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The Rise of r-Process in Dwarf Galaxies

Guilherme Limberg (IAG/USP) Abstract: Multimessenger observations of gravitational wave event GW170817 of a neutron star merger (NSM), have confirmed that these sites are capable of producing copious amounts of heavy elements through the rapid neutron capture process (r-process). However, because NSMs are expected to be delayed by billions of years, it is unclear how much they can actually contribute to the chemical enrichment of galaxies. Prompt sources of r-process, such as exotic kinds of supernovae, are theoretically promising for producing heavy elements in the early universe, but observational evidence is lacking. One way to investigate which is the dominant source of r-process is to look at the chemical evolution of dwarf galaxies, which are relatively simple systems in comparison to the Milky Way. We studied the r-process signature in a disrupted dwarf galaxy in the form of a stellar stream in the Galactic halo, referred to as Wukong or LMS-1. Stars in Wukong/LMS-1 are much closer than classical surviving Milky Way satellites and are, hence, much brighter and amenable to high-resolution spectroscopy, which is necessary to detect the heaviest elements. We discovered that Wukong/LMS-1 is the first example of a galaxy that has been enriched in r-process elements predominantly by NSMs. This finding confirms that NSMs not only do happen, but are actually important contributors to the chemical evolution of galaxies. Future observations of additional disrupted and/or surviving dwarf galaxies will finally answer if NSMs alone contribute to all r-process across cosmic history or if prompt sources are also involved.