Testing the nature of dark compact objects with gravitational waves

TL;DR

This paper reviews how gravitational-wave observations can test whether dark compact objects are black holes or exotic alternatives, exploring their structure, deformability, and near-horizon features.

Contribution

It provides an overview of current and future methods to distinguish black holes from other compact objects using gravitational-wave data.

Findings

Inspiral tests constrain multipolar structure

Ringdown analysis probes near-horizon physics

Echo searches test for exotic horizon structures

Abstract

Within Einstein's theory of gravity, any compact object heavier than a few solar masses must be a black hole. Any observation showing otherwise would imply either new physics beyond General Relativity or new exotic matter fields beyond the Standard Model, and might provide a portal to understand some puzzling properties of a black hole. We give a short overview on tests of the nature of dark compact objects with present and future gravitational-wave observations, including inspiral tests of the multipolar structure of compact objects and of their tidal deformability, ringdown tests, and searches for near-horizon structures with gravitational-wave echoes.