2013/04/30 by Rodrigo Fernández, Brian D. Metzger · 1 citation
Physics and Astronomy · #astro-ph.HE #astro-ph.SR #gr-qc #nucl-th
paper · pdf · doi:10.1093/mnras/stt1312
Accepted for publication in MNRAS with minor changes. New Figure 3 showing evolution of neutrino luminosities and temperature. Animation of Figure 4 still available at http://sns.ias.edu/~rafernan/nsdisk/Figure4.mp4
arxiv created 2013/07/16 · arxiv updated 2015/06/15
Expulsion of neutron-rich matter following the merger of neutron star (NS) binaries is crucial to the radioactively-powered electromagnetic counterparts of these events and to their relevance as sources of r-process nucleosynthesis. Here we explore the long-term (viscous) evolution of remnant black hole accretion disks formed in such mergers by means of two-dimensional, time-dependent hydrodynamical simulations. The evolution of the electron fraction due to charged-current weak interactions is included, and neutrino self-irradiation is modeled as a lightbulb that accounts for the disk geometry and moderate optical depth effects. Over several viscous times (~1s), a fraction ~10% of the initial disk mass is ejected as a moderately neutron-rich wind (Ye ~ 0.2) powered by viscous heating and nuclear recombination, with neutrino self-irradiation playing a sub-dominant role. Although the properties of the outflow vary in time and direction, their mean values in the heavy-element production region are relatively robust to variations in the initial conditions of the disk and the magnitude of its viscosity. The outflow is sufficiently neutron-rich that most of the ejecta forms heavy r-process elements with mass number A >130, thus representing a new astrophysical source of r-process nucleosynthesis, distinct from that produced in the dynamical ejecta. Due to its moderately high entropy, disk outflows contain a small residual fraction ~1% of helium, which could produce a unique spectroscopic signature.