What happens in gravitational
Gravitational lensing occurs when light from a distant source passes through the gravitational field of another object. The gravity of the intervening object bends the path of the light rays, similar to how the base of a wine glass bends, distorts and magnifies light. In weak lensing, the light is only slightly bent, distorting the shape of background galaxies. In strong lensing, light from the background source is bent so much that it splits into multiple images. Strong lensing requires the background source and foreground lens to be nearly perfectly aligned along the line of sight.
Gravitational lensing is used to study both the lenses and the sources. Sometimes it is used to map out the distribution of matter – including dark matter – in the lens. Other times we can take advantage of the magnification effect to study source galaxies that would otherwise be too faint and too far away.
Microlensing is a term used when the lenses are individual stars. In microlensing, we measure the change in magnification as a function of time as a background source star and a foreground lens star move in and out of alignment.
Jennifer Yee is an astrophysicist at the Harvard & Smithsonian Center for Astrophysics in Cambridge, Massachusetts