The space beyond our galaxy contains billions of-other galaxies and some of these are strong emitters at radio wavelengths. Extra-galactic radio sources are often divided into two groups: "normal" galaxies and "radio" galaxies. The great Andromeda galaxy (M.3,I) is an example of a normal radio galaxy as are the Large and Small Magellanic Clouds. Our own galaxy is also normal at radio wavelengths with an output of less than 1022 watts.

The so-called "radio" galaxies have a power output of a very different order. The second strongest radio source is Cygnus A (Cas A is the first),a remote galaxy located some 184 Mpc. in distance from our Sun, with a radio output of some 1038 watts! In the words of radio astronomy pioneer John D. Kraus: "The tremendous magnitude of Cygnus A's power may take on more significance if we note that the radio wave energy radiated by Cygnus A in just one millionth of one second is sufficient to supply all of the world's electric power requirements for all purposes (light, heat, mechanical work, etc.) at a million times the present rate for the next 10 million years." That is hot stuff!

Some other strong radio galaxies include Virgo A, Perseus , Centaurus A, Fornax A and Hercules A. Included elsewhere is a list of the stronger of the known radio sources within and without the galaxy. Some attempt has been made to indicate the nature of the radiating object in the notes column. The column marked "flux" will provide the reader with some idea as to the relative strength of the various radio sources. The values listed (under flux) are for 1400 Mhz, with the exception of those marked with an asterisk which are for 178 Mhz. The reader should keep in mind that some of these objects are very remote, while others are within out galaxy. The bibliography at the end of this series lists some of the source catalogs for these objects and readers are referred to the excellent book by John D. Kraus, Radio Astronomy, for further details.

Copyright (c) 1997-99 Michael Erlewine