Space Phenomena:

Black Holes

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Black holes are formed when a star exhausts so much nuclear energy that the core of the star can not stand the pressure of the heat caused by the energy. This pressure can be up to a quintillion (1,000,000,000,000,000) times that of water. When enough pressure builds up in a star larger that 3 solar masses (the mass of our sun) the gravitational pull can get so strong that the star actually collapses in on itself. When this happens, the star actually has a negative mass. The black hole's gravity pulls everything, including light, into it.

This picture shows the different stages of a black hole being formed: