Evidence that the Milky Way became thinner and flatter as it evolved is:
A. that halo population stars have fewer absorption lines than disk population stars.
B. the presence of spiral arms that stretch out from the nuclear bulge to the edges.
C. that halo population stars are less luminous than disk population stars.
D. that dark matter is located out in the halo, but not in the disk.
Answer:A
Evidence that the Milky Way became thinner and flatter as it evolved is:
A. that halo population stars have fewer absorption lines than disk population stars. B. the presence of spiral arms that stretch out from the nuclear bulge to the edges. C. that halo population stars are less luminous than disk population stars. D. that dark matter is located out in the halo, but not in the disk.