Capture and Critical Scattering of a Long Cosmic String by a Rotating Black Hole

TL;DR

This paper investigates how a rotating black hole interacts with an infinitely long cosmic string, analyzing conditions for scattering or capture, and exploring relativistic effects like coil formation through numerical simulations.

Contribution

It introduces a detailed numerical analysis of cosmic string capture and scattering by rotating black holes, including the effects of black hole spin and string velocity.

Findings

Critical impact parameter depends on black hole rotation and string velocity.

Prograde motion has a lower critical impact parameter than retrograde.

Ultrarelativistic strings near extremal black holes exhibit multiply valued impact parameter curves.

Abstract

The capture of a straight, infinitely long cosmic string by a rotating black hole with rotation parameter $a$ is considered. We assume that a string is moving with velocity $v$ and that initially the string is parallel to the axis of rotation of the black hole and has the impact parameter $b$. The string can be either scattered or captured by the black hole. We demonstrate that there exists a critical value of the impact parameter $b_c(v,a)$ which separates these two regimes. Using numerical simulations we obtain the critical impact parameter curve for different values of the rotation parameter $a$. We show that for the prograde motion of the string this curve lies below the curve for the retrograde motion. Moreover, for ultrarelativistic strings moving in the prograde direction and nearly extremal black holes the critical impact parameter curve is found to be a multiply valued function of $v$. We obtain real time profiles of the scattered strings in the regime close to the critical. We also study critical scattering and capture of strings by the rotating black hole in the relativistic and ultrarelativistic regime and especially such relativistic effects as coil formation and wrapping effect.