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Stars and the Universe

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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