Signatures of hypermassive neutron star lifetimes on r-process nucleosynthesis in the disc ejecta from neutron star mergers

By Jonas Lippuner, R. Fern'andez, Luke F. Roberts, Francois Foucart, D. Kasen, B. Metzger, Christian D. Ott. 2017

142 citations recorded by the source corpus.

We investigate the nucleosynthesis of heavy elements in the winds ejected by accretion discs formed in neutron star mergers. We compute the element formation in disc outflows from hypermassive neutron star (HMNS) remnants of variable lifetime, including the effect of angular momentum transport in the disc evolution. We employ long-term axisymmetric hydrodynamic disc simulations to model the ejecta, and compute r-process nucleosynthesis with tracer particles using a nuclear reaction network containing ∼8000 species. We find that the previously known strong correlation between HMNS lifetime, ejected mass and average electron fraction in the outflow is directly related to the amount of neutrino irradiation on the disc, which dominates mass ejection at early times in the form of a neutrino-driven wind. Production of lanthanides and actinides saturates at short HMNS lifetimes (≲10 ms), with additional ejecta contributing to a blue optical kilonova component for longer-lived HMNSs. We find good agreement between the abundances from the disc outflow alone and the solar r-process distribution only for short HMNS lifetimes (≲10 ms). For longer lifetimes, the rare-earth and third r-process peaks are significantly underproduced compared to the solar pattern, requiring additional contributions from the dynamical ejecta. The nucleosynthesis signature from a spinning black hole (BH) can only overlap with that from an HMNS of moderate lifetime (≲60 ms). Finally, we show that angular momentum transport not only contributes with a late-time outflow component, but that it also enhances the neutrino-driven component by moving material to shallower regions of the gravitational potential, in addition to providing additional heating.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/90797908366ba02b6aae8629b5d89dc0d15d5ef2

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Citations in the corpus

GW170817: Joint Constraint on the Neutron Star Equation of State from Multimessenger Observations (2017, background): “…by neutrino, viscous, or magnetically driven outflows from the merger remnant (Metzger et al. 2008, 2009; Dessart et al. 2009; Fernández & Metzger 2013; Metzger & Fernández 2014; Perego et al. 2014; Siegel et al. 2014; Just et al. 2015; Wu et al. 2016; Lippuner et al. 2017; Siegel & Metzger 2017).”
Long-term GRMHD simulations of neutron star merger accretion discs: implications for electromagnetic counterparts (2018, background): “…involves mainly light r-process elements, with varying amounts of material with A > 130 depending on parameters such as the strength of angular momentum transport or the lifetime of a hypermassive neutron star (HMNS) (Just et al. 2015; Martin et al. 2015; Wu et al. 2016; Lippuner et al. 2017).”
Neutron-star Radius Constraints from GW170817 and Future Detections (2017, background): “We note that evidence for a long-lived merger remnant (e.g. Lippuner et al. 2017; Margalit & Metzger 2017) further strengthens our arguments.”
Mass Ejection from the Remnant of a Binary Neutron Star Merger: Viscous-radiation Hydrodynamics Study (2017, background): “Pair-annihilation heating has not been considered in most recent works (e.g., Martin et al. 2015; Lippuner et al. 2017).”
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).”
Origin of the heaviest elements: The rapid neutron-capture process (2019, background): “3 (Metzger and Fernández, 2014; Lippuner et al., 2017; Fujibayashi et al., 2018).”
The Origin of r-process Elements in the Milky Way (2017, background): “…ejecta should have a higher electron fraction (Ye = 0.2 − 0.5) than the dynamical ejecta, thus producing isotopes in the range between the 1st and 2nd r-process peaks, or even near the iron peak for particularly high Ye values (Lippuner & Roberts 2015; Lippuner et al. 2017; Martin et al. 2015).”
The Combined Ultraviolet, Optical, and Near-infrared Light Curves of the Kilonova Associated with the Binary Neutron Star Merger GW170817: Unified Data Set, Analytic Models, and Physical Implications (2017, background): “…outflow from a black hole accretion disk (Just et al. 2015) but would disfavor a particularly longlived (100 ms) hyper-massive or supra-massive neutron star remnant (Metzger & Fernández 2014; Murguia-Berthier et al. 2014; Kasen et al. 2015; Lippuner et al. 2017; see also Margalit & Metzger 2017).”
AT 2017gfo: An Anisotropic and Three-component Kilonova Counterpart of GW170817 (2017, methodology): “0.5 for an extremely long-lived MNS (Lippuner et al. 2017).”
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).”
Kilonova from post-merger ejecta as an optical and near-infrared counterpart of GW170817 (2017, background): “In addition, we speculate that a relatively long-lived massive NS is present after the merger (Metzger & Fernández 2014; Kasen et al. 2015; Lippuner et al. 2017) so that neutrino emission from the central NS can increase Ye of the surrounding disk as well as the ejecta from the disk.”