A shock wave bigger than the Milky Way

Stephan’s Quintet is located in Pegasus constellation, being a visual grouping of five gallaxies of which four form the first compact galaxy group ever discovered. It was dicovered by Édouard Stephan in 1877 at Marseilles Observatory, becoming the most studied of all compact galaxies groups.

The brightest member of the grouping is NGC 7320 that is shown to have extensive H II regions, identified as red blobs, where active star formation is occurring. Four of the five galaxies in Stephan’s Quintet form a physical association, Hickson Compact Group 92, and are involved in a cosmic dance that most likely will end with the galaxies merging.

These galaxies have stirred interest among reseachers because of their violent collisions, as radio observations in the early 1970s revealed a mysterious filament of emission which lies in the inter-galactic space between the galaxies in the group. This region can be perceived in the faint glow of ionized atomic hydrogen seen in the visible part of the spectrum as the magnificent green arc in the picture to the right.

Two space telescopes have recently provided new insight into the nature of the strange filament, which is now believed to be a giant intergalactic shock-wave (similar to a sonic boom but traveling in intergalactic gas rather than air) caused by one galaxy (NGC 7318B) falling into the center of the group at several millions of miles per hour. As NGC 7318B collides with gas in the group, a huge shock wave bigger than the Milky Way spreads throughout the medium between the galaxies, heating some of the gas to temperatures of millions of degrees, where they emit X-rays detectable with the NASA Chandra X-ray Observatory.

Distance from Earth: ~ 210 – 340 million light years.

Click below for full resolution picture of Stephan’s Quintet