- Stars form from interstellar gas clouds.
- Once a star has formed, nuclear reactions in its core supply it with energy.
- For most of a star’s life, its energy is supplied by the fusion of hydrogen atoms into helium atoms.
- When a star uses up the hydrogen in its core, the core shrinks and the outer layers of the star expand and cool. This makes the star turn into a red giant.
- Eventually a star consumes all its available fuel and collapses.
- Stars much more massive than the Sun end their lives by exploding.
- Stars like the Sun may lose material from their outer layers; their core then becomes a white dwarf.
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