We find active Super Massive Black Holes at the centers of massive galaxies. Our Galaxy also has its own black hole at its center measuring 2.6 million solar masses. Our black hole is not active today, but we presume it was active in the past.
We would like to know if active galactic nuclei change over cosmic time. Do black holes feed and grow in the same way over the history of the Universe?
Despite the enormous changes in the space density of back holes, the individual engines powering active galactic nuclei are remarkably stable.