Read more: http://www.newscientist.com/article/dn16369?DCMP=youtube
This new movie of the supernova remnant Cassiopeia A was made by combining Chandra X-ray satellite observations taken in January 2000, February 2002, February 2004 and December 2007. The debris is expanding more slowly than expected, probably because the energy of the explosion is being used to magnetically accelerate particles, turning them into cosmic rays
(Courtesy of NASA/CXC/SAO/D Patnaude et al.)