•Small
fraction of galaxies have extremely
bright
“unresolved” star-like nuclei
–Very
large energy generation
–Brightness
often varies quickly
•Implies
small size (changes not smeared out by light-travel time)
–High
velocities often seen (> 10,000 km/s in lines)
–Emission
all over the electro-magnetic spectrum
•
•Jets
seen emerging from galaxies