Unified Description of Dark Matter at the Center and in the Halo of the Galaxy

Neven Bilic1, Gary B. Tupper2 and Raoul D. Viollier2

1 Ruder Boskovic Institute, P.O. Box 180, 10002 Zagreb, Croatia
2 Institute of Theoretical Physics and Astrophysics, Department of Physics,
University of Cape Town, Private Bag, Rondebosch 7701, South Africa

E-mail contact: viollier@physci.uct.ac.za

astro-ph/0111366

We consider a self-gravitating ideal Fermi gas at finite temperature as a model for dark matter in the Galaxy. The temperature-mass ratio of the fermions is determined by fitting the Galactic rotation curve, taking into account the contributions from the baryonic bulge and disk. The dark halo of solar masses, enclosed within a radius 200 kpc, implies the existence of a quasi-degenerate supermassive compact dark object at the Galactic center that is in hydrostatic and quasi- thermal equilibrium with the halo. The central object, having a maximal mass of 2.3 x 106 solar masses and a minimal radius of 20 mpc for a fermion mass 15 keV, is consistent with the motion of stars within 10 mpc of the Galactic center, the infrared drop of the spectrum of Sgr A* at 1013 Hz and quiescent state X-ray emission observed by the Chandra satellite within 0.5 arcsec or 20 mpc of the Galactic center. The required 15 keV fermion could be a sterile neutrino that decays into an active neutrino and a photon of 7.5 keV with a lifetime of about 1020 years.