The following questions refer to the sketch below of an H-R diagram for a star cluster.

-Based on its main-sequence turnoff point,the age of this cluster is
A)less than 1 billion years.
B)about 1 billion years.
C)about 2 billion years.
D)about 10 billion years.
E)more than 15 billion years.

Question

The following questions refer to the sketch below of an H-R diagram for a star cluster.
 
-Based on its main-sequence turnoff point,the age of this cluster is
A)less than 1 billion years. 
B)about 1 billion years. 
C)about 2 billion years. 
D)about 10 billion years. 
E)more than 15 billion years.

Quizplus · Accepted Answer

The main-sequence turnoff point of a star cluster is a key indicator of its age. A cluster with a turnoff point indicating stars are leaving the main sequence to become red giants at a relatively low mass (which corresponds to a cooler temperature and redder color) suggests an older age. This is because lower mass stars have longer main sequence lifetimes. A turnoff point indicating an age of about 10 billion years means the cluster is quite old, as it has stars that have been on the main sequence for a long time before evolving into later stages.

The Following Questions Refer to the Sketch Below of an H-R