A Star is Born: Stages in the Stellar Cycle (Essay Sample)

A Star is Born: Stages in the Stellar Cycle David Moadel December 19, 2011 A Star is Born: Stages in the Stellar Cycle  Astronomy is often thought of as a source of fascination for scientists and other sky-gazing intellectuals. However, the heavenly bodies in our skies should not only interest the privileged few. Consider, for example, the life cycle of a star. Stars, like living organisms, experience an inevitable sequence of stages. Throughout the phases of nebula, collapse, proto-star, and main sequence star, the stellar cycle can hold great interest for even the most casual observer. Any star, large or small, begins as a nebula, or a cloud of dust composed primarily of hydrogen and helium (ASPIRE Lab, 2010b). The nebula may be thought of as the nursery out of which a star emerges. Through a natural process known to scientists as accretion, the nebula gathers mass into clumps, and as the clumps get bigger, the nebula's gravitational pull increases. This, in turn, causes more mass to be pulled into the nebula. Over time, the star forms when enough matter clumps together to reach a critical mass of approximately 80 times the size of Jupiter (Stellar Birth, 2006). At this point, the internal pressure of the mass rises to an extraordinary degree -- high enough, in fact, to ignite nuclear fusion. As intense as this may seem, it is merely the beginning. The next phase of a star's life cycle is the collapse of the nebula. With its incredibly high temperatures, the hydrogen atoms in the newly formed star begin to fuse together (The Birth of a Star, n.d.). This proves to be a good news-bad news situation. The good news is that light and heat, giving rise to the star's "shine," are emitted. The bad news is that the star's mass becomes greater than it can bear, and it collapses. Can this poor star recover from its near-death experience? To discover the answer, we must explore the next phase: the proto-star. Perhaps the most exciting phase of the stellar cycle, the proto-star phase entails the rebirth and rebuilding of the star. In this phase, clumps of gas and dust group together in the nebula, and by this stage, the gas is sufficiently dense that it does not lose heat (Stellar Birth, 2006). This process typically requires hundreds of thousands of years, and eventually we end up with a giant clump of matter called a proto-star. Thus, the center of the former nebula shrinks as it heats up, essentially creating a new star (The Star Cycle, n.d.). To borrow a Hollywood cliché, star is born -- or, more accurately, reborn. At this point, the star enters into the phase known as the main sequence, where it lives out the majority of its life (ASPIRE Lab, 2010a). This stage of the stellar cycle is comparable to adulthood in humans. As you may have surmised, our sun is a main sequence star. This type of star shines light into space for billions of years, losing energy in the process. In addition, a main sequence star gradually contracts, or pulls inward, due to the strong gravitational force at its core. Sadly, all good things must come to an end. Stars do not last forever, as their fuel will be used up sooner or later (Star Death, n.d.). Most stars, including our own sun, will convert their hydrogen to helium over many years through nuc...