Understanding Red Giants in Stars

What happens to a star when it becomes a red giant?

A. It shrinks. B. It expands and cools. C. It shines hotter. D. It shrinks and cools.

Answer:

It expands and cools.

The correct answer is : B

Explanation:

When a star becomes a red giant, it signifies a critical stage in its evolution. This transformation occurs in stars like our Sun when they exhaust their core hydrogen fuel. During this phase, the star's core contracts while its outer layers expand outward dramatically. The expansion happens because the core's gravitational pull weakens due to the depletion of hydrogen, causing the outer layers to move away from the core.

As the star expands, it also cools down. This cooling is a consequence of the outer layers moving away from the hot core. Red giants have surface temperatures lower than those in earlier stages of their life cycle, making them appear reddish in color.

This phase of a star's life cycle is temporary. Eventually, red giants undergo further changes, such as helium burning in their cores and the ejection of outer layers, leading to the formation of a planetary nebula or, in the case of more massive stars, a supernova explosion.