Their galactic cores are made of many neutron stars that orbit each other.
They occur only at locations in which smaller black holes and neutron stars are also present in the sky.
They emit their energy continuously and smoothly, as is the case with much smaller stars and galaxies.
The same features of an accretion disk, strong magnetic fields, and the spiraling in of infalling material are present in active galaxies as in other processes, but in larger scale.
They show peaks of emission activity that match the peaks in known neutron-star pulsars.