The Life Cycle of A Star

By Lara Stokes

Interstellar Medium

An interstellar medium is the matter that is in between stars. They are mainly made of gas and dust. About 99% of the interstellar medium is made up of interstellar gas. The gas is made up of hydrogen and helium. When light passes through the dust it is either blocked completely causing dark nebulae, or is only somewhat dimmed causing a phenomenon called extinction.
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Protostars

Protostars are the first stage in the life cycle of stars. Stars are formed in a nebula. A nebula is a a clump of gas and dust, about 97% hydrogen and 3% helium. The protostar begins as a large amount of mass. A process called accretion starts when atoms are added to the center of a protostar. The star is unstable due to various reactions occurring at the same time. If the protostar wants to successfully become a star it must reach equilibrium. Equilibrium is between gravity pulling atoms into the center, and gas pressure pushing heat and light away. This is difficult for a star to do and if it can not maintain equilibrium it will die.
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Main Sequence

The next stage of life for a star is the main sequence. It begins after a it has reached equilibrium. It begins to fuse hydrogen into helium. The process is called nuclear fusion. The star's core is contracting due to gravity trying to maintain equilibrium. As the core contracts atoms are packed even tighter. Heat trying to escape into space causes the outer shell to expand. When this happens it means that the star has reached the next stage in its life. It is now classified as a red giant.
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Red Giant

Now that the star is a red giant, it is releasing more energy than before due to the helium burning. The red giant is bigger than a star in the main sequence, but it is less stable. When the star runs out of fuel to burn helium it will contract once again to begin carbon burning. This is the last type of fusion.
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Death of the Star

What the star becomes when it dies is determined by it mass. A medium star will form a supernova. A large star will form a neutron star. A small star will form a white dwarf. A star with a very large mass will create a black hole.

Neutron Star

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Red Shift

Red shift is when the wavelengths on the emission spectrum are lengthened. It does not necessarily mean that the light looks red though. This shows that the galaxies are moving away from us support the Big Bang theory.
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Work Cited



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