15 November 2009
Jeans Instability, despite its name, has nothing to do with the inherent tendencies of denim-based clothing to split, rend or fail during mission critical applications. This is almost a shame, as the notion of unstable trousers is, to the majority of mankind, far more comprehensible than the following.
Waves and instabilities are often related, and it is in relation to acoustic waves that Jeans Instability arises. When an area of gas is compressed, the pressure increases. This compression is smoothed out by the gas, and in the process acoustic waves are produced - futher areas of compression. Any more compressed areas of gas, however, possess enhanced gravity and thus more gas is pulled into the compressed region.
Normally, this isn't a problem. The minute fluctuations in gravity produced by typical sound waves in the air is negligible, as are the effect. Really - it might as well not have happened for all the effect it has. But transfer this theory to astronomical-sized bodies of gas floating about in deep space, Under such situations the changes in gravity are no longer negligible. More material is pulled to the compressed regions of gas, triggering an instability, and since the nature of this instability was first demonstrated by Jeans in 1902, the instability takes his name.
What form does this instability take? Well, under certain conditions the fluctuations will simply die out; the cloud of gas will disperse and return to its original state. Under other conditions the fluctuations will overpower the pressure of the gas, the perturbation will grow and the gas will continue to contract. It is believed that the stars and galaxies we see around us are the end results of perturbations which initially began as Jeans instabilities.
It should be noted that the instability only occurs for wavelengths greater than a certain size, known as the Jeans length. This length is dependent on density. The Jeans length may, in this case, be directly responsible for the size and distribution of galaxies and other matter in space.