A technique for detecting massive collapsed objects in the dark halo of the galaxy

If the Galaxy possesses a dark halo of massive objects, they will produce small but potentially detectable distortions in the images of distant, extended objects due to gravitational lensing effects. We present an illustrative analytic and a more realistic numerical model for calculating the number and angular sizes of these distortions and describe a specific example of a digital filter which could be used for the identification of such distortions. The sensitivity of possible searches for the effect in the image of M31 and the Galactic Center are discussed in some detail. Simulated images of distortions of various angular sizes in these fields as they would be expected to appear in ground-based and Space Telescope CCD frames are presented. A Galactic halo of black holes such as that proposed by Lacey and Ostriker might well be detectable in a practically realizable experiment.