Solar Flares May Be Way Hotter Than Researchers Previously Thought

Scientists recalculated the temperature of solar flares using modern data and new models

Sara Hashemi | Daily Correspondent

September 5, 2025

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Solar flares—intense releases of electromagnetic radiation into the sun’s atmosphere—could be more than six times hotter than solar physicists previously believed, say the authors of a new report.

These stunning events involve two particles: electrons and ions. Previous measurements of solar flare temperatures were based on the temperature of electrons, and it was assumed that electrons and ions would have the same temperature. But using computer simulations to recalculate the temperature of solar flares with modern data, the researchers found that there could actually be important differences in the temperatures of the two particles that can last several minutes. In fact, solar flares could be as hot as 180 million degrees Fahrenheit.

The findings were published in the Astrophysical Journal Letters on September 3.

The new work offers a “paradigm shift” in the understanding of flare spectral lines, according to a statement. Since the 1970s, researchers have tried to find out why these dark or bright lines in what’s an otherwise uniform spectrum are broader than expected. One controversial hypothesis was that they occurred because of turbulent motions, but scientists have never been able to explain what caused that turbulence.

“The new ion temperature fits well with the width of flare spectral lines, potentially solving an astrophysics mystery that has stood for nearly half a century,” says Alexander Russell, a physicist at the University of St. Andrews in Scotland and the study’s lead researcher, in a statement.

James Drake, a physicist at the University of Maryland who was not involved in the work, tells Nell Greenfieldboyce at NPR that he’s glad to see this new analysis. “We've been confronting the solar physicists,” says Drake, “telling them that even though they've measured in a lot of detail what's going on with the electrons, they're missing something big.”

The findings might also have important implications for objects like satellites and other spacecrafts. While the Earth’s magnetic field and atmosphere protect humans and animals from the effects of solar flares, the radiation from these events can affect satellites and pose a risk to astronauts. The events can also disrupt various communications, so understanding their true intensity can help researchers build better equipment in the future.

"We're already busy on the next steps," Russell says to NPR. The team is now developing models of the effects hotter ions have on solar flares.

Sara Hashemi | Read More

Sara Hashemi is a science writer and fact-checker currently based in New York City. Her work has appeared in Sierra, The Body, Maisonneuve magazine and more.