SEZIONE DI ROMA III
If a fraction of the dark matter in the universe is composed of primordial black holes, their merger rate can be enhanced by the formation of a density spike around a massive black hole. We review the general relativistic treatment for the formation of a dark matter spike around a Kerr black hole, and the effects of both the density and the velocity distribution on the merger rate. The increased density gives a significant boost to the number of events originated in galactic halos. Nevertheless, the LIGO signal should still be dominated by mergers from binaries formed in the early universe.