Active galactic nucleus

As an active galactic nucleus ( AGK, English: active galactic nucleus, AGN ) is called mostly the inner region of active galaxies such as radio galaxies, Seyfert galaxies and BL Lacertae objects. There is also, by definition moderate overlap; so today, for example, quasars, blazars and LINER galaxies are referred to as cores rather than as independent galaxies.

The three most important characteristics of AGK are:

A AGK is in the core region of a supermassive black hole, around which forms an accretion disk. Perpendicular to this accretion disk level, a collimated jet from (length up to megaparsecs ) forms. Above the accretion disk is the so-called Broad Line Region ( BLR), that is, a region in the highly ionized clouds at high speeds ( about 1,000 to 10,000 km / s) move, which is evident in the observed spectrum of the source is noticeable by strongly broadened lines. Often these core region is still surrounded by a dusty torus. Further afield is the narrow -line region ( NLR) in which, similar to the BLR, are clouds, but which move more slowly ( about 100 km / s). Therefore, these emission lines are less strongly broadened in the spectrum. This standard model of AGK was published in 1995 by Urry and Padovani.

What AGK type one now observed, depends on the angle between the observer and the axis of the jet, how much mass has the black hole and how much mass accretes the black hole.

In the high-energy blazars, one starts from a few degrees difference in the viewing angle of the axis of rotation, so you can see directly on the jet. For other objects (eg Seyfert galaxies ), however, sees no characteristic signal of the accretion disk and no strongly broadened emission lines, as you can see here at a 90 ° angle to the jet axis to the object and thus the dust torus, the view of the inner region of the AGK obscured.

The jets consist of matter, which ejects the core region nearly the speed of light. Probably the jet is accelerated by magnetic field lines are " wrapped " by the Lense- Thirring effect in the ergosphere of the black hole and a very high magnetic pressure is created under the laws of magnetohydrodynamics, which pushes out the material. The spirally arranged magnetic field lines then also provide for the pooling of the beam. Within these jets move plasmoids, called blobs, which present very strong, very hard radiation. Such outbreaks usually are taking place on time scales of days.

One of the most intense bursts, which was observed from the gamma to a telescopic EGRET Blazar, showed a doubling of intensity within a few hours. More active phases are observed in AGK in periods of weeks and months, while the quieter periods last longer.

Both AGK and their accretion disks, jets and tori are the subject of today's research.

Observations at the Pierre Auger Observatory AGK identified as a possible source of the highest-energy component of cosmic rays.

Distance measurement

Cosmologists to Darach Watson of the University of Copenhagen have developed a method using AgKS cosmic distances to be determined. The method is based on the relationship between the absolute brightness of galactic nuclei and their brightness as it appears from Earth.

If matter in the central black hole of the galaxy, it heats up greatly and are as a result of high-energy radiation. Through these adjacent gas clouds are ionized and thereby stimulated to emit light. A brighter central region around the black hole leads to lower ionization of the surrounding gas clouds, and thus also to a broader scope, glow in the gas clouds. Changes in the brightness of the central region express themselves with delay in the brightness of nearby gas clouds. In that case the size of the glowing gas clouds, and then the absolute magnitudes of the AGK now were even intended for 38 AGK first. In this way, distances of up to a redshift of 4 can be determined, corresponding to approximately 55 % of the radius of the visible universe.

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