Linking Solar Magnetism, Extreme Solar Particle Events and Stellar Superflares

The magnetic field of the Sun drives a wide range of eruptive phenomena, from small-scale nanoflares to large flares and coronal mass ejections (CMEs). While direct observations of solar activity cover only the past few decades, indirect evidence indicates that the Sun can occasionally produce events orders of magnitude stronger than any recorded ones in the modern era. Two complementary lines of evidence exist. First, extreme solar particle events (ESPEs) have been inferred from prominent spikes in cosmogenic isotope concentrations preserved in precisely dated natural archives such as tree rings and ice cores over the past 15 millennia. Second, high-precision space-borne photometry has revealed superflares on thousands of stars similar to the Sun. Whether these solar and stellar extremes are physically related remains an open question. We summarise the present state of understanding and discuss physical mechanisms that may link them. Although superflares and ESPEs are both extremely energetic manifestations of magnetic energy storage and release, their relationship does not appear to be one-to-one. Their occurrence and energetics likely depend on how magnetic flux and topology govern the partitioning of released energy between radiation, mass ejection, and particle acceleration.

💡 Research Summary

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The paper provides a comprehensive review of two extreme manifestations of solar and stellar magnetic activity: extreme solar particle events (ESPEs) inferred from cosmogenic isotope spikes in natural archives, and superflares observed on Sun‑like stars through high‑precision space photometry. The authors begin by outlining the historical context of solar activity research, noting that while direct observations of flares, coronal mass ejections (CMEs), and solar energetic particles (SEPs) span only a few decades, indirect proxies extend the record back fifteen millennia.

In the first major section, the authors describe the discovery of “Miyake events” – abrupt increases of ¹⁴C, ¹⁰Be, and ³⁶Cl in tree rings and ice cores that correspond to short, intense bursts of high‑energy particles. Using a multi‑proxy reconstruction that fits the measured isotope enhancements with scaled spectra of known SEP events, they derive integral fluences above 200 MeV (F₂₀₀) that are roughly two orders of magnitude larger than the strongest directly observed ground‑level enhancements (e.g., the 1956 GLE#5). Seven confirmed ESPEs and two candidates have been identified, implying an average recurrence interval of about 1,500 years, though the distribution is highly irregular. The authors also incorporate lunar regolith measurements of ²⁶Al, which indicate that SEPs with energies >30 MeV contribute a mean flux of 38 ± 7 cm⁻² s⁻¹ over geological timescales, and that ESPEs may account for 40–80 % of the long‑term SEP budget.

The second major section shifts to stellar superflares. Data from Kepler and TESS have recorded thousands of flare events on main‑sequence stars with energies ranging from 10³⁴ to 10³⁶ erg. The occurrence rate is strongly correlated with stellar rotation period and magnetic activity indicators; rapidly rotating, magnetically active stars exhibit superflares at rates up to 10⁻³ yr⁻¹, whereas Sun‑like stars with solar rotation periods show much lower rates but still produce occasional superflares. This statistical approach effectively extends the observational baseline for a Sun‑like star to hundreds of thousands of years, providing a context for the rarity of ESPEs.

A central theme of the paper is the relationship between ESPEs and superflares. Both phenomena arise from the rapid release of stored magnetic energy via reconnection, yet the partitioning of that energy into electromagnetic radiation, mass ejection (CMEs), and particle acceleration can differ dramatically. The authors argue that magnetic flux magnitude and topology (e.g., toroidal versus dipolar configurations) are the key parameters governing this partitioning. Complex, highly sheared magnetic structures may favor both large CMEs and efficient particle acceleration, leading to events that could be classified simultaneously as a superflare and an ESPE. Conversely, simpler magnetic geometries might produce intense radiative flares with relatively modest SEP output. Consequently, while ESPEs and superflares are linked by a common energy reservoir, a one‑to‑one correspondence does not exist.

The paper concludes with a discussion of the potential societal impacts of such extreme events. An ESPE occurring today could devastate satellite constellations, induce widespread power‑grid failures, and expose aviation crews to hazardous radiation, especially during periods of weakened geomagnetic shielding such as geomagnetic excursions or reversals. If a superflare is accompanied by a massive CME, the resulting geomagnetic storm would compound these effects. The authors stress the need for improved magnetic field observations, high‑resolution reconnection modeling, and further isotopic analyses of lunar and meteoritic samples to refine the statistical relationship between ESPEs and superflares. Their synthesis underscores that understanding the magnetic flux and topology of the Sun—and by extension Sun‑like stars—is essential for assessing the probability and consequences of the most extreme solar and stellar eruptions.