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Inouye Solar Telescope Resolves Solar Flare Loops as Thin as 21 Kilometers

A peer-reviewed ApJL analysis pins down coronal loop scales, sharpening constraints for flare physics with potential gains for space‑weather modeling.

A high-resolution image of the flare from the Inouye Solar Telescope, taken on August 8, 2024, at 20:12 UT. The image is about 4 Earth-diameters on each side.
Image
A high-resolution image of the flare from the Inouye Solar Telescope, taken on August 8, 2024, at 20:12 UT. The image is about 4 Earth-diameters on each side. Labels of the different relevant regions of the image are added for clarity: flare ribbons (bright areas of energy release in the dense lower solar atmosphere) and an arcade of coronal loops (arcs of plasma outlining magnetic field lines that transport energy from the corona to the flare ribbons). Image credit: NSF / NSO / AURA.

Overview

  • Using DKIST’s Visible Broadband Imager at the H-alpha wavelength, researchers imaged an X1.3 solar flare on August 8, 2024 at 20:12 UT during its decay phase.
  • Loop strands averaged 48.2 km in width, with some features at the ~24 km instrumental limit and possibly narrowing to ~21 km.
  • The dataset constitutes DKIST’s first observation of an X-class flare and the highest‑resolution H-alpha flare imagery reported to date.
  • VBI’s resolving power—over two and a half times sharper than the next-best solar telescope—enabled direct measurements at long‑theorized 10–100 km scales.
  • Authors propose the ultra‑fine strands may be elementary flare structures, a hypothesis flagged for follow‑up as the results appear in The Astrophysical Journal Letters.