Sagittarius a radio source located in the center of the milky Way, presumably consisting of a supermassive black hole, fragments of a supernova and ionized gas and dust clouds. According to scientists, Sagittarius And about eight billion years ago there was an active galactic nucleus (AGN) emitting x-rays and deep ultraviolet light for tens or hundreds of millions of years.

Scientists evaluated the effects of AGN on potentially habitable planets in our galaxy. The rays are deep ultraviolet must "rip off" of the atmosphere on objects which are near enough to the center of the milky Way. Even if the radiation was strongly attenuated by gas and dust surrounding the galactic core, all of earth-like planets that were to Sagittarius And closer than a thousand parsecs (3.2 thousand light years), completely lost their gaseous envelopes by the end of phase activity of the nucleus.

According to the findings of researchers, the radiation emanating from the center of the milky Way, was deadly for complex multicellular organisms that lived on planets far from Sagittarius And for 2-8 thousand parsecs. Single-celled to withstand this radiation, but died in the 0.25-0.81 kiloparsec from the galactic core. These values were calculated for luminosity AGN, equal to 10-100% of critical.

Critical (Eddingtons) luminosity is called the maximum power of electromagnetic radiation at which gravity and radiation pressure are balanced. When this limit is exceeded there is a strong stellar wind, when the substance of the object begins to expire in interstellar space.