Scattering of cosmic strings by black holes: loop formation

TL;DR

This paper investigates how a rotating black hole can deform a cosmic string, potentially leading to loop formation, but finds such events are rare and depend on specific collision parameters.

Contribution

It introduces a detailed analysis of cosmic string deformation by Kerr black holes and identifies the conditions under which loop formation can occur.

Findings

Loop formation is a rare event in cosmic string-black hole interactions.

The likelihood of loop formation depends on string velocity, impact parameter, and black hole spin.

Most cosmic strings are either scattered or captured, not looped.

Abstract

We study the deformation of a long cosmic string by a nearby rotating black hole. We examine whether the deformation of a cosmic string, induced by the gravitational field of a Kerr black hole, may lead to the formation of a loop of cosmic string. The segment of the string which enters the ergosphere of a rotating black hole gets deformed and, if it is sufficiently twisted, it can self-intersect chopping off a loop of cosmic string. We find that the formation of a loop, via this mechanism, is a rare event. It will only arise in a small region of the collision phase space, which depends on the string velocity, the impact parameter and the black hole angular momentum. We conclude that generically, the cosmic string is simply scattered or captured by the rotating black hole.