Dark Matter May Be Made of Primordial Black Holes

Could dark matter — the elusive substance that composes most of the material universe — be made of black holes? Alexander Kashlinsky, an astronomer at the NASA Goddard Space Flight Center in Maryland, thinks that black holes that formed soon after the Big Bang can perfectly explain the observations of gravitational waves, or ripples in space-time, made by the Laser Interferometer Gravitational-Wave Observatory (LIGO) last year, as well as previous observations of the early universe.