Gravitational Microlensing by the Globular Cluster Stars

Abstract

The microlensing of background stars by compact objects in globular clusters is analyzed. The main strength of the proposed search is the direct relationship between the lens mass and the time scale of the microlensing event. The main problem is the low overall rate of expected events which implies that a ground based search should last for about a decade to generate a non trivial number of events, like a few dozen. A space borne experiment could increase the rate by a large factor by increasing the number of stars which could be monitored thanks to the much better seeing. The clusters M22 with the galactic bulge background, and 47 Tuc with the SMC background, are the two examples of possible targets.