A spiral (S or SB) galaxy contains
A) mostly lower-main-sequence stars and giants.
B) mostly upper-main-sequence stars and giants.
C) mostly upper-main-sequence stars and gas and dust.
D) upper- and lower-main-sequence stars and gas and dust.
E) mostly white dwarfs and supergiants.

Question

Quizplus · Accepted Answer

Spiral galaxies contain both upper-main-sequence stars (which are hot and blue) and lower-main-sequence stars (which can be cooler and redder). Additionally, spiral galaxies are known for containing a significant amount of gas and dust, which can be observed as dark lanes or bright emission regions in optical and infrared images. Therefore, the best choice is D, which includes upper- and lower-main-sequence stars as well as gas and dust.

A Spiral (S or SB) Galaxy Contains