Einstein Crossing Times of Dark Compact Object Populations

The detection of low-mass black holes through gravitational microlensing, the temporal magnification of a stellar source due to a compact lens, from Rubin Observatory’s Legacy Survey of Space and Time (LSST) may reveal new insights into compact object formation beyond the traditional stellar collapse. Historically, microlensing has been the preferred method to search for compact dark matter candidates. While primordial black holes (PBHs), formed from overdensities in the early universe, have long been the benchmark scenario, dark black holes (DBHs), formed from the cooling and collapse of dissipative dark matter halos would constitute a distinct population characterized by unique mass distributions and spatial and velocity profiles. These differences arise at a population level in one of the most important parameters for microlensing, the Einstein crossing time, as it encodes the geometry and kinematics of the events. Using population synthesis techniques, we generate mock populations of PBHs and DBHs in the Milky Way consistent with their astrophysically motivated priors of mass, distance, and velocity and compute their microlensing timescale distributions.