Abstract

As shown by gravitational wave detections, galaxies harbour an unknown population of black holes at high masses of either stellar or primordial origin. In our Galaxy, such dark objects can be found and studied solely via gravitational microlensing method. So far, microlensing provided one of the tightest constraints on dark matter primordial black holes in the halo in the mass range between 0.01 and few Solar masses. Also, microlensing indicates that the dark lenses mass distribution does not show the mass-gap seen between neutron stars and X-ray binary black holes. I will describe our search for black hole lenses in both archival OGLE data and among on-going microlensing events found by Gaia. The combination of time-domain astrometry from Gaia and photometry from the ground and Spitzer space mission will allow to uniquely derive masses and distances of lenses, and hence to recognise the nature of dark lenses.