All galaxies emit radio waves as well as light.
Most are relatively weak sources, like this edge-on spiral galaxy mapped here by the Ryle telescope. These we see as quasars or radio galaxies as the jets collide with the tenuous intergalactic gas, somewhat like immense versions of the structures produced in regions of star formation. This explains why we often see one very bright jet - the one coming towards us. Quasars, the most powerful sources, often show a prominent jet, strong radio galaxies like the one to the right more usually don't. The most powerful of these radio sources can be detected at immense distances in the Universe - the signals have taken thousands of millions of years to reach us.