In Stephan's Quintet, the shock wave is due to the intruder galaxy traveling at speeds greater than Mach 100 as it plows into intergalactic gas within the cluster.
It's a little bit analogous to dropping a stone into a pond, and watching a ripple and then sometimes a second ripple go out from the center.
We know that these galaxies are involved in vast mergers and collisions. It's possible that some of the emission we see from them is created not by stars, but by vast shocks in the gas between colliding galaxies.
This website focuses on proverbs in the Swedish, Danish and Norwegian languages, and some parts including the links below have not been translated to English. They are mainly FAQs, various information and webpages for improving the collection.
This website focuses on proverbs in the Swedish, Danish and Norwegian languages, and some parts including the links below have not been translated to English. They are mainly FAQs, various information and webpages for improving the collection.