Magnetized White Dwarf Collapse Identified as Source of Heavy Elements and Kilonova Signals
Researchers have published the first end-to-end simulation linking the accretion-induced collapse (AIC) of a magnetized, rapidly rotating white dwarf to observable kilonova signatures, finding it can produce heavy r-process elements. Unlike previous unmagnetized AIC models that predicted proton-rich ejecta, strong magnetic fields in the new model drive roughly 0.2 solar masses of neutron-rich material outward before neutrino irradiation can alter the electron fraction. The findings offer a new candidate progenitor for long-duration gamma-ray bursts accompanied by kilonova signals, and the synthetic light curves match observations of AT 2023vfi/GRB 230307A without parameter tuning.
A study published in Monthly Notices of the Royal Astronomical Society presents the first complete computational pipeline connecting the accretion-induced collapse of a magnetized, rapidly rotating white dwarf to detectable kilonova emission. Using 2D general-relativistic neutrino-magnetohydrodynamic simulations combined with radiation hydrodynamics, an in-situ nuclear network, and 2D Monte Carlo radiative transfer, the team found that strong magnetic fields eject approximately 0.2 solar masses of neutron-rich material with a mean electron fraction of about 0.24 on dynamical timescales. This occurs before neutrino irradiation can raise the electron fraction, enabling robust r-process nucleosynthesis extending to and beyond the so-called third peak of heavy elements. The resulting kilonova is lanthanide-rich (lanthanide mass fraction ~8%) and dominated by near-infrared emission, consistent with signatures expected from heavy r-process material. Synthetic light curves computed in LSST and JWST bands show striking agreement with observations of the kilonova AT 2023vfi associated with GRB 230307A, particularly for polar viewing angles, without any parameter tuning. The results challenge the previous consensus that AIC events produce only proton-rich, nickel-56-dominated ejecta, and establish magnetized AIC as a plausible alternative channel for heavy element production alongside neutron star mergers.
What's missing
The study does not discuss the expected rate or volumetric frequency of magnetized AIC events relative to neutron star mergers, which would be needed to assess their overall contribution to cosmic r-process enrichment.
What different sources said
- arXiv astro-phCenter
Collapse of Magnetized White Dwarfs as site of Heavy Element Formation and Kilonova Signal
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