  Using simple physical reasoning we have estimated the wavelengths and
line-widths of spectral lines arising from the decays of massive neutrinos. We
have, also, to some extent, discussed the possible consequences of these decays
in observable astrophysical settings. We have compared our conclusions with the
predictions of the decaying dark matter (DDM) model and cold + hot dark matter
(${\rm C\nu ^2DM}$) model.
