Galaxy formation and evolution

The study of galaxy formation & evolution is concerned with the processes that formed a heterogeneous universe from a homogeneous beginning, the formation of the first galaxies, the way galaxies alter over time the processes that have generated the variety of structures observed in nearby galaxies. It is of the most active research areas in astrophysics.

Galaxy formation is hypothesized to occur, from structure formation theories, because of tiny quantum fluctuations in the aftermath of the Massive Bang. The simplest model for this that is in general agreement with observed phenomena is the  Cold Dark Matter cosmology; that is to say that clustering & merging is how galaxies gain in mass, & can also choose their shape & structure.