Cygnus A

Cygnus A

Radio-emitting galaxy lying in the constellation Cygnus, about 700 million light-years from Earth. It is the brightest cosmic source of radio waves in the sky and the first radio galaxy to be detected. Because of its peculiar divided appearance, it was once thought to be two galaxies colliding. Astronomers now believe it to be a single galaxy with a large black hole at its core; emanating from this central region are two opposing jets of hot gas that end in radio- and X-ray-emitting lobes called "hot spots." See also active galactic nucleus.