GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral (1710.05832v1)

Abstract: On August 17, 2017 at 12:41:04 UTC the Advanced LIGO and Advanced Virgo gravitational-wave detectors made their first observation of a binary neutron star inspiral. The signal, GW170817, was detected with a combined signal-to-noise ratio of 32.4 and a false-alarm-rate estimate of less than one per $8.0\times10^4$ years. We infer the component masses of the binary to be between 0.86 and 2.26 $M_\odot$, in agreement with masses of known neutron stars. Restricting the component spins to the range inferred in binary neutron stars, we find the component masses to be in the range 1.17 to 1.60 $M_\odot$, with the total mass of the system $2.74^{+0.04}{-0.01}\,M\odot$. The source was localized within a sky region of 28 deg$^2$ (90% probability) and had a luminosity distance of $40^{+8}_{-14}$ Mpc, the closest and most precisely localized gravitational-wave signal yet. The association with the gamma-ray burst GRB 170817A, detected by Fermi-GBM 1.7 s after the coalescence, corroborates the hypothesis of a neutron star merger and provides the first direct evidence of a link between these mergers and short gamma-ray bursts. Subsequent identification of transient counterparts across the electromagnetic spectrum in the same location further supports the interpretation of this event as a neutron star merger. This unprecedented joint gravitational and electromagnetic observation provides insight into astrophysics, dense matter, gravitation and cosmology.

• The paper demonstrates the first gravitational-wave detection from a binary neutron star inspiral, achieving an SNR of 32.4 and precise 28 square degree localization.
• The paper links the merger event to electromagnetic observations, including a gamma-ray burst detected 1.7 seconds post-coalescence and an optical counterpart near NGC 4993.
• The paper enables independent Hubble constant measurements and tests of fundamental physics, confirming neutron star equations of state and the speed of gravity.

Overview of GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral

The paper “GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral” by B.P. Abbott et al. reports on the first detection of gravitational waves (GWs) from a binary neutron star (BNS) inspiral. On August 17, 2017, the Advanced LIGO and Virgo gravitational-wave detectors identified the event GW170817, marked by dominant gravitational-wave signals and associated electromagnetic counterparts, including a gamma-ray burst (GRB) 1.7 seconds post-coalescence, thereby substantiating the link between neutron star mergers and short gamma-ray bursts (sGRBs).

Key Results and Analysis

The GW170817 event was documented with an impressive signal-to-noise ratio (SNR) of 32.4 and a remarkably low false-alarm rate, ensuring a high confidence level in its detection. The component masses were estimated to lie between 0.86 and 2.26 solar masses (M⊙), aligning with known neutron star masses. Specifically, under restricted spin assumptions, component masses narrowed to 1.17–1.60 M⊙, suggesting a total system mass around 2.74 M⊙, a standard for BNS systems.

Sky localization refined the source's position to a 28 square degree region, at a luminosity distance of approximately 40 megaparsecs (Mpc). This high-precision localization allowed electromagnetic follow-up, confirming an optical counterpart near galaxy NGC 4993, further corroborating the neutron star merger hypothesis.

Importantly, the gravitational-wave signal yielded valuable astrophysical insights, allowing an independently inferred Hubble constant and enabling tests of fundamental physics such as the speed of gravity and Lorentz invariance. These findings offer extensive corroboration with astrophysical models, which indicate that BNS mergers substantially contribute to the stochastic gravitational-wave background observed in the universe.

Implications and Future Developments

The implications of GW170817 span multiple domains—astrophysics, cosmology, and fundamental physics. Practically, this observation enhances our understanding of gravitational-wave physics and neutron star equations of state (EOS), and it holds substantial promise for multimessenger astrophysics by linking gravitational and electromagnetic observations.

Theoretically, the event allows constraints on the tidal deformability of neutron stars, shaping future EOS models. Furthermore, the simultaneous GW and electromagnetic detections enable improved estimates of the Hubble constant independent of traditional cosmic distance ladders, offering crucial insights into cosmological parameters.

Looking forward, as gravitational-wave detectors gain sensitivity, detection rates are anticipated to increase, with expectations reaching hundreds of BNS mergers annually. This suggests a notable role for future observations in discerning the population and characteristics of compact objects in the universe, ultimately informing the theorization of the stochastic gravitational-wave background and offering robust tests for theories of gravity beyond the standard model.

Conclusion

GW170817 represents a significant advance in gravitational-wave astronomy and neutron star research. It elucidates the considerable potential of gravitational-wave detection as a tool for astronomically corroborated discoveries and underscores the synergistic power of multimodal observational astronomy. Ongoing advancements in detector sensitivity and methodology are poised to unlock further insights into both the cosmic milieu and the underlying physics of these phenomena.