Astronomy Cast Ep. 682: Ultra-Diffuse Galaxies & Dark Matter by Fraser Cain & Dr. Pamela Ga Streamed live on May 15, 2023. Astronomers first noticed the strange behaviors of rotating galaxies almost 100 years ago, suggesting there's an invisible dark matter hold them together with gravity. Or maybe we just don't understand how gravity works at the largest scales. Observations are much better now, and astronomers have found examples of galaxies that are almost entirely made of dark matter. Does this tell us anything? This video was made possible by the following Patreon members: Burry Gowen Stephen Veit Jordan Young Venkatesh Chary Andrew Poelstra Brian Cagle David Truog Jeanette Wink Gerhard Schwarzer David THANK YOU! - Fraser and Dr. Pamela