Quasars (2) ...
The adjacent right animation shows
VLBA observations of a jet from the
quasar 3C 120.
The observing frequency was 15 Ghz and the resolution is milli-arcseconds.
Superluminal motion
refers to an optical illusion where knots in a jet may
appear to move faster than the speed of light.
The quasar 3C 120 also belongs to the class of active
galaxies called blazars.
The illusion of superluminal motion is common in blazars.
We shall discuss both blazars and superluminal motion in more detail later in this chapter.
The Host Galaxies
The enormous energy output, large redshifts, and jets and other structure to be
discussed shortly make it clear that quasars are not stars. The fuzziness and jets suggest
that maybe quasars are associated in some way with distant galaxies and that they appeared
star-like in the original observations because they are so far away. We shall find this to be
the case, and indeed in favorable cases we now have images showing the "host galaxy" of the
quasar. Thus, far from being stars, quasars appear to be enormously energetic
phenonena that occur in certain
spiral or elliptical galaxies.
