Stars eject their outer atmosphere into space during their lifetime. Consider that the visible surface of our sun isn't actually it's surface, it's just the po

Stars eject their outer atmosphere into space during their lifetime. Consider that the visible surface of our sun isn't actually it's surface, it's just the point that the temperature is low enough that electrons can bind to protons, yielding hydrogen gas that is transparent to light. Underneath the photosphere, the charged particles are dissociated; photons scatter off of them. Outside the photosphere there is still lots of hydrogen gas. The outermost boundary of the sun is regarded by astronomers as the heliopause. It's the point at which the solar wind as deflected by the flow of interstellar gas. Voyager 1 crossed into the heliopause a few years ago - it's way beyond the orbit of pluto.