NGC 5128 - "Centaurus A"

Taken from SSRO/PROMPT/CTIO,Chile Processed by Mark Hanson

 Description by "Sakib Rasool"

 This dramatic galaxy portrait depicts the disturbed and peculiar galaxy NGC 5128 in the constellation of Centaurus. The result of a merger between an elliptical galaxy and a spiral galaxy, it displays a wide variety of kinematical features. It is the closest known active galaxy at 11 million light years.

 The remnant of the original spiral galaxy is represented by its central dust lane highlighted along its edges with the signatures of star formation such as blue star clusters and red emission nebulae. Many cosmic collisions between galaxies trigger a massive starburst of starforming activity as the neutral gas reservoir is increased and pressure and gravity compress gas clouds into active sites of starbirth. The original collision has also strewn small dust globules across the disk of the galaxy.

 This intergalactic encounter between two galaxies has also deformed the structure of the original elliptical galaxy and faint tidal shells envelop the galaxy. They were originally discovered by the astronomers David Malin and David Carter in the 1970's through special photographic amplification techniques. Their discovery prompted the publication of a catalogue of shell elliptical galaxies in 1983 and there are a few hundred known to belong to this category. Images with a wider field of view than this show multiple interlocking shells that extend even further. The origin of these shells are minor mergers with multiple smaller galaxies and are created by the disruption of orbits of captured stars.

 NGC 5128 is also known as Centaurus A and this particular naming scheme denotes the first radio source to be discovered in a particular constellation. As it has been detected by astronomers in observations made with radio telescopes, it belongs to another category of radio galaxies. Radio galaxies are so-called as they radiate more emission in radio than in optical. They are a type of active galactic nucleus (usually abbreviated to AGN). As the name suggests, galaxies that feature an AGN have an energetic nuclear region centered around a supermassive black hole.

 Although not immediately apparent, the AGN activity in Centaurus A is represented optically by a long filamentary jet, which can be seen north of the core. The jet arises from an outflow of gas that has built up in the accretion disk surrounding the supermassive black hole and its narrow appearance is the product of interacting magnetic fields associated with the black hole. This jet appears as an impressive bipolar outflow in x-ray and radio images.