NGC 5128 was discovered on 29 April 1826 by
James Dunlop during a survey at the Parramatta Observatory. 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." In 1949
John Gatenby Bolton, Bruce Slee and Gordon Stanley localized NGC 5128 as one of the first extragalactic radio sources. 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. The first detection of X-ray emissions, using a sounding rocket, was performed in 1970. In 1975–76 gamma-ray emissions from Centaurus A were observed through the
atmospheric Cherenkov technique. The
Einstein Observatory detected an X-ray jet emanating from the nucleus in 1979. Ten years later, young blue stars were found along the central dust band with the Hubble Space Telescope. The
Chandra X-ray Observatory identified in 1999 more than 200 new point sources. Another space telescope, the
Spitzer Space Telescope, found a parallelogram-shaped structure of dust in near infrared images of Centaurus A in 2006. Evidence of gamma emissions with very high energy (more than 100 GeV) was detected by the
H.E.S.S Observatory in Namibia in 2009. The following year, Centaurus A was identified as a source of
cosmic rays of highest energies, after years of observations by
Pierre Auger Observatory. 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. ==Morphology==