270
See also: Marie Curie 190–95 ■ Albert Einstein 214–21 ■
Ernest Rutherford 206–13 ■ Georges Lemaître 242–45 ■ Fritz Zwicky 250–51T
he idea that stars generate
energy through the process
of nuclear fusion was first
proposed by British astronomer
Arthur Eddington in 1920. Stars,
he argued, were factories for fusing
nuclei of hydrogen into helium.
A helium nucleus contains slightly
less mass than the four hydrogen
nuclei required to create it. This
mass is converted into energy in
accordance with the equation
E = mc^2. Eddington developed a
model of star structure in terms of
the balance between the inward
pull of gravity and the outward
pressure of escaping radiation, but
he did not figure out the physics of
the nuclear reactions involved.Making heavier elements
In 1939, German-born US physicist
Hans Bethe published a detailed
analysis of the different pathways
that hydrogen fusion might take.
He identified two routes—a slow,
low-temperature chain that
dominates in stars like our Sun, and
a rapid, high-temperature cycle that
dominates in more massive stars.Between 1946 and 1957, British
astronomer Fred Hoyle and others
developed Bethe’s ideas to show
how further fusion reactions
involving helium could generate
carbon and heavier elements up
to and including the mass of iron.
This explained the origin of many
of the universe’s heavier elements.
We now know that elements
heavier than iron form in supernova
explosions—the death throes
of massive stars. The elements
needed for life are made in stars. ■WE ARE MADE
OF STARDUST
FRED HOYLE (1915–2001)
IN CONTEXT
BRANCH
AstrophysicsBEFORE
1854 German physicist
Hermann von Helmholtz
suggests that the Sun
generates heat through slow
gravitational contraction.1863 English astronomer
William Huggins’ spectrum
analysis of stars shows they
share elements found on Earth.1905–10 Astronomers in the
US and Sweden analyze stars’
luminosity and group them
into dwarfs and giants.1920 Arthur Eddington argues
that stars turn hydrogen into
helium through nuclear fusion.1934 Fritz Zwicky coins the
term “supernova” for a massive
star’s explosive end.AFTER
2013 Deep-sea fossils reveal
what may be biological traces
of iron from a supernova.Space isn’t remote at all.
It’s only an hour’s drive
away if your car could go
straight upwards.
Fred Hoyle