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New axion bounds derived from the 100-parsec Gaia DR3 white dwarf luminosity function

M. L. Alberino, M. M. Miller Bertolami, M. E. Camisassa, A. Caputo, S. Torres

Abstract

The axion, a well-motivated hypothetical particle arising in extensions of the Standard Model, can be produced copiously within the hot, compact cores of white dwarf stars. The shape of the white dwarf luminosity function (WDLF) is a powerful tool for constraining theoretical particles that would imply an additional cooling channel in white dwarfs. In this work, and for the first time, we use the 100-parsec Gaia DR3 white dwarf sample and compare it with theoretical predictions. We have simulated synthetic populations of white dwarfs using a population synthesis code based on Monte Carlo techniques, incorporating realistic observational errors, and based on state-of-the-art white dwarf models that incorporate the anomalous cooling caused by the presence of axions. Axion bremsstrahlung emission rates were implemented using the latest theoretical calculations. We find that, for the brightest white dwarfs in the sample ($M_{\mathrm{Bol}} < 10$), the $χ^2$ statistic is largely insensitive to the assumed stellar formation rate (SFR), which is typically the dominant uncertainty in modeling the Galactic-disk WDLF. The resulting $χ^2$ analysis disfavors a sizable additional cooling contribution. This conclusion contrasts with earlier studies in which axion-electron couplings in the range $0.7 \times 10^{-13} < g_{ae} < 2.1 \times 10^{-13}$ provided mildly improved fits to the Galactic-disk WDLF. We attribute the discrepancy to simplifying assumptions in previous modeling and to the substantially improved observational quality of the 100-pc Gaia DR3 sample. We obtain the upper limit $g_{ae} < 1.68 \times 10^{-13}$ ($95\%$ C.L.), which is among the strongest available.

New axion bounds derived from the 100-parsec Gaia DR3 white dwarf luminosity function

Abstract

The axion, a well-motivated hypothetical particle arising in extensions of the Standard Model, can be produced copiously within the hot, compact cores of white dwarf stars. The shape of the white dwarf luminosity function (WDLF) is a powerful tool for constraining theoretical particles that would imply an additional cooling channel in white dwarfs. In this work, and for the first time, we use the 100-parsec Gaia DR3 white dwarf sample and compare it with theoretical predictions. We have simulated synthetic populations of white dwarfs using a population synthesis code based on Monte Carlo techniques, incorporating realistic observational errors, and based on state-of-the-art white dwarf models that incorporate the anomalous cooling caused by the presence of axions. Axion bremsstrahlung emission rates were implemented using the latest theoretical calculations. We find that, for the brightest white dwarfs in the sample (), the statistic is largely insensitive to the assumed stellar formation rate (SFR), which is typically the dominant uncertainty in modeling the Galactic-disk WDLF. The resulting analysis disfavors a sizable additional cooling contribution. This conclusion contrasts with earlier studies in which axion-electron couplings in the range provided mildly improved fits to the Galactic-disk WDLF. We attribute the discrepancy to simplifying assumptions in previous modeling and to the substantially improved observational quality of the 100-pc Gaia DR3 sample. We obtain the upper limit ( C.L.), which is among the strongest available.
Paper Structure (12 sections, 6 equations, 9 figures, 1 table)

This paper contains 12 sections, 6 equations, 9 figures, 1 table.

Table of Contents

  1. Introduction
  2. White dwarf models and input physics
  3. Standard white dwarf physics
  4. Axion emission in white dwarfs
  5. Initial models and white dwarf model grid
  6. Construction of the white dwarf luminosity function
  7. Monte Carlo population synthesis code
  8. Observed and theoretical white dwarf luminosity functions
  9. The bright WDLF and its independence from the star formation history
  10. Impact of the axion emission in the WDLF
  11. Conclusions and future work
  12. Effects of stellar formation bursts on the WDLF

Figures (9)

  • Figure 1: Evolutionary tracks of white dwarfs with $Z = 0.01$ and masses in the range $0.48–1.05\; M_\odot$. Each panel considers different values of $g_{ae}$. The color scale shows the intensity of axion emission relative to the surface luminosity.
  • Figure 2: Left panel: Metallicity Distribution Function (MDF) of the solar neighborhood in terms of [Fe/H], in agreement with 2011AA...530A.138C. Right panel: $Z$ distribution, related to [Fe/H] via $Z = Z_0\;\cdot10^{\;\mathrm{[Fe/H]}}$, where we used $Z_0 = 0.016$ as the total solar metallicity, according to 2025arXiv250305402B.
  • Figure 3: Hess diagrams for the Gaia 100-pc DA white dwarf sample from JE2023 (left panel), against a synthetic thin-disk DA white dwarf population of equal number of objects. Thin blue lines indicate the evolutionary tracks of white dwarfs of different masses. From top to bottom, 0.4, 0.5, 0.6, 0.8 and 0.9 $M_\odot$. The red lines define the selected region of the color-magnitude diagram.
  • Figure 4: left panel: the color-magnitude diagram of the 100 pc white dwarf population classified into DA and non-DA by JE2023. Color palette indicates the DA probability of each WD. Right panels: DA prob. distribution histograms for $9<M_G<11$, $11<M_G<13$, $13<M_G<15$, and $M_G>15$.
  • Figure 5: Contribution of different stellar age bins (0–1.5 Gyr, 1.5–3 Gyr, 3–4.5 Gyr, 4.5–6 Gyr, 6–7.5 Gyr, 7.5-9 Gyr and 9-10.5 Gyr) to each magnitude bin in the WDLF.
  • ...and 4 more figures