How Common Are Common Envelopes? Quantifying Their Role in Forming Gravitational-Wave Sources
Abstract
A central goal of gravitational-wave astronomy is to use merging binary black hole (BBH), black hole-neutron star (BHNS), and binary neutron star (BNS) systems as fossils to reconstruct the formation and evolution of massive stars across cosmic time. In practice, this inference relies on population-synthesis models that map massive stellar binaries to merging compact objects. However, these models disagree on the dominant orbital-hardening mechanisms within isolated binary evolution, particularly on whether common-envelope (CE) evolution is required. To address this, we compile and systematically compare formation-channel predictions from more than 200 isolated-binary population-synthesis simulations, organized within a unified hierarchical taxonomy. We find that BBH and BHNS formation pathways span nearly the full allowed range from CE-dominated to without-CE-dominated evolution (0-100%), while often predicting similar merger rates, revealing a fundamental degeneracy: merger-rate measurements alone do not uniquely constrain the underlying evolutionary pathways. In contrast, BNS formation proceeds almost exclusively through channels involving at least one CE phase (>90-100%), suggesting CE evolution plays a qualitatively different role in BNS than in BBH and BHNS formation. The relative contributions of with-CE and without-CE pathways are governed primarily by assumptions controlling mass-transfer stability, angular-momentum loss, CE efficiency, and supernova physics, which often act non-linearly and in correlated fashion, such that trends from one-at-a-time parameter variations do not generalize across simulation frameworks. Robust interpretation of gravitational-wave populations will therefore require transparent formation-channel definitions, reproducible analysis pipelines, systematic cross-code comparisons, and observational constraints that extend beyond merger rates alone.
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BibTeX
@misc{broekgaarden2026common,
title = {{How Common Are Common Envelopes? Quantifying Their Role in Forming Gravitational-Wave Sources}},
author = {Floor S. Broekgaarden and Ana Lam and Sasha Levina and Jakub Klencki and Kyle A. Rocha and Lieke van Son and Steffani M. Grondin and Monica Gallegos-Garcia and Brian D. Metzger and Enrico Ramirez-Ruiz and Angela Twum and Melanie Santiago and Julia Haynes and Tyler B. Smith and Amedeo Romagnolo and Edo Berger and Lucas M. de Sá},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2606.05322},
eprint = {2606.05322},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2606.05322},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - How Common Are Common Envelopes? Quantifying Their Role in Forming Gravitational-Wave Sources
AU - Floor S. Broekgaarden
AU - Ana Lam
AU - Sasha Levina
AU - Jakub Klencki
AU - Kyle A. Rocha
AU - Lieke van Son
AU - Steffani M. Grondin
AU - Monica Gallegos-Garcia
AU - Brian D. Metzger
AU - Enrico Ramirez-Ruiz
AU - Angela Twum
AU - Melanie Santiago
AU - Julia Haynes
AU - Tyler B. Smith
AU - Amedeo Romagnolo
AU - Edo Berger
AU - Lucas M. de Sá
PY - 2026
DA - 2026/10/26
PB - arXiv
DO - 10.48550/arxiv.2606.05322
UR - https://arxiv.org/abs/2606.05322
AB - A central goal of gravitational-wave astronomy is to use merging binary black hole (BBH), black hole-neutron star (BHNS), and binary neutron star (BNS) systems as fossils to reconstruct the formation and evolution of massive stars across cosmic time. In practice, this inference relies on population-synthesis models that map massive stellar binaries to merging compact objects. However, these models disagree on the dominant orbital-hardening mechanisms within isolated binary evolution, particularly on whether common-envelope (CE) evolution is required. To address this, we compile and systematically compare formation-channel predictions from more than 200 isolated-binary population-synthesis simulations, organized within a unified hierarchical taxonomy. We find that BBH and BHNS formation pathways span nearly the full allowed range from CE-dominated to without-CE-dominated evolution (0-100%), while often predicting similar merger rates, revealing a fundamental degeneracy: merger-rate measurements alone do not uniquely constrain the underlying evolutionary pathways. In contrast, BNS formation proceeds almost exclusively through channels involving at least one CE phase (>90-100%), suggesting CE evolution plays a qualitatively different role in BNS than in BBH and BHNS formation. The relative contributions of with-CE and without-CE pathways are governed primarily by assumptions controlling mass-transfer stability, angular-momentum loss, CE efficiency, and supernova physics, which often act non-linearly and in correlated fashion, such that trends from one-at-a-time parameter variations do not generalize across simulation frameworks. Robust interpretation of gravitational-wave populations will therefore require transparent formation-channel definitions, reproducible analysis pipelines, systematic cross-code comparisons, and observational constraints that extend beyond merger rates alone.
ER -