Can local White Dwarfs constrain Dark Matter interactions?

TL;DR

This work assesses whether nearby white dwarfs can constrain DM–nucleon interactions by exploiting DM capture in WD interiors and annihilation into long-lived mediators that decay to gamma rays outside the star. Using a local WD sample within 13 pc and a finite-temperature relativistic EoS to model the cores, the authors compute capture rates, evaporation masses, and the possibility of capture–annihilation equilibrium, then predict a box-shaped gamma-ray spectrum from mediator decays. An analysis of 16 years of Fermi-LAT data yields no significant gamma-ray excess, establishing current bounds that are limited by geometric capture in this regime; however, projected sensitivities for CTA, LHAASO, and SWGO indicate that DM–nucleon cross sections as low as $\sim 10^{-41}\,\text{cm}^2$ could be probed for $m_χ$ in the TeV–PeV range, with CTA-South and LHAASO providing the strongest constraints. Overall, the results highlight the complementary role of WD-based indirect searches alongside direct-detection experiments like LZ, expanding the accessible DM parameter space and motivating systematic WD studies in future DM explorations.

Abstract

We investigate whether nearby white dwarfs (WDs) can constrain dark matter (DM) interactions with ordinary matter. As experimental sensitivity improves, driven by the Gaia mission, the sample volume of nearby WDs has been increasing over recent years. We carefully select a sample of ten cold, isolated, non-magnetic WDs within 13~pc of the Sun. We model their carbon-oxygen interior using a finite temperature relativistic equation of state and model atmospheres to infer their core temperatures. This enables us to perform a thorough estimation of the DM capture rate and evaporation mass using actual astrophysical observations. Given the low local DM density, we focus on DM that annihilates into long-lived mediators, which escape the WD and later decay into photons. While \textit{Fermi}-LAT data shows no significant gamma-ray excess, future telescopes, CTA North \& South, LHAASO, SWGO, could probe DM-nucleon cross sections down to $\sim 10^{-41}~\text{cm}^2$ for DM masses above the TeV scale. Our results are competitive with current direct detection bounds (e.g., LZ) in the multi-TeV regime. This work underscores the importance of systematic WD studies in the broader landscape of DM detection and demonstrates the synergy between astrophysical and terrestrial searches in exploring DM interactions.

Figures (5)

• Figure 1: Radial profiles for the core density (left) and escape velocity (right) for six of the ten sources in Table \ref{['tab:source_datails']}. Profiles were calculated for the core temperatures in the second column of Table \ref{['tab:wd_evaporation']}.
• Figure 2: Finite temperature effects on the DM capture rate for six WDs in our local sample. The dashed lines denote the evaporation mass.
• Figure 3: Geometric (threshold) DM-proton cross section, above which the DM capture rate saturates the geometric limit, for the same WDs as in Fig. \ref{['fig:Cfinitetemp']}.
• Figure 4: Sensitivity projections on the DM-proton scattering cross sections from three local white dwarfs, for (a) CTA North, (b) CTA South, (c) SWGO, (d) LHAASO.
• Figure 5: Sensitivity projections from source 9 for future gamma-ray telescopes and comparison with the LZ spin-independent limits (shaded regions) for single LZ:2024zvo and multiple scattering LZ:2024psa.