Seminar
Limits on the Mass and Abundance of Primordial Massive Black Holes

Abstract

The lack of detection of elementary particles that could explain dark matter and the recent detection of gravitational waves by the LIGO experiment have renewed interest in the hypothesis that dark matter can be made of Primordial Massive Black Holes (PMBH). We review very briefly the outcomes and limits of the classical MACHO experiment, used to probe the dark matter in the halo of the Milky Way from galactic microlensing, and introduce the more universal scenario of quasar microlensing. Quasar microlensing is sensitive to any population of compact objects in the lens galaxy, to their abundance and to their mass. Using microlensing data from 24 lensed quasars, we conclude that the fraction of mass in any type of MACHO is negligible outside of the 0.05 MSun<M<0.45 MSun mass range. This excludes any significant population of intermediate mass PBH. We estimate a fraction of halo mass in microlenses of 20%. The range of masses and abundances are in agreement with those expected for the stellar component. Using the mean mass estimate and some limits derived from multiwavelength microlensing observations we speculate about the stellar Present Day Mass Function.