What happens when the solar wind and the interstellar medium collide?
Even though the interstellar mediumAll the gas and dust found between stars. has a low densityThe amount of mass or number of particles per unit volume. In cgs units mass density has units of gm cm-3. Number density has units cm-3 (particles per cubic centimeter)., it still has a pressure (similar to air pressure). The solar windA stream of charged particles, mostly protons and electrons, that escapes into the Sun's outer atmosphere at high speeds and streams out into the solar system. also has a pressure. Close to the Sun, the solar wind has a large pressure and can easily push the interstellar medium away from the Sun. Further away from the Sun, the pressure from the interstellar medium is strong enough to slow down and eventually stop the flow of solar wind from traveling into its surroundings. The entire area or bubble inside the boundary of the solar system is called the heliosphereThe region around the Sun where the solar wind dominates over the interstellar medium.. The place where the solar wind slows down and begins to interact with the interstellar medium is called the heliosheathThe place where the solar wind slows down and begins to interact with the interstellar medium. The heliosheath has a few parts: the termination shock (the innermost part of the boundary), the heliopause (the outermost part of the boundary) and the part in between the inner and outer boundary.. The heliosheath has a few parts: the termination shockThe boundary marking one of the outer limits of the Sun's influence. At the termination shock, solar wind particles slow down as they begin to press into the particles forming the interstellar medium. The solar wind particles then continue to travel outward at a slower rate of speed. This is similar to cars speeding along a highway which then slow down as they encounter many more cars involved in a traffic jam. The jammed cars continue to move outward, although much more slowly. (the innermost part of the boundary), the heliopauseThe boundary between the Sun's solar wind and the interstellar medium. (the outermost part of the boundary) and the part in between the inner and outer boundary.
Since the Sun is moving relative to the interstellar medium around it, the heliosphere forms a wave or shock in the interstellar medium like a boat in the ocean. This is called the bow shock or wave.
About the Boundary of the Solar System