Our solar system consists of ten planets revolving around the Sun. The Sun serves as a magnet that uses its gravitational pull to hold the solar system together. If the Sun were to disappear, what would hold the planets together? The answer might be a black hole. A black hole is a theorized body whose gravity is so strong that even light cant escape from within it (Shipman 64). If light cant escape from a black hole, then it must be invisible - therefore how can we know that the black holes exist? How do they form and where can we find them? This paper will discuss the theory behind the black holes and physical evidence of their existence.In order to understand black holes properties better, lets review basic principles of gravity. Lets assume that a person standing on a planets surface throws a rock in the air. The rock will rise up to a point until the gravity will pull it back, making the rock fall. If the person will throw rock hard enough, it will escape planets gravity. The speed at which the rock will leave a gravitational pull of a planet is called the escape velocity. The escape velocity differs on the planets mass; the more mass the planet has the higher escape velocity will be. A black hole has so much mass concentrated in a small radius that its escape velocity is greater than the velocity of light (Bunn). Since it is impossible for anything to travel faster than light, it means that nothing can escape a black hole (Gribbin and White 75).Black holes may form after a star is overwhelmed by its gravitational force, that it cant keep from collapsing. During their lifetime stars remain at a constant size, because they contain a balance of forces: heat generated by burning nuclear fuel expands the star outward while the force of gravity pulls it in. This is illustrated in Figure 1, taken from the book Black Holes, Quasars, and the Universe.Figure 1. Excess pressure in the hot core (white arrow) counterbalances the weight of th...
