Emission processes The radio emission from radio-loud active galaxies is synchrotron emission , as inferred from its very smooth, broad-band nature and strong polarization . This implies that the radio-emitting plasma contains, at least, electrons with relativistic speeds ( Lorentz factors of ~10 4 ) and magnetic fields . Since the plasma must be neutral, it must also contain either protons or positrons . There is no way of determining the particle content directly from observations of synchrotron radiation. Moreover, there is no way to determine the energy densities in particles and magnetic fields from observation: the same synchrotron emissivity may be a result of a few electrons and a strong field, or a weak field and many electrons, or something in between. It is possible to determine a minimum energy condition which is the minimum energy density that a region with a given emissivity can have, but for many years there was no particular reason to believe that the true energies were anywhere near the minimum energies. 
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This note was uploaded on 12/15/2011 for the course AST AST1002 taught by Professor Emilyhoward during the Fall '10 term at Broward College.