Characterizing Astrophysical Binary Neutron Stars with Gravitational Waves

Abstract

Merging binary neutron stars are thought to be formed predominantly via isolated binary evolution. In this standard formation scenario, the first-born neutron star goes through a recycling process and might be rapidly spinning during the final inspiral, whereas the second-born star is expected to have effectively zero spin at merger. Based on this feature, we propose a new framework for the astrophysical characterization of binary neutron stars observed from their gravitational wave emission. We further propose a prior for the dimensionless spins of recycled neutron stars, given by a gamma distribution with a shape parameter of 2 and a scale parameter of 0.012, extrapolated from radio pulsar observations of Galactic binary neutron stars. Interpreting GW170817 and GW190425 in the context of the standard formation scenario and adopting the gamma-distribution prior, we find positive support (with a Bayes factor of 6, over the nonspinning hypothesis) for a spinning recycled neutron star in GW190425, whereas the spin of the recycled neutron star in GW170817 is small and consistent with our prior. We measure the masses of the recycled (slow) neutron stars in GW170817 and GW190425 to be $1.34_{-0.09}^{+0.12}$ $(1.38_{-0.11}^{+0.11})$ $M_{\odot }$ and $1.64_{-0.11}^{+0.13}$ $(1.66_{-0.12}^{+0.12})$ $M_{\odot }$, with $68\%$ credibility, respectively. We discuss implications for the astrophysical origins of these two events and outline future prospects of studying binary neutron stars using our framework.

To match the published version on ApJ Letters; 18 pages, 12 figures, 2 tables

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• The Impact of Spin in Compact Binary Foreground Subtraction for Estimating the Residual Stochastic Gravitational-wave Background in Ground-based Detectors
• A MeerKAT view of the double pulsar eclipses -- Geodetic precession of pulsar B and system geometry
• Stable Case BB/BC Mass Transfer to Form GW190425-like Massive Binary Neutron Star Mergers
• Measuring spin in coalescing binaries of neutron stars showing double precursors
• Methods for relativistic self-gravitating fluids: From binary neutron stars to black hole-disks and magnetized rotating neutron stars
• Optimized localization for gravitational-waves from merging binaries
• Cosmology with Binary Neutron Stars: Does Mass-Redshift Correlation Matter?
• Rapid Hierarchical Inference of Neutron Star Equation of State from multiple Gravitational Wave Observations of Binary Neutron Star Coalescences
• Kinematic Evidence for Open Cluster Origins of Galactic Binary Neutron Stars