Non-thermal emission mechanisms in astronomy.

The need to invoke nonthermal emission mechanisms has been recognized in radio astronomy since the early 1950s when Alfven and Herlofson suggested that synchrotron radiation might be responsible for the radio emission from discrete sources. The present paper considers nonthermal emission processes that may be important at IR and shorter wavelengths. Attention is given to spontaneous emission processes and to processes of interaction with the radiation field.