R-process enrichment of the lightest galaxies by fast merging neutron star binaries

Abstract:  The recent aLIGO/aVirgo discovery of the gravitational wave from the neutron star merger (NSM) GW170817, and the follow up kilonova observations have shown that NSMs produce copious amount of r-process material. Assuming neutron star mergers are the dominant sources of r-process elements in the universe, we study the chemical evolution of the Milky Way and ultra faint dwarf (UFD) galaxies through a novel set of zoom cosmological simulations. Our results indicate that fast merging channels of neutron star binaries are required in order to explain the observed statistics of the r-process enriched UFDs and metal poor r-process enhanced stars in the MW's halo. Moreover, in order to explain the r-process UFDs statistics, these systems should have lost a significant fraction of their stellar mass. Two candidate fast merging channels for the NSBs would be: (i) those on highly eccentric orbits, and (ii) those assembled through case BB unstable mass transfer. I discuss the implications of existence of such channels for GW detectors.