Which way does a star of about 1 M ? evolve, on the Hertzsprung-Russell diagram, at the end of its main-sequence lifetime?
A)toward lower luminosity and higher temperature-progressing through the main sequence toward the white dwarf stage
B)toward higher luminosity and lower temperature-away from the main sequence
C)toward higher luminosity and higher temperature-upward along the main sequence
D)toward lower luminosity and temperature-downward along the main sequence

Question

Quizplus · Accepted Answer

A star of about 1 M ε, at the end of its main sequence lifetime, has exhausted its hydrogen fuel and begins to fuse helium in its core. This causes the core to contract and heat up, which leads to an expansion of the star's outer layers, causing it to move away from the main sequence towards higher luminosity and lower temperature. This evolution is represented by a diagonal track on the Hertzsprung-Russell diagram known as the red giant branch.

Which Way Does a Star of About 1 M