Spin-Orbit Alignment in Merging Binary Black Holes Following Collisions with Massive Stars
Persistent URL
Author(s)
Kiroglu, Fulya
Lombardi, James C., Jr. (Jamie)
Kremer, Kyle
Vanderzyden, Hans D.
Rasio, Frederic A.
Date Issued
April 4, 2025
Abstract
Merging binary black holes (BBHs) formed dynamically in dense star clusters are expected to have uncorrelated spin–orbit orientations since they are assembled through many random interactions. However, measured effective spins in BBHs detected by LIGO/Virgo/KAGRA hint at additional physical processes that may introduce anisotropy. Here we address this question by exploring the impact of stellar collisions and accretion of collision debris on the spin–orbit alignment in merging BBHs formed in dense star clusters. Through hydrodynamic simulations, we study the regime where the disruption of a massive star by a BBH causes the stellar debris to form individual accretion disks bound to each black hole (BH). We show that these disks, which are randomly oriented relative to the binary orbital plane after the initial disruption of the star, can be reoriented by strong tidal torques in the binary near pericenter passages. Following accretion by the BHs on longer timescales, BBHs with small but preferentially positive effective spin parameters (χeff ≲ 0.2) are formed. Our results indicate that BBH collisions in young massive star clusters could contribute to the observed trend toward small positive χeff, and we suggest that the standard assumption often made that dynamically assembled BBHs should have isotropically distributed BH spins is not always justified.
Journal
Astrophysical Journal Letters
Department
Physics
Citation
Fulya Kıroğlu et al 2025 ApJL 983 L9
Publisher
IOP Publishing Ltd
Version of Article
Published version
DOI
10.3847/2041-8213/adc263
ISSN
2041-8205
2041-8213
Rights
© 2025. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
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