- interstellar medium
Content of the region between the stars, including vast, diffuse clouds of gases and minute solid particles.Such tenuous matter in the Milky Way Galaxy accounts for about 5% of its total mass. By no means a complete vacuum, the interstellar medium contains mainly hydrogen gas, with a smaller amount of helium and sizable quantities of dust particles of uncertain composition. Primary cosmic rays also travel through interstellar space, and magnetic fields extend across much of it. Most interstellar matter occurs in cloudlike concentrations, which can condense to form stars. Stars, in turn, continually lose mass through stellar winds (see solar wind). Supernovas and planetary nebulae also feed mass back to the interstellar medium, where it mixes with matter that has not yet formed stars (see Populations I and II).
* * *region between the stars that contains vast, diffuse clouds of gases and minute solid particles. Such tenuous matter in the interstellar medium of the Milky Way (Milky Way Galaxy) system, in which the Earth is located, accounts for about 5 percent of the Galaxy's total mass.The interstellar medium is filled primarily with hydrogen gas. A relatively significant amount of helium has also been detected, along with smaller percentages of such substances as calcium, sodium, water, ammonia, and formaldehyde. Sizable quantities of dust particles of uncertain composition are present as well. In addition, primary cosmic rays travel through interstellar space, and magnetic fields thread their way across much of the region.In most cases, interstellar matter occurs in cloudlike concentrations, which sometimes condense enough to form stars. These stars, in turn, continually lose mass, in some instances through small eruptions and in others in catastrophic explosions known as supernovae. The mass is thus fed back to the interstellar medium, where it mixes with matter that has not yet formed stars. This circulation of interstellar matter through stars determines to a large degree the amount of heavier elements in the cosmic clouds. Interstellar matter in the Milky Way Galaxy is found primarily in the system's outer parts (i.e., the so-called spiral arms), which also contain a large number of young stars and nebulae. This matter is closely concentrated in a plane, a flat region commonly known as the galactic disk.The interstellar medium is studied by several methods. Until the mid-20th century, virtually all information was obtained by analyzing the effects of interstellar matter on the light from distant stars with the aid of optical telescopes. Since the early 1950s, much research has been conducted with radio telescopes (radio telescope), which enable astronomers to study and interpret radio waves emitted by various constituents of the interstellar medium. For example, neutral (i.e., non-ionized) hydrogen atoms absorb or emit very small amounts of radio energy of a particular wavelength—namely, 21 cm. By being measured at this point and compared with nearby wavelengths, absorbing or radiating hydrogen clouds can be detected.Optical and radio emissions have provided much of the information on the interstellar medium. In recent years, the use of infrared (infrared astronomy) telescopes on orbiting satellite observatories has also contributed to knowledge of its properties, particularly the relative abundances of the constituent elements.
* * *
Look at other dictionaries:
Interstellar medium — Interstellar redirects here. For other uses, see Interstellar (disambiguation). The distribution of ionized hydrogen (known by astronomers as H II from old spectroscopic terminology) in the parts of the Galactic interstellar medium visible… … Wikipedia
interstellar medium — noun interstellar space including streams of protons moving from the stars • Hypernyms: ↑interstellar space … Useful english dictionary
Interstellar cloud — is the generic name given to an accumulation of gas, plasma and dust in our and other galaxies. Put differently, an interstellar cloud is a denser than average region of the interstellar medium. Depending on the density, size and temperature of a … Wikipedia
Interstellar (disambiguation) — Interstellar means between the stars.Interstellar may also refer to:* Interstellar medium, the name astronomers give to the gas and dust that is scattered throughout interstellar space * Interstellar travel, unmanned or manned travel between… … Wikipedia
Interstellar space — may mean:* In astronomy: all the space within a galaxy not occupied by stars or their planetary systems. The interstellar medium resides – by definition – in interstellar space. * Interstellar Space , a 1967 album by John Coltrane … Wikipedia
Medium — may refer to: Contents 1 Communication 2 Natural science 3 Entertainment … Wikipedia
Interstellar travel — Montage of fusion powered rocket concepts from 1987–2004, which could form the basis for an interstellar vehicle. Included are: VISTA (Lawrence Livermore National Laboratories,1987), Discovery II (NASA/GRC, 2002), Human Outer Planet Exploration… … Wikipedia
Interstellar nitrogen monohydride — Nitrogen monohydride (NH) is a simple compound that has been detected in interstellar space. Contents 1 History 2 Chemistry 3 Significance 4 See also … Wikipedia
Interstellar probe — An interstellar probe is a space probe which has left or is expected to leave the solar system and enter interstellar space (typically defined as the region beyond the heliopause). Alternatively, the term interstellar probe is used to refer to a… … Wikipedia
Interstellar reddening — In astronomy, interstellar reddening is a phenomenon associated with interstellar extinction where the spectrum of electromagnetic radiation from a radiation source changes characteristics from that which was emitted. Reddening occurs due to the… … Wikipedia