Good things always come in 3s: trimodality in the binary black-hole chirp-mass distribution supports bimodal black-hole formation

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Main Authors: Willcox, Reinhold, Schneider, Fabian R. N., Laplace, Eva, Podsiadlowski, Philipp, Maltsev, Kiril, Mandel, Ilya, Marchant, Pablo, Sana, Hugues, Li, Tjonnie G. F., Hertog, Thomas
Format: Preprint
Published: 2025
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author Willcox, Reinhold
Schneider, Fabian R. N.
Laplace, Eva
Podsiadlowski, Philipp
Maltsev, Kiril
Mandel, Ilya
Marchant, Pablo
Sana, Hugues
Li, Tjonnie G. F.
Hertog, Thomas
author_facet Willcox, Reinhold
Schneider, Fabian R. N.
Laplace, Eva
Podsiadlowski, Philipp
Maltsev, Kiril
Mandel, Ilya
Marchant, Pablo
Sana, Hugues
Li, Tjonnie G. F.
Hertog, Thomas
contents The latest GWTC-4 release from the LIGO-Virgo-KAGRA (LVK) collaboration nearly doubles the known population of double compact object mergers and reveals a new trimodal structure in the chirp-mass distribution of merging binary black holes (BBHs) below 30 Msun. Recent detailed stellar evolution models show that features in the pre-collapse cores of massive stars produce a bimodal black hole (BH) mass distribution, which naturally extends to a trimodal BBH chirp-mass distribution. Both distributions depend only weakly on metallicity, implying universal structural features which can be tested with LVK observations. Using a new compact-remnant mass prescription derived from these models, we perform rapid population synthesis simulations to test the robustness of the predicted chirp-mass structure against uncertainties in binary evolution and cosmic star formation history, and compare these results with the current observational data. The trimodal chirp-mass distribution emerges as a robust outcome of the new remnant-mass model, persisting across variations in binary and cosmic physics. In contrast, traditional BH formation models lacking a bimodal BH mass spectrum fail to reproduce the observed trimodality. The updated models also predict lower BBH merger rates by a factor of a few, in closer agreement with LVK constraints. Intriguingly, the central chirp-mass peak, dominated by unequal-mass BBHs, originates from a previously underappreciated formation pathway in which strong luminous blue variable winds suppress binary interaction before the first BH forms. If isolated binary evolution dominates BBH formation below 30 Msun, the relative heights of the three chirp-mass peaks offer powerful observational constraints on core collapse, BH formation, binary evolution, and cosmic star formation. These universal structural features may also serve as standard sirens for precision cosmology.
format Preprint
id arxiv_https___arxiv_org_abs_2510_07573
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Good things always come in 3s: trimodality in the binary black-hole chirp-mass distribution supports bimodal black-hole formation
Willcox, Reinhold
Schneider, Fabian R. N.
Laplace, Eva
Podsiadlowski, Philipp
Maltsev, Kiril
Mandel, Ilya
Marchant, Pablo
Sana, Hugues
Li, Tjonnie G. F.
Hertog, Thomas
Solar and Stellar Astrophysics
High Energy Astrophysical Phenomena
The latest GWTC-4 release from the LIGO-Virgo-KAGRA (LVK) collaboration nearly doubles the known population of double compact object mergers and reveals a new trimodal structure in the chirp-mass distribution of merging binary black holes (BBHs) below 30 Msun. Recent detailed stellar evolution models show that features in the pre-collapse cores of massive stars produce a bimodal black hole (BH) mass distribution, which naturally extends to a trimodal BBH chirp-mass distribution. Both distributions depend only weakly on metallicity, implying universal structural features which can be tested with LVK observations. Using a new compact-remnant mass prescription derived from these models, we perform rapid population synthesis simulations to test the robustness of the predicted chirp-mass structure against uncertainties in binary evolution and cosmic star formation history, and compare these results with the current observational data. The trimodal chirp-mass distribution emerges as a robust outcome of the new remnant-mass model, persisting across variations in binary and cosmic physics. In contrast, traditional BH formation models lacking a bimodal BH mass spectrum fail to reproduce the observed trimodality. The updated models also predict lower BBH merger rates by a factor of a few, in closer agreement with LVK constraints. Intriguingly, the central chirp-mass peak, dominated by unequal-mass BBHs, originates from a previously underappreciated formation pathway in which strong luminous blue variable winds suppress binary interaction before the first BH forms. If isolated binary evolution dominates BBH formation below 30 Msun, the relative heights of the three chirp-mass peaks offer powerful observational constraints on core collapse, BH formation, binary evolution, and cosmic star formation. These universal structural features may also serve as standard sirens for precision cosmology.
title Good things always come in 3s: trimodality in the binary black-hole chirp-mass distribution supports bimodal black-hole formation
topic Solar and Stellar Astrophysics
High Energy Astrophysical Phenomena
url https://arxiv.org/abs/2510.07573