Fig 1: How are radio jets formed? This picture shows what astronomers think.

The big question is: "what process or motor, confined in a tiny nucleus of only a few  light years,can produce an energy which, through narrow channels, feeds an entire radio source hundreds of thousands of light years away?" It is by now universally recognised that the nuclei of radio galaxies and quasars contain massive black holes (millions of solar masses in size), concentrated in an area not much bigger than that of the solar system. The black hole rotates and all the material around it (gas, star dust), attracted by gravity, is forced by a viscosity effect to arrange itself in a rotating disc (called accretion disc) before falling into the black hole.

 From the black hole two channels are created, perpendicular to the rotating accretion disc, and through these channels the more energetic material can escape attraction in two opposing directions. These channels are radio jets inside which charged  particles move at a speed close to the that of light, spiralling along  the magnetic field lines

.

Fig 2: On the left, the radio image (in orange) and the optical image (in blue) of NGC 4261. obtained with observations from earth. On the right, the nucleus of the galaxy observed from the Hubble Space Telescope, where the accretion disc appears for the first time. The two radio jets are orthogonal to the dust disc, rotating around the nucleus of the galaxy. This image is taken as further proof of the existence of a massive black hole in the galaxy NGC 4261. (Credits: STScI/NRAO)