A patchy warm ring surrounds a dark solar pore

Looking beyond a dark patch

Solar pores are small, dark magnetic features, resembling sunspots without their surrounding filamentary penumbra. Their strong, mostly vertical magnetic fields make them useful laboratories for studying how magnetism interacts with moving gas and energy transport.

In a study led by Ana Belén Griñón-Marín, researchers reconstructed the atmosphere within and around one pore and found a patchy ring of enhanced temperatures in the middle photosphere, part of the Sun’s visible atmospheric layer. The patches coincide with a stronger horizontal magnetic-field component, consistent with an expanding magnetic canopy. That association is a clue, not proof of a particular heating mechanism.

The arXiv manuscript, posted on November 9, 2026, states that it has been accepted for publication in The Astrophysical Journal Letters.

Reconstructing an atmosphere from light

The observations came from the Sunrise Chromospheric Infrared SpectroPolarimeter aboard the balloon-borne Sunrise III observatory on July 10, 2024. The instrument measured both the spectrum and polarization of light from a solar active region. Spectral shapes carry information about temperature and motion, while polarization helps constrain magnetic fields.

The team analyzed three scans covering approximately 1.85 hours, with scan starts about 37 minutes apart. Each scan was assembled sequentially rather than captured as an instantaneous photograph. A pointing jump also left part of the pore uncovered in the third scan; only valid observations were analyzed.

To interpret the measurements, the researchers used atmospheric modeling software called STiC. It adjusted temperature, velocity and magnetic-field profiles until calculated spectra matched the observations. Iron lines and a nearby continuum window mainly constrained deeper layers, while a calcium line extended the sensitivity upward.

The calculations allowed atomic populations to depart from local thermodynamic equilibrium: radiation, not just local gas conditions, can influence how atoms absorb and emit light. They also accounted for telescope blurring and coupled neighboring model pixels. However, radiation traveling horizontally between atmospheric columns was not included.

Warm patches without a surface-brightness ring

The reconstructed pore showed familiar properties: a cool interior and strong magnetic fields dominated by the vertical component. Around its boundary, the calcium line’s wings revealed scattered bright patches that collectively formed a ring-like pattern. There was no clear matching feature in the continuum brightness, which samples lower layers.

Compared with nearby reference regions, the patches had a median temperature excess reaching approximately 300 kelvin. Their deeper-layer temperatures were similar to those of the reference sample. The enhancement therefore points to a difference above the lowest sampled photosphere, rather than a uniformly warmer atmospheric column.

The models place the enhancement broadly around 100–400 kilometers above the local reference layer where visible-light optical depth equals one. That height estimate assumes hydrostatic equilibrium. The spectral diagnostics respond across overlapping depth ranges, so they cannot pinpoint a thin heated layer. Comparing regions at equal optical depth also does not necessarily compare identical geometrical heights.

For the statistical comparison, the team repeatedly paired bright-patch atmospheric columns with randomly selected reference columns. The reported percentile ranges describe the spread of those differences, not formal measurement uncertainties. The reference regions were themselves inside an active region, rather than pristine quiet Sun.

Enough magnetic energy, but no identified engine

The inferred temperature excess corresponds to an additional thermal-energy density reaching about 170 joules per cubic meter. This describes extra thermal energy associated with the temperature difference, not a measured heating rate.

As an energy-budget comparison, the authors calculated that converting magnetic energy entirely into heat could supply this excess through an equivalent field-strength reduction of roughly 20–30 gauss, at most about 2% of the inferred local field. They did not observe such a reduction or demonstrate that magnetic conversion occurred.

Possible explanations include wave dissipation, small-scale magnetic reconnection and other magnetic dissipation processes. Sideways radiation from hotter neighboring gas could also contribute, but the modeling cannot quantify it. Calculated calcium and magnesium radiative rates indicate stronger net cooling in the patches; sustaining that cooling and the temperature excess would require continued energy input. These calculations omit hydrogen and are not a complete radiative budget.

The ring-like pattern appears in all three scans, but the spacing cannot distinguish enduring patches from repeatedly forming ones. Separately, localized downflows reached 7–9 kilometers per second, approaching or exceeding a representative sound-speed estimate. Their potentially supersonic character remains conditional on local conditions.

The result is a detailed association between warm patches and an expanding magnetic canopy—not a solved heating mechanism. Faster observations could help distinguish how the patches evolve and which processes maintain them.