Riccardo Giacconi

Riccardo Giacconi Winner of Wolf Prize in Physics - 1987
Riccardo Giacconi


The Physics Prize Committee has unanimously chosen the following three candidates to equally share the 1987 Wolf Prize in Physics:

Herbert Friedman
United States Naval Research Laboratory
Washington, D.C., USA

for pioneering investigations in solar X-rays;

Riccardo Giacconi
Space Telescope Science Institute and
Johns Hopkins University
Baltimore, MD, USA

Bruno B. Rossi
Massachusetts Institute of Technology
Cambridge, Massachusetts, USA

for the discovery of extra-solar X-ray sources and the elucidation of their physical processes.

All three scientists are honored for seminal contributions to X-ray astrophysics.

Friedman, Rossi, and Giacconi are universally recognized as the principal founders of X-ray astrophysics, a new field of astronomical science which has proved to be a prolific source of fundamental discoveries and deeper physical understanding about high energy processes in the universe. Their work has profoundly influenced virtually every area of astronomical research, from the study of the sun and other stars of all types and luminosity classes to investigations of the interstellar medium, galaxies, clusters of galaxies and the distant quasars. Their brilliant insights, technical inventiveness, and bold leadership stimulated the rapid growth of X-ray astronomy from its early stages of speculation and exploration in the 1950´s and 1960´s to its recent high level of productive research. All agencies engaged in space science are now developing major orbiting facilities for X-ray observations which will playa vital role in the future of astronomical science.

Using novel ultraviolet and X-ray photon counters in a rocket experiment carried out in 1948, Dr. Herbert Friedman and his associates at the United States Naval Research Laboratory detected X rays from the sun, thereby directly confirming the earlier hypothesis of Edward Hulburt that such radiation is a principal cause of ionization in the E region of the earth´s ionosphere. This pioneering research opened the field of solar X-ray astronomy which was explored extensively and almost exclusively during the 1950´s by the Friedman group. Among their achievements were the discovery of X-ray emissions from solar flares, the measurement of wide variations in the spectrum of solar X rays correlated with changes in solar activity, the first sustained observations of solar X-ray emissions by satellite-borne detectors, and the first imaging of the sun in X rays with a pinhole camera. Beginning in 1963 Friedman and his associates made important contributions to the rapidly growing field of extra-solar X-ray astronomy, including the identification of supernova remnants as powerful X-ray sources, and the first detection of X rays from an extragalactic source.

Professor Bruno B. Rossi initiated in 1959 research aimed at utilizing the burgeoning space technologies in a search for extra-solar X-ray sources. Motivated by a lifelong interest in the nature and origins of cosmic radiations, a field of study to which he had been making major contributions since the early 1930´s, Rossi persuaded the management and scientists at American Science and Engineering, Inc, to undertake a study of the theoretical and experimental prospects for X-ray astronomy. This study, carried out under
the leadership of Riccardo Giacconi, led to proposals for new forms of X-ray optics utilizing grazing incidence reflection, and exploratory rocket experiments to scan the sky with X-ray detectors of much greater sensitivity than had previously been used. In a series of four flights, sponsored by the United States Air Force and carried out from 1961 to 1963, the AS&E group discovered discrete extra- solar X-ray sources and the X-ray background. In discussing the origin of X rays in celestial bodies, Rossi drew attention to the process of thermal bremstrahlung emission by extremely hot low-density gas, now known to be the production mechanism in most X-ray sources,

Upon completing a study of the prospects for X-ray astronomy, initiated in 1959 at the suggestion of Bruno Rossi, Professor Riccardo Giacconi undertook the development at American Science and Engineering, Inc. of improved methods for the detection and analysis of X rays of very low intensities with the goal of conducting an exploratory search for non-solar X-ray sources, He proposed, with Rossi, the use of grazing incidence reflection from parabolic mirrors to concentrate X rays for more sensitive detection. He also proposed the adaptation of the principles of image-forming X-ray optics, developed previously in connection with X-ray microscopy, to the construction of high resolution Xray telescopes. With his associates at AS&E, Giacconi carried out a series of rocket flights which discovered the first discrete extra-solar X-ray sources, including Sco X-I, and the diffuse X-ray background. During the next two decades he conducted additional rocket investigations, and conceived and directed the NASA sponsored projects which produced the solar X-ray spectrographic telescope on Skylab, the first orbiting X-ray observatory, Uhuru, and the orbiting Einstein Observatory carrying the first high resolution X-ray telescope for extra-solar observations. Among the most important discoveries made with these satellite facilities were coronal holes and X-ray bright points in the sun´s atmosphere, accretion powered binary X-ray pulsars, X-ray emitting gas in clusters of galaxies, and ubiquitous X-ray emissions by stars of all types and luminosity classes.