Centaurus A

Centaurus A (NGC 5128) is the name of a galaxy in the constellation Centaurus. NGC 5128 is a strong radio source. NGC 5128 has an angular extent of 25.7 ' x 20.0 ' and an apparent brightness of 6.6 mag. Centaurus A is in accordance with Messier 81, the second brightest galaxy outside the Local Group and the fünfthellste the sky. It lies at a distance of about 12 million light years and is part of the M83 group.

Discovery

The name Centaurus A it receives as brightest radio source in the constellation Centaurus.

Special

Centaurus A is the nearest radio galaxy and the third brightest radio source in the sky. Is an elliptical galaxy which is traversed by an unusual band dust. In addition, it is a strong source of X-ray and gamma radiation. A relativistic jet is emitted from the core. Their proximity is one of the most studied active galaxies. The unusual activity of Centaurus A can be explained that they had a collision with a small spiral galaxy some 100 million years ago and completely recorded by it. Thus, there was a violent star formation phase, which activated the black hole in the center of the galaxy. This has a mass of 200 million solar masses.

Construction

In the optical spectrum of the galaxy has a diameter of 150,000 × 120,000 light years and has the shape of an ellipsoid. It contains an active galactic nucleus. The central region consists mainly of older red stars. This area is crossed by a dust disk in the recently emerged new stars. More than 100 star-forming regions have been discovered in this area. It is surrounded by extensive radio emission regions.

Observations

Optical

With the Hubble Space Telescope, the inner region was examined more closely. These clusters were discovered with newly formed hot young stars at the edge of the dust disk. The dust disk itself has a tilt angle of 10 to 20 degrees to our line of sight.

The normal optical photographs only show the inner region of the galaxy. The Australian astronomer David Malin was able to examine the edges of the galaxy in more detail by a special technique. This demonstrates the enormous size of the galaxy. In this case, also a covering structure was discovered by a plurality of shells, which is due to the collision with another galaxy.

1986, a supernova was discovered in Centaurus A (SN 1986G ).

Infrared

Observations made with the Spitzer Space Telescope revealed a parallelogram - like structure in the central dust lane. This strange shape is explained by that Centaurus A has swallowed a small spiral galaxy and the disk was bent and twisted during the recording process.

With the Spitzer Space Telescope in 2006 a shell-like structure expanding around the core with a radius of 150 light- years was found.

Radio

The radio emission of Centaurus A is emitted from two regions. The inner region extends symmetrically into two arms each 16,000 light years from the core ( see the first figure ). The external radio source is also symmetrical and rotated by 40 degrees with respect to the inner region. The outer radio source has a diameter of 2.5 million light years, making it one of the most extensive such objects in the sky. ( The apparent diameter is 9 degrees, which corresponds to twenty full moon diameter). These radio clouds probably consist of thin hot gas which has been ejected from the core. The radio emission itself is generated by fast moving electrons moving in the magnetic field of the radio clouds, thereby surrendering synchrotron radiation.

X-rays

Observations with the Chandra X-ray telescope show a 30,000 light-years extended jet emanating from the nucleus of the galaxy. The brightness of the nucleus in the X-ray range may change within a few days, so the source can only be a maximum of one hundredth of a light year in size. The X-ray radiation of the core probably comes from an accretion disk around a massive black hole.

Gamma radiation

Observations in the gamma-ray range show that Centaurus A case emits 200 times more energy than radio waves.

Video

• What feeds Centaurus A? from the TV - series alpha Centauri (about 15 minutes). First broadcast on 29., 2006.