The effect of triples on the Chemically Homogeneous Evolution Channel for producing Gravitational Wave Sources
Abstract
Despite the growing number of gravitational-wave (GW) detections, the formation of merging binary black holes (BBHs) is still debated. One of the proposed formation channels is Chemically Homogeneous Evolution (CHE), which makes distinct predictions for the properties of the resulting black holes (BHs): high masses (≳35 M⊙) and large, orbitally-aligned spins. These predictions are based on studies that consider this channel only in isolated binaries. However, most massive stars reside in triples. We investigate how a tertiary affects the CHE channel. We use detailed binary models computed with MESA for the inner CHE systems coupled with analytical prescriptions for the hierarchical triple dynamics. Specifically, we study the von Zeipel-Lidov-Kozai mechanism that can accelerate the merger of the inner BBHs through high-eccentricity excitations. We show that a tertiary companion enables mergers at higher metallicities, where the classical binary CHE channel does not operate. At Z⊙/3, triples produce BHs with lower masses (around 15 M⊙) and lower spins (around 0.25) compared to the low-metallicity classical scenario. We further expect triple dynamics to lead to spin-orbit misalignment and potential residual eccentricities at merger. In triples at Z⊙/3, half of the mergers occur within 1 Gyr. Moreover, 10% of the population leads to prompt mergers within 1 Myr (1% within 1 kyr) that are of potential interest for electromagnetic counterparts. We conclude that the triple CHE channel is promising as (i) it may contribute more substantially to the local merger rate than had been expected for the classical CHE channel due to the shorter delay times and effectiveness at higher metallicities and (ii) produces mergers with properties that more closely resemble the lower masses and lower spins inferred for most of the observed GW merger population.
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BibTeX
@misc{popa2026effect,
title = {{The effect of triples on the Chemically Homogeneous Evolution Channel for producing Gravitational Wave Sources}},
author = {Silvia A. Popa and Selma E. de Mink and Stephen Justham and Jakob Stegmann and Alejandro Vigna-Gomez and Lieke A. C. van Son},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.14353},
eprint = {2610.14353},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.14353},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - The effect of triples on the Chemically Homogeneous Evolution Channel for producing Gravitational Wave Sources
AU - Silvia A. Popa
AU - Selma E. de Mink
AU - Stephen Justham
AU - Jakob Stegmann
AU - Alejandro Vigna-Gomez
AU - Lieke A. C. van Son
PY - 2026
DA - 2026/10/09
PB - arXiv
DO - 10.48550/arxiv.2610.14353
UR - https://arxiv.org/abs/2610.14353
AB - Despite the growing number of gravitational-wave (GW) detections, the formation of merging binary black holes (BBHs) is still debated. One of the proposed formation channels is Chemically Homogeneous Evolution (CHE), which makes distinct predictions for the properties of the resulting black holes (BHs): high masses (≳35 M_⊙) and large, orbitally-aligned spins. These predictions are based on studies that consider this channel only in isolated binaries. However, most massive stars reside in triples. We investigate how a tertiary affects the CHE channel. We use detailed binary models computed with MESA for the inner CHE systems coupled with analytical prescriptions for the hierarchical triple dynamics. Specifically, we study the von Zeipel-Lidov-Kozai mechanism that can accelerate the merger of the inner BBHs through high-eccentricity excitations. We show that a tertiary companion enables mergers at higher metallicities, where the classical binary CHE channel does not operate. At Z_⊙/3, triples produce BHs with lower masses (around 15 M_⊙) and lower spins (around 0.25) compared to the low-metallicity classical scenario. We further expect triple dynamics to lead to spin-orbit misalignment and potential residual eccentricities at merger. In triples at Z_⊙/3, half of the mergers occur within 1 Gyr. Moreover, 10% of the population leads to prompt mergers within 1 Myr (1% within 1 kyr) that are of potential interest for electromagnetic counterparts. We conclude that the triple CHE channel is promising as (i) it may contribute more substantially to the local merger rate than had been expected for the classical CHE channel due to the shorter delay times and effectiveness at higher metallicities and (ii) produces mergers with properties that more closely resemble the lower masses and lower spins inferred for most of the observed GW merger population.
ER -