IAU Symposium 256
The Magellanic System: Stars, Gas, and Galaxies
28 July - 1 August 2008            Keele University (UK)

Outreach: The Interstellar and Intergalactic Mediums
The gas and dust found between stars in space is called the interstellar medium. About 99% of the interstellar medium is gas; the rest is dust. It has a very low density, up to a few hundred million particles per metre. This is not a lot of matter when you consider that the particles are molecular in size.

A simulation of the intergalactic mediumStars form from the interstellar medium in its densest parts. When stars die, the matter is returned to the interstellar medium through planetary nebulae and supernovae.

Intergalactic space contains far less. On average, there is less than one atom for every cubic metre of space. The intergalactic medium surrounds galaxies and stretches between them. It is thought to be ionised hydrogen, which is a plasma containing the same number of protons as electrons.

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