Question

What starts a black hole?

Answer 1

The Star having mass 8-25 more than mass of sun they become a black hole. The all nearby celestial bodies get attracted towards this black hole not can emit from black holes not even light.

Answer 2

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Black hole is a place in space where gravity pulls so much that even light can not get out. The gravity is so strong because matter has been squeezed into a tiny space. This can happen when a star is dying. Because no light can get out, people can't see black holes.

The first black hole known as such was Cygnus X-1, identified by several researchers independently in 1971.