{
  "abstract": "We investigate close encounters between stellar-mass black holes (BHs) in the gaseous discs of active galactic nuclei (AGNs), during which binary black holes (BBHs) may form. We perform a suite of 483 2D adiabatic viscous hydrodynamic simulations within a shearing box prescription using the Eulerian grid code Athena++. We co-evolve the two embedded BHs with the gas. To probe the dependence of capture on non-circular initial conditions, we vary the initial radial separation $b$, the eccentricity $e$ of one of the stellar BHs around the central supermassive black hole, and the eccentric phase angle $ϕ_e$. We consider eccentricities from $e=0$ to $e=0.1$ and compare them with the local disc aspect ratio $h=H/R_0\\simeq0.005$. We find that small eccentricities shift the capture window in the parameter space. Eccentricities of order the disc aspect ratio, in particular $e\\sim h$--$2h$, produce successful captures at initial separations that do not capture in the circular models. By contrast, systems with $e \\gg h$ retain less gas before encounter and have lower capture fractions across the sampled parameter grid. We find that the first periapsis distance is a useful predictor of direct capture. Predicting direct capture for $r_{\\rm p}<0.1r_H$ correctly classifies $92.7\\%$ of Hill sphere encounters. The Hill sphere gas mass helps identify gas-poor failures, but provides no clear additional capture boundary within this suite, in which the initial disc density, temperature, and viscosity parameter are held fixed. Pre-encounter eccentricity modifies gas-assisted BBH formation through its combined effects on the first-encounter geometry and the gas reservoir available for orbital energy dissipation.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.19281",
  "author_total": 3,
  "authors": [
    {
      "name": "Andrew Imai"
    },
    {
      "name": "Henry Whitehead"
    },
    {
      "name": "Bence Kocsis"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/07twqtqvjas7r.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.19281",
  "fulltext_url": null,
  "id": "07twqtqvjas7r",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.19281",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "http://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "astro-ph.GA"
    ],
    [
      "arxiv",
      "astro-ph.HE"
    ],
    [
      "openalex",
      "3103|Astrophysical Phenomena and Observations"
    ]
  ],
  "openalex": "W7213608441",
  "pdf_url": "https://arxiv.org/pdf/2609.19281",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-16",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/07twqtqvjas7r.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:22:19Z",
      "native_id": "2609.19281",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.19281"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.GA",
      "subfield": "galaxies"
    },
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.HE",
      "subfield": "high-energy-astrophysics"
    }
  ],
  "title": "Hydrodynamic Simulations of Eccentric Black Hole Encounters in AGN Discs",
  "title_text": "Hydrodynamic Simulations of Eccentric Black Hole Encounters in AGN Discs",
  "type": "preprint",
  "updated_at": "2026-10-30T12:22:19Z",
  "url": "https://research.draconitic.com/paper/07twqtqvjas7r",
  "venue": "arXiv",
  "versions": []
}