Prof. Peter Birmann, The Nature of Dark Matter

Friday 16 Mar 2007, 11:00 → 12:00 Europe/Bucharest

Dark matter could light up the first stars in the universe if the dark matter is made up of weakly interacting neutrinos, right-handed neutrinos, or also called 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 main prediction of warm dark matter, that all dwarf spheroidal galaxies should have the same dark matter mass, has been verified; the galaxy mass suggests also a keV dark matter particle. The X-ray emission from neighboring dwarf and normal 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. The high pulsar velocities may also be explained with a transition from normal to sterile neutrinos. While all pieces of evidence may find a separate solution, a keV right handed neutrino could provide a unifying picture. This may lead to a decisive step in determining the nature and mass of the dark matter particles, suggesting as one solution a Weakly Interacting Neutrino, or WIN, of a few keV.