Who Discovered the Hoyle Level?

Abstract

The prediction of Hoyle that the nucleus of 12 C must have a resonance at 7.62MeV was the trigger to the Anthropic Principle. We review the history of the discovery of this level and investigate to what extent this was a genuine prediction.Keywords: anthropic principle -nuclear physics -stellar evolution. Who Is WhoThree dominant personalities were involved in the present story: Sir Fred Hoyle FRS , who was one of the greatest astrophysicists in the second half of the twentieth century with major contributions to Stellar structure (nuclear astrophysics -synthesis of the elements) and to Cosmology -(Steady state theory dubbed the name Big Bang) as well as planetary formation. William A. Fowler (1911-1995, who can be considered as the father of nuclear astrophysics and Edwin Salpeter top theoretical astrophysicist, who has numerous seminal contributions in many astrophysical fields as well as in physics. Fred HoyleWilly Fowler Ed Salpeter Edwin E What Is the Hoyle LevelThe synthesis of helium into carbon in stars proceeds via resonant reaction, namely the three α particles fuse into an excited energy level in the 12 C nucleus. The rate of the reaction was calculated before the existence of this level was known and was found to be very low compared to the rate of destruction of 12 C by collisions with α particles. As a consequence, it was impossible to predict the evolution off the main sequence towards the Red-Giant branch and the calculation implied that all the 12 C is converted into 16 O. But stars do evolve and we know that somehow carbon is synthesized. In view of the impass, Hoyle predicted therefore, that 12 C has an energy level just at the right place and the reaction of carbon synthesis proceeds via this resonance level. The level was then discovered in the laboratory. This chain of events: prediction the existence of a nuclear level from astrophysical constraints, wa s considered as a big victory for astrophysics and the level was named the Hoyle level.