Gravitational Lensing
The bending of light rays from a background astronomical source around a massive foreground object acting as a gravitational lens.
Governing formula
θ_deflection = (4 G M) / (c² b)
SI unit
Arcseconds (Angular Deflection)
In depth
Because massive objects warp surrounding spacetime, passing light rays follow curved geodesics. Strong lensing produces multiple images, arcs, or Einstein rings; weak lensing distorts background galaxy shapes.
Examples in the real world
The Abell 370 galaxy cluster lensing background galaxies into glowing arcs, mapped by the Hubble Space Telescope.