Further Strong Evidence that Dark Matter Exists


In August 2006, NASA announced new and very strong evidence of dark matter.  David Clowe and his colleagues used NASA’s Chandra X-Ray Satellite to image the Bullet Cluster of galaxies, which consists of two clusters that have been colliding for millions of years.  Since stars are so far apart, the stars of the two galaxies passed right through each other.  Most of the "normal" matter in the universe (baryonic matter) is in the form of gas particles, which interact with each other.  In a merging cluster, these interactions cause the gas to collide and remain in the center of the image in red.  The Dark Matter, believed to be non-interacting or very weakly interacting, stays behind with the stars/galaxies.  Astronomers used the weak gravitational lensing technique to "weigh" the components and that's what's colored in blue:  where most of the mass is located.  It's not centered on the collisional gas, where most of the baryons are, but rather on the individual galaxies.  This is contradictory to the prediction of Modified Newtonian Gravity (MOND), a alternative theory to Dark Matter.
Further details are available at: http://www.nasa.gov/vision/universe/starsgalaxies/dark_matter_proven.html
An even more recent discovery of dark matter by the Hubble Space Telescope can be found at: http://www.nasa.gov/mission_pages/hubble/news/dark_matter_ring_feature.html