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We present initial results from a JWST survey of the youngest Galacticcore-collapse supernova remnant Cassiopeia A (Cas A), made up of NIRCam andMIRI imaging mosaics that map emission from the main shell, interior, andsurrounding circumstellar/interstellar material (CSM/ISM). We also present fourexploratory positions of MIRI/MRS IFU spectroscopy that sample ejecta, CSM, andassociated dust from representative shocked and unshocked regions. Surprisingdiscoveries include: 1) a web-like network of unshocked ejecta filamentsresolved to 0.01 pc scales exhibiting an overall morphology consistent withturbulent mixing of cool, low-entropy matter from the progenitor's oxygen layerwith hot, neutrino and radioactively heated high-entropy matter, 2) a thicksheet of dust-dominated emission from shocked CSM seen in projection toward theremnant's interior pockmarked with small (approximately one arcsecond) roundholes formed by knots of high-velocity ejecta that have pierced through the CSMand driven expanding tangential shocks, 3) dozens of light echoes with angularsizes between 0.1 arcsecond to 1 arcminute reflecting previously unseenfine-scale structure in the ISM. NIRCam observations place new upper limits oninfrared emission from the neutron star in Cas A's center and tightly constrainscenarios involving a possible fallback disk. These JWST survey data andinitial findings help address unresolved questions about massive starexplosions that have broad implications for the formation and evolution ofstellar populations, the metal and dust enrichment of galaxies, and the originof compact remnant objects.

A JWST Survey of the Supernova Remnant Cassiopeia A