The Life of a Star

The Life of a Star

One night while little Jimmy was out camping with his father, he asked his father how a star is made? And his father said there are high-mass stars, intermediate-mass stars, and low-mass stars. The life cycles of stars follow three general patterns each associated with a range of initial mass. Much like human beings stars have a life cycle, they go threw birth, evolution, and death. And little Jimmy said how is that possible?

First the star must be born. Many astronomers believe that a star is formed when large compression waves traveling through gas clouds create dense knots of gas is the cloud. The gravity of these knots then pules the other gas molecules. As the knot grows larger and larger the gravity starts attracting more and more gas molecules. Eventually, the knot coalesces into a growing sphere of compressed gas that reaches internal temperatures of a few million degrees Celsius. At this point the gases in the knot’s interior become so hot that their atomic nuclei begin fusing, creating large amounts of nuclear energy and forming a new star. Pressure from the radiation of new stars in turn causes more, higher-density zones to form in the gas cloud, which initiates the birth of more stars.

Next the evolution and main sequence of a star, as it’s going through puberty. In its earliest stage, a typical star is large and emits infrared light. Within a million years, the gravitational attraction of the star’s material for itself causes the star to shrink to the present size of the sun. The added pressure caused by this collapse in size raises the star’s internal temperature high enough to trigger nuclear reactions in the core. The main sequence stars fall along the diagonal line that goes from the upper left to the lower right on the H-R diagram. During its main-sequence phase, a star gradually exhausts its hydrogen supply.

The next stage of a star’s evolution involves dramatic stages of expansion and contraction the star approaches the end of its life cycle. After the star has used all of its hydrogen in the core, the core begins to shrink, converting hydrogen into helium in ever-larger shells around the inner core. The star’s core shrinks because the outward pressure of heat generated by the nuclear reactions no longer balances the inward gravitational attraction of the stars mass for itself.