Gravitational lensing

Gravitational lensing was predicted as a consequence of Albert Einstein's general theory of relativity, published in 1915. The first observational confirmation came during the total solar eclipse of 1919, when British astronomer Sir Arthur Eddington measured the deflection of starlight passing near the Sun.

Strong gravitational lensing occurs when a very massive foreground object, such as a large galaxy cluster, bends light from a background galaxy enough to produce visible distortions like arcs, rings (called Einstein rings), or multiple duplicated images. The first Einstein ring was conclusively observed in 1988 by astronomers using the Very Large Array radio telescope.

Because dark matter does not emit or absorb light, its presence can only be detected gravitationally, and lensing provides a direct way to map its distribution. By measuring how much background light is bent by galaxy clusters, astronomers can reconstruct the mass distribution—including invisible dark matter—of the foreground lensing object.

Yes, a technique called gravitational microlensing detects exoplanets when a foreground star and its planet pass in front of a background star, briefly magnifying its light. The Microlensing Observations in Astrophysics (MOA) and Optical Gravitational Lensing Experiment (OGLE) collaborations have discovered dozens of exoplanets using this method.