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
Think about the implications of jets. Timescales, angular momentum.
What do they imply?