Could next-gen detectors tell black holes from spinning exotic objects?

Using post-Newtonian waveform models, the authors assess how well current and future gravitational-wave detectors could characterize binaries containing sub-solar-mass black holes or superspinars — exotic objects that spin faster than general relativity normally allows. While Advanced LIGO struggles with these low-mass systems, third-generation detectors like Einstein Telescope and Cosmic Explorer could pin down the primary spin to within 0.001, achieving SNRs of 100–350. That precision would be enough to observationally separate near-extremal black holes from superspinars in the 0.1–2 solar-mass range.