Life Cycle Of Stars

The Birth of a Star

A star is a massive, luminous ball of plasma that is held together by gravity. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth. Other stars are visible in the night sky, when they are not outshone by the Sun. Historically, the most prominent stars on the celestial sphere were grouped together into constellations, and the brightest stars gained proper names. Extensive catalogues of stars have been assembled by astronomers, which provide standardized star designations. In space, there exists huge clouds of gas and dust. These clouds consist of hydrogen and helium, and are the birthplaces of new stars. Gravity causes these clouds to shrink and become warmer. The body starts to collapse under its own gravity, and the temperature inside rises. After the temperature reaches several thousand degrees, the hydrogen molecules are ionized (electrons are stripped from them), and they become single protons. The contraction of the gas and the rise in temperature continue until the temperature of the star reaches about 10,000,000 degrees Celsius (18,000,000 degrees Fahrenheit). At this point, nuclear fusion occurs in a process called proton-proton reaction. Briefly, proton-proton reaction is when four protons join together and two are converted into neutrons; an 4He nucleus is formed. During this process, some matter is lost and converted to energy as dictated by Einstein's equation. At this point, the star stops collapsing because the outward force of heat balances the gravity.( Clark, 356)

A star is born in a huge cloud of gas and dust known as a nebula (plural: nebulae). This nebula is about 21 light-years (125 trillion miles) across. Part of the nebula begins to shrink under the pull of its own gravity. This forms a protostar which is about 60 million miles across. The star begins to take shape. The temperature continues to rise and nuclear fusion begins to take place. The pressure from inside the star finally equalizes the gravity pushing in, and the star stops contracting.

The Hydrogen Burning Stage

The proton-proton reaction occurs during a period called the hydrogen-burning state, and its length depends on the star's weight. In heavy stars, the great amount of weight puts a large amount of pressure on the core, raising the temperature and speeding up the fusion process. These heavy stars are very bright, but only live for a short amount of time. After the energy from this deuteron-hydrogen fusion process ends, the star begins to contract again, and the temperature and pressure subsequently increase. Nuclear fusion occurs between the hydrogen and lithium & other light metals in the star, but this process soon ends. Contraction starts again, and the extreme high temperature and pressure cause the hydrogen to transform into helium through the carbon-nitrogen-oxygen cycle. When all the hydrogen has been used up, the star is at its largest size, and it is called a red giant. Different things can happen to the star now.

In order for stars to go through the ...