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surface gases sufficient energy to
escape the gravitational attraction of
the star as stellar wind. At this point in
its lifecycle, the star is considered a T-
Tauri Star.
Conservation of Angular Momentum: An ice skater is
spinning on the tip of her skate with her arms
extended. Her angular momentum is conserved
because the net torque on her is negligibly small. In
the next image, her rate of spin increases greatly
when she pulls in her arms, decreasing her moment
of inertia. The work she does to pull in her arms
results in an increase in rotational kinetic energy
Further development of a star is
determined by its mass. Mass is
typically compared to the mass of the
Sun: 1.0 M☉ (2.0×10 kg) means 1
solar mass.
The core temperature of a protostar
with a mass greater than 0.08 M☉
(1.6× 10 kg) eventually, over 100
million years, reaches 15 million ºC,
allowing nuclear fusion to occur at its
core. At this point in its life cycle, the
star is considered a Main Sequence
Star. Nuclear fusion converts hydrogen
to helium. This reaction is exothermic;
it gives off more heat than it requires,
and so the core of a main sequence star
releases a tremendous amount of
energy as light. All of this light pushes
outward on the star, and counteracts
the gravitational force pulling it
inward.
75% of the matter in the universe is
hydrogen and 23% is helium. These
elements exist in large stable dust
clouds of cold molecular gas called
Nebulae. A star's life cycle is
determined by its mass. The larger its
mass, the shorter its life cycle. A star's
mass is determined by the amount of
matter that is available in its nebula.
The birth of a star takes place in a
nebula.
The birth of a star begins with the
collapse of a nebula. An intergalactic
collision or a nearby supernova
explosion causes pockets of matter
inside of the nebula to collapse under
their own weight. As it collapses,
gravitational forces cause the nebular
fragments to be pulled together and
spin. As the stellar material pulls
tighter and tighter together, its
temperature rises, creating outward
energy that counters further
gravitational collapse. At this point in
its lifecycle, the rotating sphere of
gaseous material is known as a
Protostar. This phase lasts about
100,000 years.
Surrounding the protostar is a circumstellar
disk of gas and dust from the collapsing
nebula. Some of this continues to spiral
inward, layering additional mass onto the
star. The rest will remain in place and
eventually form a planetary system.
As a protostar evolves and continues to
pull inward, it spins even more rapidly
due to the principle of “conservation
of angular momentum”. Rising core
pressure creates rising core and
surface temperatures, which gives