Massive primordial black holes in contemporary universe

TL;DR

This paper investigates primordial black holes as dark matter candidates, adjusting their initial mass spectrum based on observational data, and discusses potential resolutions for discrepancies with observed MACHO densities.

Contribution

It proposes a method to fit primordial black hole mass spectra to observational data and explores possible explanations for MACHO abundance discrepancies.

Findings

Predicted MACHO density is about ten times lower than observed.

Adjustments to the initial PBH mass spectrum could reconcile theory with observations.

MACHOs might be primordial black holes or dead primordial stars.

Abstract

The parameters of the original log-normal mass spectrum of primordial black holes (PBH) are approximately adjusted on the basis of existing observational data on supermassive black holes in the galactic centers and the mass distribution of the near-solar mass black holes in the Galaxy. Together with the assumption that PBHs make all or a noticeable mass fraction of the cosmological dark matter, it allows to fix the parameters of the original mass spectrum. The predicted, in this way, the number density of MACHOs is found to be about an order of magnitude below the observed value. A possible resolution of this controversy may be prescribed to the non-isotropic and inhomogeneous distribution of MACHOs or to the modification of the original spectrum, e.g. assuming a superposition of two-maximum log-normal spectra of PBHs. A competing possibility is that MACHOs are not PBHs but dead primordial compact stars.