Examining the Heart of Type Ia Supernova 2021aefx with Ultra-Late Time Spectra

Type Ia supernovae (SNe Ia) are the explosive, thermonuclear deaths of white dwarf stars in multi-star systems. Despite decades of intensive study,
the true nature of their progenitors and the physical mechanism by which they explode are still unknown. SNe Ia provide crucial insights into other
areas of astronomy, including: understanding sources of systematic errors in the use of SNe Ia as cosmological probes, the final phases of stellar
evolution, and the origin and distribution of elements formed in nuclear statistical equilibrium. NIR and MIR ultra-late time spectra with NIRSpec
and MIRI are a new probe, enabled by the sensitivity of JWST to address these longstanding questions. We request 19.8 hrs of JWST time to obtain 3
NIR+MIR spectra of SN 2021aefx between 750-1150 days after B-band max light. These observations will be the first ever ultra-late time SNe Ia
spectra in the NIR and MIR. These data will: (1) reveal the ions responsible for flux redistribution to the IR in late-time SNe Ia, enabling full use of
accurate bolometric light curves; (2) measure the location, composition, and mass of radioactive electron capture elements like 57Co and 55Fe; (3)
determine the origin, strength, and evolution of the magnetic field in the SN; (4) probe macroscopic mixing between the electron capture and nuclear statistical equilibrium regions; and (5) and monitor for potential late-onset H/He interaction signatures. This data will be truly groundbreaking and
push SN physics and observations into previously unexplored areas. Significant progress will be made in our understanding of the heavy elements in
the Universe and SNe Ia as distance indicators.