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The subject of the fate of imploding stars re-opened with vigor when both Robert Oppenheimer and John Wheeler, two of the really great names of physics, attended a conference in Brussels in 1958. Oppenheimer believed that his 1939 papers said all that needed to be said about such implosions. Wheeler disagreed, wanting to know what went on beyond the well-established laws of physics.
When Oppenheimer and Snyder did their work in 1939, it had been hopeless to compute the details of the implosion. In the meantime, nuclear weapons design had provided the necessary tools because, to design a bomb, nuclear reactions, pressure effects, shock waves, heat, radiation, and mass ejection had to be taken into account. Wheeler realized that his team had only to rewrite their computer programs so as to simulate implosion rather than explosion. However his hydrogen bomb team had been disbanded and it fell to Stirling Colgate at Livermore, in collaboration with Richard White and Michael May, to do these simulations. Wheeler learned of the results and was largely responsible for generating the enthusiasm to follow this line of research. The term 'black hole' was coined by Wheeler.
The theoretical basis for supernova explosions is said to have been laid by E. M. Burbidge, G.R. Burbidge, W. A. Fowler, and Fred Hoyle in a 1957 paper2. However, even in Hoyle and Narlikar's text book, "The Physics-Astronomy Frontier" (1980), no consideration is given to a role for neutrinos in the explosive conduction of energy away from the core of a supernova. In their 1957 paper, Hoyle and his co-workers proposed that when the temperature of an aging massive star rises to about 7 billion degrees K, iron is rapidly converted into helium by a nuclear process that absorbs energy. In meeting the sudden demand for this energy, the core cools rapidly and shrinks catastrophically, implodes in seconds, and the outer envelope crashes into it. As the lighter elements are heated by the implosion they burn so rapidly that the envelope is blasted into space. So, two years after the first publication of The Urantia Book, the most eminent authorities in the field of star evolution make no reference to the "vast quantities of tiny particles devoid of electric potential" that the book says escape from the star interior to bring about its collapse. Instead they invoke the conversion of iron to helium, an energy consuming process now thought not to be of significance.
Following on from the forgotten 1940's paper of Gamow and Schoenfeld paper, the next suggestion that neutrinos may have a role in supernovae came from Ph.D. student, Hong-Yee Chiu, working under Philip Morrison. Chiu proposed that towards the end of the life of a massive star, the core would reach temperatures of about 3 billion degrees at which electron-positron pairs would be formed and a tiny fraction of these would give rise to neutrino-antineutrino pairs. Chiu speculated that X-rays would be given off by the star for about 1000 years and that the temperature would ultimately reach about 6 billion degrees when an iron core would form at the central region of the star. The flux of neutron-antineutrino pairs would then be sufficiently great to carry off the explosive energy of the star in a single day. The 1000-year period predicted by Chiu for X-ray emission was reduced to about one year by later workers. Chiu's proposals appear to have been first published in a Ph. D. thesis submitted at Cornell University in 1959. Scattered references to it are made by Philip Morrison3 and by Isaac Asimov1.
No neutral current, no supernova
Dennis Overbye, in his book "Lonely Hearts of the Cosmos5" records that, for supernovae, almost all the energy of the inward free fall comes out in the form of neutrinos. The success of this scenario (as proposed by Chiu) depends on a feature of the weak interaction called the neutral currents. Without this, the neutrinos do not supply enough 'oomph' and theorists had no good explanation for how stars explode. In actuality the existence of the neutral current for the weak interaction was not demonstrated until the mid 1970's.
A 1985 paper (Scientific American) by Bethe and Brown entitled "How a Supernova Explodes" showed that understanding of the important role of the neutrinos was well advanced by that time. These authors attribute this understanding to the computer simulations of W. David Arnett of the University of Chicago and Thomas Weaver and Stanford Woosley of the University of California at Santa Cruz.
The opportunity to confirm the release of the neutrinos postulated to accompany the spectacular death of a giant star came in 1987 when a supernova explosion, visible to the naked eye, occurred in the Clouds of Magellan that neighbors our Milky Way galaxy. Calculations indicated that this supernova, dubbed SN1987A, should give rise to a neutrino burst at a density of 50 billion per square centimeter when it finally reached the earth, even though expanding as a spherical 'surface' originating at a distance 170,000 light years away.
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