2.3.10 Black hole cannibal
How can anyone find black holes? No light can escape from one, so it might seem impossible to observe them, but they can have a detectable influence on nearby objects.
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As you can see in the animation, if a star orbits too closely to a black hole, the intense gravitational field of the black hole tears material from the surface of the star, which then falls into the black hole. As the material falls in, it heats up to very high temperatures and the energy can be radiated away as X-rays.