Spiral galaxies that have fallen at least to the core of both the Virgo and Coma clusters have had their gas (neutral hydrogen) depleted in this way and simulations suggest that this process can happen relatively quickly, with 100% depletion occurring in 100 million years to a more gradual few billion years. As galaxies fall toward the center of a cluster, more and more of their gas is stripped out, including the cool, denser gas that is the source of continued star formation. Ram pressure stripping is thought to have profound effects on the evolution of galaxies. These ram pressure stripped galaxies will often have a large trailing tail and because of this they are commonly called "Jellyfish galaxies." Evidence of this ram pressure stripping can be seen in the image of NGC 4402.
This pressure can strip gas out of the galaxy where, essentially, the gas is gravitationally bound to the galaxy less strongly than the force from the intracluster medium 'wind' due to the ram pressure. P ram = ρ u i u j the speed of the galaxy relative to the medium. It causes a drag force to be exerted on the body. Ram pressure is a pressure exerted on a body moving through a fluid medium, caused by relative bulk motion of the fluid rather than random thermal motion. Note the dust (brown) trailing behind (toward upper right) the galaxy, versus the dust-free (blue-white) leading edge. Ram pressure stripping in NGC 4402 as it falls towards the Virgo Supercluster (off image, toward bottom left).
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