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Title: Does neon-22 distillation fully explain the Gaia white-dwarf Q branch delay?
Plain: Gaia found a group of heavy white dwarfs that stop cooling for billions of years, piling up in a narrow strip (the Q branch) of the color-brightness diagram. One proposed cause is that crystals rich in neon float upward and release energy, but whether this works in detail is not settled.
Precise: About 6 percent of white dwarfs with $M \sim 1.08 \text{ to } 1.23\,M_{\mathrm{sun}}$ show an extra cooling delay of approximately 8 Gyr on the Q branch (Cheng, Cummings and Menard 2019). Determine whether 22Ne distillation (buoyant 22Ne-depleted crystals and gravitational energy release in a C/O/22Ne mixture) reproduces the delay length, the fraction of delayed stars and the mass range with a physically motivated 22Ne abundance, and identify which progenitors (single stars, mergers) have that composition.
Settled by: Cooling-model fits with distillation physics to the Gaia Q-branch kinematics and number counts, with a progenitor composition derived from merger or high-metallicity evolution models.
Kind: well-posed
Answer type: yes-no
References: (empty)
Literature status: partially-resolved
Status note: Bedard et al. (Nature, 2024) showed distillation can halt cooling for billions of years if 22Ne is enhanced; a 2026 study found Q-branch merger remnants lack strong magnetism (Ould Rouis et al., ApJ, 2026).
Posed since: 2019