Hierarchical Triples as Early Sources of $r$-process Elements

Understand

Neutron star mergers have been proposed as the main source of heavy $r$-process nucleosynthesis in the Universe.

• However, the mergers' significant expected delay after binary formation is in tension with observed very early $r$-process enrichment, e.g., in the dwarf galaxy Reticulum II.
• The LIGO and Virgo gravitational-wave observatories discovered two binary mergers with lighter companion masses ($\sim 2.6$ M$_\odot$) similar to the total mass of many binary neutron star systems in the Galaxy.
• The progenitor of such mergers could be a neutron star binary orbiting a black hole.