For nearly half a century, scientists have puzzled over one of the Sun’s strangest behaviors: the inexplicably broad light signatures of solar flares. These dramatic bursts of energy—eruptions that can heat parts of the Sun’s atmosphere to more than 10 million degrees—seemed to defy explanation. The broadness of the spectral lines, the fingerprints of radiation emitted during these flares, suggested that something extraordinary was happening inside the Sun’s outer atmosphere. But what?
Now, new research from the University of St Andrews has delivered a groundbreaking solution. The study reveals that particles in solar flares are not just hot—they are 6.5 times hotter than scientists previously thought. This insight doesn’t just revise a number; it reshapes our understanding of the Sun itself and offers a long-awaited resolution to a solar enigma dating back to the 1970s.
What Exactly Are Solar Flares?
Solar flares are colossal eruptions in the Sun’s outer atmosphere, or corona. They occur when tangled magnetic fields in the Sun suddenly snap and realign in a process known as magnetic reconnection. In seconds, this releases staggering amounts of energy—equivalent to millions of nuclear bombs exploding at once.
During these events, plasma—an electrified soup of charged particles made of electrons and ions—is heated to extreme temperatures. Solar flares light up space in bursts of X-rays and ultraviolet radiation, often traveling across the solar system in moments.
Here on Earth, their effects ripple outward. Flares can disturb satellites, threaten astronauts with dangerous radiation, and disrupt communications and navigation systems by altering our planet’s upper atmosphere. They are both awe-inspiring and hazardous, making their study not just a scientific curiosity but a matter of real-world importance.
Rethinking Solar Heat: The Ion Breakthrough
For decades, solar physics operated under an assumption: ions and electrons in flares must be heated equally. After all, both make up plasma, and their energy should balance out. But new research led by Dr. Alexander Russell, Senior Lecturer in Solar Theory at the University of St Andrews, has upended that belief.
His team discovered that ions—the positively charged particles in plasma—can reach staggering temperatures of over 60 million degrees during a flare. This makes them not just hotter, but vastly hotter, than electrons. The difference is so large that it rewrites the rules of solar physics.
“We were excited by recent discoveries that a process called magnetic reconnection heats ions 6.5 times as much as electrons,” Dr. Russell explained. “This appears to be a universal law, and it has been confirmed in near-Earth space, the solar wind, and computer simulations. However, nobody had previously connected work in those fields to solar flares.”
By redoing calculations with modern data and incorporating this overlooked imbalance, the team found that ions can remain superheated for tens of minutes within solar flares. That persistence opens a new way of looking at the Sun’s fiery behavior—and, at last, explains the long-standing spectral mystery.
Solving a 50-Year Puzzle
Since the 1970s, scientists have wondered why flare spectral lines—the bright emissions seen in extreme-ultraviolet and X-ray light—are far wider than expected. Traditional thinking pinned the blame on turbulence, tiny chaotic motions within the plasma that could broaden the lines. Yet, despite decades of searching, the exact nature of this turbulence remained elusive.
The new St Andrews research offers a simpler and more elegant answer: super-hot ions themselves can broaden the spectral lines. The sheer speed and energy of these ions create the widening effect, eliminating the need to invoke mysterious turbulence.
In one stroke, this reinterpretation resolves a half-century-old astrophysical riddle. What once seemed like chaos now looks like order, governed by universal rules of plasma physics.
Why This Matters for Earth and Beyond
Understanding solar flares is not an abstract pursuit. Our modern world—dependent on satellites for communication, GPS, weather forecasting, and defense—is directly vulnerable to solar activity. A massive flare or solar storm could damage power grids, disrupt navigation systems, or endanger astronauts aboard spacecraft.
By knowing more precisely how energy is distributed between ions and electrons in solar flares, scientists can build better models of space weather. More accurate predictions of flare intensity and timing could provide critical warnings, protecting satellites, astronauts, and even the infrastructure we rely on daily.
Moreover, this research deepens our knowledge of plasma physics, a field with applications far beyond solar studies. From nuclear fusion experiments on Earth to understanding cosmic explosions across the universe, the lessons learned from our Sun ripple outward into countless scientific frontiers.
A Paradigm Shift in Solar Physics
The St Andrews team’s work is more than a correction to past assumptions—it represents a paradigm shift in how we view the Sun’s energy. It shows that even in the nearest and most studied star, there are still surprises waiting to be uncovered. The fact that ions dominate the thermal landscape of solar flares is not a small adjustment; it’s a revelation that redefines decades of solar theory.
Science often advances this way—not in sweeping revolutions, but in the careful re-examination of what we thought we knew. The Sun, constant and familiar in our skies, still holds secrets vast enough to challenge our understanding. And with each discovery, we are reminded that science is not the end of curiosity, but the never-ending journey of asking deeper questions.
The Sun Still Has Secrets
This breakthrough is a milestone, but not the final word. It opens new avenues of research: How exactly do these super-hot ions evolve during a flare? Could their behavior help explain other solar mysteries, such as coronal heating—the puzzle of why the Sun’s outer atmosphere is hotter than its surface?
As we build more powerful telescopes, launch advanced solar missions, and refine our models, the Sun will continue to reveal itself piece by piece.
For now, the University of St Andrews research reminds us of a humbling truth: even with centuries of study, our nearest star still has the power to astonish us. In its searing light and superheated plasma, the Sun tells a story not only of physics but of wonder—a reminder that mystery and discovery burn just as brightly as the star itself.
More information: Solar Flare Ion Temperatures, The Astrophysical Journal Letters (2025). DOI: 10.3847/2041-8213/adf74a
