Galactic Dynamical Evolution:
Collisions/Accretions/Mergers

The field of galaxy evolution is primarily concerned with changes in the contents of galaxies with time; star formation rates, gas depletion, AGN phenomenon. It is usually assumed that after the formation epoch, galaxies take on a form or morphology that they maintain for all time (the Hubble sequence).

Timeline of Galaxy Formation

A second form of galaxy evolution deals not with internal changes in stellar populations, but rather changes in a galaxy due to dynamical influences, i.e. gravitational changes on the structure of the galaxy = dynamical evolution.