  We have calculated stationary models for accretion disks around super-massive
black holes in galactic nuclei. Our models show that below a critical mass flow
rate of ~3 10**-3 M_Edd advection will dominate the energy budget while above
that rate all the viscously liberated energy is radiated. The radiation
efficiency declines steeply below that critical rate. This leads to a clear
dichotomy between AGN and normal galaxies which is not so much given by
differences in the mass flow rate but by the radiation efficiency. At very low
mass accretion rates below 5 10**-5 M_Edd synchrotron emission and
Bremsstrahlung dominate the SED, while above 2 10**-4 M Edd the inverse Compton
radiation from synchrotron seed photons produce flat to inverted SEDs from the
radio to X-rays. Finally we discuss the implications of these findings for AGN
duty cycles and the long-term AGN evolution.
