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Ryle, Sir Martin (1918–1984), radio astronomer, was born on 27 September 1918 at Brighton, Sussex, the second son and second child in a family of three sons and two daughters of , a professor of medicine, and his wife, Miriam Power (1893/4–c.1986), the daughter of William Charles Scully, a civil servant, of Cape Town, who came from a landowning family in co. Tipperary. His father was to become regius professor of physic at Cambridge and, after the Second World War, the first professor of social medicine at Oxford. An uncle, Gilbert Ryle, was professor of philosophy at Oxford.

Ryle's early education was entrusted to a governess, who taught him and his siblings at the family home at 13 Wimpole Street, London. He then attended Gladstone's Preparatory School in Eaton Square before entering Bradfield College at the age of thirteen. His ability with his hands was fostered at home, where regular instruction was provided to him and his elder brother by a professional carpenter. In 1936 he went to Christ Church, Oxford, where he obtained first-class honours in physics in 1939. His enthusiasm for radio engineering and electronics was already apparent. By the time he left school he had built his own radio transmitter and acquired a Post Office licence to operate it. At Oxford, he and E. Cooke-Yarborough, a fellow undergraduate, set up the university amateur radio station.

Wartime service

In 1939 Ryle joined J. A. Ratcliffe's ionospheric research group at the Cavendish Laboratory, Cambridge. On the outbreak of the Second World War, Ratcliffe joined the Air Ministry Research Establishment, later to become the Telecommunications Research Establishment (TRE), and Ryle followed in May 1940. For the first two years he worked mainly on the design of antennae and test equipment. In 1942 he became the leader of group 5 of the newly formed radio countermeasures division, whose task was to provide jamming transmitters against the German radar defence system and radio-deception operations. Among the latter was the electronic ‘spoof-invasion’ on D-day, which led the German high command to believe that the invasion was to take place across the Strait of Dover.

Radar techniques developed at an astounding pace during these years, and Ryle and his colleagues worked in a frantic atmosphere, constantly having to find immediate practical solutions for the electronic defence of the RAF's bomber fleet. Sir Bernard Lovell remarked that ‘Ryle's extraordinary inventiveness and immediate scientific insight were of great importance in this work and often led him to be intolerant of those not similarly blessed’ (DNB). But he also learned how to motivate groups of research workers. In a letter to the present writer, written only two months before his death, he said:
Presumably I knew some physics in 1939—but this evaporated during the six succeeding years—though it was replaced by other things. But six years of designing/installing/flying boxes of electronics gave one ‘state of the art’ electronics, a fair intimacy with aircraft and the ability to talk constructively with Air Vice-Marshals—or radar mechanics—and above all gave one the privilege of flying with the in-between-operational-tours aircrew who flew our aircraft.
According to Sir Francis Graham-Smith, perhaps Ryle's greatest achievement was to discover a vulnerable element in the V-2 rocket radio guidance system. The system developed by Ryle and his old college friend Cooke-Yarborough successfully disrupted the accurate aim of the V-2 rockets and probably contributed to the abandonment of radio control only a few weeks later.

Solar radio-emission

After the war Ryle returned to Cambridge on a fellowship from Imperial Chemical Industries, and soon turned his energies to understanding the nature of the radio emissions from cosmic sources which had interfered with anti-aircraft radars. The pioneer radio astronomer J. S. Hey had found that the jamming was caused by intense radio outbursts from the sun, apparently associated with large solar flares and sunspot groups. The angular resolving power of the radio antennae available at that time was not sufficient to resolve the disc of the sun, let alone locate the origin of the radio emission. Ryle and D. D. Vonberg adapted surplus radar equipment and developed new receiver techniques for metre wavelengths to create a radio interferometer, the antennae being separated by several hundreds of metres in order to provide high enough angular resolution. Only later was it realized that they had reinvented the radio equivalent of the Michelson interferometer. A massive sunspot occurred in July 1946, and their observations showed conclusively that the radio emission originated from a region on the surface of the sun similar in size to that of the sunspot region.

In addition to the emission from the sun, Hey had discovered a discrete source of radio emission in the constellation of Cygnus, and Ryle and Graham-Smith adapted the solar interferometer to observe the radio source, which became known as Cygnus A. In 1947 the source was successfully observed, and in addition another even more intense discrete source was found in the nearby constellation of Cassiopeia. By 1950 Graham-Smith had measured very precisely the position of Cygnus A, and it turned out that the source was associated with a distant massive galaxy.

During the time in which the fledgeling radio group began to take shape, Ryle married (Ella) Rowena Palmer, the youngest sister of Graham-Smith's wife, Elizabeth, on 19 June 1947. It was a wonderfully happy marriage, and they had three children, Alison (b. 1949), John (b. 1951), and Claire (b. 1952). Somewhat to his surprise, midway through his fellowship Ryle was appointed a university lecturer (1948). In 1952 he was elected a fellow of the Royal Society.

Radio interferometry

Ryle appreciated that radio interferometry was the way to overcome the problem of the low angular resolution of single-dish radio antennae, and over the next twenty-five years he and his colleagues developed a series of radio interferometers of increasing complexity and ingenuity which enabled surveys of the sky to be carried out and the structures and nature of the radio sources to be unravelled. His contribution of genius was the development of the concept of aperture synthesis, the technique by which images of radio sources can be created by combining interferometric observations made with modest-sized radio telescopes located at different interferometer spacings. The technical problem was to measure both the relative amplitudes and the phases of the incoming signals, which contain all the information needed to reconstruct the distribution of radio intensity on the sky.

Throughout the 1950s and 1960s, one of Ryle's major objectives was to produce reliable catalogues of all the bright radio sources in the northern sky. In his review of the new science of radio astronomy published in 1950, he had believed that most of the ‘radio stars’ belonged to our own galaxy, but increasingly it became clear that, in directions away from the Milky Way, the bulk of them were associated with distant galaxies. The bombshell was dropped in 1955 in his Halley lecture at Oxford, when he announced the results of the second Cambridge survey of radio sources. This survey had found vastly more faint radio sources than could be explained by any of the standard cosmological models—Ryle inferred that the only reasonable interpretation of these observations was that the universe had changed with time, so that there had been many more radio sources in the distant past. This interpretation flew in the face of the steady state theory, propounded by Bondi, Gold, and Hoyle in 1948, according to which the universe should have the same overall appearance at all cosmic epochs. It soon became apparent that the intensities of the faintest sources had been systematically overestimated because of the effects of source confusion. An acrimonious dispute resulted, not only with the proponents of steady state theory, but also with the Sydney radio astronomers, who did not observe the excess of faint sources found by Ryle in their surveys of the southern sky. The correct answer was discovered by Ryle's colleague Peter Scheuer, who analysed the survey records statistically and found that there was indeed a significant excess of faint sources, but not to the extent originally claimed. In the 1960s the revised third and fourth Cambridge catalogues showed that Ryle's interpretation was correct.

The Mullard Observatory

These events had positive and negative impacts on the work of the Cambridge radio astronomy group. The negative side was that the group became more defensive in its interaction with outside groups. The positive side was that new astrophysical and cosmological opportunities were opened up. In 1956 the radio observatory moved to a disused wartime Air Ministry bomb store at Lord's Bridge, near Cambridge, and, in acknowledgement of a grant of £100,000 from the electronics company Mullard Ltd, the new observatory was opened in 1957 as the Mullard Radio Astronomy Observatory.

Aperture synthesis

In 1959 Ryle was appointed professor of radio astronomy. At the same time his most ambitious experiment was under way—the use of the rotation of the earth to carry telescopes at fixed points on the earth about each other as observed from a point on the celestial sphere. The germ of this idea had already appeared in his notebooks in 1954. By 1959 digital computers were fast enough to cope with the demands of this form of synthesis mapping, and, in a classic set of observations, Ryle and Ann Neville created the first earth-rotation aperture synthesis map of a region of sky about the north celestial pole. The angular resolution of the survey was 4.5 minutes of arc and the sensitivity eight times greater than that of the original antenna system. The success of this project pointed the way to the future. The succeeding generations of aperture synthesis arrays employed fully steerable antennae—the One-Mile Telescope completed in 1965 and the Five-Kilometer Telescope in 1972. Both of these telescopes were far ahead of the radio astronomical capability of any other telescope system in the world. Ryle was personally involved in every aspect of these very complex telescope systems. As remarked by Scheuer, the development of aperture synthesis:
was the story of one remarkable man, who not only provided the inspiration and driving force but actually designed most of the bits and pieces, charmed or savaged official persons according to their deserts, wielded shovels and sledgehammers, mended breakdowns, and kept the rest of us on our toes.
Intellectually, he relied almost completely on his well-honed physical intuition as the way to solve any problem, be it in engineering, astrophysics, or cosmology—indeed, he believed this was the only way research should be conducted. Ryle was knighted in 1966.

The Nobel prize

These telescopes were central to understanding the nature of the radio sources. Radio astronomy has played a crucial role in the realization that high-energy astrophysical activity involving supermassive black holes and general relativity are part of the large-scale fabric of the universe.

From the beginning, led by the dynamism and vision of Ryle, the Cambridge radio astronomy group developed a remarkably coherent and focused research programme. Ryle was fortunate in being supported by an outstanding group of physicists. Among these, Antony Hewish had played a central role in the development of aperture synthesis and in 1964 had begun the study of the flickering, or scintillation, of radio sources due to irregularities in the outflow of material from the sun—what is known as the solar wind. A remarkable by-product of these studies was the discovery of pulsating radio sources, now called pulsars, by Hewish and his graduate student Jocelyn Bell. These objects were soon convincingly identified as rapidly rotating, magnetized neutron stars, which had been predicted to exist on theoretical grounds. Their serendipitous discovery at long radio wavelengths was a crucial event for all astronomy. In 1974 Ryle and Hewish were awarded jointly the Nobel prize for physics, the citation explicitly describing the development of aperture synthesis as Ryle's major contribution. His list of honours was extensive, including foreign memberships of the Royal Danish Academy (1968), the American Academy of Arts and Sciences (1970), and the USSR Academy of Sciences (1971). Among many medals were the gold medal of the Royal Astronomical Society (1964), the Popov medal of the USSR Academy of Sciences (1971), and the royal medal of the Royal Society (1973).

Anti-nuclear campaigns

In 1972 Ryle was appointed astronomer royal, the first time the post had been separated from the directorship of the Royal Greenwich Observatory. This coincided with a period of grave deterioration in his health, originating from a malfunctioning heart and aggravated by stress. Medical examination exposed lung cancer, for which he had surgery in 1977. Over the same period his main preoccupations shifted away from radio astronomy. His acute awareness of the dangers of nuclear power fuelled a passionate ethical sense of crusade concerning the potential misuse of science. His conviction was that man breaks the natural laws at his peril. His deep concern for alternative energy sources led to an enthusiasm for wind energy, a natural outcome of his expertise as a sailing-boat designer, and he began a successful research and development programme at Lord's Bridge involving the construction of wind-powered generators. He was passionate about the proliferation of nuclear weapons and wrote a monograph, Towards the Nuclear Holocaust, which, as expressed by Graham-Smith,
is partly a cry of pain and a desperate plea for a halt in the arms race, and partly an indictment of all those concerned with the civil nuclear programme, which he regarded as sustainable only on account of its production of plutonium for military purposes. (Graham-Smith, 517–8)
Ryle died on 14 October 1984 at the family home, 5A Herschel Road, Cambridge, and was cremated at Cambridge crematorium. His legacy went far beyond the technical brilliance of his contribution to radio astronomy. When he began his career after the war, the UK could not compete with the United States in observational astronomy. Through his technical and scientific contributions, as well as his inspiring leadership, Ryle played a major role in rejuvenating British astronomy and bringing it to the forefront of world astronomy.

Malcolm S. Longair

Sources  

F. Graham-Smith, Memoirs FRS, 32 (1986), 497–524 · B. Lovell, Quarterly Journal of the Royal Astronomical Society, 26 (1985), 358–68 · ‘Martin Ryle’, Les prix Nobel en 1974 (1975), 80–99 · P. A. G. Scheuer, ‘Radio source counts’, Modern cosmology in retrospect, ed. B. Bertotti and others (1990), 331–45 · M. S. Longair, ‘Astrophysics and cosmology’, Twentieth century physics, ed. L. M. Brown, A. Pais, and B. Pippard, 3 (1995) · M. Ryle, N. Kurti, and R. L. F. Boyd, Search and Research, ed. J. P. Wilson (1971) · J. S. Hey, The evolution of radio astronomy (1973) · W. T. Sullivan III, ed., The early years of radio astronomy (1984) · W. T. Sullivan III, Classics of radio astronomy (1982) · DNB · personal knowledge (2004) · private information (2004)

Archives  

CAC Cam., further corresp. and papers; papers · U. Cam., Cavendish Laboratory, corresp. and MSS |  Nuffield Oxf., corresp. with Lord Cherwell  

FILM

 

U. Cam., Cavendish Laboratory

 

SOUND

 

BBC Archives, talks


Likenesses  

E. Leigh, photograph, 1974, repro. in Graham-Smith, Memoirs FRS · photographs, U. Cam., Cavendish Laboratory

Wealth at death  

£4267: probate, 11 July 1985, CGPLA Eng. & Wales