What JWST sees when galaxies act as cosmic magnifying glasses

Massive galaxies and clusters bend background light into arcs and multiple images — a natural telescope that both magnifies faint sources and maps invisible dark matter. This review traces how JWST has extended that tool far beyond what Hubble could reach, enabling detection of objects at greater distances and fainter fluxes than were previously accessible. Key applications include probing dark matter substructure, confirming redshifts through image multiplicity, and catching transient or variable sources mid-event. The review closes with near-future prospects as JWST data continues to accumulate.