Shock Waves

Shock waves (often termed "shocks") are important in astronomy. A shock wave forms when the speed of sound (the speed of pressure waves) is exceeded. For example, the sonic boom associated with an airplane breaking the sound barrier is a shock wave. Here is a Java animation that illustrates the formation of a shock wave.

Shock waves are common in astrophysics because often a wave passes from a region of higher density to one of lower density. Because the speed of sound goes down as density decreases, eventually the speed of sound can be exceeded and a shock can form. Shock waves lead to disruption and large heating of the material that they pass through.