This false-color composite image of the Stephan's Quintet galaxy cluster clearly shows one of the largest shock waves ever seen (the green arc above), produced by one galaxy falling toward another at over a million miles per hour. It is made up of data from NASA's Spitzer Space Telescope and a ground-based telescope in Spain. What makes the Stephan's Quintet of galaxies so fascinating are the rare red blobs found in NGC 7320, the brightest of the group.
These extensive red H II regions have hyper active star formation. Space telescopes have recently provided new insight into the nature of the strange green filament, which is now believed to be a giant intergalactic shock-wave caused as NGC 7318B collides into the center of the group creating a huge shock wave bigger than the Milky Way that 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.