Astronomy quiz question: spiral arm composition

Astronomy 210 Quiz 7, spring semester 2018
Cuesta College, San Luis Obispo, CA

The spiral arms of a galaxy are primarily composed of:
(A) dark matter.
(B) massive stars.
(C) globular clusters.
(D) type Ia and type II supernovae.

Correct answer (highlight to unhide): (B)

Massive main-sequence stars, which are the brightest and shortest-lived stars, form and die within a short time, essentially traveling the width of a spiral arm. Dark matter and globular clusters are mainly found in the halo of a galaxy, above and below the disk.

Section 30674
Exam code: quiz07nen4
(A) : 2 students
(B) : 8 students
(C) : 9 students
(D) : 2 students
(No responses: 1 student)

Success level: 41% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.86

Section 30676
Exam code: quiz07SumM
(A) : 3 students
(B) : 16 students
(C) : 17 students
(D) : 2 students

Success level: 46% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.48