The Life of a Sun-like Star.
The star forms from a collapsing cloud of gas and dust. As the gas and
dust get compressed by gravity, the temperature in the core rises. This
eventually leads to the start of nuclear fusion in the core which creates
an outward pressure to balance the inward pressure of gravity. At this
point the star is on the Main Sequence and is relatively stable continuing
to fusion hydrogen to helium in the core. For a sun-like star this stage
continues for about 10 billion years. When the star has exhausted most of
its hydrogen fuel, it moves off of the main sequence, begins to swell and
becomes red. Eventually turning into a Red Giant. It quickly blows away
it's atmosphere which becomes a planetary nebula. The nebula then fades
and the small compact core is left. This core is very hot and is called a
white dwarf. It has no energy source to maintain it's high temperature and
thus will eventually fade to a brown dwarf.
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