Solar flares reach 60 million°C, solving a decades-old space puzzle

Scientists at the University of St Andrews discovered ions in solar flares can hit 60 million°C—6.5 times hotter than thought. This breakthrough may solve a 50-year mystery of flare spectral lines and reshape our understanding of solar physics.

For half a century, scientists have puzzled over a strange solar mystery: why the light from solar flares looks wider, or “broader,” than expected. Now, new research from the University of St Andrews may have finally cracked the code — and the answer is hotter than anyone imagined.

A team led by Dr. Alexander Russell discovered that ions in solar flares — the charged particles that make up much of the Sun’s plasma — can heat up to more than 60 million degrees Celsius, a temperature about 6.5 times hotter than previously thought.

Why this matters

Solar flares are gigantic bursts of energy from the Sun’s outer atmosphere, heating its plasma to tens of millions of degrees. These fiery events send streams of radiation and X-rays hurtling toward Earth, posing risks to satellites, astronauts, and even the stability of our planet’s upper atmosphere.

Until now, scientists believed that ions and electrons inside solar flares shared the same temperature. But Dr. Russell and his team showed that ions can actually get much hotter than electrons — and these scorching ions may explain the decades-old mystery of unusually broad spectral lines seen in solar flare light.

A universal rule of plasma heating

The key lies in a process called magnetic reconnection, when twisted solar magnetic fields snap and release massive amounts of energy. Recent discoveries show that reconnection tends to heat ions far more than electrons, a finding seen not just on the Sun but also in near-Earth space, the solar wind, and advanced simulations.

By applying this rule to solar flares, the St Andrews team revealed that ions remain super-hot for several minutes, helping explain flare behavior and reshaping how scientists think about these cosmic explosions.

Solving a decades-old puzzle

Since the 1970s, astrophysicists have debated why the “spectral lines” from solar flares — bright features in ultraviolet and X-ray light — appeared much broader than theory predicted. The common explanation was turbulence, but that idea never fully added up.

Now, with ion temperatures soaring beyond 60 million degrees, the new research suggests a simpler explanation: it’s not turbulence at all, but the blazing-hot ions themselves widening the light spectrum.

A new era in solar physics

Dr. Russell calls the finding a “paradigm shift” for solar physics:

“We’ve shown that ions and electrons don’t always share the same temperature. Super-hot ions not only explain the mystery of flare line widths but also open a new window into how the Sun unleashes its power.”

The research, published in Astrophysical Journal Letters, not only rewrites textbooks but also offers crucial insights for space weather forecasting — a growing necessity in our technology-driven world.