Bright rings around sunspots

There are two possible explanations for why sunspots are dark: the partial suppression by the sunspot magnetic fields of convective energy transport from the underlying layers', or the removal of energy from the sunspot by enhanced hydromagnetic wave radiation(2). Both processes would reduce the energy emitted radiatively, The first explanation is currently favoured(3), and predicts that the blocked energy should show up as a bright ring around the spot(2), with the actual brightness of the ring sensitive to details of solar convective transport and sunspot structure(4), Previous searches(5) for these bright rings were inconclusive because of the presence of bright, vertical magnetic nux tubes near the spots, and a lack of sufficient precision in the observations. Here we report high-photometric-precision observations of bright rings around eight sunspots. The rings are about 10 K warmer than the surrounding photosphere and extend at least one sunspot radius out from the penumbra, About 10% of the radiative energy missing from the sunspots is emitted through the bright rings. We also report observations of a second set of sunspots, for which simultaneous magnetic field measurements demonstrate that the rings are not associated with vertical nux tubes.