4 The central engine

4.1 Introduction: the active galactic nuclei (AGN)

From Section 3 you will have discovered that one thing all active galaxies have in common is a compact nucleus, the AGN, which is the source of their activity. In this section you will study the two properties of AGNs that make them so intriguing - their small size and high luminosity - and learn about the energy source at the heart of the AGN, the central engine.