Tracing the ejecta structure of supernova 1987A: Insights and diagnostics from 3D magnetohydrodynamic simulations

Context. Supernova (SN) 1987A provides a unique window into the aftermath of a massive stellar explosion, offering key insights into the ejecta’s morphology, composition, explosion mechanism, progenitor system, and circumstellar medium (CSM) interaction. Aims. This study employs high-resolution three-dimensional magnetohydrodynamic (3D MHD) simulations to investigate large-scale ejecta asymmetries in SN 1987A. By comparing the simulations with JWST observations and making predictions for XRISM, we aim to refine our understanding of the explosion mechanism and the remnant’s evolution. Methods. We performed 3D MHD simulations that trace the evolution of SN 1987A from the SN to its remnant, extending model predictions up to 5000 years into the future, while considering the Ni-bubble effects. We compared the simulation results with JWST observations and used them to predict XRISM spectra in order to provide a means of evaluating the accuracy of the modeled ejecta structure. Results. Our simulations reproduce the large-scale Fe-rich ejecta morphology observed with JWST, revealing two prominent clumps suggestive of a bipolar explosion. The Ni-bubble effect in the first year enhances Fe-rich ejecta expansion, accelerating their interaction with the reverse shock. However, discrepancies with JWST observations in clump velocities and spatial distribution suggest stronger explosion asymmetries than modeled. According to the simulations, since 2021 the contribution of shocked ejecta to the X-ray emission has steadily increased; it now rivals that of the shocked CSM and is expected to soon dominate as the CSM emission continues to fade. Future XRISM observations will trace the evolution of these ejecta structures and help refine constraints on the explosion geometry. Early remnant asymmetries from CSM interaction may persist for at least 100 years. Conclusions. Our findings reinforce the role of highly asymmetric core-collapse mechanisms in shaping SN 1987A’s ejecta and provide critical constraints on explosion geometry. Future studies should investigate more extreme explosion asymmetries, potentially arising from stochastic processes in neutrino-driven core collapse or magneto-rotational SN models in order to identify the mechanism that best explains SN 1987A’s nearly bipolar Fe-rich ejecta structure.