The centre of the Milky Way is believed to contain a black hole, with a mass of about one million Suns.

The recognition of that structure started with the radio astronomy observations of Karl Jansky (see above photo), who found that there were strong radio emissions from the nucleon of the Milky Way, produced by high-speed electrons circling magnetic fields, which indicated the existence of a compact central object, the source of these electrons. Because visible light from the centre of the Milky Way is absorbed by interstellar dust before it reaches the Earth, the composition of the centre must be determined by infrared and radio observations. From these, it appears that material in the innermost spiral arm around the centre of the Milky Way is expanding away from the centre. At the very Centre, astronomers have identified a source of radio emissions of enormously high energy, but no larger than the solar system-it is presumed to be a black hole.