¤Stages in the Life Cycle of a Star¤

¤Stages in the Life
Cycle of a Star¤

1. Nebula Stars are born from
... clouds of dust and
gas in space. These
clouds, called nebula,
coalesce as a result of
of the gravitational pull of the particles
themselves as well as
nova shock waves,
passing stars or
galaxies.

2. Protostar The newly formed
protostar continues
to grow, devouring
the material of the
nebulae. When the
protostar contracts, it begins to develop its
own "wind". This
blows away the
remaining dust and
gas that envelop the
protostar beyond its gravity. As the star
material takes shape,
some dust and gas
has not been blown
away. It remains
trapped in the protostars gravity
and forms an
accretion disk. Matter
within the disk can
clump together to
form planets if there is sufficient material
left in the disk.

3. The Main Sequence Depending on the
mass of the protostar,
at some point nuclear
fusion begins at the
core of the star
where hydrogen is turned into helium
causing a release of
vast amounts of
energy.

4. Life Span Throughout the main
sequence, the star
very slowly contracts
to compensate for the
loss of energy as heat
and light. With contraction, the core
becomes more dense
and the pressure at
the core rises. At the
same time, the
temperature of the core rises because of
the gravitational
crush of the denser
makeup of the
contracting star.

5. Giant Once a star begins to
use up the hydrogen
at its core, the core
collapses creating
more heat. If it gets
hot enough, nuclear fusion ignites the
hydrogen in the
outer shell. This
creates increased
outward gas
pressure and causes the shell to expand
rapidly and cool.

6. Old Age A low mass star may
survive for billions of
years, but the
hydrogen and helium
gets used up before it
gets hot enough to fuse carbon. When
that happens, the star
blows away its outer
layers and creates
what is called a
planetary nebulae, which provides
material for more
protostars.

7. Types of Stars in the
Cycle Protostars are stars
that have not lit up
yet. They sit at the
center of a cloud of
dust and gas
collecting enough stuff to start a
nuclear reaction. The
smallest mass possible
for a star is about 8
percent that of our
own Sun.