MACHO Messages from the Big Bang

Abstract

The present day mass spectrum for dark matter compact objects is calculated based on the assumption that a uniform population of PBHs was created at a definite redshift with a uniform mass and that the mass spectrum evolved as a result of gravitational radiation. The predicted present day spectrum extends over many decades of mass and allows one to connect the abundance of MACHOs in the halo of our galaxy with the abundance of galactic seeds. Present day astrophysical constraints on the abundance of dark matter PBHs appear to be consistent with our predicted mass spectrum if it is assumed that the seeds for the present day dark matter MACHOs were created at a time ∼ 10 −4 seconds after the big bang. Remarkably the total cosmological energy density at this time obtained by extrapolating the sum of the present day dark matter and CMB energies backward in time and is very close to the mass-energy density in an Einstein-de Sitter universe at the same time. This suggests that the radiation precursor to the CMB was created at about the same time as the seeds for the present day dark matter.DOI: 10.31526/LHEP.1.2018.04Some time ago it was suggested [1], [2] that the dark matter component of the matter in today's universe might consist entirely of primordial black holes (PBHs). It was also pointed out [3] in a flat universe whose mass-energy density is dominated by primordial black holes it would perhaps be natural for all matter to eventually consist of horizon mass black holes. Of course these proposals begged the question as to why dark matter should consist of black holes rather than some other exotic form of non-baryonic matter such as WIMPs or axions. On the other hand the persistent failure to find any evidence for WIMPs or cosmic axions has perhaps tipped the balance in favor of PBHs [4], [5] In this letter we focus on the question of what the present day spectrum of dark matter compact objects might have to say about the form of matter near the onset of the big bang. We show that if an initially uniform population of PBHs evolves as a result of gravitational radiation during binary collisions, then the present day mass spectrum for primordial compact objects will smoothly interpolate between the MACHO objects which could form the halo of our galaxy [6] and the massive seeds for the compact objects at the center of galaxies [7], [8],[9]. This puts constraints on the redshift where the initial PBHs were formed, which naturally leads to the question as to the form matter took prior to this redshift. An intriguing possibility is that the PBH precursors to the present day MACHOs and the radiation precursors to CMB were both created at the same redshift by the release of entropy from massive compact objects created at the onset of the big bang.Our basic assumption is that the present day population of dark matter MACHOs evolved from an initial population of compact objects with nearly the same mass M DM created at a specific redshift z r .We will also assume that during the radiation dominated era z < z r the...

PopSyCLE: A New Population Synthesis Code for Compact Object Microlensing Events

“…The additions above are necessary to provide support for primordial black holes (PBHs) in PopSyCLE. Ultimately, we plan to implement a PBH mass spectrum such that PBHs can be injected with their own position, velocity, and mass distributions that differ from the underlying stellar halo (Carr et al 2016;Chapline & Barbieri 2018). Similar to the IFMR, a variety of different mass spectra could be implemented.…”