Galaxies of a third kind, irregular galaxies , lack a simple shape. Some consist mostly of blue stars and puffy clouds of gas, but little dust. The Magellanic Clouds are irregular galaxies of this type. Others are made up mostly of bright young stars along with gas and dust. Galaxies move relative to one another, and occasionally two galaxies come so close to each other that the gravitational force of each changes the shape of the other.
Galaxies can even collide.
If two rapidly moving galaxies collide, they may pass right through each other with little or no effect. However, when slow-moving galaxies collide, they can merge into a single galaxy that is bigger than either of the original galaxies. Such mergers can produce spiral filaments of stars that can extend more than 100,000 light-years into space. Emissions from galaxies. All these forms of radiation together make up the electromagnetic spectrum.