Black holes form when massive stars collapse under their own gravity. They then get bigger and bigger as they pull in more and more things from around them because of their incredibly strong gravity. There isn’t really a point to them as such, they just exist!
It’s crazy because light is also sucked into the black which means that we can’t see black holes. We can only tell they are there by looking at what happens to things nearby. Stars get ripped apart by black holes for example.
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