Question

The source of stellar energy is _____________ .
A) nuclear fission
B) nuclear fusion
C) nuclear fission and fusion
D) nuclear decay

Answer 1

Hint:Stellar energy refers to the energy radiated by a star. This energy is obtained from an internal source of the star. The internal source corresponds to the energy produced when two lighter nuclei combine to form a heavier nucleus. This process is referred to as a fusion reaction.

Complete step by step answer.
Step 1: Describe a fusion reaction to get a better understanding of what happens in the interior of a star.

The process of fusion involves two lighter nuclei fusing to form a heavier nucleus with the release of some energy. The heavier nucleus will be more tightly bound.

In the beginning, it is the thermonuclear fusion that produces energy. The fusion is attained by raising the temperature of the star so that the lighter nuclei involved in the reaction have sufficient kinetic energy to overcome their Coulomb repulsive behaviour to fuse to form the heavier nuclei.

Sun is a star whose fusion reaction involves the burning of hydrogen into helium. The nuclear fuel of the Sun is thus its hydrogen core. The fusion reaction of the Sun is called the proton-proton cycle as it repeats itself when a cycle is complete.

In fission, a heavier nucleus splits into lighter nuclei while in radioactive decay, an unstable nucleus decays over time with the release of energy.

So the correct option is B.

Additional information:Once the burning of hydrogen in the Sun stops, its outer envelope will expand and turn it into a red giant. It is estimated that there is enough hydrogen in the Sun for another 5 billion years.

Note:Helium is not the only element that can be formed in the interior of a star. As the hydrogen core changes to helium, the core will start to cool causing the star to collapse under its own gravity. This again increases the temperature and fusion will again take place but now, two helium nuclei will combine to form a carbon nucleus. It is termed as the carbon-nitrogen cycle. More massive elements get generated through this fusion.