Heavy element nucleosynthesis in neutron star mergers

The merger of neutron star binaries is accompanied by the ejection of neutron-rich matter that undergoes r-process nucleosynthesis, enriching our Universe with heavy elements. Since the detection of the kilonova associated with the neutron star merger event GW170817, we have the first strong evidence that such mergers are indeed a site where heavy element nucleosynthesis takes place. However, significant uncertainties remain when it comes to the details of heavy element production, with respect to both nuclear physics processes and hydrodynamical modeling. The post-merger evolution of the merger remnant is the most uncertain piece of the problem, and research on this phase is undergoing intense development due to its importance for linking numerical simulations and astrophysical observations. In this talk, I will review our current understanding of r-process nucleosynthesis in neutron star mergers. I will discuss outflows from post-merger remnants, various mass ejection mechanisms, and the role of neutrinos in setting nucleosynthesis yields. Detailed and accurate modeling of the post-merger phase is vital for making optimal use of multi-messenger observations and developing a complete picture of the origin of the heavy elements.