Fission and r-process nucleosynthesis*

Following the dawn of multi-messenger observations enabled by LIGO we have now seen heavy element formation in the act via the signature of lanthanide elements on the observed light curve from the merger of two neutron stars. This new wave of observational capabilities provides the opportunity to make big leaps in our understanding of heavy element production over the next decade. An outstanding issue which directly impacts our interpretation of such nucleosynthesis observables lies in modeling the production of actinides in astrophysics. For instance, it remains unknown how high of a mass number astrophysical environments are able to reach before the nucleosynthesis is terminated by fission. Stellar spectroscopy and meteorites have revealed the presence of uranium, thorium, plutonium, and curium, showing that astrophysical phenomena are capable of synthesizing up to at least atomic number 96 and mass number 247. But is the rapid neutron capture process (r-process) solely responsible for the actinide content of our galaxy? And which types of astrophysical events can reach such heavy species? Recent work over the last few years has introduced several potential observables of actinide production which could shed light on these questions, from late-time fission heating effects on merger light curves, to MeV gamma-rays unique to the fission process, as well as hints of fission products in metal-poor star abundance patterns. Using observables to unravel the mystery of actinide production in astrophysics however requires careful consideration of the impact of the nuclear physics uncertainties associated with the vastly uncharted territory of neutron-rich nuclei. I will discuss potential observables of actinide production and highlight how rare isotope beam facilities like ARIEL and FRIB can contribute towards an understanding of the ultimate termination point of heavy element synthesis.