From : http://www.spacetelescope.org/news/heic1404/
“These streaks are actually hot young stars, encased in wispy streams of gas that are being torn away from the galaxy by its surroundings as it moves through space. This violent galactic disrobing is due to a process known as ram pressure stripping — a drag force felt by an object moving through a fluid [1]. The fluid in question here is superheated gas, which lurks at the centres of galaxy clusters.”
