What is entirely absent in the light signature of an elliptical galaxy compared to an actively forming region like a spiral arm?

Answer

Hot, massive stars burning quickly

Hot, massive stars burn quickly and die young, leaving behind a blueish light signature. In old elliptical galaxies, these bright, short-lived blue stars are entirely absent.

What is entirely absent in the light signature of an elliptical galaxy compared to an actively forming region like a spiral arm?
galaxyastronomytypestarstellar death