{
  "abstract": "Event Horizon Telescope (EHT) images of black holes appear as rings with a brightness asymmetry. Here, we expand on our previous study of the asymmetry magnitude a 1 to study the position angle of the peak brightness asymmetry P A 1 in general relativistic magnetohydrodynamic (GRMHD) models. For larger spin magnitudes ( a * > 0 and a * ≲ − 0.5 ), the mean P A 1 falls within 1 σ of the approaching limb of the black hole, regardless of viewing inclination, disk magnetization, or source. By comparing the ( a 1 , P A 1 ) distribution in M87* observations with models, we demonstrate that we can mildly disfavor low-magnitude spins and strongly disfavor all spin vectors that point toward Earth. The alignment of P A 1 relative to the large-scale jet axis may suggest that M87 ’s disk does not have a large tilt. By combining P A 1 with the pattern speed measured in optimistic 2026 M87 video conditions, the EHT can constrain whether M87* is prograde or retrograde with ∼ 84 % accuracy. In Sgr A*, we show that a detection of ( a 1 , P A 1 ) could constrain the magnitude and direction of the galactic center spin vector. Finally, if future EHT expansions increase the sample of horizon-scale sources, a simple set of observables (ring diameter, asymmetry magnitude, and asymmetry angle) could enable robust constraints on black hole mass, spin, and inclination.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": null,
  "author_total": 7,
  "authors": [
    {
      "name": "Nicholas S. Conroy"
    },
    {
      "name": "Michi Bauböck"
    },
    {
      "name": "Vadim Bernshteyn"
    },
    {
      "name": "Paul Tiede"
    },
    {
      "name": "Abhishek V. Joshi"
    },
    {
      "name": "Cora Prather"
    },
    {
      "name": "Charles F. Gammie"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/4xq66fanze7x9.bib",
  "cited_by": 0,
  "doi": "10.33232/001c.172040",
  "fulltext_url": null,
  "id": "4xq66fanze7x9",
  "issns": [
    "2565-6120"
  ],
  "landing_url": "https://astro.theoj.org/article/172040-ring-position-angles-and-spin-in-m87-and-sgr-a",
  "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": null,
  "native_subjects": [
    [
      "openalex",
      "3103|Astrophysical Phenomena and Observations"
    ]
  ],
  "openalex": "W7164331269",
  "pdf_url": null,
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-02",
  "publisher": "Maynooth University",
  "ris": "https://research.draconitic.com/paper/4xq66fanze7x9.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:18:19Z",
      "native_id": "10.33232/001c.172040",
      "source": "crossref",
      "url": "https://astro.theoj.org/article/172040-ring-position-angles-and-spin-in-m87-and-sgr-a"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "journal-openalex:3103|Galaxies: Formation, Evolution, Phenomena",
      "subfield": "galaxies"
    }
  ],
  "title": "Ring Position Angles and Spin in M87* and Sgr A*",
  "title_text": "Ring Position Angles and Spin in M87* and Sgr A*",
  "type": "peer-reviewed",
  "updated_at": "2026-10-30T12:18:19Z",
  "url": "https://research.draconitic.com/paper/4xq66fanze7x9",
  "venue": "The Open Journal of Astrophysics",
  "versions": [
    {
      "doi": "10.48550/arxiv.2606.11322",
      "pid": "6v7n20w0jjtvz",
      "relation": "preprint",
      "title": "Ring Position Angles and Spin in M87* and Sgr A*",
      "venue": "arXiv"
    }
  ]
}