Interstellar Medium

Material between the stars, consisting of gas, dust and cosmic rays (high energy charged particles moving at nearly the speed of light). It comprises ~10% of visible matter in the disk of our Galaxy (Milky Way). Until recently it was generally assumed that silicates in the ISM were amorphous, but the Infrared Space Observatory (ISO) has discovered crystalline silicates. Crystalline silicates appear to be ubiquitous (except for the diffuse ISM) and sometimes even in very large quantities (>50 % of the small dust particles).

Some or all content above used with permission from J. H. Wittke.