Intergalactic space

Intergalactic space is the physical space between galaxies. Generally free of dust and debris, intergalactic space is very close to a vacuum. The average density of the Universe is less than one atom per cubic meter. 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 extremely rarified conditions in vast voids that have lower density than the Universe's average. Surrounding and stretching between galaxies, there is a rarified gas that is thought to possess a cosmic filamentary structure 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 -- which implies the mass of 10 to 100 hydrogen atoms per cubic meter.

Related Topics:
Galaxies - Vacuum - Universe - Atom - Planets - Stars - Black holes - Plasma - Electrons - Protons

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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 only "warm" by astrophysical standards). As gas falls into the Intergalactic Medium from the voids, it heats up to temperatures of 10^5 - 10^7 degrees, which is too hot for hydrogen nucleii to retain their electrons. At these temperatures, it is called the Warm-Hot Intergalactic Medium (WHIM); and computer simulations indicate that on the order of half the atomic matter in the universe might exist in this warm-hot, rarified state.

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Since the Intergalactic Medium is a plasma, it has the characteristics of a plasma, even at the extremely low particle density, (ie. it can carry a magnetic field, is highly electrically conductive, can produce filamentation and double layers).

Related Topics:
Plasma - Double layer

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