How do we know that halo stars are older,on average,than disk stars?
A)Halo stars orbit in random directions but disk stars have more ordered orbits.
B)There are no blue halo stars.
C)There are no red disk stars.
D)Theories of galaxy formation tell us that the halo formed earlier than the disk.
E)We see evidence for new stars forming in the disk today.

Question

Quizplus · Accepted Answer

Halo stars are older because they lack blue stars, which are short-lived and indicate recent star formation.

How Do We Know That Halo Stars Are Older,on Average,than