Dark-matter spike at the galactic center? art. no. 043504

The past growth of the central black hole (BH) might have enhanced the dens ity of cold dark matter halo particles at the galactic center. We compute t his effect in realistic growth models of the present (2-3) x 10(6) M-., BH from a low-mass seed BH, with special attention to dynamical modeling in a realistic galaxy environment with merger and orbital decay of a seed BH for med generally outside the exact center of the halo. An intriguing "very-den se spike" of dark matter has been claimed in models of Gondolo and Silk wit h a density high enough to contradict with experimental upper bounds of neu tralino annihilation radiation. This "spike" disappears completely or is gr eatly weakened when we include important dynamical processes neglected in t heir idealized or restrictive picture with cold particles surrounding an at -the-center zero-seed adiabatically growing BH. For the seed BH to spiral i n and settle to the center within a Hubble time by dynamical friction, the seed mass must be at least a significant fraction of the present BH. Any su bsequent at-the-center growth of the BH and steepening of the central Keple rian potential well can squeeze the halo density distribution only mildly, whether the squeezing happens adiabatically or instantaneously.