String dynamics and ejection along the axis of a spinning black hole

TL;DR

This paper investigates the dynamics of relativistic strings around Kerr black holes, revealing mechanisms for string ejection along the axis that could relate to astrophysical jet formation.

Contribution

It introduces a detailed analysis of string motion boundaries and trajectories in Kerr spacetime, highlighting a novel ejection process involving energy transformation.

Findings

Strings can be ejected along the black hole axis with relativistic speeds.

The study identifies parameter regions for different string behaviors.

Numerical simulations illustrate bouncing and ejection phenomena.

Abstract

Relativistic current carrying strings moving axisymmetrically on the background of a Kerr black hole are studied. The boundaries and possible types of motion of a string with a given energy and current are found. Regions of parameters for which the string falls into the black hole, or is trapped in a toroidal volume, or can escape to infinity, are identified, and representative trajectories are examined by numerical integration, illustrating various interesting behaviors. In particular, we find that a string can start out at rest near the equatorial plane and, after bouncing around, be ejected out along the axis, some of its internal (elastic or rotational kinetic) energy having been transformed into translational kinetic energy. The resulting velocity can be an order unity fraction of the speed of light. This process results from the presence of an outer tension barrier and an inner angular momentum barrier that are deformed by the gravitational field. We speculatively discuss the possible astrophysical significance of this mechanism as a means of launching a collimated jet of MHD plasma flux tubes along the spin axis of a gravitating system fed by an accretion disk.