An astronomer studying a globular cluster plots its stars on a Hertzsprung-Russell diagram and finds that certain stars in the cluster lie on the horizontal branch. What does this astronomer immediately know about these stars?
A)They are still contracting toward the main sequence.
B)They are burning hydrogen into helium in their cores.
C)They are burning helium into carbon and oxygen in their cores.
D)They are burning helium into carbon and oxygen in a shell around their cores.

Question

Quizplus · Accepted Answer

Stars on the horizontal branch of the Hertzsprung-Russell diagram are in a phase where they are burning helium into carbon and oxygen in their cores.

An Astronomer Studying a Globular Cluster Plots Its Stars on a Hertzsprung-Russell