Figure 2. Schematic illustration of the formation mechanism of the strong field. The horizontal flows from the right (S-pole umbra) compress the magnetic field near the left umbra (N-pole) and the magnetic field is enhanced. (©NAOJ)

Okamoto explains, "HINODE's continuous high-resolution data allowed us to analyze the sunspots in detail to investigate the distribution and time evolution of the strong magnetic field and also the surrounding environment. Finally, the longtime mystery of the formation mechanism of a stronger field outside an umbra than in the umbra, has been solved." These results were published as Joten Okamoto and Takashi Sakurai, "Super-strong Magnetic Field in Sunspots," in The Astrophysical Journal Letters, 852 (2018).

(*1) 10 gauss = 1 milli-tesla.