Answer the following question.

Why do stars evolve?

We know that stars are continuously emitting energy and hence there is a decrease in energy. There are two forces acting on the star:

(i) Gravitational Force acting inward

(ii) Pressure of Hot gas outside

For maintaining balance gas pressure and gravitational force, temperature should remain constant.

Energy is generated by burning of fuel at centre of star to maintain a constant temperature. The reason of evolution of star is the burning of fuels and hence the decrease in the amount of fuel.

Evolution is the change in properties of star with time that occur due to burning of fuel to balance the forces of gas and pressure.