Radio Signals from Axion Star-Neutron Star Binaries

TL;DR

This paper proposes that axion star-neutron star binaries could produce distinctive, detectable radio signals due to axion-photon conversion in strong magnetic fields, offering a new method to search for axion dark matter.

Contribution

It introduces the idea that axion star-neutron star binaries generate unique modulated radio signals, providing a novel observational approach to detect axions.

Findings

Signals are within reach of current and upcoming radio telescopes.

Binary systems produce doubly modulated signals due to neutron star spin and orbital motion.

Potential to use these signals as an astronomical laboratory for axion detection.

Abstract

Axion stars could form binaries with neutron stars. Given the extremely strong external magnetic field exhibited by individual neutron stars, there can be a substantial conversion of axions to photons in these binaries. The photon emission is doubly modulated due to the neutron star spinning and the axion star orbiting, yielding a unique discovery signal. Similar features are also generated in binaries between a neutron star and an axion-clouded black hole. Encouragingly, such binaries are found to be within the reach of ongoing and upcoming experiments (e.g., the Five hundred meter Aperture Spherical Telescope and the future Square Kilometer Array) for certain parameter regions. They thus provide a promising astronomical laboratory for detecting axions and axion dark matter.