Astronomy quiz question: spiral arm tracers

Astronomy 10 Quiz 11, Spring Semester 2008
Cuesta College, San Luis Obispo, CA

Astronomy 10 learning goal Q11.2

[3.0 points.] Which one of the following statements best explains why massive main sequence stars are used to map the spiral arm structure of the Milky Way?
(A) They emit 21 cm radio waves.
(B) They are extremely metal-poor.
(C) They will explode as type II supernovae.
(D) They will become neutron stars or black holes.
(E) They are very luminous and short-lived.

Correct answer: (E)

Due to the dust and gas in the disk of the Milky Way, only a very small fraction of our galaxy is visible from the Earth. Thus massive main sequence stars, which are very luminous, would be most visible through the interstellar medium. These massive stars also have the property of forming as they enter the spiral arms, and due to their short lives die as they leave the spiral arms, making them de facto "spiral arm tracers."

Student responses
Section 5166
(A) : 10 students
(B) : 6 students
(C) : 1 student
(D) : 2 students
(E) : 31 students