Quantum Aspects of Ergoregion Instability

TL;DR

This paper investigates the quantum behavior of scalar fields around rapidly rotating stars with ergoregions, revealing unstable modes and spontaneous energy radiation due to ergoregion instability.

Contribution

It introduces a canonical quantization method for unstable modes in ergoregions, showing a non-Fock-like Hilbert space and spontaneous radiation phenomena.

Findings

Existence of unstable normal modes with non-Fock-like Hilbert space representation

Spontaneous energy radiation from stars with ergoregions

Quantization framework for scalar fields in ergoregion backgrounds

Abstract

It has been known classically that a star with an ergoregion but no event horizon is unstable to the emission of scalar, electromagnetic and gravitational waves. This classical ergoregion instability is characterized by complex frequency modes. We show how to canonically quantize a neutral scalar field in the presence of such unstable modes by considering a simple model for a rapidly rotating star. Some of interesting results is that there exists a physically meaningful mode decomposition including unstable normal mode solutions whose representation turns out to be a non-Fock-like Hilbert space. A ``particle" detector model placed in the in-vacuum state also shows that stars with ergoregions give rise to a spontaneous energy radiation to spatial infinity until ergoregions disappear.