Jeans instability

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Jeans instability

An instability in a cloud of gas in space when fluctuations in the density of the gas cause clumping of the matter as a result of its mutual gravitational attraction. In 1902, Sir James Jeans worked out a criterion, now known as the Jeans criterion, which determines the conditions for this instability to occur in terms of the density and temperature of the gas. This calculation used Newtonian gravity in a static Universe. Extension of this calculation to the case of general relativity theory in an expanding Universe provides the starting point for understanding structure formation in the Universe.
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A thermodynamic problem also occurs with any expression attempting to define the Jeans mass, [M.sub.j], an extensive property, in terms of temperature and mean density, both of which are intensive properties.
Further, this value corresponds to the characteristic gravitational mass, close to the Jeans mass during recombination:
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