Extragalactic space. Computer artwork showing the structure of extragalactic space, with a spiral galaxy at lower right and other galaxies seen in the background. Extragalactic space is much emptier than interstellar space, or the space within the Solar System, but it is still not quite a void. Gas surrounds the galaxies and exists between them in a great web-like structure, shown in a hypothetical form in this illustration. The region of space shown here is many millions of light years across.