Characterizing the Properties and Constitution of Compact Objects in Gravitational-Wave Binaries

TL;DR

This paper investigates how gravitational wave signals can distinguish black holes from exotic compact objects by analyzing tidal heating effects, improving waveform models, and assessing parameter measurability for current and future detectors.

Contribution

It introduces an improved waveform model incorporating tidal heating effects and demonstrates how to use these effects to differentiate black holes from horizonless objects.

Findings

Tidal heating effects are stronger in late inspiral phases.

Enhanced waveform models improve parameter estimation accuracy.

Potential to identify exotic compact objects with current and future GW detectors.

Abstract

Astrophysical observations point toward strong evidence for the existence of black holes (BHs). Nevertheless, it is yet to be established or ruled out with confidence whether some exotic compact objects (ECOs), capable of mimicking black holes from an observational point of view, are indeed doing so. In classical General Relativity (GR), a horizon is the defining feature of a black hole, which prevents any event inside from causally affecting the outside Universe. The quest for distinguishing black holes from horizonless compact objects using gravitational wave (GW) signals from compact binary coalescences (CBCs) can be helped by utilizing the phenomenon of tidal heating (TH), which leaves its imprint on the binary waveforms through the horizon parameters. First, we study the measurabilities of these parameters within the inspiral regime. Then, to extend our investigation for heavier binaries, we construct an inspiral-merger-ringdown waveform by using post-Newtonian calculations for the inspiral and numerical relativity data for the merger-ringdown part that incorporates the effects of tidal heating of black holes in the phase and the amplitude. The new model shows improvements in waveform accuracy when compared to numerical relativity data. In the late inspiral phase when the compact objects are closer to each other, the effects of tidal heating are stronger, opening up the possibility of identifying the objects more precisely. We demonstrate, from numerical relativity data of binary black holes, how one can model tidal heating in the late inspiral regime and leverage this knowledge to test for horizonless compact objects mimicking black holes. These studies bear significance in determining the nature of compact objects having masses in the entire range that LIGO and future ground-based gravitational-wave detectors can detect.