The potential role of binary neutron star merger afterglows in multimessenger cosmology

Understand

Binary neutron star mergers offer a new and independent means of measuring the Hubble constant $H_0$ by combining the gravitational-wave inferred source luminosity distance with its redshift obtained from electromagnetic follow-up.

• This method is limited by intrinsic degeneracy between the system distance and orbital inclination in the gravitational-wave signal.
• Observing the afterglow counterpart to a merger can further constrain the inclination angle, allowing this degeneracy to be partially lifted and improving the measurement of $H_0$.
• In the case of the binary neutron star merger GW170817, afterglow light-curve and imagery modeling thus allowed to improve the $H_0$ measurement by a factor of 3.