Weak Lensing

Small distortion and amplification of background galaxy images by foreground mass concentrations. In the weak lensing regime, distortion of an individual image is undetectably small (unlike in strong lensing), and the effect must be detected by searching for correlated distortions of thousands of source images. Weak lensing has been used to map the projected mass distribution of a number of galaxy clusters and used statistically to constrain the masses and sizes of dark galaxy halos.