 Solution

Infer the component masses and spins from the gravitational wave phasing, using the chirp mass together with binary mass ratio information. The paper's representative pairs have total masses $2.8$, $11.4$ and $20M_{\odot }$, and the more massive mergers terminate their inspirals at lower frequencies. A black-hole ringdown and its quasi-normal modes identify the final compact remnant, although both a neutron-star–black-hole merger and a sufficiently massive neutron-star pair can also leave a black hole.

Tidal deformability and any disruption cutoff provide a more direct signature of a neutron star than total mass alone. A disrupted neutron star may supply a gamma-ray burst, kilonova and afterglow; these help distinguish matter-containing mergers from a clean black-hole pair. Their absence does not establish a black-hole pair, because jets are beamed and ejecta may be faint or swallowed. Measured gravitational wave masses are redshifted detector-frame masses; association with a host can supply the redshift needed for source-frame masses. Classification should combine the waveform and any electromagnetic evidence, allowing for parameter degeneracies.