Which phenomenon is not thought to result from galaxy collisions or interactions?

The existence of both disk and halo components in spiral galaxies is primarily a result of the processes involved in galaxy formation and evolution, rather than the direct consequence of galaxy collisions or interactions. The disk contains stars, gas, and dust, while the halo consists of dark matter and older stars. These components formed during the early stages of the universe when galaxies coalesced from smaller structures due to gravitational attraction.

In contrast, the other phenomena—such as the formation of new stars in dense regions, the merging of two galaxies into one, and changes in the spiral arms of a galaxy—are directly influenced by interactions between galaxies. When galaxies collide, the gravitational forces can trigger intense star formation in regions where gas and dust are compressed. Furthermore, mergers lead to the combination of galaxies, often resulting in significant morphological changes such as the evolution from spiral to elliptical galaxies. The spiral arms can also be altered due to interactions, as gravitational forces can distort a galaxy’s structure, leading to new arm formations or the reconfiguration of existing ones.