A rotating black hole is a black hole that possesses angular momentum. In particular, it rotates about one of its axes of symmetry.

The boundaries of a Kerr black hole relevant to astrophysics. Note that there are no physical "surfaces" as such. The boundaries are mathematical surfaces, or sets of points in space-time, relevant to analysis of the black hole's properties and interactions.[1]:35

Types of black holes

There are four known, exact, black hole solutions to the Einstein field equations, which describe gravity in general relativity. Two of those rotate: the Kerr and Kerr–Newman black holes. It is generally believed that every black hole decays rapidly to a stable black hole; and, by the no-hair theorem, that (except for quantum fluctuations) stable black holes can be completely described at any moment in time by these eleven numbers:

mass-energy M,

linear momentum P (three components),

angular momentum J (three components),

position X (three components),

electric charge Q.

While from an infalling observer's perspective the plunge into a rotating black hole occurs in a finite proper time and with very high rapidity (left), from the perspective of a coordinate observer at infinity they slow down, approaching zero velocity at the horizon relative to a stationary probe on site while being whirled around forever by the black hole's frame-dragging effect (right).

Prograde bound orbit around a black hole rotating with a spin parameter of a/M=0.9.

These numbers represent the conserved attributes of an object which can be determined from a distance by examining its electromagnetic and gravitational fields. All other variations in the black hole will either escape to infinity or be swallowed up by the black hole. This is because anything happening inside the black hole horizon cannot affect events outside of it.

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

Non-rotating (J = 0) Rotating (J > 0)

Uncharged (Q = 0) Schwarzschild Kerr

Charged (Q ≠ 0) Reissner–Nordström Kerr–Newman

Note that astrophysical black holes are expected to have non-zero angular momentum, due to their formation via collapse of rotating stellar objects, but effectively zero charge, since any net charge will quickly attract the opposite charge and neutralize. For this reason the term "astrophysical" black hole is usually reserved for the Kerr black hole.[2]

Formation

Rotating black holes are formed in the gravitational collapse of a massive spinning star or from the collapse or collision of a collection of compact objects, stars, or gas with a total non-zero angular momentum. As all known stars rotate and realistic collisions have non-zero angular momentum, it is expected that all black holes in nature are rotating black holes. Since observed astronomical objects do not possess an appreciable net electric charge, only the Kerr solution has astrophysical relevance.

In late 2006, astronomers reported estimates of the spin rates of black holes in The Astrophysical Journal. A black hole in the Milky Way, GRS 1915+105, may rotate 1,150 times per second,[3] 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. This happens through the Penrose process in the black hole's ergosphere, an area just outside its event horizon. 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, although the Kerr black hole's rotation velocity will never quite reach zero.

Kerr metric, Kerr–Newman metric

Rotating black hole from the perspective of the distant observer. The different frames show the black hole from different angles.

Further information: Kerr metric and 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.

State transition

Rotating black holes have two temperature states they can exist in: heating (losing energy) and cooling. In 1989, Paul Davies argued that the transition between the two states occurs when the square of the black hole's mass-to-angular-momentum ratio, in Planck units, equals the golden ratio.[4] This claim was later found to be incorrect and in contradiction with Davies' earlier work.[5]

In popular culture

Kerr black holes are featured extensively in the 2009 visual novel Steins;Gate (also TV / manga) , for their possibilities in time travelling.[6] These are, however, magnified greatly for the purpose of story telling. Kerr black holes are also key to the "Swan Song" project by Joe Davis (artist).[7][8]

See also

Black hole spin parameter

Kerr black holes as wormholes

BKL singularity – solution representing interior geometry of black holes formed by gravitational collapse.

Penrose process

Ergosphere

Black hole Spin-flip

Black hole bomb

Stellar black holes

References

arXiv:0706.0622 [gr-qc].

Capelo, Pedro R. (2019). "Astrophysical black holes". Formation of the First Black Holes. pp. 1–22.arXiv:1807.06014. doi:10.1142/9789813227958_0001. ISBN 978-981-322-794-1. S2CID 119383808.

Hayes, Jacqui (24 November 2006). "Black hole spins at the limit". Cosmos magazine. Archived from the original on 7 May 2012.

Davies, Paul C. W. (1989). "Thermodynamic phase transitions of Kerr-Newman black holes in de Sitter space". Classical and Quantum Gravity. 6 (12): 1909–1914. Bibcode:1989CQGra...6.1909D. doi:10.1088/0264-9381/6/12/018.

Baez, John C. (28 February 2013). "Black Holes and the Golden Ratio". Azimuth. Retrieved 26 July 2019.

"想定科学『Steins;Gate(シュタインズゲート)』公式Webサイト". steinsgate.jp (in Japanese). Retrieved 29 April 2020.

Mark Hay (23 July 2020). "Meet the man trying to send a warning about history's worst tragedies back to 1935". Mic.

"Летняя школа космического искусства. Summer School of Space Art with Joe Davis". 10 August 2020.

Further reading

C. W. Misner, K. S. Thorne, J. A. Wheeler, J. Wheeler, and K. Thorne, Gravitation (Physics Series), 2nd ed. W. H. Freeman, September 1973.

Macvey, John W., Time Travel, Scarborough House, 1990

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

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Black holes

Types

Schwarzschild Rotating Charged Virtual Kugelblitz Primordial Planck particle

Size

Micro

Extremal Electron Stellar

Microquasar Intermediate-mass Supermassive

Active galactic nucleus Quasar Blazar

Formation

Stellar evolution Gravitational collapse Neutron star

Related links Tolman–Oppenheimer–Volkoff limit White dwarf

Related links Supernova

Related links Hypernova Gamma-ray burst Binary black hole

Properties

Gravitational singularity

Ring singularity Theorems Event horizon Photon sphere Innermost stable circular orbit Ergosphere

Penrose process Blandford–Znajek process Accretion disk Hawking radiation Gravitational lens Bondi accretion M–sigma relation Quasi-periodic oscillation Thermodynamics

Immirzi parameter Schwarzschild radius Spaghettification

Issues

Black hole complementarity Information paradox Cosmic censorship ER=EPR Final parsec problem Firewall (physics) Holographic principle No-hair theorem

Metrics

Schwarzschild (Derivation) Kerr Reissner–Nordström Kerr–Newman Hayward

Alternatives

Nonsingular black hole models Black star Dark star Dark-energy star Gravastar Magnetospheric eternally collapsing object Planck star Q star Fuzzball

Analogs

Optical black hole Sonic black hole

Lists

Black holes Most massive Nearest Quasars Microquasars

Related

Black Hole Initiative Black hole starship Compact star Exotic star

Quark star Preon star Gamma-ray burst progenitors Gravity well Hypercompact stellar system Membrane paradigm Naked singularity Quasi-star Rossi X-ray Timing Explorer Timeline of black hole physics White hole Wormhole

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