The Fraction Of Distilled White Dwarfs With Long-Lived Habitable Zones

After carbon and oxygen, ²²Ne is the most abundant element in white dwarf interiors. As C/O white dwarfs (WDs) crystallize, they are predicted to go through a distillation process in the central layers if they have a sufficiently high ²²Ne mass fraction of ≳2.5%.

Observational evidence for distillation comes from an over-density of WDs on the Q-branch in Gaia color-magnitude diagrams, which indicates that ∼6% of massive WDs are delayed in their cooling by as much as ∼10 Gyr.

However, it is unclear how these stars end up with such a high concentration of ²²Ne and if a significant fraction of the more common average-mass WDs go through distillation. We argue that a significant metal-rich stellar population in the solar neighborhood should lead to distilled WDs, without requiring a binary merger.

We use MESA along with the CNO abundances derived from high-resolution spectroscopy of stars included in the Hypatia catalog to predict the ²²Ne mass fraction in their descendant WDs. We find that 0.6-2.5% of the WDs in the solar neighborhood have sufficient ²²Ne in their interiors to go through multi-Gyr cooling delays, which could significantly inflate their numbers in the observed samples.

Hence, ²²Ne distillation and long-lived habitable zones around WDs should be relatively common in the solar neighborhood. We also use a Galactic model to predict the fraction of WDs that go through distillation as a function of Galactocentric distance. The fraction of distilled WDs is ∼2-8% near the Galactic center, and declines steadily toward the outer disk.

Manuel Barrientos, Mukremin Kilic, Simon Blouin, Michael R. Hayden, Sanjib Sharma, Matthew J. Green

Comments: Accepted for Publication in ApJL. 7 pages, 4 figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2508.12600 [astro-ph.SR] (or arXiv:2508.12600v1 [astro-ph.SR] for this version)
https://doi.org/10.48550/arXiv.2508.12600
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Submission history
From: Manuel Barrientos
[v1] Mon, 18 Aug 2025 03:26:32 UTC (305 KB)
https://arxiv.org/abs/2508.12600

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