290 The Poetry of Physics and The Physics of Poetry
Brahe and Kepler, respectively. It was the appearance of the second
supernovae, which helped confirm the Copernican hypothesis that the
heavens are not immutable but also subject to change.
The exact nature of a supernovae explosion is the subject of some
theoretical speculation since the observation of these events is so rare.
The following scenario describing a supernova is believed to provide a
fairly accurate portrayal of the most powerful stellar events known in
today’s universe. The energy released by a supernova is 10^43 Joules
rivaled only by exploding galaxies and quasars. When a supernova blows
it becomes brighter than the entire galaxy that contains it. If the carbon
core of a red giant is massive enough the contraction of the core will
produce temperatures in excess of 600 million degrees. If the star is not
massive enough these temperatures will not be reached and the core
evolves into a white dwarf star. When the core temperature of a massive
star reaches 600 million degrees, the carbon will begin to fuse to form
higher mass elements such as silicon. Once the carbon fuel is exhausted
the core will contract once again reaching still higher temperatures at
which point the silicon begins to undergo fusion producing still heavier
elements, which, in turn, will contract and ignite once the silicon fuel is
exhausted. This process of ignition, and fuel exhaustion, and contraction
continues rapidly until the core has been completely transmuted to iron
and then it stops.
Elements lighter than iron release energy when they undergo
thermonuclear reaction. Iron is different. It absorbs energy when it
reacts. The production of elements more massive than iron, therefore,
ceases. This explains why the abundancy in the universe of elements
heavier than iron are so small. With the cessation of nuclear fusion the
iron core continues to shrink to the point where there is literally no space
between the nuclei. The core has a radius of 10 to 50 kilometers at this
point. The density and temperature of the iron core becomes so great that
small amounts of heavier elements are produced. The contraction of the
core that results is so rapid that a violent explosion ensues in which half
the material of the star is ejected violently into the interstellar medium of
the galaxy. This material mixes with the gas and dust clouds from which
other stars such as our Sun are formed. This explains the presence of
the heavier elements found in the Sun and on the Earth. The very
material, which you, my reader, and I are composed, was produced in a
supernovae explosion by a massive dying star.