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Interstellar Matter

Significance Of The Interstellar Medium

Neutral hydrogen atoms in the interstellar medium emit radio waves at a wavelength of 8 in (21 cm). Studies of this 8 in (21 cm) emission are not just important for studying the interstellar medium. Mapping the distribution of this interstellar hydrogen has revealed to us the spiral structure of the Milky Way galaxy.

The interstellar medium is intimately intertwined with the stars. Stars are formed from the collapse of gas and dust in molecular clouds. The leftover gas around newly formed massive stars forms the HII regions. At various times stars return material to the interstellar medium. This recycling can be gentle in the form of stellar winds, or it can be as violent as a supernova explosion. The supernovas are a particularly important form of recycling in the interstellar medium. The material recycled by supernovas is enriched in heavy elements produced by nuclear fusion in the star and in the supernova itself. With time the amount of heavy elements in the composition of the interstellar medium and of stars formed from the interstellar medium slowly increases. The interstellar medium therefore plays an important role in the chemical evolution of the galaxy.

See also Stellar evolution.



Bacon, Dennis Henry, and Percy Seymour. A Mechanical History of the Universe. London: Philip Wilson Publishing, Ltd., 2003.

Morrison, David, Sidney Wolff, and Andrew Fraknoi. Abell's Exploration of the Universe. 7th ed. Philadelphia: Saunders College Publishing, 1995.

Verschuur, Gerrit L. Interstellar Matters. New York: Springer-Verlag, 1989.


Knapp, Gillian. "The Stuff Between The Stars." Sky & Telescope 89 (May 1995): 20-26.

Paul A. Heckert


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Dark cloud

—A cloud of dust that block light from stars behind it.

HI region

—A cloud of neutral hydrogen.

HII region

—A cloud of ionized hydrogen.

Interstellar medium

—The matter between the stars.


—An atom that has lost or gained one or more electrons. In astronomy it will virtually always have lost electrons.

Molecular cloud

—An interstellar cloud of molecules.


—An interstellar cloud of gas and/or dust.

Reflection nebula

—A cloud of dust that glows from reflected starlight.

Additional topics

Science EncyclopediaScience & Philosophy: Incomplete dominance to IntuitionismInterstellar Matter - Components of the interstellar medium, Significance of the interstellar medium