Chapter 33, Problem 11RQ

To determine

The cause of expansion of star outwards.

Answer to Problem 11RQ

When the helium fusion is intensified due to gravity, the outer layer of the star expands outwards.

Explanation of Solution

The temperature rises as the burned-out hydrogen core contracts because of gravity. At, a certain point, the temperature becomes high in the core to launch the fusion of helium to carbon, which is also called helium burning.

Helium fuses to carbon at the star’s centre while hydrogen fuses to helium in surrounding shell. The energy is the output source, which makes the star grow larger.

With the intensified helium fusion within a star, the outward force of thermal pressure causes the expansion of the star outwards.

Conclusion:

Therefore, when the helium fusion is intensified due to gravity, the outer layer of the star expands outwards.