Collision of an object in the transition from adiabatic inspiral to plunge around a Kerr black hole

TL;DR

This paper studies high-energy collisions of objects near Kerr black holes during the transition from inspiral to plunge, revealing conditions for ultra-high energy impacts and implications for dark matter and astrophysics.

Contribution

It demonstrates that gravitational radiation fine-tunes angular momentum during inspiral, enabling near-maximal collisions around rapidly rotating black holes.

Findings

High-velocity collisions occur near maximally rotating black holes.

Centre-of-mass energies can exceed Planck scale for dark matter particles.

Collision energies can reach 10^{58} erg for stellar mass objects around supermassive black holes.

Abstract

An inspiralling object of mass $\mu$ around a Kerr black hole of mass $M (\gg \mu)$ experiences a continuous transition near the innermost stable circular orbit from adiabatic inspiral to plunge into the horizon as gravitational radiation extracts its energy and angular momentum. We investigate the collision of such an object with a generic counterpart around a Kerr black hole. We find that the angular momentum of the object is fine-tuned through gravitational radiation and that the high-velocity collision of the object with a generic counterpart naturally occurs around a nearly maximally rotating black hole. We also find that the centre-of-mass energy can be far beyond the Planck energy for dark matter particles colliding around a stellar mass black hole and as high as $10^{58}$ erg for stellar mass compact objects colliding around a supermassive black hole, where the present transition formalism is well justified. Therefore, rapidly rotating black holes can accelerate objects inspiralling around them to energy high enough to be of great physical interest.