Solar flares heat ions far more intensely than electrons, providing a fresh explanation for the broadening of spectral lines.

Researchers at the University of St Andrews have found that particles in solar flares can become up to 6.5 times hotter than previously estimated, potentially solving a decades-old mystery about the Sun.

Solar flares—intense bursts of energy in the Sun’s outer atmosphere—can push temperatures past 10 million degrees and significantly increase solar X-rays and radiation reaching Earth, posing risks to spacecraft, astronauts, and the upper atmosphere. Published in Astrophysical Journal Letters, the study shows that solar plasma, made of electrons and ions, behaves differently than long assumed, with positively charged ions reaching temperatures exceeding 60 million degrees.

Figure 1. Solar Limb Flare Comparable in Size to Earth

Ions Experience Greater Heating Than Electrons

Using insights from other fields, Dr. Alexander Russell and his team, from the School of Mathematics and Statistics, concluded that solar flares are likely to heat ions far more intensely than electrons. Figure 1 shows Solar Limb Flare Comparable in Size to Earth.

Dr. Russell explained that recent discoveries show magnetic reconnection heats ions 6.5 times more than electrons—a phenomenon observed in near-Earth space, the solar wind, and computer simulations. However, this connection had not been previously applied to understanding solar flares.

Rethinking Key Assumptions in Solar Physics

“Traditionally, solar physics assumed ions and electrons share the same temperature. However, updated calculations using modern data reveal that temperature differences between ions and electrons can persist for tens of minutes in key regions of solar flares, allowing for the presence of super-hot ions,” explained Dr. Russell.

He added that the new ion temperature also aligns with the observed broadening of flare spectral lines, potentially resolving a decades-old astrophysics mystery.

Since the 1970s, scientists have wondered why flare spectral lines—bright spikes in the Sun’s extreme-ultraviolet and X-ray light—appear broader than expected. These were traditionally attributed to turbulent motions, but attempts to pinpoint the source of the turbulence have been inconclusive. After nearly 50 years, the new research suggests a paradigm shift: elevated ion temperatures may play a major role in explaining the unusually wide spectral lines of solar flares.

Reference:

1. https://scitechdaily.com/solar-flares-are-6-5-times-hotter-than-we-thought/

Cite this article:

Janani R (2025), Solar Flares Are 6.5 Times Hotter Than Previously Estimated, AnaTechMaz, pp.551