Red stars and big bulges: How black holes shape galaxies

The universe we can see is made up of thousands of millions of galaxies, each containing anywhere from hundreds of thousands to hundreds of billions of stars. Large numbers of galaxies are elliptical in shape, red and mostly made up of old stars. Another (more familiar) type is the spiral, where arms wind out in a blue thin disk from a central red bulge. On average stars in spiral galaxies tend to be much younger than those in ellipticals. Now a group of astronomers has found a (relatively) simple relationship between the color of a galaxy and the size of its bulge: the more massive the bulge, the redder the galaxy.

from Space & Time News — ScienceDaily

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