The aftermath of a cosmic cataclysm, supernova remnant Cassiopeia A (Cas A) is a comfortable 11,000 light-years away. Light from the Cas A supernova, the death
explosion of a massive star, first reached Earth just 330 years ago. Still
expanding, the explosion's debris cloud spans about 15 light-years near the center of this composite image. The scene combines color data of the starry field and fainter filaments of material at
optical energies with image data from the orbiting NuSTAR X-ray telescope. Mapped to false colors, the X-ray data in blue hues trace the fragmented outer boundary of the
expanding shock wave, glowing at energies up to 10,000 times the energy of the optical photons.