Dwarf galaxies spanning six orders of magnitude in stellar mass, with stellar mass decreasing towards the right and bottom. The Large Magellanic Cloud, WLM, and Pegasus are dwarf irregular galaxies that contain gas and continue to form stars today. The remaining six galaxies lack gas and currently show no star formation. The faintest galaxies shown in this image can only be detected in regions relatively close to the Milky Way. Of particular interest for this work are the final two galaxies, Eridanus II and Pictoris I, which fall within the category of ultra-faint galaxies. Image credits: Eckhard Slawik (LMC); ESO/Digitized Sky Survey 2 (Fornax); Massey et al. (2007; WLM, Pegasus, and Phoenix); ESO (Sculptor); Mischa Schirmer (Draco); Vasily Belokurov and Sergey Koposov (Eridanus II and Pictoris I). Composition: Bullock & Boylan-Kolchin (2017).