RT fingers evident in the Crab Nebula
The Rayleigh-Taylor instability, or RT instability, or, less commonly, the Richtmyer-Meshkov instability, occurs any time a dense, heavy fluid is being accelerated by light fluid. This is the case with a cloud and shock system, or when a fluid of a certain density floats above a fluid of lesser density, such as oil floating above water.
Two completely plane-parallel layers of immiscible fluid are stable, but the slightest perturbation leads to tangential gravity. Any small local minimum will quickly be amplified by material flowing down under the influence of this force. Dimples are quickly magnified into sets of inter-penetrating RT fingers as the heavy material moves down and the light material flows up.
This process is evident not only in many terrestrial examples, from boiling water to weather inversions , but also in astrophysics and astronomy. RT fingers are especially obvious in the Crab Nebula, in which hot gas from the explosion is ramming into the surrounding interstellar medium, and they give rise to the familiar clumpy appearance of material in these and several other astronomical objects.
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