Shocks, Interstellar

Synonyms

Shock front; Shock wave

Definition

Shocks are highly nonlinear compression waves in a medium, which may be a fluid or solid, where the waves carry energy and where the physical parameters of the medium change abruptly. Astrophysicists recognize two types of shocks in the interstellar medium, C-type and J-type. C-type shocks are supersonic, multi-fluid flow structures occurring in weakly ionized plasma in which the physical variables (density, temperature) undergo a continuous change over the scale of the flow. In this case, the speed of the disturbance, the shock speed, is less than that of the magnetosonic speed in the plasma. In contrast, a J-type shock is a supersonic flow structure in which the physical variables (density, temperature) undergo a discontinuous change (jump) at the shock front. In this case, the speed of the disturbance, the shock speed, is greater than that of the sound speed in the gas. Interstellar shocks are produced, for example, by the propagation of...