4.1.2. Formation of a Star from Protostar

The protostar is a highly dense gaseous mass, which continues to contract further due to tremendous gravitational force. As the protostar begins to contract further, the hydrogen atoms present in gas cloud collide with one another more frequently. These collisions of hydrogen atoms raise the temperature of protostar more and more. The process of contraction of protostar continues for about a million years during which the inner temperature in the protostar increases from a mere, -173°C in the beginning to about 107°C. At this extremely high temperature, nuclear fusion reactions of hydrogen start taking place. In this process, four small hydrogen nuclei fuse to produce a bigger helium nucleus and a tremendous amount of energy is produced in the form of heat and light. The energy produced during the fusion of hydrogen to form helium makes the protostar glow and it becomes a star. This star shines steadily for a very, very long time.