Number 59 (Story #1), December 18, 1991 by Phillip F. Schewe and Ben Stein SOME QUASARS PRODUCE ONE-SIDED JETS , streams of radio-emitting plasmas that can extend for hundreds of light years and propagate at apparently faster-than-light speeds. The favored theory explains these features, and the lack of a jet propagating in the opposite direction, by supposing that jets are produced on both sides of the quasar but that relativistic effects diminish the appearance of the receding jet (almost to nothingness) and distort the appearance of the on-coming jet so as to suggest superluminal velocities. New radio measurements of the jet from quasar 3C273 by a team of astronomers from Jodrell Bank (UK) and Caltech bear on this theory in two respects. (1) The apparent superluminal motion of the jet has in this case been established out to a distance of 400 light years from the quasar core, in keeping with the theory's insistence on relativistic speeds for the whole length of the jet column (previous jet studies had only established superluminal motion over tens of light years). (2) The non-appearance of a receding jet was measured to an unprecedented degree, to less than 1 part in 5300 of the brightness of the approaching jet. (R.J. Davis, Nature, 5 Dec. 1991.)