Astrometric Microlensingwith the GAIA Satellite

Abstract

The capabilities of the GAIA satellite for thedetection of microlensing events are analyzed. The all-sky averagedphotometric optical depth is ~7×10^-8 and there are~4000 photometric microlensing events during the five yearmission lifetime. The all-sky averaged astrometric microlensingoptical depth is ~5×10^-5and ~50 000 sources willhave a significant variation of the centroid shift, together with aclosest approach, during the mission lifetime. We show that GAIA isthe first instrument with the capability to measure the mass locallyin very faint objects like black holes and very cool white and browndwarfs.