  Although there are estimated to be 100 million isolated black holes (BHs) in
the Milky Way, only one has been found so far, resulting in significant
uncertainty about their properties. The Galactic Bulge Time Domain Survey
provides the only opportunity in the coming decades to grow this catalog by
order(s) of magnitude. This can be achieved if 1) Roman's astrometric potential
is fully realized in the observation strategy and software pipelines, 2)
Roman's observational gaps of the Bulge are minimized, and 3) observations with
ground-based facilities are taken of the Bulge to fill in gaps during non-Bulge
seasons. A large sample of isolated BHs will enable a broad range of
astrophysical questions to be answered, such as massive stellar evolution,
origin of gravitational wave sources, supernova physics, and the growth of
supermassive BHs, maximizing Roman's scientific return.
