The conventional explanantion for the superluminal motions observed in
many quasar-type jets is that it is an optical illusion due to the jets
being oriented at a fairly narrow angle to our line of sight.

Some salient question marks over this a-

As early as 1983, for the relatively few superluminal objects then
known, the jets did not seem to be in general oriented close to the
line of sight;

In 1993 Mackay et al suggested, based on Hubble Telescope observations,
that the jet of the quasar 3C273 was nearly perpendicular, rather than
nearly parallel, to the line of sight (superluminal motion of up to
~9.6c has been observed in the inner jet);

The jet of the galaxy M87 does not seem to have a narrow-enough angle
with our line of sight to explain motion of up to ~6c observed in it.

(I summed up the material at
http://uk.geocities.com/chrisori2000/superjet.htm )



Various technical tricks, such as multiple jet-beams and twisting jets,
or precessing jets, have been proposed, as ways out. Devices which
seem increasingly convoluted in more senses than one, and perhaps as
artificial as that spectrum of tricks proposed to save the "ether" at
the turn of the 19th/20th centuries.