Primordial black holes are considered candidates for components of dark matter. Early constraints on primordial black holes as dark matter usually assumed most black holes would have similar or identical ("monochromatic") mass, which was disproven by LIGO/Virgo results. In 2024, a review by Bernard Carr and colleagues concluded that primordial black holes forming in the quantum chromodynamics epoch prior to 10 seconds after the Big Bang can explain most observations attributed to dark matter. Such black hole formation would result in an extended mass distribution today, "with a number of distinct bumps, the most prominent one being at around one solar mass."