Barotropic equation of state and nonlinear electrodynamics in dynamical black hole spacetimes

Models of black holes that differ from idealized vacuum and electrovacuum solutions of Einstein’s equations often contain parameters whose physical interpretation is unclear. However, to propose a black hole model for experimental verification, we must clearly understand which parameters describe the black hole and what physical constraints can be imposed on each parameter. When considering dynamical black holes with a barotropic equation of state [Formula: see text], an additional integration constant arises, the nature of which remains unclear except for a few specific values of the equation of state coefficient [Formula: see text]. Nevertheless, when examining solutions such as Husain’s or Kiselev’s, we can observe remarkable effects related to black hole evaporation, which are associated with the violation of null energy conditions. However, the main issue lies in the fact that while violations of energy conditions may occur in nature, the ambiguity in the values of parameters describing black holes makes it difficult to determine whether such violations result from natural physical processes or are purely mathematical artifacts that should be excluded from consideration. Moreover, energy conditions play a crucial role in the evolution of a black hole’s shadow a characteristic that can potentially be observed experimentally. In this paper, we elucidate the parameter arising in Husain’s and Kiselev’s solutions using nonlinear electrodynamics. We demonstrate that for physically relevant equations of state, the additional parameter represents a combination of electric and magnetic charges.