What happens when the solar wind and the interstellar medium collide?
Even though the interstellar medium has a low density, it still has a pressure (similar to air pressure). The solar wind 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 heliosphere. The place where the solar wind slows down and begins to interact with the interstellar medium is called the heliosheath. 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. 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
