The existence of dark matter, which makes up roughly 85% of the matter in the Universe, indicates a critical gap in our understanding of fundamental physics. To date, we have been unable to directly detect or produce this mysterious substance in terrestrial laboratories. However, we have learned an enormous amount about dark matter from astronomical observations. In particular, the smallest, faintest, and most dark-matter-dominated galaxies have proven to be exceptional laboratories for studying the fundamental properties of dark matter. Our Milky Way galaxy is surrounded by dozens of these ultra-faint “dwarf” galaxies, which have only recently been discovered thanks to the unprecedented sensitivity of digital sky surveys. As telescopes grow larger and more powerful, we continue to find fainter, more distant, and more dark-matter-dominated galaxies inhabiting our “cosmic backyard”. I will describe recent advances in searches for the faintest galaxies, and how observations of our tiny galactic neighbors can help address one of the foremost open questions in physics.
