Observational bounds on dark matter-admixed neutron stars from gravitational wave data

Recent gravitational-wave (GW) observations offer a unique opportunity to probe the fundamental nature of compact objects. A growing body of research has focused on exploring the role of dark matter (DM) through the concept of DM-admixed neutron stars (NSs), where the presence of DM can significantly alter key physical properties of NSs, such as their mass, radius, and tidal deformability, ultimately affecting the predicted GW waveform emitted during binary coalescences. In this work, we present a novel observational test that, for the first time, uses GW inspiral waveforms in terms of DM parameters to place constraints on the influence of DM inside NSs using real GW data. By reanalyzing signals from events such as GW230529, GW200115, and GW200105, we derive new upper bounds on the DM fraction, ${F}_{\ensuremath{\chi}}$, and particle mass, ${m}_{\ensuremath{\chi}}$, under the assumption that DM is described by a scalar field with a self-interaction potential. We find that the upper bound on ${F}_{\ensuremath{\chi}}$ depends on the specific binary system under analysis, indicating that different DM configurations can be consistent with observations in different ways. In particular, the event GW190814 may be compatible with a DM halo configuration. In contrast, the other events analyzed (GW230529, GW200105, and GW200115) are consistent with DM forming a core inside the NS, yielding strong upper bounds on ${F}_{\ensuremath{\chi}}$. The corresponding values for the mass scale ${m}_{\ensuremath{\chi}}$ are also discussed in the text. This work offers a new approach to probing DM in the context of compact NS objects through GW observations.