Editing Centaurus A (section)

== Observational history ==
NGC&nbsp;5128 was discovered on 29 April 1826 by [[James Dunlop]] during a survey at the Parramatta Observatory.<ref>{{Cite journal |last1=Robertson |first1=Peter |last2=Cozens |first2=Glen |last3=Orchiston |first3=Wayne |last4=Slee |first4=Bruce |last5=Wendt |first5=Harry |date=2010 |title=Early Australian Optical and Radio Observations of Centaurus A |url=https://www.cambridge.org/core/product/identifier/S1323358000000503/type/journal_article |journal=Publications of the Astronomical Society of Australia |language=en |volume=27 |issue=4 |pages=402–430 |arxiv=1012.5137 |bibcode=2010PASA...27..402R |doi=10.1071/AS09071 |issn=1323-3580 |s2cid=54580482}}</ref><ref>{{Cite journal |last=Dunlop |first=James |date=1828-12-31 |title=A catalogue of nebulæ and clusters of stars in the southern hemisphere, observed at Paramatta in New South Wales, … |journal=Philosophical Transactions of the Royal Society of London |language=en |volume=118 |pages=113–151 |doi=10.1098/rstl.1828.0010 |issn=0261-0523 |doi-access=free}}
Centaurus A is listed on p. 138 as entry number 482.  A sketch of Centaurus A appears as Fig. 20 on the plate between pages 114 and 115.</ref>

In 1847 [[John Herschel]] described the galaxy as "two semi-ovals of elliptically formed nebula appearing to be cut asunder and separated by a broad obscure band parallel to the larger axis of the nebula, in the midst of which a faint streak of light parallel to the sides of the cut appears."<ref>{{Cite book |last=Herschel |first=John F. W. |author-link=John Herschel |url=https://archive.org/details/outlinesofastron00hersuoft/mode/2up |title=Outlines of astronomy |date=1878 |publisher=London Longmans, Green |isbn=978-1-108-01377-2 |edition=1 |pages=602 |doi=10.1017/cbo9780511709111}}</ref>

In 1949 [[John Gatenby Bolton]], Bruce Slee and Gordon Stanley localized NGC&nbsp;5128 as one of the first extragalactic radio sources.<ref>{{cite journal
   |author1=J. G. Bolton |author2=G. J. Stanley |author3=O. B. Slee |title=Positions of Three Discrete Sources of Galactic Radio-Frequency Radiation
   |journal=Nature
   |volume=164
   |issue=4159
   |date=1949
   |pages=101–102 |doi=10.1038/164101b0|bibcode = 1949Natur.164..101B |s2cid=4073162 }}</ref> Five years later, [[Walter Baade]] and [[Rudolph Minkowski]] suggested that the peculiar structure is the result of a merge event of a giant elliptical galaxy and a small spiral galaxy.<ref>{{cite journal|title=On the Identification of Radio Sources.|first1=W.|last1=Baade|first2=R.|last2=Minkowski|date=1 January 1954|journal=Astrophysical Journal|volume=119|pages=215|via=NASA ADS|doi=10.1086/145813|bibcode=1954ApJ...119..215B}}</ref> The first detection of X-ray emissions, using a sounding rocket, was performed in 1970.<ref>{{cite journal
   |author1=C. S. Bowyer |author2=M. Lampton |author3=J. Mack |author4=F. de Mendonca |title=Detection of X-Ray Emission from 3C&nbsp;273 and NGC&nbsp;5128
   |journal=Astrophysical Journal
   |volume=161
   |date=1970
   |doi=10.1086/180559 |bibcode=1970ApJ...161L...1B |page=L1|url=http://urlib.net/8JMKD3MGP3W34P/3L6DNS2 }}</ref> In 1975–76 gamma-ray emissions from Centaurus A were observed through the [[IACT|atmospheric Cherenkov technique]].<ref>{{cite journal|title=Evidence for the detection of gamma rays from Centaurus A at gamma-ray energies above 300 GeV|first1=J. E.|last1=Grindlay|first2=H. F.|last2=Helmken|first3=R. H.|last3=Brown|first4=J.|last4=Davis|first5=L. R.|last5=Allen|date=1 April 1975|journal=Astrophysical Journal Letters|volume=197|pages=L9–L12NASA ADS|doi=10.1086/181764|bibcode=1975ApJ...197L...9G}}</ref>

The [[Einstein Observatory]] detected an X-ray jet emanating from the nucleus in 1979.<ref>{{cite journal
   |author1=E. J. Schreier |author2=E. Feigelson |author3=J. Delvaille |author4=R. Giacconi |author5=D. A. Schwartz |title=EINSTEIN Observations of The X-Ray Structure of Centaurus&nbsp;A: Evidence For The Radio-Lobe Energy Source
   |journal=Astrophysical Journal, Part 2
   |volume=234
   |date=1979
   |pages=39–43
   |doi=10.1086/183105 |bibcode=1979ApJ...234L..39S|doi-access=free}}</ref> Ten years later, young blue stars were found along the central dust band with the Hubble Space Telescope.<ref>{{cite web
   |title=HubbleSite – NewsCenter – Hubble Provides Multiple Views of How to Feed a Black Hole (05/14/1998) – Background Info
   |url=http://hubblesite.org/newscenter/archive/releases/1998/14/background/
   |access-date=14 October 2015
   |archiveurl=https://web.archive.org/web/20071030030708/http://hubblesite.org/newscenter/archive/releases/1998/14/background/
   |archivedate=2007-10-30}}</ref>

The [[Chandra X-ray Observatory]] identified in 1999 more than 200 new point sources.<ref>{{cite journal
   |author1=R. P. Kraft |author2=J. M. Kregenow |author3=W. R. Forman |author4=C. Jones |author5=S. S. Murray |title=Chandra Observations of the X-Ray Point Source Population in Centaurus&nbsp;A
   |journal=Astrophysical Journal
   |volume=560
   |issue=2
   |date=20 October 2001
   |pages=675–688
   |doi=10.1086/323056
   |bibcode=2001ApJ...560..675K|doi-access=
   }}</ref> Another space telescope, the [[Spitzer Space Telescope]], found a parallelogram-shaped structure of dust in near infrared images of Centaurus A in 2006.<ref>{{cite journal
   |author1=Alice C. Quillen |author2=Mairi H. Brookes |author3=Jocelyn Keene |author4=Daniel Stern |author5=Charles R. Lawrence |title=Spitzer Observations of the Dusty Warped Disk of Centaurus&nbsp;A
   |journal=Astrophysical Journal
   |volume=645 Nummer = 2
   |issue=2 |date=10 July 2006
   |pages=1092–1101
   |doi=10.1086/504418
   |bibcode=2006ApJ...645.1092Q|arxiv = astro-ph/0601135 |s2cid=18443587 }}</ref>

Evidence of gamma emissions with very high energy (more than 100&nbsp;GeV) was detected by the [[High Energy Stereoscopic System|H.E.S.S-Observatorium]] in Namibia in 2009.<ref>{{cite journal
   |author1=F. Aharonian |author2=A. G. Akhperjanian |author3=G. Anton |author4=U. Barres de Almeida |author5=A. R. Bazer-Bachi |title=DISCOVERY OF VERY HIGH ENERGY γ-RAY EMISSION FROM CENTAURUS&nbsp;A WITH H.E.S.S.
   |journal=Astrophysical Journal
   |volume=695
   |issue=1
   |date=10 April 2009
   |pages=L40–L44
   |doi=10.1088/0004-637x/695/1/l40
   |bibcode=2009ApJ...695L..40A|arxiv = 0903.1582 |s2cid=18160745 }}</ref>

The following year, Centaurus A was identified as a source of cosmic rays of highest energies, after years of observations by [[Pierre Auger Observatory]].<ref>{{cite journal
   |author1=J. Abraham |author2=P. Abreu |author3=M. Aglietta |author4=C. Aguirre |author5=D. Allard |title=Correlation of the highest-energy cosmic rays with the positions of nearby active galactic nuclei
   |journal=Astroparticle Physics
   |volume=29
   |issue=3
   |date=1 April 2008
   |pages=188–204
   |doi=10.1016/j.astropartphys.2008.01.002
   |arxiv = 0712.2843 |bibcode = 2008APh....29..188P }}</ref> In 2016 a review of data from Chandra and [[XMM-Newton]], unusual high flares of energy were found in NGC 5128 and the galaxy [[NGC 4636]]. [[Jimmy Irwin]] of [[University of Alabama]] hypothesized the discovery as potentially a black hole in a yet unknown process or an [[intermediate-mass black hole]].{{citation needed|date=December 2020}}