The main source of energy for a star as it grows in size to become a red giant is
A)hydrogen fusion in the central core.
B)helium fusion in the central core.
C)hydrogen fusion in a shell surrounding the central core.
D)gravitational contraction.

Question

Quizplus · Accepted Answer

As a star grows in size and its core temperature decreases, hydrogen fusion in the core slows down. However, the outer layers continue to contract, increasing the pressure and temperature of the surrounding layer of hydrogen. Eventually, this leads to hydrogen fusion in a shell surrounding the central core, providing the star with the energy it needs to continue expanding into a red giant.

The Main Source of Energy for a Star as It