Stellar Evolution in Astronomy

A star, like humans, is born and goes through many changes throughout its lifetime. These changes are known as stellar evolution in astronomy. The evolution of these changes will be the focus of this report.

Birth

"In the beginning God created the heavens and the earth. Now the earth was formless and empty, darkness was over the surface of the deep, and the spirit of God was hovering over the waters" (Genesis 1:1 New International Version). This formless and empty darkness is known today as a giant molecular cloud (GMC) or a stellar nursery. As GMC's rotate around the galaxy many phenomena may trigger its collapse. "A collapsing GMC fragments as it collapses, breaking into smaller and smaller chunks. In these fragments, the gas is heated as it collapses due to the release of gravitational potential energy, and the cloud becomes a protostar as it forms into a spherical rotating object" (2007). This rotating object, if it is the right solar mass and chemical composition, will begin to create a nuclear fusion reaction which "leads over a relatively short time to a hydrostatic equilibrium in which energy released by the core prevents further gravitational collapse. The star thus evolves rapidly to a stable state" (2007). Of course, rapidly is a relative term; therefore, rapidly to humans and rapidly to the Universe may be two different things.

Maturity

The nuclear fusion reaction of the sun will eventually run out of hydrogen as its nuclear fuel, because hydrogen is constantly being fused into helium. The helium build-up will cause an increase in the rate of fusion which will have the effect of increasing the core temperature. Once hydrogen is exhausted in the core, the core has two different paths it can follow. The core can contract until electron degeneracy prevents further collapse or the core may become hot enough, around 100 megakelvins, to cause helium fusion. In the case of our sun, it is expected that "in 4-5 billion years, it will enter a red giant phase, its outer layers expanding as the hydrogen fuel in the core is consumed and the core contracts and heats up. Helium fusion will begin when the core temperature reaches around 100 MK, and will produce carbon and oxygen." (2007)

Death

Once the sun becomes a red giant it will come into a phase where it will throw

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