The Survey and Time-domain Astrophysical Research eXplorer (STAR-X;
http://star-x.xraydeep.org) is a Medium Explorer class mission
recently selected for a competitive NASA Phase A study. It comprises a
wide-field, high-throughput, high-angular-resolution X-ray Telescope
(XRT) and a complementary UV Telescope (UVT) on an agile spacecraft
bus. STAR-X will conduct high-cadence, deep-and-wide surveys, and
respond rapidly to transient events discovered by other observatories
such as LIGO, Rubin/LSST, Roman/WFIRST, and SKA.
The science theme for the mission is “to study the fast, furious and
forming Universe.” In this talk I will first present an overview of
the mission concept and observing capabilities, and then focus on the
key "furious" science pillar, which will explore feeding and growth of
massive black holes through sensitive, time-domain studies.
STAR-X will uniquely probe the physics of rapid accretion that allowed
the formation of the first supermassive black holes, and will catch
transient, extreme black hole feeding events, such as Tidal Disruption
Events (TDEs). Critically, STAR-X will discover TDEs in the X-ray
band, providing direct evidence for newborn accretion disks. Also, by
monitoring their X-ray and associated UV emission, STAR-X will
constrain the timescales of disk formation and their
evolution. Finally, STAR-X will perform detailed reverberation mapping
of AGN distributed over a broad range of Eddington ratios, revealing
how the accretion flow geometry depends on the accretion rate.