Black holes are extremelydense masses jammed into single points of space. At their centers, all thematter is crushed to infinite density inside a space of zero volume, called asingularity. There, the pull of gravity is thought to be infinitely strong,warping space-time to be infinitelycurved.
Yet, for all the bizarre happenings inside black holes, ifyou are sufficiently far enough away from them, they act like any other matter.That means that if the sun were replaced with a black hole of the same mass,all the planets would continue to orbit around it just as usual, scientistshave said, though Earth would not be habitable due to lack of sunlight.
Black holes are thought to form during the explosive deathsof very massive stars. When a star exhausts all its fuel, it implodes under thecrushing force of gravity into a denser and denser ball, eventually reducingdown to a black hole. Meanwhile, the outside layers of the star are expelled ina powerful blast called a supernova.