| Abstract from DBPedia | Seyfert galaxies are one of the two largest groups of active galaxies, along with quasars. They have quasar-like nuclei (very luminous, distant and bright sources of electromagnetic radiation) with very high surface brightnesses whose spectra reveal strong, high-ionisation emission lines, but unlike quasars, their host galaxies are clearly detectable. Seyfert galaxies account for about 10% of all galaxies and are some of the most intensely studied objects in astronomy, as they are thought to be powered by the same phenomena that occur in quasars, although they are closer and less luminous than quasars. These galaxies have supermassive black holes at their centers which are surrounded by accretion discs of in-falling material. The accretion discs are believed to be the source of the observed ultraviolet radiation. Ultraviolet emission and absorption lines provide the best diagnostics for the composition of the surrounding material. Seen in visible light, most Seyfert galaxies look like normal spiral galaxies, but when studied under other wavelengths, it becomes clear that the luminosity of their cores is of comparable intensity to the luminosity of whole galaxies the size of the Milky Way. Seyfert galaxies are named after Carl Seyfert, who first described this class in 1943.セイファート銀河（セイファートぎんが、Seyfert galaxy）は活動銀河の一種である。カール・セイファートが1940年代に初めて分類したことからこの名が付けられている。銀河の形態は渦巻銀河または不規則銀河で、極端に明るい中心核を持つのが特徴である。中心核の輝度は銀河本体よりも明るい場合もある。この中心核の活動性は中心に存在する大質量ブラックホールによるものと考えられている。中心核から放射される光は1年以下の時間尺度で変光することから、この光を放出している領域は直径1光年以下の非常に小さな範囲であることが示唆されている。 (Source: http://dbpedia.org/resource/Seyfert_galaxy) |
