Question

What reaction occurs within a star in stellar equilibrium?

Answer 1

Equilibrium basically refers to a stable state more precisely there is no forward or backward action taking place at such a stage. A star has basically a huge mass and hence there is gravitational force which ties to collapse the star. At the same time the reaction source inside the star generates thermal energy resulting in an outward pressure. Hence from the above information the stellar equilibrium of a star is accordingly defined.

Complete step by step answer:
Stars are very much massive. Due to the gravitational force of the star there is a central pressure directing inwards such that it tries to collapse the star. As the average radius of the star decreases, the pressure inside the star keeps on increasing resulting in the temperature of the star to increase. A star normally stays in equilibrium until the supply of hydrogen in the core is depleted. Even after the radius decreases, the increase in the temperature is so much that the protons of the atoms overcome the distance of the closest approach and come together and fuse initiating the fusion reaction at stellar equilibrium. The fusion reaction from which all it begins is the reaction where two protons (hydrogen-1) fuse together, producing deuterium (hydrogen-2) and positron plus the heat energy. Mathematically this is given by,
$_{1}^{1}H+_{1}^{1}H\to _{1}^{2}H+{{e}^{+}}+v+0.42MeV$
Therefore in stellar equilibrium the fusion reaction occurs in stars.

Note: It is to be noted that classically, the distance of minimum approach of 2 protons due to the repulsion is approximately equal to 1/billion of a cm. But quantum mechanically this barrier is overcome due to increase in the temperature. If the order of the temperature is ten to the power of seven and above, the distance of minimum approach keeps on decreasing and at a point the protons fuse together.