Why do some galaxies look blue while others look red?
Quick Answer
Blue galaxies are usually forming many young, hot stars, while red galaxies contain older stellar populations with little new star formation. Dust can also make galaxies appear redder.
The Full Story
A galaxy’s color reflects the kinds of stars it contains and how much new star formation is happening. Young massive stars emit strongly in blue and ultraviolet light, so active star-forming galaxies often look blue. Older galaxies are dominated by cooler, longer-lived stars that emit more red and yellow light. Dust within a galaxy can absorb blue light and make the whole system look redder than it really is.
Key Facts
YouTube Angle
Suggested video title for this topic:
"Why are some galaxies cosmic blue flames and others red embers?"
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