{
  "abstract": "Several hundred ring-like structures seen at $8μ$m in the Spitzer GLIMPSE surveys share a uniform morphology: the shell thickness $ΔR$ is a nearly constant fraction of the outer radius $R$, $ΔR/R\\sim0.3$, across a factor of 40 in size and all exciting spectral types. This invariance is unexplained. We ask what sets this thickness and whether its near-constancy is physical or a measurement artifact. We derive analytic constraints on the location, temperature, and heating of the emitting grains, and confront the predicted scaling with radius against the GLIMPSE I and II catalogs (591 objects, 91 with kinematic distances). Grains in radiative equilibrium at the observed radii reach only 20-35 K and fall short of the required $8μ$m emissivity by more than 20 orders of magnitude; the emission must come from stochastically heated PAHs and very small grains, and therefore from the photon-dominated region, where the ring width is the far-ultraviolet penetration depth. This gives $ΔR/R=A_V^{\\rm PDR}/A_V^{\\rm cloud}$, independent of radius; a swept-up shell instead predicts $ΔR/R\\propto(R/R_S)^{3/2}$, with $R_S$ the initial Strömgren radius. We find a pronounced angular-resolution systematic that inflates the ratio for the smallest bubbles; once this is accounted for, $ΔR/R=0.217$, with a residual dependence on physical radius of $0.03\\pm0.05$, consistent with zero. A fixed ambient density is excluded at $20σ$, the swept-up shell at 9-28$σ$. The implied columns are $N_{\\rm cloud}\\approx8.7\\times10^{21}$ cm$^{-2}$ with only 0.112 dex of scatter. The near-universal appearance of mid-infrared bubbles follows from the ratio of two nearly invariant column densities -- the dust-opacity-fixed far-ultraviolet shielding column and the Larson-like column of the parent molecular cloud -- and requires no reference to stellar winds.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2610.07361",
  "author_total": 2,
  "authors": [
    {
      "name": "Michael M. Schulreich"
    },
    {
      "name": "A. Beate C. Patzer"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/7cpy325557mv2.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2610.07361",
  "fulltext_url": null,
  "id": "7cpy325557mv2",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2610.07361",
  "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"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2610.07361",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-05",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/7cpy325557mv2.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:27:22Z",
      "native_id": "2610.07361",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2610.07361"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.GA",
      "subfield": "galaxies"
    }
  ],
  "title": "The universal thickness of mid-infrared bubbles",
  "title_text": "The universal thickness of mid-infrared bubbles",
  "type": "preprint",
  "updated_at": "2026-10-30T12:27:22Z",
  "url": "https://research.draconitic.com/paper/7cpy325557mv2",
  "venue": "arXiv",
  "versions": []
}