The nature of dark matter

Peter L. Biermann (Bonn/Tuscaloosa), Alex Kusenko (Los Angeles),
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.