{
  "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 $\\mathrm{PA}_1$ in general relativistic magnetohydrodynamic (GRMHD) models. For larger spin magnitudes ($a_{*}>0$ and $a_{*}\\lesssim-0.5$), the mean $\\mathrm{PA}_1$ falls within $1σ$ of the approaching limb of the black hole, regardless of viewing inclination, disk magnetization, or source. By comparing the $(a_1, \\mathrm{PA}_1)$ 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 $\\mathrm{PA}_1$ relative to the large-scale jet axis may suggest that M87*'s disk does not have a large tilt. By combining $\\mathrm{PA}_1$ with the pattern speed measured in optimistic 2026 M87* video conditions, the EHT can constrain whether M87* is prograde or retrograde with $\\sim 84\\%$ accuracy. In Sgr A*, we show that a detection of $(a_1, \\mathrm{PA}_1)$ 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": "Journal reference: The Open Journal of Astrophysics 9 (October), 2026",
  "arxiv": "2606.11322",
  "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/6v7n20w0jjtvz.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2606.11322",
  "fulltext_url": null,
  "id": "6v7n20w0jjtvz",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2606.11322",
  "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.HE"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2606.11322",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-30",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/6v7n20w0jjtvz.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:26:45Z",
      "native_id": "2606.11322",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2606.11322"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.HE",
      "subfield": "high-energy-astrophysics"
    }
  ],
  "title": "Ring Position Angles and Spin in M87* and Sgr A*",
  "title_text": "Ring Position Angles and Spin in M87* and Sgr A*",
  "type": "preprint",
  "updated_at": "2026-10-30T12:26:45Z",
  "url": "https://research.draconitic.com/paper/6v7n20w0jjtvz",
  "venue": "arXiv",
  "versions": [
    {
      "doi": "10.33232/001c.172040",
      "pid": "4xq66fanze7x9",
      "relation": "published-as",
      "title": "Ring Position Angles and Spin in M87* and Sgr A*",
      "venue": "The Open Journal of Astrophysics"
    }
  ]
}