COLLIMATION OF ELECTROMAGNETIC-RADIATION IN OPTICALLY THICK ASTROPHYSICAL SYNCHROTRON SOURCES

COLLIMATION of energy output into two oppositely directed beams seems to be very common in the Universe, particularly in extra-galactic radio sources, but also within the Galaxy, for example SS433. The collimation mechanism is still in doubt. Here I discuss the possibility of collimation arising from anisotropic synchrotron absorption whereby electromagnetic waves are less strongly absorbed when propagating parallel, rather than perpendicular, to a magnetic field. This discussion can apply to any object which is optically thick to synchrotron emission, but I particularly have in mind the collimation of infrared/optical/ultraviolet radiation in active galactic nuclei. The beamed radiation may be seen in blazars1 and in the recent observations by di Serego Aligheri et al. 2. The beams may also drive double radio sources. © 1990 Nature Publishing Group.