Illustration: (Left) John Gay, U.S. Navy photograph; (Right) Adapted from [3]

Figure 1: (Left) The shock wave and Mach cone associated with an F-18 Hornet jet fighter aircraft breaking the sound barrier. (Right) The same phenomenon might occur when a fast parton moves faster than the speed of sound through the partonic fluid at RHIC. The perturbation to the energy density, as calculated in [3], is shown for a particle moving in the $z$ direction.