Can you imagine living in this region of space? Just think of the beautiful views you’d have in the sky – that is, if you survived the chaos as one galaxy is passing through the core of three other galaxies at ridiculous (ludicrous?) speeds (3.2 million km per hour / 2 million miles per hour) generating a shock wave of gas and X-rays.
This is Stephen’s Quintet, A compact group of galaxies, discovered about 130 years ago, located about 280 million light years from Earth. The curved, light blue ridge running down the center of the image shows X-ray data from the Chandra X-ray Observatory. The galaxy in the middle, NGC 7318b is passing through the core of the other galaxies at high speed and is thought to be causing the ridge of X-ray emission by generating a shock wave that heats the gas. The most prominent galaxy in front (NGC 7320) is actually far away from the other galaxies and is not part of the group.
Additional heating by supernova explosions and stellar winds has also probably taken place in Stephan’s Quintet. A larger halo of X-ray emission – not shown here – detected by ESA’s XMM-Newton could be evidence of shock-heating by previous collisions between galaxies in this group. Some of the X-ray emission is likely also caused by binary systems containing massive stars that are losing material to neutron stars or black holes.
Stephan’s Quintet provides a rare opportunity to observe a galaxy group in the process of evolving from an X-ray faint system dominated by spiral galaxies to a more developed system dominated by elliptical galaxies and bright X-ray emission. Being able to witness the dramatic effect of collisions in causing this evolution is important for increasing our understanding of the origins of the hot, X-ray bright halos of gas in groups of galaxies.