Empirical flare energy limits for the largest historical sunspots

TL;DR

This paper estimates the maximum possible energy of solar flares based on historical sunspot data, suggesting that extremely large active regions could produce flares with energies comparable to stellar superflares.

Contribution

It introduces an empirical method to estimate the upper limit of solar flare energies using historical sunspot records and flare ribbon area relations.

Findings

Large sunspot groups could produce flares with energies of a few 10^34 erg.

The Sun's maximum flare energy may be comparable to stellar superflares.

Empirical upper limits are consistent with observed extreme events.

Abstract

Extreme solar particle events reveal that the Sun can occasionally produce eruptions significantly more energetic than those observed in the modern era. These events are thought to originate from powerful coronal mass ejections, typically associated with large solar flares triggered by magnetic field reconnection in complex active regions. Stellar observations indicate that Sun-like stars can host superflares exceeding 10^34 erg roughly once per century, yet it remains uncertain whether the Sun can reach such flare energies. We empirically estimate the upper limit of solar flare energies using statistical relations between flare - ribbon areas and released energy derived from modern observations. By extrapolating these upper-envelope relations to the largest sunspot group recorded since 1859 - the Great Sunspot of 8 April 1947 - we find that exceptionally large and complex solar active regions could, in principle, produce flares with bolometric energies of a few 10^34 erg.