• Q
2 If the stars turning off the main sequence in the H-R diagram of a star cluster have masses of about 15
times solar, how old
is the cluster?
•a.About 1 million years.
•b.About
11 million years.
•c.About 90 million years.
•d.About 500 million years.
•e.About 3 billion years.
•
•We
need the main sequence lifetime, which is the mass of the star raised to the -2.5 power (giving us
an answer in solar
lifetimes, where the solar lifetime is 10 billion years). 15-2.5 =
0.0011, which when multiplied by 10 billion years gives us 11 million years.