Radio Galaxies and Quasars, I

Abstract

If we observe the sky with a radio telescope operating at metre wavelengths, we find first a continuous background mainly due to the Milky Way — which we observe undimmed by the obscuration which spoils our optical view. In addition we find compact sources, a few minutes of arc or less in extent. About 8000 of these compact sources have now been discovered using large instruments, but only a few hundred of the most intense have been studied in any detail; a few are within our Galaxy and represent the emission from the remnants of supernova explosions, but many of them are found to be associated with faint galaxies. From their distances we can conclude that their radio emission is very great, in some cases more than a million times greater than that from our own Galaxy or the Andromeda nebula. These powerful sources are known as ‘radio galaxies’.