... What cosmic wallpaper is on the sky? ... The Coma Cluster of Galaxies . ... Each of these galaxies houses billions of stars - just as our own Milky Way Galaxy does. ... At least that was the conventional wisdom when it was first realized that the space between the stars is filled with hydrogen, a strong absorber of extreme ultraviolet light. ... The result, shown above, is the most complete sky map of the most common visible light emitted from the most abundant element in our Galaxy: hydrogen. ...