Mapping the Universe Expansion: Enabling percent-level measurements of the Hubble Constant with a single binary neutron-star merger detection

Understand

The joint observation of the gravitational-wave and electromagnetic signal from the binary neutron-star merger GW170817 allowed for a new independent measurement of the Hubble constant $H_0$, albeit with an uncertainty of about 15\% at 1$\sigma$.

• Observations of similar sources with a network of future detectors will allow for more precise measurements of $H_0$.
• These, however, are currently largely limited by the intrinsic degeneracy between the luminosity distance and the inclination of the source in the gravitational-wave signal.
• We show that the higher-order modes in gravitational waves can be used to break this degeneracy in astrophysical parameter estimation in both the inspiral and post-merger phases of a neutron star merger.