2018/12/31 by Martti Raidal, M. Raidal, Christian Spethmann +2 · 5 citations
Physics and Astronomy · #Astrophysics #Binary black hole #Binary number #Cosmology and Gravitation Theories #Dark matter #Galaxies: Formation, Evolution, Phenomena #Gravitational wave #LIGO #Physics #Primordial black hole #Pulsars and Gravitational Waves Research #Universe #astro-ph.CO #astro-ph.HE #hep-ph
paper · pdf · doi:10.1088/1475-7516/2019/02/018
published as JCAP 1902, 018 (2019) · 32pages, 12 figures, typos corrected, references added, figures updated, matches version published in JCAP
openalex created_date 2018/12/11 · openalex publication_date 2019/02/12 · arxiv created 2019/02/27 · arxiv updated 2019/03/01 · openalex updated_date 2026/08/05
The abundance of primordial black holes (PBHs) in the mass range 0.1–10 3 M ⊙ can potentially be tested by gravitational wave observations due to the large merger rate of PBH binaries formed in the early universe. To put the estimates of the latter on a firmer footing, we first derive analytical PBH merger rate for general PBH mass functions while imposing a minimal initial comoving distance between the binary and the PBH nearest to it, in order to pick only initial configurations where the binary would not get disrupted. We then study the formation and evolution of PBH binaries before recombination by performing N-body simulations. We find that the analytical estimate based on the tidally perturbed 2-body system strongly overestimates the present merger rate when PBHs comprise all dark matter, as most initial binaries are disrupted by the surrounding PBHs. This is mostly due to the formation of compact N-body systems at matter-radiation equality. However, if PBHs make up a small fraction of the dark matter, f PBH ≲ 10%, these estimates become more reliable. In that case, the merger rate observed by LIGO imposes the strongest constraint on the PBH abundance in the mass range 2–160 M ⊙ . Finally, we argue that, even if most initial PBH binaries are perturbed, the present BH-BH merger rate of binaries formed in the early universe is larger than 𝒪 (10) Gpc −3 yr −1 f PBH 3 .