Let's consider cosmic jet propagation. Cosmic jet is well found from galactic nuclei, proto stellar objects, and so on as the steeply collimated high speed flow from the source.

[Initial Condition]

Placing the exit of supersonic (Mach number is 6.0) gas at -1 < x < 1 & z = 0 into the rest gas, we will follow succeeding evolution.

In the figure, color shows density, and arrows show velocity.

[Evolved Stage]

Jet compresses the rest gas at its front and propagates with making arc shaped bow shock.

Density is decreasing from Red, to Orange, Olive, Green, Aqua, Blue, Perple, and Black.