One hundred years of testing general relativity: from Eddington’s eclipse to general relativistic MHD

In 1919, the observation during a solar eclipse of the deflection of light rays from stars near the Sun decreed the validity of Einstein's general relativity. One hundred years later, the image of the black hole M87* by the Event Horizon Telescope collaboration proved the existence of these fascinating objects on the one hand, and on the other, the validity of general relativistic magnetohydrodynamics (GRMHD) in the strong gravity regime. Numerical simulations have been used to model the accreting plasma around the black hole, whose emission is at the base of the synthetic images compared with data. Here, we briefly discuss the methods and the initialization employed for these simulations, and we briefly report the results of GRMHD axisymmetric simulations where a dynamo mechanism operates inside the disk, enhancing the magnetic field from its initial seed values up to those needed to explain the observed plasma emission.