The Energy Diet of a

Radio source jets usually contain a series of brightly emitting "knots" as can be seen in Figure 12.1. This is expected because the jet does contain a magnetic field, which sometimes gets kinks or knots in it. Matter will pileup at a knot and cause a brightening, due to increases in the local magnetic field strength where more synchrotron emission is generated. This will cause cooling, just as anything that radiates away energy cools down, and so this region of the jet will contract, and possibly even collapse as it gets cooler. This collapse increases the field strength and m

Figure 12.2. The Seyfert galaxy 3C219. Its radio image (red and yellow) is superimposed on an optical image. The overall size of the radio source is over 1 million light-years. The radio lobes are tilled with networks of filaments and the core of the galaxy itself is a bright radio source. Investigators: David A. Clarke, Alan H. Bridle, Jack O. Burns, Richard A. Perley, and Michael L. Norman. (Image courtesy of NRAO/AUI.)

the emission. This cycle can continue indefinitely and creates an instability, which can play havoc with the smooth flow in the jet. The magnetic kinks may be expected to move with the flow. Should anything get in the way, such as a cold cloud in the surrounding galaxy (and some have been observed near the core of Centaurus-A), it will likely get swept up and accelerated until it is also part of the flow,

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