Properties of the binary neutron star merger GW170817 (1805.11579v3)

Abstract: On August 17, 2017, the Advanced LIGO and Advanced Virgo gravitational-wave detectors observed a low-mass compact binary inspiral. The initial sky localization of the source of the gravitational-wave signal, GW170817, allowed electromagnetic observatories to identify NGC 4993 as the host galaxy. In this work, we improve initial estimates of the binary's properties, including component masses, spins, and tidal parameters, using the known source location, improved modeling, and recalibrated Virgo data. We extend the range of gravitational-wave frequencies considered down to 23 Hz, compared to 30 Hz in the initial analysis. We also compare results inferred using several signal models, which are more accurate and incorporate additional physical effects as compared to the initial analysis. We improve the localization of the gravitational-wave source to a 90% credible region of $16~\mathrm{deg}^2$. We find tighter constraints on the masses, spins, and tidal parameters, and continue to find no evidence for nonzero component spins. The component masses are inferred to lie between 1.00 and 1.89 $M_\odot$ when allowing for large component spins, and to lie between 1.16 and 1.60 $M_\odot$ (with a total mass $2.73^{+0.04}_{-0.01} \, M_\odot$) when the spins are restricted to be within the range observed in Galactic binary neutron stars. Under minimal assumptions about the nature of the compact objects, our constraints for the tidal deformability parameter $\tilde \Lambda$ are $(0,630)$ when we allow for large component spins, and $300^{+420}_{-230}$ (using a 90% highest posterior density interval) when restricting the magnitude of the component spins, ruling out several equation-of-state models at the 90% credible level. Finally, with LIGO and GEO600 data, we use a Bayesian analysis to place upper limits on the amplitude and spectral energy density of a possible post-merger signal. (Abridged)

• The paper refines the estimation of critical astrophysical parameters such as component masses, spins, and tidal deformability using a Bayesian approach.
• It improves source localization from 28° to 16° and confirms low or aligned spins, supporting the binary neutron star merger scenario.
• The study constrains tidal deformability by ruling out stiffer EOS models, offering vital insights for gravitational-wave astronomy and dense matter physics.

Insights Into Binary Neutron Star Merger GW170817: Analysis and Implications

The paper entitled "Properties of the Binary Neutron Star Merger GW170817" offers a comprehensive investigation into the noteworthy observation of the binary neutron star merger, GW170817, detected by the Advanced LIGO and Virgo gravitational-wave detectors. The analysis refines the estimation of critical astrophysical parameters such as the component masses, spins, and tidal deformability of the merging objects, thanks to improved modeling, source localization, and recalibration of data. This paper stands as a seminal contribution to our understanding of neutron star mergers and their implications for astrophysics and fundamental physics.

Detailed Analysis and Computational Approach

The research leverages a sophisticated Bayesian approach to infer parameters from the detected gravitational-wave signals. Among the pivotal parameters, the chirp mass is found to be exceptionally well-constrained, showcasing the robustness of current analytical techniques in handling gravitational wave data. The analysis confirms that the component masses lie within the range typically expected for neutron stars, providing further reassurance of the authenticity of the detection as originating from a binary neutron star system. Notably, no substantial evidence was detected for non-zero component spins, implying either very low to moderate spins aligned with the orbital angular momentum or intrinsically low spins in the descendants of such systems as known from Galactic binaries.

The improvements in celestial localization from 28 deg² to an impressive 16 deg² credible region highlight advanced optimizations in instrument calibration and signal processing. This accuracy was attained without relying on electromagnetic observations, underscoring the capability of gravitational-wave detectors to autonomously identify and examine cosmic events.

Constraints on Tidal Deformability and Implications for Neutron-Star Structure

The paper critically addresses the topic of tidal interactions and the tidal deformability parameter, Λ, which informs about the internal structure and equation of state (EOS) of neutron stars. The results notably rule out several stiffer EOS models at the 90% credible level, thus providing constraints on the dense-matter physics not easily obtainable through other means. Improved estimates of Λ further suggest that these objects are not significantly deformed by tidal forces, in line with our assumptions about neutron star material responses.

Future Directions and Theoretical Implications

The findings reported hold considerable implications for gravitational-wave astronomy, suggesting the order of magnitude for detector sensitivity improvements needed to probe postmerger signals. With ongoing developments in detector technology, specifically towards achieving and exceeding design sensitivity at higher frequencies, future similar events might provide crucial insights into postmerger dynamics and physics, which are still beyond current observational reach.

Additionally, the results offer a profound potential for testing General Relativity and alternative theories of gravity under extreme conditions. Specifically, the ability to constrain neutron star EOSs presents a promising avenue for bridging the gap between gravitational-wave astrophysics and nuclear physics.

Conclusion

Overall, the paper significantly advances our understanding of neutron-star mergers while setting a benchmark for precision in gravitational-wave parameter estimation. The methodology and discoveries pave the way for future research directions both in gravitational-wave astrophysics and related fields, most notably in the paper of matter at supra-nuclear densities and tests of general relativity in its strong-field regime. The nuanced analysis and refined parameter constraints from GW170817 provide critical benchmarks as the scientific community continues to explore the fundamental physics of such catastrophic cosmic events.