The Life Cycle of a Star

Belle Seabury

Introduction

The life cycle of a star is a lot like that of a human. They both have four stages, and at the end of their lives, they die.
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Stage One: Protostar

The star begins to form from a nebula, made up of hydrogen and helium. Inside of a nebula, gravity causes dust and gas to clump together, forming protostars. Protostars must maintain equilibrium in order to survive. Equilibrium is a balance between gas pressure and gravity. A star dies if it loses its equilibrium.

Stage Two: Main Sequence

The longest stage in a star's life cycle is its main sequence. During this stage, the star is achieving nuclear fusion. This means that the star is creating energy by combining two atoms of hydrogen together to make one atom of helium. The star giving off energy causes the temperature in the center to slowly rise.

Stage Three: Red Giant

While a star is a red giant, the helium in the core of the star is still very hot. The star has turned a bright red and the outer core expands so the heat in the core doesn't escape. The star is bigger but less stable because fusion is releasing more energy during helium burning. The core will eventually run out of helium. For the core to keep equilibrium, it will have to start carbon burning.

Stage Four: Death

A star dies when it can no longer maintain equilibrium. Stars with a smaller mass become white dwarfs the size of earth. In this case, the star's outer layer becomes planetary nebula. Stars with a larger mass make an explosion called a supernova, creating a neutron star. Finally, massive stars leave space and form a black hole. A black hole is a place in space where nothing can escape because the gravity pulls so much.

What does a star's light tell us?

Astronomers can figure out many things by observing the light stars give out. They can tell the distance the star is away from earth, temperature, mass, what the star is made up of, and the star's size.

Where do the elements come from?

Hydrogen, helium, and lithium were formed during the big bang. Afterwards, other elements were created by nuclear fusion in stars. They were then emitted into the interstellar medium by supernovas.

Works Cited

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