Magnetic Bright Points – The smaller end of the Sun's dynamic magnetic fields

On large scales, magnetic fields cause sunspots or flares. But the Sun also hosts smaller magnetic fields not larger than a few hundred kilometres. Dr. Dominik Utz, from  University of Graz (Austria), explains more about them.



Observations taken at the Swedish 1-m Solar Telescope with the CRISP instrument. Credit: Tanmoy Samanta and Vasco Henriques

The dynamic appearance of the Sun is caused by magnetic fields. On large scales we observe sunspots producing flares and coronal mass ejections. But the Sun does not only host large scale magnetic fields. No, there is indeed a whole zoo of magnetic fields and features reaching down to single flux tubes not larger in diameter than a few hundreds kilometres. These features are highly dynamic and responsible for physical processes like wave triggering, propagation, and wave guiding to the higher atmosphere. They also increase the total radiation emitted by the Sun and change its spectral composition due to their higher irradiance at smaller wavelengths, which is important for climate research on Earth.

To study the fast dynamics of small-scale magnetic fields one can use magnetic bright points (MBPs), which are the cross-section of strong magnetic flux elements on the visible surface of the Sun. MBPs allow magnetic features to be tracked using intensity rather than polarization measurements.

The movie shows the time evolution of MBPs in different layers of the atmosphere by scanning through the Halpha spectral line. One can think of the photons detected in the line wing as being emitted from the photosphere while the ones coming from the line centre are created higher up in the chromosphere. These observations demonstrate the close relationship between MBPs (small-scale magnetic fields) and jets (dark chromospheric structures) blowing out and up from them.

The European Solar Telescope multi-wavelength capabilities together with its high spatial resolution will allow us to study small magnetic bright points in an unprecedented way. We expect to further disentangle the small-scale structures of the bright points.

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