•Have to account for:
•high luminosities
•non-stellar radiation
•variability ®
compact nuclei (£ 1 pc diam)
•explosive activity – jets
•rapid internal motions (broad emission lines)
•¯
•accretion onto a compact object
•® supermassive black hole
•millions
– billions x M¤ can have radius 20
AU
•infalling material ® gravitational energy® kinetic energy® thermal energy® radiation
•jets
accompany accretion disks
•
•