Fanaroff &Riley observed that there was a reasonably sharp divide in luminosity between the two classes: FRIs were low-luminosity, FRIIs were high luminosity.

• 因此电浆体必然是中性的，质子或正子必然是其中的成分之一，但是没有办法从同步加速辐射中直接观察出微粒的种类。