Solar Superflare Potential Now Accepted As More Common Than Once Believed

                                        

                                        Ordinary flare and size of Earth (bottom left) 

                                                                                  

Superflares, monstrous explosions from our Sun that have occurred in the past, could wreak havoc on our little world - its technological infrastructure and life forms.  Habitually, they have been written off as "unlikely" but this may be premature. From the time of my original paper linking sunspots to solar flares, 

http://adsabs.harvard.edu/full/1983SoPh...88..137A

It’s been known that solar flares are closely correlated with sunspot group evolution and that the intensity of solar flare eruptions is related to the size of sunspot groups, the number of sunspots in groups, and the complexity of the magnetic field. The more complex the structures and magnetic field polarities are, the more likely large solar flares will erupt.

Now, a new paper ('Sun-like stars produce superflares roughly once per century') by Vasilyev et al. has found superflares are much more common for sunlike stars than originally believed.  This is also supported by a paper delivered by Yuto Notsu at the Solar Dynamics Observatory workshop, e.

 SDO 2025 Science Workshop: A Gathering of the Helio-hive!

2025_SDOworkshop_Cryo_Intro.pdf - Google Drive

Here is the core finding:  Vasilyev et al. investigated brightness measurements of 56,000 Sun-like stars observed by the Kepler space telescope. They identified almost 3000 bright stellar flares with energies ranging from 10³⁴ to 10³⁵ erg, which are called superflares. The occurrence rate is about one superflare per star per century. If the Sun behaves like the stars in this sample, then it could produce superflares at a similar rate. Prof. Kazunari Shibata also indicated - in his June, 2020 presentation- that such superflares were conceivable for the Sun. He used the diagram below:

Stellar superflares are energetic outbursts of electromagnetic radiation that are similar to solar flares but release more energy, up to 10³⁶ erg on main-sequence stars. True it's unknown whether the Sun can generate superflares and, if so, how often they might occur. But one can't rule them out. Vasilyev et al.  identified 2889 superflares on 2527 Sun-like stars, out of 56,450 observed. This detection rate indicates that superflares with energies >10³⁴ erg occur roughly once per century on stars with Sun-like temperature and variability. The resulting stellar superflare frequency-energy distribution is consistent with an extrapolation of the Sun’s flare distribution to higher energies, so they suggested that both are generated by the same physical mechanism.  

If twist in the magnetic field is the key signature then one can surmise that a large enough sunspot,  say >  3500  msh in area, and subjected to a twist or shear of its magnetic field, could reach the point of releasing a 10³⁴ to 10³⁵ erg solar flare.

The twist for a magnetic flux tube is defined: 

T(r)  =  (L B _q(r))/  (r  B _z (r))  

                                       Giant spot which could produce a super flare.

Let  L be the length of the giant flux tube bearing the sunspot proposed by Shibata.  Then r is the radius and  B _q(r)) and B _z (r)) denote the respective magnetic field components.  The tube becomes kink unstable when: T(r) >2p.  If enough free energy has been accumulated it can then potentially be released.