Detecting Axion Stars with Radio Telescopes

TL;DR

This paper estimates the radio signals produced when axion stars interact with neutron stars, suggesting current and future radio telescopes could detect these events and help identify axion stars as dark matter components.

Contribution

It provides a detailed calculation of the electromagnetic radiation power from axion star-neutron star encounters, including interference and medium effects, and assesses detectability with existing telescopes.

Findings

Radiation power can reach 10^{11} W for dense axion stars.

Transient radio signals of about 0.1 seconds may be detectable within our galaxy.

Current and upcoming radio telescopes have high potential to discover dense axion stars.

Abstract

When axion stars fly through an astrophysical magnetic background, the axion-to-photon conversion may generate a large electromagnetic radiation power. After including the interference effects of the spacially-extended axion-star source and the macroscopic medium effects, we estimate the radiation power when an axion star meets a neutron star. For a dense axion star with $10^{-13}\,M_\odot$, the radiated power is at the order of $10^{11}\,\mbox{W}\times(100\,\mu\mbox{eV}/m_a)^4\,(B/10^{10}\,\mbox{Gauss})^2$ with $m_a$ as the axion particle mass and $B$ the strength of the neutron star magnetic field. For axion stars occupy a large fraction of dark matter energy density, this encounter event with a transient $\mathcal{O}(0.1\,\mbox{s})$ radio signal may happen in our galaxy with the averaged source distance of one kiloparsec. The predicted spectral flux density is at the order of $\mu$Jy for a neutron star with $B\sim 10^{13}$ Gauss. The existing Arecibo, GBT, JVLA and FAST and the ongoing SKA radio telescopes have excellent discovery potential of dense axion stars.