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Rotating black hole

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Arotating black holeis ablack holethat possessesangular momentum.In particular, it rotates about one of its axes of symmetry.

All celestial objects –planets,stars(Sun),galaxies,black holes – spin.[1][2][3]

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 spacetime, relevant to analysis of the black hole's properties and interactions.[4]: 35 

Types of black holes[edit]

There are four known, exact, black hole solutions to theEinstein field equations,which describe gravity ingeneral 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 theno-hair theorem,that (except for quantum fluctuations) stable black holes can be completely described at any moment in time by these 11 numbers:

While from an infalling observer's perspective the plunge into a rotating black hole occurs in a finite proper time and with very highrapidity(left), from the perspective of a coordinate observer at infinity theyslow down,approaching zero velocity at the horizon relative to a stationary probe on site while being whirled around forever by the black hole'sframe-draggingeffect (right).
Prograde bound orbit around a black hole rotating with aspin parameterof 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.[5]

Formation[edit]

Rotating black holes are formed in thegravitational collapseof a massive spinningstaror from the collapse or collision of a collection of compact objects, stars, or gas with a total non-zero angular momentum. As all known starsrotateand realistic collisions have non-zero angular momentum, it is expected that all black holes in nature are rotating black holes.[1][2]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 inThe Astrophysical Journal.A black hole in the Milky Way,GRS 1915+105,may rotate 1,150 times per second,[6]approaching the theoretical upper limit.

Relation with gamma ray bursts[edit]

The formation of a rotating black hole by acollapsaris thought to be observed as the emission ofgamma ray bursts.

Conversion to a Schwarzschild black hole[edit]

A rotating black hole can produce large amounts of energy at the expense of its rotational energy.[7][8]This can happen through thePenrose processinside the black hole'sergosphere,in the volume outside its event horizon.[9]In some cases of energy extraction, a rotating black hole may gradually reduce 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.[10]

Kerr metric, Kerr–Newman metric[edit]

Rotating black hole from the perspective of the distant observer. The different frames show the black hole from different angles.
Further information:Kerr metricandKerr–Newman metric

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

In the vicinity of a black hole, space curves so much that light rays are deflected, and very nearby light can be deflected so much that ittravels several timesaround the black hole. Hence, when we observe a distant background galaxy (or some other celestial body), we may be lucky to see the same image of the galaxy multiple times, albeit more and more distorted.[11]A complete mathematical description for how light bends around the equatorial plane of a Kerr black hole was published in 2021.[12]

In 2022, it was mathematically demonstrated that the equilibrium found byRoy Kerrin 1963 wasstableand thus black holes—which were the solution to Einstein's equation of 1915—were stable.[13]

State transition[edit]

Rotating black holes have two temperature states they can exist in: heating (losing energy) and cooling.[14]

In popular culture[edit]

Kerr black holes are featured extensively in the 2009visual novelSteins;Gate(alsoTV/manga), for their possibilities intime travelling.[15]These are, however, magnified greatly for the purpose of story telling. Kerr black holes are also key to the "Swan Song" project byJoe Davis.[16][17]They are also a key element in the 2014 filmInterstellar.

See also[edit]

References[edit]

  1. ^ab"Why and how do planets rotate?".Scientific American.14 April 2003.
  2. ^abEthan Siegel(1 August 2019)."This Is Why Black Holes Must Spin At Almost The Speed Of Light".Forbes.
  3. ^Robert Walty (22 July 2019)."It is said that most black holes likely have spin. What exactly is it that spins?".astronomy.
  4. ^Visser, Matt(15 January 2008). "The Kerr spacetime: A brief introduction".arXiv:0706.0622[gr-qc].
  5. ^Capelo, Pedro R. (2019). "Astrophysical black holes".Formation of the First Black Holes.pp. 1–22.arXiv:1807.06014.doi:10.1142/9789813227958_0001.ISBN978-981-322-794-1.S2CID119383808.
  6. ^Hayes, Jacqui (24 November 2006)."Black hole spins at the limit".Cosmos magazine.Archived fromthe originalon 7 May 2012.
  7. ^Cromb, Marion; Gibson, Graham M.; Toninelli, Ermes; Padgett, Miles J.; Wright, Ewan M.; Faccio, Daniele (2020). "Amplification of waves from a rotating body".Nature Physics.16(10): 1069–1073.arXiv:2005.03760.Bibcode:2020NatPh..16.1069C.doi:10.1038/s41567-020-0944-3.S2CID218571203.
  8. ^Michelle Starr (25 June 2020)."After 50 Years, Experiment Finally Shows Energy Could Be Extracted From a Black Hole".
  9. ^Williams, R. K. (1995). "Extracting X rays, Ύ rays, and relativistic e−e+pairs from supermassive Kerr black holes using the Penrose mechanism ".Physical Review D.51(10): 5387–5427.Bibcode:1995PhRvD..51.5387W.doi:10.1103/PhysRevD.51.5387.PMID10018300.
  10. ^Koide, Shinji; Arai, Kenzo (August 2008)."Energy Extraction from a Rotating Black Hole by Magnetic Reconnection in the Ergosphere".The Astrophysical Journal.682(2): 1124.arXiv:0805.0044.Bibcode:2008ApJ...682.1124K.doi:10.1086/589497.ISSN0004-637X.S2CID16509742.
  11. ^Communication, N. B. I. (9 August 2021)."Danish Student solves how the Universe is reflected near black holes".nbi.ku.dk.Retrieved23 July2022.
  12. ^Sneppen, Albert (9 July 2021)."Divergent reflections around the photon sphere of a black hole".Scientific Reports.11(1): 14247.Bibcode:2021NatSR..1114247S.doi:10.1038/s41598-021-93595-w.ISSN2045-2322.PMC8270963.PMID34244573.
  13. ^Giorgi, Elena; Klainerman, Sergiu; Szeftel, Jeremie (19 October 2022).A Researcher Shores Up Einstein's Theory With Math(Monograph).Columbia University.arXiv:2205.14808.
  14. ^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.S2CID250876065.
  15. ^"Tưởng định khoa học 『Steins;Gate(シュタインズゲート)』 công thức Webサイト".steinsgate.jp(in Japanese).Retrieved29 April2020.
  16. ^Mark Hay (23 July 2020)."Meet the man trying to send a warning about history's worst tragedies back to 1935".Mic.
  17. ^"Летняя школа космического искусства. Summer School of Space Art with Joe Davis".YouTube.10 August 2020.Archivedfrom the original on 22 December 2021.

Further reading[edit]

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