Galaxy evolution and merging, illustration. Spiral galaxies are thought to have formed from elliptical galaxies, the first type to form in the early universe (left), but some later elliptical galaxies formed from the merger of spiral galaxies. This merging process is shown in this diagram, with the number of galaxies decreasing from left to right. Five galaxies eventually merge to form one massive elliptical galaxy, with intermediate stages where spiral galaxies re-form before more merging takes place.