r -PROCESS NUCLEOSYNTHESIS IN DYNAMICALLY EJECTED MATTER OF NEUTRON STAR MERGERS

Abstract

Although the rapid neutron-capture process, or r-process, is fundamentally important for explaining the origin of approximately half of the stable nuclei with A > 60, the astrophysical site of this process has not been identified yet. Here we study r-process nucleosynthesis in material that is dynamically ejected by tidal and pressure forces during the merging of binary neutron stars (NSs) and within milliseconds afterwards. For the first time we make use of relativistic hydrodynamical simulations of such events, defining consistently the conditions that determine the nucleosynthesis, i.e., neutron enrichment, entropy, early density evolution and thus expansion timescale, and ejecta mass. We find that 10 −3 -10 −2 M are ejected, which is enough for mergers to be the main source of heavy (A 140) galactic r-nuclei for merger rates of some 10 −5 yr −1 . While asymmetric mergers eject 2-3 times more mass than symmetric ones, the exact amount depends weakly on whether the NSs have radii of ∼15 km for a "stiff" nuclear equation of state (EOS) or ∼12 km for a "soft" EOS. R-process nucleosynthesis during the decompression becomes largely insensitive to the detailed conditions because of efficient fission recycling, producing a composition that closely follows the solar r-abundance distribution for nuclei with mass numbers A > 140. Estimating the light curve powered by the radioactive decay heating of r-process nuclei with an approximative model, we expect high emission in the B-V-R bands for 1-2 days with potentially observable longer duration in the case of asymmetric mergers because of the larger ejecta mass.

Systematic and Statistical Uncertainties in Simulated r-Process Abundances due to Uncertain Nuclear Masses

“…In Fig. 1, we show the ranges of abundance patterns obtained from the application of six DFT mass tables from [4] to an r-process calculation with a neutron star merger trajectory from [5]. Capturing the full influence of the different mass tables requires updating all other sets of theoretical nuclear data self consistently, including neutron capture rates and β-decay properties.…”

“…The study begins with a baseline r-process simulation. Here we use a neutron star merger trajectory from [5] as in Sec. 2.…”

Impact of Neutrino Interactions on Outflows of Neutron-Star Mergers

“…[3]) and relativistic simulations ignoring ν-interactions (e.g. [4]) have produced massive dynamical ejecta that were throughout neutron-rich enough to enable strong r-processing with fission recycling. Given such conditions, the solar abundance pattern was recovered for elements with mass numbers A > ∼ 130 in a robust fashion (i.e.…”

Nucleosynthesis in Supernovae, Hypernovae/Gamma-ray Bursts and Compact Binary Mergers

“…Optical and near-infrared observations of such an event, accompanying the short-duration GRB130603B have been reported [71] (see also [4]). After the first detailed nucleosynthesis predictions (following ideas of [33]) of such an event [13], many more and more sophisticated investigations have been undertaken, involving quite a number of authors [5,12,16,17,27,32,39,42,51,56,61,78] as well as the black hole accretion disk system after the formation of a central black hole [27,70,78,82].…”