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Implications of the LISA stochastic signal from eccentric stellar mass black hole binaries in vacuum

Ran Chen1,2,3,*, Rohit S. Chandramouli3,4,5,†, Federico Pozzoli6, Riccardo Buscicchio7,8,9, and Enrico Barausse3,4,5

  • *Contact author: ranchen@pmo.ac.cn
  • †Contact author: rchandra@sissa.it
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Phys. Rev. D 114, 063026 – Published 10 September, 2026

DOI: https://doi.org/10.1103/pbdv-rf6j

Abstract

Astrophysical formation channels of stellar-mass binary black holes (sBBHs) can induce significant orbital eccentricities in their early inspiral. We analyze the implications on the stochastic gravitational-wave background (SGWB) from unresolved sBBHs, which can be detected with the Laser Interferometer Space Antenna (LISA). We develop an improved SGWB model for the case of an idealized Dirac-delta eccentricity distribution, and extend it to the more astrophysical case of a thermal distribution. Using a fully Bayesian framework, we find that, if all binaries have a high initial eccentricity e0≳0.9 at an orbital frequency of forb=10−4  Hz, the resulting SGWB can be robustly distinguished from a background of quasicircular sBBHs. For a thermal eccentricity distribution, the SGWB is consistent with a circular model when binaries form at forb=10−5  Hz, but leads to significant systematic biases if formation occurs at forb=10−4  Hz. We also show that, when eccentricity is properly accounted for, environmental effects such as dynamical friction can be distinguished from vacuum evolution, but only for sufficiently dense environments with gas densities ρ≳10−7  g cm−3. Finally, we show that a LISA detection of the sBBH SGWB would place an upper bound on the maximum eccentricity of the sBBH population in the band of ground-based detectors, with direct implications for template modeling and data analysis. Our results highlight the importance of incorporating eccentricity in SGWB modeling to enable accurate astrophysical interpretation of LISA observations.

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Environmental effects in the LISA stochastic signal from stellar-mass black hole binaries

Ran Chen, Rohit S. Chandramouli, Federico Pozzoli, Riccardo Buscicchio, and Enrico Barausse
Phys. Rev. D 112, 084053 (2025)

Article Text

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Phys. Rev. D 114, 063026– Published 10 September, 2026
  • Received 8 May 2026
  • Accepted 10 August 2026
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