ABSTRACT
The evolution of a star from its birth to its death may be schematically described as follows. A diffused cloud of matter starts to contract due to the gravitational force acting between its constituents. If no counterforce develops to stop the contraction, the matter will continue to contract until it collapses to the centre of gravity. But with the contraction, the density and the temperature of the matter increase. The increased density and temperature create pressure which counters the gravitational force and de celerates the contraction. When the force created by the pressure gradient in the star equals the gravitational force, the contraction stops and a hy drostatic equilibrium forms. The density and the temperature gradients create the pressure gradient. Thus during most of stellar life the pressure, density, and temperature are highest at the stellar centre.
