20
Evolution
of Galaxies
•Galaxies live in clusters
–Rich clusters: thousands of galaxies
–Poor clusters: Few than a thousand
•Fundamental difference between stars and
galaxies:
–Stars live isolated lives:
•They are much smaller than distance
between them
•They virtually never collide
–Galaxies are not isolated
•They are only slightly smaller than the
distances between them
•The can (and do) collide, and interact
with gas within clusters
