Mahapatra, Parthapratim, Chattopadhyay, Debatri, Gupta, Anuradha, Favata, Marc, Sathyaprakash, B. S.  ORCID: https://orcid.org/0000-0003-3845-7586 and Arun, K. G.
2025.
Predictions of a simple parametric model of hierarchical black hole mergers.
Physical Review D (particles, fields, gravitation, and cosmology)
111
(2)
, 023013.
10.1103/PhysRevD.111.023013
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Abstract
The production of black holes with masses between ∼50M⊙−130M⊙ is believed to be prohibited by stellar processes due to (pulsational) pair-instability supernovae. Hierarchical mergers of black holes in dense star clusters are proposed as a mechanism to explain the observations of binary black holes with component masses in this range by LIGO/Virgo. We study the efficiency with which hierarchical mergers can produce higher and higher masses using a simple model of the forward evolution of binary black hole populations in gravitationally bound systems like stellar clusters. The model relies on pairing probability and initial mass functions for the black hole population, along with numerical relativity fitting formulas for the mass, spin, and kick speed of the merger remnant. We carry out an extensive comparison of the predictions of our model with clusterBHBdynamics (cBHBD) model, a fast method for the evolution of star clusters and black holes therein. For this comparison, we consider three different pairing functions of black holes and consider simulations from high- and low-metallicity cluster environments from cBHBD. We find good agreements between our model and the cBHBD results when the pairing probability of binaries depends on both total mass and mass ratio. We also assess the efficiency of hierarchical mergers as a function of merger generation and derive the mass distribution of black holes using our model. We find that the multimodal features in the observed binary black hole mass spectrum—revealed by the nonparametric population models—can be interpreted by invoking the hierarchical merger scenario in dense, metal-rich, stellar environments. Further, the two subdominant peaks in the GWTC-3 component mass spectrum are consistent with second and third-generation mergers in metal-rich, dense environments. With more binary black hole detections, our model could be used to infer the black hole initial mass function and pairing probability exponents.
| Item Type: | Article |
|---|---|
| Date Type: | Publication |
| Status: | Published |
| Schools: | Physics and Astronomy |
| Publisher: | American Physical Society |
| ISSN: | 2470-0010 |
| Date of First Compliant Deposit: | 3 February 2025 |
| Date of Acceptance: | 11 December 2024 |
| Last Modified: | 03 Feb 2025 15:00 |
| URI: | https://orca.cardiff.ac.uk/id/eprint/175411 |
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