An observer detects a galaxy with a blue color,lots of 21-cm emission,and a moderate total mass.It is most likely a(n):
A) irregular.
B) elliptical.
C) lenticular.
D) spiral.

Question

Quizplus · Accepted Answer

A galaxy with blue color and lots of 21-cm emission indicates ongoing star formation, which is commonly found in spiral galaxies. An irregular galaxy would also have ongoing star formation, but 21-cm emission is usually stronger in spiral galaxies. An elliptical galaxy typically has little or no ongoing star formation, and a lenticular galaxy is a transition between spiral and elliptical galaxies, but still has less ongoing star formation. The moderate total mass does not provide strong clues for classification since all four types of galaxies can have moderate masses.

An Observer Detects a Galaxy with a Blue Color,lots of 21-Cm