Chapter 13, Problem 18A

To determine

The two competing factors determine the size of the star

Explanation of Solution

Introduction:

Star’s life begins with the contraction of nebula gas and dust. Due to increase in the density of the nebula gas and dust,gravity increases. Under this high gravity, gases material and dust collapse which results into the heating the material. This heated cloud inside the core creates the star.

High heat produced at the core of the star is responsible for the nuclear fusion reaction. Due to high temperature, helium atoms get formed by fusion of the hydrogen atoms. Nuclear fusion reaction is responsible for the supply of heat and energy from the star.Due to formation of helium from fusion of hydrogen, large amount of energy is generated in the deep interior. From the central core part, this overflow energy creates a pressure which pushes star outward.This outward push of the energy is balanced by the gravitational force of the star. Gravitational force of the earth pushes it inward while energy generated due to the fusion reaction pushes it outward. The balance of these two forces forms a stable star.

Conclusion:

Therefore, the energy from nuclear fusion pushes the star outward, whereas gravitational force of star pulls it inward. These two competing effects determine the size of the star.