The Sun doesn’t just fuel almost all life on Earth. It’s also our astrophysical laboratory, the only star close enough to observe in sufficient detail.
This enormous ball of hydrogen and helium is made of plasma – extremely hot, electrically charged gas. The churning of plasma within the Sun produces an invisible magnetic field that envelops our entire Solar System.
Up close, at the Sun’s surface, the plasma is turbulent, dragging the magnetic field with it. It roils and bubbles and occasionally bursts out clouds of material known as coronal mass ejections.
Over the years, scientists have made many close-ups of the Sun’s surface with various telescopes and observatories. Now, we have the highest-resolution images yet, thanks to the Daniel K. Inouye Solar Telescope (DKIST) on Maui, Hawai’i.
In a study published in Nature, a team led by researchers from the US National Solar Observatory and Max Planck Institute for Solar System Research delivers new observations of the surface of the Sun with unprecedented precision – revealing a feature never seen before.
A solar mystery
The Sun’s magnetic field drives what we call space weather. Explosive flares in the outer atmosphere of the Sun – the corona – can cause radiation storms on Earth, disrupting satellites, power grids and communications.
And there’s a major mystery concerning the corona. The Sun’s surface is about 5,500°C. That’s much cooler than its core, about 27 million degrees Celsius. But the corona, rising above the surface, reaches millions of degrees.
To heat it, energy must pass through cooler intermediate layers. Why does the temperature, after dropping, suddenly rise again? To pin down which mechanism is responsible, we need to observe physical processes on the Sun’s surface that unfold over short times and small distances.
DKIST’s four-metre mirror, advanced optics and high-speed cameras resolve features as small as 20 kilometres across, which is tiny compared to the Sun’s radius of 696,000km. They’ve captured subtle brightness variations and magnetic structures with unmatched clarity.
Connecting the loops
On the Sun’s surface, the roiling flows of plasma drag magnetic fields with them. Sometimes they form coherent magnetic sunspots; at others times they twist and tangle.
These surface magnetic fields extend upward into the corona, and the mechanics at the surface cause magnetic fields aloft to snap and reconnect. This reconfiguration of the magnetic field can release stored energy into heat and fast flows, sometimes triggering explosive solar flares.
The key challenge is to connect these small, short events at the surface to the large-scale heating and eruptions in the Sun’s atmosphere above.
Solving that link would make a huge advance towards understanding why the corona is so hot. It would also improve our ability to predict space weather and how it might affect Earth, as well as interpret the magnetic activity and space weather of distant stars.
In the new study, the team presents the first clear evidence on the Sun of one of nature’s most striking patterns – the Kelvin–Helmholtz instability.
These rolling, wave-like billows form when fast fluid slides past slower fluid. Sometimes you can see it along the edges of windswept clouds.
This instability was theoretically predicted to exist in the Sun’s plasma, but it was unknown at what scales and what role it might play.
To turn observations into insight, the team paired DKIST data with sophisticated computer simulations, creating “synthetic observations” to match what the telescope saw.
This revealed these instabilities are likely key in mixing plasma and braiding the magnetic fields. It means small-scale billows and vortices near the Sun’s surface pump energy upward, priming the corona for its extreme temperatures and setting the stage for explosive flares.
Making a simulation always involves some approximations. The models can’t reproduce the Sun’s extreme physics, but they do closely match up to the observations, which is really impressive.
The simulation results also suggest that despite looking coherent on the surface, the magnetic fields beneath features like dark pores are fragmented.
This is super exciting, because we know that the magnetic field is generated somewhere inside the Sun – but we don’t know how or where. The fragmentation beneath suggests these magnetic features are only formed once they reach the surface, not deeper below. If correct, this will really challenge existing models of how sunspots and magnetic regions form.
The Sun is the only star we can study up close. By connecting its smallest magnetic twists to its largest outbursts, we unlock the key to interpreting every other star.
Author
Hannah Schunker
ARC Future Fellow, Physics, University of Newcastle
Disclosure statement
Hannah Schunker previously worked at the Max Planck Institute for Solar System Research, and two of the authors of the new study (R. Cameron, D. Przybylski) are her colleagues.
DOI
https://doi.org/10.64628/AA.nynwrjpp4
Originally published by The Conversation. Read the original article.
Facts Only
* The Sun is made of plasma, an extremely hot, electrically charged gas of hydrogen and helium.
* Plasma churning produces an invisible magnetic field enveloping the Solar System.
* The surface temperature of the Sun is about 5,500°C; the core temperature is about 27 million degrees Celsius.
* Solar flares in the corona can cause radiation storms on Earth.
* DKIST provided high-resolution images of the Sun’s surface.
* Plasma flows on the surface drag magnetic fields.
* Surface magnetic fields extend into the corona, causing magnetic field reconfiguration and energy release.
* The Kelvin–Helmholtz instability forms when fast fluid slides past slower fluid.
* Instabilities are suggested to mix plasma and braid magnetic fields, pumping energy upward.
* Simulations suggest magnetic fields beneath features like dark pores are fragmented.
Executive Summary
Full Take
The narrative presented connects micro-scale plasma physics on the Sun’s surface directly to macro-scale space weather phenomena through the mechanism of magnetic field evolution. The core implication is that understanding the small, turbulent dynamics—specifically Kelvin–Helmholtz instabilities acting on plasma flows—is necessary to explain the coronal heating puzzle and predict solar eruptions affecting Earth. The observation that magnetic fields appear fragmented beneath visible features like pores challenges established models regarding the origin and structure of magnetic fields within the Sun. This points toward a necessity for updating theoretical frameworks that link surface magnetic topology to internal field generation, suggesting that mechanisms causing extreme energy release are localized at the boundary layer rather than being solely dictated by deep interior physics. The reliance on synthetic observations from simulations, while impressive in matching data, highlights an ongoing gap between observed reality and current theoretical modeling of plasma behavior. The focus shifts from simply observing solar activity to understanding the dynamic interplay where surface turbulence dictates atmospheric extremes, which has profound implications for interpreting stellar magnetic cycles across the galaxy.
Bridge Questions: What are the specific observational constraints that would most strongly favor one mechanism (e.g., kinetic vs. thermal driving) over another in coronal heating models? How can the fragmentation of subsurface magnetic fields be directly measured or inferred from remote observations, and what does that imply about internal dynamo processes? If surface instabilities are key to energy transfer, how do these small-scale effects scale up to govern global magnetic field evolution across stellar lifetimes?
Sentinel — Human
This text reads as a sophisticated summary of scientific findings, successfully weaving together observation, theory, and implication in a manner consistent with expert reporting.