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Comprehensive nucleosynthesis analysis for ejecta of compact binary mergers

par Just, Oliver;Bauswein, Andreas;Ardevol Pulpillo, R.;Goriely, Stéphane ;Janka, Hans-Thomas
Référence Pos proceedings of science, 07-11-July-2015, 103
Publication Publié, 2014

Article révisé par les pairs

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Résumé :

We present a comprehensive study of r-process element nucleosynthesis in the ejecta of compact binary mergers (CBMs) and their relic black-hole (BH)-torus systems. The evolution of the BH-accretion tori is simulated for seconds with a Newtonian hydrodynamics code including viscosity, pseudo-Newtonian gravity for rotating BHs, and an energy-dependent two-moment closure neutrino transport scheme. The investigated cases are guided by relativistic double neutron star (NS-NS) and NS-BH merger models. Our nucleosynthesis analysis includes the dynamical ejecta expelled during the CBM phase and the neutrino and viscously driven outflows of the relic BH-torus systems. While typically ∼20-25% of the initial torus mass are lost by viscously driven outflows, neutrino-powered winds contribute at most another ∼1%. Since BH-torus ejecta possess a wide distribution of electron fractions and entropies, they produce heavy elements from A 80 up to the actinides, with relative contributions of A > 130 nuclei being subdominant. The combined ejecta of CBM and BH-torus phases can reproduce the solar abundances amazingly well for A > 90. Varying contributions of the torus ejecta might account for observed variations of lighter elements with 40 < Z < 56 relative to heavier ones, and a considerable reduction of the prompt ejecta compared to the torus ejecta, e.g. in highly asymmetric NS-BH mergers, might explain the composition of heavy-element deficient stars.