John Bolton and the discovery of discrete radio sources

John Bolton was born in Sheffield in 1922 and educated at Cambridge University. After wartime service in the Royal Navy, in 1946 he joined the CSIRO's Radiophysics Laboratory in Sydney and began work in the fledgling field of radio astronomy. Radio emission from our Galaxy had been discovered and studied during the 1930s by the Americans Karl Jansky and Grote Reber. It was thought that the emission emanated from interstellar space, but the mechanism was unknown.

In June 1947, observing from Dover Heights near the entrance to Sydney Harbour, Bolton discovered that strong emission from the constellation of Cygnus came from a discrete point-like source. By the end of the year, with colleagues Gordon Stanley and Bruce Slee ( a co-author of this paper) , Bolton had discovered a further five of these discrete sources. However, the positions measured for them were not accurate enough to allow them to be identified optically with any known celestial objects.

In 1948 Bolton organised a three-month expedition to New Zealand where there were observing sites superior to the one at Dover Heights. The new observations gave more accurate positions and allowed Bolton to identify three of the sources: one was a supernova remnant in our Galaxy and two were unusual extragalactic objects. This paper will document this remarkable chapter in the development of twentieth century astronomy.