JOHN FOSTER / SCIENCE PHOTO LIBRARY JOHN FOSTER / SCIENCE PHOTO LIBRARY
Active galaxy. Artwork of an active, spiral Seyfert galaxy (at upper centre) with an alien planet (in the lower frame). About 1% of spiral galaxies are Seyferts. Seyfert galaxies have a small, bright core in their nucleus. This core produces light which is predominantly blue, as well as ultraviolet light, infrared radiation, and sometimes radio waves. The light from the core changes in brightness over a period of months. The core is surrounded by fast clouds of hot gas which have been ionised by the ultraviolet light from the core. It is thought that Seyfert galaxies are closely related to radio galaxies and quasars.
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