
%0 Journal Article
%A McVittie, GC 
%T Counts of Extragalactic Radio Sources and Uniform Model Universes
%J Australian Journal of Physics
%D 1957/09/01
%V 10
%N 3
%P 331-350
%K 
%R https://doi.org/10.1071/PH570331
%U https://www.publish.csiro.au/paper/PH570331 
%X The radio sources are assumed to be galaxies sharing in the red-shift phenomenon. The counts of such sources to successive limits of flux density are interpreted in terms of the model universes of general relativity. The flux density in each infinitesimal interval of frequency is assumed to be proportional to a power of the frequency and to a multiplicative parameter, both these quantities being regarded as functions of the red-shift, i.e. of the time of travel of the radiation. All sources at the same distance from the observer are assumed to be identical radiators; this permits the introduction of a standard comparison source. The data in the Sydney catalogue can then be interpreted in terms of radio sources of constant strength·(i.e. which are independent of the red-shift) if they are similar to NGC 1275, taken as standard. If they are similar to Cygnus A, the data imply that the sources were radiating more strongly when their radiation left them than is Cygnus A now. This type of conclusion appears to be unavoidable for the data of the Cambridge catalogue. It is briefly explained how to modify the theory to take account of a variation with time of the space-density of sources and also of a mixture of comparison sources. 
