I don't know if this belongs in Astronomy or Cosmology, mods, move it if you see fit. As far as I'm aware the idea of Dark Matter was introduced because of the rotation of galaxies. Closer to a galaxy's centre matter should move faster because of the stronger gravitational pull, and further away from the centre matter should move more slowly. However, matter at the edge of a galaxy appears to be moving at the same speed as matter near the centre of a galaxy. This is only explainable if we have dark matter - the further away from a galaxy's centre, the more mass is needed to create a stronger gravitational pull and so the further away from a galaxy's centre the more dark matter there should be to balance out the gravitational pull and keep everything moving at the same speed. However in 2003 WMAP showed that small density fluctuations in the CMBR were too slight to create galaxies and large-scale structure in the Universe, and could be explained by having clumps of dark matter which photons (the CMBR) didn't interact with. Visible "light" matter then was attracted to these dark matter cores, causing the fluctuations in the CMBR, and then later evolved into galaxies. This would imply that dark matter should be at the centre of galaxies, which contradicts the findings shown in spiral arms. A theory is that quasars are (or were; they are billions of light years away so the light left them billions of years ago and we are seeing them as they were back then) young galaxies exploding into existence. Quasars give out huge amounts of energy and radiation in two jets from the top and bottom - my question is, when galaxies first formed, did they contain a lot of central dark matter? Then when they became active, did the quasar jets effectively clear the dark matter from the centre of the galaxy and the surroundings, leaving the central part of the galaxy virtually devoid of dark matter and the outer regions full of it, meaning that the WMAP findings and the spiral arm rotation curve can get on in perfect harmony? Bear in mind that I am nearly 16 years old and have had no real education in this; my knowledge comes entirely from books, magazines and the internet, so if there is a flaw in my physics I'd be more than happy to have this pointed out to me.