Researchers report that certain charged black holes with a Newman–Unti–Tamburino (NUT) parameter carry narrow lines, called Misner strings, that behave like real electric and magnetic charges. By examining the fields tied to these strings, the authors show that the strings are not empty bookkeeping devices. Instead they carry singular, uneven flows of electric and magnetic field that act like short, physical charge distributions near the horizon.

The work builds on an earlier finding by McGuire and Ruffini that electric and magnetic monopole features appear on these strings. The new paper studies the electromagnetic fields on the strings in detail. The authors find that the field flows along the strings have nonzero divergence. In plain terms, the fields look as if there are charge densities sitting along the string, even though the underlying geometry is what produces them.

At a high level, Misner strings are line-like features that accompany black holes with a NUT parameter. The NUT parameter adds a kind of gravitational “twist” to the solution. When the black hole is charged, the strings carry singular, nonuniform electric and magnetic field lines. A related concept, a Dirac string, appears in magnetic monopole theory as the line needed to describe a magnetic charge. The combined Misner–Dirac strings in these solutions create a local electromagnetic “hair” zone just outside the horizon, meaning extra structure that affects the fields in that region.

This matters because it shows a new, classical way for a black hole to have observable structure beyond its total mass, net charge and spin. In black hole physics people often refer to additional distinguishing features as “hair.” The strings here produce a complex short-range electromagnetic hair that is, according to the authors, classically observable in the solutions they study. The paper also notes that rotation by itself can generate similar hair even when the NUT parameter is absent.