Prospects for detection of primordial black holes captured in cold dark matter haloes around massive objects

The capture of cold dark matter species, and especially primordial black holes, during the formation of gravitationally bound objects is analyzed. It is shown that the best conditions for an efficient gravitational capture were at the epoch preceding the galaxy formation, when the first astrophysical objects with masses of the order of Jeans mass 105–106 M were forming. Black hole haloes around old globular clusters, dark matter clusters and Population III stars are considered, and in each case the total mass of the halo and its luminosity due to the Hawking emission are found. Among all the objects considered, large (M >∼ 105 M ), nearby (within ∼ 5 kpc from the Sun) globular clusters are shown to provide the best prospects for detection of the black holes. First, black hole haloes around the globular clusters have the highest brightness near 100 MeV, which is within the reach of EGRET capabilities, and provide distinct observational features. Second, globular clusters are extensively studied at other wavelengths and represent a welldefined target for γ-ray detectors. We have also considered the probability of detecting an isolated black hole bound to the Sun. Our estimates of the mass of gravitationally captured haloes are applicable to any cold dark matter particles.