Seyfert galaxy
Seyfert galaxies are spiral or irregular galaxy with a very bright galactic nucleus. The spectra of these cores show characteristic emission lines that are not excited by stars. Seyfert galaxies are a subordination of active galactic nuclei. The Seyfert galaxies are named after the astronomer Carl Keenan Seyfert, who in the 1940s worked very intensively with them.
Appearance, classification into type 1 and type 2
Typical of Seyfert galaxies are often very bright nuclei and electromagnetic spectra with very bright spectral lines of, among others, hydrogen, helium, nitrogen and oxygen. The intensity ratios of these lines are significantly different from those in HII regions, which are excited by hot stars.
These spectral lines often exhibit strong Doppler broadening, which indicate velocities of the emitting gas of up to 10,000 kilometers per second. From this widening Seyfert galaxies were classified into two originally different types:
- Type 2: only " narrow " lines of up to about 1000 km / s width;
- Type 1: Adds " broad " line components of some lines of up to 10,000 km / s width.
Later, Donald Osterbrock, intermediate types were defined as 1.5 and 1.9, in which broad components are seen only in some of the lines that they would have in type 1. It turns out that forbidden lines with low transition probability, which can occur only in a thin gas in the spectrum are always narrow. Width components are observed only in permitted lines that are strongly emitted in dense gas because of their higher transition probability. In Seyfert 1 galaxies is thus a compact and dense "Broad Line Region " and a sprawling thinner " Narrow Line Region " visible in Seyfert 2 galaxies only the latter.
In addition, Seyfert galaxies emit large radiation over much of the electromagnetic spectrum from radio waves to microwaves, infrared, ultraviolet, X-ray to gamma rays. The intensity of the emitted radiation from the core may change significantly within a year. It follows that the diameter of the emitting area must be less than a light-year.
Energy source
The energy source of Seyfert galaxies generally Materieeinströmung is considered a supermassive black hole today. This can even lead to the surrounding galaxy is outshone by the core. There is a continuous transition between the most luminous Seyfert galaxies and quasars even more extreme.
The incident matter is energy released by friction, probably in an accretion disk surrounding the central black hole. The accretion is the source of much of the light emitted from the Seyfertgalaxie electromagnetic radiation generated secondary phenomena, such as the emission lines observed in the visible light upon impingement on more external matter.
Unified Models
Unified models explain the difference between type 1 and type 2 are not affected by presence or absence of a broad-line region. They assume that this is always present, but is obscured by dense interstellar matter and dust in Seyfert 2 galaxies in our line of sight. Consistent with this notion can be observed in polarized light in some Seyfert 2 galaxies the broad spectral component. Polarization indicates that we have achieved indirectly by scattering of hot gas or dust to the core of the light. This effect was first discovered in the type -2 galaxy NGC 1068. Be further supports unified models by the observation that X-ray radiation from the core of the Seyfert galaxies in objects of type 2 are stronger signs of slowdown shows as in objects of type 1