Does neon-22 distillation fully explain the Gaia white-dwarf Q branch delay?
In plain words
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 statement
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.
What would settle it
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.
Status in the literature
Unverified 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).