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Fusion of nuclei inside stars switches from exothermic to endothermic for Iron and elements heavier than Iron. Supernovas not only achieve fusion of transuranides (albeit in trace relative quantities), but they also release a huge excess of energy that is comparable to the fusion energy generated during its whole lifetime

How well do we understand the mechanism that causes this huge mass-energy conversion?

Also, considering that fission releases 0.1% at most of rest mass, and fusion releases 1% at most, what is the fraction of mass-energy that is converted by the underlying mechanism in supernovas?

diffeomorphism
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1 Answers1

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The energy released in (mainly) neutrinos, along with light and the kinetic energy of the exploding envelope is around $10^{46}$ J. This is equivalent to 0.05 solar masses being converted into energy. This is less than a percent of the progenitor mass.

The energy source is gravitational potential energy. At the heart of a supernova, there was an Earth-sized ball of iron, of about 1.2 solar masses, that collapses to a radius of 10 km. This releases a few $10^{46}$ J, which is sufficient to power the supernova, dissociate the iron into its nucleons, endothermically make neutrons out of the protons, and have a tiny bit left over to make the traces of r-process elements you mention.

Most of the energy "lost" in a supernova is transferred to neutrinos during (well understood) beta decays and inverse beta decays taking place as the core collapses and then in the first few seconds after an extremely hot proto-neutron star is formed.

ProfRob
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