Intergalactic space is the physical space between galaxies. Generally free of dust and debris, intergalactic space is very close to a total vacuum. Some theories put the average density of the Universe as the equivalent of one hydrogen atom per cubic meter^[1][2]. The density of the Universe, however, is clearly not uniform; it ranges from relatively high density in galaxies (including very high density in structures within galaxies, such as planets, stars, and black holes) to conditions in vast voids that have much lower density than the Universe's average. The temperature is only 2.73 Kelvin^[3]. NASA's COBE mission(COsmic Background Explorer) measured the temperature as 2.725 +/- 0.002 K Intergalactic is a single by the Beastie Boys from their album Hello Nasty. ... For other uses, see Galaxy (disambiguation). ... Look up Vacuum in Wiktionary, the free dictionary. ... For other uses, see Universe (disambiguation). ... Properties For other meanings of Atom, see Atom (disambiguation). ... This article is about the astronomical term. ... This article is about the astronomical object. ... For other uses, see Black hole (disambiguation). ... For other uses, see Kelvin (disambiguation). ... This article is about the American space agency. ... The Cosmic Background Explorer (COBE), also referred to as Explorer 66, was the first satellite built dedicated to cosmology. ...

Surrounding and stretching between galaxies, there is a rarefied gas that is thought to possess a cosmic filamentary structure^{[citation needed]} and that is slightly denser than the average density in the Universe. This material is called the intergalactic medium (IGM) and is mostly ionized hydrogen, i.e. a plasma consisting of equal numbers of electrons and protons. The IGM is thought to exist at a density of 10 to 100 times the average density of the Universe (10 to 100 hydrogen atoms per cubic meter). It reaches densities as high as 1000 times the average density of the Universe in rich clusters of galaxies. Ionization is the physical process of converting an atom or molecule into an ion by changing the difference between the number of protons and electrons. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... For other uses, see Plasma. ... For other uses, see Electron (disambiguation). ... For other uses, see Proton (disambiguation). ... ...

The reason the IGM is thought to be mostly ionized gas is that its temperature is thought to be quite high by terrestrial standards (though some parts of it are only "warm" by astrophysical standards). As gas falls into the Intergalactic Medium from the voids, it heats up to temperatures of 10⁵ K to 10⁷ K, which is high enough for the bound electrons to escape from the hydrogen nuclei upon collisions. At these temperatures, it is called the Warm-Hot Intergalactic Medium (WHIM). Computer simulations indicate that on the order of half the atomic matter in the universe might exist in this warm-hot, rarefied state. When gas falls from the filamentary structures of the WHIM into the galaxy clusters at the intersections of the cosmic filaments, it can heat up even more, reaching temperatures of 10⁸ K and above. For other uses, see Plasma. ... For other uses, see Kelvin (disambiguation). ...

References

• 1. Davidson, Keay & Smoot, George. Wrinkles in Time. New York: Avon, 1993: 158-163
• 2. Silk, Joseph. Big Bang. New York: Freeman, 1977: 299.
• 3. NASA COBE website[1]

See also

• Intracluster medium
• Interstellar medium
• Heliosphere
• Solar space
• Solar system
• Stellar system

In astronomy, the intracluster medium (or ICM) is the superheated gas present at the center of a galaxy cluster. ... The interstellar medium (or ISM) is the name astronomers give to the tenuous gas and dust that pervade interstellar space. ... The heliosphere is a bubble in space produced by the solar wind. ... This article is about the Solar System. ... A star system or stellar system is a group of stars (and possibly smaller bodies such as planets or asteroids) that orbit one another (a system with planetary bodies orbiting stars, are referred to as solar systems or planetary systems). ...

External links

Look up intergalactic in
Wiktionary, the free dictionary.

• Intergalactic Space, Natural History, Feb 1998