Sunspot light bridges
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Dark features in sunspot light bridges
Goode Solar Telescope (GST)
This movie shows the temporal evolution of light bridges in a sunspot umbra as observed on 2015 June 20 with the 1.6-m Goode Solar Telescope at Big Bear Big Bear Solar Observatory (BBSO). A broadband filter isolating TiO molecular lines around 705.7 nm was used to sample the photosphere. The images have a pixel size of 24 km on the solar surface.
Light bridges are long, narrow features that split sunspot umbrae in two or more parts. They can show a filamentary structure or a granular structure, resembling quiet Sun granular cells. Light bridges are thought to be manifestations of convection in the strong magnetic field of the umbra. They usually show a central dark lane associated with upflows and intergranular lanes where donwflows occur, supporting the convective nature of light bridges.
The GST observations reveal for the first time the presence of another type of dark feature in light bridges: dot-like dark knots, with sizes in the ranges of 80-200 km. Many dark knots migrate away from the penumbra along the light bridge. Several of these structures may appear superimposed on the central dark lane, just like beads strung on a string. Dark knots also show donwflows, and may have a similar origin as intergranular lanes in sunspot light bridges.
To download the movie, click HERE
Movie credit: Wenda Cao (Big Bear Solar Observatory). BBSO operation is supported by New Jersey Institute of Technology and U.S. NSF AGS-1821294 grant
Publication: Zhang et al., 2018, The Astrophysical Journal, 865, 29