Why Solar Magnetic Flux Concentrations Are Bright in Molecular Bands

Using realistic ab initio simulations of radiative magnetoconvection, we show that the bright structures in images taken in the "G band," a spectral band dominated by lines of the CH molecule, precisely outline small-scale concentrations of strong magnetic fields on the visible solar surface. The brightening is caused by a depletion of CH molecules in the hot and tenuous magnetic structures, thus confirming the model of radiatively heated magnetic flux concentrations. These results provide a firm basis for observational studies of the evolution and dynamics of the small-scale solar magnetic field derived through "proxy magnetometry" with G-band images.