Cassiopeia A, located 11,000 light-years away as observed by NuSTAR. This is the first map of radioactivity in a supernova remnant, the blown-out bits and pieces of a massive star that exploded.

Since the first few minutes after the Big Bang, when the temperature and density of the Universe fell below that which is required for nuclear fusion, stars have been slowly converting their raw materials (predominantly hydrogen and helium) to heavier elements. As stars evolve, the heavier elements that are produced settle into the core of the star until the star can no longer maintain the balance between the force of gravity that is attempting to collapse the star and the pressure from the heat produced by the nuclear burning in the core that prevents the star from collapsing. As the competing forces fall out of balance the can spectacularly explode as either novae or supernovae and eject the heavy elements created during its life back into the galaxy to seed a new generation of stars.

NuSTAR is advancing our understanding of this lifecycle through study of supernovae and supernova remnants. Observations of supernovae probe the physics in the cores of dying stars and provide unique astrophysical laboratories for studying nuclear physics in extreme conditions only dreamed of in laboratories on Earth. The relics of these explosions, supernova remnants, serve as a primary force in driving the chemical evolution of galaxies through successive generations of stars.

NuSTAR is studying the radioactive ash from the supernovae explosions in exquisite detail. This radioactive material serves as a tracer of the supernova explosion and carries information about the otherwise hidden, extreme conditions under which they were produced.

Supernova remnants shape the evolution of galaxies by driving vast blast waves through their stellar neighborhoods, sweeping up material into shock fronts that stimulate the next generation of star formation. These giant shock waves are also believed to power the acceleration of cosmic-ray particles in the local universe. Previous X-ray missions began to address this science, but NuSTAR, with its dramatic improvement in sensitivity, imaging resolution, and spectroscopy, is providing a powerful new tool for studying the processes occurring in these engines.