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    "story_id": "mp-2026-09-20-026",
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    "headline": "Rubin Found Seven Almost-Dark Galaxies Near Virgo",
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    "dek": "The faint systems carry only about one million to ten million solar masses in stars.",
    "summary": "The faint systems carry only about one million to ten million solar masses in stars.",
    "body_text": "Rubin Observatory’s second data preview revealed seven extremely low-surface-brightness galaxies around M49 near the Virgo Cluster. If they lie at Virgo’s distance, their half-light radii span 0.6 to 4.6 kiloparsecs and their stellar masses roughly one million to ten million Suns. Their central brightness resembles the faintest known Local Group satellites, extending that population beyond the immediate neighborhood. The paper presents them as a preview of what the ten-year LSST survey may find, not yet a statistical constraint on dark matter.",
    "why_it_matters": "The faint systems carry only about one million to ten million solar masses in stars.",
    "limitations": [
      "The paper presents them as a preview of what the ten-year LSST survey may find, not yet a statistical constraint on dark matter."
    ],
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    "first_published_at": "2026-09-20T09:00:00.000-04:00",
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        "text": "The faint systems carry only about one million to ten million solar masses in stars.",
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        "qualification": "The paper presents them as a preview of what the ten-year LSST survey may find, not yet a statistical constraint on dark matter."
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    "tags": [
      "Rubin Observatory",
      "Virgo Cluster",
      "faint galaxies"
    ],
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  "sources": [
    {
      "source_id": "source-2026-09-20-015",
      "title": "arXiv preprint 2609.19246",
      "publisher": "arXiv",
      "url": "https://arxiv.org/abs/2609.19246",
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      "published_at": "2026-09-16T14:00:00.000-04:00",
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    "title": "Rubin Found Seven Almost-Dark Galaxies Near Virgo",
    "publisher": "The Machine Press",
    "published_at": "2026-09-20T09:00:00.000-04:00",
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