On the Identification of Exotic Compact Binaries with Gravitational Waves: a Phenomenological approach

Abstract

Gravitational wave (GW) astronomy has been hailed as a gateway to discovering unexpected phenomena in the universe. Over the last decade there have been close to one hundred GW observations of compact-binary mergers. While these signals are largely consistent with mergers of binary black holes, binary neutron stars, or black hole-neutron star systems, some events suggest the intriguing possibility of binaries involving exotic compact objects (ECOs). Identifying and characterising an ECO merger would require accurate ECO waveform models. Using large numbers of numerical relativity simulations to develop customised models for ECO mergers akin to those used for binary black holes, would be not only computationally expensive but also challenging due to the limited understanding of the underlying physics. Alternatively, key physical imprints of the ECO on the inspiral or merger could in principle be incorporated phenomenologically into waveform models, sufficient to quantify generic properties. In this work we present a first application of this idea to assess the detectability and distinguishability of ECO mergers, and we propose a phenomenological approach that can iteratively incorporate features of ECO mergers, laying the groundwork for an effective exotic compact object identifier in compact binary coalescences. Using Bayesian parameter estimation on the data for the GW event GW150914, we find the inferred compactness to be consistent with that expected for black holes, within this framework. The efficacy of the identifier can be refined by adding information from numerical relativity simulations involving fundamental fields. Conversely, such an identifier framework can help focus future numerical relativity and modeling efforts for exotic objects.