How does a gravitational lens magnify a distant galaxy?

Einstein’s general relativity predicts that mass curves spacetime, and light follows that curve. When a massive galaxy or cluster lies between us and a more distant object, its gravity can bend the background light and create a lensing effect. Strong lensing can produce arcs, rings, or multiple images, while weak lensing causes subtle distortions that still reveal hidden mass. Astronomers use gravitational lenses to study very distant galaxies that might otherwise be too faint to see. Lensing also helps map dark matter, since the effect depends on total mass, not just visible matter.