Editing Crab Nebula (section)

===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"/>