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arXiv · 2108.11389

Cooling Delays from Iron Sedimentation and Iron Inner Cores in White Dwarfs

M. E. Caplan·I. F. Freeman·C. J. Horowitz·A. Cumming·E. P. Bellinger
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Abstract

Do white dwarfs have inner cores made of iron? Neutron rich nuclei like $^{56}$Fe experience a net gravitational force and sediment toward the core. Using new phase diagrams and molecular dynamics simulations, we show that $^{56}$Fe should separate into mesoscopic Fe-rich crystallites due to its large charge relative to the background. At solar abundances, these crystallites rapidly precipitate and form an inner core of order 100 km and $10^{-3} M_\odot$ that may be detectable with asteroseismology. Associated cooling delays could be up to a Gyr for low mass white dwarfs but are only $\sim$0.1 Gyr for massive white dwarfs, so while this mechanism may contribute to the Q-branch the heating is insufficient to fully explain it.

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M. E. Caplan, I. F. Freeman, C. J. Horowitz, A. Cumming, E. P. Bellinger. 2021-08-25. Cooling Delays from Iron Sedimentation and Iron Inner Cores in White Dwarfs. https://doi.org/10.3847/2041-8213%2Fac1f99

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