The Sun is not only our closest stellar neighbor, it's also the star we understand the most. As we've observed it over the centuries, we've learned that the Sun is not an immortal constant. It goes through active and quiet cycles, it has become warmer over geologic time scales, and it occasionally batters the Earth with solar flares. We've generally thought that other main sequence stars behave in much the same way, but when it comes to solar flares, that isn't always true.
There are many similarities. For example, just as the Sun has sunspots, other stars have starspots. The number of sunspots varies along an 11-year cycle, and this correlates with the amount of magnetic activity and solar flares. Observing starspots is difficult, but we have been able to do it for about 400 stars. Through this, we know that other stars also have a cycle of activity, though the period varies from 3 to 20 years depending on the star. By looking at the spectral lines of these stars, we also know that magnetic activity generally follows the same cycle.
Since a star's magnetic field is what drives solar flares, you would think that stellar flares would follow the same cycle. So we should see more flares where there are lots of starspots and fewer in a region without starspots. This is precisely what we see with the Sun. Sunspots and solar flares appear in similar locations around the same time. But a new study shows that isn't the case.
We can't observe starspots on thousands of stars, so the team used an indirect measure. Using data from the Transiting Exoplanet Survey Satellite (TESS), they looked at how the brightness of stars varied. The idea is that when there are lots of starspots, a star is slightly dimmer when the spots face us than when they are on the far side of the star. As the star rotates, the fluctuation of brightness follows that cycle. They also looked for short spikes of brightness that would indicate a stellar flare. Since we can only see flares on the side of the star facing us, the team could correlate the two.
Based on observations of more than 14,000 stars, the authors observed more than 200,000 stellar flares. They then looked at the correlation. For the Sun, this would strongly correlate. So when we see a solar flare, it's almost certain that there are also sunspots facing us. But for the stars, the team found this was only true half the time. In other words, when we see a stellar flare, the chance that there are sunspots in the area is essentially random chance. The two aren't correlated at all.
It turns out the Sun is unusual. For most stars, the exact mechanism driving flares and spots is different. Why sunspots and solar flares correlate so strongly is something we don't yet understand.
Reference: Zhang, Andy B., et al. "Starspots and Flares are Generally Not Correlated." *arXiv preprint* arXiv:2512.01051 (2025).
