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Magnetic tubes that expand upward open a path for low-frequency sound waves.
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The Sun has quiet regions where the magnetic field is barely visible. But even there, sound waves find loopholes to rise higher. These loopholes are magnetic tubes that expand upward like funnels. Inside them, sound travels more freely.
The new SCIP instrument on the stratospheric telescope Sunrise III has for the first time measured the magnetic field not only at the surface but also at two heights in the chromosphere. It turned out that inside the tubes, the field weakens and expands with height. Inside the tubes, the gas oscillates with a period of 5 minutes, while around them only 3 minutes. The waves inside the tubes become steep, like ocean waves near the shore, and turn into shock waves.
A magnetic tube works like an acoustic funnel: low sounds that usually do not pass through rise up along it.
Such tubes were found not only in the bright network but also in the weak inter-network areas. This means that portals for sound exist almost everywhere on the quiet Sun. This helps to understand how energy reaches the chromosphere and heats it.
The 5-minute period is the fundamental tone of solar oscillations, like the breathing of the star. Under normal conditions, it does not pass higher, but in magnetic funnels it slips through.