Radio galaxies are galaxies that are extremely bright in the radio part of the spectrum. In the majority of detected radio galaxies a strong emission of radio waves was found in the area near the center of the galaxy, and often occurs the radio-bright halo. Discovered radio waves are very often highly polarized, as astronomers have interpreted as the radio show very high energy electrons, moving near the speed of light. It is believed that the cause was a very dramatic event, where the freed energy is equivalent to that which is released with annihilation of ten million stars.
Stronger sources are at greater distances from the weaker. Looking deeper into the universe at the same time we look further into the past, so the above findings suggest the evolution of radio galaxies from stronger to weaker sources. It is the big bang theory, unlike competing theories, based on the idea of evolution of the universe.
Radio galaxies form subspecies of galaxies with active galactic nucleus, which are particularly bright in radio wavelengths of the electromagnetic spectrum. In general they are very massive elliptical galaxies with supermassive black hole at the center. Radio galaxies are usually divided into two categories, Fanaroff - Riley type I (FR I) and Fanaroff-Riley type II (FR II). The categories are named by scientists in 1974th which proposed distribution of radio galaxies based on differences in morphology. FR I sources are the brightest in its central part (central core and inner jet region), while the largest part of the gloss FR II sources comes from the outer parts of radio galaxies (from an expanded area of diffuse radiation and hot spots).
Radio galaxies are of great importance in astrophysical and cosmological research as they are highly suitable for observation. A powerful radio sources can be detected in relatively short exposure time and at very large distances, for which observations in the optical or X-ray region is almost impossible because it scatters radiation passing through areas filled with dust and gas on the way to us.