Balloon-borne Sunrise-III finds thread-like magnetic structures above the quiet Sun

A team of researchers led by the National Astronomical Observatory of Japan (NAOJ) has discovered unexpectedly intricate magnetic structures above quiet-Sun regions, using observations made by the balloon-borne solar observatory Sunrise-III during its 2024 flight in Earth's stratosphere.

The Sunrise-III observations revealed thin, elongated, thread-like magnetic structures embedded within the magnetic canopy above a quiet-Sun region. The magnetic canopy forms in the solar atmosphere, or chromosphere, as magnetic fields concentrated at the solar surface, or photosphere, arc outwards with increasing altitude, creating an arch of magnetic structures. The new observations show that this canopy is not a simple, uniformly expanding structure but contains numerous thin, elongated magnetic substructures.

A numerical simulation reproduced the thread-like structures seen by Sunrise-III and showed that they are associated with magnetic field lines twisted by motions at the solar surface.

In separate observations of a quiet-Sun region near the solar limb, the visible edge of the Sun, Sunrise-III mapped the magnetic fields of spicules, jet-like structures extending upward from the solar surface, and showed how the distribution of the magnetic field varies with height above the limb.

Regions of the Sun without activity such as sunspots are referred to as "quiet." Quiet-Sun regions cover most of the solar surface. The magnetic fields in these regions are weaker than in active regions, which makes detailed measurements difficult for ground-based telescopes because of blurring by Earth's atmosphere.

Sunrise-III is an international collaborative project that observes the Sun with a 1-meter telescope carried by a balloon floating in the stratosphere at an altitude of 35 km. At that altitude the Sun can be observed with very little atmospheric blurring. The gondola carried three instruments developed by different countries. Among them, the near-infrared spectropolarimeter SCIP (Sunrise Chromospheric Infrared spectroPolarimeter), developed under NAOJ's leadership, can continuously observe the magnetic field from the photosphere up through the chromosphere.

The high-precision observations from the stratosphere made it possible to map the structure of the chromospheric magnetic field above quiet-Sun regions in fine detail. The findings provide important clues to how energy is transported up from the solar surface to heat the solar atmosphere.

The study was published in The Astrophysical Journal Letters.

CONTACT: Natsuki Yonetani, National Astronomical Observatory of Japan, [email protected]