Lives of the Stars
The birth, life and death of stars are complex processes, but we now
have a good idea of what happens throughout the life of a star. Stars
are born out of vast clouds of cold dust and gas. A large enough cloud
will contract under its own weight, shrinking and heating until it
starts to shine as a protostar. As the core reaches 10 million degrees
C, nuclear reactions begin and the outpouring of energy halts the
contraction.
Hydrogen is the nuclear fuel that powers most stars, and for most of
their lives stars steadily convert hydrogen to helium just as the Sun
is doing today. When the hydrogen runs out, the star swells to become
a gaint, and more complex energy-producing reactions continue in the
core.
What happens the depends on the mass of the star. A heavier star
eventually explodes as a supernova, producing a glowing mass of debris
(a supernova remnant) with a rapidly spinning pulsar at its centre. A
less massive star, like the Sun, puffs off its outer layers and ends
its life as a compact, burned-out hot cinder known as a white
dwarf.
The Pleiades, a cluster of young stars still partly shrouded in
the dust and gas out of which they were born.
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