{
  "abstract": "In dense stellar environments such as globular clusters and active galactic nucleus (AGN) disks, stellar-mass black holes (sBHs) may frequently collide with massive stars. We investigate this process using semi-analytic models, three-dimensional hydrodynamical simulations, and one-dimensional stellar evolution calculations, focusing on collisions between sBHs and a $100\\,M_\\odot$ main-sequence star. We find that gas drag retains the BH within the stellar envelope unless the impact velocity exceeds $\\sim2\\sqrt{G(M_\\star+M_\\bullet)/R_\\star}$. The post-collision outcome depends primarily on the BH-to-star mass ratio. For $M_\\bullet\\gtrsim30\\,M_\\odot$, the retained envelope is either quasi-spherical or disc-like, but remains dynamically unstable because of shock heating. In contrast, for $M_\\bullet\\lesssim10\\,M_\\odot$, the collision forms a ``black hole star'' (BH*): a quasi-hydrostatic, extended stellar envelope surrounding the embedded BH. These results agree with our analytic prediction that BH* formation necessarily requires $M_\\bullet\\lesssim0.2\\,M_\\star$. Follow-up \\texttt{MESA} calculations further show that, for these low-mass BHs, the shock-heated remnant thermally relaxes without triggering runaway expansion. We discuss several astrophysical implications of BH*s, including their evolution, the possibility of gravitational-wave events from BH binaries assembled within a stellar envelope, and repeated star--sBH collisions as a pathway for rapid BH growth in dense stellar systems. This mechanism may contribute to the formation of massive BHs in high-redshift nuclear star clusters and may be relevant to the origin of the ``little red dots'' discovered by JWST.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2608.27596",
  "author_total": 5,
  "authors": [
    {
      "name": "Yanlong Shi"
    },
    {
      "name": "Qingru Hu"
    },
    {
      "name": "Zhenghao Xu"
    },
    {
      "name": "Douglas N. C. Lin"
    },
    {
      "name": "Norman Murray"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/efmevd3m9dd4j.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2608.27596",
  "fulltext_url": null,
  "id": "efmevd3m9dd4j",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2608.27596",
  "language": null,
  "licence": "LicenseRef-arXiv-nonexclusive-1.0",
  "licence_label": "arXiv licence",
  "licence_source": "article",
  "licence_url": "http://arxiv.org/licenses/nonexclusive-distrib/1.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "astro-ph.GA"
    ],
    [
      "arxiv",
      "astro-ph.HE"
    ],
    [
      "arxiv",
      "astro-ph.SR"
    ],
    [
      "openalex",
      "3103|Astrophysical Phenomena and Observations"
    ]
  ],
  "openalex": "W7204802404",
  "pdf_url": "https://arxiv.org/pdf/2608.27596",
  "pmcid": null,
  "pmid": null,
  "published": "2026-08-27",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/efmevd3m9dd4j.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:17:22Z",
      "native_id": "2608.27596",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2608.27596"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.GA",
      "subfield": "galaxies"
    },
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.HE",
      "subfield": "high-energy-astrophysics"
    },
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.SR",
      "subfield": "stellar"
    }
  ],
  "title": "Formation of black hole stars via star--black hole collisions",
  "title_text": "Formation of black hole stars via star--black hole collisions",
  "type": "preprint",
  "updated_at": "2026-10-30T12:17:22Z",
  "url": "https://research.draconitic.com/paper/efmevd3m9dd4j",
  "venue": "arXiv",
  "versions": []
}