Energy Dissipation of Axionic Boson Stars in Magnetized Conducting Media

Axions are possible candidates of dark matter in the present Universe. They have been argued to form axionic boson stars with small masses $\sim 10^{-12}M_{\odot}$. Since they possess oscillating electric fields in a magnetic field, they dissipate their energies in magnetized conducting media. We show that colliding with a magnetized white dwarf, the axionic boson stars dissipate their energies and heat the white dwarf. Consequently the white dwarf cooled sufficiently can emit detectable amount of radiations with the collision. Using a recent evaluation of the population of the white dwarfs as candidates of MACHOs, we estimate the event rate of the collisions and obtain a result that the rate is large to be detectable.