Sunspots are the most noticeable manifestation of solar magnetic field concentrations in the photosphere. A typical mature sunspot has an umbra and a penumbra. Light bridges (LBs) are the strip-like bright features, two ends of which connect the penumbra and span the umbra of a sunspot.
Click here for original story, Researchers find potential mechanism of solar light bridge formation and penumbra disappearance
Source: Phys.org