Echoes from a singularity

TL;DR

This paper investigates how the gravitational wave ringdown signals differ between black holes and naked singularities, specifically analyzing the JNW spacetime's echoes and quasinormal modes to aid observational distinction.

Contribution

It provides the first detailed analysis of the ringdown profile of the JNW naked singularity under axial gravitational perturbations, highlighting the presence of echoes and mode shifts.

Findings

Low scalar field strength leads to prominent echoes in the ringdown.

Increasing scalar field strength suppresses echoes, revealing characteristic quasinormal modes.

Distinct ringdown signatures can help differentiate naked singularities from black holes.

Abstract

Though the cosmic censorship conjecture states that spacetime singularities must be hidden from an asymptotic observer by an event horizon, naked singularities can form as the end product of a gravitational collapse under suitable initial conditions, so the question of how to observationally distinguish such naked singularities from standard black hole spacetimes becomes important. In the present paper, we try to address this question by studying the ringdown profile of the Janis-Newman-Winicour (JNW) naked singularity under axial gravitational perturbation. The JNW spacetime has a surfacelike naked singularity that is sourced by a massless scalar field and reduces to the Schwarzschild solution in absence of the scalar field. We show that for low strength of the scalar field, the ringdown profile is dominated by echoes which mellows down as the strength of the field increases to yield characteristic quasinormal mode frequency of the JNW spacetime.