Few molecules are hardy enough to exist at the high temperatures of emission nebulae, and so consequently scientists find that they contain mostly atoms and atomic ions. Absorption nebulae, a different type of gas-dust cloud, are also found in the interstellar medium. In turn, these molecules can stick to the cold dust grains in an absorption nebula and be altered by high-energy light to form still other, different molecules. The adjacent photo shows an irregular dark patch where stars seem to be missing. The dark patch is actually Bernard 86, an absorption nebula.
Reflection nebulae are a third type of gas-dust cloud found in the interstellar medium.
These nebulae normally display a blue color due to light scattered by their dust grains, the light originating in nearby stars. A famous example is the nebulosity around the stars of the Pleiades cluster in Taurus. All three types of nebulae can sometimes be found in a single photograph. Here is an image of the Horsehead Nebula. In addition to these three nebular types, the space between the stars contains gaseous hydrogen atoms and dust particles.