Rotating black hole

A rotating black hole is a black hole that possesses angular momentum.

Types of black holes

There are four known, exact, black hole solutions to Einstein's equations. These equations describe gravity in General Relativity. Two of these (Kerr black hole or Kerr-Newman black hole) are rotating. It is generally believed that all black holes will eventually be similar to a stationary black hole and that stationary black holes can be characterized by three (and only three) quantities "M, J" and "Q", namely:
* mass "M",
* angular momentum "J",
* electric charge "Q".

In terms of these properties, the four types of stationary black holes can be defined as follows:

Formation

Rotating black holes are formed in the gravitational collapse of a massive spinning star or from the collapse of a collection of stars or gas with an average non-zero angular momentum. As most stars rotate it is expected that most black holes in nature are rotating black holes. In late 2006, astronomers reported estimates of the spin rates of black holes in Astrophysical Journal. A black hole in the Milky Way, GRS 1915+105, may rotate 1,150 times per second, [ [http://www.cosmosmagazine.com/node/873 Black hole spins at the limit | COSMOS magazine ] ] approaching the theoretical upper limit.

Relation with gamma ray bursts

The formation of a rotating black hole by a collapsar is thought to be observed as the emission of gamma ray bursts.

Conversion to a Schwarzschild black hole

A rotating black hole can produce large amounts of energy at the expense of its rotational energy. In that case a rotating black hole gradually reduces to a Schwarzschild black hole, the minimum configuration from which no further energy can be extracted.

Kerr metric, Kerr-Newman metric

A rotating black hole is a solution of Einstein's field equation. There are two, known exact solutions, the Kerr metric and the Kerr-Newman metric, which are believed to be representative of all rotating black hole solutions, in the exterior region.

See also

* BKL singularity – solution representing interior geometry of black holes formed by gravitational collapse.
* Penrose process
* Spin-flip

References

Further reading

* Melia, Fulvio, "The Galactic Supermassive Black Hole", Princeton U Press, 2007