Astronomy quiz question: Milky Way monolithic collapse evidence

Astronomy 210 Quiz 6, Spring Semester 2011
Cuesta College, San Luis Obispo, CA

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.

Correct answer: (A)

In the monolithic collapse model for the evolution of the Milky Way, its shape evolved from spherical to thinner and flatter over time, as supported by the older generation metal-poor stars found in the halo, versus the younger metal-rich stars found in the disk (which would have more metal absorption lines in their spectra).

Section 30676
Exam code: quiz06SoR3
(A) : 12 students
(B) : 15 students
(C) : 9 students
(D) : 3 students

"Success level": 36% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.55