It is a general knowledge that magnetic field plays an important role in the process of accretion onto black holes, and this process is responsible for some of the bright X-ray sources in our Galaxy, but also for over a million of well known quasars (active galaxies) seen in the sky. It was proposed many years ago that a strong large-scale magnetic field is able to temporarily stop the accretion process leading to a stage named MAD - magnetically arrested disk. In the Science article co-authored by prof. B. Czerny direct evidence is presented for the first time that such a phenomenon actually happens. The authors analyzed multi-wavelength observational data collected during an outburst of a galactic source MAXI J1820+070 and determined that the radio and the optical fluxes are delayed by about 8 and 17 days, respectively, as compared to the X-ray flux. By careful modelling, they interpreted this as evidence for the formation of a MAD.