Galaxies speeding through clusters of their neighbours

Galaxies speeding through clusters of their neighbors were imaged by the Hubble Space Telescope being stripped of their gas.

NGC 4522, the galaxy pictured above, is traveling at 6.2 million miles per hour, astronomers estimate. It’s about 60 million light-years away in the Virgo cluster. The bright blue areas to the right and left are star-forming regions.

Unlike our own Milky Way galaxy with its delicate spiral arms, fast-moving galaxies like NGC 4522 get deformed by the strong winds generated by their movement. The process is known as “ram pressure stripping” and it’s analogous to what would happen were you to hold a dandelion parachute ball out a car window. The lighter parts get stripped away.

Galaxy NGC 4402, pictured below, shows off the convex gas and dust disc that is characteristic of galaxies undergoing ram pressure stripping. The hot gas between galaxies in a cluster (known as the intra-cluster medium) actually sweeps the gas away, creating the odd shape in the process.

The images were taken by the Advanced Camera for Surveys instrument before it suffered a power failure in 2007. The images were recovered when astronauts restored the unit in May of this year on the last Hubble Servicing Mission. Both are deep enough to show distant background galaxies.