This event was recorded on August 19th, 2026 at Flug Forum, produced by Aspen Center for Physics, in partnership with Aspen Public Radio.
Our Milky Way Galaxy is surrounded by dozens of smaller galaxies. By proximity, the Milky Way’s satellite galaxy population includes the faintest and lowest mass systems in the known Universe. These “ultra-faint” galaxies are several million times fainter than the Milky Way itself, providing a rare window into how the first galaxies formed, and they may help us test ideas about dark matter—the invisible material thought to make up most of the matter in the universe. In this talk, Marla Geha will trace the discovery of ultra‑faint galaxies around the Milky Way over the past decade, and preview new surveys that may reveal even fainter companions in the next few years. She will explain how these surprising objects are reshaping a basic question: what, exactly, counts as a galaxy?
Marla Geha is a professor and astrophysicist at Yale University. Her research uses the world's largest telescopes to understand the Universe's smallest galaxies. Geha obtained a B.S. in Applied and Engineering Physics from Cornell University and a PhD in Astrophysics from University of California Santa Cruz. She has received honors including an Alfred P. Sloan Research Fellow, a John S. Guggenheim Fellowship, and Yale's Dylan Hixon'88 Prize for teaching excellence in the natural sciences. Geha serves on the executive board of the Warrior Scholar Project and is the director of the Research Experience for Veteran Undergraduates (REVU) program.