The current accepted model for galaxy formation basically describes galaxies as collapsed clouds of gas and dust. While galaxies certainly contain gas and dust, the Ball-of-Light Particle Model predicts this gas and dust was made by decaying balls-of-light such as the stars within the galaxy. Images from deep in space, like the Hubble Space Telescope's Deep Field View, do not see the predicted clouds of gas and dust that made galaxies. (See also, Where's the Dust?) Instead they see small exploding galaxies.
This animation shows how the Ball-of-Light Particle Model would explain the formation of a spiral galaxy:
To make this animation, I used a Hubble Space Telescope Image of a spiral galaxy, and hand-modified each frame. There is some background stars I wish I could have removed. Also, you can't "see through" the galaxy and see a non-rotating background of stars and galaxies. Maybe someday I will be able to create a better animation of what I visualize.
See also, Galaxy Formation, Zones of Instability