Galaxy collision forces physicists to reconsider dark matter thoery


Far away from the milky way, many galaxies are coalescing into a massive super-galaxy. This observation has forced physicists to rethink the existing theories of dark matter. Dark matter does not absorb nor emit light, and is thought to make up 90% of the mass of the universe.
http://news.nationalgeographic.com/news/2007/08/070822-dark-matter.html