On the Universal Cuspy Behavior in Black Hole Shadows

TL;DR

This paper reveals universal cusp formation phenomena in black hole shadows, independent of specific spacetime metrics, applicable to various compact objects including Kerr black holes and traversable wormholes.

Contribution

It introduces a model-independent framework demonstrating universal cusp behavior and critical phenomena in black hole shadows across diverse compact objects.

Findings

Cusps are linked to topological charge transitions and an equal-area law.

Universal critical scaling behavior is observed in shadow structures.

The framework applies to Kerr black holes and traversable wormholes.

Abstract

This work investigates the universality of cusp formation in the shadows of compact objects. The emergence of cusps is accompanied by three interrelated phenomena: a topological charge transition, an equal-area law governing the self-intersecting structure, and universal critical scaling behavior. We demonstrate that, because these phenomena originate from the global morphology of the shadow, they are fundamentally independent of specific spacetime metric details and apply across diverse models. These features are systematically analyzed for the Kerr black hole endowed with a running Newton coupling. By extending our framework to rotating traversable wormholes, we confirm that the same universal behavior persists in more general compact objects. Our study uncovers the universality underlying cusp formation, offering a model-independent framework for identifying non-Kerr signatures in future black hole observations.