What phenomenon makes a black hole bend and magnify light from a more distant object?

Gravitational lensing makes a black hole bend and magnify light from a more distant object.

According to general relativity, mass and energy curve spacetime. Light follows that curved geometry, so a black hole can deflect rays passing nearby. If the alignment is suitable, the background source may appear brighter, stretched into arcs, or duplicated into multiple images.

A black hole’s lensing can be especially strong because its compact mass produces a steep gravitational field. The appearance depends on the alignment among the black hole, the background source, and the observer. Perfect alignment can produce an Einstein ring, although real observations often show imperfect arcs or changing distortions.

Gravitational lensing does not require light to cross the event horizon. Most lensed rays pass outside it. This distinguishes lensing from the black hole’s shadow, which is produced by photon paths that are captured or strongly redirected near the horizon.