Deciphering the Remnants of Core-Collapse Supernovae: Reconstructing Progenitor Star Properties and Explosion Mechanisms

Recent observations of the supernova remnant (SNR) Cassiopeia A (Cas~A) with the James Webb Space Telescope (JWST) have revealed unprecedented details of its structure, including an intricate network of ejecta filaments and an enigmatic structure known as the "Green Monster" (GM), characterized by a pockmarked appearance with nearly circular holes and rings. These discoveries offer unique insights into the mechanisms governing supernova (SN) explosions and the subsequent evolution of ejecta and circumstellar medium (CSM) interactions. In this contribution, I present recent theoretical work based on high-resolution three-dimensional (3D) hydrodynamic (HD) and magnetohydrodynamic (MHD) simulations of a neutrino-driven SN explosion resembling Cas A. The models follow the system from core collapse to an age of $\sim 1000$ years, with the aim of investigating the origin and evolution of these newly observed structures. The simulations incorporate key physical processes, including neutrino-driven explosion dynamics, hydrodynamic instabilities, Ni-bubble effects, and radiative losses, while accounting for deviations from ionization equilibrium and electron–proton temperature equilibration. The new studies show that a web-like network of ejecta filaments, closely resembling those observed by JWST, naturally forms during the early stages of the explosion as a consequence of hydrodynamic instabilities and the dynamic interplay of hot neutrino-driven bubbles. These filaments preserve a "memory" of the initial explosion conditions before being gradually disrupted by the reverse shock over centuries. In parallel, the peculiar morphology of the GM can be reproduced by the interaction of dense clumps and fingers of ejecta with an asymmetric, forward-shocked CSM shell. Radiative cooling and non-equilibrium ionization further enhance fragmentation, producing dense knots and thin filaments that penetrate the shell and create the observed network of holes and rings. Our model highlights how the complex structures observed today in Cas~A reflect both the imprint of the early SN explosion and the later interactions of ejecta with the surrounding medium, offering a unified view of the remnant's rich morphology.