  Not all astrophysical mechanisms of the emission of electromagnetic radiation
including $X$-- and $\gamma$-- rays coming from the space are clear. We find
that charged unstable particles as well as neutral unstable particles with
non--zero magnetic moment which live sufficiently long may emit electromagnetic
radiation. This new mechanism is connected with the properties of unstable
particles at the post exponential time region. Analyzing the transition time
region between exponential and non-exponential form of the survival amplitude
it is found that the instantaneous energy of the unstable particle can take
very large values, much larger than the energy of this state for times from the
exponential time region. Basing on the results obtained for the model
considered, it is shown that this purely quantum mechanical effect may be
responsible for causing unstable particles to emit electromagnetic--, $X$-- or
$\gamma$--rays at some time intervals from the transition time regions.
