Gravitational microlensing eects on the broad emission lines of quasars

Multiple images of QSOs are formed when the gravitational field of an inter- vening galaxy bends the trajectories of the light rays. The granulation of the lens galaxy mass distribution (either in stars or compact dark matter objects) could induce non corre- lated variability between di erent images of the lensed QSO (microlensing). The relevance of microlensing depends on the source size and, on light of some recent results, could a ect to the Broad Emission Lines of QSOs. In this contribution we review the e ects on the BLR of microlensing by an isolated microlens, a straight fold caustic and a caustic network.