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Actinide-Boosting r Process in Black-Hole-Neutron-Star Merger Ejecta
Shinya Wanajo1,2, Sho Fujibayashi1,2,3, Kota Hayashi1,4
1<a href="https://ror.org/03sry2h30">Max-Planck-Institut für Gravitationsphysik (Albert-Einstein-Institut)</a>, Am Mühlenberg 1, D-14476 Potsdam-Golm, Germany.
Black-hole-neutron-star mergers can explain the origin of heavy elements like actinides. Simulations show their ejecta create a solar-like r-process pattern, crucial for understanding these cosmic events.
Area of Science:
- Astrophysics
- Nuclear Physics
- Computational Science
Background:
- Black-hole-neutron-star mergers are key astrophysical events.
- Understanding nucleosynthesis in their ejecta is crucial for astrophysics and nuclear physics.
- Previous studies lacked long-term simulations of merger ejecta.
Purpose of the Study:
- To investigate nucleosynthesis in black-hole-neutron-star merger ejecta.
- To analyze the contribution of dynamical and postmerger ejecta to element formation.
- To constrain nuclear equations of state using nucleosynthetic signatures.
Main Methods:
- Performed long-term neutrino-radiation-magnetohydrodynamics simulations.
- Analyzed the composition of merger ejecta, focusing on electron fraction and velocity.
- Compared simulated nucleosynthetic abundances with observations of r-process-enhanced stars.
Main Results:
- The combined ejecta reproduce a solar-like r-process abundance pattern.
- Actinide enhancement is sensitive to the electron fraction and velocity of dynamical ejecta.
- A mean electron fraction of ≳0.05 in dynamical ejecta is required to match observed abundances.
Conclusions:
- Black-hole-neutron-star mergers are potential sources for r-process elements, including actinides.
- The neutron richness of tidal ejecta provides constraints on nuclear equations of state.
- These findings link merger simulations to observational constraints from actinide-boost stars.
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