Electromagnetic instability of compact axion stars

Abstract

If the dark matter is composed of axions, then axion stars are expected to be abundant in the Universe. We demonstrate in fully non-linear (3+1) numerical relativity the instability of compact axion stars due to the electromagnetic Chern-Simons term. We show that above the critical coupling constant $g_{a\gamma }^{\mathrm{crit}}\propto M_s^{-1.35}$, compact axion stars of mass $M_s$ are unstable. The instability is caused by parametric resonance between the axion and the electromagnetic field. The existence of stable compact axion stars requires approximately Planck-suppressed couplings to photons. If the coupling exceeds the critical value, then all stable axion stars are necessarily non-compact. Unstable axion stars decay leaving behind a less massive, less compact, remnant. The emitted radiation peaks at frequency $\omega \sim 1/R_s$, where $R_s$ is the axion star radius.

7 pages, 5 figures

References in corpus (8)

• Cosmic Structure as the Quantum Interference of a Coherent Dark Wave
• Dilute and dense axion stars
• Relativistic axions from collapsing Bose stars
• GRChombo: An adaptable numerical relativity code for fundamental physics
• Gauge-field production during axion inflation in the gradient expansion formalism
• Lessons for adaptive mesh refinement in numerical relativity
• Photons from dark photon solitons via parametric resonance
• Electromagnetic emission from axionic boson star collisions

Cited by in corpus (7)

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• Dark Spin-2 Field Solitons as a Source of Electromagnetic Radiation
• Multimessenger signals from compact axion star mergers
• Exploring the viability of pseudo Nambu-Goldstone boson as ultralight dark matter in a mass range relevant for strong gravity applications
• Detecting the $\pi$-axiverse through parametric resonance