English

Eccentric Black Hole Mergers in Active Galactic Nuclei

High Energy Astrophysical Phenomena 2021-01-27 v2 Astrophysics of Galaxies

Abstract

The astrophysical origin of gravitational wave (GW) transients is a timely open question in the wake of discoveries by LIGO/Virgo. In active galactic nuclei (AGNs), binaries form and evolve efficiently by interaction with a dense population of stars and the gaseous AGN disk. Previous studies have shown that stellar-mass black hole (BH) mergers in such environments can explain the merger rate and the number of suspected hierarchical mergers observed by LIGO/Virgo. The binary eccentricity distribution can provide further information to distinguish between astrophysical models. Here we derive the eccentricity distribution of BH mergers in AGN disks. We find that eccentricity is mainly due to binary-single (BS) interactions, which lead to most BH mergers in AGN disks having a significant eccentricity at 0.01Hz0.01\,\mathrm{Hz}, detectable by LISA. If BS interactions occur in isotropic-3D directions, then 88--30%30\% of the mergers in AGN disks will have eccentricities at 10Hz10\,\mathrm{Hz} above e10Hz0.03e_{10\,\rm Hz}\gtrsim 0.03, detectable by LIGO/Virgo/KAGRA, while 55--17%17\% of mergers have e10Hz0.3e_{10\,\rm Hz}\geq 0.3. On the other hand, if BS interactions are confined to the AGN-disk plane due to torques from the disk, with 1-20 intermediate binary states during each interaction, or if BHs can migrate to 103pc\lesssim10^{-3}\,\mathrm{pc} from the central supermassive black hole, then 1010--70%70\% of the mergers will be highly eccentric (e10Hz0.3e_{10\,\rm Hz} \geq 0.3), consistent with the possible high eccentricity in GW190521.

Keywords

Cite

@article{arxiv.2010.10526,
  title  = {Eccentric Black Hole Mergers in Active Galactic Nuclei},
  author = {Hiromichi Tagawa and Bence Kocsis and Zoltan Haiman and Imre Bartos and Kazuyuki Omukai and Johan Samsing},
  journal= {arXiv preprint arXiv:2010.10526},
  year   = {2021}
}

Comments

9 pages, 3 figures, accepted in ApJL

R2 v1 2026-06-23T19:29:58.796Z