A black hole is an astrophysical phenomenon with gravity of sufficient strength that it prevents even light from escaping. Black holes suck in matter. Black holes typically resulted from the supernova of extremely large stars (typically supergiants), which resulted in matter so heavy that they could push into the fabric of space, though some were thought to have been created in the initial moments of the formation of the universe. Black holes are common in the universe and are very dangerous to starships as they can destroy most objects. The opposite of a black hole is a white hole, which emits matter. Though most objects are destroyed when entering a black hole, a very small number of substances can resist black holes and may enter them to come out of a white hole. Black holes and white holes together form a wormhole.