The jellyfish galaxy JW39 hangs calmly in this image from the NASA/ESA Hubble Space Telescope. This galaxy is located 900 million light-years away in the constellation Coma Berenices and is one of several jellyfish galaxies that Hubble has been working on for the past two years.

Despite the placid appearance of the jellyfish galaxy, it is being brutally dragged into a hostile environment: a galaxy cluster. Compared to their more isolated counterparts, galaxies in galaxy clusters are often distorted by the gravitational pull of larger neighbors, which can bend galaxies in various ways. If that wasn't enough, the space between galaxies in a cluster is also occupied by a scorching hot plasma known as the intracluster medium. While this plasma is extremely weak, galaxies moving through it experience it almost like swimmers battling a current, and this interaction can extract the galaxies' star-forming gas.

This interaction between the intra-cluster medium and galaxies is called impact pressure stripping, and it is the process responsible for the posterior branches of the jellyfish galaxy. As JW39 moved through the cluster, the pressure of the intra-cluster environment split the gas and dust into long star-forming lanes that now extend away from the galactic disk.

Astronomers using Hubble's Wide Field Camera 3 have studied these back branches in detail, as they are a particularly extreme environment for star formation. Surprisingly, they found that star formation in the 'tentacles' of jellyfish galaxies was not markedly different from star formation in the galaxy disk.

 

Source: 1