  A Bose star passing through cold molecular clouds may capture atoms,
molecules and dust particles. The observational signature of such an event
would be a relatively small amount of matter that is gravitationally bound.
This binding may actually be provided by invisible dark matter forming the Bose
star. We may expect a relative excess of heavier atoms, molecules, and solid
dust compared to the content of giant cold molecular clouds since the velocity
of heavy particles at a given temperature is lower and it may be small compared
to the escape velocity, $v_\mathrm{rms} = \sqrt{3k_\mathrm{B} T/m_\mathrm{gas}}
\ll v_\mathrm{esc}=\sqrt{2GM/R}$. Finally, the velocity of this captured matter
cloud may correlate with the expected velocity of free dark matter particles
(e.g. expected axion wind velocity relative to Earth).
