus et al. 1999; Wanajo et al. 2014; Rosswog 2015; Just et al. 2015; Hirai et al. 2015; Wu et al. 2016; Beniamini et al. 2016b).”
Long-term GRMHD simulations of neutron star merger accretion discs: implications for electromagnetic counterparts (2018, methodology): “Given that our disk models achieve temperatures of 5 × 109 K (onset of nucleosynthesis) at radii ∼ 5 × 107 cm (e.g., Wu et al. 2016), the required expansion times are achieved for velocities vr & 0.3c.”
Constraints on the neutron star equation of state from AT2017gfo using radiative transfer simulations (2018, background): “…of state (EOS) of NSs (Bauswein, Baumgarte & Janka 2013a; Abbott et al. 2017a; Bauswein et al. 2017; Radice et al. 2018), the formation of heavy elements (Just et al. 2015; Wu et al. 2016; Abbott et al. 2017f; Roberts et al. 2017) and the expansion rate of the universe (Abbott et al. 2017c).”
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).”
A Magnetar Origin for the Kilonova Ejecta in GW170817 (2018, background): “…accretion torus, which is created around the central compact object following the merger (e.g., Metzger et al. 2008a, 2009; Fernández & Metzger 2013; Metzger & Fernández 2014; Perego et al. 2014; Just et al. 2015; Martin et al. 2015; Wu et al. 2016; Lippuner et al. 2017; Siegel & Metzger 2017b).”
Impact of ejecta morphology and composition on the electromagnetic signatures of neutron star mergers (2017, methodology): “The influence of the radioactive heating rates was studied by Lippuner & Roberts (2015), who found that the heating profile remains quite featureless (see also Barnes et al. 2016; Rosswog et al. 2017; Wu et al. 2016).”
Signatures of hypermassive neutron star lifetimes on r-process nucleosynthesis in the disc ejecta from neutron star mergers (2017, methodology): “More recent work has employed tracer particles from long-term hydrodynamic simulations of the disk when a BH is the central object (Just et al. 2015; Wu et al. 2016).”
Kilonova from post-merger ejecta as an optical and near-infrared counterpart of GW170817 (2017, background): “Therefore, the NS mergers seem to synthesize a full range of r-process elements (e.g., Just et al. 2015; Wu et al. 2016).”
Binary Neutron Star Mergers: Mass Ejection, Electromagnetic Counterparts, and Nucleosynthesis (2018, background): “…2018; Dessart et al. 2009; Lee et al. 2009; Fernández & Metzger 2013; Metzger & Fernández 2014; Perego et al. 2014; Siegel et al. 2014; Just et al. 2015; Martin et al. 2015; Wu et al. 2016; Fujibayashi et al. 2017, 2018; Lippuner et al. 2017; Siegel & Metzger 2017, 2018; Fernández et al. 2019).”