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STARS ARE FACTORIES
FOR THE CHEMICAL
ELEMENTS
NUCLEOSYNTHESIS
IN CONTEXT
KEY ASTRONOMER
Fred Hoyle (1915 –2001)BEFORE
1928 George Gamow
constructs a formula based
on quantum theory that can
be used to determine how
various atomic nuclei join.1929 Welsh astronomer
Robert Atkinson and Dutch
physicist Fritz Houtermans
figure out how, at the
temperatures inside stars,
nuclei of light elements could
join up, while at the same
time releasing energy.AFTER
1979 Scientists discover that
almost all nuclei of the light
elements lithium, beryllium,
and boron in the universe are
made by the impact of cosmic
rays (highly energetic particles)
on other nuclei in space, and
not in stars.U
ntil the late 1940s, it was
not known where the atoms
of most chemical elements
in the universe—for example,
carbon, oxygen, and iron—had
come from, nor how they had been
made. It had been established in
the 1920s that the two lightest
elements, hydrogen and helium,
made up most of the universe’s
matter, and in 1948, George Gamow
and Ralph Alpher showed how all
of the hydrogen, most of the helium,
and tiny amounts of lithium could
have been made in the “Big Bang.”
However, the origin of other
elements was a mystery.Building to iron
The discovery of their origin was
made largely thanks to the work
of British astronomer Fred Hoyle.
Starting from chance conversations
with leading astronomers in the
US during an academic tour in
1944, he developed an idea that
most chemical elements might be
created step-by-step by nuclear
reactions in stars—a process called
nucleosynthesis. Hans Bethe
had already shown in 1939 that
hydrogen could combine to make
helium in star cores, but Bethe
offered no suggestions for howExtreme conditions for
other elements occur when
giant stars disintegrate in
supernova explosions.All but a few elements
can be created in stars by
eight distinct processes.Suitable conditions
for the creation of many
elements occur in the
evolution of giant stars.Stars are factories
for the chemical
elements.Heavier elements require
high temperatures
to be created.