# Cosmic strings in axisymmetric black hole spacetimes; the C--metric "engines"

## TL;DR

This paper models cosmic strings in black hole spacetimes using the Bonnor rocket solution, revealing they are composed of null dust with unique energy density, and shows their role in black hole acceleration.

## Contribution

It introduces a new model for cosmic strings in black hole spacetimes using explicit construction from the Bonnor rocket solution, clarifying their stress-energy tensor and effects.

## Key findings

- Cosmic strings modeled as null dust with delta function derivatives.
- Presence of momentum flux causes black hole acceleration.
- Application to Schwarzschild and C--metric spacetimes.

## Abstract

The interpretation of so-called cosmic string in black hole spacetimes has settled down to an unsatisfactory state. In this article we try to provide a different model for these cosmic strings by explicit construction of these spacetimes from the Bonnor rocket solution. It is shown that the correct stress-energy tensor is that of null dust with a rather strange energy density --- first derivative of Dirac delta distribution. We will discuss the Schwarzschild solution and the C--metric. In the latter case we will show that there is a momentum flux through the cosmic string, causing the acceleration of the black hole.