Molecules in Interstellar Space In our home galaxy, the Milky Way, as well as in external galaxies, the space between the stars is filled with an interstellar medium consisting of gas and dust, like the beautiful Orion Nebula. While accounting for only a small fraction of the Galaxy's mass, the interstellar medium is nevertheless an important part of the Galactic ecosystem. Gravitational collapse of dense interstellar clouds leads to the formation of new stars, which produce heavier elements in their interiors by nucleosynthesis. A few elements (H, C, N, O, S, P) have provided the raw material for the formation of organic molecules, which are now widespread in our Galaxy and beyond. Elements heavier than iron are formed in supernovae At the end of their lives stars return material to the interstellar environment by mass outflows, either by forming expanding shells and envelopes or by violent explosions (supernovae) Detection of molecules in space Observations at radio, millimetre, sub-millimetre, and infrared wavelengths have led to the discovery of well over a hundred different molecules in interstellar clouds and circumstellar shells (see the list), many of them organic in nature. Some of these are organic species of considerable complexity, with C6H6 and HC11N being the largest detected so far. There are also several prebiotic molecules such as HCN and H2CO among the detected species. Large molecules and dust Dust particles form in the extended atmospheres of cool stars from where they are blown into interstellar space where they may be observed along with the gas. Though not unambiguously identified, much larger carbon molecules than those now known and solid carbonaceous dust particles are assumed to be present in interstellar clouds and solar system bodies.

The star-forming region of Orion Listing of interstellar and circumstellar molecules observed in 2001