Constraints on Axion-like Particles from a Hard $X$-ray Observation of Betelgeuse

TL;DR

This study uses hard X-ray observations of Betelgeuse to search for axion-like particles, setting new upper limits on their coupling to photons based on non-detection of expected signals.

Contribution

First to utilize Betelgeuse's hard X-ray data to constrain axion-like particles, providing novel limits on their properties through astrophysical observations.

Findings

No significant excess detected in X-ray data

Set upper limits on ALP-photon coupling constant

Constraints depend on Galactic magnetic field models

Abstract

We use the first observation of Betelgeuse in hard $X$-rays to perform a novel search for axion-like particles (ALPs). Betelgeuse is not expected to be a standard source of $X$-rays, but light ALPs produced in the stellar core could be converted back into photons in the Galactic magnetic field, producing a detectable flux that peaks in the hard $X$-ray band ($E_\gamma>10\mathrm{\,keV}$). Using a 50 ks observation of Betelgeuse by the $NuSTAR$ satellite telescope, we find no significant excess of events above the expected background. Using models of the regular Galactic magnetic field in the direction of Betelgeuse, we set a 95% C.L. upper limit on the ALP-photon coupling of ${g_{a\gamma}<(0.5-1.8)\times10^{-11}}$ GeV$^{-1}$ (depending on magnetic field model) for ALP masses ${m_{a}<(5.5-3.5) \times10^{-11}}$ eV.