Structure densities vary greatly. Also many exhibit evidence of black hole formation in their nuclei. BlackHoles exist when matter density is great enough to cause the gravitational retraction of matter and radiation. Our galaxy appears to have a black hole in it's nucleus. Many earlier galaxies contain Quasars in their cores.
Quasars are huge black hole accretion disks that are much brighter than their host galaxy.
Scientists are continuing to study galaxy morphology. Current studies show early galaxies exhibit prolific star formation and heavy element production compared to later galaxies as a result of higher galaxy collision rates.