The search for dark matter axions from neutron stars in the inner parsecs of the Milky Way with AtLAST

TL;DR

This work proposes a cm–mm axion search in the Galactic Center by leveraging resonant axion–photon conversion in neutron-star magnetospheres, amplified by an extreme dark matter density spike and a large population of NSs. The approach relies on detecting narrow spectral features produced when the local plasma frequency matches the axion mass ($ω_p ∼ m_a$) in magnetized NS environments, with the integrated signal from many NSs enabling detectability. The key contribution is outlining how AtLAST’s combination of collecting area, sensitivity, wide field-of-view, and cm–mm coverage uniquely enables probing a previously inaccessible region of axion parameter space. If successful, this method would provide a new, astrophysical probe of the QCD axion or axion-like particles and significantly constrain the axion–photon coupling $g_{aγγ}$ for relevant mass ranges.

Abstract

The magnetospheres of neutron stars in the Galactic Center provide an exceptional environment to search for dark matter axions through their resonant conversion into photons. The combination of extreme magnetic fields and high dark matter density in this region creates ideal conditions for axion-photon conversion across the centimetre-to-submillimetre wavelength range. Detecting the cumulative emission from these neutron star populations demands a facility with unprecedented sensitivity, spatial resolution, and broad frequency coverage in the submillimetre domain, capabilities essential to explore a previously inaccessible region of axion parameter space.

Figures (3)

• Figure 1: Conceptual overview of the proposed AtLAST search for Dark Matter axions in the Galactic Centre.
• Figure 1: Current limits on the axion--photon coupling, $g_{a\gamma\gamma}$, as a function of axion mass. The green band labelled "Neutron stars" is relevant to this white paper (black arrow). Reprinted from ciaran_o_hare_2020_3932430.
• Figure 2: Resonant axion--photon conversion frequency versus altitude above the NS surface. The calculation DEMIGUEL2025139328 compares two magnetospheric models: a young pulsar (blue; Timokhin et al.) and a magnetar (red; Beloborodov). Solid lines mark the resonance condition $\omega_p\!\sim\!m_a$, and dotted lines the GJ prediction. Pulsar: $B_0=10^{13}\,$G, $P=0.1$ s; magnetar: $B_0=5\times10^{14}$ G, $P=5$ s. All calculations assume $R_\ast=12$ km.