14. Irregularities In Young Stellar Models: Are Starspots To Blame?

Abstract

Starspots are dark areas on a star’s surface formed by intense magnetic fields that actively suppress the flow of energy, causing the area to become cooler and darker than its surroundings. Starspots threaten a star’s equilibrium because they prevent energy from leaving the star, causing a buildup of pressure. The prevailing assumption is that increased pressure will cause the star to inflate, producing a cooler and larger star. For this reason, starspots have been proposed to explain why some stars appear cooler and larger than we expect. This requires energy blocked by a spot to be trapped deep within the star where it cannot easily escape. However, the location of trapped energy directly relates to physical processes that produce starspots, but the process is still highly debated. To establish where in a star energy becomes trapped, we developed a mathematical toy model that predicts how starspots affect a star's color and brightness using six adjustable parameters that directly relate to starspot formation processes. We present results of a systematic study exploring how a star's color and brightness are affected by each model parameter, linking spot formation theories to direct observables. We find that starspots cause unique observational changes depending on whether energy is trapped near the stellar surface or deeper within the star. When compared against properties of real stars, our model can distinguish between different starspot formation theories, contributing a way to test whether starspots are responsible for the anomalous properties of young stars.