RESOLUTION OF MAGNETIC-FLUX TUBES ON THE SUN

MAGNETIC flux at the surface of the Sun is predominantly concentrated in discrete areas with kilogauss field strengths1. Except for sunspots, these areas are too small to have been resolved by conventional observations. These magnetic flux tubes are an essential part of the physics of the activity and heating of the outer atmosphere of the Sun and other late-type stars2, but although their average properties have been studied in considerable detail3,4, direct observations of them have been lacking because of turbulence in the Earth's atmosphere, which limits resolution to approximately 400 km. Using a newly developed technique of speckle interferometry5, we have obtained simultaneous direct observations of the white-light and magnetic field signature of flux tubes. Individual flux tubes are seen, with resolved diameters of approximately 200 km and continuum brightness contrast of at least +30%. Magnetic features larger than 300 km in size tend, however, to be darker than their surroundings.