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Stars - Life Cycle - Birth.
Stars are made from a large cloud of
dust and gas called a nebula.
A nebula contains mainly
hydrogen
with smaller amounts of helium
and dust.
If the
mass of
hydrogen is large enough, the large amount
of gravity will start to
pull the hydrogen in on
itself.
The cloud of gas will start to contract and
form a ball.
The ball of hydrogen is called a protostar.
As the
protostar continues to contract under its own gravity,
the hydrogen atoms accelerate (see Newton's Second Law)
and their kinetic
energy increases (they get faster).
The extra kinetic energy raises the
temperature of the hydrogen
and the atoms collide with each other more
frequently.
This
process continues until the hydrogen
atoms are moving
so fast
that they
overcome the force of
repulsion between them
and undergo a nuclear reaction
called fusion
when they collide.
Fusion turns hydrogen into helium
and releases a huge amount of energy
as heat
and light.
At this stage the protostar
bursts into flame and a star is
born.
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