Primordial Black Holes

Primordial Black Holes lead as the most observationally testable dark matter candidate, sparked by LIGO's 2015 detection of unexpectedly massive black hole mergers resurrecting Hawking and Carr's 1970s theory that early universe density fluctuations could form PBHs comprising dark matter. However, microlensing surveys using Japan's Subaru telescope impose strict constraints, showing fewer than 1% of dark matter can exist in PBHs of 10-100 solar masses. This empirical testability outperforms #6 SIDM, yet PBHs remain plausible for sub-solar mass ranges, with a concrete 0.1 solar mass window still viable from gravitational lensing data.