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Cassiopeia A is a young Galactic supernova remnant, containing expanding stellar debris, shock-heated gas and a compact central object. Observations at different wavelengths reveal different physical components rather than interchangeable pictures of the same emission process.

X-rays trace very hot material and elemental signatures, while infrared observations can reveal cooler dust and gas. Comparing spatial distributions and velocities helps reconstruct how the star exploded and how its ejecta interact with surrounding material.^[ref]

A supernova remnant is the expanding stellar debris and shocked surrounding gas left by a supernova. The debris drives an outward shock wave into the ambient interstellar medium; a reverse shock wave heats the ejecta as the expansion is decelerated. Hot plasma emits X-rays, while accelerated electrons produce synchrotron radiation in the magnetic field. Comparing successive images measures expansion, and X-ray spectroscopy maps the expelled chemical elements. In Cassiopeia A, the Chandra X-ray Observatory resolves the outer shock and heated debris. Such observations connect an explosion's kinetic energy and newly produced elements to the subsequent heating and enrichment of the interstellar medium.^[ref]