Editing Crab Nebula (section)

==Observational history==
{{further|SN 1054}}
The earliest recorded documentation of observation of astronomical object SN 1054 was as it was occurring in 1054, by Chinese astrononomers and Japanese observers, hence its numerical identification. Modern understanding that the Crab Nebula was created by a supernova traces back to 1921, when [[Carl Otto Lampland]] announced he had seen changes in the nebula's structure.{{Ref label|D|d|none}}<ref name=lampland/> This 
eventually led to the conclusion that the creation of the Crab Nebula corresponds to the bright [[SN 1054]] supernova recorded by medieval astronomers in AD 1054.<ref>{{cite web |url=http://bc.ub.leidenuniv.nl/bc/tentoonstelling/Jan_Oort/object7.htm#7 |title=A short biography of Jan Hendrik Oort: 7. Crab Nebula |publisher=Leiden University Library |first1=J. |last1=Katgert-Merkelijn |first2=J. |last2=Damen |name-list-style=amp |date=2000 |access-date=9 March 2015  |archive-url=https://web.archive.org/web/20140904090251/http://bc.ub.leidenuniv.nl/bc/tentoonstelling/Jan_Oort/object7.htm#7 |archive-date=4 September 2014}}</ref>

===First identification===
[[File:M1rosse.jpg|thumb|left|upright|Reproduction of the first depiction of the nebula by [[Lord Rosse]] (1844) (colour-inverted to appear white-on-black)]]
[[File:The Crab Nebula M1 Goran Nilsson & The Liverpool Telescope.jpg|thumb|[[H-alpha|HaRGB]] image of the Crab Nebula from the [[Liverpool Telescope]], exposures totalling 1.4 hours.]]
[[File:Stack 252frames 8064s ps-.jpg|thumb|The Crab Nebula M1]]
The Crab Nebula was first identified in 1731 by [[John Bevis]].<ref name=Barrow2008>{{cite book |last1=Barrow |first1=John D. |title=Cosmic Imagery: Key Images in the History of Science |publisher=Random House |page=45 |date=2008 |url=https://books.google.com/books?id=uRg6iN10JCIC&pg=PA45 |isbn=978-0-224-07523-7}}</ref> The nebula was independently rediscovered in 1758 by [[Charles Messier]] as he was observing a bright [[comet]].<ref name=Barrow2008/> Messier catalogued it as the first entry in his [[Messier Catalogue|catalogue]] of comet-like objects;<ref name=Barrow2008/> in 1757, [[Alexis Clairaut]] reexamined the calculations of [[Edmund Halley]] and predicted the return of [[Halley's Comet]] in late 1758. The exact time of the comet's return required the consideration of perturbations to its orbit caused by planets in the Solar System such as Jupiter, which Clairaut and his two colleagues [[Jérôme Lalande]] and [[Nicole-Reine Lepaute]] carried out more precisely than Halley, finding that the comet should appear in the [[constellation]] of [[Taurus (constellation)|Taurus]]. It was in searching in vain for the comet that [[Charles Messier]] found the Crab Nebula, which he at first thought to be Halley's comet.<ref name=Pugh2011>{{cite book |last1=Pugh |first1=Philip |title=Observing the Messier Objects with a Small Telescope: In the Footsteps of a Great Observer |publisher=Springer Science |pages=8–10 |date=November 2011 |url=https://books.google.com/books?id=jDbjx-FSv5cC&pg=PA10 |isbn=978-0-387-85357-4}}</ref> After some observation, noticing that the object that he was observing was not moving across the sky, Messier concluded that the object was not a comet. Messier then realised the usefulness of compiling a catalogue of celestial objects of a cloudy nature, but fixed in the sky, to avoid incorrectly cataloguing them as comets. This realization led him to compile the "[[Messier object|Messier catalogue]]".<ref name=Pugh2011/>

[[William Herschel]] observed the Crab Nebula numerous times between 1783 and 1809, but it is not known whether he was aware of its existence in 1783, or if he discovered it independently of Messier and Bevis. After several observations, he concluded that it was composed of a group of stars.<ref name="Mayall"/> [[William Parsons, 3rd Earl of Rosse]] observed the nebula at [[Birr Castle]] in the early 1840s using a {{convert|36|in|m|1|adj=on}} telescope, and made a drawing of it that showed it with arms like those of a crab.<ref name=Ridpath/> He observed it again later, in 1848, using a {{convert|72|in|m|1|adj=on}} telescope but could not confirm the supposed resemblance, but the name stuck nevertheless.<ref>{{cite journal |last=Parsons |first=William |title=Observations on Some of the Nebulae |journal=Philosophical Transactions of the Royal Society of London |volume=134 |date=1844 |at=fig. 81, plate xviii, p. 321 |url=https://archive.org/stream/jstor-108366/108366#page/n5/mode/2up |jstor=108366 |doi=10.1098/rstl.1844.0012|s2cid=186212669 }}</ref><ref>{{cite book |last=Jones |first=Kenneth Glyn |title=The Search for the Nebulae |publisher=Alpha Academic |date=1975 |isbn=978-0-905193-01-4 |url=https://books.google.com/books?id=vGW1AAAAIAAJ}}</ref>

===Connection to SN 1054===
[[File:A whole new view of the Crab Nebula.jpg|thumb|The nebula is seen in the visible spectrum at 550&nbsp;nm (green light).]]

The Crab Nebula was the first astronomical object recognized as being connected to a supernova explosion.<ref name="Mayall"/> In the early twentieth century, the analysis of early [[astrophotography|photographs]] of the nebula taken several years apart revealed that it was expanding. Tracing the expansion back revealed that the nebula must have become visible on Earth about 900&nbsp;years before. Historical records revealed that a new star bright enough to be seen in the daytime had been recorded in the same part of the sky by Chinese astronomers on 4 July 1054, and probably also by Japanese observers.<ref name="Mayall">{{cite journal |last=Mayall |first=Nicholas Ulrich |author-link=Nicholas Mayall |title=The Crab Nebula, a Probable Supernova |journal=[[Astronomical Society of the Pacific Leaflets]] |volume=3 |issue=119 |page=145 |date=1939 |bibcode=1939ASPL....3..145M}}</ref><ref>{{Cite book |last=Leverington |first=David |url=https://books.google.com/books?id=r47qBwAAQBAJ |title=A History of Astronomy: from 1890 to the Present |publisher=Springer Science & Business Media |year=2012 |isbn=978-1-4471-2124-4 |page=197 |language=en}}</ref><ref name="Lundmark">{{cite journal |last=Lundmark |first=Knut |author-link=Knut Lundmark |title=Suspected New Stars Recorded in Old Chronicles and Among Recent Meridian Observations |journal=[[Publications of the Astronomical Society of the Pacific]] |volume=33 |issue=195 |pages=225–238 |date=1921 |bibcode=1921PASP...33..225L |jstor=40668518 |doi=10.1086/123101|s2cid=120275870 |url=https://zenodo.org/record/1431279 }}</ref>

In 1913, when [[Vesto Slipher]] registered his [[spectroscopy]] study of the sky, the Crab Nebula was again one of the first objects to be studied. Changes in the cloud, suggesting its small extent, were discovered by [[Carl Lampland]] in 1921.<ref name=lampland>{{cite journal |title=Observed Changes in the Structure of the "Crab" Nebula (N. G. C. 1952) |journal=[[Publications of the Astronomical Society of the Pacific]] |last=Lampland |first=C. O. |author-link=Carl Otto Lampland |volume=33 |issue=192 |pages=79–84 |date=1921 |bibcode=1921PASP...33...79L |jstor=40710638 <!--|alternate url=https://archive.org/details/jstor-40710638--> |doi=10.1086/123039|s2cid=122115955 }}</ref> That same year, [[John Charles Duncan]] demonstrated that the remnant was expanding,<ref name=duncan>{{cite journal |last=Duncan |first=John Charles |title=Changes Observed in the Crab Nebula in Taurus |journal=[[Proceedings of the National Academy of Sciences]] |volume=7 |issue=6 |pages=179–181 |date=1921 |bibcode=1921PNAS....7..179D |doi=10.1073/pnas.7.6.179 |pmid=16586833 |pmc=1084821|doi-access=free }}</ref> while [[Knut Lundmark]] noted its proximity to the guest star of 1054.<ref name="Lundmark"/><ref name=Srinivasan1997>{{cite book |last=Srinivasan |first=G. |chapter=Neutron Stars |title=Stellar Remnants |publisher=Springer Science |series=Lecture Notes 1995, Swiss Society for Astrophysics and Astronomy |page=108 |date=1997 |isbn=978-3-540-61520-0 |chapter-url=https://books.google.com/books?id=79OhUC30PkkC&pg=PA108}}</ref>

In 1928, [[Edwin Hubble]] proposed associating the cloud with the star of 1054, an idea that remained controversial until the nature of supernovae was understood, and it was [[Nicholas Mayall]] who indicated that the star of 1054 was undoubtedly the supernova whose explosion produced the Crab Nebula. The search for historical supernovae started at that moment: seven other historical sightings have been found by comparing modern observations of supernova remnants with astronomical documents of past centuries.{{Citation needed|date=July 2023}}

After the original connection to Chinese observations, in 1934 connections were made to a 13th-century Japanese reference to a "[[Guest star (astronomy)|guest star]]" in [[Meigetsuki]] a few weeks before the Chinese reference.<ref name="Usui2007">{{cite web|title=Why and how did a Japanese poet record the Supernova of AD 1054?|url=http://homepage3.nifty.com/silver-moon/teika/teika-e.htm|last=Usui|first=Tadashi|date=11 January 2007|archive-url=https://web.archive.org/web/20160303193701/http://homepage3.nifty.com/silver-moon/teika/teika-e.htm|archive-date=3 March 2016|access-date=4 March 2015}}</ref><ref>{{cite book|author=Fujiwara no Sadaie|title=Meigetsuki|date=c. 1200|trans-title=Record of the Clear Moon|author-link=Fujiwara no Teika}}</ref><ref>{{Cite journal |last1=Stephenson |first1=F. Richard |last2=Green |first2=David A. |year=2003 |title=Was the supernova of AD 1054 reported in European history? |journal=Journal of Astronomical History and Heritage |volume=6 |issue=1 |page=46 |bibcode=2003JAHH....6...46S |doi=10.3724/SP.J.1440-2807.2003.01.05 |s2cid=128868531}}</ref> The event was long considered unrecorded in Islamic astronomy,<ref>{{cite journal|last=Gingerich|first=Owen|author-link=Owen Gingerich|date=April 1986|title=Islamic astronomy|url=http://www.as.utexas.edu/astronomy/education/spring05/bromm/readings/islam.pdf|journal=Scientific American|volume=254|issue=10|page=74|bibcode=1986SciAm.254d..74G|doi=10.1038/scientificamerican0486-74}}</ref> but in 1978 a reference was found in a 13th-century copy made by [[Ibn Abi Usaibia]] of a work by [[Ibn Butlan]], a [[Nestorian]] Christian physician active in Baghdad at the time of the supernova.<ref name="Usaybia">{{cite book|author=Ibn Abi Usaibia|title=Lives of the Physicians|date=1971|others=Kopf, Lothar (trans.)|chapter=Chapter 10: On the Classes of Physicians of Iraq, al-Jazirah and Diyar Bekr|author-link=Ibn Abi Usaibia|orig-date=1245–1246|chapter-url=http://www.tertullian.org/fathers/ibn_abi_usaibia_02.htm#CHAPTER_X}}</ref><ref name="Green03">{{cite book|last1=Green|first1=David A.|last2=Stephenson|first2=F. Richard|chapter=Historical Supernovae |title=Supernovae and Gamma-Ray Bursters |date=2003|publisher=Springer|isbn=978-3-540-44053-6|editor1-last=Weiler|editor1-first=K. W.|series=Lecture Notes in Physics|volume=598|location=Berlin|pages=7–19|arxiv=astro-ph/0301603|bibcode=2003LNP...598....7G|doi=10.1007/3-540-45863-8_2|s2cid=17099919|name-list-style=amp}}</ref>

Given its great distance, the daytime "guest star" observed by the Chinese could only have been a [[supernova]]—a massive, exploding star, having exhausted its supply of energy from [[nuclear fusion]] and collapsed in on itself.<ref>{{Cite book|last=Tao|first=Li|title=Xu Zizhi Tongjian Changbian|publisher=Zhonghua Book Company|year=2004|volume=176|location=Beijing|page=4263|language=zh|quote=己丑，客星出天关之东南可数寸。嘉祐元年三月乃没。}}</ref><ref>{{Cite book|title=Song Huiyao|language=zh|quote=嘉佑元年三月，司天监言：'客星没，客去之兆也'。初，至和元年五月，晨出东方，守天关。昼如太白，芒角四出，色赤白，凡见二十三日。}}</ref> Recent analysis of historical records have found that the supernova that created the Crab Nebula probably appeared in April or early May, rising to its maximum brightness of between [[apparent magnitude]] −7 and −4.5 (brighter even than Venus' −4.2 and everything in the night sky except the [[Moon]]) by July. The supernova was visible to the [[naked eye]] for about two years after its first observation.<ref name="Collinsetal1999">{{cite journal |last1=Collins |first1=George W. II |last2=Claspy |first2=William P. |last3=Martin |first3=John C. |display-authors=1 |title=A Reinterpretation of Historical References to the Supernova of A.D. 1054 |journal=[[Publications of the Astronomical Society of the Pacific]] |volume=111 |issue=761 |pages=871–880 |date=1999 |bibcode=1999PASP..111..871C |doi=10.1086/316401 |arxiv=astro-ph/9904285|s2cid=14452581 }}</ref>

===Crab Pulsar===
{{Main|Crab Pulsar}}
[[File:Chandra-crab.jpg|thumb|Image combining optical data from [[Hubble Space Telescope|Hubble]] (in red) and [[X-ray astronomy|X-ray]] images from [[Chandra X-ray Observatory]] (in blue).]]

In the 1960s, because of the prediction and discovery of [[pulsar]]s, the Crab Nebula again became a major center of interest. It was then that [[Franco Pacini]] predicted the existence of the [[Crab Pulsar]] for the first time, which would explain the brightness of the cloud.  In late 1968, [[David H. Staelin]] and Edward C. Reifenstein III reported the discovery of two rapidly variable radio sources in the area of the Crab Nebula using the [[Green Bank Telescope]].<ref name="Howard1968">{{Cite journal |last1=Howard |first1=W. E. |last2=Staelin |first2=D. H. |last3=Reifenstein |first3=E. C. |date=1968-01-01 |title=Pulsating radio sources near Crab Nebula. |journal=International Astronomical Union Circular |issue=2110 |pages=2 |bibcode=1968IAUC.2110....2H |issn=0081-0304}}</ref><ref name="Craft1968">{{Cite journal |last1=Staelin |first1=David H. |last2=Reifenstein |first2=Edward C. |date=December 1968 |title=Pulsating Radio Sources near the Crab Nebula |journal=Science |language=en |volume=162 |issue=3861 |pages=1481–1483 |bibcode=1968Sci...162.1481S |doi=10.1126/science.162.3861.1481 |pmid=17739779 |issn=0036-8075}}</ref> They named them NP 0527 and NP 0532. The period of 33 milliseconds and precise location of the Crab Nebula pulsar NP 0532 was discovered by [[Richard V. E. Lovelace]] and collaborators on 10 November 1968 at the [[Arecibo_Observatory|Arecibo Radio Observatory]].<ref name="Lovelace1968">{{Cite journal |last1=Lovelace |first1=R. V. E. |last2=Sutton |first2=J. M. |last3=Craft |first3=H. D. |date=November 1968 |title=Pulsar NP 0532 Near Crab Nebula |journal=International Astronomical Union Circular |issue=2113 |pages=1 |bibcode=1968IAUC.2113....1L |issn=0081-0304}}</ref><ref name="Comella1969">{{Cite journal |last1=Comella |first1=J. M. |last2=Craft |first2=H. D. |last3=Lovelace |first3=R. V. E. |last4=Sutton |first4=J. M. |last5=Tyler |first5=G. Leonard |date=February 1969 |title=Crab Nebula Pulsar NP 0532 |journal=Nature |language=en |volume=221 |issue=5179 |pages=453–454 |bibcode=1969Natur.221..453C |doi=10.1038/221453a0 |issn=0028-0836}}</ref> This discovery also proved that pulsars are rotating neutron stars (not pulsating white dwarfs, as many scientists suggested). Soon after the discovery of the [[Crab Pulsar]], David Richards discovered (using the Arecibo Observatory) that the Crab Pulsar spins down and, therefore, the pulsar loses its rotational energy. [[Thomas Gold]] has shown that the spin-down power of the pulsar is sufficient to power the Crab Nebula.

The discovery of the Crab Pulsar and the knowledge of its exact age (almost to the day) allows for the verification of basic physical properties of these objects, such as characteristic age and spin-down luminosity, the orders of magnitude involved (notably the strength of the [[magnetic field]]), along with various aspects related to the dynamics of the remnant. The role of this supernova to the scientific understanding of supernova remnants was crucial, as no other historical supernova created a pulsar whose precise age is known for certain. The only possible exception to this rule would be [[SN 1181|SN&nbsp;1181]], whose supposed remnant [[3C 58|3C]][[SN 1181|&nbsp;]]58 is home to a pulsar, but its identification using Chinese observations from 1181 is contested.<ref>{{cite journal |last=Bietenholz |first=M. F. |title=Radio Images of 3C 58: Expansion and Motion of Its Wisp |journal=[[The Astrophysical Journal]] |volume=645 |issue=2 |pages=1180–1187 |date=July 2006 |doi=10.1086/504584 |bibcode=2006ApJ...645.1180B |arxiv=astro-ph/0603197|s2cid=16820726 }}</ref>

The inner part of the Crab Nebula is dominated by a pulsar wind nebula enveloping the pulsar. Some sources consider the Crab Nebula to be an example of both a pulsar wind nebula as well as a supernova remnant,<ref>{{Cite journal |last1=Gaensler|first1=Bryan M.|last2=Slane|first2=Patrick O.|date=18 August 2006|title=The Evolution and Structure of Pulsar Wind Nebulae|journal=Annual Review of Astronomy and Astrophysics |volume=44|issue=1|pages=17–47 |doi=10.1146/annurev.astro.44.051905.092528|arxiv=astro-ph/0601081 |bibcode=2006ARA&A..44...17G|s2cid=10699344|issn=0066-4146}}</ref><ref>{{Cite web|title=X-RAY UNIVERSE :: Make a Pulsar: Crab Nebula in 3D |url=https://chandra.cfa.harvard.edu/deadstar/crab.html|access-date=31 October 2020|website=chandra.cfa.harvard.edu|quote=the [Crab] nebula is not a classic supernova remnant, as once commonly thought, but that the system is better classified as a pulsar wind nebula}}</ref><ref name="sao20161104">{{cite web |url=https://www.cfa.harvard.edu/news/su201643 |title=Pulsar Wind Nebulae |publisher=Smithsonian Astrophysical Observatory |date=4 November 2016 |access-date=26 March 2017}}</ref> while others separate the two phenomena based on the different sources of energy production and behaviour.<ref name="Hester2008"/>

===Source of high-energy gamma rays===
The Crab Nebula was the first astrophysical object confirmed to emit gamma rays in the very-high-energy (VHE) band above 100 GeV in energy.  The VHE detection was carried out in 1989 by the Whipple Observatory 10m Gamma-Ray telescope,<ref>{{Cite book |last=Gibbs |first=Kenneth Gerard |url=https://repository.arizona.edu/handle/10150/184235 |title=The application of imaging to the atmospheric Cerenkov technique: Observations of the Crab Nebula |publisher=The University of Arizona |year=1987}}</ref><ref>{{Cite journal |last=Weekes |first=T.C. |date=1989 |title=Observation of TeV Gamma Rays from the Crab Nebula Using the Atmospheric Cerenkov Imaging Technique |bibcode=1989ApJ...342..379W |journal=Astrophysical Journal |volume=342 |page=379 |doi=10.1086/167599 |s2cid=119424766 |url=http://mural.maynoothuniversity.ie/12618/1/Cawley_ObservationTeV_1989.pdf }}</ref> which opened the VHE gamma-ray window and led to the detection of numerous VHE sources since then.

In 2019 the Crab Nebula was observed to emit [[Ultra-high-energy gamma ray|gamma rays]] in excess of 100&nbsp;[[TeV]], making it the first identified source beyond 100&nbsp;TeV.<ref name="Amenomori2019">{{cite journal |title=First Detection of Photons with Energy Beyond 100 TeV from an Astrophysical Source |journal=Physical Review Letters |first=M. |last=Amenomori |display-authors=etal |volume=123 |issue=5 |page=051101 |date=June 2019 |arxiv=1906.05521 |doi=10.1103/PhysRevLett.123.051101 |pmid=31491288 |bibcode=2019PhRvL.123e1101A |s2cid=189762075}}</ref>