Shadow area growth with increasing of charge and angular momentum in the Kerr-Newman metric with irreducible mass

Abstract

The standard form of the Kerr-Newman (KN) metric contains the total mass of a charged rotating source, which includes the mass of the neutral non-rotating source (the "irreducible" mass), as well as the mass equivalents of the rotational and electric field energies. According to the Christodolou-Ruffini mass formula, at a constant irreducible mass, the total mass increases with increasing angular momentum and charge. However, ignoring this fact, at studying the dependence of the effects of gravity on parameters, the total mass was assumed to be constant with varying angular momentum and/or charge, and this error led to physically absurd results, as if an increase in charge and/or angular momentum, by increasing the energy of the source, weakens the effects of gravity. Recently, the author introduced the concept of metrics with independent parameters and formulated a new method for describing the effects of gravity based on it, leading to physically correct results (Z. Zakir 2022). The KN metric was also expressed through independent parameters, in particular through the irreducible mass, independent of charge and angular momentum (Z. Zakir 2023). It was shown that in the KN metric with irreducible mass, an increase in charge and angular momentum does not weaken the effects of gravity, as was previously accepted, but, on the contrary, enhances all these effects, as it should be when the source energy increases. This letter presents results for the shadow in the KN metric with irreducible mass. In the figures 9 shadow contours with three values of each of parameters are presented. It is shown that, as for other gravity effects, an increase in charge and/or angular momentum, increasing the source’s gravity, enhances this effect also, which is expressed in an increase in the shadow area.