# Black Holes

## what is a black hole

A black hole is a region of spacetime from where gravity prevents anything, including light, from escaping. The theory of general relativity says that a sufficiently compact mass will deform spacetime to form a black hole. The reason it is called a "black" hole is because nothing can escape it, not even light. The first modern solution of general relativity that would be similar a black hole was found by Karl Schwarzschild in 1916, even though its interpretation as a region of space from which nothing can escape was first quoted by David Finkelstein in 1958. Black holes are created after the collapse of a star with a very high mass at the end of it's life cycle. Once a black hole is formed it can grow by absorbing other things in space.

## The History Of Black Holes

The first generic idea of a black hole was interpreted by John Michell. He said and i quote "If the semi-diameter of a sphere of the same density as the Sun were to exceed that of the Sun in the proportion of 500 to 1, a body falling from an infinite height towards it would have acquired at its surface greater velocity than that of light, and consequently supposing light to be attracted by the same force in proportion to its vis inertiae, with other bodies, all light emitted from such a body would be made to return towards it by its own proper gravity.". In1796, a mathematician by the name of Pierre-Simon Laplace had also talked about the idea of black holes in two of his books. in 1915, Albert Einstein developed the theory of general relativity, showing earlier that gravity does influence light's motion. A few months later, scientist Karl Schwarzschild found a solution to Einstein theory, which talks about the gravitational field of a point mass and a spherical mass. A few months after, Johannes Droste independently gave the same solution for the point mass and wrote more extensively about its properties. This solution had a strange behaviour at what is now called the Schwarzschild radius, where it became singular, meaning that some of the terms in the Einstein equations became infinite.

## Physical Properties of a black hole

The simplest black holes have mass but not an electric charge or angular momentum. These black holes are often referred to as Schwarzschild black holes after Karl Schwarzschild who discovered them in 1916. Solutions describing more general black holes also exist. Charged black holes are described by the Reissner–Nordström metric, while the Kerr metric describes a rotating black hole. The most general stationary black hole known is the Kerr–Newman metric, which describes a black hole with both charge and angular momentum.