INSpiREzine Stars! | Page 15

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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