  The annihilation rate of weakly interacting cold dark matter particles at the
galactic center could be greatly enhanced by the growth of a density spike
around the central supermassive black hole (SBH). Here we discuss the effects
of hierarchical mergers on the central spike. Mergers between halos containing
SBHs lead to the formation of SBH binaries which transfer energy to the dark
matter particles, lowering their density. The predicted flux of annihiliation
photons from the galactic center is several orders of magnitude smaller than in
models that ignore the effects of SBHs and mergers. Measurement of the
annihilation radiation could in principle be used to constrain the merger
history of the galaxy.
