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Issue 6.07

The Astrophysics Spectator

June 3, 2009

The nuclear reactions that turn a white dwarf (degenerate dwarf) into a thermonuclear supernova convert much of the white dwarf's carbon and oxygen into nickel in less than a second.  These reactions occur at extremely high temperatures—several billion degrees Kelvin, which is a couple of hundred time hotter that the center of the Sun.  With this issue of the web site, a page is added that describes these thermonuclear reactions.

Thermonuclear supernovae, along with core collapse supernovae and red giants, produce the elements with masses between carbon and iron.  Through the continual injection of supernovae and red giant debris into space, the interstellar medium evolves from almost pure hydrogen and helium created in the big bang to a mixture of hydrogen, helium, and elements heavier than helium.  Some of these elements, such as silicon, sulfur, and argon, are more common in the interstellar medium than others—phosphorus, potassium, and chlorine, for example.  This uneven chemical composition is a telltale of how carbon and oxygen are converted into nickel during thermonuclear fusion.  Because our Earth and the other terrestrial planets precipitated from the heavier elements in the interstellar medium, the chemistry of our world depends directly on the details of thermonuclear fusion in supernovae.

Jim Brainerd

Supernovae

Nuclear Reactions in Thermonuclear Supernovae.  Carbon and oxygen are converted into nickel in a white dwarf through a complex network of reactions.  The incremental changes tend to follow the series of atomic nuclei that are multiples in composition of the helium nucleus.  For this reason, large amounts of neon-20, magnesium-24, silicon-28, and other elements with equal and even numbers of protons and neutrons are created.  But the reactions also tear down nuclei, creating many free protons, neutrons, and helium nuclei that combine with other atomic nuclei to produce elements and isotopes that do not have equal numbers of protons and neutrons or do not have an even number of protons or of neutrons.  Because thermonuclear fusion disrupts a white dwarf, the thermonuclear reactions in a white dwarf  contribute to the rich variety of chemical elements and isotopes we find throughout the universe.  (continue)

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