The Density Contrast is a parameter used in galaxy formation to indicate where there are local enhancements in matter density.
It is believed that after inflation, although the universe was mostly uniform, some regions were slightly denser than others with contrast densities on the order of 1 trillionth. As the horizon distance expanded, the enclosed causally connected (i.e. gravitationally connected) masses increased until they reached the Jeans mass and began to collapse, which allowed galaxies, galaxy clusters, superclusters, and filaments to form.
Famous quotes containing the word contrast:
“Flowers and fruits are always fit presents; flowers, because they are a proud assertion that a ray of beauty outvalues all of the utilities of the world. These gay natures contrast with the somewhat stern countenance of ordinary nature: they are like music heard out of a work-house.”
—Ralph Waldo Emerson (1803–1882)