Astronomy quiz question: massive vs. medium-mass main-sequence lifetimes

Astronomy 210 Quiz 5, Fall Semester 2009
Cuesta College, San Luis Obispo, CA

Massive main-sequence stars have shorter lifetimes than medium-mass main-sequence stars because massive main-sequence stars:
(A) have unbalanced pressure-temperature thermostats.
(B) accumulate greater amounts of unstable heavy elements.
(C) contain more hydrogen.
(D) fuse hydrogen more rapidly.

Correct answer: (D)

Massive and medium-mass stars only fuse the hydrogen contained within their cores during their main-sequence lifetimes. Although massive stars have proportionally larger cores than medium-mass stars, the massive stars are disproportionately more luminous, and thus have much faster fusion rates than medium-mass stars, and accordingly live much shorter main-sequence lifetimes until the hydrogen in their cores has been depleted.

Section 70158
(A) : 1 student
(B) : 2 students
(C) : 1 student
(D) : 37 students

Success level: 87% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.40