Born Saint Albans, Hertfordshire, England, 8 January 1918
Died Silver Spring, Maryland, USA, 15 September 2000
Australian-American radio astronomer Frank J. Kerr was the first to map out the gas disk of the half of the Galaxy visible from the Southern Hemisphere, demonstrating the existence of spiral arms, a warp in the gas disk, and some evidence for net expansion. Joined to a northern map made in the Netherlands by Gart Westerhout, this provided the definitive picture of the Milky Way as a rotating spiral for many years.
Kerr studied physics at the University of Melbourne, receiving his BSc degree in 1938 and his MSc degree in 1940. He then became a staff member at the Radiophysics Laboratory in Sydney, Australia, continuing his affiliation until 1968; Joseph Pawsey was his key mentor during these years at the Radiophysics Laboratory. Kerr held research posts at Harvard University (where he also earned an MA in astronomy in 1951), Leiden University, and the University of Texas and in 1962 was awarded the DSc degree by Melbourne University. In 1966 he joined the faculty of the University of Maryland, where he remained for the rest of his career.
Kerr’s early studies of radar and radio transmission and reception led in 1948 to his work on bouncing radar echoes off the Moon and studying the transmission and refraction of the upper ionosphere. In a classic 1952 paper, he analyzed the possibility of measuring distances, structure, and motions in the solar system using radar echoes. While visiting Harvard University, Kerr witnessed the first detection of the 21-cm line of interstellar neutral hydrogen by Harold Ewen and Edward Purcell and upon his return to Australia embarked on what was to become his life’s work, the use of this hydrogen line to study the structure of the Galaxy. He set up a Southern Hemisphere 21-cm line program, first using a 36-ft. telescope and in later years the Parkes 210-ft. radio telescope. In 1952/1953 he made the first detection and mapping observations of 21-cm hydrogen lines in galaxies other than our own, the Magellanic Clouds, showing that these relatively dust-free systems contain large amounts of cold hydrogen and demonstrating the existence of an interstellar medium of different global properties from those in the Galaxy. In 1954 Kerr, together with Gerard de Vaucouleurs , Brian Robinson, and James Hindman, mapped the hydrogen in the Large Magellanic Cloud, measured its extended hydrogen envelope and rotation curve, and made the first measurement of its mass.
In 1954 Kerr began his studies of our Galaxy, using the 36-ft. telescope to map hydrogen emission from the southern galactic plane. He found that hydrogen in the outer Galaxy bends away from the galactic plane in the opposite direction to that in the northern galactic plane and invented the term “galactic warp” to describe this global distortion. Kerr hypothesized that the warp is due to tidal interaction between the galactic disk and the Magellanic Cloud. Together with Gart Westerhout and Maarten Schmidt at Leiden University, he used the northern and southern hydrogen surveys, and Jan Oort ’srotation model, to make the first map of the entire Galaxy. Westerhout, Kerr, and Colin Gum also used these surveys to define the location of the galactic plane and the new galactic coordinate system adopted by the International Astronomical Union [IAU] in 1958.
In 1966 Kerr moved to the University of Maryland, joining his colleague Westerhout and turning it into a major center for galactic structure studies for the next decades. Kerr’s work during this period included several improvements to the hydrogen map of the Galaxy, the use of OH masers to trace the evolved stellar population throughout the Galaxy, studies of the gas dynamics in the galactic center, and investigations of the enigmatic hydrogen high-velocity clouds. He carried out much of this work at the National Radio Astronomy Observatory in West Virginia but returned many times to Australia for extended observing periods. In the 1980s Kerr and the last of his 13 PhD students, Patricia Henning, pioneered blind searching for hydrogen emission from galaxies optically hidden by the dust in the galactic plane. Altogether, Kerr published nearly 200 scientific articles.
Kerr’s service to the scientific community included the vice presidency of the American Astronomical Society (1980–1982), directorship of the Maryland astronomy program, a term (1978–1985) as provost of the Division of Mathematical and Physical Sciences and Engineering, and some years as program director of the University Space Research Association (the organization charged with oversight of several of the national observatories) beginning in 1983. Within the International Astronomical Union, he was president of Commission (33) on structure of the Milky Way (1976–1979) and active in the commissions on interstellar matter and radio astronomy (organizing committee 1965–1968). Kerr cochaired, with Donald Lynden-Bell, the 1985 IAU committee that reevaluated the structure constants of the Milky Way, concluding that our distance from the center is closer to 8.5 than to 10 kPc, the number established 20 years earlier by Oort.
Always a loyal Australian, Kerr diligently followed Australian politics, opera, and especially sports. He was predeceased by his wife, Maureen, and one of their three children.