Cluster A has no stars of spectral type O,B,and A on its main sequence,whereas cluster B has stars of all types but O on its main sequence.Which of the following correctly describes the relative ages of clusters A and B?

Question

Quizplus · Accepted Answer

The absence of stars of spectral type O, B and A on the main sequence of cluster A suggests that all stars of these types have evolved off the main sequence - either as giants, supergiants, or white dwarfs. This indicates a relatively advanced age for cluster A. On the other hand, cluster B has stars of all types except O on its main sequence, which suggests that O stars have evolved off the main sequence but the other types are still there. This implies that cluster B is younger than cluster A, but still old enough to have formed stars of spectral type B and A on its main sequence. Therefore, the relative ages of clusters A and B can be deduced from the presence or absence of certain spectral types on their main sequences, and it appears that cluster A is older than cluster B.

Cluster a Has No Stars of Spectral Type O,B,and a on Its