Question

multiple - choice question the darker red stars, along the \horizontal branch\ start to move left along the x - axis. astrophysicists believe this is due to the fact that their cores finally contract enough to ignite helium fusion in their cores, making carbon. this hotter reaction eventually makes itself known in the stars atmosphere. what does movement towards the right along the x - axis represent? the star is heating up the star is cooling down the star is getting dimmer the star is getting brighter rewatch

Explanation:

On an HR - Diagram, the x - axis represents temperature. Moving to the right along the x - axis means a decrease in temperature, which is equivalent to the star cooling down.

Answer:

the star is cooling down