What term colloquially describes elliptical galaxies due to their star formation status?
Answer
Red and dead
The term 'red and dead' is a colloquial description frequently applied by astronomers to elliptical galaxies. This phrase directly reflects their observed color and their evolutionary state. They are 'red' because their light output is dominated by older, cooler stars that emit reddish light, as the massive, blue-emitting young stars have long since died out. They are 'dead' because the essential component for stellar genesis—cold molecular gas—is almost entirely exhausted from their interstellar medium, meaning the process of creating new stars has effectively stopped or is minimal.
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