Centaurus A, an unusual starburst galaxy

 
Centaurus A, an unusual starburst galaxy

Centaurus A (also designated NGC 5128 and Arp 153) is a starburst galaxy that measures 150.000 × 120.000 light-years, and has a mass of about 1 trillion solar masses. Located in the southern constellation of Centaurus it is, at about 11 million light-years away, the closest active galaxy to Earth, and is part of the M83 group of galaxies. It is moving away from us at 547 kilometers per second.

The galaxy has an active galactic nucleus and a very unusual dust lane. Its bulge is composed mainly of evolved red stars. The dusty disk, however, has been the site of more recent star formation; over 100 star formation regions have been identified in the disk.

Centaurus A is of intermediate type between elliptical and disk (spiral) galaxies: The main body has all characteristics of a large elliptical, but the pronounced dust lane is superimposed well over the center, forming a disk plane around this galaxy. The twisted galaxy is likely the result of a smaller spiral galaxy falling into a much larger galaxy. This collision is also responsible for the intense burst of star formation.

The galaxy is a strong source of radiowaves and is one of the closest radio galaxies to Earth, so its active galactic nucleus has been extensively studied by professional astronomers. The galaxy is also the fifth brightest in the sky, making it an ideal amateur astronomy target, although the galaxy is only visible from low northern latitudes and the southern hemisphere.

A jet that seems to arise from the galaxy’s central supermassive black hole — with a million or so times the mass of the Sun, is responsible for emissions in the X-ray and radio 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 one half of the speed of light. X-rays are produced farther out as the jet collides with surrounding gases resulting in the creation of highly energetic particles. The radio jets of Centaurus A are over a million light years long.

Centaurus A is shaped like a parallelogram in infrared images. The parallelogram lies along the active galaxy’s central band of dust and stars visible in more familiar optical images.

Astronomers believe that the striking geometric shape represents an approximately edge-on view of the infalling spiral galaxy’s disk in the process of being twisted and warped by the interaction. Ultimately, debris from the ill-fated spiral galaxy should provide fuel for the supermassive black hole lurking at the center of Centaurus A.

Only one supernova has been detected in Centaurus A, the Type Ia supernova SN 1986G, discovered within the dark dust lane of the galaxy. A Type Ia supernova is a result from the violent explosion of a white dwarf star.

Image Credits: X-ray: NASA/CXC/CfA/R.Kraft et al.; Submillimeter: MPIfR/ESO/APEX/A.Weiss et al.; Optical: ESO/WFI

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