The Crafoord Prize 1997

The Royal Swedish Academy of Sciences awards the 1997 Crafoord Prize in astronomy with particular emphasis in stellar physics to Professor Fred Hoyle, Bournemouth, England and professor Edwin E. Salpeter, Cornell University, Ithaca, N.Y., USA, “for their pioneering contributions to the study of nuclear processes in stars and stellar evolution”.

The value of the 1997 Crafoord Prize is USD 500 000. The prizewinner will receive the prize at a ceremony on 29 September 1997.

Fred Hoyle and Edwin Salpeter have both made leading and remaining theoretical contributions within the study of nuclear processes in stars and of stellar evolution. These areas, and the work of the prize winners, have been of central significance for astrophysics in the 20th century.

Fred Hoyle was born in Bingley, Yorkshire, England, in 1915. He made – in addition to his important contributions to cosmology with the “Steady-state cosmology” which soon made him famous – highly significant work in exploring the structure and evolution of stars, and the origin of the chemical elements, in the 40ies and 50ies. He produced a long sequence of early theoretical papers on stellar structure and evolution, and fundamental studies on gas accretion onto stars and on the origin of the Solar system. In particular he must be remembered as a pioneer and leading representative during the 40ies and 50ies for the study of the formation of chemical elements in stars. Perhaps his most important single contribution within this field was a paper where he demonstrated that the existence of carbon in Nature implied the existence of a certain excited state in the carbon nuclei above the ground state. This prediction was later verified experimentally.

In Hoyle´s most well known work on the origin of the elements, a number of the most important stellar processes which have produced the elements were given for the stellar origin of the elements, except for the lightest of them. The elements were partly formed and shed from the stars towards the end of their evolution in supernova explosions or, for the less massive stars, by milder explosions in so-called planetary nebulae.

Later very important work by Hoyle dealt with the dating of the Solar System and the Galaxy by nuclear methods, the structure of so-called super-massive stars and production of light elements in those and in the Big Bang. His later work has in particular been directed towards cosmology and the nature of the interstellar dust. This work is characterised by new interesting ideas and, sometimes, speculation.

Fred Hoyle has also become well known as one of the foremost writers of popular-science books in the 20th century.

Edwin E. Salpeter was born in Vienna, Austria in 1924.  He has in a decisive way contributed to several different areas in astrophysics. Moreover, he has successfully worked in other fields of physics.

In stellar physics Salpeter contributed very essentially to the understanding of nuclear reactions in interiors of stars during the 50ies, e.g. as regards the reaction chain that “burns” helium to carbon and sometimes has been called “the Salpeter process” after him. In addition to this he studied other important reactions that affect the production of the light elements, and properties of dense matter in stellar interiors. He also initiated studies of fundamental significance of star formation and stellar evolution in the Galaxy, which led to the so-called “Salpeter function” which now is a standard in numerous studies of the evolution of galaxies.

During the 60ies Salpeter made important studies, with younger collaborators, of how light neutral elementary particles, neutrinos, are produced in stars, and of late stages in stellar evolution, e. g., of how less massive stars of solar type develop and shrink to so-called white dwarf stars.

An important contribution during the 60ies was a study on how matter is accreted around black holes – of great significance for the interpretation of the then newly discovered stellar X-ray sources. In a sequence of other papers Salpeter and his collaborators have studied different types of X-ray and gamma-ray sources, neutron stars and pulsars, supernova remnants and white dwarfs. During the 80ies he made pioneering investigations of stellar evolution in the Early Universe.

Other important studies by Salpeter in astrophysics deal with maser sources, and the formation of dust and molecules in the interstellar medium. Among contributions outside astrophysics is work in theoretical physics (e.g., the Bethe-Salpeter equation), plasma physics and biophysics.