The center of the galaxy contains asupermassive black hole with a mass of 55 millionsolar masses,[14] which ejects arelativistic jet that is responsible for emissions in theX-ray andradio wavelengths. By taking radio observations of the jet separated by a decade, astronomers have determined that the inner parts of the jet are moving at about half of thespeed of light. X-rays are produced farther out as the jet collides with surrounding gases, resulting in the creation of highly energetic particles. The X-ray jets of Centaurus A are thousands of light-years long, while the radio jets are over a million light-years long.[15]
It is also one of the nearest largestarburst galaxies, of which agalactic collision is suspected to be responsible for an intense burst of star formation. Models have suggested that Centaurus A was a large elliptical galaxy that collided with a smaller spiral galaxy, with which it will eventually merge.[16] For that reason, the galaxy has been of particular interest to astronomers for years. While collisions of spiral galaxies are relatively common, the effects of a collision between an elliptical and a spiral galaxy are not fully understood.[17]
NGC 5128 was discovered on 29 April 1826 byJames Dunlop during a survey at the Parramatta Observatory.[18][19]
In 1847John 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."[20]
In 1949John Gatenby Bolton, Bruce Slee and Gordon Stanley localized NGC 5128 as one of the first extragalactic radio sources.[21] Five years later,Walter Baade andRudolph Minkowski suggested that the peculiar structure is the result of a merge event of a giant elliptical galaxy and a small spiral galaxy.[22] The first detection of X-ray emissions, using a sounding rocket, was performed in 1970.[23] In 1975–76 gamma-ray emissions from Centaurus A were observed through theatmospheric Cherenkov technique.[24]
TheEinstein Observatory detected an X-ray jet emanating from the nucleus in 1979.[25] Ten years later, young blue stars were found along the central dust band with the Hubble Space Telescope.[26]
TheChandra X-ray Observatory identified in 1999 more than 200 new point sources.[27] Another space telescope, theSpitzer Space Telescope, found a parallelogram-shaped structure of dust in near infrared images of Centaurus A in 2006.[28]
Evidence of gamma emissions with very high energy (more than 100 GeV) was detected by theH.E.S.S Observatory in Namibia in 2009.[29]
Centaurus A may be described as having apeculiar morphology. As seen from Earth, the galaxy looks like alenticular orelliptical galaxy with a superimposed dust lane.[31] The peculiarity of this galaxy was first identified in 1847 byJohn Herschel, and the galaxy was included inHalton Arp'sAtlas of Peculiar Galaxies (published in 1966) as one of the best examples of a "disturbed" galaxy with dust absorption.[32] The galaxy's strange morphology is generally recognized as the result of amerger between two smaller galaxies.[33]
Zoom movie of the galaxy Centaurus A, showing different aspects of the galaxy in several wavelengths.Schematic diagram of the components of the Centaurus A galaxy
The bulge of this galaxy is composed mainly of evolved red stars.[31] The dusty disk, however, has been the site of more recentstar formation;[12] over 100 star formation regions have been identified in the disk.[34]
The first supernova, namedSN 1986G, was discovered within the dark dust lane of the galaxy byRobert Evans on 3 May 1986.[36]It was later identified as aType Ia supernova,[37]which forms when awhite dwarf's mass grows large enough to ignite carbon fusion in its center, touching off arunaway thermonuclear reaction, as may happen when a white dwarf in abinary star system strips gas away from the other star. SN 1986G was used to demonstrate that the spectra of Type Ia supernovae are not all identical, and that Type Ia supernovae may differ in the way that they change in brightness over time.[37]
The second supernova, designated SN 2016adj,[38] was discovered by Backyard Observatory Supernova Search in February 2016 and was initially classified as a Type II supernova based on its H-alphaemission line.[39][40] A subsequent classification found the spectrum best resembled the Type Ib core-collapse supernova 1999dn.[41] (SeeType Ib and Ic supernovae).
In addition to these supernovae, aluminous red nova, designated AT2020nqq (Type ILRT, mag. 17.8), was discovered on 27 June 2020.[42]
Centaurus A is close enough that classicalnovae can also be detected:
AT 2024aeql (type nova, mag. 18.47) was discovered byBlackGEM on 23 December 2024.[43]
AT 2025nok (type nova, mag. 18.706) was discovered byATLAS on 14 June 2025.[44]
Distance estimates to Centaurus A established since the 1980s typically range between 3–5 Mpc.[2][3][4][5][6][45]Classical Cepheids discovered in the heavily obscured dust lane of Centaurus A yield a distance between ~3–3.5 Mpc, depending on the nature of the extinction law adopted and other considerations.[4][5]Mira variables[45] andType II Cepheids[4][5] were also discovered in Centaurus A, the latter being rarely detected beyond theLocal Group.[46] The distance to Centaurus A established from several indicators such asMira variables andplanetary nebulae favour a more distant value of ~3.8 Mpc.[9][6]
Centaurus A is at the center of one of two subgroups within theCentaurus A/M83 Group, a nearbygroup of galaxies.[47]Messier 83 (the Southern Pinwheel Galaxy) is at the center of the other subgroup. These two groups are sometimes identified as one group[48][49] and sometimes identified as two groups.[50] However, the galaxies around Centaurus A and the galaxies around M83 are physically close to each other, and both subgroups appear not to be moving relative to each other.[51] The Centaurus A/M83 Group is located in theVirgo Supercluster.[citation needed]
In addition to dwarf galaxies, Centaurus A, like most galaxies, has a population ofglobular clusters. Some objects that appear to be globular clusters are hypothesized to be the tidally stripped cores of former galaxies. The most extreme example is the object VHH81-01, whose central black hole is estimated to be around8×105M☉.[52]
Overview over the radio structure of Centaurus A. The whole radio emitting region extends about 1.8 million light years (about 8° degrees in the sky). Through observations with the VLBI technique structures of the jet and the core smaller than a light year could be resolved (corresponding to a resolution of 0.68 x 0.41 milli-arcseconds.[53])
This view of the jets of Centaurus A was created through observations in radio waves with a wavelength of 20 cm with the VLA. The position of the radio jet and the knots within the jets matches very well with the structures seen in the x-ray jet. This region of the jet is named „Inner Lobe“.[54]
In July 2021 theEvent Horizon Telescope released a resolved image of Centaurus A showing the jet coming from the black hole at its center.
Centaurus A is located approximately 4° north ofOmega Centauri (aglobular cluster visible with the naked eye).[13] Because the galaxy has a high surface brightness and relatively large angular size, it is an ideal target for amateur astronomy observations. The bright central bulge and dark dust lane are visible even in finderscopes and large binoculars,[13] and additional structure may be seen in larger telescopes.[13] Claims have been made that Centaurus A is visible to the naked eye under exceptionally good conditions.[55]
"Hubble's panchromatic vision... reveals the vibrant glow of young, blue star clusters..."[56]
Image of the central parts of Centaurus A showing the parallelogram-shaped remains of a smaller galaxy that was absorbed about 200 to 700 million years ago
^Baade, W.; Minkowski, R. (1 January 1954). "On the Identification of Radio Sources".Astrophysical Journal.119: 215.Bibcode:1954ApJ...119..215B.doi:10.1086/145813 – via NASA ADS.
^Grindlay, J. E.; Helmken, H. F.; Brown, R. H.; Davis, J.; Allen, L. R. (1 April 1975). "Evidence for the detection of gamma rays from Centaurus A at gamma-ray energies above 300 GeV".Astrophysical Journal Letters.197: L9–L12NASA ADS.Bibcode:1975ApJ...197L...9G.doi:10.1086/181764.
^R. P. Kraft; J. M. Kregenow; W. R. Forman; C. Jones; S. S. Murray (20 October 2001). "Chandra Observations of the X-Ray Point Source Population in Centaurus A".Astrophysical Journal.560 (2):675–688.Bibcode:2001ApJ...560..675K.doi:10.1086/323056.
^abM. M. Phillips; A. C. Phillips; S. R. Heathcote; V. M. Blanco; et al. (1987). "The type 1a supernova 1986G in NGC 5128 – Optical photometry and spectra".Publications of the Astronomical Society of the Pacific.99:592–605.Bibcode:1987PASP...99..592P.doi:10.1086/132020.
^R. B. Tully (1988).Nearby Galaxies Catalog. Cambridge: Cambridge University Press.ISBN978-0-521-35299-4.
^P. Fouque; E. Gourgoulhon; P. Chamaraux; G. Paturel (1992). "Groups of galaxies within 80 Mpc. II – The catalogue of groups and group members".Astronomy and Astrophysics Supplement.93:211–233.Bibcode:1992A&AS...93..211F.
^A. Garcia (1993). "General study of group membership. II – Determination of nearby groups".Astronomy and Astrophysics Supplement.100:47–90.Bibcode:1993A&AS..100...47G.
^Roopesh Ojha; M. Kadler; M. Böck; R. Booth; M. S. Dutka (30 December 2009). "TANAMI: Milliarcsecond Resolution Observations of Extragalactic Gamma-ray Sources".2009 Fermi Symposium.arXiv:1001.0059.Bibcode:2010arXiv1001.0059O.
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