Black holes are the cold remnants of former stars, so dense that matter and light is able to escape their powerful gravitational pull.
When giant stars reach the final stages of their lives they often detonate in cataclysms known as supernova . The explosion causes it to become a black hole.In younger stars, nuclear fusion creates energy and a constant outward pressure that exists in balance with the inward pull of gravity caused by the star's own mass. But in the dead remnants of a massive supernova, no force opposes gravity so the star begins to collapse in upon itself. With no force to check gravity, a budding black hole shrinks to zero volume at which point it is infinitely dense. Even the light from such a star is unable to escape its immense gravitational pull. The star's own light becomes trapped in orbit, and the dark star becomes known as a black hole.Black holes pull matter and even energy into themselves—but no more so than other stars or cosmic objects of similar mass. That means that a black hole with the mass of our own sun would not pull objects into it any more than our own sun does with its own gravitational pull. Planets, light, and other matter must pass close to a black hole in order to be pulled into its grasp. When they reach a point of no return they are said to have entered the event horizon which is the point from which any escape is impossible because it requires moving faster than the speed of light.
