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Understanding how that shock wave can reach the mantle in the face of continuing infall onto the shock that became the theoretical difficulty. White dwarfs were proposed as possible progenitors of certain supernovae in the late 1960's, The papers of Hoyle (1946) and Hoyle (1954) and of B2FH (1957) were written by those scientists before the advent of the age of computers.
Dozens of research papers have been published in the attempt to describe the hydrodynamics of how that small one percent of the in falling energy is transmitted to the overlying mantle in the face of continuous infall onto the core.
That uncertainty remains in the full description of core-collapse supernovae.
Because the outer envelope is no longer sufficiently supported by the radiation pressure, the star's gravity pulls its mantle rapidly inward.
As the star collapses, this mantle collides violently with the growing incompressible stellar core, which has a density almost as great as an atomic nucleus, producing a shockwave that rebounds outward through the unfused material of the outer shell.
The resulting runaway nucleosynthesis completely destroys the star and ejects its mass into space.
The second, and about threefold more common, scenario occurs when a massive star (12–35 times more massive than the sun), usually a supergiant at the critical time, reaches nickel-56 in its core nuclear fusion (or burning) processes.
In 1954, the theory of nucleosynthesis of heavy elements in massive stars was refined and combined with more understanding of supernovae to calculate the abundances of the elements from carbon to nickel.
C nucleus that enables the triple-alpha process to burn resonantly to carbon and oxygen; the thermonuclear sequels of carbon-burning synthesizing Ne, Mg and Na; and oxygen-burning synthesizing Si, Al and S.
After a star completes the oxygen burning process, its core is composed primarily of silicon and sulfur.
The nuclear process of silicon burning differs from earlier fusion stages of nucleosynthesis in that it entails a balance between alpha-particle captures and their inverse photo ejection which establishes abundances of all alpha-particle elements in the following sequence in which each alpha particle capture shown is opposed by its inverse reaction, namely, photo ejection of an alpha particle by the abundant thermal photons: Ti and those more massive in the final five reactions listed are all radioactive, but they decay after their ejection in supernova explosions into abundant isotopes of Ca, Ti, Cr, Fe and Ni.