On the Origin of Sunspot Light Bridges

We propose a model of a light bridge as a current-carrying magnetic flux tube formed by convection. It is shown that convection in the sunspot penumbra provides the electric current necessary to heat the flux rope plasma and forms structures of a light bridge type. The steady-state heating mode of the light bridge is considered, since the light bridge life time (days) is much longer than the typical heating time (minutes). Radiation losses determine the current value I > 10¹¹A required to heat the light bridge to a temperature up to 6800 K. The parameters of the light bridge plasma are presented, and the observed double structure of the light bridge emission is explained.