Inferring the population properties of binary neutron stars with gravitational-wave measurements of spin

Xing-Jiang Zhu, Eric Thrane, Stefan Osłowski, Yuri Levin, Paul D. Lasky

Published 2017-11-25Version 1

The recent LIGO-Virgo detection of gravitational waves from a binary neutron star inspiral event GW170817 and the discovery of its accompanying electromagnetic signals mark a new era for multi-messenger astronomy. In the coming years, advanced gravitational-wave detectors are likely to detect tens to hundreds of similar events. Neutron stars in binaries can possess significant spin, which is imprinted on the gravitational waveform via the effective spin parameter $\chi_\text{eff}$. We explore the astrophysical inferences made possible by current and future gravitational-wave measurements of $\chi_\text{eff}$. First---using a fiducial model informed by radio observations---we estimate that $\approx15-40\%$ of binary neutron stars should have spins measurable by advanced detectors ($\chi_{\text{eff}}>0.01$) assuming the spin axis of the recycled neutron star aligns with the total orbital angular momentum of the binary. Second, using Bayesian inference, we show that it is possible to distinguish between our fiducial model and some extreme initial spin period distributions using $\gtrsim 10$ detections. Third, with $\gtrsim 50$ detections, we can confidently tell whether or not the spin axis of the recycled neutron star tends to be aligned with the binary orbit. Finally, stringent constraints can be placed on neutron star magnetic field decay after $\gtrsim 200$ detections, if the spin periods and magnetic field strengths of Galactic binary neutron stars are representative of the merging population.