Yes in principle: a black hole passing in front of a background star can reveal itself by magnifying the star’s light, and long events are especially promising because massive lenses produce longer signals. But finding the Galaxy’s full hidden population is not guaranteed. Existing work shows that microlensing can identify individual isolated black holes, while survey sensitivity, event interpretation, and competing lens populations limit how complete the census can be.
Two lenses on the same evidence. Source weight and the primary source ratio show what each rests on.
Alternative
Source weight 40%
Lens adapted to this topic: Challenges to the expected yield
A more skeptical reading does not reject microlensing, but questions how much it can establish about the Galaxy’s missing black holes. Survey results can depend strongly on photometric bands, event-selection rules, detection efficiency, self-lensing, and assumed halo models. Disagreements between major microlensing analyses show that null results or candidate counts may not translate straightforwardly into a definitive population estimate.
Different microlensing surveys have produced discrepant results, with disagreements linked to passbands, light-curve quality, event selection, detection efficiency, self-lensing, and halo models.
A major OGLE analysis reported no evidence for a substantial population of massive black holes in the Milky Way halo under its tested assumptions.
The OGLE interpretation has been challenged, including claims that it is inconsistent with earlier MACHO results and that modelling choices affect the conclusion.
Microlensing searches can constrain particular mass ranges or populations without proving that the Galaxy’s ordinary stellar-remnant black holes have all been found or excluded.