Any huge amount of matter, like a cluster of galaxies, creates a gravitational field that distorts and magnifies the light from distant galaxies that are behind it but in the same line of sight. The effect is like looking through a giant magnifying glass. It allows researchers to study the details of early galaxies too far away to be seen with current technology and telescopes.
Smaller objects, like individual stars, can also act as gravitational lenses when more distant stars pass directly behind them. For a few days, light from the more distant star temporarily appears brighter because it is magnified by the gravity of the closer object. This effect is known as gravitational microlensing.
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