Question

What happens when a star exhausts its core hydrogen supply?

• A. Its core contracts, but its outer layers expand and the star becomes bigger and brighter.
• B. It contracts, becoming smaller and dimmer.
• C. It contracts, becoming hotter and brighter.
• D. It expands, becoming bigger but dimmer.

Answer 1

Answer: (A)

Its core contracts, but its outer layers expand and the star becomes bigger and brighter.

Nuclear fusion powers a star for most of its life. Initially the energy is generated by the fusion of hydrogen atoms at the core of the main-sequence star. Later, as the preponderance of atoms at the core becomes helium, stars like the Sun begin to fuse hydrogen along a spherical shell surrounding the core. This process causes the star to gradually grow in size, passing through the subgiant stage until it reaches the red giant phase.
When they reach this phase, hydrogen in them almost becomes depleted off and they become brighter and hotter and becomes low-mass white dwarfs