As seen from Earth, a massive Milky Way star died in a supernova explosion some 325 years ago. But the dead star's burned-out core isn't fading away quietly. Astronomers have evidence that that the cinder recently underwent its own outburst.
In infrared portraits taken a year apart, NASA's Spitzer Space Telescope examined Cassiopeia A, the youngest known supernova remnant in the galaxy. The remnant consists of an outer, shimmering shell of material expelled by the supernova explosion and a dense, collapsed core known as a neutron star.