A 210 Megaparsec Ionized Structure at z=6.8 Revealed by an Astrophysics Foundation Model

Abstract

Reionization is the last major transition in the Universe that transforms the intergalactic medium (IGM) from neutral to highly ionized, yet its spatial structure remains poorly constrained. Using an astrophysics foundation model trained for James Webb Space Telescope datasets, we identify a luminous galaxy at redshift z=7.567 showing significant Lyα transmission at z=6.80±0.07. This transmission, named ``the First Lyα transmission in the Reionization Epoch at z∼7" (FLαRE-z7), indicates a cosmological-scale ionized structure extending over 210.5^+55.7_−53.5 comoving Megaparsecs at cosmic dawn. The hydrogen neutral fraction of the ionized structure is x_HI=(2.07^+0.29_−0.30)×10⁻⁶, about 10⁵ times lower than the cosmic mean at similar redshifts (x_HI≈0.4). Cosmological simulations suggest a probability of ≈10⁻⁵ for a random sightline to reproduce the transmission. We find no significant galaxy overdensity associated with the transmission region, in tension with canonical inside-out reionization models. FLαRE-z7 severely challenges existing reionization models in the standard ΛCDM Universe, indicating extreme spatial fluctuation in ionizing radiation or IGM temperature. Our result marks the first example of a foundation model discovering a previously unpredicted astrophysical phenomenon, demonstrating the power of deep learning methods for mining large astronomical datasets and finding unexpected new astrophysics.

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BibTeX RIS

BibTeX

@misc{yue2026megaparsec,
  title = {{A 210 Megaparsec Ionized Structure at $z=6.8$ Revealed by an Astrophysics Foundation Model}},
  author = {Minghao Yue and Yongda Zhu and Jiani Ding and Xiaohui Fan and Yufeng Luo},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2609.36656},
  eprint = {2609.36656},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.36656},
}

RIS

TY  - UNPB
TI  - A 210 Megaparsec Ionized Structure at z=6.8 Revealed by an Astrophysics Foundation Model
AU  - Minghao Yue
AU  - Yongda Zhu
AU  - Jiani Ding
AU  - Xiaohui Fan
AU  - Yufeng Luo
PY  - 2026
DA  - 2026/10/13
PB  - arXiv
DO  - 10.48550/arxiv.2609.36656
UR  - https://arxiv.org/abs/2609.36656
AB  - Reionization is the last major transition in the Universe that transforms the intergalactic medium (IGM) from neutral to highly ionized, yet its spatial structure remains poorly constrained. Using an astrophysics foundation model trained for James Webb Space Telescope datasets, we identify a luminous galaxy at redshift z=7.567 showing significant Lyα transmission at z=6.80±0.07. This transmission, named ``the First Lyα transmission in the Reionization Epoch at z∼7" (FLαRE-z7), indicates a cosmological-scale ionized structure extending over 210.5^+55.7_−53.5 comoving Megaparsecs at cosmic dawn. The hydrogen neutral fraction of the ionized structure is x_HI=(2.07^+0.29_−0.30)×10^−6, about 10^5 times lower than the cosmic mean at similar redshifts (x_HI≈0.4). Cosmological simulations suggest a probability of ≈10^−5 for a random sightline to reproduce the transmission. We find no significant galaxy overdensity associated with the transmission region, in tension with canonical inside-out reionization models. FLαRE-z7 severely challenges existing reionization models in the standard ΛCDM Universe, indicating extreme spatial fluctuation in ionizing radiation or IGM temperature. Our result marks the first example of a foundation model discovering a previously unpredicted astrophysical phenomenon, demonstrating the power of deep learning methods for mining large astronomical datasets and finding unexpected new astrophysics.
ER  -

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