John Bolton and the nature of discrete radio sources

John Bolton and the nature of discrete radio sources

John Bolton is regarded by many to be the pre-eminent Australian astronomer of his generation. In the late 1940s he and his colleagues discovered the first discrete sources of radio emission. Born in Sheffield in 1922 and educated at Cambridge University, in 1946 Bolton joined the Radiophysics Laboratory in Sydney, part of Australia’s Council for Scientific and Industrial Research. Radio astronomy was then in its infancy. Radio waves from space had been discovered by the American physicist Karl Jansky in 1932, followed by Grote Reber who mapped the emission strength across the sky, but very little was known about the origin or properties of the emission. This thesis will examine how the next major step forward was made by Bolton and colleagues Gordon Stanley and Bruce Slee. In June 1947, observing at the Dover Heights field station, they were able to show that strong radio emission from the Cygnus constellation came from a compact point-like source. By the end of 1947 the group had discovered a further five of these discrete radio sources, or ‘radio stars’ as they were known, revealing a new class of previously-unknown astronomical objects.

By early 1949 the Dover Heights group had measured celestial positions for the sources accurately enough to identify three of them with known optical objects. One coincided with an unusual object in the local Galaxy and two coincided with peculiar extragalactic objects. As I will show, the optical identifications built a bridge between traditional astronomy and the fledgling radio astronomy. The identifications also marked the birth of extragalactic radio astronomy, which was to have a major impact on the development of astronomy in the second half of the twentieth century.

In the early 1950s, with improved instrumentation, the Dover Heights group carried out a sky survey that revealed over 100 radio sources, consolidating its position as the world’s leading group for ‘cosmic’ radio astronomy. To conclude, I will briefly survey Bolton’s career after the closure of Dover Heights in 1954. Bolton had the unusual distinction of being the inaugural director of two major observatories, first at the California Institute of Technology (1955–60) and then at the Parkes Observatory (1961–81) in central NSW. No astronomer did more over his career to establish radio astronomy as a mature and powerful branch of astronomy.