Small galaxies, like the Pegasus dwarf spheroidal shown here, play a pivotal role in galaxy formation's big picture. The galaxy, almost obscured by the glare of foreground stars in our own Milky Way, measures just 2,000 light-years across and orbits M31, the famous Andromeda spiral. Galaxies like the Pegasus dwarf and the recently identified Ursa Major dwarf are thought to be the building blocks from which larger galaxies formed.
E. Grebel, Univ. Washington / P. Guhathakurta, UCO/Lick