Understanding the production of the heaviest elements in the cosmos through the chemical abundances of ancient stars

The atmospheres of $\sim13$-billion-year-old stars reflect the chemical composition of interstellar gas at the time of their birth, supplying details about element formation shortly after the Big Bang. A very small fraction of these rare stars formed from gas enriched by the rapid neutron-capture ($r$-) process. The $r$-process, believed to occur during the mergers of binary neutron stars or a neutron star with a black hole, produces all the heaviest naturally occurring elements in the Universe. $R$-process-enhanced stars exhibit the same distinct pattern of heavy elements found in the sun, suggesting the $r$-process is universal. I will present the chemical abundances of three ancient stars from the outskirts of the Milky Way with varying levels of $r$-process enhancement. The stars show remarkable agreement with the scaled solar $r$-process pattern, adding evidence for the universality of the $r$-process and providing further clues to the origin of heavy elements in the cosmos.