There are a number of different structures in the Universe. Solar systems, star clusters, galaxies, galaxy clusters and superclusters. Each of these has their own associated population of dust or gas within which the various planets, stars or even galaxies swirl. Moving through a fluid creates ‘ram’ pressure – the wind on your face when biking for instance. In the case of the Virgo galaxy cluster, it has been seen that this pressure is sufficient to strip gas from galaxies and even force that gas together to form new stars. The Hubble Space Telescope (before repair) took a few images of this happening to two galaxies.
NGC 4522 is a spiral galaxy that lies sixty million light years from us and travels through the dust of the Virgo cluster at ten million kilometres an hour. This extreme velocity leads to extreme ram pressure stripping and even star formation within the stripped material. The reduction of material within the galactic disc is likely to reduce the amount available for star formation inside the galaxy itself.
NGC 4402 in the same cluster is a little more sedate, but nevertheless has seemingly been warped into a convex shape by the pressures associated with ram stripping.