Very strong microlensing of distant luminous stars by relic massive black holes

We examine the possibility that a population of relic massive black holes, perhaps constituting an important component of the dark matter, might be indirectly detected via their occasional very strong gravitational lensing of individual luminous stars in distant external galaxies. For plausible, and in some respects conservative, values of the relevant physical parameters, we show that such events might be detected either in wide area surveys reaching routine CCD magnitude limits (such as the Sloan Digital Sky Survey) or in small field, very deep images (such as the Hubble Deep Field). Thus, it would be a challenging but not impossible task to detect or place limits on a cosmic population of relic massive black holes.