Impact of systematic nuclear uncertainties on composition and decay heat of dynamical and disk ejecta in compact binary mergers

TL;DR

This study assesses how uncertainties in nuclear physics models affect predictions of element synthesis and decay heat in neutron star merger ejecta, revealing modest impacts on abundance patterns but significant effects on late-time heating and stellar age estimates.

Contribution

It systematically analyzes the influence of various nuclear physics models on r-process nucleosynthesis and decay heat predictions in neutron star merger simulations.

Findings

Nuclear uncertainties modestly affect early abundance and heating rates.

Late-time heating rate is sensitive to fission model variations.

Uncertainties can lead to age estimate errors up to 2 Gyr.

Abstract

Theoretically predicted yields of elements created by the rapid neutron capture (r-) process carry potentially large uncertainties associated with incomplete knowledge of nuclear properties and approximative hydrodynamical modelling of the matter ejection processes. We present an in-depth study of the nuclear uncertainties by varying theoretical nuclear input models that describe the experimentally unknown neutron-rich nuclei. This includes two frameworks for calculating the radiative neutron capture rates and 14 different models for nuclear masses, $\beta$-decay rates and fission properties. Our r-process nuclear network calculations are based on detailed hydrodynamical simulations of dynamically ejected material from NS-NS or NS-BH binary mergers plus the secular ejecta from BH-torus systems. The impact of nuclear uncertainties on the r-process abundance distribution and the early radioactive heating rate is found to be modest (within a factor of $\sim20$ for individual $A>90$ abundances and a factor of 2 for the heating rate). However, the impact on the late-time heating rate is more significant and depends strongly on the contribution from fission. We witness significantly larger sensitivity to the nuclear physics input if only a single trajectory is used compared to considering ensembles of $\sim$200-300 trajectories, and the quantitative effects of the nuclear uncertainties strongly depend on the adopted conditions for the individual trajectory. We use the predicted Th/U ratio to estimate the cosmochronometric age of six metal-poor stars and find the impact of the nuclear uncertainties to be up to 2 Gyr.