Observing 8 kG magnetic fields in a bipolar light bridge using Hinode/SP

Our aim is to diagnose the magnetic field structure of a light bridge separating two umbrae of opposite polarity in a delta-sunspot, which shows evidence for extremely strong magnetic fields. We analyze observations from the spectro-polarimeter on board the Hinode spacecraft of the active region AR11967. The thermodynamic and magnetic configurations are obtained by inverting the Stokes profiles under the assumption of local thermodynamic equilibrium. We applied both, the traditional 1D-inversion technique and the so-called 2D coupled inversions, which takes into account the point spread function of the Hinode telescope. We used SDO/HMI to estimate the shear velocity at the light bridge based on the local correlation technique. We report a compact structure with an area of 32.7 arcsec^2 within a bipolar light bridge with field strengths exceeding 5 kG. Two regions associated with downflows of ~5 km/s harbour fields larger than 6.5 kG, covering an area of 2.97 arcsec^2. The maximum field strength is 8.2 kG, which is the largest ever observed field on the surface of the Sun up to now. Based on the induction equation, we explain that the shear acting over ~16.6 h can be the source of the amplification of the field.