Dark-matter spike at the galactic center?
The past growth of the central black hole (BH) might have enhanced the density of cold dark matter halo particles at the galactic center. We compute this effect in realistic growth models of the present (2-3)×106M⊙ 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 formed generally outside the exact center of the halo. An intriguing "very-dense spike" of dark matter has been claimed in models of Gondolo and Silk with a density high enough to contradict with experimental upper bounds of neutralino annihilation radiation. This "spike" disappears completely or is greatly weakened when we include important dynamical processes neglected in their idealized or restrictive picture with cold particles surrounding an at-the-center zero-seed adiabatically growing BH. For the seed BH to spiral in 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 subsequent at-the-center growth of the BH and steepening of the central Keplerian potential well can squeeze the halo density distribution only mildly, whether the squeezing happens adiabatically or instantaneously.
Additional Information©2001 The American Physical Society Received 29 January 2001; published 20 July 2001 We thank A. Loeb for useful discussions. This work was supported in part at Caltech by NSF AST-0096023, NASA NAG5-8506, and DOE DE-FG03-92-ER40701, and at Trieste by the RTN project under grant HPRN-CT-2000-00152. H.S.Z. wishes to thank Institut d'Astrophysique de Paris and Sterrewacht Leiden for financial support and Caltech for hospitality during his visit.
Published - ULLprd01.pdf