Cassiopeia A (Cas A) is a supernova remnant located in our Galaxy about 11,000 light years away in the constellation Cassiopeia. These are the remains of a massive star that exploded about 330 years ago, as measured in Earth's time frame. It is the brightest extrasolar radio source in the sky at frequencies above 1 GHz. At the center of the image is a neutron star, an ultra-dense star created by the supernova. Ten years of observations with Chandra have revealed a 4% decline in the temperature of this neutron star, an unexpectedly rapid cooling. This cooling is likely caused by a neutron superfluid forming in its central regions, the first direct evidence for this bizarre state of matter in the core of a neutron star. Release date February 23, 2011.