Primordial Black Hole Dark Matter Simulations Using PopSyCLE

Abstract

Primordial black holes (PBHs), theorized to have originated in the early Universe, are speculated to be a viable form of dark matter. If they exist, they should be detectable through photometric and astrometric signals resulting from gravitational microlensing of stars in the Milky Way. Population Synthesis for Compact-object Lensing Events, or PopSyCLE , is a simulation code that enables users to simulate microlensing surveys, and is the first of its kind to include both photometric and astrometric microlensing effects, which are important for potential PBH detection and characterization. To estimate the number of observable PBH microlensing events, we modify PopSyCLE to include a dark matter halo consisting of PBHs. We detail our PBH population model, and demonstrate our PopSyCLE + PBH results through simulations of the Optical Gravitational Lensing Experiment-IV (OGLE-IV) and Nancy Grace Roman Space Telescope (Roman) microlensing surveys. We provide a proof-of-concept analysis for adding PBHs into PopSyCLE , and thus include many simplifying assumptions, such as f _DM , the fraction of dark matter composed of PBHs, and ${\bar{m}}_{\mathrm{PBH}}$ , mean PBH mass. Assuming ${\bar{m}}_{\mathrm{PBH}}=30$ M _⊙ , we find ∼3.6 f _DM times as many PBH microlensing events than stellar evolved black hole events, a PBH average peak Einstein crossing time of ∼91.5 days, estimate on order of 10 ^2 f _DM PBH events within the 8 yr OGLE-IV results, and estimate Roman to detect ∼1000 f _DM PBH microlensing events throughout its planned microlensing survey.

Keywords

• Primordial black holes
• Dark matter
• Gravitational microlensing
• Astrometric microlensing effect
• Microlensing parallax
• Microlensing event rate