Gravitational waves from the merger of two primordial black hole clusters

Abstract

The orbital evolution of a binary system consisting of two primordial black hole clusters is investigated. Such clusters are predicted in some theoretical models with broken symmetry in the inflation Lagrangian. A cluster consists of the most massive central black hole surrounded by many smaller black holes. Similar to single primordial black holes, clusters can form gravitationally bounded pairs and merge during their orbital evolution. The replacement of single black holes by such clusters significantly changes the entire merger process and the final rate of gravitational wave bursts in some parameter ranges (with sufficiently large cluster radii). A new important factor is the tidal gravitational interaction of the clusters. It leads to an additional dissipation of the orbital energy, which is transferred into the internal energy of the clusters or carried away by black holes flying out of the clusters. Comparison with the data of gravitational-wave telescopes allows one to constrain the fractions of primordial black holes in clusters, depending on their mass and compactness. Even the primordial black hole fraction in the composition of dark matter ≃ 1 turns out to be compatible with LIGO/Virgo observational data, if the black holes are in clusters.

On the primordial binary black hole mergings in LIGO-Virgo-Kagra data

“…Should the twobump chirp-mass distribution of the merging binary BH persist in future enhanced statistics of sources detected in the forthcoming O4 LVK observing run, it can indicate the formation of PBHs with a narrow log-normal mass spectrum (1) around the central mass M c ∼ 30M comprising at least f pbh ∼ 10 −3 CDM fraction. Taking into account of the PBH clustering [45] will increase f pbh .…”

“…Dynamical interactions in PBH clusters offers additional channel for the orbital energy dissipation thus increasing the merging rate of PBH binaries, and the constraints on f pbh obtained by assuming a homogeneous PBH space distribution can be lower limits. A recent analysis in [45] using the PBH formation model [19,40] shows that even f pbh ∼ 0.1 − 1 is not excluded.…”

JWST data and possible interpretation

“…A recent analysis performed in paper [55] permits to conclude that a possible clustering of PBH could significantly reduce efficiency of the merger process and the final rate of gravitational wave bursts in some parameter range. As a result the fraction of PBH in dark matter could be as large as unity without distortion of LIGO/Virgo observational data.…”

Lifting the tension of HST and JWST data with conventional cosmology by PBHs

“…A recent analysis performed in ref. [31], based on the PBH formation model of papers [32,33], shows that even 𝑓 𝑃𝐵𝐻 = 0.1 − 1 is not excluded.…”