Black Holes and the Theory of Relativity

Most stars end their lives as stars known as white dwarfs or neutron stars. When a very massive star ends its life, not even the repulsion between densely packed neutrons can support the core against its own weight. If the remaining mass of the star’s core is more than about three times that of the Sun, scientific theory predicts that no known force can stop it from collapsing forever. Gravity simply overwhelms all other forces and crushes the middle of the star until it occupies a small area. A star in which this occurs may become one of the strangest objects ever predicted by theory — a black hole.

To understand what a black hole is like and how it influences its surroundings, we need a theory that can describe the action of gravity under such extreme circumstances. To date, our best theory of gravity is the general theory of relativity, which was put forward in 1916 by Albert Einstein.