gas, it takes a long time for collisions to establish an equilibrium (Maxwell-Boltzmann) velocity distribution. The time is longer than the age of the universe, so this never happens. This is how we can have an unusually large number of high energy electrons. The high energy electrons lose their energy by synchrotron radiation, rather than by collisions with lower energy electrons. The magnetic fields in the lobes are thought to be in the range 10-100 }xG. The lobes contain smaller-scale structures with extents of 103 pc and smaller.

The jets are highly collimated, being some 105 pc long by 104 pc wide. The flow velocities in the jets are hard to measure, but estimates range from 103 to 105 km/s. (Some jets are moving close to the speed of light, as discussed in Section 19.2.3.) The densities are about 10~2 elec-trons/cm3. The magnetic fields are comparable to those in the lobes.

Figure 19.11 shows one mechanism by which the jets can be collimated. We assume that there is material flowing outward in all directions. However, the source of the flow is surrounded by denser gas. This denser gas has a hole in it, and the outflowing material just follows the path of least resistance. Effectively, the material forms itself into a nozzle. One problem with this picture is that we would expect the outflowing material to drive the confining material outward.

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