Electromagnetic instability of compact axion stars

Understand

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.