a supernova produces elements heavier than iron through nucleosynthesis.
how does a supernova produce elements heavier than iron?
nucleosynthesis
the internal heating within stars is so great that (after an initial phase of gravitational contraction) they ignite and sustain thermonuclear reaction of hydrogen (with itself) to form helium, and can make heavier elements (see stellar nucleosynthesis). the sun for example has a core temperature of 13,600,000 k. the more massive and older the stars are, the more internal heating they have. during the end of its lifecycle, the internal heating of a star increases dramatically, caused by the change of composition of the core as successive fuels for fusion are consumed, and the resulting contraction (accompanied by faster consumption of the remaining fuel). depending upon the mass of the star, the core may become hot enough to fuse helium (forming carbon and oxygen and traces of heavier elements), and for sufficiently massive stars even large quantities of heavier elements. fusion to produce elements heavier than iron and nickel no longer produces energy, and since stellar cores massive enough to attain the temperatures required to produce these elements are too massive to form stable white dwarf stars, a core collapse supernova results, producing a neutron star or a black hole, depending upon the mass. heat generated by the collapse is trapped within a neutron star and only escapes slowly, due to the small surface area; heat cannot be conducted out of a black hole at all (however, see hawking radiation).
internal heating
supernovae are a major source of elements in the interstellar medium from oxygen through to rubidium, though the theoretical abundances of the elements produced or seen in the spectra varies significantly depending on the various supernova types. type ia supernovae produce mainly silicon and iron-peak elements, metals such as nickel and iron. core collapse supernovae eject much smaller quantities of the iron-peak elements than type ia supernovae, but larger masses of light alpha elements such as oxygen and neon, and elements heavier than zinc. the bulk of the material ejected by type ii supernovae is hydrogen and helium. the heavy elements are produced by: nuclear fusion for nuclei up to s; silicon photodisintegration rearrangement and quasiequilibrium during silicon burning for nuclei between ar and ni; and rapid capture of neutrons (r-process) during the supernova's collapse for elements heavier than iron. the r-process produces highly unstable nuclei that are rich in neutrons and that rapidly beta decay into more stable forms. in supernovae, r-process reactions are responsible for about half of all the isotopes of elements beyond iron, although neutron star mergers may be the main astrophysical source for many of these elements.
supernova