Radiations from Axion Miniclusters and Axion Boson Stars in Galactic Magnetic Fields

Axions have been shown to form miniclusters or boson stars typically with their mass, $\sim 10^{-12}M_{\odot}$ in the early Universe. We show that the axion miniclusters and the axion boson stars in galactic magnetic fields produce radiations with the frequency approximately equal to the mass of an axion. This is because these coherent axion clumps have oscillating electric dipole moments in the magnetic fields. In the case of axion mass, $10^{-5}$ eV, their luminosity of the radiation is given such as $\sim 10^8L_{\odot}$ ($10^{-3}L_{\odot}$) for the miniclusters (the boson stars) under the galactic magnetic field, $10^{-6}$ G.