The discovery of long-sought groups of tiny galaxies is reported online in Nature Astronomy this week. The trove of seven groups of small galaxies can offer insight into the formation of galaxies like the Milky Way.

Most galaxies are thought to form through the collision and merging of several smaller galaxies. Groups of galaxies are ideal places for this process to happen. The existence of groups of dwarf galaxies, 10 to 1,000 times smaller than the Milky Way, is a critical but until now unrealized test of this model.

Sabrina Stierwalt and colleagues have exploited the largest optical survey of the night sky, the Sloan Digital Sky Survey, to identify candidates of groups of dwarf galaxies. They then used telescopes such as the 3.5-m Telescope at Apache Point Observatory, the Walter Baade Telescope (one of the twin Magellan Telescopes) and Gemini North, to confirm that seven of these groups are indeed bound together. Their discovery provides important information for understanding how galaxies grow. Given time, such groups of dwarf galaxies may merge into galaxies of intermediate mass.

Finally, the authors also compare their data to simulations to confirm the currently accepted paradigm of a dark-matter-dominated Universe. They hope their discovery will enable future studies of the inner workings of the groups of tiny galaxies.