Abstract
In this paper, we consider the hypothesis that fractions of dark matter could be constituted by primordial black holes (PBHs). To test this possibility, we work out the observational properties of a static black hole embedded in the dark matter envelope made of a PBH source. The corresponding modifications of geometry due to such a physical system are investigated, with a particular focus on the accretion disk luminosity in spiral galaxies. The impact of the PBH presence is analyzed through modification of the disk luminosity and kinematic quantities. Thus, we discuss possible constraints on the PBH abundance in view of the most recent theoretical bounds. The results of our study indicate that suitable PBH masses are ${M}_{\mathrm{PBH}}\ensuremath{\in}[{10}^{6},{10}^{12}]\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ for PBH fractions ${f}_{\mathrm{PBH}}\ensuremath{\in}[{10}^{\ensuremath{-}3},1]$. In particular, a comparison with the predictions of the exponential sphere density profile for dark matter suggests that the best-matching configuration is achieved for ${f}_{\mathrm{PBH}}=1$ and ${M}_{\mathrm{PBH}}={10}^{6}\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$. Consequences with respect to the current knowledge on primordial black hole physics are discussed.