Answer
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Work Step by Step
Since light cannot escape black holes, we use indirect evidence to infer their existence.
i. We can observe visible objects (stars, galaxies) orbiting invisible companions, held there by gravity.
ii. We can observe matter as it accelerates toward a black hole, because it emits a characteristic spectrum of x-rays.
iii. We can observe the gravitational lensing of objects behind the black hole. Due to the bending of light rays as they pass near a black hole on their way to Earth, visible objects such as stars and galaxies are distorted, doubled, or displaced.
