Science with STAR-X, an X-ray/UV Time-domain Surveyor MIDEX

The Survey and Time-domain Astrophysical Research eXplorer (STAR-X) is a MIDEX mission proposal for an X-ray and UV time-domain surveyor with rapid response to targets of opportunity. STAR-X fulfills the Astro2020 call for an Explorer-class time-domain observatory capable of multi-messenger follow-up and complements larger time-domain survey facilities in the late 2020s. STAR-X science includes: characterizing the progenitors of infant supernovae, observing electromagnetic counterparts to gravitational wave events, measuring high-energy flare energies from low-mass stars to assess exoplanetary habitability, discovering and monitoring tidal disruption events to determine how efficiently they accrete, measuring the structure of AGN accretion disks as a function of Eddington ratio, and surveying the growth of galaxy clusters across cosmic time from z>4 to today. Many other science topics will be addressed by STAR-X surveys, including growth of high-z AGN, SMBH binaries, X-ray binary populations, and fast X-ray transients.