The Rise of Gold, Platinum, and More with HWO

[Presented at HWO25 "Towards the Habitable Worlds Observatory: Visionary Science and Transformational Technology"] 

The rapid-neutron capture (r-) process is one of the fundamental processes responsible for creating elements heavier than iron, constituting half the periodic table. A major open question is the yields of r- process elements and the rise of these heavy elements over cosmic time. Unfortunately, real-time observations of r-process enrichment events have been limited, and even then, they cannot lend extensive yields of individual r-process elements. R-process signatures preserved in metal-poor stars provide a powerful alternative method to trace the yields and buildup of r-process elements. However, absorption lines of several key r-process elements like gold, platinum, and tellurium are not accessible in the optical spectra of stars. In this talk, I will show how the signatures of 30% of the heavy elements are accessible only through UV spectroscopy, as available with the Hubble Space Telescope (HST) and in the future with the Habitable Worlds Observatory (HWO). I will show how the signatures of these elements have played a key role in constraining nuclear and astrophysical properties of r-process enrichment events. While HST has been pivotal in enabling this science, extensive r-process inventories using both UV and optical spectroscopy have been available for only ~10 metal-poor stars. I will discuss how HWO’s sensitivity will be revolutionary in enabling extensive r-process inventories of 10^2-10^3 new stars, providing an unprecedented view into the physics and properties of r-process enrichment events, as well as the rise of almost all heavy elements over cosmic time.