Charge exchange processes in the outer heliosphere produce a population of hot hydrogen gas within the heliosphere, creating a “hydrogen wall” between the heliopause and bow shock . The heliospheric hydrogen wall scatters Lyα photons passing through it, producing a detectable absorption signature in observations of H I Lyα emission from nearby stars. This heliospheric absorption has been observed using observations from various space born laboratories and telescopes, and these observations have also yielded detections of analogous “astrospheric ” absorption from material surrounding the observed stars. The astrospheric detections dramatize the importance of understanding the heliospheric interaction, since similar interactions exist around other stars . .
Around each star exists a region of hot hydrogen known as the hydrogen wall between the bow shock and the heliopause . The wall is composed of interstellar material interacting with the edge of the heliosphere .