Editing Black hole (section)

==== Golden age ====
In 1958, [[David Finkelstein]] identified the Schwarzschild surface as an event horizon, "a perfect unidirectional membrane: causal influences can cross it in only one direction".<ref>{{Cite journal |last=Finkelstein |first=D. |author-link1=David Finkelstein |date=1958 |title=Past-Future Asymmetry of the Gravitational Field of a Point Particle |journal=[[Physical Review]] |volume=110 |issue=4 |pages=965–967 |doi=10.1103/PhysRev.110.965|bibcode=1958PhRv..110..965F}}</ref> This did not strictly contradict Oppenheimer's results, but extended them to include the point of view of infalling observers. Finkelstein's solution extended the Schwarzschild solution for the future of observers falling into a black hole. A [[Kruskal–Szekeres coordinates|complete extension]] had already been found by [[Martin Kruskal]], who was urged to publish it.<ref>{{cite journal |last1=Kruskal |first1=M. |author-link1=Martin Kruskal |date=1960 |title=Maximal Extension of Schwarzschild Metric |journal=[[Physical Review]] |volume=119 |issue=5 |page=1743 |doi=10.1103/PhysRev.119.1743 |bibcode=1960PhRv..119.1743K}}</ref>

These results came at the beginning of the [[golden age of general relativity]], which was marked by general relativity and black holes becoming mainstream subjects of research. This process was helped by the discovery of [[pulsar]]s by [[Jocelyn Bell Burnell]] in 1967,<ref>{{Cite journal |last1=Hewish |first1=A. |author-link1=Antony Hewish |last2=Bell |first2=S. J. |author-link2=Jocelyn Bell Burnell |last3=Pilkington |first3=J. D. H. |last4=Scott |first4=P. F. |last5=Collins |first5=R. A. |display-authors=1 |date=1968 |title=Observation of a Rapidly Pulsating Radio Source |journal=[[Nature (journal)|Nature]] |volume=217 |issue=5130 |pages=709–713 |doi=10.1038/217709a0|bibcode=1968Natur.217..709H|s2cid=4277613 }}</ref><ref>{{Cite journal |last1=Pilkington |first1=J. D. H. |last2=Hewish |first2=A. |author-link2=Antony Hewish |last3=Bell |first3=S. J. |author-link3=Jocelyn Bell Burnell |last4=Cole |first4=T. W. |display-authors=1 |date=1968 |title=Observations of some further Pulsed Radio Sources |journal=[[Nature (journal)|Nature]] |volume=218 |issue=5137 |pages=126–129 |doi=10.1038/218126a0|bibcode=1968Natur.218..126P|s2cid=4253103 }}</ref> which, by 1969, were shown to be rapidly rotating neutron stars.<ref name="araa8_265">{{cite journal |last=Hewish |first=A. |author-link1=Antony Hewish |date=1970 |title=Pulsars |journal=[[Annual Review of Astronomy and Astrophysics]] |volume=8 |issue=1 |pages=265–296 |bibcode=1970ARA&A...8..265H |doi=10.1146/annurev.aa.08.090170.001405}}</ref> Until that time, neutron stars, like black holes, were regarded as just theoretical curiosities; but the discovery of pulsars showed their physical relevance and spurred a further interest in all types of compact objects that might be formed by gravitational collapse.<ref>{{Cite web |url=https://www.smithsonianmag.com/science-nature/Fifty-years-ago-grad-students-discovery-changed-course-astrophysics-180968288/ |title=Fifty Years Ago, a Grad Student's Discovery Changed the Course of Astrophysics |date=28 February 2018 |access-date=22 December 2023 |website=Smithsonian Magazine |last=Boissoneault |first=Lorraine}}</ref>

In this period more general black hole solutions were found. In 1963, [[Roy Kerr]] found [[Kerr metric|the exact solution]] for a [[rotating black hole]]. Two years later, [[Ezra T. Newman|Ezra Newman]] found the [[axisymmetric]] solution for a black hole that is both rotating and [[electrically charged]].<ref>{{Cite journal |last1=Newman |first1=E. T. |author-link1=Ezra T. Newman |last2=Couch |first2=E. |last3=Chinnapared |first3=K. |last4=Exton |first4=A. |last5=Prakash |first5=A. |last6=Torrence |first6=R. |display-authors=1 |date=1965 |title=Metric of a Rotating, Charged Mass |journal=[[Journal of Mathematical Physics]] |volume=6 |issue=6 |page=918 |doi=10.1063/1.1704351 |bibcode=1965JMP.....6..918N}}</ref> Through the work of [[Werner Israel]],<ref>{{cite journal |last=Israel |first=W. |date=1967 |title=Event Horizons in Static Vacuum Space-Times |journal=[[Physical Review]] |volume=164 |issue=5 |page=1776 |doi=10.1103/PhysRev.164.1776 |bibcode=1967PhRv..164.1776I}}</ref> [[Brandon Carter]],<ref>{{cite journal |last=Carter |first=B. |author-link1=Brandon Carter |date=1971 |title=Axisymmetric Black Hole Has Only Two Degrees of Freedom |journal=[[Physical Review Letters]] |volume=26 |issue=6 |page=331 |doi=10.1103/PhysRevLett.26.331 |bibcode=1971PhRvL..26..331C}}</ref><ref>{{cite book |last=Carter |first=B. |author-link1=Brandon Carter |date=1977 |chapter=The vacuum black hole uniqueness theorem and its conceivable generalisations |title=Proceedings of the 1st Marcel Grossmann meeting on general relativity |pages=243–254 }}</ref> and David Robinson<ref>{{cite journal |last1=Robinson |first1=D. |date=1975 |title=Uniqueness of the Kerr Black Hole |journal=[[Physical Review Letters]] |volume=34 |issue=14 |page=905 |doi=10.1103/PhysRevLett.34.905 |bibcode=1975PhRvL..34..905R}}</ref> the [[no-hair theorem]] emerged, stating that a stationary black hole solution is completely described by the three parameters of the [[Kerr–Newman metric]]: [[mass]], [[angular momentum]], and electric charge.<ref name="HeuslerNoHair" />

At first, it was suspected that the strange features of the black hole solutions were pathological artefacts from the symmetry conditions imposed, and that the singularities would not appear in generic situations. This view was held in particular by [[Vladimir A. Belinsky|Vladimir Belinsky]], [[Isaak Markovich Khalatnikov|Isaak Khalatnikov]], and [[Evgeny Lifshitz]], who tried to prove that no singularities appear in generic solutions. However, in the late 1960s [[Roger Penrose]]<ref name="penrose1965">{{cite journal |last1=Penrose |first1=R. |author-link1=Roger Penrose |date=1965 |title=Gravitational Collapse and Space-Time Singularities |journal=[[Physical Review Letters]] |volume=14 |issue=3 |page=57 |doi=10.1103/PhysRevLett.14.57 |bibcode=1965PhRvL..14...57P |s2cid=116755736|url=http://pdfs.semanticscholar.org/faad/1f4358fddf70df2e00c0a290b7e4501c27de.pdf |archive-url=https://web.archive.org/web/20201011221750/http://pdfs.semanticscholar.org/faad/1f4358fddf70df2e00c0a290b7e4501c27de.pdf |archive-date=11 October 2020 }}</ref> and [[Stephen Hawking]] used global techniques to prove that singularities appear generically.<ref>{{cite journal |last1=Ford |first1=L. H. |date=2003 |title=The Classical Singularity Theorems and Their Quantum Loopholes |journal=[[International Journal of Theoretical Physics]] |volume=42 |issue=6 |pages=1219–1227 |doi=10.1023/A:1025754515197 |arxiv=gr-qc/0301045 |bibcode=2003gr.qc.....1045F |s2cid=14404560}}</ref> For this work, Penrose received half of the 2020 [[Nobel Prize in Physics]], Hawking having died in 2018.<ref>{{Cite web|title=The Nobel Prize in Physics 2020|url=https://www.nobelprize.org/prizes/physics/2020/summary/|access-date=8 October 2020|website=NobelPrize.org|archive-date=24 April 2021|archive-url=https://web.archive.org/web/20210424115309/https://www.nobelprize.org/prizes/physics/2020/summary/|url-status=live}}</ref> Based on observations in [[Royal Greenwich Observatory|Greenwich]] and [[David Dunlap Observatory|Toronto]] in the early 1970s, [[Cygnus X-1]], a galactic [[X-ray]] source discovered in 1964, became the first astronomical object commonly accepted to be a black hole.<ref>{{citation | last=Rolston | first=Bruce | date=10 November 1997 | url=http://news.utoronto.ca/bin/bulletin/nov10_97/art4.htm | title=The First Black Hole | publisher=University of Toronto | access-date=11 March 2008 | archive-url = https://web.archive.org/web/20080307181205/http://www.news.utoronto.ca/bin/bulletin/nov10_97/art4.htm | archive-date = 7 March 2008 }}</ref><ref name="Shipman1975">{{citation | last1=Shipman | first1=H. L. | date=1975 | title=The implausible history of triple star models for Cygnus&nbsp;X-1 Evidence for a black hole | journal=Astrophysical Letters | volume=16 | issue=1 | pages=9–12 | bibcode=1975ApL....16....9S | doi=10.1016/S0304-8853(99)00384-4 | last2=Yu | first2=Z | last3=Du | first3=Y.W }}</ref>

Work by [[James Bardeen]], [[Jacob Bekenstein]], Carter, and Hawking in the early 1970s led to the formulation of [[black hole thermodynamics]].<ref>{{Cite journal |last1=Bardeen |first1=J. M. |author-link1=James M. Bardeen |last2=Carter |first2=B. |author-link2=Brandon Carter |last3=Hawking |first3=S. W. |author-link3=Stephen Hawking |date=1973 |title=The four laws of black hole mechanics |journal=[[Communications in Mathematical Physics]] |volume=31 |issue=2 |pages=161–170 |doi=10.1007/BF01645742 |mr=0334798 |zbl=1125.83309 |bibcode=1973CMaPh..31..161B |s2cid=54690354 |url=http://projecteuclid.org/euclid.cmp/1103858973 |access-date=4 June 2021 |archive-date=16 May 2020 |archive-url=https://web.archive.org/web/20200516211604/https://projecteuclid.org/euclid.cmp/1103858973 |url-status=live }}</ref> These laws describe the behaviour of a black hole in close analogy to the [[laws of thermodynamics]] by relating mass to energy, area to [[entropy]], and [[surface gravity]] to [[temperature]]. The analogy was completed when Hawking, in 1974, showed that [[quantum field theory]] implies that black holes should radiate like a [[black body]] with a temperature proportional to the surface gravity of the black hole, predicting the effect now known as [[Hawking radiation]].<ref name=Hawking1974 />