2.30 pm Monday 8 October 2001
The Chandra X-ray Observatory detects X-rays emitted during the accretion of matter onto supermassive black holes, even when they are highly obscured. A cosmic census of AGN contributing to the X-ray background is nearing completion. Follow-up observations with ground-based telescopes provide new knowledge about distant black holes. From optical data we find the duration and times of black hole activity. Surprisingly, the duty cycle is about half a billion years, and accretion is still occurring at cosmologically recent times. With the addition of submillimeter and radio data, we estimate the history of accretion from the earliest times to the present.