University of Leipzig’s scientists in Germany found out that the inner horizon of the black hole can be charged both positively and negatively. The results of the study are published in the magazine Physical Review Letters.
According to the general theory of relativity, if the black hole is electrically charged, then inside it there is a “surface”, resembling the properties of the event horizon and called the inner horizon. This surface is theoretically bound by the boundary, with the intersection of which determinism is broken, that is, it is impossible to predict the properties of space-time based on knowledge of the state of the universe at some point in the past. In other words, the journey of an observer crossing the inner horizon will no longer be determined by the initial data.
British mathematician Roger Penrose predicted that in fact, near the inner horizon, the space-time is twisted so much that any observer will be destroyed when approaching it. Thus, the inner horizon is a singularity. Recent studies have shown that in the charged black holes in the expanding universe, the singularity can be quite weak so that it can be crossing it. In the new work, scientists showed the effect of quantum perturbations on gravitational fields inside a black hole in the expanding universe.
Since an electrically charged black hole can occur only from electrically charged matter, scientists studied quantum charge perturbations near the inner horizon. It was originally believed that currents inside the black holes are associated with spontaneous appearance of oppositely charged particles, which are then accelerated in opposite directions. This would lead to the discharge of the area of the black hole behind the inner horizon.
It turned out that the dominant contribution to the electric current generated by quantum effects on the inner horizon can be both positive and negative depending on the parameters of the space-time and quantum field. When parameters close to the maximum allowable charging of the black hole, the current seeks to reduce the inner horizon charge. This contradicts the expected picture and contrasts with what happens on the external horizon of events, where quantum effects are expected to reduce the charge.