The Bakerian Lecture 1978 - Cosmic exploration by X-rays

Abstract

Bakerian Lectures dealing with astronomical topics have occurred roughly every ten years during this century. They have therefore something of the character of reports on progress and one need read no further back than Hoyle’s ‘Review of recent developments in cosmology’ (Hoyle 1968) and Ryle’s ‘The nature of the cosmic radio sources’ (Ryle 1958) to discover the background against which are to be seen the dramatic changes of the ensuing period. It stretches from the conception of X-ray astronomy through its birth, with the discovery of the first non-solar source (Giacconi et al . 1962), to its maturity with the availability of satellites to provide long exposures. Nor is it any accident that the root κóσμoς is prominent in the titles of recent lectures for while those of Jeans, Eddington, Milne and Blacket were concerned with our Galaxy, the drama is now truly cosmic. Cosmic X-ray astronomy grew out of the study of the Sun and for this reason its founding father is Herbert Friedman. Giacconi describes well the early history of the subject (Giacconi & Gursky 1974) and tells how, in June 1962, having been interested in the idea by Rossi in September 1959, he and his colleagues detected flux coming neither from the Sun nor from the Moon. Friedman had discussed as early as 1956 ‘how his group obtained puzzling results, which might have been due to celestial X-ray fluxes’, and reported this at the I. A. U. meeting in Moscow in 1958. Stimulated by our solar studies with the Skylark rocket, similar thinking was taking place under the auspices of this Society. Mention of this was made at a conference in the United States in June 1961 (Boyd 1962) but a meeting of the Astronomy Working Group of the British National Committee on Space Research (N. C. S. P./34, 1959 a ) had discussed, in May 1959, the possibility, of mounting ‘Directive X-ray counters’ on the proposed U. K. -I satellite. The minute read ‘Current theories suggested that there may be objects in the sky with strong X-ray emission although inconspicuous visually. A search for these is a matter of great interest and importance.’ It is noteworthy that Hoyle, who had discussed Friedman’s speculations with him, was present at the meeting.