Matter swirling around supermassive black holes creates bursts of light that “echo” in nearby dust clouds. These traveling signals could serve as a new cosmic yardstick. When you look up at the night sky, how do you know whether the specks of light that you see are bright and far away, or relatively faint and … Continue reading “Echo Mapping” Light Bursts From Supermassive Black Holes in Faraway Galaxies to Measure Vast Cosmic Distances