Echoes from backreacting exotic compact objects

TL;DR

This paper investigates how backreaction effects influence gravitational wave echoes from exotic compact objects, revealing that such effects can alter echo signals significantly, which is crucial for future detection strategies.

Contribution

It introduces the first analysis of backreaction effects on gravitational wave echoes from exotic compact objects, highlighting their impact on echo signal characteristics.

Findings

Backreaction can cause non-periodic and altered echo signals.

Absorption effects can lead to expansion or shutdown of compactness.

New features identified are important for future gravitational wave searches.

Abstract

The possible detection of echoes in late gravitational-wave signals is the most promising way to test horizonless alternatives to general relativistic black holes, and probe the physics of these hypothetical ultra-compact objects. While there is currently no evidence for the presence of such signatures, better accuracy is expected with the growing wealth of data from gravitational waves observatories. So far, several searches for these specific signals have been performed considering equidistant intervals between consecutive echoes, i.e. quasi-periodic wave-forms, and ignoring possible backreaction effects of the incoming waves. Here we study scalar perturbations in exotic compact object scenarios that account for possible backreaction phenomena. In particular, we find that if one considers the increase of the central object mass due to the partial absorption of the energy carried by the perturbation, the echo signal can be quite different and non-periodic. Apart from this simple scenario, we also consider the case in which, in order to preserve its compactness above the black hole limit, the compact object absorption shuts down in a finite amount of time or leads to an expansion. In both these cases we find interesting new features that should be taken into account in future searches.