  We investigate the motion of free relativistic particles relative to the
ambient medium around a gravitationally collapsed system. If the relative speed
exceeds a critical value given by c/sqrt(2), the gravitational tidal effects
exhibit novel features that are contrary to Newtonian expectations. In
particular, ultrarelativistic jet clumps moving freely outward along the
rotation axis strongly decelerate with respect to the ambient medium, while
ultrarelativistic particles strongly accelerate in directions normal to the jet
axis. The implications of these direct consequences of general relativity for
jets in microquasars and the origin of the high-energy cosmic rays are briefly
mentioned.
