Gravitational lensing occurs when massive objects warp the fabric of spacetime,
bending the trajectories of light and other radiation from background sources.
The object responsible for the deflection is known as the lens, and can range from stars and black holes
to entire galaxies.
According to Fermat's Principle, light always follows paths of stationary travel time, which can produce multiple possible light paths
and distorted images in curved spacetime. Using a lens model known as the Singular Isothermal Ellipsoid (SIE), up to four
duplicate images may form depending on the source position relative to the optical axis, with each image potentially differing in magnification and time delay.