An astronomer is observing a distant galaxy which looks blue. Which of the following can she conclude from this observation?
A) the galaxy must be moving toward us (must have a blue shift)
B) the galaxy must be extremely large (probably a giant elliptical)
C) the galaxy must have a lot of star formation going on at the time we are seeing it
D) the galaxy must be rotating very slowly or not at all
E) the galaxy must contain only older stars (those that formed billions of years ago)

Question

Quizplus · Accepted Answer

A galaxy appearing blue indicates that there is ongoing star formation, as young, hot stars emit blue light. A galaxy with a red appearance would indicate older stars, as they emit more red light. The color alone does not provide information about motion or size.

An Astronomer Is Observing a Distant Galaxy Which Looks Blue