S0 galaxies may be formed by collisions between spiral galaxies, which sweep out the gas and dust. Clumps of stars fromed when gravity caused the clouds to collapse. The clumps merged into larger systems that became galaxies. Describe the Local Group of galaxies. The Local Group of galaxies contains about 30 galaxies in total.
Clusters are prominent in the large-scale distribution of galaxies in the universe.
Since the distances between stars are so large, stars do not collide with each other in the course of a galaxy collision. However, since gas clouds are large, extended objects, clouds do collide with each other during a galaxy collision. Low-speed collisions between galaxies tend to lead to mergers. A merger between two spirals is likely to produce an elliptical. Collisions between gas clouds in such a merger can trigger the clouds to collapse and form stars.