The nature of dark matter
Peter L. Biermann (Bonn/Tuscaloosa), Alex Kusenko (
Faustin Munyaneza
(London/Bonn), \& Jaroslaw Stasielak
(Bonn/Cracow)
Dark matter could light up the first stars in the universe if the dark matter
is made up of sterile neutrinos. We have shown that sterile neutrino decays
could speed up the formation
of molecular hydrogen and light up the first stars as early as 20-100 million
years after the big bang. The light from these first stars could ionize the
interstellar gas by 150-400 million years after the big bang, in accordance
with the observations. Formation of central galactic black holes, as well as
structure on subgalactic scales favor some form of
warm dark matter, such as sterile neutrinos, as dark matter. The consensus of
several indirect pieces of evidence leads one to believe that the long
sought-after dark-matter particle may, indeed, be a sterile neutrino. The
Galactic center black hole and its mass may provide a crucial limit for the mass
of the sterile neutrino: Assuming that the mass of the Galactic Center
Black hole is all due to dark matter growth, and that there is little
additional baryonic growth, gives a lower limit to the dark matter particle mass.
The X-ray emission from neighboring galaxies, the Virgo cluster as well as the
X-ray background give an upper limit at almost the same number; the Lyman
$\alpha$-forest gives also a lower limit. This may lead to a decisive step in
determining the nature and mass of the dark matter particles, suggesting as one
solution a sterile neutrino of a few to a few tens of keV.