Gravitational lensing occurs when a massive celestial body — such as a galaxy cluster — causes a sufficient curvature of spacetime for the path of light around it to be visibly bent, as if by a lens. The body causing the light to curve is accordingly called a gravitational lens.
Gravitational lenses are one of the most fascinating phenomena predicted by Einstein’s theory of general relativity. Imagine space as a fabric, and massive objects like stars and galaxies as weights pressing down on this fabric, creating curves and warps.
