The Chandra Deep Field-North image was made by observing an area of the sky over half the size of the full moon for 23 days. It is the most sensitive or "deepest" X-ray exposure ever made. By combining the Chandra and Hubble data for this field, astronomers can take a census of the fraction of young galaxies that contain active supermassive black holes back to a time when the universe was only about one billion years old, less than 10 percent of its present age. The data show that these very distant supermassive black holes are rare, more so than some expected.