  Sterile neutrinos may be one of the best Warm Dark Matter candidates we have
today. Both lower and upper bounds on the mass of the sterile neutrino come
from astronomical observations. We show that the proper inclusion of the
neutrino momentum distribution reduces the allowed region to be 2.6 keV < m < 5
keV for the simplest models. A search for a spectral line with E=m/2 is thus
more interesting than ever before.
