Chang–Refsdal lens

The Chang- Refsdal lens is a point mass gravitational lens which is disturbed by a shear term.

The name comes from Kyongae Chang and Sjur Refsdal, 1979 an article in the scientific journal Nature published which described that individual foreground stars can affect the brightness of quasars.

Physical background

This gravitational lens type represents a model for the effect of a single star, in the line of sight of one of the images of a background object (for example, quasar ) is caused by the gravitational lensing of a galaxy. Kyongae Chang has shown in her thesis (1980 ) that this image can be split into up to four sub-images. Due to the very small angular distance, these images can not be directly observed. However, it may in the formation of the images when the star runs in the line of sight, come to drastic characteristic brightness variations from which information about the mass of the star or the structure of the background object can be obtained. The consideration of one or more stars that will produce this effect called microlensing.