Tiny Magnetic Corkscrews Detected on the Sun — A Major Clue to Why the Corona Is So Hot

Tiny magnetic 'corkscrews' found in the solar corona

Using the Daniel K. Inouye Solar Telescope (DKIST) in Hawaii, researchers have for the first time directly observed small-scale twisting magnetic motions in the Sun's outer atmosphere. These motions—called torsional Alfvén waves—are corkscrew-like disturbances in the Sun's magnetic field that carry energy through the hot, electrically charged plasma that makes up the corona.

What was observed
During DKIST's commissioning in October 2023, the team tracked emission from iron ions heated to roughly 1.6 million °C and detected faint Doppler shifts—red on one side of a magnetic loop and blue on the opposite side. This red/blue pattern is the hallmark signature of torsional Alfvén waves: plasma rotating about magnetic field lines in opposite directions on each flank of a loop.

"This discovery ends a protracted search for these waves that has its origins in the 1940s," said Richard Morton, the study's lead author and a professor at Northumbria University.

How they detected such subtle motions
The twisting motions are too small to be seen directly in images and are masked by larger swaying motions of the plasma. Morton and colleagues used high-resolution spectroscopy to measure tiny Doppler shifts in wavelength and developed a method to remove the dominant swaying signal, isolating the torsional component.

Why this matters
Alfvén waves were first predicted by Hannes Alfvén in 1942 and have long been proposed as a mechanism to transport energy from the Sun's lower atmosphere into the corona. The corona is puzzlingly hotter than the visible surface of the Sun—millions of degrees versus about 5,500 °C at the photosphere—and these newly observed torsional waves provide strong observational support for theories in which magnetic turbulence carries and deposits energy high in the atmosphere. The team reports that these waves appear even in relatively quiet coronal regions, suggesting they could be a continuous source of coronal heating and a contributor to the solar wind's energy budget.

Implications and next steps
The direct detection allows scientists to test and refine models of how magnetic energy is transported and dissipated in the corona. Future work will focus on measuring the energy flux in these waves, tracking how and where they dissipate, and determining their overall contribution to coronal heating and solar wind acceleration.

A paper describing these results was published Oct. 24 in Nature Astronomy.

Key facts at a glance

• Instrument: Daniel K. Inouye Solar Telescope (DKIST), 4-meter aperture
• Observation period: commissioning, October 2023
• Signature: opposing Doppler shifts (red/blue) across coronal loops
• Phenomenon: torsional Alfvén waves — small-scale twisting motions of magnetic field lines
• Significance: supports mechanisms for continuous energy transport into the corona and possible source of coronal heating