Final answer:
Gravitational lensing is the astronomical phenomenon that causes the distortion or stretching of images of distant galaxies when they are observed through nearby galaxies. This effect occurs because the gravitational pull of the nearby galaxy bends the path of light from the distant galaxy, creating multiple images of the same galaxy.
Step-by-step explanation:
Gravitational lensing is the astronomical phenomenon that causes the distortion or stretching of images of distant galaxies when they are observed through nearby galaxies. This effect occurs because the gravitational pull of the nearby galaxy bends the path of light from the distant galaxy, creating multiple images of the same galaxy.
For example, when light from a distant galaxy travels close to an intermediary galaxy on its way to Earth, it can be bent around the intermediary galaxy by gravity. This produces several images of the distant galaxy, which can be seen in photographs. Each image has the same spectrum but a larger redshift than the intermediary galaxy.
Gravitational lensing is a result of the bending of light by mass, as explained by Albert Einstein's theory of general relativity. It provides evidence for the existence of dark matter and allows astronomers to study the distribution of matter in galaxy clusters.