JWST Spectroscopy Reveals New Details About Type Ia Supernovae Explosion Mechanisms
Astronomers using the James Webb Space Telescope obtained detailed mid-infrared spectra of two normal Type Ia supernovae, SN 2022aaiq and SN 2024gy, in their nebular phase, uncovering novel narrow emission features from stable nickel at their cores. The observations, spanning 0.35 to 28 microns, reveal a central enhancement of stable nickel consistent with either a near-Chandrasekhar-mass white dwarf progenitor or a high-metallicity sub-Chandrasekhar-mass progenitor, and a spectral morphology matching predictions for deflagration-to-detonation transition explosions. These findings demonstrate that JWST's resolved line profiles can serve as powerful diagnostics for supernova explosion geometry, central density, and progenitor mass—key unknowns in understanding the standard candles used to measure cosmic distances.
A large international team of astronomers has published JWST spectroscopic observations of two normal Type Ia supernovae, SN 2022aaiq and SN 2024gy, covering an unprecedented continuous wavelength range from 0.35 to 28 microns during the nebular phase when the ejecta become transparent. Medium-resolution JWST spectra revealed narrow [Ni II] emission features at 1.94 and 6.64 microns in both supernovae, with the 6.64-micron line displaying a distinct narrow core atop a broader base—a signature interpreted as a central concentration of stable nickel produced at high central densities. Detailed line-profile inversions of SN 2024gy allowed the team to map spatially distinct ejecta zones containing stable iron-group elements, radioactive material, and intermediate-mass elements. A 'broken-slope' morphology in the [Ni III] 7.35-micron line of SN 2024gy matches theoretical predictions for delayed detonation explosions in which deflagration and detonation ashes are spatially separated, providing observational support for the deflagration-to-detonation transition (DDT) model. Comparing stable nickel luminosities across four supernovae—including archival JWST data for SN 2021aefx and the subluminous SN 2022xkq—the authors infer that SN 2024gy produced roughly 5–10 times more stable nickel than SN 2022xkq, favoring a near-Chandrasekhar-mass progenitor for SN 2024gy and a sub-Chandrasekhar-mass progenitor for SN 2022xkq. The study, accepted to The Astrophysical Journal, underscores JWST's unique capability to resolve internal ejecta structure and constrain the long-debated progenitor systems of Type Ia supernovae.
What's missing
The study relies on nebular-phase spectra of only four Type Ia supernovae in total (two new, two archival), limiting statistical generalization of the progenitor mass inferences. The authors acknowledge degeneracy between a near-Chandrasekhar-mass progenitor and a high-metallicity sub-Chandrasekhar-mass progenitor as explanations for the central stable nickel enhancement, meaning the progenitor scenario cannot be uniquely determined from these data alone.
What different sources said
- arXiv astro-phCenter
JWST Spectroscopy of SN Ia 2022aaiq and 2024gy: Evidence for Enhanced Central Stable Ni Abundance and a Deflagration-to-Detonation Transition
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